Environmental aspects of construction with waste materials: proceeding[s] of the International Conference on Environmental Implications of Construction Materials and Technology Developments, Maastricht, the Netherlands, 1-3 June 1994

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONALCONFERENCE ON ENVIRONMENTAL I...

Author: Th.G. Aalbers | H.A. van der Sloot | J.J.J.M. Goumans

50 downloads 465 Views 14MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!

Report copyright / DMCA form

DOWNLOAD PDF

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONALCONFERENCE ON ENVIRONMENTAL IMPLICATIONS OF CONSTRUCTIONMATERIALS AND TECHNOLOGY DEVELOPMENTS, MAASTRICHT, THE NETHERLANDS, 1-3 JUNE 1994

This Page intentionally left blank

Studies in Environmental Science 60

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONAL CONFERENCE ON ENVIRONMENTAL IMPLICATIONS OF CONSTRUCTION MATERIALS AND TECHNOLOGY DEVELOPMENTS, MAASTRICHT, THE NETHERLANDS, 1-3 JUNE 1994

Edited by

J.J.J.M. Goumans Netherlands Agency for Energy and the Environment (NOVEM), P.0. Box 8242, 3503 RE Utrecht, The Netherlands

H.A. van der Sloot Netherlands Energy Research Foundation (ECN), P.0.Box 1, 1755ZG Petten, The Netherlands

Th. G. Aalbers National Institute of Public Health and Environmental Protection (RI VM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands

ELSEVIER Amsterdam

-

London

-

NewYork

- Tokyo

1994

ELSEVIER SCIENCE B.V. Molenwerf 1 P.O. Box 21 1,1000 AE Amsterdam, The Netherlands

ISBN 0-444-81853-7

01994 Elsevier Science B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A. - This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the publisher. No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This book is printed on acid-free paper. Printed in The Netherlands

Studies in EnvironmentalScience Other volumes in this series 1 2

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

30 31 32

33

Atmospheric Pollution 1978 edited by M.M. Benarie Air Pollution ReferenceMeasurement Methods and Systems edited by T. Schneider, H.W. de Koning and L.J. Brasser Biogeochemical Cycling of Mineral-Forming Elements edited by P.A. Trudinger and D.J. Swaine PotentialIndustrialCarcinogensand Mutagens by L. Fishbein IndustrialWaste Management by S.E. Jergensen Tradeand Environment: ATheoretical Enquiry by H. Siebert, J. Eichberger, R. Gronych and R. Pethig Field Worker Exposure during Pesticide Application edited by W.F. Tordoir and E.A.H. van Heemstra-Lequin Atmospheric Pollution1980 edited by M.M. Benarie Energetics and Technology of Biological Eliminationof Wastes edited by G. Milazzo Bioengineering,ThermalPhysiologyand Comfort edited by K. Cena and J.A. Clark Atmospheric Chemistry. Fundamental Aspects by E. Meszaros Watersupply and Health edited by H. van Lelyveld and B.C.J. Zoeteman Man under Vibration. Sufferingand Protection edited by G. Bianchi, K.V. Frolov and A. Oledzki Principlesof Environmental Science and Technology by S.E.Jergensen and I. Johnsen Disposalof RadioactiveWastes by Z. Dlouhy Mankind and Energy edited by A. Blanc-Lapierre Quality of Groundwater edited by W. van Duijvenbooden, P. Glasbergen and H. van Lelyveld Educationand Safe Handlingin PesticideApplication edited by E.A.H. van Heemstra-Lequin and W.F. Tordoir PhysicochemicalMethods for Water and Wastewater Treatment edited by L. Pawlowski Atmospheric Pollution 1982 edited by M.M. Benarie Air Pollution by NRrogenOxides edited by T. Schneider and L. Grant Environmental Radioanalysis by H.A. Das, A. Faanhof and H.A. van der Sloot Chemistry for Protectionof the Environment edited by L. Pawlowski, A.J. Verdier and W.J. Lacy Determination and Assessment of PesticideExposureedited by M. Siewierski The Biosphere: Problems and Solutions edited by T.N. VezirMlu Chemical Events in the Atmosphere and their Impacton the Environment edited by G.B. Marini-Bettolo Fluoride Research 1985 edited by H. Tsunoda and Ming-Ho Yu Algal Biofouling edited by L.V. Evans and K.D. Hoagland Chemistryfor Protectionof the Environment 1985 edited by L. Pawlowski, G. Alaerts and W.J. Lacy Acidification and its Policy Implicationsedited by T. Schneider Teratogens: Chemicals which Cause Birth Defects edited by V. Kolb Meyers Pesticidechemistryby G. Matolcsy, M. Nadasy and Y. Andriska Principlesof EnvironmentalScience and Technology (secondrevisededition) by S.E. Jergensen and I. Johnsen

34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

57 58 59

Chemistry for Protectionof the Environment 1987 edited by L. Pawlowski, E. Mentasti, W.J. Lacy and C. Sarzanini Atmospheric Ozone Researchand its Policy Implicationsedited by T. Schneider, S.D. Lee, G.J.R. Wolters and L.D. Grant Valuation Methods and Policy Making in Environmental Economics edited by H. Folmer and E. van lerland Asbestos in Natural Environment by H. Schreier How to Conquer Air Pollution.A Japanese Experience edited by H. Nishimura Aquatic BioenvironmentalStudies: The HanfordExperience, 1944-1984 by C.D. Becker Radon in the Environment by M. Wilkening Evaluationof Environmental Data for Regulatory and ImpactAssessment by S. Ramamoorthy and E. Baddaloo EnvironmentalBiotechnology edited by A. Blazej and V. Privarova Applied Isotope Hydrogeology by F.J. Pearson Jr., W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, Tj. Peters, H. Schmassmann and A. Gautschi Highway Pollutionedited by R.S. Hamilton and R.M. Harrison Freight Transport and the Environment edited by M. Kroon, R. Smit and J.van Ham Acidification Research inThe Netherlands edited by G.J. Heij and T. Schneider Handbook of RadioactiveContamination and Decontamination by J. Severa and J. Bar Waste Materials in Construction edited by J.J.J.M. Goumans, H.A. van der Sloot and Th.G. Aalbers Statistical Methods in Water Resources by D.R. Helsel and R.M. Hirsch Acidification Research: Evaluationand Policy Applications edited by TSchneider Biotechniques for Air PollutionAbatement and Odour Control Policies edited by A.J. Dragt and J. van Ham EnvironmentalScience Theory. Concepts and Methods in a OneWorld, Problem-OrientedParadigm by W.T. de Groot Chemistry and Biology of Water, Air and Soil. Environmental Aspects edited by J. Tolgyessy The Removalof NitrogenCompoundsfrom Wastewater by B. Halling-Serensen and S.E. Jergensen EnvironmentalContamination edited by J.-P. Vernet The Reclamation of Former Coal Mines and Steelworks by I.G. Richards, J.P. Palmer and P.A. Barratt Natural Analogue Studies in the GeologicalDisposalof Radioactive Wastes by W. Miller, R. Alexander, N. Chapman, I. McKinley and J. Smellie Water and Peace in the Middle East edited by J. Isaac and H. Shuval Environmental Oriented Electrochemistry edited by C.A.C. Sequiera

vii

mREw0RD The Organizing and Scientific Committees of the Second International Conference on Environmental Implications of Construction Materials and Technology Developments, WASCON '94, present herewith the Proceedings of this Conference, which will be held from 1-3 June, 1994 in Maastricht, The Netherlands.

SCOPE OF THE CONFERENCE The concept of "Sustainable Development", implicating the protection of soil and groundwater, the limitation of waste production and the re-use of solid waste materials is still the leading theme of WASCON '94. Although it is clearly recognized in most countries that products derived from solid waste materials can be applied as construction materials, research is still needed to assess various environmental problems. With respect to the prediction and control of release of contaminants, there is a trend towards consensus on the usage of the various leaching tests which have been developed. In addition, scientific research regarding, e.g., speciation of chemical elements is generating results which can be transferred to technical studies and also to more general studies dealing with environmental and life cycle analysis. As is reflected in the amount of contributions, two topics are currently the subject of study in many countries. Firstly, there is the problem of municipal waste, stabilization of waste materials and their use in civil works is the subject of research and legislation. Within these fields it can be seen that transfer of knowledge and know-how is helping to find environmentally acceptable solutions, also with respect to establishing criteria and standards. Secondly, as far as technology development is concerned, it can be seen that research has encompassed a wider variety of materials. Furthermore, quality control and standardization has been applied to these types of materials. The incorporation of environmental quality standards is the next step to be taken, and is already the subject of some studies. In general, technical studies are often already accompanied by environmental aspects as an integral part of research. The Organizing Committee hopes that WASCON '94 will contribute to the solution of environmental and technical problems concerning the re-use of waste materials and, thus, to sustainable development in building practice.

SCIENTIFIC COOPERATION

The International Society for Construction with Alternative Materials (ISCOWA) was founded as a result of the First Conference, held in 1991. To date over 110 members from 15 different countries have been registered, and the Society is still growing. ISCOWA is actively participating in the scientific committee and in the organization of WASCON '94. Many ISCOWA members have submitted contributions to the Conference, arid the Chairmen of the ISCOWA working groups have prepared state-of-the-art documents.

viii

ACKNOWLEDGEMENT Organizing an international conference means a lot of work for many people, we therefore wish to express our thanks to the following: The members of the Honorary Committee and the Scientific Committee. The Dutch National Institute of Public Health and Environmental Protection (RIVM), the Netherlands Energy Research Foundation (ECN), Environment Canada, The United States Environmental Protection Agency (USA-EPA), Community Bureau of References, Commission of the European Community (BCR), The Danish National Agency for Environmental Protection, European Association for Use of the By-products of Coal Fired Power Stations E.V. (ECOBA), the Center for Applied Research, Norway, and the Netherlands Agency for Energy and the Environment (NOVEM) for supporting the Conference. The Netherlands Ministries of Housing, Physical Planning and the Environment and of Economic Affairs, which have sponsored the Conference. Van Namen and Westerlaken Congress Organization Services, De Boer and Van TeyIingen Public Relations and the staff of Elsevier Science B.V. All Authors, Participants of the Conference, and all others who have contributed to WASCON '94. On behalf of the Organizing Committee, Dr J.J.J.M. Goumans Chairman of ISCOWA Utrecht, The Netherlands, 21 March 1994

ix CONTENTS Preface

...................................................................................................

vii

SECTION 1: Opening The International Ash Working Group: A Treatise on Residues from MSW Incinerators .............................................................................................. S.E. SAWELL, A.J. CHANDLER, T.T. EIGHMY, J. HARTLEN, 0. HJELMAR, D. KOSSON, H.A. VAN DER SLOOT and J. VEHLOW

3

International Progress in Solid Waste Management J.H. SKINNER

..............................................

7

Life Cycle Analyses; Results of Some Case Studies J. CRAMER

.............................................

17

SECTION 2: Environmental Aspects Chemical Processes Controlling the Mobility of Waste Material Contaminants in Soils L.G. WESSELINK, P.M. DEKKER and T.G. AALBERS

..

31

Leaching of Slags and Ashes - Controlling Factors in Field Experiments versus Laboratory Tests ....................................................................................... A.-M. FALLMAN and J. HARTLEN

39

Validation of Leaching Model on Actual Structures ............................................. G . VAN DER WEGEN and C. VAN DER PLAS

55

Intercompanson of Leaching Tests for Stabilized Waste ...................................... H.A. VAN DER SLOOT, G.J.L. VAN DER WEGEN, D. HOEDE and G.J. DE GROOT

63

Immobilisation Potential of Cementitious Materials F.P. GLASSER

...............................................

Coal Fly-Ash Leaching Behaviour and Solubility Controlling Solids R. GARAVAGLIA and P. CARAMUSCIO Modelling Ca-Solubility in MSWI Bottom Ash Leachates R.N.J. COMANS and J.A. MEIMA

........................

87

....................................

Particle Petrogenesis and Speciation of Elements in MSW Incineration Bottom Ashes T.T. EIGHMY, J.D. EUSDEN, JR., K. MARSELLA, J. HOGAN, D. DOMINGO, J.E. KRZANOWSKI and D. STAMPFLI

77

103

..

111

X

An Approach to the Assessment of the Environmental Impacts of Marine Applications of Municipal Solid Waste Combustion Residues ................................................. 0. HJELMAR, E.A. HANSEN, K.J. ANDERSEN, J.B. ANDERSEN and E. BJ0RNESTAD Quality Assessment of Granular Combustion Residues by a Standard Column Test: Prediction versus Reality ............................................................................. M. JANSSEN-JURKOVICOVA, G.G. HOLLMAN, M.M. NASS and R.D. SCHUILING

137

161

Geochemical Factors Controlling the Mobilization of Major Elements during Weathering of MSWI Bottom Ash .................................................................. C. ZEVENBERGEN and R.N.J. COMANS

179

Leaching Behaviour of Building Materials with Byproducts under Practical Conditions ............................................................................................... P.J.C. BLOEM, F.L.M. LAMERS and L. TAMBOER

195

FGD Gypsum Definitions and Legislation in the European Communities, in the OECD and in Germany ........................................................................................ F. WIRSCHING, R. HULLER and R. OLEJNIK

205

In-situ Utilization of Waste Bentonite Slurry N. UCHIYAMA and S. HORIUCHI

.....................................................

217

..................................

227

The use of MWI Fly Ash in Asphalt for Road Construction J.B.M. HUDALES

Enhanced Natural Stabilization of MSW Bottom Ash: A Method for Minimization of Leaching ............................................................................................. J.J. STEKETEE and L.G.C.M. URLINGS Immobilization of Slag Material by Foam Bitumen J.H. DIJKINK

233

.............................................

239

..........................

247

Immobilisation of Phenol and PAH by Special Hydraulic Binders P. VOGEL and M. SCHMIDT

Leaching of Organic Contaminants from Contaminated Soils and Waste Materials ...... M. WAHLSTROM, H. THOMASSEN, J. FLYVBJERG, A.C. VELTKAMP, C. OSCARSSON, J . - 0 . SUNDQVIST and G.A. ROOD

257

Investigating a Leaching Test for PCBs and Organochlorine Pesticides in Waste and Building Materials ................................................................................ G.A. ROOD, M.H. BROEKMAN and T.G. AALBERS

27 1

French Qualification Procedure for Solidification Processes ................................... J. MEHU, P. MOSZKOWICZ, R. BARNA. P. PHILIPPE and V. MAYEUX

281

xi Utilization Status, Issues and Criteria Development for Municipal Waste Combustor Residues in the United States ....................................................................... D.S. KOSSON, B.A. CLAY, H.A. VAN DER SLOOT and T.T. KOSSON

293

........................

305

Validation of Dutch Standard Leaching Tests Using NEN-IS0 5725 G.J. DE GROOT and D. HOEDE

The Laconia, New Hampshire Bottom Ash Paving Project ..................................... C.N. MUSSELMAN, M.P. KILLEEN, D. CRIMI, S. HASAN, X. ZHANG, D.L. GRESS and T.T. EIGHMY

315

Application of Fly Ash and other Waste Materials for the Construction of an Off-Shore Island Opposite the Coast of Tel-Aviv ............................................................. Y. ZIMMELS, G. SHELEF and A. BOAS

329

Fly Ash Utilisation in Civil Engineering .......................................................... J.G. CABRERA and G.R. WOOLLEY

345

High Pressure Mixing: A New Technology to Re-use Waste Materials Containing CaO and/or MgO ...................................................................................... R. HAVERKORT, W. DEKKER and J. SENDEN

357

Environmental Compatibility of Cement and Concrete ......................................... S. SPRUNG, W. RECHENBERG and G. BACHMANN

369

.................................................

387

European Standardization of Additions for Concrete ........................................... J.M.J.M. BIJEN

397

State of the Art of Waste Characterization on European Level ............................... A. TUKKER. M. VAN DEN BERG and H.A. V A N DER SLOOT

409

Leaching Properties of Cement-bound Materials I. HOHBERG and R. RANKERS

Leaching Behavior Assessment of Wastes Solidified with Hydraulic Binders: Critical Study of Diffusional Approach ............................................................ P. MOSZKOWICZ, R. BARNA, J . MEHU, H. VAN DER SLOOT and D. HOEDE Burning of Hazardous Wastes as Co-Fuel in a Cement Kiln Does it Affect the Environmental Quality of Cement? .......................................... K.H. KARSTENSEN Approach towards International Standardization: A Concise Scheme for Testing of Granular Waste Leachability ..................................................................... H.A. VAN DER SLOOT, D.S. KOSSON, T.T. EIGHMY, R.N.J. COMANS and 0. HJELMAR Speciation of As and Se during Leaching of Fly Ash E.E. VAN DER HOEK and R.N.J. COMANS

..........................................

42 1

433

453

467

xii Measurement of Redox Potential During Standardized Column Tests J. KEIJZER and A.J. ORBONS

.......................

477

The Influence of Reducing Properties on Leaching of Elements from Waste Materials and Construction Materials ........................................................................... H.A. VAN DER SLOOT, D. HOEDE and R.N.J. COMANS Hydrology and Chemistry of Pulverized Fuel Ash in a Lysimeter or the Translation of the Results of the Dutch Column Leaching Test into Field Conditions ..................

483

49 1

R. MEIJ and H.P.C. SCHAFTENAAR Role of Facilitated Transport in the Emissions of Secondary Raw Materials J.J. STEKETEE, J.C.M. DE WIT, G.J. VAN ROSSUM and L. G. C.M. URLINGS

...............

507

Immobilization of Heavy Metal Ions by the Alkali Activated Slag Cementitious Materials ................................................................................................. J. MALOLEPSZY and J. DEJA

5 19

Integrated Treatment of MSWI-residues: Treatment of Fly Ash in View of Metal Recovery ......................................................................................... B. LAETHEM, P. VAN HERCK, P. GEUZENS and C. VANDECASTEELE

525

Life Cycle Assessment of a Road Embankment in Phosphogypsum: Preliminary Results .................................................................................... J.W. BROERS, F.E.T. HOEFNAGELS and H.L. ROSKAMP

539

Co-combustion of Coal and Waste Wood, Consequences for the By-product Quality M.L. BEEKES, C.H. GAST and A.J.A. KONINGS

.....

543

SECTION 3: Technical Aspects Use of Demolition Concrete to produce Durable Structural Concrete P.J. WAINWRIGHT and J.C. CABRERA

.......................

553

Improvement of Portland Cement/Fly Ash Mortar Strength using Classified Fly Ashes ............................................................................................... J. PAYA, V. BORRACHERO, E. PERIS-MORA, A. ALIAGA and J. MONZd

563

Ground Fly Ashes: Characteristics and their Influence on Fresh and Hardened Mortars .................................................................................................. J. PAYA, V. BORRACHERO, J. MONZO, E. PERIS-MORA and A. ALIAGA

571

Development of Cementitious Products using Industrial Process Wastes as Sources of Reactive Sulfate and Alumina ......................................................... G. BELZ, J. BERETKA, R. CIOFFI, L. SANTORO, N. SHERMAN and G.L. VALENTI

579

xiii Potentials for Utilisation of PFBC Ash ............................................................ J. ROGBECK and P. ELANDER

589

..................................

599

Recycling of Magnesium Slags in Construction Block Form M. COURTIAL, R. CABRILLAC and R. DUVAL

Improving the MSWI Bottom Ash Quality by Simple In-Plant Measures I. SCHNEIDER, J. VEHLOW and H. VOGG

...................

Potentials in Quality Improvement of Processed Building Rubble by Demolition and Treatment Technics .............................................................................. J.O.V. TRANKLER and I. WALKER Quantities and Qualities of Municipal Waste Incinerator Residues in the Netherlands J.G.P. BORN

605

62 1

....

Upgrading Techniques for the Quality Improvement of Municipal Waste Incineration Residues ................................................................................. F.J.M. LAMERS and J.G.P. BORN Re-use of Colliery Spoils in Construction Materials using Fluidized Bed Combustion J.J.M. HEYNEN, H.N.J. A. BOLK, G.J. SENDEN and P.J. TUMMERS

...

633

645

655

Recovery of Raw Materials from Reclaimed Asphalt Pavement .............................. E. MULDER, C. DE GROOT, C. JONKER and J. VAN DER ZWAN

665

.............................

673

Applications for Coal-use Residues: An International Overview L.B. CLARKE

Specifications and the Use of Wastes in Construction in the United Kingdom ............. R.J. COLLINS and C.J. ATKINSON Overview of Coal Ash Use in the USA S.S. TYSON

..........................................................

687

699

Environmental Life Cycle Analysis of Construction Products with and without Recycling ................................................................................................ M.S. A.M. SCHUURMANS-STEHMANN

709

Assessment of the Environmental Compatibility of Industrial By-products and Recycled Materials .................................................................................... R. BIALUCHA, J. GEISELER and K. KRASS

719

...................................

727

Environmental Management in Large Construction Projects E.K. LAURITZEN

A Concept for the Environmental Evaluation of Waste Management Benefits A. TUKKER and D.J. GIELEN

.............

737

......

749

Technological and Environmental Properties of Concretes with High PFA Content H.A.W. CORNELISSEN and R.E. HELLEWAARD

xiv Towards Sustainability with Construction and Demolition Waste in Belgium? G. DESMYTER, B. LAETHEM, B. SIMONS, J. VAN DESSEL and J. VYNCKE Disintegration of Fly Ashes i? the Rotary-vibration Mill J.SIDOR and M.A. WOJCIK

.............

.......................................

759

775

Release of Heavy Metals from a Municipal Solid Waste Incineration Residue Stabilized in Non-traditional Matrices ............................................................. V. ALBINO, R. CIOFFI, B. DE VITO, M. MARROCCOLI and L. SANTORO

789

Applications of By-products from Coal Gasification Power Plants: Quality- and Environment-Related Aspects ........................................................................ M.L. BEEKES, J.W. VAN DEN BERG and A.J.A. KONINGS

80 1

Quality Improvement of MSW Fly Ash and APC Residue from MSW Incinerator Amsterdam-West using Different Iinmobilisation Processes ................................... H.T.M. VAN DE LAAR, J. SLAGTER, R.F. DUZIJN and J.H. DE ZEEUW

81 1

Certification System for Aggregates Produced from Building Waste and Demolished Buildings ................................................................................................ C.F. HENDRIKS

82 1

Sampling and Sub-sampling of Primary and Secondary Building Materials: A Statistical Treatise .................................................................................. A.M.H. VAN DER VEEN and D.A.G. NATER

835

Industrial Scale Application of the Alkali Activated Slag Ceinentitious Materials in the Injection Sealing Works ...................................................................... W. BRYLICKI, J. MALOLEPSZY and S. STRYCZEK

84 1

The use of MSWI Bottom Ash in Asphalt Concrete ............................................. M.M.T. EYMAEL, W. DE WIJS and D. MAHADEW

85 1

How to Prevent Expansion of MSWI Bottom Ash in Road Constructions? ................. M.M.C. ALKEMADE, M.M.T. EYMAEL, E. MULDER and W. DE WIJS

863

Microstructure of Concretes Containing Artificial and Recycled Aggregates J.A. LARBI and P. STEIJAERT Frost Susceptibility of Recycled Aggregate M.M. O’MAHONY

................

877

.......................................................

889

...............................

897

Use of Crushed Tile and Concrete as Filling in Pipe Trenches J. FOLKENBERG

XV

Use of Ashes from MSW Incineration in Cementitious Building Materials A. GERDES and F.H. WITTMANN

................. 905

Effect of Grain Size Composition of the Calcium-sulphate Fly Ashes on the Properties of Autoclaved Building Materials ..................................................... Z. PYTEL and J. MALOLEPSZY Sulphate and Acid Attack on Concrete i n Ground and Landfill C. PLOWMAN

...............................

909 917

Contaminated Soil Cement Stabilizations for Application as a Construction Material .................................................................................................. P.J. KROES and J . VAN LEEUWEN

925

The Assessment of a Pollutant Charge of Dredged Sediments as a Tool to Minimize Adverse Environmental Effects ...................................................................... E. PERIS-MORA, J. MONZO, J. PAYA and J.M. MESA

929

Minestone Substraturn,Behaviour under Loading ................................................ K.M. SKARZYNSKA and E. ZAWISZA

939

Ecological and Energy-saving Advantages and Benefits of Building with Earth .......... H. HOUBEN

94 1

Fly Ash and Slag Reactivity in Cements - TEM Evidence and Application of Thermodynamic Modelling ........................................................................... H.S. PIETERSEN and J.M.J.M. BlJEN

949

SECTION 4: Closing State of the Art Report: Use of Waste Materials in Construction Technological Development .......................................................................... G.R. WOOLLEY

963

...............................

979

A Unified Approach to Leaching Behavior of Waste Materials T.T. EIGHMY and H.A. VAN DER SLOOT

This Page Intentionally Left Blank

SECTION 1: Opening

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA.van der SIoot and Th.G. Aalbers (Editors) @I994 Elsevier Science B. V. All rights resewed.

3

THE INTERNATIONAL ASH WORKING GROUP A TREATISE ON RESIDUES FROM MSW INCINERATORS

S.E. Sawell', A.J. Chandler*, T.T. Eighmy3, J. HartlCn4, 0. Hjelmars, D. Kosson6, H.A. van der Sloot' and J. Vehlow8 'Compass Environmental Inc., Burlington,Ontario; 2 k J . Chandler C Associates Ltd., Willowdale, Ontario; Wniversity of New Hampshire, Durham, N H 4SwedishGeotechnical Institute, Linkoping, Sweden; SDanishWater Quality Institute, H0rsholm, Denmark; 6RutgersUniversity, Piscataway, NJ; 'Netherlands Energy Research Foundation,Petten NL; and *KernforschungszentrumKarlsruhe, Germany. INTRODUCTION Historically, public opposition to the siting and operation of MSW incinerators has been based on concerns over emissions of contaminants to the atmosphere. During the late seventies and early eighties, much of this concern was justifiable in light of the poor performance of inadequately designed and operated facilities. In addition, the enhanced ability of scientists to detect trace contaminants a t very low concentrations placed further pressure on the industry to reduce emissions. During the last decade, the industry has responded positively. Most of the concerns related to emissions have been addressed by optimizing incinerator design and operation through improved combustion control. This and the implementation of new air pollution control technologies has dramatically reduced atmospheric emissions. The advent of more efficient incinerator operation and better designed air pollution control systems has resulted in concern shifting from air emissions to the disposal of the captured residues. Today, ash disposal is one of the major issues limiting the acceptance of new incinerator facilities.

The Incinerator Ash Issue In 1988, several individuals actively involved with ash research were prompted to suggest that the global data base on incinerator ash needed to be compiled, reviewed and critically evaluated. The major concern over incinerator ash centred on the potential for human exposure to contaminants, specifically trace metals in the ash. The potential exposure routes were deemed to be either through the inhalation of fugitive dust or the ingestion of contaminated groundwater. While the industry was moving to address these issues, environmental groups continued to push for more stringent regulations for the disposal of the residues. Several factors contributed to this situation:

o The heterogeneity of the ash characteristics often resulted in contradictory laboratory results; o Residue sampling and analytical protocols were not well established, thereby compounding the variability of the data; o Different combustion technologies and air pollution control systems produce additional variations in the quality of the residues, and thus the data bases exhibit large variations;

4

o Cursory groundwater studies provided an inadequate data base on the long-term effects of monofills on groundwater; and, o The management of these residues had to consider the contentious issue of potential long-term effects, particularly in view of the changing nature of the MSW stream. All of these factors contributed to a highly fragmented data base, which in turn, had resulted in much confusion and a preponderance of misconceptions. The researchers thought that a critical review of the data would provide an opportunity to clarify many of the issues. Thus, in April of 1989, a proposal entitled: "MUNICIPALWASTE INCINERATION: AN INTERNATIONAL PERSPECTIVE ON THE CHARACTERISTICS, DISPOSAL, TREATMENT and UTILIZATION OF RESIDUALS"

was submitted to the International Energy Agency (IEA) for consideration and this led to the establishment of an International Ash Working Group (IAWG). OBJECTIVES While the general purpose of the project was to put the MSW incinerator ash issue into proper perspective, the project had some specific objectives. 1. Provide a compilation of existing knowledge concerning MSW incinerator residues;

2. Define uniform protocols for the sampling and full characterization (including defining chemical, physical, and leaching properties) of incinerator residues; 3. Describe the fate and behaviour of contaminants during the incineration process including documenting the effects of different incinerator designs, air pollution control systems, incinerator operations and refuse feedstocks; 4. Evaluate and develop recommendations with regard to current or proposed disposal, treatment

utilization and recovery practices; 5. Provide regulators with recommended standard performance criteria for the residues under

different management scenarios; 6. Identify areas for further research and development.

APPROACH

The IAWG has formally met 12 times over the past four years. In addition, international seminars have been held on several occasions to bring together regulators and researchers to discuss economically and environmentally sound ash management practices. For example, the IAWG has held two major seminars on leaching protocols, one in Europe and the other in North America. Most of each meeting was devoted to review of specific topics as selected from the original outline. Members of the group prepared for the meetings by gathering together information on the selected subject(s) and provided this material to the group at the meetings. The discussions that ensued lead

5

to the development of draft chapter outlines, which were used to develop the full chapters. Draft chapters were then distributed to the sponsoring agencies for review and comment. In addition to the original mandate of the Group, the IAWG has been designated as a full Activity under the International Energy Agency’s Bioenergy Agreement - Conversion of MSW to Energy Task XI. Consequently, the IAWG now has a mandate to meet through 1994 to consider revisions to the final report based on the review of any new evidence from current research topics.

Benefits

The IAWG is committed to providing the sponsors with the information necessary to make sound decisions regarding MSW incinerator residue management. 1. Outline criteria for data gathering to assist other researchers with project development and generation of quality comparable data; 2. Develop a framework on which to build characterization protocols for assessing incinerator residues;

3. Provide a bench-mark for other researchers by compiling the data and identifying areas requiring further research; 4. Enable regulators, the public and industry to make decisions on the environmental acceptability

of alternative management options for the residues; 5. Develop a framework for international collaboration on managing other wastes.

Sponsorship In order to ensure objectivity, the IAWG sought out funding based on equal contributions from a large number of government agencies, private organizations and companies. The IAWG gratefully acknowledges the support provided by: Maior Soonsors Asea Brown Boveri Ltd Danish Ministry of Energy Energy, Mines & Resources Canada Environment Canada European Economic Community KernforschungszentrumKarlsruhe International Energy Agency Integrated Waste Services Association Minor SDonsors American Society of Mechanical Engineers Greater Vancouver Regional District Northeast Waste ManagementOfficiabAssociation

International Lead Zinc Research Organization LAB France

NOVEMlRIVM Netherlands Swedish National Board for Industrial & Technical Development United Kingdom Department of the Environment United States Environmental Protection Agency Wheelabrator EnvironmentalSystems Inc.

New Jersey - Solid Waste Administration Waste Processing Association Netherlands

6 REPORT OUTLINE In order to develop better options for the management of MSW incinerator ash, full characterisation of the different residues and knowledge of the factors which influence those characteristics are necessary. Consequently, the scope of the report was expanded far beyond that originally anticipated. The current document now includes discussions on a wide range of topics directly related to ash management, including:

o the physical and chemical composition of municipal solid waste, and a summary of how it is managed in the various countries;

o the variations in incinerator and air pollution control technology and how these will influence the characteristics of the residues; o the regulations governing the operation of incinerator facilities and residue disposal; o recommended sampling and analysis methodologies for the residues; o the characteristics of various residue streams based upon the recommended characterisation protocol; o the fate of elements during incineration as a function of waste feed input, incinerator/APC technologies and operation; o the leaching of residues, including a discussion of fundamental physical and chemical aspects, as well as interpretation of appropriate test methods, leaching modelling and detailed discussions of laboratory and field leaching data; o the potential fate of elements in the environment as a function of management practices; o the treatment and modification of residues including a generic outline of possible alternatives and detailed discussions of solidification/stabilization,separation, and thermal treatment. o the chemical, physical and leaching properties of products made from treated incinerator residues; o the disposal or utilization of residues, including a review of the alternatives available and the influence of fate and transport systems, i.e., short and long term impacts; and o identification of areas for further study.

Overall, the report represents a comprehensive examination of the complex issues pertaining to MSW incinerator residues. The IAWG has prepared a summary of the full report which will be distributed in conjunction with this conference. It is anticipated that the full document will be published in hard-cover form and made available to the public in the near future.

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, HA.VM der S I w t and l71.G.Aalbers (Editors) @I994 Elsevier Science B.K AN rights reserved.

7

International Progress in Solid Waete Management John H. Skinner, Ph.D. President of ISWA the International Solid Waste Association Bremerholm 1, Copenhagen K, Denmark DK 1069

Introduction: Solid Waste Management, The Environmental Issue of the '90's. Solid waste management has moved to the forefront of the environmental agenda. The level of activity and concern by citizens and governments worldwide have reached unprecedented levels. Nations are considering restrictions on packaging and controls on products in order to reduce solid waste generation rates. Local and regional governments are requiring wastes to be separated for recycling, and some have even established mandatory recycling targets. Concerns about emissions from incinerators and waste-to-energy plants have resulted in imposition of state-of-the-art air pollution controls. Landfills are being equipped with liners, impervious caps and leachate collection systems, and gas and groundwater is being routinely monitored. There is wide scale public opposition to siting of new solid waste treatment and disposal facilities. As a result, the costs of solid waste management are increasing rapidly. Previously considered a local issue, it is now clear that solid waste management has international and global implications. Concerns about transboundry shipment of hazardous waste has led to the adoption of the Base1 Convention by the United Nations. Recognizing the interrelationship between solid waste standards and economic development, the European Community is moving forward to harmonize waste disposal requirements in member countries. Around the globe countries are discovering thousands of sites where hazardous wastes have been spilled, dumped or otherwise discarded resulting in contamination of soils, surface waters and ground water. The economic costs of clean-up these sites will stress national economies and at the same time offer enormous international business opportunities. Solid waste management in countries with developing economies poses a special set of problems. In these countries quite often financing is not available for the construction of waste treatment facilities, and there is a lack of trained personnel to operate waste management systems. Also, there are generally no regulations or control systems, no administrative body responsible for solid waste control and no obligation for industry to dispose of wastes properly. The United Nations Environment Programme has focused on solid waste management in developing economies as a priority concern. More than ever before, solid waste management policy makers world wide need sound and reliable information on the technical performance, environmental impact and costs of solid waste

8

collection, recycling, treatment and disposal systems. ISWA, the International Solid Wastes and Public Cleansing Association is putting forward a number of programs that are trying to address that need.

The Mission and Organization of ISWA. The objective of ISWA is to promote the adoption of effective and economically sound solid waste management practices that protect the environment and conserve materials and energy resources. ISWA is a professional association open to members from all countries in the world. Its activity is solely in the public interest through professional development of its members; it does not pursue any commercial or political aims. ISWA is truly an international organization in that its governing body, the General Assembly, is made up of National Members from 20 countries around the world. Most countries with an established solid waste management infrastructure hold National Membership in ISWA. National Members must be national organizations representing all professional activities related to solid waste management in the member country. National Members are encouraged to form national committees of solid waste professional associations within their countries to assure a broad representation in ISWA. It is this international network of National Member organizations that provides ISWA the ability to reach thousands of solid waste professionals throughout the world. ISWA also has over 700 individual and organizational members in over 60 countries. Recognizing the special solid waste management problems in developing countries, ISWA also provides a Development Membership category pending the establishment of a fully functioning National Member organization.

ISWA Programe. ISWA carries out its mission through a series of efforts to collect and disseminate information to its members. The ISWA Journal, Waste Management and Research is published six times a year by Academic Press and has a ten year history of successful issues containing high quality peer reviewed articles. Our newsletter, the ISWA Times is published quarterly and provides practical and useful information to its readers. The ISWA Yearbook, the International Directory of Solid Waste Management and Public Cleansing, provides extensive listings of companies and organizations in the solid waste field, as well as a wide range of articles summarizing activity throughout the industry. ISWA sponsors and cosponsors a number of conferences, workshops and symposia. Important ISWA conferences and congresses for the next several years include: 1994 ISWA Annual Conference, in conjunction with the UK Institute of Wastes Management, Torbay, UK, June 14-17, 1994.

9

ISWA 25th Anniversity Congress, Vienna, Austria, October 16-20, 1995. ISWA Quadrennial Congress, Yokohama, Japan, October 27November 1, 1996. In order to provide the opportunity for the development of specialized ISWA activities, working groups on the following seven subjects have been established: Hazardous Waste Sanitary Landfill Incineration Recycling and Waste Minimization Collection and Transport Sewage and Water Works Sludge Biological Waste Treatment. ISWA members can belong to these working groups and engage in practical information exchanges with members from other countries. Through these working groups ISWA holds many specialized symposia and workshops and has developed an international solid waste professional book and report series.

Integrated Solid Waste Management. ISWA members and most other solid waste management professionals recognize that there is no single, simple solution to solid waste problems. Instead an integrated approach is necessary combining the elements of several techniques. In the United States, the Environmental Protection Agency published The Solid Waste Dilemma: An Agenda for Action, which outlines an integrated set of strategies for dealing with solid waste management. These strategies are very similar to those recommended by the European Commission, the United Nations Environment Programme and countries around the world. Integrated solid waste management is a comprehensive strategy involving four key elements applied in a hierarchial manner: 1.

Reducing the volume and toxicity of the solid waste that is generated,

2.

Recycling or reusing as much as possible of what is generated,

3.

Recovering energy from the remaining waste through combustion systems equipped with the best available pollution control technology, and

4.

Utilizing landfills with adequate environmental controls.

In the following sections each of the elements of this strategy will be discussed in turn. Also recent data on U.S. practices will be presented for purposes of illustration.

10

Waste Reduction. Waste reduction activities are important to halt or slow down the increasing rate of waste generation per-capita. For example, the most recent data from the U . S . indicates the total amount of municipal solid waste increased from 180 million tons in 1988 to 196 million tons in 1990, which represents an increase in the per capita generation rate from 1.82 to 1.95 kg. per person per day. Waste reduction has several aspects, all of which should be addressed. One is toxicity reduction, in which the nature of waste is changed by reducing manufacturer's use of toxic materials in consumer products. Another is volume reduction-cutting the amount of waste generated by using less material in the first place. A prime example of this is a reduction in packaging. Waste reduction also includes encouraging the production of products that can be recycled more easily, such as shifting from multimaterial to one-material packaging. Other options to reduce wastes include the redesign of products, material use changes, and restrictions on specific product types. The approach to reducing waste must be broadly based incorporating actions that can be taken by industries, individuals, commercial enterprises and governmental agencies. Industry can reduce waste through raw material substitution and redesign of products and processes. Individuals, commercial enterprises and agencies can use their purchasing power to create a demand for low waste products or items produced from recycled materials. Governments should investigate the use of economic and other incentives to encourage waste reduction. Waste reduction efforts also need to focus on consumer behavior. Education and information dissemination programs can be effective means of causing desired behavioral and attitudinal changes. There are many cases of successful reduction of wastes produced by industrial processes. Experience has shown that modifications to industrial processes that reduce waste also result in lower raw material, energy and waste disposal costs. Productivity is often enhanced and liabilities related to release of hazardous substances are reduced. The fact that waste reduction quite often pays has been demonstrated repeatedly.

Recycling. There are two basic approaches to recycling solid wastes. The first involves separating recyclable materials by the waste generator and separately collecting and transporting these materials to recycling markets. The second involves collecting mixed wastes or commingled recyclable materials and separating them at a central processing facility. In the U.S., through a combination of these practices the percentage of the municipal solid waste stream recovered for recycling or composting increased from 13 percent in 1988 to 17 percent in 1990. Prior separation of recyclable materials has the advantage that the materials are not contaminated by other wastes.

11

However, this requires the waste generator (e.g. householder) to separate the wastes correctly and store them in separated form. Also, the generator needs to transport the separated material to recycling centers or separate or compartmentalized collection vehicles need to be used. Key factors in success of preseparation efforts are the cooperation and willingness of the generator to participate in the program over the long tern, and the additional collection and transport costs that may be required. Mixed solid waste can be separated for recycling at local processing centers or materials recovery facilities (MRFs). Inn the U.S. for example, there are over 200 MRFs in operation, construction, or advance planning stages. Some plants process segregated recyclables; others separate mixtures of glass bottles, aluminum cans and steel cans; still others process mixed residential or commercial wastes, separating the recyclable materials. The success of these plants depends on the processing costs and the quality of the recyclable material produced. A major factor affecting recycling economics is the difference in cost between disposal and recycling. In many locales this cost difference is narrowing. For example, in the U.S. the disposal fee for landfills and waste-to-energy plants has increased dramatically over the past 10 years. Today, on the average, a solid waste management system in the U.S. can avoid $25 to $40 per ton in disposal costs for every ton it recycles, whether or not it gets paid for the recycled material. In some locations the savings are even higher. A major recycling impediment is the question of continued viability and availability of secondary materials markets. Can manufacturers expand markets so they can accept all of the material that is being collected by the new residential programs? Topping the list of problematic waste material markets is the market for old newspaper. In the late 1980s, there was dislocation in markets due to an oversupply created by the large number of municipal collection programs that were all bringing new supplies to markets simultaneously. Many U.S. municipalities were forced to pay to recycle collected newspapers. Current market figures show that the value of old newspaper varies from $40/ton to a -(negative) $4O/ton. Problems are also being experienced in other recycled material markets, including those for glass, plastic and for compost produced from yard waste and mixed municipal solid waste. There are some encouraging trends that suggest the problem of oversupply of old newspaper could be reduced. Some newsprint producers in the U.S. and Canada have announced plans for new facilities to make use of recycled fiber. Others have undertaken feasibility studies for new facilities. It is important to understand that separation of materials from the solid waste stream in itself does not constitute recycling. Recycling only occurs when these materials are incorporated into products that enter commerce. Therefore requirements to separate certain fractions of materials from waste may produce a supply of materials, but these requirements

12

in themselves will not ensure recycling. In fact, if markets for these materials are not found, and the materials are subsequently disposed of, all of the costs of recycling are experienced with none of the benefits. Similarly, requirements to incorporate separated waste materials in products will not result in recycling unless these products are of a quality and price that they successfully compete in the marketplace. To analyze the economic feasibility of recycling one must consider the price received for the recycled material, the solid waste collection and disposal costs avoided and the costs of separation, collection and processing the separated materials. In making these cost comparisons it is important that all environmental costs and benefits are internalized. Also, the benefits to future generations in terms of natural resources conserved or landfill space conserved must be considered. Any virgin raw material subsidy that artificially drives down the price must be accounted for so that virgin materials and recycled materials compete in an equitable manner. Similarly, procurement specifications that arbitrarily discriminate against recycled materials should be eliminated. In order to effectively carry out successful recycling programs, solid waste managers must operate in a business-like manner as raw material suppliers. They must treat the users of their materials as customers. This means they must produce recyclable materials meeting the customer's material quality requirements, and offer recyclable materials at a price competitive with other material supplies. They must operate their separation, collection and processing systems to produce competitively priced, quality materials at the lowest possible costs. The elements of success of a recycling operation are the same as for any successful business; staying close to the customer, understanding and meeting their quality needs and operating in a cost effective manner to produce a competitively priced product.

Combustion with Energy Recovery. Waste-to-energy facilities can achieve an 85% volume reduction in the waste burned. In the U.S. these plants have increased their handling of solid wastes from a negligible percentage of the municipal solid waste stream in the early 1980s to almost 16% of municipal solid waste today. Waste-to-energy plants have faced two main problems in their fight to win public acceptance: air pollution concerns and the heavy metal content of the ash generated in the combustion process. On January 14, 1991, the U.S. EPA issued regulations for new municipal (New Source Performance Standards, or NSPS) and guidelines for existing plants. These standards incorporate good combustion practices, emissions monitoring and highly efficient air pollution control systems to control organic emissions (dioxins and furans), metals, acid gases and other pollutants. The standards are similar to those used in other countries to regulate incinerators. EPA estimated that in 1994 the national costs of these rules will be $170 million a year for new

13

facilities and $302 million a year for existing facilities. Therefore in the U.S. there will be a substantial financial investment to upgrade the environmental performance of municipal incinerators. Another environmental concern that has developed over the past several years involves the disposal of ash residues from municipal waste incinerators. Usually significant amounts of lead, cadmium, zinc, mercury, arsenic, and other metals are found in incinerator ash, especially fly ash. The environmental concern is the potential for these metals to leach out of the residue when disposed of with other wastes in a sanitary landfill. This has led to the utilization of monofills or landfills used solely for ash disposal. In September 1992, the U . S . EPA issued an opinion that ash generated by solid waste-toenergy incinerators is not considered a hazardous waste under Federal law and that the new requirements for solid waste landfills will ensure that ash is disposed of in a manner that protects human health and the environment. Also, technologies have been developed to chemically extract metals from incinerator ash or to solidify and stabilize the ash by adding cement or kiln dust to create a concrete like substance. While these technologies are effective in removing or stabilizing metals, they do result in added disposal costs. Some of these costs can be offset if the ash is treated to the extent that it can be used safely and sold as an aggregate or building material. In the U.S. over 8 million tons of incinerator ash are produced annually.

Landf i 11s. Landfill technology has advanced very rapidly over the past decade. Today's state-of-the-art landfills are equipped with leachate collection systems, liner systems, systems for control of landfill gas, groundwater monitoring, closure and post-closure care and much more. The objective is to ensure that landfilling is performed in a manner that greatly reduces the change of environmental degradation--and also, that any degradation that occurs is quickly detected and remediated. In the U . S . the number of landfills continues to decrease, two main consequences are seen: first, communities face longer transport distances to deliver their solid waste to disposal sites; secondly, several large facilities, designed to serve a limited number of communities for a given number of years, are seeing their lifespans drastically foreshortened by the influx of waste from outside their service areas. Due to more stringent landfill regulations, many small facilities will shut down because they will be unable to meet the new requirements. A hoped-for-result is a decrease in opposition to landfills, stemming from greater public faith in the environmental soundness of facilities that are allowed to operate.

14

Some observers believe the combination of continued strong public opposition and tougher landfill rules will result in a system of large, remotely located regional landfills. Signs of this can be seen already.

A Strategy for Continuous Improvement. Over the past 20 years there has been substantial progress in addressing solid waste problems. However, many problems still exist and we understand them to be very complex. To deal with them, the strategies that have been used in the past will not be enough. As we move towards the 21st Century, a number of forces must come together to lead to continuous improvement in solid waste management. These include:

Continued, Rigorous Enforcement of Environmental Laws and Environmental standards must be rigorously Regulations. enforced in order to assure the public that our solid waste systems are operated in ways that protect human health and the environment. Enforcement must create an incentive for compliance with environmental standards. It must level the playing field so that violators are not at a competitive economic advantage to the good citizens that comply. Waste Reduction as the Strategy of Choice. The traditional approach to solid waste management has been a pollution control strategy where wastes are collected and treated or disposed of after they are generated, or waste is cleaned up after it has occurred. A waste reduction strategy is different, it means not creating the waste in the first place. This can be accomplished through changing product designs, increasing process efficiencies, and extending product lifetimes. Waste reduction results in reduction in waste treatment and disposal costs, reduced liability for environmental damages, lower raw material costs and process efficiencies. Risk-Based Decision Making. Solid waste management decision-making must be based on a comparative analysis of the relative environmental risks of the various options available. Quite often there is public opposition to a particular facility because of concern about environmental risk. While the public expresses a preference for recycling over waste-to-energy or landfill, it is often forgotten that the recycling process itself produces waste or residuals that must be managed or disposed of (eg. waterborne wastes produced from the deinking of recycled newsprint or increased air pollution from additional collection vehicles). In order to make an informed decision, the risk of one option must be compared to the alternatives. Priorities must be based on relative environmental risk. In order to do this we need to develop better and more reliable risk assessment methodologies and put them to use. Significant advances need to be made in our capabilities to assess the risks to ecological systems. An investment in risk assessment research will certainly pay off. Public Information to Encourage Voluntary Action. Providing data and information to those who make or influence decisions can

15

lead to voluntary actions with significant environmental benefits. A good example is the Toxic Release Inventory (TRI) in the US. Each year industries are required to publish the total release of certain toxic wastes to the environment and make this information publicly available. When the public for the first time realized the total environmental releases from all of these plants and facilities, they demanded that something be done about it. This led to the establishment of the 33/50 Program. Under this program companies voluntarily agree to reduce their waste discharges of by 33 percent by the end of 1992 and 50 percent by the end of 1995. Over 700 companies have made written commitments which will reduce the discharge to the environment of 150,000 tons of toxic chemicals by 1995. Information is a powerful tool which can stimulate real results.

Environmental Education. As the above example shows an informed public can be an effective force in environmental protection. However, professionals in the field must do a much better job in explaining to the public the true nature of environmental risks and what can be done about them. The National Environmental Education Act which was passed in the US in 1991 provides some excellent vehicles for doing this including (1) support for environmental curriculum development, (2) assistance for teacher training and ( 3 ) scholarships and fellowships for environmental science and engineering. It is very important to increase environmental literacy to build public support for environmental programs and train future generations of environmental professionals. Economic Incentivee. Market based economic incentives can be used as an alternate to regulation or as a means of making regulations more effective. For example, the liability standards under the US Superfund legislation make a waste generator liable for environmental damages caused by that waste. This produces a very strong economic incentive for waste reduction and on-site waste treatment. Other economic incentives such as pollution charges and deposit systems should also be evaluated for future solid waste management policies. Research and Development. A sustained, long term research and development effort is necessary to improve our understanding of the environmental impacts of solid waste management systems and develop solutions. What are the health effects of environmental releases from solid waste management systems. How do pollutants move through the environment and change in their physical and chemical form? What are the routes of exposure for human populations and ecological systems? How can we monitor and detect pollutant levels in real time? What are the most cost effective approaches to waste reduction, recycling, combustion nd disposal. These are just a few of the questions that research must address. However, research should not be limited to technological and physical science issues. Research into the social and economic aspects of solid waste management is necessary to understand and better design economic incentives and information and education programs.

16

-

Technology Transfer Domestic and International. Research and development alone is not enough, the results must be transferred into the field as new and improved solid waste management systems are developed. Therefore, outreach efforts to apply the results of research are essential. This is especially true on an international basis where there are potentially large market opportunities for cost effective environmental technologies. Technology transfer to countries with developing economies is especially important, if we expect these countries to be able to participate effectively in improving the global environment. Integration of Solid Waste Management Policy With Other Policies. Other national and international policies can have as strong or stronger influence on solid waste management as can environmental policies. Consider the effect of: (1) energy policy on the incentives for waste-to-energy facilities, (2) transportation policy on freight charges for recycled materials, (3) agricultural policy on the uses of sludges as fertilizers or soil conditioners. Other examples include the effect of financial policy on investment into environmental technologies and military policy's effect on clean-up of defense installations. Solid waste management professionals must play a role assuring the solid waste management implications of these policies are assessed in national and international forum. These are the issues that will be facing the solid waste professional of the future. There remains a tremendous opportunity to improve waste management through technological development. However it will be necessary to combine technical and engineering skills with risk assessment, market forces, public information and education, enforcement strategies, pollution prevention, research and development and technology transfer. Solid waste management professionals must show leadership in developing broad based strategic initiatives to bring about continuous improvement in integrated solid waste management. To find out more about ISWA programs and activities including membership information contact the General Secretariat in Copenhagen Denmark.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A van der Sloot and Th.G. Aalbers (Edtors) 01994 Elsevier Science B.V. All rights resewed.

17

LIFE CYCLE ANALYSES; RESULTS OF SOME C A S E STUDIES

J . Cramer, TNO Centre for Technology and Policy Studies,

P . 0 . Box 541, 7300 AM Apeldoorn, The Netherlands

INTRODUCTION

Environment-oriented product policy has become a central focus of Dutch environmental policies. The aim of this policy is Yo prevent, or at least reduce, the effects on the environment caused by products in the various phases of the product life cycle'. Up to now the government has placed the emphasis mainly on developing methods of analyzing the environment-friendliness

of

products

(environmental life

cycle

analyses). Experience has been gained in the application of life cycle analysis for various purposes. Of particular interest a r e four different applications :

-

the use of life cycle analysis in 'eco-design'

-

the use of life cycle analysis in 'integrated chain management'

-

the use of life cycle analysis in information exchange between

the use of life cycle analysis in product comparisons

producers in a product chain

In this contribution the experiences with these four types of application will be discussed on the basis of case studies. Many of these case studies have been conducted on behalf of the Netherlands Company for Energy and the Environment (NOVEM) (often together with the State Institute for Public Health and Environmental Hygiene (RIVM))

.

18 LIFE CYCLE ANALYSIS

Before dwelling upon the various applications of life cycle analysis I shall first explain in more detail the principles of life cycle analysis. A

life cycle analysis of a product is the systematic analysis of the environmental impact of a product, calculated over the entire life cycle of a product ('from cradle to grave'). Life cycle analysis is often combined with an assessment of the environmental impact of a product (together called 'life cycle assessment' ( L C A )

.

A full life cycle assessment is made up of five components which

together form a comprehensive structure. These components are (Heijungs et al. , 1992):

*

goal definition, including a consideration of the type of potential application;

* *

inventory analysis of environmental interventions ; classification and modelling of environmental interventions on the basis of their potential environmental effects;

*

evaluation of the product based on its potential environmental effects ;

*

improvement analysis aimed at changes which are desirable on environmental grounds.

There are various bottlenecks standing in the way of the further development and application of the LCA method, principally relating to its complexity. In practice, setting up an extensive LCA is extremely time-consuming , especially for individual companies. The development of environmental indicators has been promoted as a way of reducing the complexity of the LCA method. Environmental indicators are index numbers that express the environmental impact of

19 particular products in terms of a limited number of relevant units, specifically raw materials,

energy,

emissions, nuisance,

waste,

recyclability, reparability and the product's life. They a r e intended for communication purposes, for initiating an increase in environmental awareness and for regulation purposes (TAUW Infra Consult, 1992). Four main stages can be distinguished in the process of establishing environmental indicators (TAUW Infra Consult, 1992). Stage one involves setting the objectives : what a r e we establishing environmental indicators for? Stage two consists of the stock-taking: the entire chain is described and checked for impacts on the environment. Stage three

involves the classification: all the pieces of information obtained a r e classified according to workable categories. Finally, stage four consists of the evaluation: the data collected is evaluated, assessed and translated into environmental indicators.

I n principle, the purpose of environmental indicators is to present the

data from a LCA in a clear and simple form and so to simplify the exchange of information between the parties in the market. In a number of recent trial projects, for instance, environmental indicators have been drawn up for paper, plant trays, margarines, printer ribbons, paints, light sources, insulating plates and a particular make of high performance heating boiler.

It proved possible, in principle, to present L C A data in terms of environmental indicators. However, i t did not usually reduce the workload. In order to establish environmental indicators one still needs some form of life cycle assessment. A s a result, environmental indica-

20 tors a r e regarded as the results of a particular type of L C A , although the approach adopted for the LCA may vary.

THE USE OF LIFE CYCLE ANALYSIS IN PRODUCT COMPARISONS Up to now, a great deal of time and energy has been devoted to applying L C A to product comparison. For instance, what a r e the effects on the

environment of, respectively, a wooden, an aluminium or a plastic window frame or of an ordinary light bulb or a long-life light bulb or the milk carton as opposed to the milk bottle throughout the entire product life cycle ? Such comparisons are made, for example, in the context of ecolabelling or of debates elicited in society about the environmentunfriendliness of particular products. The results of these product comparisons have frequently been the subject of debate. This is due to the fact that various assumptions have to be made in assessing the environmental performance of a product. For instance, the results depend on how the boundaries of the object of study are defined. Moreover, the results will vary according to the technical qualities of the two products to be compared. For example, comparing a milk bottle with a milk carton requires assumptions about the technical qualities of both types of products. Finally, a lack of information on specific environmental aspects forces one to assess on the basis of incomplete data.

Thus, the value of LCA in product comparison is very much dependent on the acceptance of the data used, the system boundaries and the methodological aspects of

data interpretation, classification and

evaluation. In order to minimize the degree of subjectivity in assessing the environmental performance of products, attempts are being made to

21 establish an internationally accepted methodology. At the international level, SETAC (Society of Environmental Toxicology and Chemistry) is the leading forum for the development of such an accepted methodology.

THE USE OF LIFE CYCLE ANALYSIS I N 'ECO-DESIGN' The LCA approach ha5 not generated a great deal of experience in the systematic improvement of products. It does, however, play a role in

' environment-oriented p r o d u c t development i n companies', commonly known as 'ecodesign'

. Environment-oriented product development can

be described as: designing and developing a product in such a way that environmental criteria a r e given equal weight to other criteria.

This

method seeks to limit, or if possible prevent, deleterious effects on the environment throughout the product's life cycle.

A number of demonstration projects have already been conducted in the

Netherlands in the field of environment-oriented product development, especially in the context of programmes such as Ecodesign and Milion. The designs have included an environment-friendly office chair, a reusable plant tray for flower auctions and a new package for dried coffee creamer. There has also been a growth in international demand for environmentally aware product design and development. This was also evident from the first European 'Design for the Environment' Conference which was held in Nunspeet, the Netherlands between 21-23 September 1992 (National Reuse of Waste Research Programme, 1992).

To date, the demonstration projects have been instituted mainly in cooperation with interested individual companies. The major problem in the implementation of these demonstration projects has been a lack of

22 environmental information. This could be a lack of information about the environmental properties of substances and materials that might be used,

for instance. Nor was there always adequate information

regarding the application of materials in products, the use of products or the disposal of the waste produced by them.

In view of this lack of information, it proved difficult in practice to use an extensive LCA. Moreover, resource limitations and time constraints led to the application of a simplified, 'streamlined' LCA. This implies that only the major environmental bottlenecks in the product chain were identified and improvements to the product were concentrated on these. The selection of these improvement options is still largely based on an ad-hoc approach. Improvement options are not systematically compared.

As a result,

environment-oriented product development initially

developed separately from the LCA method. This is gradually changing, however. On the basis of the experience already gained with environment-oriented product development there a r e a number of follow-up steps that could be taken (Cramer ( e d . ) , 1993). The first step would be to extend the attention to environment-oriented product development within the company as a whole. Up to now the projects have concentrated mainly on the design process in a company, which only involves one department.

A second advance would be to intensify the linkage between process and

product improvement. In the context of waste prevention and emissions, companies still concentrate mainly on process improvement; in this respect, the product is generally ignored.

23 On the other hand, with environment-oriented product development the production process is generally unaffected.

A third step would be to stimulate product improvement throughout the

entire chain o r column of companies involved in the manufacture of a certain product. This requires intensive cooperation between the various suppliers and customers in a given chain. The basis for such collaboration is the effective exchange of information between producers and within a product chain.

In response to the three problems raised above a third type of application has been initiated: the application of integrated chain management within companies.

THE USE OF LIFE CYCLE ANALYSIS IN 'INTEGRATED CHAIN MANAGEMENT' Integrated chain management has become a central concept in Dutch environmental policies. It is not a familiar concept abroad. In other countries, for example, the terms 'lifecycle management' o r 'productstewardship' a r e used in much the same way as the term 'integrated chain management'. Integrated chain management aims to ensure that substance cycles in product chains a r e managed in an environmentally, socially and economically responsible manner.

To realize such a 'sustainable

substance cycle' the relevant product must generate the least possible emissions and consume the least possible amount of energy in all phases of that product's life cycle (from extraction of the raw materials, the manufacture of the material and the product, via use by the consumer,

24 up to the disposal of the product in the waste s t a g e ) . This is why 'integrated chain management' transcends the individual company level and includes the whole product chain from cradle to grave. To encourage the adoption of integrated chain management in industry, in association with three companies TNO has developed a concrete methodology for i t s practical application. The participating companies were: AKZO Chemicals, EPON ( t h e Electricity Production Company for East and North Netherlands) and Van den Bergh Nederland (Cramer et a l . , 1993). In principle, this methodology does not differ fundamentally from that

.

of 'ecodesign' In practice, however, the present approaches diverge. The 'ecodesign' approach is to generate and select improvement options in a rather ad-hoc way, while 'integrated chain management' attempts to do this in a very structured way. Central to the method TNO and the three companies have developed is the identification and comparison of various options for bringing about environmental improvements both in the company itself and throughout the rest of the product chain. In this way, the company taking the initiative for chain management can act as a catalyst for change throughout the entire product chain.

The first step in the methodology for implementing integrated chain management is to select one major environmental bottleneck to be improved. This identification of environmental bottlenecks is based on a simplified, 'screening' life cycle analysis. The next step is a structured comparison of various improvement options on the basis of an ecological assessment.

25 To provide an indication of the extent to which a certain option constitutes an improvement from an environmental perspective, the "concept of environmental merit'lis introduced. "Environmental merit" is the difference in the environmental impact before and after the implementation of a given improvement option (including both the primary and secondary environmental impacts of the improvement option). After comparing the potential improvement options on the grounds of a purely ecological assessment, the social, technological and economic feasibility of the options and their suitability for the specific company a r e assessed. The option finally adopted will be determined by weighing up the ecological assessment and the social, technological and economic feasibility and the company-specific feasibility. The resulting step-by-step plan for implementing integrated chain management in individual companies has been tested in the participating companies. Although the approach followed should be further developed and evaluated, the experiences of the companies involved have been positive.

THE USE OF LIFE CYCLE ANALYSIS IN INFORMATION EXCHANGE BETWEEN PRODUCERS I N A PRODUCT CHAIN In order to bring about actual changes in products and production processes the information exchange between producers in a product chain is crucial. To date no structural system for such an exchange of information exists. In this context, the introduction of 'environmental product profiles' ( E P P ) is being investigated within the framework of

.

the Economic Commission for Europe ( E C E ) An environmental product profile is defined as an objective set of relevant environmental

information relating to a product and aspects of its life cycle, especially for producers and professional users (Weterings et al., 1993). The question, however, is which type of information should be exchanged among producers. To answer this question three case studies were carried out by TNO and TAUW Infra Consult in close cooperation with manufacturers. Three (groups of) products were selected: printer ribbons, roofing plates and carpets. The aim of the experiments was to test which type of information exchange was considered useful and advisable. The information presented was based on a 'screening' life cycle analysis. The quantitative data were presented by means of environmental indicators, such as the consumption of raw materials, energy consumption, greenhouse gas emissions, emissions of gases contributing to acidification, etcetera. In order to compare different forms of presentation, two versions with different levels of data aggregation have been developed: -

.

a long version (approx 10 to 20 pages) in which the environmental data consist of a classification of the (potential) environmental effects per step in the product chain and an evaluation of the most important environmental effects;

-

a short version (approx. 5 to 10 pages) in which the environmental data are limited to the evaluation of the most important environmental effects.

In response to these two sets of data those interviewed criticized the way in which environmental data were presented by means of environmental indicators. The amount of oil, gas and coal used, and the volume of several categories of emissions and waste products were quantified per product unit. Although, in general, quantitative data

27 were regarded as useful, most respondents felt the way in which the data w e r e presented was meaningless. They lacked the expertise to understand the quantitative indicators without a lengthy explanation of the reasoning behind the methodology and about the reliability of the resulting data. A few respondents even preferred one grade for all environmental aspects together. Based on the experiments it was concluded that authorities should take a cautious step-by-step approach in implementing E P P s. The content and presentation of environmental product profiles should be further developed

in

organisations

close

cooperation with

manufacturers

and

their

.

CONCLUSIONS

The above examples show the importance of life cycle analysis for various applications. Some bottlenecks in the use of life cycle analysis come to the fore as well. Due to the complexity of life cycle assessment ( L C A ) (including life cycle analysis) an extensive L C A is very time-

consuming. Moreover, an internationally accepted methodology of LCA i s still in development. In practice, therefore, simplified, so-called screening L C A ' s a r e often used. While the approaches used in various applications have been developed separately, there now seems to be a demand for closer attuning of these various approaches. This is a hopeful sign. Ultimately, coherence is needed in the methodologies for assessing and improving the environmental performance of products. This growing consensus will

28 stimulate both government and industry to put environment-oriented product policy into practice.

REFERENCES Cramer, J . et a l . , Theorie en praktijk van integraal ketenbeheer (Theory and practice of integrated chain management), NOVEM/RIVM, TNO- Apeldoorn, 1993.

Cramer, J. (ed. )

. , Productgericht

milieubeheer (Product-oriented

environmental management), Advisory Council for Research on Nature and Environment ( R M N O ) , publication nr. 78, Rijswijk, 1993.

Heijungs, R . et al., Environmental life cycle assessment of products, Guide and Backgrounds, NOVEM/RIVM, Centrum voor Milieukunde, Leiden, 1992.

National Reuse of Waste Research Programme, First NOH European conference; 'Design for the environment',

21-23 September 1992,

Nunspeet, the Netherlands, Utrecht , 1992.

TAUW Infra Consult, Environmental indicators; An evaluation of the pilot projects, NOVEM/RIVM, TAUW Infra Consult, Deventer, 1992.

Weterings, R . et al., The exchange of environmental product profiles between professional users : three case studies in the Netherlands, Discussion paper to the ECE-Seminar on low-waste technology and environmentally sound products, Warsaw, Poland, 24-28 May 1993, TNOApeldoorn, 1993.

SECTION 2: Environmental Aspects

This Page Intentionally Left Blank

Environmentol Aspects of Consttuction with Wmte Moterials JJJM Goumons, H A von &r SImt and l71.G. Aalbers (Edtom) a1994 Elsevier Science B. K All rights reserved.

31

Chemical Processes Controlling the Mobility of Waste Material Contaminants in Soils

L.G. Wesselink', P.M. Dekker' & Th. G. Aalbers' 1) National Institute of Public Health and Environmental Protection, P.O. Box I 3720 BA

Bilthoven, the Netherlands.

ABSTRACT

Effects of solid waste materials on the chemistry of underlying soils are investigated experimentally and through modelling of fundamental soil chemical processes.

INTRODUCTION

Solid waste materials are increasingly re-used in construction works [ 11. Release of contaminants from these waste materials may affect the chemistry of underlying soils and groundwaters. Metal ions are known to bind to soil organic matter and (hydr)oxides [ 2 ] , which strongly reduces their mobility in soils. Current knowledge of the fundamental mechanisms underlying these binding processes has been compiled in the ECOSAT model [3, 41. ECOSAT combines chemical speciation calculations with surface complexation- and transport models. Here, we report laboratory column experiments in which effects of leachates from steel- and phosphorous slag (P-slag) on four sandy soils were studied. The ECOSAT model will be applied to these experiments to identify and quantify processes that control contaminant mobility in soils under waste materials. To assess the potential hazards of waste materials to soils and groundwaters, knowledge of these processes is indispensable 11 I.

32 MATERIALS AND METHODS

Column studies

Steel- and phosphorous slag (P-slag) were percolated in large columns, up-flow with synthetic rain water @H ~ 4 . 5 )The . columns (30 cm diameter) held 90 kg of slag, and a flow rate of 0.2 US (l/kg) per day was maintained. Subsequently, slag effluents were percolated up-flow through four different columns holding 1 kg of soil, also at a flow rate of 0.2 L/S per day. The chemical composition of percolates at L/S= 0.1, 0.5, 1-5, 7.5, 10, 12.5 and 15 was analyzed. General characteristics of the soils are given in Table 1. Table 1. Soil characteristics

a is surface soil, b is sub soil, ox refers to oxalate extractable Fe aid Al

Model calculations

ECOSAT [3,4] calculates chemical equilibria involving speciation in solution, mineral

dissolution/precipitation and sorption on organic matter and hydroxide surfaces. In addition, transport (convective and dispersive) of dissolved species is calculated. Proton and metal binding to humic substances can be described by several variable or non-variable charge modules within ECOSAT. In this study, metal and proton binding was modelled using the multicomponent Langmuir-Freundlich equation (1). which considers the natural heterogeneity in binding properties of humic ligands [3, 51:

33 where O,., is the fraction of total available surface groups

(a,,,) covered with metal or proton

i, Ki the metal or proton surface complexation constant and m (O<m
RESULTS AND DISCUSSION

PH Percolates from steel- and P-slag were strongly alkaline with pH around 13 and 9.5 respectively (Fig. 1). Soils under P-slag were able to buffer the pH around a value of six throughout the experiments whereas soils under steel slag approached relatively quickly to the extreme high pH governed by steel slag (Fig. 1). The pH breakthrough observed in the soils under steel slag appeared in the order of soils D, A, C and B (extreme cases B and D shown in Fig. I), which is probably related to organic carbon content of these soils (Table 1).

Calcium Calcium was the dominant cation in both P- and steel-slag percolates, with extreme high concentrations in the latter (see Fig. 2). Calcium concenuations in steel slag percolates were close the Ca(OH), equilibrium, whereas Ca in P-slag had a lower solubility. Calcium was strongly retained in all soil columns (Table 2). Surprisingly, most soils maintained Casolubility below that of CaCO, (Fig. 2). The observed pH buffering around a value of six and Ca retention in the soils may be explained by Ca-proton (Ca-H) exchange on soil organic matter [3, 51. This is supported by observed Ca-H exchange ratios of around 0.6 (as derived from the slope in the pH-pCa diagram left of the CaCO, line in Fig. 2). This value is typical for Ca-proton exchange on humic substances [3, 51. Notice, that organic carbon contents in our soil are rather low (Table 1). Yet, even a organic carbon content of 1% may provide around 100 meq/kg-soil of carboxylic (-COOH) potential binding groups 161. In soils under steel slag, Ca inputs strongly exceeded this estimated potential binding capacity (Table 2). which explains the rapid breakthrough of pH in these soils. In Column-B (2.2% C)

,

5

14

steel-slag

12

I I

I

I D

I

W

P

I I I I I I

0

4

I

I I

I

I

I

B -

10

m

++

3

+

0

Ia

Y

c31

0 -

8

'

I I I D P-slag ..,."'.._,,I1 ..' ................................. ,... ..'..._.. .I,__ '.I...::."' __.. .._....'. .. ". ....,__.. " 't /,.: I I I II

I

i

I

'.'

,

I I jCaCO3 I I I I I

1

... 10

0

20

L/S ratio W k g soil)

,

CaCHi

I

0

4

0

8

II I

B

6

a

2

2

4

8

6

1 0 1 2 1 4

PH

Fieure 1: =-

Figure 2:

pH with dme in percolates of steel- and P-slag and soils (A, D) underlying these slags.

Calcium activities in percolates from slags and soils. Calcium ahvines were calculated with ECOSAT [3]. Srabiliry lines for CaOH, and CaCO, (at pC02=2.5) arc indicated. (+) arc pacolates from s t 4 slag and soils under steel slag and ( ) are percolates kom P-slag and soils under P-slag.

~~

35 approximately 250 meqkg of Ca was retained in the soil column until the moment of pHbreakthrough. This appears to match well with the estimated potential binding capacity of soil organic matter in soil B (220 meqkg). After the pH breakthrough, Ca solubility quickly approached that of Ca(OH),, as governed by steel slag (Fig. 2). In soils under P-slag, Ca retention during the experiment remained well below the estimated potential binding capacity. It is therefore expected that pH-buffering through Ca-H exchange in these soils will continue over prolonged time periods.

Table 2. Input-output balances of soil columns at L/S-soil=lS. Inputs are from slag percolates, outputs from soil percolates. Shown is input minus output in mmol/kg of soil material. Soils under P-slag

Ca A1 Fe

K Mg

A.

B.

C.

D.

-2.40 0.45 0.20 0.73 0.25

-3.13 0.47 7.30 0.89 1.24

-6.91 0.14 0.32 0.77 0.63

-3.13 -0.09 0.01

1.27 0.23

Soil under steel slag

________________________________

Ca A1 Fe

K Mg

-30 0.49 0.04 0.96 0.04

-153 1.07 2.37 0.80 0.47

-86 1.13 0.05 0.40 0.06

-61 1.17 0.023 0.64 0.01

Heavy metals

Generally, the pH is regarded as an important control on metal solubility 121.This is for our study illustrated in Fig.3 which shows that pH buffering toward a value of six decreases heavy metal solubility. Cadmium, Pb and Zn concentrations in our soils (below pH

7) were undersaturated with respect to mineral phases. Similar to Ca, observed pH-pM(etal) relationships between 0.5 and 1 (Fig. 4) can be explained by binding to soil organic matter surface groups [3,51.

d r

N

36

7

rl d

r

0

m ro

0

d

0 0 0 0

o n 0

I

h

N

0

I

co

M

d

37

Modelling Here, ECOSAT [3] will be applied to calculate the chemistry of the soil columns. For this purpose, a 'model' soil column is proposed in which metals and proton binding to soil organic matter is calculated. Binding to soil organic matter is described with the LF formulation (Eq. 1). The total binding capacity will be estimated from total carbon content, as discussed previously. Initial binding of metals to soil organic matter will estimated from pyrophosphate extractions (in prep.). Estimates for binding constants of metals and protons on humic compounds, and their heterogeneity, are available from recent studies [3, 5,7J.Thus it will be tested whether an independent set of model parameters can be applied to our experiments.

CONCLUSIONS

Laboratory column experiments indicated that exchange processes of H, Ca and heavy metals on organic matter control the solubility of these components in the investigated soils. Recent developments in soil science allow mechanistic modelling of these processes, which is of great importance to properly assess the potential hazards of waste materials to soils and groundwaters. Modelling results will be included in a full paper to be available at the WASCON '94 meetings.

REFERENCES

[l]

Aalbers, Th. G.et al., 1993. Milieuhygienische kwaliteit van primaire en secundaire bouwmaterialen in relatie tot hergebruik en bodem- en oppervlaktewaterbeschedng. RNM-report no. 771402006.

[2]

McBride. M.B., 1989. Reactions Controlling Heavy Metal Solubility in Soils. Advance in Soil Science, Volume 10.

[3]

de Wit, H. 1992. Proton and metal binding to humic substances. Phd-thesis, Agricultural University Wageningen, the Netherlands

38 [4]

Keizer, M.G. et al., 1992. ECOSAT, Technical note, Department of Soil Science and Plant Nutrition, Wageningen Agricultural University, the Netherlands.

[5]

Beneditti. M.F. et al., 1994. Metal ion binding to hurnic substances: experiments and modelling. J. Coll. and Int. Science. in press.

[6]

B u m a n , P. 1985. Carbon/sesquioxide ratios in organic complexes and the transition albic-spodic horizon. J. of Soil Science, 36. 355-260.

[7]

Tipping, E., and Hurley, M.A. 1992. A unifying model of cation binding by hutnic substances. Geochirn. Cosrnochirn. Acta 56, 3627-3641.

Envimnmental Aspcts of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) @I994 Elsevier Science B.V. All rights reserved.

39

-

Leaching of slags and ashes controlling factors in field experiments versus in laboratory tests A-M. Fallman and J.Hartlen Swedish Geotechnical Institute, S-581 93 Linkoping, Sweden, Abstract Significant differences in pH and redox potential were obtained in field experiments in comparison with the values obtained in laboratory column tests. Tested materials were blast furnace slag, steel slag, municipal waste incineration bottom ash (MSWI BA) and wood ash. All but the MSWI BA showed significantly lower pH in the lysimeter leachates. A result of the different controlling conditions in the field experiments was significant changes in leached amounts of some metals in comparison with laboratory tests. Other laboratory tests such as availability, oxidised availability and pH static tests were used to investigate the complex influences of pH and oxidation on leachate composition. 1. INTRODUCTION

Residues are the non-profitable end products in many industrial processes and energy production utilities. In combustion and smelting processes, slags and ashes are produced which in many cases have properties similar to geological materials. These materials can be used as filling and construction materials instead of being landfilled if the net environmental impact is acceptable. However, many residues have not been considered for utilisation purposes, while others have been discussed widely but are not yet accepted mostly because of possible environmental impact. It is important to identify the factors that classify a residue as usable or unusable. In the assessment of the suitability of such materials, not only the technical characteristics need to be considered but also the assessment of the possible environmental impact. During recent years, the processes governing leaching have increasingly become the focus in the discussions of leaching from residues. The actual leachate concentrations are regarded as a result of primary processes, the so-called controlling factors. van der Sloot et al (1991a) divided the factors into chemical, physical and biological factors. The chemical factors listed were: pH, redox, complexation of other components and reaction kinetics. The main physical factors relate to the water flow, while biological activities relate to changes in redox or concentrations of complexing components. Among the chemical factors influencing leaching processes and leachate concentrations, pH is so far the one studied most. Results from batch tests on coal combustion residues and MSWI residues show that leachate concentrations are highly pH-dependent for many substances (van der Sloot et al 1991b, DiPietro et al 1989). It was also shown that the same component gave different pH behaviour for different materials. van der Sloot (1992b) showed that pH dependency also changes with the amount of leachant

40

used, A study made by Hjelmar (1991a) on coal fly ash showed good agreement between laboratory column tests and lysimeter results. Some disagreement was seen for reduced ashes, where redox conditions changed during the lysimeter test. In the field of mine waste remediation, the problem of acid and metal contaminated mine drainage is of major concern. The problem is related to the instability of sulphides in atmospheric conditions. The sulphides are oxidised, producing both sulphuric acid and dissolving metals from the minerals (Steffen Robertson and Kirsten 1989). Almost all oxidation of sulphur species results in production of protons and thus a decrease in pH (Lindsay 1979). The solubility of the metals is also increased by the decrease in pH. Under these conditions, the factors controlling the leaching process are both redox and pH. Laboratory tests regularly used for investigating the leachability of residues, except for mine waste, are mostly relate leached amounts to the amount of percolated water (Fallman and Hartlen 1993). In these tests, pH and redox in the leachates are mainly dictated by the residue itself under water saturated conditions. Minor quantities of air are dissolved in the leachant and also minor amounts of acid when the leachant is acidified to simulate acid rain. Coarse grained material will rarely be water saturated under field conditions. Changes in the controlling factors in the field situation in comparison to what is obtained in the laboratory may change the entire pattern of leaching from a residue. Therefore there is a need for studying the influence of outdoor atmospheric exposure of different materials and the changes in the values of the factors controlling leaching. At the Swedish Geotechnical Institute (SGI) a project focussing on the factors controlling leaching from residues from smelting and combustion processes was started in 1992. Materials in this study have been chosen based on the following criteria: the materials must have physical properties relevant for utilisation in constructions, they must possess environmental properties that are not obviously environmentally non-acceptable and they must be produced in considerable quantities. Four materials were chosen: blast furnace slag (BF slag), steel slag, sorted municipal solid waste incineration bottom ash (MSWI BA) and wood ash, all of which are regarded as potentially secondary raw materials in constructions. BF slag has been widely used in road constructions in Sweden and sorted MSWI BA is discussed for utilisation purposes. In this paper, the results from laboratory leaching experiments are compared with the composition of the leachate obtained during almost one year run of the lysimeters. The comparisons focus on the differences in the values of the controlling factors pH, redox and flow in the laboratory tests versus the field tests and the consequences of these differences for the leachate composition. 2. MATERIALS AND METHODS 2.1 Materials

The samples for laboratory analyses and tests were taken from the material used in the lysimeters. The samples were dried at 105 "C and divided into laboratory samples before storage. The composition was analysed by using two different digestion methods: lithium borate melt for the main components and nitric acid in Teflon bomb and micro wave oven for certain trace elements. The analyses were made on ICP-AES and with ICP-MS for low detection by SGAB.Table 1 shows the composition of the materials.

41

Table 1 Total composition of the slags and ashes used. The materials were digested in lithium metaborate melt for main components and with nitric acid in Teflon bomb for certain trace elements (I). All elements were analysed on ICP-AES. ICP-MS was used for low concentrations. Results are means for duplicates. M S W BA Wood Ash Substance Unit BF Slag Steel Slag -

Al

%

Ca Fe K Ms

YO YO

Mn Na P S Si Ti Asi Ba Be Cdi CO' Cr CU' Hg' M O

Nb

Ni' Pb' Sn Sr V W Zn' Zr LOI, 550°C

6.48 22.4 0.17 0.49 11.8

2.19 22.1 24.2 0.046 4.52

5.69 8.79 10.8 1.43 1.13

4.86 8.25 2.83 4.03 1.09

0.41 0.43 0.013 1.71 14.6

3.93 0.037 0.46 0.126 5.77

0.136 2.64 0.45 0.856 20.88

0.48 1.22 0.50 0.544 22.2

PPm PPm PPm PPm

1.57 <0.7 406 7.0 <0.40

0.28 5.3 728 <1.2 0.45

0.62 16.0 1660 1.78 5.8

0.29 38.2 1320 2.3 4.50

PPm PPm PPm PPm PPm

0.5 1 34.6 5.7 C0.40 C6.0

5.8 7760 166 <0.41 20.6

19.1 274 3400 C0.39 16.0

11.1 94.5 88.7 <0.39 16.0

PPm PPm PPm PPm PPm

35.2 7.3 C0.40 14.5 324

198 45.0 21.5 17.5 178

13.1 138 737 130 285

13.5 40.0 253 64.7 407

PPm PPm PPm PPm

353
1210 410 244 55.2
58.7 33.9 3080 200 4.3

53.9

% %

YO %

YO YO % %

Yo

<14

1840 168 17

Blast furnace (BF) slag is one of the residues from ore based iron production and is mainly composed of silica and lime. Sulphur is the highest content among the four materials and comes mainly from the coke used in the process. From Table 1, it can be seen that the BF slag

42 contains low concentrations of trace elements. The melted slag from the blast furnace is poured into basins, left to cool, then dug out, sorted and stored before utilisation mainly in road bases. The slag in this study has a particle size of 0-300 mm. The steel slag used in the study is generated in scrap based electric arc krnace steel production. The process results in a slightly reduced slag mainly composed of iron and calcium, and containing 0.7% chromium and 0.1 % vanadium. Among the other trace elements, copper and zinc may be mentioned. The slag is sorted by magnetic separation and consists of the particle sizes 0-300 mm. The bottom ash from municipal waste incineration (MSWI) and wood firing ash both come from Linkoping and are sorted by magnetic separation and screening to a fraction of 2-35 mm. The incineration plant burns 200,000 tonnes MSW annually and has an advanced air pollution control system. The fly ash and APC residues are treated and deposited separately from the bottom ash. In the wood firing plant, both primary wood chips and secondary wood materials are used. Therefore the ash content of trace elements is higher than if only primary wood chips are used. The zinc content is probably originates from galvanised nails in demolition waste. 2.2 Lysimeters The lysimeters were built at the lysimeter field outside the SGI building. The field contains installations to facilitate the collection and sampling of leachates. One lysimeter was built for each residue. The dimensions were dictated by the criteria used for columns, i.e. that the largest particle size must not be larger than 1/10 of the column diameter (Hjelmar 1991b). The largest particle size was 300 mm, resulting in a lysimeter size of 3.0 x 3.0 x 1.2 m3, The walls of the lysimeters are made of plywood and covered with pre-formed HDPE liner. A geotextile with a fixed synthetic draining layer covers the bottom liner of the lysimeter and prevents particles entering the leachate collecting system. The percolate is collected at the centre of the bottom and flows into the draining system by first passing a water seal that prevents the entry of air into the system. The percolate flows are continuously measured by a tipping bucket system, all the equipment being made of noncontaminating materials placed indoors in the basement of a nearby building. Samples are collected proportional to the flow by every second tipping of the bucket. After sampling, leachates are stored under argon gas in a confined system with a minimum of contact with the atmosphere to prevent C 0 2 take-up as well as oxidation. No surface run-off from the materials is expected and the wall of each lysimeter is higher than the top surface of the filled material. In addition to the collection of leachate at the bottom of the lysimeter, cups are installed at two levels in the lysimeter material. The cups are placed at 1/3 and 2/3 of the hight from the bottom, with four cups at each level. The cups are reached by a thin pipe and the water is sucked up. A meteorological station for continuous collection of data on wind, temperature, humidity and precipitation is permanently established on the lysimeter field. The first and second lysimeters containing blast hrnace slag and steel slag were built in December 1992 and the third and fourth lysimeters with bottom ash from MSW incineration and wood firing were built at the beginning ofFebruary 1993. The lysimeters contain 12 tonnes BF slag, 21 tonnes steel slag, 14 tonnes MSWI BA and 10 tonnes wood ash respectively. Leachates are collected as closely as possible to predefined liquid to solid ratios (L/S-ratios). The L/S-ratios increase logarithmically: L/S=O.OOl, 0.003, 0.01, 0.03, 0.1, 0.3 and 1.0. The L/S-ratios are based on the actual amount of material in the lysimeter and collected amounts of water will thus vary between the lysimeters.

43 2.3 Laboratory tests The materials were tested in the laboratory by availability and column test. These test methods are regularly used when characterising waste at the SGI laboratory. In addition, oxidised availability tests and pH-static batch tests were conducted. By using these tests, leaching under different controlled conditions can be measured. The availability test is designed to give the total amount of element concentration that will be leached without the material previously being weathered. In this test, factors limiting leaching such as buffer capacity, solubility constraints and large grain size are eliminated. The elements bound in silicate minerals are not expected to be leached in the test (Groot et al 1989). The availability test used follows with some modifications the procedure proposed in the Dutch draft standard procedure NVN 7341. Finely ground material, 95% 4125 pm, is leached twice in serial batch at L/S=lOO. pH is held constantly at pH 7 for 3 hours in the first step and at pH 4 for 4 hours in the second step by the addition of nitric acid. The two leachates are combined before analysis. The oxidised availability test is used to examine the redox dependency of the leaching process for certain substances and minerals and to estimate the potential for leaching under oxidised conditions. The test is conducted in the same manner as the ordinary availability test, except that the redox potential is kept at the level of fully oxidised conditions of demineralised water for the actual pH by the addition of peroxide. The column tests were conducted on materials crushed to 420 mm to match the column size. The columns were made of transparent polyacrylate with a diameter of 0.19 m and a height of 1.0 m. The experiments were conducted under up-flow water saturated conditions at a constant rate of L/S=O.Vday and run until L/S=4 was reached. As leachate, a synthetic rain water was used, consisting of demineralised water acidified with nitric acid to initial pH=4. The leachates were filtered directly by an on-line filter system with 0.45 pm filters, before storage under nitrogen atmosphere. Samples were taken out at accumulative L/S=O. 1, 0.3, 0.7, 1.0, 2.0 and 4.0. pH-static tests were carried out to characterise the pH-dependent leaching behaviour for different substances under the redox conditions dictated by the residue. L/S=5 was used to perform a leaching test where chemical equilibrium may be obtained and the amount of acid added is still realistic. This L/S-ratio was also used by DiPietro et al (1989) and van der Sloot (1992b). The materials were crushed to <4 mm. Leaching tests were carried out for 24 hours and at pH4, 6, 8, 10 and 12.

2.4 Leachate analyses The leachates were analysed on the basis of general parameters such as pH, redox, electric conductivity and total dissolved solids, metals and salts. The metals were analysed on ICPA E S and ICP-MS for low concentrations. The leachates from the BF slag could not be analysed with the normal procedure on the ICP because gaseous hydrogen sulphide was driven off at the acidification of the samples, giving an excessive detection of sulphur. These samples had to be analysed unacidified. 3. RESULTS

The residues have been exposed to natural weather conditions in the lysimeters since the end of 1992 and beginning of 1993 respectively. The precipitation and percolation flows, as presented

44

in Figure 1, show the dynamics in the lysimeters where evaporation and storage play an important role in reducing the percolate in comparison to the precipitation. The response in percolation in January and February for BF slag and steel slag comes from occasions when the accumulated snow melted in a short time. 1993 was warmer and drier than normal during the first half of the year and wetter and colder than normal during the second half of the year (Vhder och Vatten 1993). As a consequence, very little percolate was produced during spring and early summer 1993, see Figure 1. The steel slag gave the earliest and largest response to rainfall. This is a compact slag with little porosity. BF slag and MSWI BA gave a slower response due to greater storage and evaporation capacity. BF slag is more porous than steel slag. Wood ash is finer than the other residues and has a higher content of organic material. These factors play an important role since the wood ash has only produced small amounts of percolate during the year and the ash does not seem to have become saturated until November after the evaporation has decreased. The lysimeters have been more or less unsaturated during long periods in 1993, especially during the spring, and the residues have been more or less freely exposed to atmospheric conditions.

120

100 Precipitation 80

BF slag

60

--

40

-.

IIIU Steel slag

v

MSWI BA Wood ash

-

R .

Jan

Feb

Mar

April May

June

July

Aug

Sep

Oct

1993

Figure 1 . Measured monthly percolation in the lysimeters during 1993 compared to precipitation measured at the Malmslatt, Linkoping weather station (Vader och Vatten 1993). The percolate samples from the lysimeters had been accumulated to target L/S-ratios, as mentioned previously. These US-ratios were reached at individual times in the different lysimeters. The development of pH in the percolates from the lysimeters differs more or less strongly from the pH obtained in the laboratory column tests, as can be seen in Figure 2. The pH in the leachate from wood ash and steel slag lysimeters is not strongly alkaline as in the column tests, but is about pH 9. This is probably a result of the exposure of the material under unsaturated conditions to carbon dioxide. The wood ash samples were collected in October

45

and November.The first and second steel slag samples were collected during the snow-melt in January and February and the third one not until the beginning of August. The first BF slag percolate was collected after a snow-melt in February and showed a somewhat greater pH decrease than the steel slag, but in the next two samples, after 6 and 7.5 months respectively, the pH had decreased to around pH 4. The decrease in pH is similar to what has been seen in lysimeters with mine waste and old copper slag (Fallman 1991) and is probably the result of oxidation of the reduced sulphides and other sulphur species in the BF slag. Only the leachate production in the MSWI BA lysimeter resulted in an overlap between the lysimeter and the column test results, which in this case show good agreement in pH. The sampled percolated leachates from the lysimeters are stored under argon gas and are thus exposed neither to oxygen nor carbon dioxide. The only contact the water has with the atmosphere is from dripping from the pipe until tipping of the bucket, which is probably of minor importance. The measured pH values may therefore be regarded as representative for the constructed field situation. The measurements have shown that pH in the leachates from laboratory column experiments and the field-like situations may differ considerably for alkaline materials and reduced sulphur containing materials.

-

BF slag, column A

-*-

BF slag, column B BF slag, lysimetcr

Steel slag, column

--c

Stecl slag, lysiineter

--ct.

MSWI BA, column MSWI BA, lysimeter Wood ash, column

------i

0,001

0,Ol

031

1

10

Wood ash, lysimeter

us Figure 2. pH in leachates from the lysimeters and the laboratory column tests as a function of the L/S-ratio (leachate/solid material). Redox measurements have been made in all tests in the laboratory and on the leachates from the lysimeters. A material that shows reduced conditions in laboratory leachate will eventually be oxidised when exposed to the atmosphere, as in the field situation. The presentation of redox potential related to the pH provides information on the redox situation in a material and on the possible behaviour of redox sensitive minerals and substances. All materials showed more or less reduced conditions in the leachates from the column and availability tests, as can

46

be seen in Figures 3 and 4. The most reduced conditions were obtained in the leachates from BF slag. Even the lysimeter leachate shows reduced conditions in spite of the full exposure to air and also through the change in pH. Leachate sampled from the cups in this lysimeter shows somewhat less reduced conditions. Even after one year, the lysimeter still smells of sulphur. The leachate from the MSWI BA lysimeter also shows slightly reduced redox potential, which is comparable to the level obtained in the columns. In the other two lysimeters, more or less oxidised conditions are obtained in the later lysimeter leachates. In the steel slag, measurements in the cups show reduced conditions.

Redox in leachates, BF slag -X-

Demin water, ox

1

Availability Availability, ox

O

-

Column A

-A-

Column B

pH-stat 2 -400

4

6

8

B

1

Lysimeter, cups oct

+

Lysimter, cups dec

PH

Redox in leachates, Steel Slag 800 -x-

-

600

s

Demin. water, ox Availability Column

400

+- pH-stat

i3

200

Lysimeter +

0

Lysimeter, cups oct

I

0

2

4

6

8

1 0 1 2 1 4

Lysimeter, cups dec

PH

Figure 3 . Redox measurements as a function of pH in the laboratory tests and lysimeter leachates for BF slag and steel slag.

47 The use of oxidised availability renders a possibility to estimate the change in leachability due to oxidation of the material. In the ordinary availability test, oxidation may occur due to the amount of dissolved oxygen in the water at high L/S-ratio and the open test system. The comparison between the tests thus shows the difference between a somewhat oxidised test and a full oxidation test. Triplicates have been made for the ordinary availability test and duplicates for the oxidised test. Reproducibility was good for the ordinary test but less satisfactory for the oxidised test. In the oxidised test with wood ash, organic material may become oxidised. The consequences of this for leachability complexing organics have not been investigated.

Redox in Ieachates. MSWI Bottom Ash

8oo

1

Demin. water, ox

-X-

Availability

-

+

2oo

PH-stat

1

Lysimeter

O J

0

Column

1

2

4

6

8

+

Lysimeter, cups oct

1 0 1 2 1 4

PH Redox in leachates. Wood Ash 8oo

1

Dcmin. watcr, ox

-x-

600

5

Availability

400

--

200

+

-----t

pH-stat

i5

Lysimetcr

+

01 0

Column

Lysinieter, cups oct

I

2

4

6

8

1 0 1 2 1 4

PH Figure 4. Redox measurements as a hnction of pH in the laboratory tests and the lysimeter leachates for MSWI BA and wood ash.

48 Comparisons between the results from the two tests are shown in Figures 5 and 6 . The main components were generally little influenced by the oxidation, except for iron, which was clearly reduced in the leachates by the oxidation in all materials except for wood ash. In the bottom ash leaching, also silica is reduced. Among the trace elements, copper, lead and cadmium, which are known to form sulphides with low solubility, gave the highest response to the oxidising conditions. Zinc would be expected to behave in the same manner but did not

Availability, Blast Furnace Slag

100000

2 8 2

v

B

4

10000 1000 100

h

10

~

1 0,1

0,001 0*01

Innl-luull Ca Fe K Mg Na

I

S

Si

II Zn

Al As Ba Cd Co Cr Cu Ni Pb

V

0Availability, oxidised

Availability

Availability, Steel slag

1000000

-

38 Y

3

<8

100000 10000 1000 100 10 1

0,1 0,Ol Ca Fe

K Mg Na

I

S

Si

Availability

A1 As Ba Cd Co Cr Cu Ni Pb

-

1

V

Zn

0Availability, oxidised

Figure 5. Availability for leaching of main constituents and trace elements in BF slag and steel slag under redox potential dictated by the material and oxidised conditions respectively. Values below detection limit are marked with <,

49

respond differently in the two tests. This shows that the sulphides have probably been oxidised in the ordinary availability test. Chromium, arsenic and vanadium, which all form complexes with different solubility depending on the oxidation state, show response to the oxidation. The leachability is increased for chromium in all materials, for vanadium in all but one and for arsenic in the ashes where the results were above the detection limit.

Availability,MSWI bottom ash 1000000 100000

3

c!$

10000 1000

v

3

100 10

4

1 0,1

0,Ol

Ca Fe K Mg Na

S

Si

A1 As Ba Cd Co Cr Cu Ni Pb

V

Zn

V

Zn

0Availability, oxidised

Availability

Availability, Wood ash 1000000

P

p

v

3

100000 10000 1000 100

cl

a

4

10

1 0.1 0.01

Ca Fe

K Mg Na

I

S

Si

Availability

Al

As Ba Cd Co Cr Cu Ni Pt

0Availability, oxidised

1

Figure 6. Availability for leaching of main constituents and trace elements in MSWI bottom ash and wood ash under redox potential dictated by the material and oxidised conditions. Values below detection limit are marked with c.

50

The influence of pH changes on the leachability of the materials was studied in the pH static tests. These were conducted in the range of pH 4 to 12 in steps of two units. The results from the pH static tests are applied to the pH levels obtained in the column tests and the lysimeter leachates, or as closely as possible. The leachabilities at the chosen pH levels are compared, see Table 2. This shows the likely pH effect on the leachability of the materials in the lysimeters, in comparison with the column tests. The decrease in pH leads to a higher leachability for most substances, with some exceptions for substances that were not affected or reduced in leachability. In the BF slag, the highest increase in leached amounts was obtained, as well as the largest pH change in the lysimeter. Table 2 Change in leachability with pH as obtained in the pH-static tests. Symbols indicate change in leached amounts in an interval of pH change representing the difference between the pH in the leachate from column test and that obtained in the lysimeter leachate: +++ = >lOO-fold increase, ++ = 10-100-fold increase, + = 2-10-fold increase, 0 = rt 2-fold, - = 2-10-fold decrease, - - = >lO-fold decrease, < = both values are below detection limit. BF Slag Steel Slag MSWI BA Wood Ash Substance pH, column 12,l-11,4 12,2-11,s 7,3-8,0 10,s-11,2 8,s-9,3 7,6-8,0 9,s-8,7 pH, lysimeter 7,7-4,1 Discussed pH-change 12 --> 4 12 --> 8 No difference 10 --> 8

Al Ca Fe K Mg Mn S Si As Ba

Cd co Cr cu Ni

++ +

__

m

0

I,

0

0

I,

0

__

+++ +++

')

++ 0

+ + ++ ++ <

++

++

++ ++ _

Not applicable

0

I,

+

I,

I, 0,

++ ++ +

,,

0

I,

+

,I

I!

,I

0

8,

<

II

-

I,

Pb V Zn ++ _ I ) Unsuccesshl analyses of sulphur at pH=lO and 12.

++ ++ 0

0

+ + + + 0 0

+ ++

51

The differences in the leachate composition between column tests and lysimeters can not be directly compared because by November 1993, none of the lysimeters had produced so much percolate that the L/S-ratio overlapped the first samples from the column tests. Instead a comparison is made between the extrapolation of the curve of accumulated amounts from the lysimeter and the values obtained from the column tests. The extrapolation is made from the two latest L/S data points and with an extension of the L/S-ratio by a factor of approximately 3. The comparisons are presented with the precision of magnitudes in Table 3. Table 3. Comparisons by the magnitude of the accumulated leached amounts from the lysimeter, extrapolated from the latest two data points, and from the column tests. ++ = > I 00 times more leached in the lysimeter, + = 10-100 times more, f = 10 times more to 10 times less, - = 10-100 times less leached in the lysimeter, - - = >lo0 times less, < = values below detection limit. Substance BF slag Steel slag MSWI BA

Al

f

__

-

Ca Fe Mg Mn

f

f

f

<

<

<

++ ++

+

f

-

S

f

f

Si As Ba Cd

'>

f f

<

+ +

f

f

f

<

f

+

*

f

<

f f

f f

f

-

f

++

=k

co Cr cu Ni Pb

*

++

V + Zn + I ) No values obtained for column tests.

f

f

< f

<

+

Wood ash results are not compared because of the small amounts of leachates so far from the lysimeter. 4. DISCUSSION

The exposure of the alkaline and more or less reduced residues, BF slag, steel slag and wood ash, to atmospheric conditions clearly influences the controlling factors of pH and redox potential in the leaching process. This is seen in the comparisons, Figure 2, between the pH in column test leachates and the lysirneter leachate. The lower pH values obtained in the lysimeter leachates are responses to the exposure of the material to air, i.e. oxygen and carbon dioxide.

52

The loose filling of the material and low water retention in the coarse materials in the lysimeters provide good exposure to air. A more water retaining and less air permeable structure can be obtained by the use of compaction techniques and a content with smaller particle sizes. This may reduce the rate of the pH change to a level lower than indicated by these field experiments. Lysimeter experiments conducted on a mixture of steel slag and BF slag covered with a sealing of asphalt and grass (Mulder 1991), showed maintained highly alkaline conditions in the leachates, pH 12-12.5. In that study, the material was not readily exposed to air. The actual air and water saturation conditions for a residue in a utilisation or deposition object are thus important for prediction of the leaching conditions. Non-water saturated conditions and free exposure to the atmosphere may lead to a lowering of the pH values, as found in these lysimeter tests, and leaching conditions different to those predicted in laboratory tests. The carbon dioxide reservoir in the atmosphere reduces the pH in an alkaline solution to pH 8-9 (Stumm and Morgan 1981), which is the same pH as obtained in the lysimeters with steel slag and wood ash. The MSWI BA leachate was approximately neutral in the column test, and the lysimeter leachate held about the same pH. The decrease to pH 4 in the leachate from the BF slag lysimeter is probably a combination of the oxidation of the considerably reduced material containing sulphur and the buffering of carbon dioxide. Although pH is one of the most important factors controlling leachate composition, the change in pH in a leachate may in itself be caused by redox reactions. The composition of the leachate from these materials is influenced by oxidation, as shown in Figures 5 and 6, to increased or decreased leachability. Metals bound to minerals unstable under oxidising conditions were released, such as cadmium, copper, nickel and lead bound in sulphides. Substances such as chromium and vanadium formed more soluble complexes after oxidation, while iron decreased due to precipitation. Barium concentrations were lower in the steel slag lysimeter leachate than in the column leachate, probably due to barium sulphate precipitation after oxidation of sulphur species to sulphate, see Table 3 . This was not seen in the BF slag, where a slight increase, within one order of magnitude, in leached amounts of barium was seen in the lysimeter. Redox conditions in the BF slag lysimeter still had sufficient reducing potential to prevent the reduced sulphur species from being oxidised to sulphate. The combination of the effects of oxidation and pH change may produce a larger or smaller net impact on the leachate composition than the effect of the individual changes. The larger extrapolated leached amounts of copper from BF slag in the lysimeter in comparison with the column test are the result of increased availability due to oxidation and increased solubility due to pH decrease. This increase is of more than two orders of magnitude (concentrations of 5 - 10 mg Cu/l). The application of the results from the pH static tests on the pH differences between column tests and lysimeter tests in Table 2 show that lower pH in the leachate from the lysimeter compared to the column mainly results in increased solubility. In some cases, decreased solubility is obtained. This is seen in the pH static tests on steel slag for the decrease in pH from 12 to 8. In these lysimeter leachates, the increased availability due to oxidation of sulphides and reduced solubility due to pH decrease le to virtually no difference in the leached amounts of copper and to a decrease in leached amounts of lead in comparison with the column results. The magnitude of the influence of pH and redox, see Figures 5 and 6 and Table 2, show that pH influences solubility to a greater extent than oxidation.This comparison is based on the oxidised availability test and the pH static tests. However oxidation makes the metals readily available for pH influence.

53 Leached amounts from the MSWI BA lysimeter and column tests are mainly in good agreement, which is expected due to the small difference in pH and the similar redox appearance. The effects of changes in controlling factors on the leaching of main components is as important as the trace element (im)mobilisation. A change in the leachability of these elements may change the physical properties of the materials. Hitherto, the changes in controlling factors have not significantly changed the matrixes of the materials. However, leaching of calcium from the BF slag is so high that an increase in leaching rate within one magnitude may influence the physical properties of the material. The interactions between pH and redox potential caused cartain problems in the tests applied in the laboratory. The pH static tests were used to investigate pH influence on the leaching process. As can be seen from Figures 3 and 4, the redox potentials were changed more by the pH than the curve for demineralised water. The results cannot be interpreted as solely pH dependent without further evaluation. The results used in the evaluation in Table 2 for BF and steel slags are less influenced by redox changes and are regarded as reliable. The wood ash results showed oxidised conditions at pH 10. The availability and oxidised availability tests show the influence of redox on leachability. However, The ordinary availability test may be somewhat oxidising as the tests are carried out at high L/S-ratio in demineralised water with normally dissolved amounts of air and exposure to the atmosphere. This implies that the true redox influence on leachability may be greater than observed in Figures 5 and 6 . The test procedures for both pH static tests and oxidised availability need to be further developed regarding redox control. Special interest needs to be paid to the oxidation of organic substances in the samples in the oxidised availability test. 5. CONCLUSIONS

The comparisons between the laboratory tests and the one year lysimeter tests have so far shown that significant changes in controlling factors may occur within a time interval that must be considered as short in comparison with 100 years of utilisation or 1,000 years of deposition. The effects of these changes after one year, with some extrapolations, were a more than 100fold difference in the leached amounts for a few substances and a more than 10-fold difference in the leached amounts of a number of substances. The lysimeter tests at SGI, in comparison with laboratory tests, show that it should be possible to use laboratory tests for prediction of field behaviour. However, laboratory tests must be designed to reflect the parameters influencing leaching, such as pH and redox. Field data are important for further studies of the impact of other factors, such as organic complexing substances and flow conditions. It can be clearly concluded that one single batch test would not have been sufficient for testing these materials.

ACKNOWLEDGEMENTS This paper contains results from a research project focusing on the leaching processes of residues with a potential for utilisation. The financial support is provided by the Swedish Waste Research Council.

54 REFERENCES de Groot, G.J., Wijkstra, J., Hoede, D. and van der Sloot, H.A. (1989): Leaching characteristicsof selected elements from coal fly ash as a hnction of the acidity of the contact solution and the liquid/solid ratio. Environmental Aspects of Stabilization and SolidificationofHazardous and Reactive Waste, ASTM STP 1033, P.L. CBt6 and T.M. Gilliam, Eds. ASTM, pp170-183. DiPietro, J.V., Collins, M.R., Guay, M. and Eighmy, T.T. (1989): Evaluation of pH and oxidation-reduction potential on leachability of municipal solid waste incinerator residues. International Conference on Municipal Waste Combustion, April 11-14, 1989, Hollywood, Florida, session 2B, pp 21-43. Fallman, A-M. (1991): Uppsamlingsanlaggningar- varp och slagg i Falun. (Lysimeters - waste rock and copper slag in Falun.) The Dalalven Commission Mine Waste Project 4:2.SGIVaria 323, SGI, Linkiiping (in Swedish). Fallman, A-M. and Hartlen, J. (1993): Karakteriserhg och klassificering av avfall. Genomglng av olika landers system (Characterisation and classificationof waste. Survey of the systems in different countries.) Rapport 4226, Naturvlrdsverket, Solna (in Swedish). Hjelmar, 0. (1991b): Personal communication. Hjelmar, O., Aagaard Hansen, E., Larsen, F. and Thomassen, H. (1991a): Leaching and soil/groundwater transport of contaminants from coal combustion residues. EFP 1323/86+1323/86-19+1323/89 Water Quality Institute, Hsrsholm. Lindsay, W.L. (1979): Chemical Equilibria in soils. John Wiley and Sons, New York. Mulder, E. (1991): The leaching behaviour of some primary and Secondary Raw materials used in pilot-scale road bases in "Waste Materials in Construction",Proceedings of the international conference on environmentalimplications of construction with waste materials, Maastricht, The Netherlands, 10-14 November, 1991 ( Goumans, J.J.J.M., van der Sloot, H.A., Aalbers Th.G. eds), pp. 255-264. Studies in Environmental Sciences 48, Elsevier, Amsterdam. NVN 7341: Leaching characteristics of building and solid waste materials - Leaching tests determination of availability of inorganic components for leaching. Draft, June 1992. Steffen Robertson and Kirsten (BC) Inc. (1989): Draft acid rock drainage technical guide. Volume 1. Prepared for the British Columbia Acid Mine Drainage Task Force, Vancover, British Columbia. van der Sloot, H., de Groot, G.J., Hoede, D. and Wijkstra, J. (1991a): Mobility of trace elements derived from combustion residues and products containing these residues in soil and groundwater. ECN-C--91-059, Netherlands Energy Research Foundation (ECN), Petten. van der Sloot, H., E.E. van der Hoek, de Groot, G.J. and Comans, R.N.J. (1992b): Classificationof pulverized coal ash: Part 1. Leaching behaviour of coal fly ash. ECN-C-92-059, Netherlands Energy Research Foundation (ECN), Petten. van der Sloot, H., Hoede, D. and Bonouvrie, P. (1991b): Comparison of different regulatory leaching test procedures for waste materials and constructions materials. ECN-C--9 1-082, Netherlands Energy Research Foundation (ECN), Petten. Vader och Vatten (1993), SMHI, Norrkoping.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goitmans, H A . van der Slmt and l3.G. Aalbers (Editors) 81994 Elsevier Science B.V. AN rights resewed.

55

Validation of leaching model on actual structures G. van der Wegen" and C . van der Plasa aIntron, institute for materials and environmental research B . V . , P.O. Box 5187, 6130 PD Sittard, The Netherlands

Abstract In The Netherlands a standard set of leaching tests has been developed to assess the environmental impact of building materials, especially if waste materials are incorporated. For monolithic building materials a diffusion test is used for this purpose. The results of a research programme on the validation of the diffusion-controlled leaching model for actual cement and asphaltic concrete structures are presented. For fully submerged concrete the concentration profiles measured can be explained by diffusion processes. Exposed to atmospheric conditions there is an outer zone in the concrete which is dominated by moisture movement due to wet/dry cycles while the behaviour in the zone at greater depth is dominated by diffusion processes. 1. INTRODUCTION In The Netherlands legislation with respect to the environmental impact of building materials is in a well-developed stage [1,2]. In order to assess the leaching behaviour of building materials, standarized test methods as well as related acceptance criteria are necessary. Such standarized test methods [3-51 and criteria [2] have been developed in The Netherlands. For pollutants in monolithic materials, these criteria are based on a diffusion controlled leaching mechanism. From tank leaching experiments over a period upto 3 years [6] a diffusion controlled release of pollutants from stabilized waste materials was observed. Moreover, it is well known that penetration of chloride ions from seawater into submerged concrete over a period of decades can be described by a diffusion controlled process [7]. On the other hand exposure of stabilized coal-waste blocks in seawater for a period of 8 years did not show concentration profiles purely determined by diffusion [8]. In order to validate the assumed leaching model for monolithic building materials (diffusion) it was decided to determine concentration profiles of relevant anorganic pollutants in actual structures exposed to leaching for a long period.

2. SELECTION OF SUITABLE ACTUAL STRUCTURES Actual structures exposed to leaching for a long period were selected on the following criteria:

56

1. a cement or asphaltic concrete structure; 2. containing a homogeneously distributed waste material (powder), having a sufficient high pollutant concentration level; 3 . an age of at least 10 years and preferably more than 20 years; 4. an accurate knowledge of the climatic conditions, especially the time of wettness; 5. permission from the owner to drill cores for experimental research. After an extensive search for candidate structures meeting above-mentioned requirements, the following two were selected: A lock for ships in the Dortmund-Ems canal at Alte Rheine, Germany built in 1975. In the concrete walls powdercoal fly ash (EFA-Fuller, RM) has been used. The concrete composition was documented as 290 kg/m3 portland blast furnace slag cement, 50 kg/m3 of above-mentioned fly ash and a water cement ratio of 0.55. The lower parts of the wall have been wetted continuously (except for a few short maintenance works), whereas the upper parts have been exposed to atmospheric conditions. Asphaltic concrete as a protective top layer on the shore of the Veersemeer, a lake in The Netherlands. This asphaltic concrete was applied in 1966 and contains powdercoal fly ash as a filler (about 5% m/m). The water level of the Veersemeer is artificially controlled. Each year on 1. April the water level is raised to 0 m. NAP, whereas on 1. November the water level is lowered to -0.7 m. NAP. No parts of the asphaltic concrete top layer have been wetted continuously. Hence, only samples could be obtained from the 'tidal' zone (i.e. 7 months continuously wet, followed by 5 months of atmospheric conditions).

3. EXPERIMENTAL PROCEDURES 3.1. Sampling From the concrete wall of the lock at Alte Rheine cores 100 mm in diameter and about 150 mm in length have been drilled in December 1992 (age = 17 years). Two cores have been drilled in the atmospheric zone and two cores in the zone below the lowest water level (continuously wet zone). From the asphaltic concrete top layer on the shore of the Veersemeer two cores 100 mm in diameter and about 100 mm in length have been drilled in November 1992. The age of the asphaltic concrete top layer at that time is about 26 years, which corresponds to a total submerged period of about 15 years (7 out of 12 months submerged). The moisture content of the cores have been preserved by adequate sealing in plastic bags until the time of specimen preparation. 3.2. Specimen preparation Starting from the top surface (i.e. external surface of actual structure) of the cores, layers of about 1 mm in thickness each have been grinded to dust. The dust generated has been collected in a cyclone connected with a vacuum cleaner. Pretests have shown that in this way about 95% of the grinded cement concrete and about 85% of the grinded asphaltic concrete is retained by the cyclone. The asphaltic concrete cores have been frozen down to -20°C prior to grounding to obtain brittle behaviour (i.e. better grinding performance). After grinding each layer and collecting the dust generated, the full equipment has been cleaned to prevent 'contamination' of the next layer to be sampled.

57

3.3. Chemical analysis About half of each of the subsamples obtained by the preparation technique described above was used for determination of the cement respectively the bitumen content. The cement content was calculated from the loss-of-ignition and the insoluble residue in hydro-chloric acid according to the British Standard BS 1881:part 124. The bitumen content was estimated from the loss-of-ignition at 950°C. 'Total' concentration of the elements investigated in the grinded subsamples have been measured after dissolution in a strong acid and subsequent analysis by atomic absorption spectroscopy. In addition, for the cement concrete cores obtained below the lowest water level (continuously wet) also the concentration of pollutants extracted by saturated lime water (representative for the pore water in the concrete considered) has been determined. 4. EXPERIMENTAL RESULTS

4.1. Cement concrete cores The 'total' concentration of the pollutants Cu and Mo as a function of distance to concrete surface is shown in Figure 1 for both cores drilled in the atmospheric zone of the concrete wall. For both elements in both cores two clear maxima in concentrations, i.e. at the surface and at a depth of about 20 mm respectively, can be seen. Although the elements As and V were also investigated, no clear concentration profiles were obtained because these concentrations were near or below the detection limit of the analysing technique. 3 m -

-.-core

-bT 2

1

* care 2

25w'

m

Figure 1. 'Total' concentration profiles of the pollutants Cu and Mo in both cement concrete cores drilled in the atmospheric zone. The 'total' concentration of the above-mentioned pollutants for both cores drilled in the zone below the lowest water level showed an almost constant value, i.e. almost no dependence on distance to concrete surface. The concentration of these pollutants extracted by saturated lime water, however, did clearly show a marked decrease near the

58

concrete surface as illustrated in Figure 2 for the elements Ba and Mo. - 0.- 6.E-14(d/r) A

0

15

30

core ci Core CZ

45

A

corec1 Core CZ

60

distance to surtace (mm)--t

0

distance to surface (mm)-+

Figure 2. Concentration profiles (extracted by saturated lime water) of the pollutants Ba and Mo in both cement concrete cores drilled in the zone below the lowest water level. The solid line is the calculated profile based on Fick's second law of diffusion.

4.2. Asphaltic concrete cores The 'total' concentration of Cu and Mo relative to bitumen content as a function of the distance to the top surface of the asphaltic concrete is shown in Figure 3 for both cores drilled. From this figure one can observe a decreased concentration level for the outer 5 mm for both elements and both cores. No such concentration profile was observed for Na . 3.m

.

distance to surtace

(mm)--.

dlatance to surtace

(mm) --.

Figure 3. 'Total' concentration profiles of the pollutants Cu and Mo in both asphaltic concrete cores.

59

Comparing Figure 3 with Figures 1 and 2 it shows that the scatter in results is much higher for the asphaltic concrete cores than for the cement concrete cores. This is probably due to the greater inaccuracy of the determination of the bitumen content compared to the cement content.

5. DISCUSSION 5.1. Cement concrete cores Atmospheric zone The concentration profiles of the elements Cu and Mo in both cores drilled in the atmospheric zone of the concrete wall (see Figure 1) show a constant concentration level at greater distances from the surface (for Cu: > 60 mm; for Mo: > 30 mm). This concentration level is most likely the original content of these pollutants in the concrete. Hence, in the atmospheric zone no leaching out of Cu and Mo has occurred. This can be explained by the absence of physical contact of the concrete surface with external water (except for rain and splash water which is of minor importance). On the contrary Cu and Mo are enriched in the outer zone of about 60 mm and 30 mm respectively. The concentration profiles for both elements and cores are very typical: two maxima, one near the concrete surface and one at a depth of about 20 mm from the concrete surface. The concentration profile at a depth of 20 mm and larger can be explained by a diffusion controlled process as is illustrated in Figure 4. In this figure the concentration profiles for two ’surface’ concentrations (i.e. both peak values at a depth of 20 mm in Figure 1) of Cu have been calculated by Fick’s second law of diffusion [9]. In these calculations the age of the concrete (= 17 years), the original Cu content (= 200 ppdbinder) and an estimate of the effective diffusion coefficient of Cu = 1.1O-l’ m2/s [ 10,111 has been substituted. The calculated profiles compare well with the corresponding part of the measured profiles.

--CO=1800 mglkg

0‘ 20

40

0

dlstance to surface (mm) --t

Figure 4. Concentration profiles for Cu according to Fick’s second law of diffusion. Effective diffusion coefficient = 1.10-’3m2/s; diffusion time = 17 years.

60

According to Reference 12 the depth in concrete over which wet/dry conditions of the atmosphere are noticable, is about 20 mm irrespective of type of cement or water cement ratio of the concrete. This compares very well with the first part of the concentration profiles shown in Figure 1. Under dry atmospheric conditions the concrete will dry out, i.e. the water in the concrete pores will evaporate leaving non-volatile components behind. This process starts at the concete surface and proceeds by moving the moisture front to increasing depth in the concrete. Due to the evaporation of the water in the concrete pores the concentration of the (non-volatile) pollutants in the remaining pore water will increase. This explains the building up of a concentration maximum at a depth of about 20 mm. At greater depth no moisture variations occur and hence diffusion processes are the main transport mechanism. Subsequently by splash water as well as by capillary suction of pore water from the lower submerged parts of the structure, canal water, containing amongst others Cu (concentration = 4 pg/l), is absorbed in this zone causing rewetting and enrichment with pollutants like Cu. This ’pumping’ mechanism due to wetldry cycles explains the enrichment of these pollutants as well as the concentration profile observed in the outer layer of the concrete structure. Submerged zone The ’total’ concentration profiles of As, Cu, Mo and V did not show any significant leaching or enrichment. In addition to the fact that the concentrations of As and V were near the detection limit of the analysing technique, this is probably due to the fact that under these conditions most of these pollutants are chemically bounded in the cement matrix. Only a small fraction of the total concentration is free available in the pore water for diffusion processes [ 111. Therefore, additional measurements have been performed in which concentration profiles have been determined based on extraction with saturated lime water (i.e. simulation of pore water). The results given in Figure 2 clearly show leaching of Ba and Mo from the concrete into the canal water. In this figure the solid lines represent the concentration profiles calculated by Fick’s second law of diffusion, using an effective diffusion coefficient of 5*10-14m2/s and 3.1014 m2/s for Ba and Mo respectively. These values obtained by curve fitting compare well with literature data [10,11], taking into account the effect of redox conditions present in portland blast furnace slag cement [13].

5.2. Asphaltic concrete cores The concentration profiles of the elements Cu and Mo in both asphaltic concrete cores drilled in the shore protection layer of the Veersemeer show within the scatter a more or less constant concentration level at depths greater than about 5 mm from the surface. This concentration level is most likely the original content of these pollutants in the asphaltic concrete. The decreased concentrations in the zone between the surface and 5 mm depth is due to leaching of these pollutants into the water of the lake. The extend of this leached zone corresponds very well with that of the concentration profile calculated by Fick’s second law of diffusion, using an effective diffusion coefficient of 1.10-” m2/s for both elements in asphaltic concrete [ l l ] , see Figure 5. The apparent increase in concentration of both elements near the surface is probably due to the evaporation of polluted water in the rough surface texture (due to erosion) of the material.

61

-

dlaancs lo aufface (mm)

Figure 5. Relative concentration profiles for Cu and Mo according to Fick's second law of diffusion. Effective diffusion coefficient = 1*10-'*m2/s; effective diffusion time = 15 years.

6. CONCLUSIONS The leaching of cement concrete which is continuously submerged in water is diffusion controlled, at least for the pollutants investigated. The leaching of cement concrete surfaces which are exposed to atmospheric conditions is determined by two mechanisms: an outer zone of about 20 mm (for climatic conditions as in Western Europe) is dominated by moisture movements due to wet/dry cycles, while the zone at greater depth is dominated by diffusion processes. The measured leaching depth of the elements Cu and Mo in asphaltic concrete can be explained by Fick's second law of diffusion using literature values for the effective diffusion coefficient. For Na no consistent leaching behaviour in the asphaltic concrete was observed. 7. ACKNOWLEDGEMENT

The authors are grateful for the financial support from NOVEM and the Dutch Ministry of Public Health, Physical Planning and Environment, which made this research programme possible to perform.

8. REFERENCES 1 'Pre-decree building materials soil and surface water protection', Staatscourant No. 121, June 1991, The Netherlands (in Dutch).

62 2 Th.G. Aalbers, et al., 'Environmental quality of primary and secundary building materials in relation to reuse and soil protection'; RIVM-report No. 771402005, June 1992, Bilthoven, The Netherlands (in Dutch). 3 Pre-NEN 7341, 'Leaching characteristics of building and solid waste materials Leaching tests - Determination of the availability of inorganic components for leaching', October 1992, Delft, The Netherlands (in Dutch). 4 Pre-NEN 7343, 'Leaching characteristics of building and solid waste materials Leaching tests - Determination of the leaching of inorganic components from granular building and waste materials', October 1992, Delft, The Netherlands (in Dutch). 5 Pre-NEN 7345, 'Leaching characteristics of building and solid waste materials Leaching tests - Determination of the leaching behaviour of inorganic components from building materials, monolitic waste and stabilized waste materials', October 1992, Delft, The Netherlands (in Dutch). 6 H.A. van der Sloot, 'Leaching behaviour of waste and stabilized waste materials; characterization for environmental assessment purposes', ECN-report No. 89-185, December 1989, Petten, The Netherlands. 7 CUR-report No. 100, 'Durability of marine structures', April 1981, Gouda, The Netherlands (in Dutch). 8 D.E. Hockley and H.A. van der Sloot, Environ. Sci. Technol., 25, No. 8 (1991) 1408-1414. 9 J. Crank, 'The mathematics of diffusion', Oxford, U.K., 1990. 10 H.A. van der Sloot, et al., 'Environmental aspects of stabilization and solidification of hazardous and radioactive wastes', ASTM STP 1033 (1989), p. 125-149. 11 G.J. de Groot, et al., 'Characterization of the leaching behaviour of products', Mammouth-report No. 9, ECN-report No. C-90-007, March 1990, Petten, The Netherlands (in Dutch). 12 CUR-report No. 90-3, 'Carbonation, corrosion and moisture', June 1990, Gouda, The Netherlands (in Dutch). 13 H.A. van der Sloot, et al., 'Influence of redox conditions on the leaching behaviour of waste materials', ECN-report No. C-93-037, June 1993, Petten, The Netherlands (in Dutch).

Environmental Aspects of Construction with Waste Materials J.J.M. Goumans, H A . V M &r SImt and Th.G. Aalbers (Editors) el994 Elsevier Science B. K AN rights reserved.

63

INTERCOMPARISON OF LEACHING TESTS FOR STABILIZED WASTE H.A. van der Sloot” , G.J.L. van der Wegenb , D. Hoedea, G.J. de Groot’. a

Netherlands Energy Research Foundation, P.O. Box 1, 1755 ZG Petten, The Netherlands INTRON B.V., P . 0 Box 5187, 6130 PD Sittard, The Netherlands.

Abstract The emphasis on treatment of waste by solidificatiodstabilization has led to the need for leaching tests to assess the environmetal benefits of such treatment processes. In this paper the intercomparison of leaching tests for stabilized waste. In this study Municipal Solid Waste Incinerator fly ash was used. The sample preparation, the testing for homogeneity of sample batches and the verification of the repeatability of leaching in one laboratory using the tank leaching test used as common method to be carried out by all participants is described. The influence of prolonged hardening of the cement-based stabilization product is discussed as well as influences of forced air and carbondioxide exposure on the release. An explanation of the observations and the implications for testing are given.The repeatability and reproducibility standard deviation of analysing a Standard Leachate for Na proved to be resp. 2.5 and 5.3 % (mean value: 56.85 mg/l). The repeatability and reproducibility standard deviation of the effective diffusion coefficient of Na obtained form the tank leaching test (expressed as pD, = log D,) proved to be resp. 0.071 and 0.095 (in pD,units) at a mean value of 11.46 (N=l6). 1. INTRODUCTION

The potential environmental hazards caused by waste materials varies strongly between wastes from different sources. Although elimination and minimization of waste streams have the highest priority, it is obvious that significant waste streams remain. These have to be dealt with in an environmentally acceptable manner. Some bulk wastes and treated wastes can be applied beneficially in construction [I]. Several waste streams will require treatment, such as stabilization, before disposal to minimize adverse environmental effects. At present, proper methods to address potential environmental effects from monolithic waste forms are not implemented in regulation. Therefore, proper performance criteria for the evaluation of the effectiveness of the immobilization technologies are lacking. Current regulatory test procedures based on single extraction of crushed material at a fixed liquid to solid ratio are inadequate to assess environmental impact from these type of solid specimen [2]. The mechanism controlling release from monolithic specimen is neglected when crushed materials are used. In addition, for quality control purposes a need for reference materials exists in this field. This paper describes pre-normative work in the form of an intercomparison of testmethods for stabilized waste materials, which focusses on the factors controlling release

64 from monolithic materials. In view of the increased need for treatment of waste, the methodologies evaluated in this intercomparison will be highly relevant for the Community Directive on Landfill of Waste Materials and future regulations in the field of waste minimization, treatment and utilization. The work consists of - preparation of a sufficiently large number of representative samples of stabilized waste (cement-based), - testing of homogeneity and repeatability of leaching within one laboratory, - intercomparison of test results from all participating countries for one common test (tank leaching test) in comparison with other tests currently applied at the national level for these type of materials, - data interpretation and statistical evaluation of test results, - dissimination of findings to respective national bodies and to CEN. More than 25 laboratories from EEC and EFTA countries participate in this intercomparison. 2. EXPERIMENTAL 2.1 Preparation of tests specimen

Test cubes of 4 x 4 ~ 4cm composed of very rapid hardening Portland cement, municipal solid waste incinerator (MSWI) fly ash, natural sand and water were produced to meet requirements with respect to homogeneity, sufficient durability to avoid loss of cohesion during the leaching test and a low permeability. To ensure specimen homogeneity the fly ash was sieved to remove material larger than 0.5 mm. The fraction < 0.5 mm was homogenized using a spinning riffler and subsequently divided in 25 subsamples of 2 kg each. The intended composition needed modification due to an unacceptable degree of swelling and retardation of setting of the mortar. The following composition was used: Portland cement class C (540 kg/m3), MSWI fly ash (210 kg/m3), natural sand (0.5-1 mm ; 560 kg/m3), silver sand (125-500 vm; 560 kglm3) and water (300 kglm3). After two days of curing in the molds at 20 "C and > 95 % relative humidity (R.H.) the specimen have been stored in airtight plastic bags at 20 "C and > 95 % R.H. A total number of 140 batches of 12 cubes were prepared. 2.2 Material properties The physical homogeneity of the samples was checked by measuring the apparent density and the vacuum porosity. From seven out of 14 production dates one batch was selected at random, of which 4 cubes were tested following RILEM CPC-I 1.3 [3]. Based on an analysis of variance one batch proved slightly different for both density and vacuum porosity. The average apparent density proved to be 1968 kg/m3 with a standard deviation of 7.9 kg/m3. The one batch deviates less than 0.7 % in density from the others. The average vacuum porosity amounts to 22.2 % VJV with a standard deviation of 0.2 % VJV. The deviation of the one batch is less than 2.7 % from the overall average. This leads to the conclusion that except for a small difference in one batch the cubes can be considered homogeneous with respect to the physical properties apparent density and vacuum porosity. The compressive strength was measured after 7, 28, 90 and 182 days. The results are: 7 days: 48.1 * 1.7 MPa; 28 days: 54.4 * 3.5 MPa; 90 days: 60.7 * 0.9 h4Pa and 182 days: 64.0 1.6 MPa. This level of compressive strength indicates that no problems with the durability are to

65 be expected. The permeability of the specimen was tested by a water penetration test, which led to a value of 4.9 * 10 - I 2 m/s. 2.3 Chemical composition To verify the homogeneity of the specimen between cubes and within one cube out of 7 production dates a single cube was selected at random and analysed after size reduction to less than 125 pm and complete homogenization. A subsample was taken for analysis by ICP, Atomic Absorption Spectrometry and Ion Chromatography. One cube was selected at random and cut in equally sized slices, which were size reduced to below 125 pm, homogenized and analysed with the same techniques. The samples were brought in solution by bomb destruction for Cu, Li, Mo, S and Cd using a HNO3 ,HF,HC104 mixture. For Ca, Mg, K, Na, Ba, Sr, Zn, Pb, Co and Si a fusion with lithium metaborate was applied. 2.4 Availability for leaching To be able to define a driving force for release by diffusion the availability for leaching is determined using a method described in NEN 7341 (formerly NVN 2508[4]), which is based on leaching a fine ground sample under pH control at pH =7 using a liquid to solid ratio (L/S) of 50 Vkg and subsequently at pH=4 using again L/S=50. The extracts are combined and analysed using the same methods as for the analysis of solid samples. 2.5 Tank leaching test (common procedure)

The common procedure used in the intercomparison is a tank leaching test similar to the NEN 7345 (formerly NVN 5432 [5]), which in its general principle resembles the ANS16.1 procedure [6]. This method allows distinction of release mechanisms, such as wash-off effects, dissolution and the main process diffusion controlled release. In addition, physical restriction (tortuosity) and chemical retention of individual constituents can be calculated, when the release of an inert constituent (no retention in the matrix) is measured. Often Na, K or CI can be used for that purpose. A short description of the method is given below. The procedures deviates from the NEN procedure as the procedure has been shortend to 16 days to limit the occurrence of possible depletion of mobile constituents from the 4 cm cubes [7]. Procedure: After rinsing the tank or vessel with acid and washing with water the specimen is placed in the tank on a support. The vessel is filled with water using 5 times the volume of the speciment to be tested. The specimen must be submersed completely. The leachate is removed and replaced by fresh leachant after 2 , 8 , 2 4 , 4 8 , 72, 102, 168, and 384 hours (16 days). The proposed renewal time series follows from the formula: tn = n2 . t l using t l = 0.083days (2 hours) and n= I , 2, 3, 5, 6, 7, 9 and 14. The leachate is filtered and after measurement of pH and conductivity acidified pH=2. Part of the sample in kept unacidified for analysis of e.g. sulfate, bromide, chloride. To demonstrate the reproducibility of the leaching procedure the leaching test was carried out in one laboratory on 10 cubes randomly selected from the different batches. To demonstrate the consistency of the shorter procedure (16 days) in comparison with the full procedure (64 days) the test was also carried out on specimen of lOxlOxl0 cm. To be able to identify possible changes in leachability with time due to further curing of the specimen the test was also carried out three month and seven month after the first test.

66 2.6 Calculations From the leachate analysis data the release (ms/m2) in each time interval is calculated. Based on the assumption that this release is entirely based on diffusion an effective diffusion coefficient is calculated from:

D,i = z (Ei)2/ (4. Uavaii.p)2.(dti -

in m2/s

In which De,i is the effective diffusion coefficient for a component calculated for fraction I; E; is the measured release of the component in fraction i in mg/m2 ; Uavail.is the availability for leaching according to NEN 7341 in mg/kg dry matter; p is the density of the product in kg/m3 ;ti is the time of liquid renewal of fraction I in s and ti.l is the liquid renewal time of fraction I1. The effective diffusion coefficient is usually expressed as pD. = - log D,. By averaging the thus obtained effective diffusion coefficients (De in m%) for an interval of several points, in which the first and last cycles may be omitted due to resp. wash-off effects or depletion, an average D, is obtained, which can subsequently be used to calculate release for other geometries and other time intervals. 2.7 Other test methods applied

Apart from the common method other leaching tests have been: Tank leach test as described but in stead of using a closed vessel air was bubbled through the solution causing an almost neutral pH in the leachate. Tank leach test as described but in stead of using a closed vessel carbon dioxide was bubbled through the solution resulting in a pH between 5 and 6 in the leachate. The German standard DIN 38414 S4 [8], the new proposed CEN procedure for waste [9], the Swiss TVA procedure [lo], the US - EPtox and TCLP method [ll], a modified availability test with pH control at pH =12.5, a pH static procedure [2,12] and the AFNOR method for stabilized waste [ 131. 2.8 Standard leachate A standard leachate has been prepared by extracting a 1 : 1 mixture of MSWI fly ash ( metals: Pb, Cu , Cd and Zn) and coal fly ash (oxyanions: Mo, B, V) at liquid to solid ratio (LS) = 10 using pH control at pH = 4.This leachate needs to be diluted 10 times before use as a standard leachate. The aim of the leachate is to provide a common solution to be analysed by all participants, which will allow conclusions on the degree of agreement between analytical methods used. Therefore the concentration level of constituents is chosen such that with the currently applied methods measurement should be sufficiently accurate.

3. RESULTS AND DISCUSSION 3.1 Material homogeneity The data obtained for the chemical composition of 10 randomly sampled cubes and the results obtained on 8 separately analysed slices from one cube to are given in table I. The following elements were analysed: Ba, Br, Ca, Cd, CI, K, Li, Mo, Na, Pb, S, Si, Sr and Zn. In the table the average and standard deviation and relative standard deviation (RSD) for both datasets are given. The data indicate that the relative standard deviation is less than 6% for several elements both in the individual cubes as well as within one cube. The high relative standard deviation for Mo is entirely due to the limited analytical sensitivity for this element. For Sr

67

and Zn in the individual cubes a RSD slightly higher than 6 YOis observed. For Ba and Pb in the slices of one cube a RSD of respectively 7 and 9% is observed. This higher variability is not due to statistically rejectable outliers. Based on an analysis of variance of the two datasets it can be concluded that Na, Pb and Si do not fUllfill the nulhypothesis at 95% confidence. In the case of Si this can be attributed to the very low RSD in the slices from one block. If the same more realistic RSD as for the separate blocks is applied the condition is hllfilled. In case of Na the difference is just significant, but not critical. In case of Pb the difference is significant, which may be attributed to known heterogeneity of MSWI ash samples. The occurrence of minute metallic particles may cause such effects [ 141. The results of the analysis of individual cubes from different batches as well as the analysis of subsamples taken from one cube indicate that the cubes are sufficiently homogeneous to Table I. Verification of homogeneity of test specimen based on chemical composition between cubes and within one cube. 10 Cubes

Br Ba Ca Cd K Li Mo Na Pb S Si Sr Zn

One Cube

Mean

SD

RSD

55.5 244.0 130325 28.3 5544 17.1 7.5 4581 692 6890 27998 1 324 1826

2.43 4.38 58.7 13.58 5.57 257 6676 5.12 132646 29.9 1.23 4.34 5.09 6109 282 0.85 4.97 17.9 2.28 30.37 5.6 188 4.11 4871 5.83 763 40 4.46 7291 307 3.65 284946 10207 6.69 330 22 6.38 1902 117

Mean

SD

RSD

3.81 2.24 18 7.06 5.20 690 1 5.02 1S O 5.26 321 0.92 5.11 1.26 22.52 302 6.20 70 9.13 5.34 389 1.67 4750 16 4.75 112 5.87

F

P

1.18 1.78 1.07 1.49 1 29 1.16 3.25 2 58 2.98 1.60 4.62 1.91 1.09

0.42 0.19 0.45 0.26 0.34 0.40 0.05 0.07 0.05 0.23 0.02 0.18 0.46

Fcrit 3.31 2.30 2.30 2.30 2.30 2.30 3.31 2.30 2.30 2.30 3.3 1 3.31 3.31

warrant the leaching intercomparison studies. From other work the role of total composition of elements has been shown to be of limited importance for the leaching behaviour of constituents and Pb in particular, which would imply that the somewhat larger variability of Pb may not be reflected in the leaching results [ 151. 3.2 Availability In table I1 the data obtained for the availability test on fine ground materials is given. In addition to the availabilities for individual elements in mdkg used as driving force in the calculation of the effective diffusion coefficients for the elements, the acid consumption in the test is reported. The two step extractions required about 5.95 mequiv of acid/g to control the pH at pH=7 and about 3 mequiv of acid/g for pH control at pH=4.

68

Table 11. Availability (mglkg) and acid consumption (mmoVg) Ba 1 102.9 2 94.6 3 111.6

Na 1 3797 2 3828 3 4005

Br

Ca

Cd

CI

K

Mo

Li

50 51

114200 116400 122500

22.9 14.6

8450 9164

5382 4874 5148

2.2 1.6 2.4

11.4 11.6

Pb

S

Si

Sr

Zn

Acid

71 72.7 61.5

6630 6850 7020

5315 4483

270 272

1249 1178 1304

7.1 6.5 6.2

The sum is 113 mequiv of acid. The three series of availability tests carried out in May 1993(1), September 1993 (2) and January 1994 (3) point at a significant reduction in acid consumption, which is tentatively attributed to carbonation. The plastic wrappings, in which the samples are stored, are not sufficiently airtight to prevent uptake of carbondioxide. Relative to the composition the availability for leaching amounts to about 34 % for Ba, 90 % for Br, Ca and CI, 100 YOfor K and S, 75 % for Cd, 30 % for Mo, 62 YOfor Li, 80% for Na, 10 % for Pb, 2 % for Si, 70 % for Sr and 60% for Zn. The reproducibility of the availability test is good for elements that can be analysed with sufficient analytical accuracy at the concentration levels encountered in the availability test. 3.3 Standard leachate The composition of the standard

standard deviations as indicated in table 111. In general the relative standard deviation is close to or within the desired analytical precision of 5 %, except for V and Mo with respectively 13 and 32 % RSD. This is caused by the analytical limitations of the methods used at the concentration levels in the leachate. The

Figure 1. Na in Standard Leachate

h

9

69 67 6 5 . . 63

N

_ . _ - - - _2 _ - - - . * - . :, : * ; . : * ! ;

3 -

61

3.= z

579 ; 5 55 53 ~

51;

' t :

, -

;: ~

8

'

t

- - - - - - - - -

4 9 - " " ' ~ " " ~ " " ' ~ ~

69 3.4 Tank leaching data

TableIII. Average composition and standard deviation of the standard leachate (mg/l).

3.4.I Effective dijjuusion coefjcierit Mean Stdev RSD N As was shown in several studies [17,18,19] the leaching of constituents Ba 0.0476 0.003 6.3 from stabilized waste is not related to 4 Ca 227 7.0 3.1 the chemical composition. So in 4 Cd 0.835 0.042 5.0 addition to establishing the homo10 0.542 0.010 1.8 cu 10 geneity in terms of chemical comF 5.65 0.39 6.8 8 position the reproducibility of leaching 0.0055 0.0018 32.0 Mo 10 of 10 randomly selected samples was 55.8 2.1 3.8 12 Na tested to ensure a usehl inter0.275 0.0136 5.0 Pb comparison. To assess the difference 4 52.8 S 12 1 . 5 2.8 in sample size on the release three 0.0062 0.0008 13.4 V 10 cubes of lOxlOxl0 cm were tested in 28.2 Zn parallel. Since the release is related to 1.2 4.4 12 the surface area, the diffusion coefficients should be the same, which has been tested statistically. the results are Figure 2. pDe versus given in table IV. The agreement relative analytical SD. between the effective diffusion coefficients, expressed as pDe = - log 18 I 1 I D, , between the smaller and larger cubes is generally good with the exception of S, Ca and to a lesser extent CI. The release of Ca from the larger cubes appears to be slightly higher than from the smaller cubes. With an increase in pD, the standard deviation generally goes up as well due to the fact that the concentration levels associated with higher pD, 's are 12 also lower and therefor closer to detection limits. In figure 2 this is 11 illustrated. The elements Na, K , Br and to a lesser extent CI can be 10' ' ' ' ' ' ' ' ' regarded as inert i.e. non-reactive with 0 10 20 30 40 50 60 70 80 90 100 the productmatrix and as such can be Rel. analytical SD (%) used to calculate the tortuosity or physical restrictivity [7,15]. Their DD,'~are verv close. Constituents such as Cd and Pb show high pD, 's (= low mobility) caused by a strong interaction with the productmatrix. The difference between the pD for inert constituents and reactive components can be expressed in a chemical retention value. This value is a knction of pH, redox condition, complexing constituents in the pore solution and sorption reactions on the walls of the pores.

i

1;

1

'

1

-

70

Table IV. Effective diffusion coefficients, standard deviations and relative standard deviations for 10 randomly selected 4 x 4 ~ 4cm cubes and 3 cubes of lOxlOxl0 cm. 10 Cubes Mean

CI Ba Ca Cd Br K Li Mo Na Pb S Si Sr Zn

11.69 13.43 13.80 16.09 11.36 11.14 12.22 13.66 11.24 15.51 15.06 14.85 13.10 17.32

3 Cubes

SD 0.04 0.08 0.04 0.06 0.03 0.02 0.04 0.08 0.02 0.13 0.04 0.05 0.05 0.26

RSD 7.98 16.26 9.46 13.64 7.58 4.66 8.64 17.14 5.45 25.33 9.46 11.06 9.87 9.87

Mean 11.57 13.33 13.62 15.78 11.21 11.08 12.17 13.99 11.18 15.21 14.61 14.24 12.93 16.38

SD

RSD

F

0.06 13.76 5.28 0.03 6.90 3.46 0.06 12.73 4.27 0.03 1.15 7.11 0.02 3.50 2.28 0.02 3.50 1.30 0.01 2.64 8.43 0.11 22.88 2.61 0.02 3.94 1.46 0.21 37.82 9.03 0.06 12.21 13.35 0.04 8 13 8.97 0.03 7.54 1.28 0.07 7.54 1.28

P

Fcrit

0.03 0.24 0.05 0.36 0.34 0.51 0.11 0.3 1 0.47 0.01 0.00 0.01 0.33 0.33

3.01 19.38 3.01 3.01 19.38 19.38 19.38 19.38 19.38 3.01 3.01 3.01 3.01 3.01

Of these pH is a very prominent Figure 3. Mean pDoand 95% release controling parameter as will be shown later. The relative confidence interval for Na. standard deviation ranges from 3 to 37 %. In the latter case the measurements were at or close to the detection limits of the analytical methods employed. In judging these numbers it should be remembered that these values are not directly measured, but derived from other measurements adding to the overall uncertainty of the final answer. In addition, the release derived from this leach parameter is proportional to the square root of the effective dihsion coefficient, which implies that the error is not propagated linearly in the final answer. The standard deviation in the release data as derived from the effective diffusion coefficient, the availability and the size of the specimen is discussed below. 3.4.2 Intercomparison of lank leach data.

At the time of writing of this paper only part of the dataprocessing was carried out. Therefor only data for Na are given here. For the pD, of Na the results of 18 participants in the intercomparison have been treated statistically using I S 0 5725[ 161. The repeatability and the

71

reproducibility standard deviation of the pD, for Na amount to resp. 0.071 and 0.095 (pD = 3.47 .10 - I 2 m2/s). In figure 3 the individual data units) with a mean value of 11.46 (D=,N~ obtained by the participants are given with the 95 % confidence interval. 3.4.3 Tortuosity or physical restriction Based on the mobility data for inert constituents (here Na) the tortuosity can be calculated. The results are given in table V. The tortuosity data for the small and the larger cubes are only slightly different. The tortuosity for the samples aged for another 4 month show tortuosities significantly higher than the earlier data. This is attributed to the hrther curing of the product. The samples

Table V. Tortuosity data

Series

Period

T

SD

10cubes

May93

212

18

3 cubes

May93

187

12

Aged

Sept93

379

30

exposed to leaching under a carbondioxide Air Sept 93 100 4 flush fall slightly below the aged data. It is surprising to note that the exposure to air c02 Sept93 328 40 during leaching apparently leads to a reduction of the tortuosity. This effect is not only noted for Na but also for K and Br. The reason for this observation is at present unclear

3.4.4 Release estiniates The final answer of a leaching test on monolithic specimen is a release expressed in mglm’ . The uncertainty in release estimates based on the calculated effective difision coefficients is given in table VI. The reproducibility in terms of release is satifactory for the intercomparison. The cumulative release patterns for Ca, S, Mo and Zn under different experimental conditions - after aging, exposure to air and to carbondioxide during leaching - are given in figure 4. The difference between the early measurements (1 month cure) and measurements after 5 month curing, is an overall decrease in release due to ongoing hydration of cement resulting in a denser pore structure. The release of Mo is not significantly influenced by the different conditions of leaching. In the case of Zn the release is directly related to the pH dependence of leaching. This aspect will be addressed in more detail below. Under the low pH conditions imposed by COz all of the Zn available for leaching can be leached in a relatively short period.

3.4.5 Leachingproperties as afrinction of aging and exposure to air and C02 The question has been raised to what extent the leaching properties of cement-based specimen of the type studied in this work will change appreciably as a result of aging (or rather hrther curing) Another aspect of leaching solid specimen has been the issue of leaching in a closed vessel, exposure to the air or exposure to carbondioxide In the latter two cases carbonation of the specimen occurs, which may alter the leaching behaviour of the specimen To assess this aspect, which is accompanied by a drop in pH of the leachant, pH static experiments were carried out in the pH range from 4 to 12 5 The difference in leachability between the cubes

t

100000 i

A '

100

'

" " " "

'

" " " "

10

1

"

100

200

50'

'

' " " -

'

' " " -

'

"

500

Total

_

Available ~

~

_

~

~

~

10

9

a e 9 0.1

[

0.05'

1

A

A

BI '

'

" " " "

10

0.1'

'

" " " "

100

500

1

'

'

" ' -

'

" " " "

10

100

"

500

Time (hours) Figure 4. Release of Ca, S, Mo and Zn from cement-stabilized MSWI fly ash measured in a closed vessel after l(square) and 5 month (plus) curing, exposed to the air (triangle) and CO after 5 month (dot) curing.

cured for about 4 month and the first series of measurements after 1 month curing in a closed vessel is reflected in a higher pD, for Na, K, CI and Br, which points at a increase in physical restriction (tortuosity) due to ongoing hydration resulting in a denser structure of the cementitious matrix. A final series of measurements after about 9 month curing points at a stabilization of the curing process, because about the same pD, for Na is obtained as in September 1993. The same trend is observed for CI, which also shows a stabilization of the pD, after 4 to 5 month of curing (figure 5 ) . The mobility of Ba and Ca is more significantly

73

reduced, which is most likely related to the behaviour of sulfate, as it behaves quite different in the aged series. In stead of diffusion controlled release sulfate shows a marked surface wash-off effect in the aged samples. This is probably the result of carbonation, which decomposes the monosulfate phase in the cement matrix. The cubes were stored wrapped in plastic, which also may have led to some surface carbonation. In the test with forced exposure to air (air bubbling through the solution) the mobility of Ba and Ca decrease hrther (pD. higher). Zn mobility is also decreased. In the test with forced exposure to carbondioxide (COZ bubbling through the solution) the mobility of Ca is significantly increased and that of Zn is more than 4 orders of magnitude higher. This effect is caused by the leachability of Zn as a function of pH (figure 6) as obtained from a pH static leaching test on finely ground cube samples. This figure confirms that from a leachate pH around 10 to a leachate pH between 5 and 6 about 4 orders of magnitude difference in leachability exists. From other studies incite (Zn(0H)Z ) was found to be the solubility controlling phase[ 121. Here the same mineral phase appears to be solubility controlling. In case of Mo the difference between the test conditions is limited, which is in accordance with the pH static data shown in figure 6. With the forced carbondioxide exposure a slightly higher mobility is noted compared to the data obtained in a closed vessel and with air exposure. The pH stat data agree qualitatively with other studies [20]. The forced exposure to carbondioxide, which is supposed to represent accelerated carbonation and aging, leads to unrealistic release data for z" some metals as sorption reactions are usually too slow to follow the rapid change brought about by excessive CO2 exposure. The pD, values and Na release data obtained by 13 participants are given in figure 5 and compared with the data obtained in the verification study. In figure 5 the pD. values for Na are plotted as a function of time showing the change in tortuosity with time due to the ongoing curing process and the agreement between these data and the results

Table VI. Release (mglm2), standard deviation and relative standard deviation for cubes after 28 days of curing. 10 Cubes ( 4 x 4 ~ 4cm)

Mean

Stdev

RSD ~

Br Ba Ca Cd CI K Li

409 1 I0 79956 1.17 98707 80858 49.60 2.01 51047 6.93 1087 1122 426 14.90

MO

Na Pb S Si Sr Zn

10 2.39 7.64 6.95 3541 4.43 0.09 8.11 3076 3.12 1723 2.13 2.01 4.05 0.16 7.94 1335 2.62 0.93 13.40 47 4.34 61 5.46 20 4.63 3.00 20.12

Figure 5. Change in tortuosity upon curing 11.90 9

11.70

11.50

11.30

*

A

11.10

0

2

4

6

8

Curing time (month)

10

74 500

0.5

.

100

h

d

OD

E

v

10

4 : : A

-8 0.1 % 3 +l

I

I

A

*

t

1

0

e

0.1

e 0.01 A

0.01

0.w1

Mo ~

0.005 3

4

"

5

'

6

'

7

'

8

'

9

'

1011

'

0.m1

1213

3

4

5

6

7

8

9 1 0 1 1 1 2 1 3

PH Figure 6. Leachability of Mo and Zn from crushed cement-stahilized MSWI fly ash as measured in a pH controlled test.

Table VI. Effective diffusion coefficients derived from measurements on different sized cubes, aged products and products exposed to air and COz (pD, = - log D, , D, in m2/s). Blocks( 10) 4x4x4cm May-93

CI Ba

Ca Br K MO Na Pb S Zn

11.69 13.43 13.80 11.36 11.14 13.66 11.24 15.51 15.06 17.32

Blocks(3) 10x10x1Ocm May-93

Aged blocks Sep-93

Air pH=7 Sep-93

c02 pH=5 Sep-93

11.73 14.80 14.54 11.37 11.35 13.48 11.49 15.28 15.03 17.99

11.66 16.60 16.44 10.45 10.99 13.57 10.91 15.23 14.80 18.18

12.19 13.59 13.12 10.99 11.36 13.21 11.43 15.24 14.19 13.16

11.57 13.33 13.62 11.21 11.08 13.99 11.18 15.21 14.61 16.38

obtained by participating laboratories in Europe 3.5 Potential uses of the tank leaching test This type of test is a usehl characterization test to identify the leaching controlling parameters and conditions for a given material or class of materials[7, 15, 17 - 191. Then shorter procedures should be developed as compliance tests to assess basically the same parameters

75

however with less accuracy due to the limited number of data points used to quantify the parameters. Options for developing such shorter procedures should aim at minimizing initial wash-off effects, ensure timely wetting of the entire product, make use of the square-root of time dependence of diffusion controlled release and optimize the liquid to surface area ratio in the test to facilitate chemical analysis. Based on the type of leach parameters derived from this test predictions of release at longer time scales than those corresponding with the actual test duration can be made. Based on the pH static information supplied other leaching conditions in terms of pH can be largely explained and most likely modelled after some firther studies into this issue. In addition, the leach parameters obtained can be used for management purposes to improve product quality and performance[7, 211. 4. CONCLUSIONS The tank leaching test studied in the framework of this intercomparison is a good characterisation method for the leaching behaviour of monolithic materials as it provides knowledge on release controlling parameters and allows prediction of release at longer time scales by the leaching parameters derived form the test results. The homogeneity of the specimen prepared for the intercomparison prove to be sufficient between batches as well as within one specimen. The leaching data obtained in one laboratory on randomly selected specimen prove to be sufficiently reproducible in terms of release for most elements studied. In a few cases the concentrations to be measured are close to the analytical detection limit leading to a higher relative standard deviation for those elements. Based on the mobility data for Na and CI , which reflect the tortuosity of the matrix, it can be concluded that the product has changed in leaching properties in the first few months. It appears to be stabilizing in its properties after about half a year. Upon aging the cement-based product is changing in its leaching properties. This is an aspect that can not be avoided for any type of cement-based product. By measuring the release parameters in one laboratory in three time intervals covering the period of analysis by the other participants the results can be placed in the proper perspective. Leaching under different pH conditions was studied, which results in differences in release, which can be largely explained by the results of pH stat experiments carried out on crushed material. Based on this longer test shorter procedures with a close correlation with this test can be derived, which may largely provide the same basic information. Standardization of such a short compliance method will start in the framework of CEN TC 292. It is recommended that the characterization method is also standardized by CEN TC 292.

Acknowledgenienl This work is carried out in the framework of the EEC Measurements and Testing programme (BCR) 93/94. Participants are: University of Aberdeen, GB (Prof.Dr. F.P. Glasser); POLDENINSAVALOR, FR (Dr. J. Mehu): RIVM, NL ( Drs. G.A. Rood); ENEA ,IT( Drs. S. Balzamo): VKI, DK (Dr. 0. Hjelmar); K K , DE (Dr. J. Vehlow ); WRc, GB (N. Blakey, K.Lewin); SGI, SE (J. Hartlen); VTT, FI (M. Wahlstrom); VITO, BE ( Ir. B. Leathem); Institute Quimic de Sarria, ES (Dr. J. Obiols): Junta de Residus, ES (Mrs H. Sala); INASMET, ES (G. Ortiz); Umwelt Bundesamt, DE (P. Henschel); UNINOVA, PT (Dr. A. Steiger Gargao); ISDS , IT (L. Musmeci); WTC, Canada (J. Stegemann).

76 5. REFERENCES 1. Waste Materials in Construction: Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials,Eds. J.J.J.M. Goumans, H.A. van der Sloot, Th.G. Aalbers, Elsevier Science Publishers, Amsterdam, 1991. 2. H.A. van der Sloot. Leaching behavior of waste and stabilized waste materials; characterization for environmentalassessment purposes. Waste Management and Research, 8, 1990,215-228. 3. RILEM CPC-I 1.3. Methods for the determinationof apparent density and vacuum porosity.1984. 4. NEN 7341 (formerly NVN 2508). Determination of leaching characteristics of inorganic components from granular (wastes) materials. "I, Delft. 1993. 5. NEN 7345 (formerly Draft NVN5432). Determination of the release of inorganic constituents Delft. 1993. from construction materials and stabilized waste products. "I, 6. ANS. 16.1 Measurement of the leachability of solidified low-level radioactive wastes by a short-term test procedure. American Nuclear Society, Illinois 60525 USA 1986. 7. G.J de Groot and H.A van der Sloot. Proc. Sec. Int. Symp. Stabilizatiodsolidification of Hazardous, Radioactive and Mixed wastes. Williamsburg, Virginia, May, 29 to June 1, 1990. 8. DIN 38414 S4: Geman standard procedure for water, wastewater and sediment testing - group S (sludge and sediment); determination of leachability (S4). Institut fiir Normung, Berlin, 1984. 9. CEN TC 292 document: Proposed leaching test for granular solid waste. H.A van der Sloot, 0. Hjelmar, Th.G. Aalbers, M. Wahlstrom and A,-M. Fallman, February, 1993. 10 Bericht zum Entwurf fur eine technische Verordenung iiber Abfalle (TVA), 1988. Departement Federal de I'Interieur. Switzerland. 11 Toxicity Characteristic Leaching Procedure(TCLP). Federal Register Vol 5 1 No 114, Friday, June 13, 1986, 21685-21693 (proposed rules). Federal Register, Vol No 261, March 29, 1990 (final version). EPA Toxicity Test Procedure (EP-tox), Appendix 11, Federal register, Vol45(98), 1980, 33127 - 33128. Govemment Printing Ofice, Washington D.C. 12 R.N.J.Comans, H.A.van der Sloot, P.Bonouvrie. Proc. Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania. 1993. 667 -679. 13 J. Mehu, Y.Perrodin, B. Sarrazin and J. Veron. Reference I . page293 - 300. 14 C.W. Versluijs, I.H. Anthonissen and E.A.Valcntijn. Mammcet '85. Report 738504008. RIVM, June 1990. 15 S.E.Sawell, A.J.Chandler, T.T.Eighniy, J.Hartlen, O.Hjelmar, D.Kosson, H.A. van der Sloot, J.Vehlow. The International Ash Working Group: Treatise on MSW Incinerator Residues. This conference Special Session. 16 IS0 5725. Accuracy (trueness and precision) of measurement methods and results. part 2. International Organization for Standardization, 1990. 17 P.L. C6te. Thesis : Contaminant leaching from cement-based waste forms under acidic conditions. MacMaster University, Hamilton, Canada, 1986. 18 D.S.Kosson, T.T.Kosson, H.A. van der Sloot.,"USEPA Program for Evaluation of Treatment and Utilization of Municipal Waste Combustor Rcsidues", Cooperative agreement CR 8 18178-01O.USEPA/RREL, Cincinnatti, September 1993. 19 M. Hinsenfeld. Reference 1: page 33 1-340. 20 G.J de Groot, H.A van der Sloot and J. Wijkstra. In: ASTM STP 1033, P.L. Cote and T.M. Gilliam, Eds, ASTM, Philadelphia, 1989, pp 170 - 183. 21 H.A van der Sloot, G.L. van der Wegen and E. Vega. Beoordeling van immobilisaten. Een voorstel voor criteria en testmethoden. CUR report 93-6. Civieltechnisch Centrum Uitvcering Research en Regelgeving. Gouda. 1993.

EnvironmentalAspects of Construction with Waste Materials J J J M Goumans, H A . van der SIoot and 7b.G. Aalbers (Editors) el994 Elsevier Science B. V. All rights reserved.

77

Immobilisation Potential of Cementious Materials F.P. Glasser Department of Chemistry, University of Aberdeen, Old Aberdeen, Scotland. Abstract The immobilisation potential of lime and Portland cement matrices is two-fold. They afford physical immobilisation by converting liquids, sludges and particulates to solids. They also afford a chemical immobilisation potential, sorbing and precipitating otherwise soluble species. Both the physical and chemical potentials are difficult to quantify. The chemical immobilisation potential is perhaps easiest to measure and model by laboratory simulations. Progress in this area, of characterizing mechanisms of insolubilisation, is described using the Cr-Mo-U triad as examples. Remaining problems necessary to predict the performance of cement-conditioned wastes are discussed. 1. INTRODUCTlON Lime and Portland cement are relatively inexpensive manufactured products having consistent properties. Cement and Ca(OH)2 may also be mixed with each other and with a variety of other reactive wastes including slags, coal-combustion fly ash etc., to form solid matrices. These have been used successfidly to immobilize a range of waste materials. Conner reviews commercial technologies (1). Physical containment is most important for mobile liquids, dusts, sludges and solutions. Because cements are tolerant of wet wastes and can, within limits, neutralize acids and tolerate salts, wastes can frequently be dispersed throughout a cementitious matrix. The matrix affords both physical resistance to leaching and a definite chemical immobilization potential. Characterizing these potentials requires special methodologies. The porositypermeability relations of cementitious matrices are not well understood; most reports have been restricted to formulations intended for load-bearing constructional applications. Most of the intrinsic porosity of well-made cement matrices is less than Ipm effective radius, so the matrix has only limited permeability. However, extrinsic porosity is often introduced at grain-paste boundaries and the amount of such porosity increases rapidly with increased water content (2). This, in turn, affects permeation properties. The mix water used in formulating cementitious matrices is partially combined in the cementitious solids. Normally an excess of water, beyond that required for complete hydration of the cement, is needed to achieve the necesary plasticity or fluidity for The chemically mixing: also, to achieve economic loadings of wet wastes. uncombined water is held in pores, from whence it can be extracted by pore fluid expression (3). Analyses of the expressed pore fluid provides a unique method of determining how much of the added waste species remains soluble. The pore fluid comprises the most leachable portion, and its analysis provides an immediate quantification of the source term for leaching. The solids of cement have high surface area and provide potential for sorption and a source of reactive species for precipitation and hence exert a strong modifjmg influence on pore water composition.

78 2. PHYSICAL IMMOBILISATION Several methods are available to determine pore structures in hardened cement paste. Mercury intrusion can be used to determine pore sizes in the range 0.005-5pm (approximately), with neutron scattering used for finer pores. However the bulk diffusional and leaching properties are determined by the larger pores, within the range of mercury intrusion, as well as by pore interconnectivity. A special type of porosity arises at the interface between particles and cement paste. Fig. 1 illustrates schematically the different ranges of porosity. Interface porosity characteristically arises when grains are physically unequal in size. The standard for comparison is that of the cement, lime, fly ash etc. particles, typically 5-50pm, with larger particles, especially >50-IOOpm, giving rise to intefacial porosity. The larger pores become partly filled with crystals, notably Ca(OH)2 and ettringite, a hydrated calcium sulfoaluminate. The remaining space is occcupied by a permeating aqueous phase. The picture is representative of the state of hydration achieved within a few weeks or

-

20 % Intruded Volume

Slag Cement blend, mcist cured at 18°C

/d

10

0.1 Pore entry diameter

Fig. 1. Mercury intrusion porosimetry scan of a typical slag-cement blend cured for 30d and 2 years. Pore entry diameter in pm. Slow hydration of slag converts much of the open porosity to closed porosity and the pore size distribution shifts to finer pores.

0.01

Fig. 2. Microstructure of a cement containing particulate material. The main part of the Figure is on a micrometer scale. A large particle occupies the lower lefthand corner. Porous regions, ( I ) , exist in partly hydrated paste, but a process zone of enhanced porosity occurs, (2), in the vicinity of the particle. The inset shows on a nanometer scale the structure of the paste. A large part of the intrinsic nanoporosity, (3), is associated with the gel constituent of the paste.

79 months. The presence of residual cement or blending agent indicates that the system still has the capacity for formation of more hydrate. Some of this additional hydrate goes into blocking pores, although interfacial porosity, shown as region 2 in Fig. I , Fig. 2, showing mercury intrusion data for a typical remains little affected. constructional cement, indicates how the porosity continues to decrease with cure. It should be recalled that mercury intrusion only measures uccrssihle porosity: upon continued hydration, pore blocking contributes to the decrease in accessible porosity. However the actual permeation properties achieved may represent a compromise between achieving good waste loadings and realizing low permeability. The permeation properties of cements intended for waste conditioning have received less study. Table 1 summarizes some of the anticipated similarities and differences between constructional mixes and conditioned wastes. A particular concern is that high waste loadings will degrade the microstructure which, in turn, will adversely affect the permeation properties. The intrinsic permeation properties achieved may thus represent a compromise between achieving good waste loadings and realizing low permeability. The formulations which are used in waste treatment do not generally require high strengths. Nevertheless, most cementitious matrices acceptable for conditioning will gain strength and become susceptible to cracking, which increases the effective surface area available for leaching. Cracking may arise from purely mechanical causes, e.g settlement, shrinkage, but it may also arise as a consequence of inherent dimensional instability, from chemical reactions with waste components or those in the disposal environment. To act as a conduit or channel for leachants, cracks have to be relatively large, greater than 1-2pm. Therefore, if cracking cannot be prevented, it is better to have a dense network of microcracks rather than a lower density of relatively wider cracks. However, at present, little theoretical or practical guidance be given on the prevention or occurrence of cracking and, where cracking does occur, on crack density.

Table 1 Physical Properties of Some Cement Formulations Property

Waste Treatment

Constructional Materials

water:solid ratio

as high as possible to minimise cost

generally as low as practicable

intrinsic porosity

apt to be high

low, except in air-entrained materials

interfacial porosity

variable, depends on waste

always present in normal mortars and concretes

microstructure

influenced by presence of soluble component

relatively constant (see Fig. 1).

permeability

highly variable

'ordinary' materials; 10-8 to 10-10 m / s ; 'special' materials, 10-10 to 10-12 m / s

80

3. CHEMICAL FIXATION 3.1 General principles Cements provide a strongly alkaline internal environment. Ca(OH)2 and calcium silicate hydrogel (shorthand, C-S-H) are available to buffer the pH to about 12.4 at 18°C. In the short term, any alkali in the cement or waste tends to raise the pH above 12.4 because counterions - other than OH- - are relatively insoluble: chloride and nitrate are the main exceptions. Hence the pH of a lime- or cement-conditioned matrix is likely to be within the range 12.4-14 and is well-buffered by the cement solids.

10

-

F

1

:

Pb

Zn

Cd

~~

0.001 -

pH range in alkaline cements I

I

I+

1

Fig. 3 . pH control of the solubilities of a few selected heavy metals. The examples shown are for amphoteric elements. The characteristic internal pH of Ca(OH)2, Portland and blended Portland cements is shown Many metals are relatively insoluble in alkaline aqueous environments. However, there are many examples of amphoteric elements, so-called because they are soluble at low and high pHs. In strongly basic solution they form soluble anionic complexes, e.g. (At(OH)4-: tin and chromium (111) are also examples). Fig. 3, taken after reference (4) is a guide to these relations. The thermodynamics of metal speciation are well known and it might at first sight seem that the chemical conditioning action of cement would not be too effective for amphoteric species. However, these considerations are too simplistic because they fail to include the often specific and very strong interactions between cement components and waste species. These interactions depress solubilities, perhaps by orders of magnitude. However, the conditioning action arises from a number of mechanisms; examples will be given . The cement components vary in composition and crystallinity. Some, like the gel binding phase - a calcium silicate hydrate - are largely non-crystalline but have a very high specific surface, leading to a sorptive potential. The more crystalline hydrates favour crystallochemical substitution and, in the case of layer structures, intercalation. When a waste stream is mixed with water, a complex series of reactions ensue. Assuming for simplicity an initially soluble species, the general sequence is as shown in Fig. 4.

81

I initial Waste Concentration :',

.= ._ n %

Pcn

-

I

initially

';Relatively ,-

Amorphous':, Precipitates.!,, Sorption, e t c j :'

Crys:allization.

Fig. 4. Decline in solubility of waste species in a cement matrix as a hnction of time. Not all species undergo all the reactions shown, but the declie in solubility with time is characteristically encountered The first stage of reaction, usually achieved within the first few minutes of mixing, is the precipitation of relatively insoluble precipitates of oxides, hydrous oxides or precipitates containing other readily-soluble anions hrnished by cement, e.g. sulfate, which precipitates barium. These precipitates are generally amorphous, so are difficult to detect directly. As the time scale of reaction is extended to weeks or These include (i) crystallization of months, a series of slower reactions occur. previously-amorphous precipitates with concomitant reduction in solubility, (ii) reaction between waste species and cement components, leading to fixation by ion exchange, sorption, etc., as a result of which waste components are bound in dilute form into matrix components and finally, (iii) reaction of initially formed precipitates with cement components to yield new phases. For example, a cement component A may react with waste component X giving a compound AmXn or AmXn zH20. Reactions in this latter category are driven by the approach to equilibrium. Since AG is thereby decreased, and AG -RTCnK where K has the dimensions of a solubility product, the overall result is a decrease in solubility. Of course, not all three classes of reaction will necessarily occur for any particular species. These considerations highlight the need for mechanistic studies. These can be pursued at different levels. Table 2 outlines briefly some of these. Single speciessingle cement component studies provide the most satisfactory way of isolating for hrther study the insolubilizing reactions. But the data obtained from simple systems may be too naive: for example, the insolubility of BaSOq has been noted. Cement systems also contain much OH and Ba(OH)2 is relatively soluble. In strongly alkaline environments will B a s 0 4 redissolve? In order to answer questions of this sort, it is almost always necessary to move to stage 2, in which the possiblity of more complex interactions can be investigated. Once this has been done, it may be possible to extrapolate the results into the future. Finally, level 3 studies are necessary to ensure

82

Table 2. Methods of Studying Fixation of Wastes in Cement

Simulate Conditions

Remarks and Notes

Selected single waste component and cement component

Results relatively easy to control, interpret and extrapolate but neglect complex interactions. Not readily accepted into action programmes, e.g. compliance with legislation.

Selected single waste component in "real", chemically complex cements and blends

More difficult to interpret results in a fundamental sense, but likely to include complex interactions and provide acceptable basis for decision making.

'Real,' mixed waste streams with chemically-complex cements and blends

Fundamental mechanisms almost impossible to interpret but results necessary to demonstrate compliance. Difficulty remains of extrapolating present performance into the future.

compliance with standards, although they do not themselves provide a mechanistic basis for understanding the basis of containment or of extrapolating into the future the performance of cemented waste forms. In general, therefore, a combination of approaches is necessary to ensure that a broadly correct perspective towards research and practice is maintained. Experimental techniques have been greatly improved whereby specific immobilization mechanisms can be identified and, if needed, isolated for firther study. Computer-based computational routines will enable fiture performance to be assessed, given site-specific information and an adequate database. 3.2 Case studies: chromium Chromium is widespread in industrial and domestic waste streams. Its toxicity is mainly associated with the upper, Cr(VI), oxidation state. The other common state, Cr(III), is known to be better immobilized in cement than Cr(V1). However, the source of the immobilisation potential is uncertain: Kindness et al. ( 5 ) have reviewed the literature and determined the source of the immobilisation potential. Cr(VI) substitutes in part for sulfate in ettringite, 3CaS04 At203 32H20. Its substitution for sulfate in other phases, e.g. in the AFm type phases, is less. However even in ettringite, where substitution is most favourable, relatively high aqueous CrO 2concentrations are required to sustain significant replacement of SO42- by CrO4 . Thus the potential for chromate immobilisation is poor. However, Cr(V1) is readily reduced to Cr(II1) by contact with metals, e.g. with Fe, or by ferrous salts. Many natural disposal environments are also likely to be reducing in nature; the reducing conditions are generated by the presence of organic matter, and bioactivity which produces CH4, C02, etc. Therefore Cr(VI), if present in waste, can be reduced to Cr(II1) and, in the majority of disposal situations, it is unlikely to reoxidise with the result that the target species for immobilisation is Cr(II1). In simulate experiments, Cr(OH)3 is rapidly precipitated in alkaline solutions. Cr(II1) is amphoteric, so precipitation may be incomplete. Moreover, the initial

4-

83 precipitate is often amorphous, or nearly so, and could be expected to have anomalously high solubility relative to crystalline Cr(OH)3. Experiment shows that the amorphous precipitate crystallizes with a few days at -18°C. But Cr(OH)3 is unstable in the cement environment. It gradually reacts with the aluminate phases, where it substitutes for A t in octahedral sites. The open, layered structures of AFm phases are kinetically most accessible to these exchanges. Kindness, et al. ( 5 ) have reported the synthesis of CaO-Cr203-H20 phases which are structural analogues of the aluminates. The denser hydrogarnet structure, based on 3Ca0 At203 6H20, is kinetically relatively inert, but synthetic experiments disclose it to be a very effective host for Cr(II1). Synthesis of various Cr-containing host phases and measurement of their corresponding Cr solubilities has shown that they are very effective hosts for the immobilisation of chromium. Since the solid solutions require time to form, pore fluid Cr(II1) concentrations tend to decrease with cure duration until an equilibrium level is reached. Theory and experiment are in good agreement that the stable solubility threshold in pore fluid is about 0.2-0.5ppm Cr(II1). Thus the potential for resolubilization, which might be expected from the amphoteric character of Cr(III), is suppressed at normal cement pH's by other factors. Further work does require to be done on the long-term behaviour of cemented Cr containing wastes. In the disposal environment ground water components, including carbonate, chloride and sulfate, may react with the aluminate phases. Comprehensive documentation about the long-term fate of Cr awaits further study of these reactions. 3.3 Case studies; molybdenum Compared to Cr, the chemistry of Mo in cements is less complex. It has only one common oxidation state, Mo(V1). With oxygen, it forms very stable M 0 0 4 ~ groups. The effective ionic size of M 0 4 groups increases in the order SO4 < CrO4 < MoO4, so that substitution of SO4 by Moo4 in calcium aluminosulfates, e.g. in ettringite, is even less favourable than for CrO4. Instead, Mo precipitates as CaMoO4, a phase isostructural with the naturally-occumng mineral powellite. Anhydrous phases of the structurally related zircon-fergusonite-scheelitefamily, to which powellite belongs, are often observed to precipitate directly from aqueous solutions across a broad range of pH's. The high lattice energies of these phases stabilize the anhydrous form; apparently, hydration energies are insufficient to form hydrates. Kindness et al. (6) have synthesized CaMoO4 and determined its solubility. Values are shown in Table 3, and the synthetic models predict quite successfully the Mo content of pore fluids made by spiking "real" cements with Mo.

Table 3. Solubility of Mo in Cement Matrices (water:ordinary Portland Cement 0.4,18"C) Aqueous Concentration after (davs) 5 10 15

20 30

Concentration. porn Mo in mix water

500 200 100 75 65 60

1ooo 500 250 125 80 60

2ooo 1000

400 200 100 60

84 3.4. Case Studies: uranium Stabilisation and immobilisation of uranium-containing

mine tailings and process residues arising from a range of sources, including phosphate processing residues, present problems. Most of the mineral residues are, however, compatible with cementitious formulations. Relatively little data exist on immobilisation mechanisms. Moroni has characterised some of the reaction products (7). Ca(OH)2 reacts readily with U(VI) solutions: the nature of the products obtained depends on the Ca/U ratio of the system. At high U loadings, becquerelite CaO 6UO3 l l H 2 0 , forms. However, such high loadings are unlikely to be encountered in practice and in any event, becquerelite appears not to be compatible with Ca(OH)2 or C-S-H gel. Nevertheless, becquerelite is much less soluble than schoepite, U 0 3 2H20, a normal weathering product of uranium under oxidising conditions. At 5 5 T , the U solubili of a becquerelite precipitate had, after repeated dispersion, decreased to between 1 0 8and 10-6M(.IC-1by 400d. Examination of the system CaO-U03-Si02-H20 is still far from complete. Present indications are that the phases likely to be formed in real cement compositions are uranophane, CaO *2UO3 2Si02 6H20, and a phase structurally related to CaU04. This synthetic phase is apparently a hydrous version of probable formula CaU04x(OH)2x. Formation of these phases, together with sorption of anionic U(V1) species on C-S-H gel, appears likely to limit U solubilities to 10-7 to 10-8hUt. Several other incompletely characterised phases occur in synthetic mixtures, but their occurrence is unlikely to affect the broad picture: at very low U concentrations, <10-8WC, sorption on C-S-H limits U solubility. At higher loadings, the buffering capacity of the cement system furnishes Ca, Si and OH necessary to form solubility-limiting phases 4. GENERAL DISCUSSION It is not generally possible to characterise the immobilisation potential of cement systems in short term experiments: weeks or months are required for reaction of cementitious components with water, as well as for reactions between waste components and cementitious material to reach a state of near completion. Given the complexity of the waste-cement-water system, it is generally not possible to conclude the equilibrium state of the system: indeed, the principal bonding component of cementitious matrices, C-S-H gel, is itself probably thermodynamically metastable. However, a steady state is frequently achieved within a few months or years, and the solubilities of waste components in entrapped water, as determined by pore fluid expression from 'real' cements, gives order-of-magnitude correspondence with solubilities determined by laboratory experiments made on simplified systems. Systems chosen for models must not be oversimplified. Simulate experiments and calculations must at least take into account likely interactions between waste species and cement components. The pore water analysis provides a good reality check between the two approaches. These are illustrated in Fig. 5. Case I corresponds to no interaction between cement and waste components. Portland cement and caseium are an example of this type of behaviour: a solubility limit for Cs is obtained only at very high concentrations. Case I1 is like case I, but the cement components show some sorption characteristically at low concentrations. Many cement phases exhibit sorption - either true chemisorption, or limited ion exchange, or both - which depresses pore water concentrations of soluble waste species. Cs in fly ash or slag cement blends is an example. Case 111 illustrates a situation where a solubility-limiting precipitate forms at low concentrations

85 of the waste species; of the examples described, Mo best fits this case. Case IV illustrates more complex interactions, where low concentrations condition sorption as with U(V1) or Cr(1II). Above some critical concentration a definite plateau occurs conditioned by formation of a solubility-limiting phase. The plateau is shown as horizontal; if, as when Cr(II1) substitutes for At?, solid solution dominates, this portion of the curve may have a definite slope or curvature. The task for the experimentalist is, therefore, to determine the nature and strengths of the interactions and calibrate the response of cement systems to different waste loadings. This requires a determination of the solubility-limiting mechanisms. As has

Ioy cciiiceiilialioii waste s p c i e s

-*

Fig. 5 Selected examples showing solubility patterns of a hypothetical waste species in pore fluid as a knction of waste loading. See text for discussion. been shown, it is not generally practicable to deduce these mechanisms without recourse to experiment. Once the chemistry has been done, the physical aspects of diffusion can be analysed. Exchange of pore fluid with groundwater by a percolation process is likely to condition releases; such exchanges are often site specific and depend crucially on the matrix formulation, surface area and mass as well as the hydrological aspects of the disposal site. Of course, alteration of the cemented waste by the action of aggressive and corrosive groundwater, and the transporting action of other complexing species released from the waste need to be assessed to complete a safety case. 5. CONCLUSIONS

It is generally possible to determine the mechanism whereby waste species become fixed in cement. for Cr(II1) Mo(VI) and U(VI), solubilities across broad ranges of concentration tend to be limited by formation of complex salts involving one or more of the cement components. These substances may require considerable time to

86

develop, but the ultimate reaction products and their solubilities can be predicted with confidence by using a mixture of laboratory studies and examination of 'real' cements loaded with the waste species. One important chemical aspect remains, which is to model the impact of cement deterioration on release. In this way, a knowledge base is being created which enables a source term to be defined leaving the way clear to determining the percolation characteristics of particular wasteforms at specific sites and the resulting impact on leachability. 1.

2.

3. 4. 5. 6. 7.

REFERENCES J.R. Conner, Chemical Fixation and Solidification of Hazardous Wastses, Van Nostrand-Reinhold, New York, 1990. T.C. Powers and T.L. Brownyard, 'Studies of the Physical Properties of Hardened Portland Cement' Bulletin 22, Portland Cement Assoc., Chicago, pp 992, 1948. P. Longuet, L. Burglen and A. Zelwer, Rev. des Materiaux de Construcion et de Travaux Publics. No. 676, 35-41, 1973. J.R. Conner in 'Chemistry and Microstructure of Solidified Waste Forms' R.D. Spence (ed.) Lewis Publishers, 1993. A. Kindness, A. Macias and F.P. Glasser. Waste Management (in press). A. Kindness, E.E. Lachoswki, A.K. Minocha and F.P. Glasser. Waste Management (submitted). L.P. Moroni 'Immobilisation of U(W) in Cement' MSc Thesis, University of Aberdeen, 1993.

Environmental Aspects of Construction with Waste Materials JJJM Goumans. H A van der Sloot and lI8.G. Aalbers (Editors) 01994 Elsevier Science B.V. All rights reserved.

87

Coal Fly-Ash Leaching Behaviour and Solubility Controlling Solids R. Garavaglia - CISE Tecnologie Innovative - Segrate Milano, Italy P. Caramuscio - ENEL Centro Ricerche Residui - Brindisi, Italy

ABSTRACT Experiments have been Carried out with large-scale (1 cubic meter) lysimeter test cells filled with different coal fly-ashes. The leaching behaviour of up to 35 elements was investigated. Lysimeters were irrigated with distilled water under controlledconditions; leachate collection system and storage tank were kept under inert gas to avoid reaction with atmospheric gases. Integrated leachate samples have been collected on a weekly basis and analyzed for complete chemical characterization. Examples of the mobilization trends are presented. Measured concentration values were used to calculate elemental speciation in solution with the geochemical code MINTEQA2. Our results support the hypothesis that geochemical reactions, which can be modelled and predicted, control the leaching of elements from coal fly-ashes. A number of solubility controlling minerals are suggested for both major and trace elements, in the pH range from 8 to 12 (Al, Ba, Ca, Cr, Cu, Fe, Mg,Mn, Ni, Pb, S, Si, Sr, and Zn). No solubility controlling solid pbases were found for As, Mo, Sb, V e U. From these results, predictions could be denved on the leachate elemental concentration as a function of pH. Generally, the predicted values are well correlated to the experimental data.

Introdktion The use of fossil fuels for electric power production has increased throughout the world in the past decade. As a result, huge amount of combustion solid waste, mainly coal fly-ash and bottom ash, are produced. At present, coal-fired power plants account for more than 15% of total Italian electric power generation, and produce about 1.5 Mton/year ashes. Though coal fly-ash is a potentially marketable secondary material, for many different reasons (last but not least Italian law enforcements) substantial amounts are currently disposed of in landfills. Both the fly-ash and the bottom-ash are enriched in major and trace elements which have the potential to adversely affect ground water quality if released into the subsoil in sufficient amount. These elements include arsenic, boron, chromium, molybdenum, selenium, sulphur, and vanadium. There is a need to: 1) accurately assess the mobilization of elements that results from the weathering of these wastes; 2) understand those chemical processes in the ashlwater system that dictate the concentrations of these elements in the leachate. The final goal of our research effort is to develop a predictive capability for short- and longterm leaching behaviour of fossil fuel solid wastes. In the past, most studies on the effects of combustion waste disposal on ground water quality have been focused on characterizing the chemical composition of the waste and collect empirical measurements of elemental extraction rates in short-term leaching tests(' to 'I.

88

Rai and others authod7 to 17) have shown that an approach based on thermochemicaldata and principles can be applied in predicting the upper limits of elemental concentration in leachates generated from these wastes. If a solubility controlling compound that has a rapid dissolutionprecipitation kinetics is present in the waste, or if a secondary phase forms that dissolves and precipitates quite rapidly, then the solid phase will be in equilibrium. In this case, the concentrations of the element in the liquid phase can be predicted on the basis of the precipitation-dissolution reactions defined by thermochemical data. This approach has been particularly successful when applied to coal fly-ash and municipal solid waste incinerator residues and has been demonstrated('*) to have general validity also for different waste materials. We are currently carrying out experiments with large-scale (1 cubic meter) lysimeter test cells filled with different coal fly-ashes. The leaching behaviour of up to 35 elements has been investigated. Measured concentration values were used to calculate elemental speciation in solution with the geochemical code MINTEQA2. Our results support the hypothesis that geochemical reactions, which can be modelled and predicted, control the leaching of elements from coal fly-ashes. From these results, predictions could be derived on the leachate elemental concentration as a function of pH. Generally, the predicted values are well correlated to the experimental data.

Ash Samples Two coal ashes were investigated: a slightly alkaline fly ash from representativecoal combustion in an Italian coal-fired 1) power plant; the choice was based on a comprehensive chemical and physical characterization of fly-ashes generated at different plants from different coals. a strongly alkaline fly-ash, derived from Flue Gas Desulphurisation experiments by 2) means of direct injection of limestone (calcium carbonate) into the burner; this results in sorption of sulphur oxide by calcium sulphatehlphite formation and decomposition of excess lime to give calcium oxide. Upon leaching, the calcium oxide tubs into calcium hydroxide, which confers high pH values to the leachate. This quite unusual fly-ash was selected in order to investigate solubility-controlling solids over a pH range spanning up to high alkaline values. Throughout this paper, those samples will be referred to as Fly Ash and Alkaline Fly Ash, respectively. The elemental composition of both samples is reported in table 1; results of quantitative mineralogical characterization are listed in table 2. Particle size distribution and radioisotopes content measurement, together with standard batch leaching procedures were also performed.

89 Table 1:

total concentration of major and trace elements in the fly ash samples used in this study.

Total concentration (mg/kg)

Table 2:

I

Ash

I

Ba

I

10001

1800

Cd

I

0.2

I

0.2

Fe

1

50300

1-

I

Ash

I

Si

I

233000

I

181000

T1

I

2.0

I

0.6

Alkaline Fly Ash

Alkaline Fly Ash

3oooO

mineralogical composition of the fly ash samples used in this study. (N.D. = not detected).

Mineralogical composition (% w/w) Fly Ash

Alkaline Fly Ash

8.4

5.0

14.4

15.3

CaSO,

N.D.

2.4

Lime

CaO

N.D.

9.2

Calcite

CaCO,

N.D.

2.3

Quartz

SiO,

Mullite

2Si0,

Anhydrite

Amorphous

+ 3A1,0,

I

77

I

65

90

Lysimeter cells The lysimeter cells are cylindrical vessels made of PVC, about 1 m3 available volume. Only inert materials (plastics and washed quartz sand) were allowed to contact the residues into the cells. Leachate was collected at the conical bottom of the vessels and stored in polyethylene tanks. In order to avoid any reaction with atmospheric gases, leachate collection system and storage tank were continuously flushed with nitrogen. The lysimeters were covered so to avoid uncontrolled rainwater to enter them, but to allow free evaporation. The cells were irrigated with distilled water through a sprayer system; 25 litres were delivered once a week, thus simulating a 25 mm rainfall. The dry ashes were mixed with an amount of water (previously determined by Proctor compaction tests), then layered over a quartz sand bottom layer, compacted and topped with more quartz sand. Hydraulic properties of the ash beds were characterized through porosity and permeabilit measurements. Edometricpermeabilities(according to ASTM D2435) turned out to be 8 10-gYand 5 lo4; total porosities resulted in 53% and 61 %, for the compacted Fly Ash and for the Alkaline Fly Ash, respectively. The latter showed a marked water reactivity, both during compaction and subsequent irrigation; moreover, it shrank so that the first few leachate samples percolated through fissuration. After that the compacted material changed and showed hydraulic permeability through porosity. The experiment on Fly Ash started in late 1991, and it has been carried on until November 1993; test on Alkaline Fly Ash begun in summer 1992 and it is still under way. During harsh winter periods, the test had to be stopped due to freezing. Leachate collection and analysis Leachate integrated samples have been collected on a weekly basis and analyzed for complete chemical characterization. Leachate was removed from the storage tank by a peristaltic pump, on-line filtered and measured for quality parameters such as pH, conductivity and redox potential. Aliquot were preserved and stored for the different analytical tasks. A variety of instrumental techniques have been used: titrimetry (for alkalinity determination); Ion Chromatography(anionsdetermination);Flame Atomic Emission, ElectrothermalAtomization Atomic Absorption, Inductively Coupled Plasma Optical Emission and Inductively Coupled Plasma Mass Spectrometry (elemental content); radionuclides were also monitored by Gamma-Ray or Alpha Spectrometry. Thanks to the multielemental capability of ICP-MS instrumentation, the concentration of up to 35 elements was routinely determined; many other elements were also monitored, their concentrations being lower than the analytical detection limit. Geochemical modelling The geochemical code MINTEQA2(”) was used to calculate the element speciation in the leachate solutions. Some implementation were done to the standard thermodynamic database of the MINTEQA2 code; two were most significant: a) the addition of the component M o o t - together with equilibrium constants for aqueous species and solids as published by complex Krupka et al.(20), and b) the modification of the stability constant for the CU(OH)~” from the original value of log K = - 13.7 to the value log K = - 16.2, as discussed by Comans et al.(17) and reported by others(21). Forecasting on element concentrationwas obtained by assuming equilibrium between leachate and potential solubility controlling minerals in the ash. These minerals were selected on the basis of their saturation indexes in prior MINTEQA2 run and the fitting of free ion activities (calculated by means of speciation runs) with theoretically expected values (from thermodynamic solubility constants).

91

Results and discusswn Leachate general characteristics Lysimetry on Fly Ash was stopped at a WS ratio of 1.32, corresponding to 2.5 pore volume; the test on Alkaline Fly Ash is still under way and it has reached a L/S ratio of 0.73 (1.19 pore volume). Figure 1 shows the leachates pH values vs. pore volume. Fly Ash gave an almost constant value between 8.5 and 9.0 during the first year of investigation, the pH then steadily arose up to 10.8 and finally dropped to about 9.2. Alkaline Fly Ash, as expected, gave a more strongly alkaline leachate, with a maximum pH value of 12.9. Both leachates had reducing properties, more pronounced for Alkaline Fly Ash, as shown by redox potential (figure 2). Leachates showed typical high sulphate content ( > 2000 mg/l), with high concentration of alkaline metals (Na up to 400 mg/l and K about 200 mg/l), and Ca (about 500 mg/l). Chloride and Mg content were also significant (with maxima of more than 50 mg/l), while B, bromide, Li, Mo, and Si were between 1 and 20 mg/l range. All other elements were at trace levels (less than 1 mg/l).

Figure 1: leachates pH values vs. pore volume

Figure 2: lachates redox potential (referred to Ag'IAgCI) vs. pore volume

Elements leaching behaviour in Fly Ash Respect to their mobilization trend, elements leached from Fly Ash can be grouped into four broad categories: 1) having an almost constant concentration throughout the investigated U S range; they are B, Ba, Ca, Co, S (sulphate), Si, Sr, W, and Zn.This behaviour is typified in figure 3 and 4 by B and Sr. showing an initial release followed by a more or less steep decrease to lower 2) concentration; these include Br, C1, Cr, Fe, K, Li, Mg, Mn, Mo, Na, and U. Examples are given in figure 5 and 6 for Mn and Mo. exhibiting delayed release, with concentration "peaks" in later stage of the leaching 3) process, as Al, Cs, Rb, Re, Se, Te, and V. Figures 7 and 8 ilkstrate this behaviour in the case of Ni and V. 4) having an increase in concentration still at the later time of the process, as shown in figure 9 for As; this group includes As, Ga, and Sb. A fifth group might include those elements whose concentration was always found to be less than the instrumental detection limit; the most significant being Cd, Th and Ti.

92 .-

I

I

O I

0 0.2 0.4 0.8 Od

1

1.2 1.4 1.8 1.0 2

r l l l l l , l l r T l l

0 0.2 0.4 0.0 0.8 1

2.2 2 4 2.8

pow vobne

1.2 1.4 1.8 ld

2

2.2 2 4 2.8

pore volum

Figure 3: B leaching behaviour vs. pore volume

Figure 4 Sr leaching behaviour vs. pore volume

.:'

,i"i-----, ,

,

,

pom volume

Figure 5: Mn leaching behaviour vs. pore volume

0 C U 0 4 0 8 Od

1

,

,

~

1.2 1 4 1 8 1.8 2 22 Z4 2 8

pare volume

Figure 7 Ni leaching behaviour vs. poxe volume

0 0

02 04 08 00

1

1 2 1 4 1.8 V.0

2

22 24 28

pore volume

Figure 6 Mo leaching behaviour vs. pore volume

0 0.2 0.4 0.8 0.8 1 1.2 1.4 1.8 1.8 2 22 2.4 1.8

pow volume

Figure 8: V leaching behaviour vs. pore volume

NOTE:instrumental detectionlimit was indicated when significant respect to measured concentration

0 0.2 0.4 0.11 Od

1

1.2 1.4 1.8 1.0 2 2 2 2 4 2.8

pore volume

Figure 10 As leaching behaviour vs. pore volume

93

Aqueous speciation and identification of solubility-controllingsolids The concentrations in the liquid phase measured in some selected leachate samples from the early stage of the lysimetry precess of both ashes were subjected to geochemical speciation using MINTEQA2 code. The calculated free ion activities and the mineral phases saturation indexes were the obtained most relevant information derived. Aluminium, The free ion activities of A13+ in speciated solution fit well with theoretical values calculated for Al(OH)3 amorphous and crystalline form (gibbsite), as shown in figure 10. It seems that Al(OH), amorphous up to pH 8.5, and gibbsite at higher pH values, are the solubility controlling minerals for Al. Those secondary solid phases dictate the upper permissible A1 concentration into leachates through a reci itation-dissolution mechanism. Similar conclusions were obtained by other authors(5p'*13* 4i17). Based on this model hypothesis, equilibrium total A1 concentration were calculated over a pH range from 7 to 13. These predicted values are well correlated to the experimental data from the lysimetry tests (figure 11; the downward segment of the solid line between pH 8.5 and 9 in figure is intended just for graphical reasons to indicate the switching over the two minerals; it should be conveniently represented by a shaded area).

P P

+

-16 -

I

5-103.2JoO.O1

7

8

s

i

I

o.rn14

561 10

11

12

IS

7

0

I

PH

10

11

11

1s

PH

Figure 10: A13+ activity vs. pH calculated from experimental data (dots) and predicted (solid lines)

Figure 11: total dissolved Al in leachates and prediction assuming equilibrium with am. Al(OH)3 and gibbsite (solid line)

Arsenic, MINTEQA2 speciation runs indicated As to be present as As(II1 ; this is consistent with results from Turner(' 1. None of the As solid phases included into MINTEQA2 data base was found to be a potential solubility-controlling solid. The leachate concentration of this element might be 0.1 controlled either by precipitation/dissolution reaction, adsorption/desorption or dissolution rate of the fly ash matrix. In a previous o Po u) a, t m i a o i u ) i m t w m o m z ( o column leaching investigation on the same Fly us Ash we had evidence of a much delayed As Figure 12: total As concentration vs. L/S ratio in release at very high W S ratio (figure 12). This suggest adsorption as a candidate controlling Fly Ash column leaching mechanism.

4

(ID

94

Barium, Ba++ ion activities in leachates did not perfectly agreed with that deriving from barite &SO4 solubility (figure 13). In Alkaline Fly Ash leachates, measured concentration were in many cases lower than the instrumental detection limit. On the other hand, no other potential solubility controlling minerals showed to fit the data. A coprecipitated (Ba, Sr)S04 solid was suggested by Ainsworth and Rai(') and others('2i 13* 14); our data on calculated activities did not support this hypothesis. Anyway, total solution concentration based on barite equilibrium gave reasonable prediction, as shown in figure 14. 1

0.1

2 -I0 -11

o.mc

i! 7

0.01

I

0.0001

8

9

10

11

te

8

9

PH

I1

10

*2

13

PH

Figure 13: B a + + activity vs. pH calculated from experimental data (dots) and predicted (solid line)

Figure 1 4 total dissolved Ba concentration in leachates and prediction assuming equilibrium with barite (solid line)

Calcium and Sulphur, Ca leaching behaviour in Fly Ash was satisfactorily explained with gypsum CaS04'2H20dissolutionlprecipitationreaction. Alkaline Fly Ash leachates had lower sulphate content and resulted grossly undersaturated; at pH greater than 11, wairakite CaAl2SipOI2*2H,O theoretical solubility curve (assuming gibbsite equilibrium, and log[H4Si04] = -4.5 from experimental figures) gave a good fit, as figure 15 shows; as it was already explained, the segment between pH 10,5 and 11 is merely conventional. The modelled total concentration confirmed agreement with experimental data (figure 16). As a consequence, also sulphate concentration could adequately be predicted on the same hypothesis (not shown).

.

1.000-

2

im-

t

10-

1-

I

-8

I

I

0

10

11

12

13

PH

Figure 15: Ca++ activity vs. pH calcualted from experimental data (dots) and predicted (solid lines)

0.1

I

! 7

0

0

10

I1

I2

1s

PH

Figure 16: total dissolved Ca in leachates and prediction assuming equilibrium with gypsum and wairakite (solid line)

95

Chromium, Due to the reducing properties of the leachates, Cr was calculated to be in present as Cr(III). Calculated c?+ ion activities are in good agreement with theoretical values for amorphous and crystalline Cr(OH)3, depending on pH (figure 17). Predicted total Cr concentration in leachates nicely match the experimental values, as shown in figure 18. Once more, the segment of the solid line between pH 8.5 and 9 is intended just for graphical reasons to indicate the switching over the two minerals; it should be conveniently represented by a shaded area. im

-5

10-

1-

90-

56,

7

om01 8

@

10

11

12

I

8

7

13

rtMI :: 0 10

PH

I

I1

I2

1s

PH

Figure 17: C?+ activity vs pH calculated from experimental data (dots) and predicted (solid line)

Figure 18: total dissolved Cr m leachates and prediction assurmng equilibrium with cristalline and amorphous Cr(0H)j (solid line)

Copper, Cu equilibrium is suitably explained with tenorite CuO dissolution reaction over the investigated pH range; this is consistent with results presented by F r ~ c h t e r ( ' ~ ~ .' ~Man , ' ~Y) of the analytical data fell below the instrumental detection limit. d

10

d1

-+

-10-

2

3 -P-10

-

-18

-

0 01

o mi D.L. 0 om1

-20 7

7

\

01

+ -12-

8

D

10

11

12

13

PH

Figure 19: Cu++ activity vs. pH calculated from experimental data (dots) and predicted (solid line)

8

-0

lo

11

12

1s

PH

Figure 20: total dissolved Cu in leachates and prediction assuming equilibrium with tenorite (solid line)

Carbonate, The total gas amount available for exchange with percolating waters is limited by diffusion through the porous media. Thus, leachate solutions resulted not to be in equilibrium with atmospheric CO,, as figure 21 shows. The calculated logs of C03= activity showed a linear relationship with pH values that might be roughly approximated as follows:

96

Equation (1) fits the experimental data and was used to model the carbonate activity in prediction of total concentration for all elements controlled by carbonate solid phases. In figure 21 both the line from equilibrium with atmospheric gases (solid) and the line from equation 1 (dotted) are plotted.

,

,?-

d7

o

D

10

ii

12

is

PH

Figure 21:calculated C03-- activities vs. pH

lrt~~~Due to the low redox potential of leachates solutions, speciation calculation indicated Fe to be present mainly as Fe(I1). Siderite FeCO,, a possible solubility controlling solid, resulted over 5 order of magnitude undersaturated. On the other hand, ferrohydrite Fe(OH), solubility could explain the calculated logs of F e + + + activity (figure 22). This is also consistent with findings of Fru~hter('~? 14). Total iron concentration are adequately predicted by this hypothesis, as figure 23 shows for an average Eh value of -100 mV.

4J! 7

a

I 0

10

11

12

19

PH

Figure 22: Fe3+ activity vs. pH calculated from experimental data (dots) and predicted (solid line)

o.m1

! 7

o

D

10

11

ia

I

ia

PH

Figure 23: total dissolved Fe in leachates and prediction assuming equilibrium with ferrohydrite (solid line) at Eh=-lOO mV

Magnesium, In the pH range from 8 to 10, which is typical of fly-ash leachates, Mg leaching behaviour appears to be controlled by dolomite precipitation-dissolution.At higher pH brucite Mg(OH)2 seems to control solubility, as reported in figure 24. The dotted line in figure 24 represents Mg equilibrium at carbonate activities derived from empirical relation (equation l), and assuming Ca ion activities corresponding to gypsum solubility. Measured Mg in leachate fits nicely with predicted total dissolved Mg concentration, as shown in figure 25 (the segment between pH 9 and 10 is meant only for graphical reasons). Brucite control at high pH values was also found by corn an^('^) for the leaching of MSW incinerator residues.

91

-10 42

! 7

I 8

D

10

11

12

0.m1

J

I

7

13

8

0

PH

10

11

12

1s

PH

Figure 24: Mg++ activity vs. pH calculated from experimental data (dots) and predicted (lines)

Figure 25: total dissolved Mg in leachates and prediction assuming equilibrium with dolomite and brucite (solid h e )

Manganese and Nickel, Once the empirical correlation (equation 1) of carbonate vs. pH was assumed, the pH dependence of calculated Mn+ and Ni+ activities closely resembled that of carbonate mineral phases: rhodochrosite MnC03 and NiC03.6H20, respectively. Other possible solubility controlling solids (hydroxides) would have given a defferent slope, equal to -2pH. Thermochemic data for NiC03.6H,0 are not included into the MINTEQA2 database, and were taken from Kr~pka(~').As figure 26 and 27 show, modelled solutions are to some degree undersaturated respect to the proposed minerals. Carbonates are known to form mixed solid phases, whose solubility is lower than the pure one. As a consequence, predicted total dissolved concentration based on MnC03 and NiC0,.6H20 solubility were one order of magnitude overestimated (not illustrated); nevertheless, they can be used to set the upper limit of possible leachate concentration. +

0

+

I

I

I -14 7

1 8

0

10

2 11

12

i 13

PH Figure 26: Mn++ activity vs. pH calculated from experimental values dots) and predicted (dotted line)

-16

-

7

8

1 0

10

4 11

12

L1 s

PH

Figure 27: N i + + activity vs. pH calculated from experimental data (dots) and predicted (dotted line)

Molvbdenum. Mo forms very mobile oxyanions and gave quite high concentration levels in the early stage of the Fly Ash leaching process (figure 6). The most insoluble Mo compound are thought to be powellite CaMo04, PbMo04, and SrMo04; none could explain the Moo4-ion activities as calculated by MINTEQA2. Powellite was already suggested as a controlling solids in the leaching of MSW incinerator residues(17) and in hot-water extract of many fly ashes('), but was excluded for coal fly-ash leaching(13714).

98

LggL Pb leaching behaviour was explained on the basis of Pb(OH), solubility (figure 28). Experimental data were satisfactorily fitted by predicted total dissolved concentration, plotted in figure 29. 1

I

d-

-

d-

+ -10 -

g.1, 8.1. -10 -

-11 -

m ! 7

I)

D

10

11

12

7

13

1

0

PH

10

11

12

13

PH

Figure 28: Pb++ activity vs. pH calculated from

Figure 29: total dissolved Pb concentration in

experimental data (dots) and predicted (solid line)

leachates and prediction assuming equilibrium with Pb(OH)2 (solid line)

Antimony, MINTEQA2 calculation showed the species Sb(OH), to be dominant. The only Sb solid that could undergo a precipitation-dissolutionreaction resulted SbO,. The equilibrium between Sb components into solution (as defined in MINTEQA2) and SbO, depends on both pH and Eh values. Calculated activities in leachates do not support SbO, as a candidate solubility controlling solid. Silicon, Si concentration resulted consistent with quartz solubility at pH lower than 10, and with wairakite CaAl2Si40,,~2H,O at pH value up to 12 (figure 30); wairakite theoretical solubility was calculated assuming gibbsite and gypsum equilibrium for A1 and Ca, respectively. Predicted leachate concentration vs. experimental data are shown in figure 31. At very high pH value, prediction are grossly overestimated, pointing out that some other control reaction has to take place.

0.1

7

8

0

10

11

12

PH

I

4 7

8

0

10

11

12

13

PH

Figure 30: HqSiOq activity vs. pH calculated from

Figure 31: total dissolved Si concentration in

experimental data (dots) and predicted (solid lines)

leachates and prediction assuming equilibrium with quartz and wairakite (solid line)

99

0 -2-.

l.m,

.--- ..

im -

-.

Y( 10-

- 4

+ &

B

--. -,*

- - - .. --. ~

-eb*

--.

4-

.lmndal.

-10 -

.--

e

1

I0.1 0.01 -

-12 7

om1

Vanadium, Calculated activities for V02+ ion vs. pH lied on a straight line that did not fit 4 the theoretical values derived neither from Ca2V207 nor from Pb2V207. We were not able to identify any other candidate solubility controlling solid. V leaching behaviour showed increasing concentration still at the end of the lysimeter test (figure 8). Previous column 1leaching experiments on the same Fly Ash O I I confirmed delayed long-term release with 0 50 im 150 2m 260 much higher concentration at L/S ratio > 20 us (figure 34). Figure 3 4 total V concentrationvs. LIS ratio in Fly Ash column leaching

Uranium, Modelled U4+ ion activities had the same slope vs. pH than the theoretical data pertinent to uraninite UOz, but resulted up to four order of magnitude lower; the latter being the most stable U solid phase in MINTEQA2 data-base. Therefore no control by a mineral phase could be proposed.

Zinc. The plot of Zn'

calculated activities vs. pH is reported in figure 35 with solubility data for different solid phases: zincite ZnO, orthosilicate Zn2Si04, and metasilicate Zn2si0, (assuming quartz equilibrium), and hydrozincite ZnS(OH),(CO,), (assuming log[CO,--l = 14 - pH). The closest fit refers to Zn2Si04. The slope of modelled data points seems to match that of hydrozincite, with two order of magnitude undersaturation. As it was the case for Ni and Mn, also for Zn mixed carbonate phases are possible, whose solubility is much less than the theoretical one. Anyway, prediction of concentration levels based on Zn orthosilicate, reported in figure 36, gave quite reasonable estimate. +

100

I

a! 7

I

8

10

11

1P

1.3

PH

Figure 35: Zn++ activity vs. pH calculated from experimental date (dots) and predicted (lines)

7

I

e

10

11

1P

1s

PH

Figure 36: total dissolved Zn in leachate and prediction assuming equilibrium with orthosilicate

Our results from large-scale lysimetry experiments support the hypothesis that geochemical reactions, which can be modelled and predicted, control the leaching of elements from coal fly-ashes. A number of solubility controlling minerals are suggested for both major and trace elements, in the pH range from 8 to 12, namely: A1 concentration in leachate seems to be consistent with Al(OH)?- equilibrium, in its amorphous or crystalline form, depending on the pH; Ba mobilization appears to be controlled by barite &SO4 solubility; Ca is controlled by gypsum CaS04.2H20 at pH lower than 10.5 and by wairakite CaA12Si4012~2H20 at higher pH; Cr is at equilibrium with amorphousor crystalline Cr(OH),, depending on pH value; Cu is controlled by tenorite CuO dissolution; Fe is at equilibrium with Fe(OH),; Mg seems to be controlled by dolomite CaMg(CO,), at pH lower than 11, and then by brucite Mg(OH)2; Mn seems to be controlled by rhodochrosite MnC0, dissolution; Ni appears to be at equilibrium with the carbonate NiC0,.6H20; Pb is controlled by its hydroxide Pb(OH)2; Si concentration is consistent with quartz solubility at pH lower than 10 and with wairakite CaAI2Si4Ol2~2H2O at higher pH value; Sr Seems to be at equilibrium with celestite SrSO, up to pH = 10 and then with strontianite SrCO,; Zn solubility seemed to match that of Zn2Si04. For those elements forming oxyanions, As, Mo, Sb, V, and U, no solubility controlling solid phases have been found. The leachate concentrationof these elements might be controlled by an adsorption-desorption mechanism. From these results, predictions could be derived on the leachate elemental concentration as a function of pH. Generally, the predicted values are well correlated to the experimental data from coal fly-ash lysimetry.

101

References

(9)

Page, A.L.; Elseewi, A.A.; Straughan, I.R.. 1979. Physical and Chemical Properties of Fly Ash from Coal-Fired Power Plants with Referece to Environmental Impacts. Residues Rev. 7 1:83. Adriano, D.C.; Page, A.L.; Chang, A.C.; Straughan, I.. 1980. Utilization and Disposal of Fly Ash and Other Coal Residues in Terrestrial Ecosystems: A Review. J. Environ. Qual. 9:333. Summers, K.V.; Rupp, G.L.; Gherini, S.A.. 1983. Physical-ChemicalCharacteristic of Utility Solid Wastes. EPRI EA-3236. Electric Power Research Institute, Palo Alto, CA . Suloway, J.J.; Skelly, T.M.; Roy, W.R. ; Dickerson, D.R.; Schuller, R.M.; Griffin, R.A.. 1983. chemical and Toxicological Properties of Coal Fly Ash. Environ. Geology Notes 105. Illinois Dep. of Energy and Nat. Resour., Champaign, IL. Ainsworth, C.C.; Rai, D.. 1987. Chemical Characterization of Fossil Fuel Combustion Wastes. EPRI EA-5321. Electric Power Research Institute, Palo Alto, CA. Wu, E.J.; Chen, K.Y.. 1987. Chemical Form and Leachability of Inorganic Trace Elements in Coal Ash. EPRI EA-5115. Electric Power Research Institute, Palo Alto, CA. Rai, D.; Ainsworth, C.C.; Eary, L.E.; Mattigod, S.V.; Jackson, D.R.. 1987. Inorganic and Organic Constituents in Fossil Fuel Combustion Residues. EPRI EA5176. Electric Power Research Institute, Palo Alto, CA. Rai, D. ; Eary, L.E.; Mattigod, S.V., Ainsworth C.C.; Zachara J.M.. 1987. Leaching Jkhaviour of Fossil Fuel Wastes: Mineralogy and Geochemistry of Calcium. p. 3-15 in G.J. McCarthy et al. (ed.) Fly Ash and Coal Conversion By-products Characterization, Utilization,and Disposal III. Materials Research Society Symposia Proceedings. Vol. 86. Materials Res. Soc., Pittsburgh, PA. Rai, D.; Mattigod, S.V. ;Eary, L.E.; Ainsworth, C.C.. 1988. Fundamental Approach for Predicting Pore-Water Composition in Fossil Fuel Combustion Wastes. p. 317. In G.J. McCarthy and F.P. Glasser (ed.) Fly Ash and Coal Conversion By-products Characterization, Utilization, and Disposal. Materials Research Society, Meterials Research Society Symposia Proceedings Vol. 113. Materials Res. Soc., Pittsburg, PA. Roy, W.R.; Griffin, R.A.. 1984. Illinois Basin Coal Fly Ashes. 2. Equilibria Relationship and Qualitative Modelling of Ash-Water Reactions. Environ. Sci. Technol. 18:739. Mattigod, S.V.. 1983. Chemical Composition of Aqueous Extracts of Fly Ash: Ionic Speciation as a Controlling Factor. Environ. Technol. Lett. 4:485. Fruchter,J.S.; Rai, D.; Zachara, J.M.. 1990. Identification of Solubility-Controlling Solid Phases in a Large Fly Ash Field Lysimeter. In Proceedings: Environmental Research Conference on Groundwater Quality and Waste Disposal. EPRI EN-6749. Electric Power Research Institute, Palo Alto, CA. Fruchter, J.S. ; Rai, D.; Zachara, J.M.; Schmidt, R.L.. 1988. Leachate Chemistty at the Montour Fly Ash Test Cell. EPRI EA-5922. Electric Power Research Institute, Palo Alto, CA. Fruchter, J.S.; Rai, D.; Zachara, J.M.. 1990. Identification of Solubility-Controlling Solid Phases in a Large Fly Ash Field Lysimeter. Environ. Sci. Technol. 24: 1173.

102 (15)

Mattigod, S.V.; Rai, D.; Eary, L.E.; Ainsworth, C.C.. 1990. Geochemical Factors Controlling the Mobilization of Inorganic Constituents fron Fossil Fuel Combustion Residues: I. Review of the Major Elements. J. Environ. Qual. 19: 188. Eary, L.E.; Rai, D.; Mattigod, S.V.;Ainsworth, C.C.. 1990. Geochemical Factors Controlling the Mobilization of Inorganic Constituents from Fossil Fuel Combustion Residues: 11. Review of the Minor Elements. J . Environ. Qual. 19:202. Comans, R.N.J.; van der Sloot, H.A.; Bonouvrie, P.A.. 1993. Geochemical Reaction Controlling the Solubility of Major and Trace Elements During Leaching of Municipal Solid Waste Incinerator Residues. In J. Kilgroe (ed.)Proceeding 1993 Municipal Waste Combustion Conference. March 30 - April 2, Williamsburg, Virginia.AWMA, Pittsburg, PA. van der Sloot, H.A.. 1991. Systematic Leaching Fkhaviour of Trace Elements from Construction Materials and Waste Materials. p. 341-352. In J.J. Goumans, H.A. van der Sloot, Th. G. Aalbers (4.)Waste Materials in Construction. Elsevier Science Pubblishers, Amsterdam, NL. Allison, J.D.; Brown, D.S.; Novo-Gradac, K.J.. 1991. MZNTEQA2IPRODEFA2,A Geochemical Assessment Model for Environmental @stems: Version 3.0 User's Manual. EPAl60013-917021. U.S. Environmental Protection Agency, Athens, GA. Krupka, K.M.; Erikson, R.L.; Mattigod, S.V.; Schranmke, J.A.; Cowan, C.E.. 1988. Thermochemical Data Used by the FASTCHEM Package. EPRI EA-5872. Electric Power Research Institute, Palo Alto, CA. Morel, F.M.M.. 1983. Principles ofAquatic Chemistry. John Wiley and Sons, New York, NY. Turner, R.R.. 1981. Oxidation State of Arsenic in Coal Ash Leachate. Environ. Sci. Technol. 15: 1062.

Environmental Aspects of Construction wilh Waste Materials JJJ.M. Goumans, H A . van der SIoot and l3.G. Aalbers (Editors) @I994 Elsevier Science B, K AN rights reserved.

103

MODELLING CA-SOLUBILITY IN MSWI BOTTOM ASH LEACHATES Rob N.J. Comans and Jeannet A. Meima Netherlands Energy Research Foundation (ECN) P.O. Box 1 , 1755 ZG Petten, The Netherlands

Abshsct This study focuses on modelling the leaching of the major element calcium from fresh MSWI bottom ash leachates. It is emphasized that Ca-minerals in bottom ash mainly control leachate pH and hence, exert a strong influence on the leaching of contaminant metals and oxyanions from these waste materials. The geochemical speciation code MINTEQA2 was used to model the dissolved Ca concentration in leachates collected from carefully controlled batch laboratory experiments with fresh bottom ash covering a range of liquidkolid ratios and pH. and gypsum (CaS04*2H,0) control It is shown that ettringite (Ca,AI,(S04),(OH),,~26H~O) Ca-leaching from fresh bottom ash at pH 10-12, and pH < 10, respectively. Ca-availability at low pH appears, therefore, to be controlled by the dissolution of gypsum. It is hypothesized that the coexistence of the minerals ettringite, gypsum, and gibbsite (AI(OH),) controls the pH of fresh bottom ash at a value of approximately 10.2. The influence of the Ca-chemistry of leachates from alkaline waste materials, such as MSWI bottom ash, on contaminant leaching is discussed.

1.

INTRODUCI'ION

Bottom ash from municipal solid waste incinerators (MSWI) is produced worldwide in ever-increasing quantities and increasingly finds its destiny in construction. The relatively high concentrations of trace metals in comparison to natural solids such as soils and rocks [ I ] causes, however, environmental concern and may limit, depending on legislation, the use of bottom ash as a construction material. In a previous study [3], we have shown that geochemical reactions control the leaching of both major and trace elements from MSWI residues. A number of possible solubility controlling minerals and complexation processes in solution have been suggested that can to a large extent explain the observed leaching behaviour as a function of pH. Knowledge of these elementary processes enables us to modeVpredict the leaching of contaminants from bottom ash under the specific conditions of the environments in which it is applied. Moreover, once we know the mechanisms leading to the critical release of contaminants, we can apply geochemical knowledge to improve the

104

quality of bottom ash by interfering in these mechanisms. Many investigators have studied the leaching behaviour of bottom ash, focusing on the potential contaminants. If however, we want to reveal the underlying geochemical mechanisms controlling the leaching of contaminants, we need to understand the overall chemical changes in the ash when it contacts water. Bottom ash consists mainly of glasses and minerals, composed of geochemically abundant elements [1,2]. The dissolution of these phases and the reprecipitation of dissolved elements in new secondary solids affect not only the major ion chemistry but control also the concentration of trace elements. The leaching of these potential contaminants is strongly related to major chemical factors such as pH, redox potential and ionic strength, which in turn are related to the chemistry of the abundant elements. In the present study we focus on the Ca-chemistry of bottom ash and attempt to complete the modelling of the Ca-solubility in fresh bottom ash, using recently published thermodynamic data. We emphasize the importance of this element in particular, because Caminerals constitute for the major part the alkalinity of alkaline waste materials, such as MSWI bottom ash [2], coal fly ash [4], and steel slag [5]. The dissolution and reprecipitation of Caminerals mainly control, therefore, leachate pH in both the fresh materials and during weathering. We believe that the ability to model leachate pH is mandatory for the prediction of contaminant leaching and, as we will discuss below, that the quality of bottom ash, and probably other alkaline waste materials, can already be improved significantly by modifying pH, through interference in the Ca-chemistry.

2.

MATERIALS AND METHODS

2.1. Bottom ash samples The MSWI bottom ash samples, AVI-1 and AVI-2, have been described in a previous study [3], and were selected from two representative Dutch incinerators. The samples (1 5-20 kg each) were ground in a jaw crusher until all material, except for < 500 g of metal scrap, passed through a 2 mm sieve. Total concentrations of the major elements in the two bottom ash samples are listed in Table 1. Table 1 . Total concentration of major elements in the bottom ash samples of this study. Total concentration ( g k g ) AVI-1

AVI-2

AVI-1

AVl-2

Na

19.4

18.8

Al

39.8

41.9

K

10.1

10.4

Fe

56.7

62.4

Ca

94.6

86.8

Mn

0.87

0.81

Mg

12.8

11.2

CI

5.17

4.60

22 1.5

246.1

Si

S,,

11.1

8.13

105

2.2. pH-stat leaching experiments Leaching experiments were performed in a pH-stat system, since the solubility of many (trace) elements is known to be strongly dependent on pH. The system allowed the pH to be monitored and adjusted to setpoint in 8 reactors simultaneously in a range between pH 4 and 13. Bottom ash suspensions in water were prepared at liquid/solid (L/S) ratios of 2, 5 and 10 by adding 75, 30 or 15 g of solid material to 150 mL of nanopure H,O in 250 mL Teflon (PFA) reactors. The reactors were kept open to the atmosphere at 25+1 OC and were stirred continuously during the 24-hour equilibration period, using a Teflon coated magnetic stirring bar. The pH was adjusted with 1 M analytical grade HNO, or NaOH. After equilibration, the suspensions were filtered through 0.45 pm membrane filters. Major elements in the solutions were analyzed using a combination of inductively coupled plasma-atomic emission spectrometry (ICP-AES), flame atomic absorption spectrometry (AAS), and ion selective electrodes (ISE). Trace element analyses and results are reported elsewhere [3].

3.

RESULTS AND DISCUSSION

3.1. Geochemical modelling The geochemical speciation model MINTEQA2 (version 3.1 1) was used to calculate the element speciation in the solutions obtained from bottom ash leaching at different pH values in a range from 4 to 13. In addition, element concentrations were modelled/predicted by assuming equilibrium between the leachates (at L/S=5) and potential solubility-controlling minerals in the bottom ash solids. These minerals were selected on the basis of their saturation indexes in prior MINTEQA2 runs and/or on their likeliness to be present or formed under the experimental conditions. The thermodynamic data from the standard MINTEQA2 (version 3.11) database were used except that the mineral ettringite (Ca6AI2(SO,),(OH),,.26H,O) was added using the solubility product recently published by Atkins et al. [6]. The model predictions are presented as total element concentrations, rather than free ion activities, in the leachate solutions at each pH. This approach enables presentation of the results together with the analytical leaching data in a graph of log-concentration versus pH which maintains the characteristic shape and concentration levels of general leaching curves.

3.2. Caleaching Calcium is the major cation that is released from the bottom ash samples below pH 10 [3]. Total dissolved calcium concentrations in the leachates are shown in Figure 1 as a function of pH. Dissolved Ca-concentrations are very low at strongly alkaline pH (> 12), increase steeply over two orders of magnitude between pH 12 and 10, and show a gradual further increase when the pH decreases towards a value of 4. The highest Ca-concentrations at each liquid/solid (L/S) ratio approach the "available" concentration, measured using the Dutch availability test [7]. Below pH 10, the concentrations increase also with decreasing L/S ratio, in a nearly proportional manner, whereas Ca-leaching at strongly alkaline pH is

106 independent of L/S ratio.

3.3. Modelling Belevi et al. [8] have suggested that the major reactions in bottom ash involving Ca are:

CaO(s)

+

H,O

#

Ca2+ +

20H

(hydrolysis of lime in unquenched bottom ash)

(solubility of portlandite in hydrolysedkpenched bottom ash). The authors postulate that hydrolysis of lime starts immediately after the quench tank and progresses during storage of the fresh bottom ash. The bottom ash samples used for the present study have been quenched and, hence, are likely to contain portlandite. Figure 1 shows the Ca-concentrations modelled with MINTEQA2 for the conditions of our experiments, assuming equilibrium with portlandite. It is evident that, at the "natural" pH of the samples (i.e. pH 10.3-10.4), the leachates are not in equilibrium with portlandite. Only at pH 1 3 (with added base in the pH-stat) do the Ca-concentrations approach the solubility line of portlandite. Belevi et al. [8] and Zevenbergen & Comans [2] have also calculated that the leachates of their quenched bottom ash samples are undersaturated with respect to this mineral. In our previous modelling study of MSWI bottom ash [3], we have not been able to model Ca-solubility between pH 10 and 12. The Ca-mineral ettringite (Ca6AI,(SO,),(OH),,~26H,O)has been shown to exist in alkaline waste materials containing sufficient Ca, Al, and SO, [9].Ettringite is a well known mineral that plays an important role in cement chemistry [e.g. 101. A solubility product for this mineral was recently published by Atkins et al. [ 6 ]and was added to the MINTEQA2 database for the purpose of this study. Caconcentrations modelled assuming equilibrium with ettringite are included in Fig. I , The concentrations measured in the leachates between pH 10 and 12 follow the same slope and are similar to the values modelled on the basis of ettringite solubility. W e postulate, therefore, that it is ettringite that controls Ca-leaching between pH 10 and 12 and, hence, at the "natural" pH of the bottom ash samples used for this study. Very recently, ettringite has indeed been identified by XRD analysis of a fresh bottom ash sample from the same incinerator as sample AVI-1 [2].

107

100000

AVI4,US=lO \

C

g m

AVI-1, U S 5

10000 A

AVI-I, U S = 2

0

AVIP.US=lO

A

AVIZ,US=2

_ _ _ _ _ ETTRlNGlTE CI\LCITE

1

2

4

6

8

10

12

14

GYPSUM PORTLANDITE

PH Figuie 1 Dissolved Ca-concentrations in leachates from the two bottom ash samples, as a function of pH and liquidkolid ratio, and MINTEQA2 predictions assuming equilibrium with different Ca-minerals.

In addition to ettringite, two other minerals containing Ca, Al or SO, may coexist in equilibrium with these bottom ash leachates at a pH of about 10: gypsum (CaSO4*2H,O) and gibbsite (AI(OH),) [3]. It is interesting to note that MINTEQAZ calculations using these three minerals as coexisting phases, in equilibrium with the leachates, predict a leachate pH of 10.14. This value is very close to the "natural" pH of bottom ash samples AVI-I and AVI-2 (10.2-10.3). In a very recent review of leaching data of about 400 MSWI bottom ash samples, it is shown that more than half of the samples have a "natural" pH of about 10 [ I l l . We hypothesize that this pH value of fresh bottom ash results from the coexistence of ettringite, gypsum, and gibbsite in the bottom ash matrix. When the pH of the bottom ash samples is lowered to values of below pH 10, the leachates become undersaturated with respect to ettringite, and Ca-concentrations increase only slightly with decreasing pH. At L/S values of 10 Lkg, the solutions are calculated to be in equilibrium with gypsum (CaS0,*2H20). At lower L/S ratios, the leachates appear to be oversaturated with respect to this mineral. Gypsum has frequently been identified by XRD analysis of fossil fuel combustion residues [9]and MSWI bottom ash [ 1,2]. As gypsum seems to control Ca-leaching at low pH, this mineral may be the phase that controls Ca-availability when measured using the Dutch availability test [see e.g. 71.

3.4. Cahnrtion piwesses

The leaching experiments shown in Fig. 1 were performed in experimental vessels which were open to the atmosphere. Hence, carbonation of the bottom ash suspensions is likely to

108

occur, especially at high pH. When CO, is absorbed by the leachates, calcium carbonate is likely to precipitate according to the reaction:

Ca2+

+

CO,(g)

+

H,O

*

CaCO,(s)

+

2H’

Fig. 1 includes a line indicating the Ca-concentrations modelled assuming equilibrium with calcite (CaCO,) and independently measured total inorganic carbonate concentrations [3]. It is obvious that Ca-concentrations in the 24-hour leachates are not in equilibrium with calcite. However, fresh bottom ash from the same incinerator as sample AVI-I, exposed to the atmosphere for 100 days in an aqueous environment, releases Ca in concentrations close to those in equilibrium with calcite and the partial pressure of CO, in the atmosphere (P = 10-3,5atm.)[2]. The pH in those experiments had decreased to 8.0, which is close to the pH of calcite in equilibrium with the atmosphere (8.4). At this point it is important to emphasize that, for reliable modelling of Ca-solubility, it is mandatory to measure total dissolved carbonate. These measurements are not only needed to enable modelling the solubility of carbonate minerals, but also because dissolved carbonate strongly affects Ca-speciation at alkaline pH, because of the stability of the dissolved CaCO: complex (see also discussion in [2]).

3.5. Implications for contaminant leaching The Ca-chemistry of bottom ash can exert a strong influence on the leaching of potential contaminants. We have previously shown that the leaching of particularly the heavy metals Cd, Cu, Pb, Zn is probably controlled by (hydr)oxide or carbonate minerals [3]. The solubility and, hence, the leaching of those phases is strongly dependent on leachate pH. The solubilityminimum for these heavy metals lies between pH 8 and 9. The carbonation process, which changes the pH of the fresh bottom ash (controlled by ettringite/gypsum/gibbsite) from 10.2 to the value controlled by calcite in equilibrium with the atmosphere, i.e. 8.4, may, therefore, reduce heavy metal leaching. A further decrease of pH, e.g. by prolonged contact with acid rain or groundwater may, however, lead to a strong increase in heavy metal leaching. The acid neutralizing capacity of Ca-minerals in bottom ash constitutes, therefore, a very important factor controlling the period of time during which the system can maintain a pH of 8. Calcium minerals may also limit contaminant leaching through direct binding of the elements. Cadmium, and to a lesser extent other heavy metals, possess a strong affinity for the surface of calcite [I21 and may be sorbed on this mineral by coprecipitation or solidsolution formation during the carbonation of bottom ash. Ettringite has been shown to have a strong affinity for oxyanions of As, Se [I31 and possibly Sb and Mo. We are currently investigating these and other binding processes of contaminants to single solid phases in MSWI bottom ash.

109 4.

CONCLUSIONS

The geochemical speciation code MINTEQA2 has proven to be very useful in modelling the dissolved Ca concentration in leachates collected from carefully controlled batch laboratory experiments with fresh bottom ash, covering a range of liquidkolid ratios and pH. and gypsum (CaS04*2Hz0) We have shown that ettringite (Ca6AI,(S04),(OH),,-26H,0) control Ca-leaching from fresh bottom ash at pH 10-12, and pH < 10, respectively. It is hypothesized that the coexistence of the minerals ettringite, gypsum, and gibbsite (AI(OH),) in fresh bottom ash controls the pH at a value of about 10.2. In contact with the atmosphere, absorption of CO, by the alkaline leachates will lead to carbonation of bottom ash and the formation of calcite. In equilibrium with the atmosphere, this mineral controls the pH at approximately 8.4. In view of the solubility-minimum of the (hydr)oxide and carbonate phases that are likely to control heavy metal leaching, the carbonation process may have a favourable effect on the leaching of these contaminants. Laboratory experiments with single solid (Ca-)phases, such as ettringite and calcite, are needed to investigate their potential to bind metallic and non-metallic contaminants and limit leaching from bottom ash.

5,

REFERENCES

Kirby, C.S. A geochemical analysis of municipal solid waste ash. Ph.D. thesis, Department of Geological Sciences, Virginia Polytechnic Institute and State University (1 993). 2. Zevenbergen, C. & Comans, R.N.J. Geochemical factors controlling the mobilization of major elements during weathering of MSWI bottom ash. These proceedings. 3. Comans, R.N.J., van der Sloot, H.A. & Bonouvrie, P.A. Geochemical reactions controlling the solubility of major and trace elements during leaching of municipal solid waste incinerator residues. In: Kilgroe, J. (ed.) Proceedings 1993 Municipal Waste Combustion Conference, Williamsburg, VA. Air and Waste Management Association, Pittsburg, PA, 1993, pp. 667-679. 4. Schramke, J.A. Neutralization of alkaline coal fly ash leachates by CO,(g). Applied Geochemistry, 7 (1992) 48 1-492. 5 . Comans, R.N.J., Van Der Sloot, H.A., Hoede, D. & Bonouvrie, P. Chemical processes at the redox/pH interface during the application of steel slag in the aquatic environment. In: Goumans, J.J.J.M., van der Sloot, H.A. & Aalbers, Th.G. (eds.) Waste Materials in Construction. Elsevier, Amsterdam, 1991, pp. 243-254. 6. Atkins, M., Macphee, D., Kindness, A. & Glasser, F.P. Solubility properties of ternary and quaternary compounds in the CaO-AI,O,-SO,-H,O system. Cement and Concrete Research, 21 (1991) 991-998. 7. Comans, R.N.J., Van Der Sloot, H.A. & Bonouvrie, P.A. Speciatie van contaminanten tijdens uitloging van AVI-bodemas (in Dutch with English abstract). ECN-C--93-090 (1993). 8. Belevi, H., Stampfli, D.M. & Baccini, P. Chemical behaviour of municipal solid waste incinerator bottom ash in monofills. Waste Materials & Research, 10 (1992) 153-167. 1.

110 9.

10.

11.

12.

13.

Mattigod, S.V., Rai, D., Eary, L.E. & Ainsworth, C.C. Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: I. Review of the major elements. Journal of Environmental Quality, 19 (1990) 188-201. Odler, I. and Abdul-Maula, S. Possibilities of quantitative determination of the AFt (ettringite) and AFm (monosulphate) phases in hydrated cement pastes. Cement and Concrete Research, 14 (1984) 133-141. Chandler, A.J., Eighmy, T.T., Hartlen, J., Hjelmar, O., Kosson, D.S., Sawell, S.E., Van Der Sloot, H.A. & Velow, J. Treatise on Municipal Solid Waste Incinerator Residues (in preparation, 1994). Comans, R.N.J. & Middelburg, J.J. Sorption of trace metals on calcite: applicability of the surface precipitation model. Geochim. Cosmochim. Acta, 51 (1987) 2587-2591, van der Hoek, E.E., Bonouvrie, P.A. & Comans, R.N.J. Sorption of As and Se on mineral components of fly ash: relevance for leaching processes. Applied Geochem. (1994, in press).

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) @1994Elsevier Science B.V. AN rights reserved.

111

Particle Petrogenesis and Speciation of Elements in MSW Incineration Bottom Ashes T.T. Eighmf, J.D. Eusden, Jr.", K Marsellab,J. Hoganb, D. Domingo", J.E. Krzanowski', and D. Stampfli' "Environmental Research Group, Department of Civil Engineering, A1 15 Kingsbury Hall, University of New Hampshire, Durham, N.H. 03824, U.S.A. bGeology Department, Bates College, Lewiston, Maine 04240, U.S.A. 'Mechanical Engineering Department, Kingsbury Hall, University of New Hampshire, Durham, N.H. 03824, U.S.A. Abstract The speciation of elements in municipal solids waste incineration bottom ash is important with respect to its impact on leaching behavior and to its treatment for utilization or disposal. We used a variety of techniques to identify the speciation of major, minor and trace elements in both intact bottom ash particles as well as bottom ash powders. Petrography and scanning electron microscopy/x-ray microanalysis (SEM/XRM) were used to classify intact particles and identify ash particle petrogenic sequences. Two distinct features were seen. Particles are comprised of about 15% of materials present in the MSW waste feed to the incinerator. The remaining portion of the particle (85%) is melt structure. A typical particle contains waste glass (10%) waste soil minerals such as pyroxenes, SiO, (quartz), and feldspars (2%), waste metals and metal alloys (2%). and waste organics (1%). Particles are also comprised of slag or melt products, derived from the MSW feed material, that include opaque glass (25%), isotropic glass (20%). schlieren (lo%), and spinel-group minerals (magnetite, hercynite, chromite) (10%) and melilite group minerals such as C%Al,SiO, (gehlenite) and MgCazSi,07 (akermanite) (20%) which precipitated out of the melt as it cooled. The paragenic sequence is similar to that described for melelite-bearing, igneous rock systems. The system can best be described petrogenically using the CaO-MgO-Al,O,-SiO,-N~O-FeO(CMASNF) system. The melt structure was formed at about 1,200"C. Thermodynamically incompatible phases are present in the ash, making it reactive to aging (oxidation, hydrolysis), weathering, and diagenesis. Increasing the silicon content of the ash could result in the formation of more geochemically stable phases. The residue was ground into powders less than 300 p n in size. Magnetic and density separations were performed to segregate powders for further analysis. The residue is comprised of approximate equal fractions of magnetic, high density; nonmagnetic, low density; and nonmagnetic, high density material. Isodynamic separation of the nonmagnetic fraction was also effective in separating minerals. SEM/XRM of powders fractions in thin section was particularly

112

effective in identifying major minerals in identifiable mineral structures as well as minerals associated with "hot spots" of minor and trace elements. These minerals include many pyroxenes, quartz, feldspars, and melilite-group minerals as well as many spinels. Lead appears to largely be incorporated in complex silicate melt structures. X-ray powder diffraction (XRPD) confirmed the presence of minerals seen by petrography and SEM/XRM. X-ray photoelectron spectroscopy (XPS) of powder surfaces also documented the presence of many of these minerals. A number of oxides and carbonates were also seen with XPS, reflecting the role of O,(g) and CO,(g) in altering the speciation of the particle exterior surface. X P S is particularly well suited for identifying phases associated with leaching at this surface. Solid phases controlling leaching, as determined with the geochemical thermodynamic code MINTEQA2, are not always the same as ones observed with the above mentioned methods. The role of mineral respeciation and diagenesis in controlling leaching is highlighted. The use of such models in predicting leaching behavior is discussed. 1.0 INTRODUCTION

Municipal solid waste incineration is a viable management strategy for treating combustible municipal solid waste that cannot be recycled. Organic material is oxidized, The volume of material is reduced while exothermic energy is recovered. Less volatile inorganic contaminants in the waste feed remain in the bottom ash while more volatile inorganic contaminants are captured in air pollution control devices. The residues from municipal solid waste incineration have been generally characterized with respect to composition and to speciation of some elements (Eighmy et al., 1993). Methods frequently employed involve petrography (Project EKESA, 1992; Vehlow et al., 1992), X-ray powder diffraction (DiPietro et al., 1990; Gardner, 1991; Kirby & Rimstidt, 1993; Ontiveros, 1988; Stampfli, 1992), Fourier transform infrared spectroscopy (Henry et al., 1983), scanning electron microscopy/)
113

speciation. Finally, the ability to understand, model, and predict longer-term leaching behavior requires fundamental knowledge about speciation. The approach taken by our group to characterize speciation of elements in municipal solid waste incineration bottom ash is shown in Figure 1. Elemental composition is determined by combinations of neutron activation analysis (NAA) and HCl/HNO,/HF total digestion coupled with inductively-coupled argon plasma (ICAP) atomic emission spectroscopy. Bulk sample mineralogy is determined by Xray powder diffraction (XRPD) and petrography; the petrography encompassing polarized light microscopy, reflectance microscopy, and scanning electron microscopy/X-ray microanalysis (SEM/XRM) of larger, intact particles. Petrography can also be used to examine particle petrogenesis and mineral paragenesis; the process by which particles form and minerals coalesce from glass phases as the particles cool. Characterization of the near-surface and surface environment is accomplished in particle size-reduced powders with SEM/XRM analysis and X-ray photoelectron spectroscopy (XPS). These methods can provide semi-quantitative compositional information and element associations by dot mapping. Element valence states, bonding environments and speciation are also provided from XF'S. X P S is particularly valuable as a surface analytical technique because its information can be coupled to leaching behavior (Eighmy et al., 1993). All of these methods are used to provide an integrated synopsis about speciation; particularly as it relates to leaching behavior. We employ two leaching procedures and the geochemical thermodynamic model MINTEQA2 to model solid phase control of leaching and compare the controlling solids to the ones observed by the other analytical methods. A fractionation scheme has been developed to separate wastes as a function of magnetic properties and particle density (Figure 2). This is necessary to help concentrate elements present at low concentration in the residue so as to allow for better chance at detection with the above mentioned methods. 300 pm minus particles are separated with a hand magnet and with 1,1,2,2-tetrabromoethane.This produces magnetic and non-magnetic, high and low density fractions. Isodynamic separation is also conducted on the non-magnetic fraction; producing O.SA magnetic, 1.OA magnetic, and 1.5A non-magnetic fractions on bottom ash specimens. The purpose of this study was to examine mineral paragenesis in municipal solid waste incineration bottom ash as well as the speciation of major, minor and trace elements in these residues. This study is one part of a much larger speciation study (Eighmy et al., 1994). The results presented here suggest that the bottom ash is comprised largely of soil grains, waste glass, and waste metals that have partially melted and become components of silicon-poor pyromaphic opaque glass, isotropic glass, schlieren, spinels and melilite group minerals. A number of spectroscopies confirm the presence of these major minerals as well as many trace minerals. Leaching behavior is only partially controlled by these solid phases; indicating the importance of respeciation and diagenesis in the leaching processes.

114 Petrography and SEM/XRM on Parllcles

SEMlXRM on Tola1 Composlllon

Powder Fracllons

XPS on

XRPD on Fracttons

Leachablilty

Figure 1.

Geochemical Modeling of Leachlng Behavlor

Approach used to characterize element speciation in municipal solid waste incineration bottom ash.

*

Powders

Denrlty Separation

Dendty Separation

114

d x

Nan-Magnetlc Non-Magnellc Low Density Hlgh Density

-31.0 Amps

Figure 2.

Magnetic Low Density

+ x

0.5 Amps Nan-Magnetic

Nan-Magnellc

1.5 Amps Magnetlc

0.5 Amps Magnetic

1.0 Amps Magnetlc

1.5 Amps Non-Magnetlc

Sample fractionation scheme.

Magnellc High Density

115

2.0 METHODS

Incinerator Description. The residues collected in this study were from a larger U.S. EPA-sponsored study on the solidification/stabilization treatment of incineration residues (Kosson et al., 1993). The facility is a modem mass bum system with a nominal capacity of 2,000 tonnes per day. The waste feed is primarily household with some commercial and non-hazardous industrial waste. The facility has three parallel trains consisting of a charging chute, primary combustion chamber and moving grates, boiler and economizer, lime slurry spray drier scrubber, and fabric filters. Boiler and economizer ash is collected and added to the bottom ash process stream prior to quenching. The bottom ash also contains grate siftings. As part of a larger EPA project (Kosson et al., 1993), bottom ash was collected on September 14-16, 1989. Full stream cuts from the vibratory conveyor were used to collect residue. The material was screened using a 5.0 cm screen. About 4,000 Kg of screened material was collected. The bottom ash was air-dried, particle-size reduced to pass 1.27 cm screens. A large baffled tank was used to homogenize the material. A dried 20 Kg subsample was sent to the University of New Hampshire for this project. The 20 Kg subsample was cone and quartered to produce a 3 Kg working sample. Processing. The 3 Kg working sample was ground using Proctor hammers and a Weber Brothers & White (Hamilton, Mich.) Model S500 pulverizer (rotary hammer mill). It was possible to grind greater than 60% of the original dry sample to produce a powder that would pass a 300 pm stainless steel sieve. Powders were stored under vacuum desiccation. Fractionation. Magnetic separation and density separation (1,1,2,2tetrabromoethane, TBE, 2.95 g/cm3 at 20°C) were used to produce four powder fractions:magnetic, high density (MHD); magnetic, low density (MLD); non-magnetic high density (NMHD); and non-magnetic low density (NMLD). Additionally, isodynamic separation using a Frantz Isodynamic Separator (S.G. Frantz Co., Trenton, N.J.) with settings of 25" forward tilt and 15" side tilt was used to produce 0.5 amp magnetic ( O S A M ) , 1.0 amp magnetic (LOAM), and 1.5 amp non-magnetic fractions (1.5 ANM). Mass fractions were determined for all the derived fractions. Thin Sections. Intact bottom ash particles in two size ranges (0.4 - 1.27 cm, 0.1-0.4 cm) as well as the powder fractions were made into petrographic thin sections using, a low viscosity epoxy (Epoxy Tech, Billerica, Mass.) and a regimen of high vacuum infiltration and pressure impregnation prior to curing. Thin sections were cut and lap polished with diamond paste prior to mounting. Total Composition. Total elemental composition (mass of element/dry weight of residue) was conducted using either neutron activation analysis (NAA) or total digestion/inductively coupled argon plasma (ICAP) atomic emission spectroscopy. Petrography on Intact Particles. Petrographic analysis, mineral identification, and particle classification of the 0.4 - 1.27 cm and 0.1 - 0.4 cm bottom ash particles in thin section was done using an Olympus BH-2 polarizing light microscope. Field of view magnification ranged from 2Ox to 4OOx. Microfiche copies of the thin sections, magnified to 200%, were used as maps to facilitate the above work. Standard

116

petrographic techniques were used to determine relative percentages of the following: isotropic, clear glass; opaque, black, metallic glass; epoxy-filled vesicles; unfilled vesicles; minerals; microstructural textures; and other miscellaneous ash products. Modal abundances of these features were estimated by comparing the unknown at a certain field of view to published charts for estimating percentage composition of rocks and sediments (Terry and Chilingar, 1955). Minerals were identified using the following standard optical methods and characteristics: pleochroism, birefringence, optic sign, mineral shape or habit, cleavage, relief, color, and extinction position. SEM/XRM on Intact Particles. To better constrain the mineral and ash chemistry, scanning electron microscopy and energy dispersive x-ray microanalysis (SEM/XRM) was done on the thin sections. The thin sections were carbon coated using a Denton Vacuum Desk-1 carbon evaporation unit. A JEOL JSM-6100 Scanning Electron Microscope equipped with a Kevex Super-Dry detector and a Kevex Delta Class IV analyzer was used for the SEM/XRM analyses. SEM/XRM on Powder Fractions. A Link AN-10,OOO energy dispersive XRM workstation was used in conjunction with a Pentafet atmosphere-thin window detector (lithium-drifted silicon crystal) and an AMR 1OOO SEM. XRPD on Powder Fractions. A Rigaku-Geigefflex goniometer was used for XRPD. A copper tube (44 kV, 34 mA, 1500 W) was employed as an X-ray source. A divergence slit of 1". a scattering slit of lo, a receiving slit (crystal) of 0.8", a receiving slit (monochromator) of 0.6" produced the best peak definition and lowest background. Powders were run in triplicate; double sided tape was used to hold the samples. A scan rate of 0.5" 28 per minute was used. Scans were conducted from 6.00 to 9.00". Most peak intensities were measured at 1,OOO to 10,OOO cps. Tungsten internal standards were employed. The goniometer output was directed to a Spectraphysics integrator (SP 4270) to precisely determine peak location and area. A PC-based search match program, MICRO-ID, was used to identify possible crystalline phases in the residues. The search procedure involved element exclusion based on NAA data, a 0.5" 28 error window, three lines of match, a minimum relative intensity of 1, and calculation of figure of merit based on weightings of 90% for peak location and 10% for peak intensity. Searches were based on PDF sets 1-41. XRPD analyses were also conducted on the leached 300 pm-minus unfractionated material from the total availability leaching test (see below). XPS on Powder Fractions. A Perkin Elmer Physical Electronics Division 5100 hybrid X P S was used to conduct quantitation and chemical shift analysis work. Samples were either packed into tiny, planchette-mounted cups or pressed onto the sticky-side of copper tape. An Art ion beam was used to etch the particle surfaces; this was done to remove adventitious carbon and oxygen. Sputter etching was usually for 3 minutes with a 4 kV beam voltage to the ion gun. A procedure was developed to initially scan the sample under low resolution from 1,100 to 0 eV, then high resolution scan the carbon 1s and silicon 2p3/2 windows for energy referencing purposes. The sample was then etched and rescanned. Finally, high resolution scans of the windows of elements of interest was done for a 2 hour total acquisition time. Adventitious carbon was used for static charge referencing to conduct charge

117

corrections. The NIST X P S database (version 1.0) was used to identify speciation from binding energy chemical shifts of principal photoelectrons. A tolerance of 0.2 eV was used. X P S analyses were also conducted on the leached 300 pm-minus unfractionated material from the total availability leaching test (see below). Leaching Tests and Leaching Modelling. Two leaching procedures were used to examine leaching behavior and solid phase control of leaching. The first procedure, based on the Dutch total availability leaching procedure [NVN 25081, was used to quantify the element mass fraction available for leaching. A sequential extraction is used; the first is conducted at pH 7 for 3h at a liquid to solid (L/S) ratio of 100 (L/Kg). 8.0g of <300 pm unfractionated bottom ash powder is added to 800 ml of Milli-Q@type 11 water and stirred in an open beaker. pH is controlled using 6N HNO,. At the end of the three hours, the leachant is filtered (0.45 pm polycarbonate filter) and the residue and filter are leached again at L/S 100 at pH 4.0 for 4h. 6N HNO, is again used to control pH. After filtration, the pH 7.0 and pH 4.0 leachants are combined and analyzed for dissolved constituents using ion chromatography (IC) or ICAP. The leached residues are dried, stored under vacumn and saved for XRPD and X P S . The pH 7.0 extraction solubilizes oxyanions. The pH 4.0 extraction solubilize cations. Both fractions, when compared to total composition, estimate the fraction that is environmentally available for leaching in a geologic timeframe. The second procedure is a pH-dependent procedure designed to examine leaching over a large pH range. A pH range of 2 to 14 with 2 pH unit increments is used. Each extraction is done at an L/S of 6.0. 65g of <300 um unfractionated bottom ash powder is placed in 500 mL plastic bottles. Milli-Q water and either HNO,, NaOH, or KOH are used to set pH values to prescribed levels. The bottles are placed on rotary tumblers and agitated for 48 h. After extraction, the leachants were filtered (0.45 pm polycarbonate filter) and quantified using IC or ICP. The geochemical thermodynamic model MINTEQA2 (Allison et al., 1990) was used to examine dissolution behavior and solid phase control of leaching as a function of pH. 3.0 RESULTS AND DISCUSSION Total Composition. The major constituents (> 10,000 mg/Kg) in the ash are Si, Fe, Ca, Al, Na, and C1. Although not qualified by NAA or total digestion/ICAP, oxygen is the most predominant element (ca. 400,000 mg/Kg) in the residue. Minor constituents (l,OOO-lO,OOOmg/Kg) include Mg, K, Ti, Zn, Cr, Pb, Mn, and Ni. Trace constituents (< 1,OOO mg/Kg) include up to 31 elements. These concentrations are typical for MSW bottom ash (Kirby and Rimstidt, 1993; Kosson et al., 1993). Fractionation. Figure 3 provides information on the mass distribution of the powdered bottom ash in the various fractions. The principal fractions from magnetic and density separation are MHD (26.25 wt %), NMHD (8.86 wt %), and NMLD (62.11 wt %). The principal fractions from isodynamic separation are magnetic (28.11 wt %), 0.5 AM (38.94 wt %), 1.0 AM (9.21 wt %), and 1.5 ANM (20.02 wt %).

118 USBA ferrous < 2.97 glcm’ 1.681

Deonty .%pimuon

-

,

USBA magnetic

USBA ferrous >2.97 gtcrn’ 26.25%

28.11% DeDsity Separation

USBA nonferrous <2.97 glcm’

Density Scpuuion

Mapodic sBp.rscion

USBA nonmagnetic

62.11%

71.14%

USBA nonferrous >2.97 gtcm’

tknsity Sepmtion

8.86%

magnetic at 0.5 amps

9.21% USBA magnetic at 1.5 amps

Magnetic Scpuuion

1.84%

I Figure 3.

I

USBA

Fractionation Data for the Bottom Ash from a U.S.Mass Bum Combustor.

I

119

Particle Classification. The municipal waste incinerator bottom ash intact particles were classified into two major groups: non-combusted waste products from the MSW feed and melt products. Non-combusted waste products consist of four principal types: waste glass; waste minerals: waste metals; and waste organics. These represent fragments of bottles, glassware, metals, cans, soils, etc. that did not or could not combust at the temperatures (and time period) they were exposed to in the incinerator. Melt products are defined as products resulting from the melting and partial melting of the waste and the minerals that crystallized from the melt. Five different types of melt products were recognized: opaque, metallic glass; isotropic silicate glass: schlieren: spinel-group minerals: and melilite-group minerals. In general 85% of the bottom ash is composed of melt products and 15% noncombusted waste products. Figure 4 shows the estimated modal abundances of the principal types of the non-combusted waste products and melt products. A common feature of all particles are vesicles or gas bubbles, presumably formed during boiling of the melt products. Vesicles comprise between 10 - 25% of the total volume of the particles, therefore providing for a significant measure of particle porosity.

Men Produd Melilile Group Mineral 20.0%

Men Produd Spinel Group Minerals 10.0%

Schlloren 10.0%

W u l a Mlnwala 20% Was10 Meld; 20% W a l e Organla 1.0% lrolroplc G l a u 20.0%

Opaque Glass 25.0%

Figure 4.

Pie graph showing percentages of non-combusted waste products and melt products in municipal waste bottom ash.

SEM/XRM Chemistry of Melilite-Group and Spinel-Group Minerals in Intact Particles. In order to better characterize the melt products, XRM spectra were acquired and representative mineral formula determined for the melilite-group and

120

spinel-group minerals. Since mineral identification using transmitted light techniques was quite successful, the XRM analyses simply confirmed the mineral identifications and provided chemical information useful for chemically subdividng the various mineral types within the melilite and spinel groups. Melilite group minerals included two general types of chemistry: gehlenite (CagU,SiO,), and akermanite (Ca, (Mg, Fe2+)Si,0,). Sodium is common in small amounts in gehlenite and is incompatible with iron and magnesium. When magnesium and iron are detected in akermanite, sodium is absent. The results of the melilite group chemical analysis agree with the description of naturally occurring melilite-group mineral chemistry described by a host of authors and summarized succinctly by Deer et al. (1992). Spinel-group minerals included three general types of chemistry: spinel-hercynite ((Mg,Fe)Al,O,), magnetite (Fe,O,), and chromite (FeCr,O,). A majority of the spectra have appreciable silicon. This is attributed to: 1) interactions of the electron beam with not only the spinel-group mineral but also the matrix silicate glass surrounding the mineral, and 2) minute inclusions of matrix silicate glass within the crystal structure due to rapid nucleation. The results of the spinel-group chemical analysis agree with the description of naturally occurring spinel-group mineral chemistry described by Deer et al. (1992) and a more exhaustive treatise by Rumble (1976). Related Natural and Experimental Ingenous Systems. Based on the known conditions of incineration and the melt products described for this study, it is believed that the incinerator paragenetic sequence is similar to that described for melilitebearing, igneous rock systems observed in both naturally occurring and experimentally produced associations (McBirney, 1993; Yoder, 1979; Soulard et al., 1992). With the exception of FeO, the CaO-MgO-Al,O,-SiO,-N~O (CMASN) experimental system described by Soulard et al. (1992) is quite similar in composition to the melt products discussed in this study. Furthermore, the pressure (1 bar) and temperatures of the experimental system are close to those within the incinerator. This system also provides a series of phase relationships many of which are consistent with the petrographic observations of the melt products. It more adequately describes the crystalline mineral phases present than, for instance, the CaO-Al,O,SiO, (CAS) system used by Lichtesteiger and Zeltner (Project EKESA, 1992) to estimate incinerator temperatures. The temperatures of the experimental runs for the study by Soulard et al. (1992) range from 1,238" to 1,143"C. Because of the presence of iron-bearing melt products, a better system to describe the incineration paragenesis for this study would be the CaO-MgO-Al,O,-SiO,-Na,OFeO (CMASNF) system. Though no such natural or experimental igneous system was discovered in the literature (it may well exist), the additional iron component would, based on thermodynamic arguments, presumably lower the melting temperature of the melt products. Therefore, using the values of Soulard et al. (1992) as a maximum, it is estimated that the melt reached temperatures no greater than approximately 1,200"C.

121

The melting and melt products within the incinerator are probably in a state of local equilibrium and the waste products are analogous to igneous xenoliths; blocks of foreign rock within in a magma. They are preserved due to the lack of complete melting and therefore assimilation into the melt. The common association of melilte and quartz in other ash residue studies (Vehlow et al., 1992; Project ESKESA, 1992) has also been mentioned as an indicator of complex heterogeneous, disequilibrium combustion and melting. It is indeed not surprising that quartz and waste glass survive incineration as their silica content make them highly refractory. Disequilibrium is also indicated by the mere presence of the opaque, metallic glass and the isotropic silicate glass. Glass is inherently at disequilibrium or in a metastable state since it is an amorphous solid lacking the arrangement of atoms into the crystallograhic state (Carmichael, 1979). Glass is formed through a two step process where a stable liquid is supercooled to finally produce a glass. The equilibrium temperature of crystallization of a liquid is higher than the glass transformation temperature. For example, Carmichael (1979) shows that the temperature of equilibrium crystallization of feldspathic liquids (producing sodic and potassium feldspars) is between 1,ooo" and 1,500"C, whereas supercooling of this liquid to produce glass occurs between 750" and 900°C. One can speculate that by varying the chemical components of the melt products and/or the external controls within the incinerator (pressure and/or temperature) a significantly different ash residue would result. For example, the melt products could be made silica-oversaturated by either completely incorporating the available waste glass, waste quartz, and waste feldspars present in the MSW feed, or by adding additional SiO, to the waste stream. In either case, the resulting mineralogy would shift to more typical silica-oversaturated melt products similar to naturally and experimentally studied granitic systems. These rocks typically have a mineralogy of quartz, plagioclase feldspar, and potassium feldspar. This might be environmentally advantageous as granitic rocks are less likely to react strongly with the atmosphere and surface or groundwaters. The tendency for alkaline, mafic, silica-undersaturated rocks (such as the incinerator residue described here) to chemically alter after crystallization is much greater and accounts for its propensity to weather and undergo diagenic reactions. SEM/XRM on Powder Fractions. Table 1 summarizes the results from SEM/XRM evaluation of powder fractions. The principal mineral phases identified with petrographic analyses of intact particles were also identified with SEM/XRM analysis of powder fractions. This minerals include ackermanite (MgC+Si,O,), gehlenite (C+Al,Si,O,), magnetite (Fe,O,), and hercynite (FeA1204). SEM/XRM analyses of powder fractions also revealed many waste soil minerals, metal alloys, and spinels. Lead was present in complex silicate melts and as lead oxide (PbO). Like petrography, SEM/XRM revealed that elements with reduced valencies are present in the material. The data also suggest some success in recovering minerals according to their magnetic properties and density. Some caution is needed in the absolute interpretation of the results because of problems associated with beam diameter and particle size as well as the confounding effects of particle location with depth in the

122

thin section. Nevertheless, SEM/XRM was particularly useful in probing mineral structures and "hot spots". Hot spots were usually regions where elements present in low concentration in the residue (e.g. Cr,Pb, Zn, etc.) were revealed with dot maps. The particle region containing the element of interest could then be probed at higher magnification. This allowed estimation of mineral formulas for minerals present at low concentration in the ash which might not be detectable by other methods. Table 1 SEM/XRM-Based Mineralogy of Ash Fractions

Mu2 MgCa#i,O (Akermanite) (Ca,Na)(Fe'5 +,Mn,Zn)Si,O, (Aegirine) Fe,O, (Magnetite) FeA1204(Hercynite) FeO (Wustite) ZnFe204(Franklinite) FeS (Pyrite) NaAlSi,O, (Albite) Fe,TiO, (Ulvaspinel) -Si,O, (spinels)

LQAM CaMg(CO,), (Dolomite) C5s(P04), (Whitlockite) SiO, (Quartz) NaA1Si30, (Albite) CaSI,O, NaAlSi,O, (Sodian Anorthite)

NMHD FeO (Wustite) MgCO, (Magnesite) Al,O, (Corundum) SiO, (Quartz) C5s(P04), (Whitlakite) Fe,04 (Magnetite) ZnO (Zincite) MgCaSi,O, TiO, (Rutile) ZnC1, (Corrunite) CaMgSi,O, (Diopside) PbO MgCa$i,O, (Ackermanite) Fe,Ni (Taenite) cu alloy Al alloy Lead Silicates

NMLD M@2°4

BaSO, (Barite) CaSO, (Anhydrite) CaHPO, Ca&,Si,O, (Gehlenite) SiO, (quartz) C (graphitic carbon)

LuuW NaA1Si30, (Sodian Anorthite) C%(PO,), (Whitlockite) CaMg(CO,), (Dolomite) AlO

XRPD on Powder Fractions. Table 2 summarizes the results from XRPD. The principal minerals identified with XRPD were quartz (SiO,), halite (NaCl), calcite (CaCO,), hematite (Fe,O,), taenite (Fe, Ni), zincite (ZnO), nantokite (CuCl),

123

Table 2 XRPD-Based Mineralogy of Ash Fractions NMHD

NMLD

Mm2

A1203(Corundum) ZnO (Zincite) Mg3A12si3012 CuCl (Nantokite) FeS (Galena) Sb,Sr

CaCO, (Calcite) SiO, (Quartz)

SiO, (Quartz) NiTiO, Fe203(Hematite) (Fe, Ni) (Taenite) Ca(Mg,AJ)(Si,Al),O, (Aluminian Diopside) C (Graphite) CaMg(SiO,), (Diopside)

NaCl (Halite) SiO, (Quartz) (Ca,Na)(Si,Al)& (Fe,Ni) (Taenite) K,HCr,AsO,,

CaCO, (Calcite) C (Graphite) NaCl (Halite) SiO, (Quartz) Ba,Sb, C%Na4(P04F)602 A&P,S6

SiO, (Quartz) CaCO, (Calcite) KNaPb8(P04)6 Rb,Fe(SO,),O

Other Ca,SiO, 0.3H20 MgSiO, NaAlSi,O, (Albite) NaAlSiO, (Nepheline) CuMgSi,O,j MgMnSi,O, (Donpeacorite) CaS04-2H,0 (Gypsum) BaSO K2CaMg(SO4)3

Pb2Si04 Pb,SiO, Pb,Si,O, Pb5Si3Oll KPb8NdF2(P04)6 Zn NaCuPO,

124

corundum (A1203), graphite (C), and diopside (CaMg (Si03)2). Also present were albite (NaAlSi,O,), nepheline (NaAlSiO,), and gypsum (CaSO,ZH,O). Many minerals from the pyroxene class were seen as were calcium and magnesium silicates. Interestingly, a number of lead silicates were observed. Many of these minerals were seen with petrographic methods and SEM/XRM on intact particles. Elemental Zn was also seen. A few minerals were identified that suggest the residues were not formed under completely oxidizing conditions. Such minerals contain reduced elements and include nantokite (CuCl), galena (FeS), and graphite (C). It is possible to have geochemically incompatible phases in bottom ash particles given the mineral paragenesis that occurs. The minerals identified here are similar to ones observed by Kirby and Rimstidt (1993) and Sthpfli (1993) in their extensive XRPD analyses of bottom ashes from MSW incineration. Triplicate XRPD analyses of unfractionated, leached bottom ash powders subjected to the total availability leaching test found the following minerals: SiO, (quartz), Fe,Ni (taenite), C (graphitic carbon), MgSO,QH,O, CaMgSi,O, (diopside), Ca(Mg,Fe,Al)(Al,Si),06 (augite), and Na4A12Si,0,. XPS on Powder Fractions. The speciation of elements in the various powder fractions as determined by XPS are shown in Table 3. XPS is a promising technique for determining element speciation. This is particularly true because of its ability to interrogate the near surface environment (e.g. lo&. This surface layer is the first layer to dissolve, sorb or desorb during leaching. While the NIST database is comprehensive, it does not contain extensive mineralogies for elements of interest (e.g. Pb, Cr, Zn, Si) that are typically found in geologic specimens or combustion residues. The most prevalent minerals identified by X P S were quartz (SiO,), calcite (CaCO,), mullite (Al,SiO,), halite (NaCl), gibbsite (Al(OH),), corundum (A1203), zincite (ZnO), hematite (Fe203),and anhydrite (CaSO,). These species were also seen in the leached ash. The method also routinely identified other oxides such as CaO and FeO. These phases, not routinely seen by petrography, SEM/XRM or XRPD, most likely represent surface oxide layers on calcium-and iron-bearing minerals. It is important to note that magnetite (Fe,O,), a bulk mineral of some predominance that was seen with petrography, SEM/XRM, and XRPD, was not seen with XPS. It is possible that at the mineral surface, under oxidizing conditions, the more oxidized hematite (Fe,O,) forms. XPS is a surface sensitive technique and would tend to identify surface species rather than bulk (interior) species. The method also identified a number of carbon species including halogenated hydrocarbons, hydrocarbons, carbides, and calcite (CaCO,). Though not seen with other methods, calcite may be an amorphous surface layer on particles. Graphite, seen with SEM/XRM and XRPD, was not seen with XPS.

125

Table 3 XPS-Based Mineralogy of Ash Fractions

M m SiO, (Quartz) A12Si05(Mullite) A12Si,0,*2H,0 CaO NaAlSi,O, (Albite) Fez03

QLW SiO, (Quartz) Al(OH), (Gibbsite) Al,O, (Corundum) A12Si05(Mullite) NaAlSi,O, (Albite) CaO NaCl (Halite) CaSO, (Anhydrite) Fe203(Hematite) ZnSO, ZnCl,

NMHD SiO, (Quartz) Al(OH), (Gibbsite) CaCO, (Calcite) Fe,O, (Hematite) NaCl (Halite) Ca,Si,09 Al,O, (Corundum) CaO ZnC1, ZnSO, NaAlSi,O, (Analcite) Carbides

NMLD SO, (Quartz) A1203(Corundum) NaCl (Halite) NaAlSi,O, (Albite) CaSO, (Anhydrite) ZnSO, ZnC1, Fe,O, (Hematite) Carbides

1.5 ANM SiO, (Quartz) Al,O, (Corundum) Al,Si,O7*2H,O NaAlSi,O, (Albite) CaO NaCl

Leaching Behavior. The data from the total availability leaching test are shown in Figure 5. Generally, about 11.4% of mass of bottom ash was lost during the leaching test. Principal constituents that readily dissolve are Ca, Cd, C1, Cu,K,Mg, Na, Pb, and Zn. The data from the pH-dependent leaching tests are shown in Figures 6-11. Figure 6 presents data for Na, K and Cl. These elements show more or less pH-independent dissolution across the entire pH range. Figure 7 shows data for Ca, SO,, Al and Si. Each of these elements shows pH-dependent dissolution phenomena and solid phase control. A clear minimum is seen for Al. Figure 8 shows the leaching data for Cd, Pb, Zn and Cu. All of these elements exhibit pH dependent leaching. Figure 9 shows pH dependent leaching of Fe, Mn,Sr and Mg. Figure 10 shows similar data

126

Bottom Ash Fraction Available for Leaching 140 120 c C

$100 Q,

a

ai 380 .m

2

6 60 .-c 0 2

LL

40

20

0

Figure 5.

Al Ca Cd CI Cr Cu Fe K Mg Mn Na Ni Pb Si Zn

Bottom Ash Element Fractions Available for Leaching.

127

10000

2

-.-F 1000 c

v K versus pH

Na versus pH

" i TIFOOO Y

0

c

E g

c

100

0

c

0

0

10

0 2 4 6 8 101214

0 2 4 6 8 101214

PH

PH

CI versus pH 10000

7

c

.-0 w L

1000

i

L

c

8 c

0

0

100

0 2 4 6 8 101214

PH

Figure 6.

pH Dependent Leaching Behavior for Na,K and C1.

128

SO4 versus pH

Ca versus pH $0000

I

10000

2

c

c

8 c

1000

0

0

100

.-c 0 c

-

E

U

I

1

I

- _ Anhydrite -. I

l””.j

F

Y

.-cg

I

.I ,

\

1000

-

-

c

8 c

0

0

I

100

I

I

I

I

I

0 2 4 6 8 101214

PH

Al versus pH

10000.0

10000.00 s l 1000.00 E 100.00 C .2 10.00

\

E ti

c 8

1.00 0.10

8

0.01

1000.0 c .G CI

-E 2

*-

0.00

Figure 7.

Si versus pH

I

I

I

8=

.‘ I

I

I

Id!’ .--.. I

I SiO, I (A,Pt

100.0 10.0 1.0 0.1

0 2 4 6 8 101214

0 2 4 6 8 101214

PH

PH

pH Dependent Leaching Behavior for Ca, SO,, Al and Si. The horizontal lines inside the graphs are detection limits. The dotted lines show solubility curves for the indicated controlling solid phase.

129

Cd versus pH 10.000

gE

Pb versus pH 1000.00

2

E 100.00

1.000

Y

.-c5. 10.00

Y

e

c

c

1.00

0

0

g

0.10

0

--...Anglesite

0.01

0 2 4 6 8 101214

0 2 4 6 8 101214

PH

PH

Zn versus pH

Cu versus pH

10.00

1 .oo ~

0.10

0 2 4 6 8 101214 PH

Figure 8.

, ,

h..;. ,

0.01 0 2 4 6 8 101214 PH

pH Dependent Leaching Behavior for Cd, Pb, Zn and Cu. The horizontal lines inside the graphs are detection limits. The dotted lines show solubility curves for the indicated controlling solid phase.

130

Fe versus pH

Mn versus pH 1000.00

Ferrihydrite

7100.00 E

Y Y

.-g 10.00 U

gc 8 c 0

0

0.01

0 2 4 6 8 101214

PH

PH

Sr versus pH

Mg versus pH 10000.0

2 1000.0

i

F

Y

Y

s

c

s

0.10

0 2 4 6 8101214

100.0

0 .= e c. C 8 C

1.00

100.0 .c

10.0

gc 8 c

. _ _ .Celestite ._ 1.o

Figure 9.

I

I

I

I

I

I

00

l~

~~

10.0 1.0

-

*

- -Magnesite

0.1

0 2 4 6 8 101214

0 2 4 6 8 101214

PH

PH

pH Dependent Leaching Behavior for Fe, Mn,Sr, and Si. The horizontal lines inside the graphs are detection limits. The dotted lines show solubility curves for the indicated controlling solid phase.

131

-

Cr versus pH

100.00

100.00 i 0, t u c 0 '= 10.00

b 4

0)

E !

10.00

C

0 .-

5

1.00

e

c

+

c

C

a,

g 0

B versus pH

a,

0.10

u

C 0

0

0

0.01

1.oo

0 2 4 6 8 101214

PH

Ni versus pH

Co versus pH

-1 00.00

10.00

2

0)

F

&E10.00

Y

C

C

0 .c

E

1.00

z s

0.10

c

8 101214

PH

\

0 .-c

0 2 4 6

1.00

e

+

8 0.10

C

C

s

0.01 0 2 4 6

8 101214

PH

Figure 10.

0.01

-

0 2 4 6 8101214

PH

pH Dependent Leaching Behavior for Cr, B, Ni and Co. The horizontal lines inside the graphs are detection limits. The dotted lines show solubility curves for the indicated controlling solid phase.

132

Ba versus pH

Mo versus pH

-i

1000.003 -

10.0

F

Y

g

1

..._.Barite 4

F

2 100.00 F c

.-0

1.0

5 + c 8 c

g!

c)

c

8 C 0

0 0

0.1

1.00 0.10 1 0.01 °

.

O

O

0 2 4 6 8 101214

0 2 4 6 8101214

PH

PH

V versus pH

-i

10.000

F 1.000

Y

c

0

-= 0.100 ! 4-

c

g 0.010

s

0.001

0 2 4 6 8 101214

PH

Figure 11.

pH Dependent Leaching Behavior for Mo, Ba and V. The horizontal lines inside the graphs are detection limits. The dotted lines show solubility curves for the indicated controlling solid phases.

~

133

for Cr, B, Ni and Co. A minimum is seen for Cr. Figure 11 shows data for Mo, Ba, and V. The nature of phases controlling solubility is discussed below. Geochemical Modeling. Only one approach was used to model leaching behavior in the bottom ash. The data from the pH dependent tests was used. The approach assumes that equilibrium-based solid phase control of leachate chemistry occurs over a wide pH range. This solid phase control approach was viewed as an appropriate use of MINTEQA2 for the type of leaching test that was used (low L/S, solid phase in equilibrium with the solution, solid phase dominates). At each pH, all leachate constituents were inputted into the model (including acid or base needed to adjust the pH). Each condition was run on MINTEQA2 without allowing solids to precipitate. Minerals with either positive or negative saturation indices close to zero were identified. A select group of 13 minerals was then inputted into the files at each pH as infinite solids (i.e. solids that will not precipitate or dissolve but which will control its aqueous phase constituents in the presence of all other solid and aqueous phase reactions and conditions). The output of the modeling was then plotted, where appropriate, in Figures 6-11. The premise here is that a solid with a saturation index close to zero is the most likely solid controlling the composition of the leachate at that pH. By reintroducing the solids into the model as infinite solids, the specified aqueous phase concentration of a component species should be close to the observed values and the solubility plot should be close to or mimic the behavior of the actual leaching data. As shown in Figure 6, no solids were identified as controlling leaching behavior for Na, K and C1. These elements demonstrate pH-independent dissolution and most likely represent the dissolution of NaCl, ZnCl,, and unidentified potassium salts such as KCl. As shown in Figure 7, Ca and SO, solubility apper to be controlled by anhydrite (CaSO,). A slightly better fit was seen for anhydrite over gypsum (CaS0,*2H20). The fit was most appropriate between pH 4 and 10. Anhydrite also controls leaching of Ca and SO, in ESP ash (Theis et al., 1993; Eighmy et al., 1994). Comans et al. (1993) found gypsum to control leaching in their MSW bottom ash. An excellent match was found for Al solubility. Gibbsite [Al(OH),] is the controlling phase for this bottom ash, ESP ash (Eighmy et al., 1994) and Dutch bottom ash (Comans et al., 1993). No clear controlling solid could be identified for Si. Amorphous SiOl was used as it most closely resembles the type of silicate minerals seen in the residue; however, the match is not a good one. Comans et al. (1993) identified wairakite (CaAI,Si4O,,*2H2O) as a controlling solid for their ash; this mineral did not provide a good match in our residue and it was not identified in the residues with the various speciation methods that were employed. As shown in Figure 8, Cd solubility was found to be controlled by otavite (CdCO,); particularly at higher pH values. A corrected p q P of 12.24 was used (Zachara et al., 1992). This solid also controls Cd solubility in ESP ash (Eighmy et al., 1994) and in Dutch bottom ash (Comans et al; 1993). Pb solubility appeas to be controlled by anglesite (PbSO,), although the data is sparse. This solid also controls Pb leaching in ESP ash (Theis et al., 1993; Eighmy et al., 1994). Comans et al.

134

(1993) found Pb(OH), to control in their bottom ash. Zn solubility is controlled by ZnSiO,; this was also seen for various ashes by Gardner (1991). Cu solubility is controlled by Cu(OH),. As shown in Figure 9, Fe solubility is controlled by ferrihydrite (Fe(OH),). This solid also controls in ESP ash (Eighmy et al., 1994) and in Dutch bottom ash (Comans et al., 1993). Sr solubility could not be modeled adequately. Celestite (SrSO,) gave the closest match; this solid does control Sr leaching in ESP ash (Eighmy et al., 1994). Mg leaching appears to be controlled by magnesite (MgCO,); particularly at higher pH values. No suitable matches were found for Mn. As shown in Figure 10, no suitable matches were found for Cr, B, Ni, and Co. B is not in the MINTEQA2 data base as a component. The solids present in the data base for Cr, Ni and Co are limited. As shown in Figure 11, Ba solubility is controlled by barite (BaSO,). V solubility may be controlled by Pb,V,O, although the match is not that good. Mo is not in the MINTEQA2 data base as a component. Some of the data presented here suggest that XPS is the preferred method to verify the presence of solids that control pH-dependent leaching behavior (i.e. Al(OH),, CaSO,). Data also suggest that some soluble solids dissolve and new solids form under aqueous conditions that ultimately control leaching (i.e. BaSO,, MgCO,, Fe(OH),, Cu(OH),). Such diagenic transformations indicate that respeciation occurs during leaching and that simple carbonate and hydroxide solids form and therefore control leaching of their constituent cations. The fact that much of the pH-dependent leaching behavior can be described by geochemical thermodynamic models means that the use of such models to predict long term leaching behavior, leaching after treatment, or leaching during specific disposals scenarios is possible. Such efforts will need to be fine-tuned, however, by expanding the thermodynamic database in the models as well as incorporating sorption phenomena. 4.0 CONCLUSIONS Bottom ash particles from MSW combustion is principally comprised of a melt structure (85%) and an MSW uncombusted or unmelted waste feed component (15%). The melt structure, formed from waste feed components, is comprised of opaque glass, isotropic glass and schlieren where spinel-group minerals (Fe,O,, FeAl,O,, CrFe,O,) and melilite-group minerals (Ca&SiO,, MgCa,Si,O,) precipitated out in the melt as it cooled. The waste feed components contain soilderived SiO,, pyroxenes, feldspars and uncombusted organic carbon. An analogous paragenic sequence for the formation of melt is a melilite-bearing igneous rock described by the Ca0-Mg0-A120,-Si0,-N~0-Fe0(CMASNF) system. The melt structure was formed at about 1,200"C. Thermodynamically incompatible phases are present in the ash, making it reactive to weathering, aging (oxidation, hydrolysis), and diagenesis. Many species in the residue were defined by SEM/XRM, XRPD, and X P S evaluations of powder fractions. Species were documented for 0, Si, Fe, Ca, Al,

135

Na, C1, Mg, Ti, Zn, Cr, Pb, and Cu. Some of these species are present at trace levels ( c 1,OOO mg/Kg). All the methods provided comparable results. X P S , however, identified mineral species at the particle surface most involved in leaching behavior. The residues exhibit pH-dependent leaching behavior. Solid phases controlling leaching sometimes differ from those seen in the unleached residues; suggesting dissolution and reprecipitation reactions are occurring that control pH dependent leaching. Overall, bottom ash is not readily leachable. 5.0 ACKNOWLEDGEMENTS

This research was supported by the U.S. EPA Risk Reduction Engineering Laboratory (CR 818157-Ol), U.S. EPA Region 1 (X1001525-01),Chemical Waste Management Inc., and Environment Canada. We thank Trish Erickson, Jim Ryan, Carlton Wiles, Juan Perez, Jesse Conner, Bill Holm, David Hay, Gordon Owen, Steven Sawell and John Martin for their assistance in this effort. 6.0 REFERENCES

Allison, J.D., Brown, D.S. & Novo-Gradac, K.J. (1990) MINTEQA2/PRODEFA2,A Geochemical Assessment Model for Environmental Systems: Version 3.0 User's Manual. Environmental Research Laboratory, U.S. EPA, Athens, Georgia. Carmichael, I.S.E. (1979) Glass and the glassy rocks, p. 233-242. In (H.S. Yoder, ed.) The Evolution of the Igneous Rock: Fiftieth Anniversary Perspective. Princeton University Press, Princeton, New Jersey. Comans, R.N.J., van der Sloot, H.A. & Bonouvrie, P. (1993) Geochemical Reactions Controlling the Solubility of Major and Trace Elements During Leaching of Municipal Solid Waste Incinerator Residues, p. 667-679. In (J. Kilgore, ed.) Proceedings 1993 International Conference on Municipal Waste Combustion, AWMA, Pittsburgh, Penn. Deer, W., Howie, R. & Zussman, J. (1992) An Introduction to the Rock Forming Minerals. Longman Scientific and Technical, Essex, England, 696 p. DiPietro, J.V., Collins, M.R., Guay, M. & Eighmy, T.T. (1990) Evaluation of pH and oxidation-reduction potential on leachability of municipal solid waste incineration residues. p. 2B:21-33. In Proceedings of the International Conference on Municipal Warte Combustion, April 11-14, Hollywood, Florida, AWMA, Pittsburgh, Penn. Eighmy, T.T., Domingo, D., Stampfli, D., Krzanowski, J., & Eusden, J.D. (1993) The Speciation of Elements in MSW Combustion Residues, p. 457-470. In (J. Kilgroe, ed.) Proceedings of the 1993 International Conference on Municipal Waste Combustion Conference; AWMA, Pittsburgh, Penn. Eighmy, T.T., Krzanowski, J., Domingo, D., Sthpfli, D., Eusden, D., Marsella, K, Killeen, K, Guardenier, H. & Hogan, J. (1994) The Nature of Lead., Cadmium and

136

Other Elements in Incineration Residues and Their Stabilued products. U.S. EPA Final Report (in press). Gardner, K.H. (1991) Characterirarion of Leachates From Municipal Incinerator Ash Maten&. Master's Thesis, Clarkson University, p. 112. Henry, W.M., Barbour, R.L., Jakobsen, R.J. & Schumacher, P.M. (1983) Inorganic Compound Ident$cation of Fly Ash Emissiom From Municipal Incinerators, EPA600/53-83-095, U.S. EPA, Cincinnati, Ohio. Kirby, C.S. & Rimstidt, J.D. (1993) Mineralogy and surface chemistry of municipal solid waste ash. Environ. Sci TechnoL, 27, 652-660. Kosson, D.S., Kosson, T.T. & van der Sloot, H. (1993) Evaluation of Solid$cation/Stabiluation Treatment Proceses for Municipal Waste Combustion Residues. USEPA/RREL Final Report. McBirney, A.R. (1993) Igneous Petrology. Jones and Bartlett Publishers, Boston, 508

P.

Ontiveros, J.-L. (1988) A Comparison of the Composition and Properties of Municipal Solid Waste Incinerator Ashes Based on Incinerator Configuration and Operation. Ph.D. Dissertation, Rutgers University, 219 p. Pliiss, A. & Ferrell, R.E. Jr. (1991) Characteristics of lead and other heavy metals in fly ash from municipal waste incinerators. Haz. Waste Haz. Mad, 8, 275-282. Project EKESA. (1992) Emksiomabschatnmgfur kehrictschlacke: Aufrtraggebergemeinschafi f u r das Projekt EKESA, Eidgenossische Anstalt fur Wasserversorgung, Abwasserreinigung, und Gewasserschutz (EAWAG), Dubendorf, Switzerland, 159 p. Rumble, D. (1976) Oxide Miner&: Mineralogical Society of America Short Course Notes, vol. 3, Mineralogical Society of America, Washington, D. C.. Soulard, H., Provost, A, & Boivin, P. (1992) Ca0-Mg0-Al,0,-Si02-N~0(CMASN) at 1 bar from low to high N%O contents: Topology of an analogue for alkaline basic rocks: Chem. Geol. 96,459-477. Stiimpfli, D. (1992) Final Report: Cements and Bottom Ash Chemistry (ClaAC) - A Study Wth X-RayPowder Difiaction. Environmental Research Group Final Report, University of New Hampshire, 69 p. Terry, R.D., & Chilingar, G.V. (1955) Summary of "Concerning some additional aids in studying sedimentary formations" by M.S. Shvetsov. J. Sed Pet. 25:229-234. Theis, T.L., Iyer, R. & Gardner, KH. (1993) Dynamic evaluation of municipal waste combustion ash leachate, p. 680-689. In (J. Kilgroe, ed.) Proceedings I993 International Confeence on Municipal Waste Combustion, AWMA, Pittsburgh, Penn. Vehlow, J., Schneider, J, & PfrangStotgG. (1992) Restoffe - Charakterisierung, behandlung verwertung. In: Furshung und Entwicklung in Kemforschungszentrum Karlsnrche zur Hausmillverbrennung: Symposium 25 jahre LIT 5 jahre TAULRA: Kerforschungszentrum Karlsruhe GMBH, Karlsruhe. Yoder, H.S. (1979) Melilite-bearing rocks and related lamprophyres, p. 391-412. In (Yoder, H. S., ed.) The Evolution of the Igneous Rock: Fifseth Anniversaty Perspectives, Princeton University Press, Princeton, New Jersey.

Environmental Aspects of Constnrction with Waste Materials J.J.J.M. Goumans, H A . van der SIoot and l k G . Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

137

An Approach to the Assessment of the Environmental Impacts of Marine Applications of Municipal Solid Waste Combustion Residues 0. Hjelmar, E.Aa. Hansen, K.J. Andersen, J.B. Andersen and E. Bjsrnestad VKI, Water Quality Institute, Agern All6 11, DK-2970 Hsrsholm, Denmark

Abstract A comprehensive approach to the assessment of the environmental impacts of marine land reclamation with municipal solid waste incinerator (MSWI) residues is described. Based on a study of the potential environmental impacts of marine foreshore land reclamation of MSWI bottom and fly ash in Bermuda, a methodology including sampling and characterization of bottom ash, fly ash and combined ash, performance of laboratory leaching tests with ocean water and rainwater on granular and solidified ash, studies of acute and chronic toxicity of ash leachates to local marine organisms, performance of baseline studies, development of acceptance criteria, modelling of the release of potential contaminants resulting from various disposal options at two locations, modelling of the dilution of released contaminants in the surrounding sea and assessment of the resulting environmental impact, is presented. 1.

INTRODUCTION

Municipal solid waste incinerator (MSWI) bottom and fly ashes have been shown by numerous studies [e.g. 1,2,3,4,5] to produce leachates which initially are characterized by high concentrations of inorganic salts and moderate to low concentrations of trace elements. As the leaching progresses with time, the contents of both salts and trace elements in the leachate may decrease to very low levels. For well burnt-out ash, the content of organic, biodegradable matter in the leachate is generally low. In practice, leaching of incinerator residues may occur over a very long period of time. This suggests the employment of a controlled contaminant release strategy for bulk application

or disposal of incinerator ash. Such a strategy would imply that the ash should be monofilled and that the application or disposal site should not be equipped with a leachate containment system. Instead it should be designed carefully to reduce the rate of transfer of contaminants out of the site to an environmentally acceptable level, and the site should be located in an environment which is not very sensitive to the anticipated impact. Proper design and proper selection of a site location therefore play crucial roles in the protection of the environment and should always be based on a preceeding assessment of the resulting environmental impacts. The rate of transfer of Contaminants out of the site may be reduced by restricting the flow of water through the site or by retarding or reducing the leaching of contaminants. Stabilization of granular ash with cement will often accomplish both of these objctives simultaneously. A

138 geologically stable, sloping top cover of low permeability combined with a surface drainage system can minimize the infiltration of rainfall into a site. The dominating components of MSWI ash leachate, inorganic salts, are totally compatible with seawater, and a location of a MSWI ash bulk application or disposal site at or in the sea would eliminate any potential groundwater pollution problems caused by leaching of salts. The efforts should then be concentrated on reducing the rate of release of trace elementslheavy metals (and possibly organic compounds) to an acceptable low level. Although the high salt content of the seawater itself may initially enhance the leaching of certain trace elements from the ash through the formation of chloride complexes, the sea offers a very stable, well buffered chemical environment with a constant pH of 8.1 which is generally favourable in terms of low trace element solubility and which is a safeguard against any substantial long term changes of the leaching conditions. During the period 1989 - 1991, the Water Quality Institute (VKI)in conjunction with Bermuda Biological Station for Research Inc. (BBSR) and the Danish Hydraulic Institute (DHI) performed a comprehensive study with the objective of assessing and minimizing the environmental impacts of disposal of MSWI bottom ash and fly ash by marine land reclamation in Bermuda [6,7,8]. The study which was carried out for Ministry of Works and Engineering, Bermuda, was initiated in order to enable the prevention of unacceptable impacts on Bermuda’s vulnerable marine environment from disposallapplication of an annual amount of approximately 16000 tonnes of combined bottom and fly ash (without acid gas cleaning residues) expected from a planned refuse incinerator designed to treat 50,000 tonnes of garbage per year. Due to the scarcity of land and the mid-ocean location, marine land reclamation of the MSWI ash was an attractive option in Bermuda, provided unacceptable emvironmetal impacts could be avoided. This paper presents an overview of the approach, the methodology and the results of the study. 2.

APPROACH

The approach of the study is outlined in figure I . Initially, a few selected disposal options were defined in terms of location (Tynes Bay and Castle Harbour, see figure 2), physical design, geotechnical and hydrogeological properties, rate and mode of disposal of ash, etc. The options or scenarios included disposal of both unsolidified and cement stabilized incinerator ash. A number of laboratory leaching tests were then designed and conducted on MSWI ash samples in order to estimate the rate of leaching of contaminants from the ash under the conditions corresponding to each disposal option, and to evaluate the effect of various efforts to minimize the rate of leaching, particularly cement stabilization of the ash. Ash samples from waste-toenergy facilities were procured from the USA (Saugus, Massachusetts) and Europe (Jersey, Channel Islands). The leaching studies which included the performance of column, batch and tank leaching tests with rainwater and seawater were set up to simulate local conditions as closely as possible. The interpretation of some of the leaching results were supported by chemical equilibrium calculations using a computer model. Several ecotoxicological tests (bioassays) were performed in the laboratory to determine the acute and chronic toxicity towards sensitive local marine lifeforms of the most contaminated leachate from the leaching tests. The dilutions needed to render the leachate non-toxic were calculated

139

Descriptionof disposal options

I

and rwtew of existing leaching data

L

I

Choke of disposal option@)

Performance of baseline study

Land reclamation and development of monitoring procedures

Is impact

Fiiure 1 Outline of the approach of the study.

and used together with chemical composition data for the development of recommended acceptance criteria. Baseline field studies were performed at both site locations to describe the present condition, the species composition and diversity of the communities of flora and fauna at the main nearshore marine habitats (rocky shores, coral reefs, sediments, seagrass beds). Bioaccumulation of selected trace elements by transplanted mussels kept in cages was investigated in preparation of future biomonitoring of the disposal site. Data were collected on the background levels of trace elements in water, sediment, and selected biological species. Samples of leachate from an existing dump site at the Civil Air Terminal at Castle Harbour were collected and analyzed.

140

Bermuda had no guidelines which define specific acceptance criteria for the environmental impact of a disposal or land reclamation site. A set of suggested acceptance criteria in terms of maximum emissions of selected trace elements has therefore been developed as part of the project work. The rate of emission of selected contaminants was then estimated for each disposal option over a period of 10 years of disposal and 20 years following that by combining the experimentally determined leaching data with a mathematical description of the rate of disposal of the ash and the flow of water through the sites. The estimated rate of emission of dissolved contaminants was used as input to a dynamic mathematical simulation model which predicted the dilution of the solutes in the marine waters surrounding the two site locations. A number of field measurements were conducted at the two sites to provide the necessary information on current and flushing conditions. Finally, an environmental impact assessment was performed for each of the disposal options considered. The calculated concentrations of leachate/contaminants in the marine waters surrounding the sites were compared to the results of the bioassays, the baseline study, available information on the toxicity of specific contaminants, and the suggested acceptance criteria. The safety margins and uncertainties involved in the entire assessment procedure was evaluated, and the disposal options were ranked in order of increasing environmental impact andlor uncertainty.

3.

DISPOSAL OPTIONS

Two locations have been considered for ash disposal. The primary site for consideration is at the Civil Air Terminal at Castle Harbour. The secondary site is at Tynes Bay in Devonshire. Both sites are shown in figure 2. Castle Harbour is the second largest of the inshore basins of the Bermuda platform, covering some 10.5 km2. The morphology, water exchange, sediments and biota have been significantly impacted by dredging, reclamation and causeway constructions in the past. The proposed disposal site is located adjacent to an existing scrap metals dump at the Civil Air Terminal. The bottom sediment in the disposal area is typically a fine silty mud, and the average water depth is 12 m. It is anticipated that the ash disposal will continue to an approximate height of 5 m above sea level. Tynes Bay is located on the north shore of Bermuda in Devonshire which is also where the incinerator will be located. The bay is open to the North Lagoon, which extends about 11 kilometers to the north and east and has a maximum depth of 20 m. The shoreline is rocky, and the seabed is sandy. The average water depth in the proposed disposal area is 5 m. As in Castle Harbour, ash disposal to a height of approximately 5 m above sea level is anticipated. Three different foreshore land reclamation disposal scenarios have been considered at each location:

141

Disposal by placing cured 1 m3 blocks of cement stabilized combined ash directly into the sea from the coastline. Above sea level, the concretelash mixture may be poured directly onto the surface of the site as it is raised. Disposal by backtipping of untreated combined ash into sequences of 15 m x 15 m compartmentshasins made of sheetpiles which have been rammed into the seabed. Combined solution. In the sheetpile compartments, cement stabilized combined ash blocks are placed below sea level. Unstabilized combined ash is placed above sea level.

Figure 2 Map of Bermuda showing the two potential site locations.

4.

SAMPLING AM) CHARACTERIZATION OF MSWI ASH

Since no incinerator ash was available in Bermuda, samples of bottom ash (BA), fly ash (FA) and combined ash (CA) were procured from two MSWIs which were chosen on the basis of their similarity to the future situation in Bermuda regarding waste feed composition, combustion and gas cleaning technology, and ash management. The Martin facility in Jersey was chosen as representing a resort island and the Wheelabrator facility in Saugus, Massachusetts was chosen as representing the strong North American influence on the consumer products and, consequently, the waste composition in Bermuda. The Jersey facility (Martin design) had a capacity of 240 tonnes of refuse per day and the Saugus facility (Von Roll design) had a capacity of 1500 tonnes of refuse per day. As will the in-

142 cinerator in Bermuda, both facilities were equipped with electrostatic precipitators for collection of fly ash, and neither of them had acid gas scrubbers at the time of sampling. At the Jersey facility, the samples were combined from a large number of subsamples collected over a period of one week. At the Saugus facility, the ash samples were collected over a period of less than one day (bottom ash and fly ash) and two days (combined ash). At the Jersey facility, the bottom ash was collected dry before it was quenched whereas the bottom ash from the Saugus facility and the combined ashes were collected after quenching. Both fly ashes were collected dry. The dry bottom ash from Jersey was crushed with a hammer. Material larger than 45 mm and ferromagnetic material were removed from the bottom and combined ashes which were then reduced to manageable sample sizes (100 - 120 kg) by means of a riffle or by coning and quartering. Representative BA and CA samples were crushed to < 2 mm in a jaw crusher and, after further subdivision by a riffle, ground to < 0.090 mm in a tungsten carbide mortar grinder. The ground BA and CA and the FA were subjected to chemical analysis. The results of the chemical analysis which are presented in table 1 indicate that the elemental compositions of the residues from Jersey and Saugus, Mass. are quite similar to each other and not very different from the compositions of similar residues from other incinerators, although the lead concentrations in the FA from both Jersey and Saugus are unusually high (about twice the level found in most fly ashes). The zinc concentrations in both FA, BA and CA from Jersey and Saugus are also relatively high. The Jersey FA reacts almost neutrally with water whereas the Saugus FA creates a higher pH upon contact with water. The Jersey BA, in contrast, has a more alkaline reaction with water than the Saugus BA, probably because the Jersey BA was sampled dry and the Saugus BA after quenching. The two combined ashes are quite similar to each other, both in pH and alkalinity. The content of organics is described in general terms as loss on ignition at 550 "C (LOI) and total organic carbon (TOC). The FA and BA samples from each facility were in addition analyzed for content of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). It appears from the TOC and LO1 results that the residues from Saugus, Mass. have a somewhat higher content of uncombusted material than the residues from Jersey. This is in accordance with the visual appearance of the residues.The concentration of PCDD and PCDF is very low in the bottom ash and somewhat higher in the fly ash from both facilities. The concentration levels found in the fly ash samples are lower than or within the lower end of the ranges reported by others. 5.

LABORATORY LEACHING TESTS ON MSWI ASH

5.1 Granular ash Samples of granular bottom ash (BA), combined ash (CA) and fly ash (FA) were subjected to column and batch leaching tests with ocean water and artificial rain (demineralized water acidified to pH = 4 with HNO,). 10 kg samples of BA and CA and 6 kg samples of FA from each facility were placed in plexiglass columns of diameter = 0.15 m and height = 0.80 m and leached with seawater and artificial rain, respectively, in upflow at a flow rate corresponding to 15-20 mm124 hours. Leachate fractions corresponding to the liquid/solid ratios (LIS) = 0.00.2, 0.2-0.5.0.5-1.0, 1.0-2.0. and 2.0-5.0 I/kg were collected from each of the 12 columns and

143 Table 1 Analyses of MSWI ash. All

ELEMENT

element analyses

UNIT

JERSEY F A C l L I T Y FA

Fe

ca K Mg Na S P Ti Mn Ag As Be Cd co Cr cu Hg Mo Ni Pb

se Sn

Sr V

Zn pH (1% s l u r r y ) ANC eqv/kg

LO1 TOC

are total analyses.

7.6 2.8 27 8.2

g/kg g/kg

FA: F l y ash BA: Bottom ash CA: C d i n e d ash

ANC: LOI:

TOC:

BA

SAUGUS FACILITY CA

FA

220 52 1.7 140 a5 12 14 22 3.5 4.2 7.2 1.7 4.1 29 2700 < 5 26 310 4800 0.26 6.3 190 2100 1.2 260 200 a4 6200

23 32 390 4800 0.28 6.4 150 5200 2.2 320 100 a6 9100

170 68 45 22 74 23 13 29 22 5.1 12 0.90 5a 140 1300 370 29 340 920 7.0 21 92 15000 7.8 1900 100 80 41000

11.1 3.5 5.9 5.5

9.9 3.1 19 7.8

10.2 2.5 45 8.0

220 53 6.3 120 a2 13 13 25 4.6 3.7 6.8 1.5 8.3 41

iaoo

BA

CA

210 52 1.2 150 69 9.2 9.4 27 6.1 2.9 7.0 1.6 7.3 38 1500 12 33 300 3400 0.22 14 190 3900 0.63 300 200 51 5300

210 56 1.1 120 76 9.8 10 25 8.9 2.7 6.7 1.3 9.2 26 1000 23 24 480 3100 0.20 4.4 160 3100 0.48 280 200 53 5500

9.6 2.0 26 13

3;o

9.7 35 17

Acid n e u t r a l i z a t i o n c a p a c i t y ( a l k a l i n i t y ) Loss on i g n i t i o n T o t a l organic carbon

Table 2 Results of PCDD and PCDF analysis of ash samples. Units: pgikg.

PARAMETER

JERSEY F A C I L I T Y FA

140 4a 0.10 0.27 1.5

PCOD ” PCDF 2,3,7,a-~c~o 2.3.7,a-TCDF TCDD-EPV (Eadon)

’’

1) 2) I’

SAUGUS F A C I L I T Y BA

FA

1.5 - 1.9 0.44 0.64 < 0.03 < 0.007 0.014 - 0.046

-

115 69 0.21 0.52 2.5

S u n o f TCOD, PnCDD, HxCDD, HpCOD and OCDD S u n o f TCOF, PnCDF, HXCDF, HpCDF and OCDF

BA

-

9.0 10 3.4 - 4.5 < 0.07 < 0.05 0.14 0.22

-

144

subjected to chemical analysis. When the column experiments were completed, two consecutive batch leaching tests, each at LIS = 10 IIkg, were performed on well mixed material from each column with the appropriate leaching medium. The two filtered fractions (0.45 pm filter) were combined to represent LIS = 5.0-25 for each leaching test. Samples of BA and CA were subjected to additional batch leaching tests with seawater at LIS = 25, 50, 75, 100, and 200 Ilkg. The collected leachate fractions were analyzed for pH, conductivity, TDS, alkalinity, sulfate, chloride, total-N, total-P, Na, K, Ca, Mg, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Se, Sn, Zn, and non-volatile organic carbon (NVOC). Some of the results are presented in terms of total leached quantities in tables 3, 4 and 5 . Table 3

Total amounts of some trace elements and NVOC leached in column and batch leaching tests with artificial rainwater (L/S = 0 - 25 I k g ) . Units: mg/kg of ash.

PARAMETER

JERSEY F A C I L I T Y FA

AS Cd Cr

cu HQ Pb Se Zn NVOC

0.12 0.05 < 0.03 < 0.12 0.05

0.7 0.40 < 0.3 104

SAUGUS F A C I L I T Y

BA

CA

< 0.01 < 0.013 < 0.02

< 0.06 < 0.02

0.42 0.094 0.05 0.063 < 0.3 490

0.61 0.11 0.21 0.12 < 0.3 440

0.038

FA

EA

0.073

0.018

< 0.06

< 0.014

< 0.03 < 0.02

< 0.02

0.084 1.1 0.18 < 0.3 170

CA

0.53 0.032 0.32 < 0.03 0.3 230

0.047 0.043 < 0.03

0.35 < 0.03

0.26

< 0.005 < 0.3

300

Table 4 Total amounts of some trace elements and NVOC leached in column and batch leaching tests with ocean water (LIS = 0 -25 I k g ) . Units: mgkg of ash.

I 11

FA As Cd Cr

cu Hg Pb

se Zn NVOC

SAUCUS F A C I L I T Y

JERSEY F A C I L I T Y

PARAMETER

0.081 2.9 < 0.02 < 0.02

0.07 15 0.42 0.8 110

BA

0.024 0.21 < 0.02

1.4 0.053 0.93 0.095 0.6 470

CA

0.060 0.71 < 0.02

0.96 0.099 5.7 0.11 2.8 220

FA

0.072 0.93

BA

0.028 1.3

< 0.02 < 0.03

< 0.02

0.08

< 0.03

18 0.24 2.6 67

2.7 0.40 < 0.03

6.6 310

CA

0.028 0.88 < 0.02 0.88 < 0.03

0.33 < 0.03 5.7 270

145 Table 5 Accumulated amounts of trace elements leached in sequential batch leaching tests on CA and BA from both facilities with seawater at L/S = 2 x 100 lkg.

RESIDUE

ACCUMULATED AHWNTS LEACHED (mg/kg)

ACCUM.

L/S

As

Cd

cu

Ni

Pb

Zn

CA Jersey CA Jersey

100 200

0.7 1.2

4.1 7.2

4.1 6.1

< 0.2 < 0.4

13 22

3.3 8.0

CA Saugus CA s a u g u s

100

0.5

200

< 0.7

3.4 5.4

2.8 3.9

< 0.2 < 0.4

11 20

3.9 7.7

BA Jersey BA Jersey

too

< 0.2 < 0.4

0.10 0.35

1.5 2.4

< 0.2 < 0.4

0.096 1.9

3.3

200

BA Saugus BA Saugus

100 200

< 0.2 < 0.4

2.6 3.7

2.6 4.8

0.4 < 0.6

4.3 7.1

7.1 12

-

The composition of the leachate is dominated by inorganic salt ions such as Cl-, SO:, Na+, K + , and Caz+, but these contaminants are of no environmental concern in a marine disposal situation. The concentration level of trace elements varies between the different tests but is generally moderate to low. Most parameters in most of the tests (but not all) appear in the highest concentrations in the first few fractions of leachate collected. Cd, Cu, Pb, and Zn are leached more extensively by seawater than by rainwater, possibly due to chloride complexation, whereas the leaching of As, C r (which is below the limit of detection), Hg, and Se is approximately the same in seawater and rainwater. The data show quite clearly that Pb, As, and Se are leached in greater amounts from FA than from BA, and that more Cu and NVOC are leached from BA than from FA. The trace elements leached in the largest amounts are Pb, Zn, Cd, and Cu. The relatively large amounts of NVOC leached could also give rise to some concern and emphasize the importance of good burn-out of the bottom ash. Improved burn-out could probably reduce the amount NVOC leached by more than 75 %. A special set of leaching tests was carried out in order to determine whether PCDDs and PCDFs could be leached from the incinerator residues with seawater. No detectable amounts of these compounds were leached, and it may be concluded that polychlorinated dioxins and furans are unlikely to be problematic in relation to leaching of incinerator residues. Any PCDDs and PCDFs present can be expected to be strongly associated with particulate matter which should be prevented from escaping.

Cement stabilized ash Combined ash from the Jersey facility was stabilized with sulfate resistant low alkali cement and allowed to cure for 7 days at 40 "C and 100 percent relative humidity before being subjected to dynamic tank leaching with seawater in order to determine the rate of release of key Contaminants from the monolithic waste forms. 5.2

146 The ash which had been crushed to 10 mm was stabilized after some of the metal pieces which had been removed earlier were returned to the ash (approximately 2 percent of the total weight). The metal was reintroduced into the ash in order to simulate an ash quality which Bermuda may produce. Two mixtures were prepared: one containing 92.6 percent (w/w) of ash and 7.4 percent (w/w) of cement and one containing 87 percent (w/w) of ash and 13 percent (w/w) of cement, both containing 12 percent of water in addition to the ash and cement. The mixtures were cast in rigid plastic molds with diameters = 10.5 cm, settled by vibration, and cured. Cube shaped specimens (approximately 6 cm x 6 cm x 6 cm) were cut out of the cured test materials and used in tank leaching experiments. Dry densities of 1.80 and 1.90 g/cm3 were obtained with 7.4 and 13 percent of cement, respectively. Due to lack of material, the compressive strength could only be determined using non-standard cylinders of height = 5 cm and diameter = 10.5 cm. For these samples the unconfined compressive strength after 7 days was found to increase from 2.5 MPa to 6.0 MPa when the cement content increased from 7.4 to 13 percent. The cut out cubes were subjected to tank leaching with ocean water at 20 "C. In the tank leaching experiments, each of the monolithic waste forms was suspended in a closed seawaterfilled polypropylene tank by a nylon string. At certain time intervals (increments of 0.7, 1 , 3, 6, 11, 18, 92, and 47 days), the water (0.9 litres) was replaced by new seawater and analyzed for pH and trace elements (As, Cd, Cu, Pb, and Zn) after filtration through a 0.45 p n filter. This allows the calculation of the flux and accumulated leached amounts of the trace elements as a function of time. The initial rates of release were highest for Cu and Pb, an order of magnitude smaller for As and Cd and below the detection limit for Zn. After approximately 6 months, the rates of release had decreased by a factor of 100 to 1000 and were below the detection limit for As and Pb. The Cu flux data were comparable to Cu fluxes determined by others in similar tests on blocks of solidified combined MSWI ash containing 18 percent (wlw) cement. The leaching of organics from the stabilized ash was not measured but may safely be assumed to be very low in comparison with the leaching of organics from granular ash. 6.

TOXICITY STUDIES

The toxic effects of the first few fractions of leachate from the column leaching experiments on FA, BA, and CA from each of the two facilities with seawater were studied both on local species, on one of the most dominant species of the zooplankton, the marine copepod Acarfia fonsa, and on a standardized marine test organism, the rotifer Brachionus plicarilis. Suitable local organisms were selected for their relevance to the potential incinerator ash land reclamation sites as well as their niche in the Bermuda ecosystem. As this project was the first of its kind in Bermuda, and was the first to utilize these organisms, exhaustive tests were carried out and various experimental techniques had to be evaluated. The effects of ash leachate on the early stages of the purple urchin Lyfechinus variegafus and the limpet Siphonaria alfernafawere studied. These organisms live along the rocky shores of Bermuda and occur in close proximity to the Tynes Bay site. Both organisms showed a similar overall response to the various ash leachates with a general trend of decreased toxicity with increasing fraction number and increased dilution. Overall, the leachates produced by the Jersey

147

bottom and mixed ash proved to be the most toxic. The leachate samples from the Massachusetts ash proved to be markedly less toxic. The copper and lead contents in the Jersey leachate correlated well with toxicity. This was in sharp contrast to the results obtained at the VKI and in Bermuda using the rotifer Brachionus plicarilis. The FA leachate from both incinerators gave results similar to each other. In this case the toxicity did not correlate to the copper and lead concentrations. A study on the effects of ash leachate on primary productivity of the symbiotic algae from the sea anemone (Aiprasiapallida) was carried out. Primary productivity is the basis of the world's food chains and the importance of this type of algae in Bermuda made it a good candidate for testing as similar algae are major organic producers on coral reefs. The results were generated using 14C-labellingtechniques on algae exposed to various concentrations and types of toxicants. Jersey BA leachate had the most pronounced effect with fractions 1-3 inhibiting productivity to some extent but only at highest leachate concentrations. The combined ash leachate had the opposite effect as fractions 1 and 2 stimulated primary productivity. Fraction 1 of the FA leachate inhibited photosynthesis but only at extremely high concentrations. The Massachusetts ash leachate were even less toxic than the Jersey ash. Tests on the effects of the incinerator ash leachates on the marine rotifer Brachionus plicarilis were carried out as this is a "standardised" test for toxicity. The rotifers were hatched from cryptobiotic cysts and exposed for 24 hours to a dilution series of the first two fractions of leachate from BA, FA and CA from both facilities. No effects were seen after the standard 24 hours nor were effects seen after the test was extended for 48 hours. The copper levels were higher in the leachates than levels of copper that would normally cause an effect. It may be that the toxicity of the metal to the organisms in this case were modified by other constituents leached from the ash. The high NVOC (480 mgll) measured in the Jersey bottom ash leachate may have an important influence on the bioavailability of copper in seawater. The chronic effects of the incinerator ash leachates on the anemone Aiprusiapallida were studied over a 120 day period. Asexual bud reproduction was the most sensitive test found in all of the studies of local species where Jersey CA leachate toxicity effects were shown at concentration of leachate at 1 mlll with no significant effect below 0.25 mM. Massachusetts CA leachate showed an effect at concentrations greater that 0.25 mVI. Other parameters such as survival, growth, biochemical measurements and metal accumulation showed no effects at the concentrations tested. The acute toxic effects of the ash leachates on adults of the marine copepod Acarria fonsa were studied over periods of 24 and 48 hours. Acarria ronsu is not native to Bermuda's waters but it is a well referenced test organism. The highest mortality were found for the FA leachates, particularly the initial leachate from Jersey FA (LCIO = 5 - 20 ml/l), whereas the BA and CA leachates, especially from the Saugus facility, were less toxic (LCIO = 23 - > 100 mlll). The chronic toxic effects of the initial leachate from Jersey FA and BA on Acarria fonsa were studied as the effect on the growth (19 days) and subsequent egg production (96 hours exposure) of fertile females of Acartia tonsa (life-cycle test). In the egg production test, EC20 values of approximately 0.5 ml/l for both the FA and BA leachates were found. The corresponding EC50 values were 0.5 - 1.0 mlll for FA leachate and > 10 ml/l for BA leachate.

148

Although they are not directly comparable, the concentration levels below which no chronic effects can be expected from the most toxic leachate fractions are of the same order of magnitude (0.25 - 1.0 mlll) both for Aiptusiapallida and Acartia tonsa. In a number of the toxicity tests on local organisms, the FA leachates were found to be less toxic than the BA leachates, whereas the FA leachates were more toxic to Acarria ronsa than the BA leachates. These apparent discrepancies may have been caused by different copper complexing capacities of the seawater types used for dilution in the various tests. 7.

BASELINE STUDIES

Various studies were carried out to evaluate present environmental conditions around the two proposed disposal areas (Tynes Bay and the Civil Air Terminal at Castle Harbour). The studies have included hydrographic, chemical and biological studies of the area as well as a "groundwater" contamination survey at an existing metals dump at the Airport. The hydrographic studies have provided physical oceanographic information on the two sites for incorporation into the physical dispersion model. The hydrologic regimes of the two areas have been described using data collected from two current surveys using Anderaa RCM 7 current meters. Data for current speed, direction, tidal oscillation, temperature and salinity have been gathered at 10 minute intervals for 1-2 weeks at a time. Generally, the currents in Castle Harbour are very weak, while the current speeds at Tynes Bay are somewhat faster. The biological measurements have consisted of benthic surveys and "mussel watch" programmes to determine the baseline environmental quality of the areas. As in the toxicity tests a locally important representative, the turkey wing mussel Arca zebra, was employed. Chemical data on water and sediments have provided baseline information on the state of the environment at the present time. Macrofaunal studies: sub-tidal surveys were carried out at eight sites in each area for the macrofauna (larger organisms such as worms, clams etc.) existing on and in the sediments. The results indicate that Tynes Bay and Castle Harbour contain different macrofaunal communities. The differences arise primarily from environmental conditions, and reflect the differing sediment characteristic of both areas. There is a significant seasonal change in species abundance (numbers of organisms) at Castle Harbour between winter and summer. There were no significant changes at Tynes Bay. There was a 30% turnover in species composition (types of organisms) at both sites which may indicate a seasonal cycle of species occurrence. Conditions should be continually assessed in the monitoring programme in order to determine future changes. Macrofloral studies: phototransects were collected for the large algae and seagrasses at all eight of the sampling sites at Tynes Bay during the winter of 1989 and the summer of 1990. Results indicate a great deal of variability between the two sampling periods. This variation may be due to seasonal differences but may also be due to continual changes within these populations. Further surveys should be carried out over time to establish firm baselines so that the an-

149

thropogenic effects can be distinguished from natural variations. The macroalgae Penicillus sp. in particular may be a good indicator organism for the determination of thermal effects in the Tynes Bay area. Meiofaunal studies: were also carried out in both areas. Meiofauna (microscopic organisms that live in sand) were collected and sorted, but were archived for later use in the monitoring programme. Rocky shore assessments were carried out at Tynes Bay as intertidal communities are exposed to contaminants from the island as well as the sea. These surveys consisted of quadrate measurements of limpets, barnacles and mussels on the rocky area of Tynes Bay. Surveys were carried out on a seasonal basis. In Bermuda there are periodic, naturally occurring die-backs of these communities which should be continually monitored so that the correct cause of these changes can be assessed. Baseline chemical studies have been carried out at eight field stations at each site. Water samples have been taken for pH, salinity and the trace metals. Concentrations of constituents in the water samples taken were of the same order as a BBSR study conducted in 1984. Sediment samples at both sites were analyzed for grain size distribution, and trace metal content. Generally, the Castle Harbour sediments are finer than those from Tynes Bay, which would be expected for this lower energy environment. These fine, silty sediments contain higher concentrations of trace metals. The closer to the airport metal dump, the higher are the concentrations of copper, zinc, lead, iron and cadmium. For the most part the concentrations decrease with increasing distance from the source. Bioaccumulation studies of trace metals by the mussel, Arcu zebra have been carried out during two periods, winter and summer, at both sites. The mussels were analyzed after one and two months' deployment in the field and were used as "sentinel" organisms. In contrast to the findings for the sediments, there were no significant gradients of trace elements between the mussels placed at different distances from the metals dump at Castle Harbour, although the highest contents of Cd, Cu, Fe, Pb, and Zn were found in mussels adjacent to and SW of the dump, particularly during the winter period. However, the concentration differences were small, and there were no gradients for Cr and Ni. The general level of trace elements in the mussels were comparable at the two sites. The use of mussels as sentinel organisms should be considered as part of the monitoring phase. In order to investigate the contamination potential of the existing metals dump at the Civil Air Terminal at Castle Harbour, three "groundwater" sampling wells were installed in the site. Chemical analysis of samples of the groundwater or leachate showed a minor contamination with organics. The concentration levels of cadmium, copper, lead, and nickel were approximately one order of magnitude higher in the water inside the site than in the surrounding Castle Harbour. Chromium concentrations were of the same order of magnitude inside and outside the site.

150

8.

ACCEPTANCE CRITERIA

Since Bermuda has no guidelines which define specific acceptance criteria for the environmental impact of a disposal site, the study has included the development of a set of proposed acceptance criteria. The overall purpose of developing acceptance criteria for the emission of contaminants into a water body is to protect the ecosystem (living pelagic or benthic organisms and the sediment) as well as humans from bioaccumulation and toxic effects. Only impacts on organisms in the water body are considered in this study. Various methods of defining and calculating acceptance criteria for single substances in the water body, including the methods developed by the U.S. EPA [9] and the OECD [lo], have been evaluated. The acceptance criteria suggested for Bermuda are based on modified U.S. EPA Water Quality Criteria for saltwater (all the modifications represent increased restrictions). It is suggested to use these single substances criteria in conjunction with another set of criteria based on the actually observed toxicities of the most toxic fractions of ash leachate tested in this study on local marine organisms. The suggested single substance acceptance criteria are expressed as two sets of maximum resulting ambient water concentrations of relevant trace elements (As, Cd, Cr, Cu, Pb, Hg, Ni, and Se) at Tynes Bay and Castle Harbour. One of the sets of criteria should ensure that no acute toxic effects occur, the other that no chronic toxic effects occur. It is suggested that the maximum calculated mean concentration of each trace element in the mixing zone should not cause any chronic effects, and the maximum concentration in the leachate at the point where it penetrates the bottom sediment should not cause acute effects. The mixing zone is suggested as the minimum compartment size used in the dilution model (250 m x 250 m). Using the results of the dilution modelling, the acceptance criteria based on chronic effects may be used to calculate the site specific rates of release of contaminants from the disposal sites at either location which result in ambient water concentrations not exceeding the criteria concentrations. The rates of release corresponding to the acceptance criteria in the mixing zones at each site are called acceptable loads (AL). Levels of e.g. lo%, 50% or 100% of the calculated acceptable loads may be chosen. At the 10% level, the calculated acceptable rates of release of Cd, Cu, Hg, and Pb are 0.07,0.34, 0.02 and 4.7 kglday, respectively, for Tynes Bay and approximately half of that at Castle Harbour, thus reflecting the less favourable dilution conditions at Castle Harbour. There may be reasons other than just specific toxic effects to reduce the release of Pb to less than the figure shown above (e.g. considerations concerning accumulation in sediments and biomass and subsequent possible effects on human health as well as the ecosystem). The other type of suggested acceptance criteria which is based on the observed toxic effects of the initial ash leachates indicate that minimum resulting leachate concentrations of 10 - 23 ml/l (corresponding to a dilution of 44 - 100 times) are required to avoid acute effects and 0.16 - 0.4 mlll (corresponding to a dilution of 2500 - 6300 times) are required to avoid chronic effects. These criteria relate to the initial leachate from granular ash. The leachate from cement stabilized ash will be much less concentrated and much less toxic at any time.

151

9.

MODELLING OF EMISSIONS

Based on the results of the ash leaching tests as well as meteorological, hydrological, and geological data and a number of assumptions and preconditions concerning the design and layout of the sites, the emission of trace elements (Pb, Cd, and Cu for granular ash and As, Cd, Cu, Pb, and Zn for cement stabilized ash) have been modelled for six disposal scenarios: Disposal of 1 m3 blocks of CA stabilized with 13 % cement directly into the sea at Tynes Bay (Scenario 1) and Castle Harbour (Scenario 4). Disposal of granular CA by backtipping into 15 m x 15 m compartments contained by sheetpiles rammed into the seabed at Tynes Bay (Scenario 2) and Castle Harbour (Scenario 5). Combined solution. In the sheetpile compartments, blocks of CA stabilized with 13% cement are placed below sea level and granular CA is placed above sea level at Tynes Bay (Scenario 3) and Castle Harbour (Scenario 6). In order to obtain an adequate description of the rate of release of Cd and Pb from the granular ash placed below sea level by backtipping, it was necessary to supplement the experimental data with calculations using the hydrogeochemical equilibrium and speciation model MINTEQ2A.

For each scenario, the rates of emission of the above mentioned trace elements were then calculated, first during a period of 10 years of disposal of an annual amount of 16,000 tonnes of combined ash, and subsequently for 20 - 30 years following that. The maximum daily emissions of each trace elements were calculated for each scenario and compared (see table 6). The lowest maximum daily emissions will occur from Scenarios 1 and 4 (disposal of cement stabilized ash blocks): 0.01 glday of Cd, 4.9 g/day of Cu, and 0.54 g/day of Pb at both locations. The highest maximum daily emissions will occur from Scenarios 2 and 5 (disposal of granular ash): 6.2 glday of Cd, 42 g/day of Cu, and 23 g/day of Pb at Tynes Bay and slightly less at Castle Harbour. The maximum daily emissions of contaminants from the combined solution (Scenarios 3 and 6) are in between those. The model predicts that in most cases the maximum daily emissions will occur at the time of maximum ash deposition, i.e. at the end of the 10 year disposal period (in a few cases later than that). After this, the emissions keep decreasing with time to a low level. This is due to the fact that the rate of release of most contaminants from the ash decreases as the leaching process progresses but it also reflects the method and rate of disposal chosen. 10. MODELLING OF DILUTION Mathematical hydrodynamic models (two-dimensional) have been set up to describe the current conditions in the marine areas at the two designated potential disposal sites. Using the current data collected, simulations have been performed with a transport-dispersion model coupled to a hydrodynamic model in order to investigate the spreading of dissolved contaminant emissions from the potential sites in the surrounding waters. For the purpose of calculations, the model uses a 250 m by 250 m grid. Mean excess concentration fields for the simulated periods have been computed and mapped for each location.

152 Table 6 Calculated maximum daily emissions of selected trace elements.

Scenario 1 Scenario 2 Scenario 3

1

Castle Harbour

I

Scenario 4 Scenario 5 Scenario 6

0.16

0.16

0.01 6.2 0.1

4.9 42 6.9

0.54 23 1.6

2.8

0.01 5.4 0.07

4.9 31 6.7

0.54 19 1.3

2.8

1.8

2.4

For the Tynes Bay location a reasonable agreement between measured and calculated current velocities was obtained. Two situations were considered: The first was dominated by moderate northerly wind and the second by moderate westerly wind. In the first case the contaminants were found to spread primarily towards the northeast along the coast. In the second situation the contaminants would spread towards the northwest, the plume keeping clear of the coast. In both cases a dilution of 10 times that in the source compartment closest to the site were reached at a distance of approximately 3500 m from the site. Generally, current velocities are low in Tynes Bay due to the sheltered and shallow nature of the area. Thus horizontal mixing is slow despite slightly favourable wind conditions.

For the Castle Harbour location, the recorded current speeds are extremely low, and no correlation to wind data is apparent. Consequently, the model calculations failed to reproduce the recorded currents. The modelled current velocities are very low, though, and indicate that the emitted contaminants will spread to all of Castle Harbour and most of Ferry Reach at concentrations ranging down to one tenth of that in the source compartment of the model. Half the amount of contaminants discharged will be flushed to the North Lagoon via Ferry Reach. The model calculations - however inadequate - along with other evidence indicate that horizontal dispersion at Castle Harbour is slower than in Tynes Bay. Recordings and modelling results indicate that the wind may induce vertical circulations which is the cause of the partial failure of the attempt to reproduce the conditions in Castle Harbour using a two-dimensional model. In terms of dilution potential Tynes Bay is the better of the two disposal sites considered. The hydraulic measurements indicate that the dilution potentials at neither of the two locations, Castle Harbour and Tynes Bay, are particularly favourable. However, a poor dilution potential does not necessarily disqualify the sites, it merely means that in order to comply with the suggested acceptance criteria, the emissions of contaminants will have to be lower than they would have to be if the dilution had been better. The initial dilution of the discharged contaminants in the source compartments adjacent to either site becomes important. The volume of seawater in this Compartment is 340,000 m3 at Tynes Bay and 755,000 m3 at Castle Harbour.

153 11.

IMPACT ASSESSMENT

The calculated emission scenarios indicate that disposal of cement stabilized combined ash may reduce the maximum emissions (glday) of key contarninants by a factor of 9 (Cu), 43 (Pb), and 620 (Cd) at Tynes Bay and 6 (Cu),35 (Pb), and 540 (Cd) at Castle Harbour as compared to disposal of granular combined ash. If the environmental impacts of the various disposal options are to be evaluated using the acceptable load (AL) values developed in this study, it must be decided which level of security should be used in relation to the water quality criteria for single elements based on chronic effects (i.e. 10%AL, 50% AL or 100% AL). These acceptable loads are expressed as emission values (kglday or g/day) and apply to a specified volume of water (250 m x 250 m x the average depth), corresponding to a mixing zone (the smallest volume of resolution considered in the dilution model). The final decision of which set of criteria should apply is a matter for local consideration. In the following, only the most restrictive of the above mentioned emission criteria (10% AL) are considered. In table 7, the calculated average excess concentrations of Cd, Cu, and Pb (and for the cement block scenarios 1 and 4 also As and Zn) in the water in the innermost compartment (the source compartment covering 250 m x 250 m, closest to the site) resulting from the maximum daily emissions are calculated and compared to the existing average background concentrations (data exist only for Cd, Cu and Pb) and the acceptance criteria (AC). None of the predicted average excess concentrations of trace elements for any of the scenarios at Tynes Bay or Castle Harbour exceed 5 % of the existing average background concentrations (most of them are much smaller), and none of the existing average background concentrations exceed 30 % of the acceptance criteria level. A comparison of the predicted maximum daily emissions of selected trace elements with the acceptable load criteria based on chronic effects of single elements (AL and 10% AL) is presented in table 8. The results indicate that the maximum emissions of trace elements for all of the scenarios will be at least 5 times lower than the most restrictive of the criteria (10% AL). The emission of Cd in scenario 2, Tynes Bay, and scenario 5, Castle Harbour, come closest to the criteria values (10% and 20 %, respectively, of the 10% AL val

It can be calculated that dilutions of 40-100 times and 2700-6300 times of the strongest leachates produced in the laboratory tests are necessary to avoid acute and chronic toxic effects, respectively. Using the dilution model, it can be calculated that the average dilution of the leachate produced in scenarios 2 and 5 (the most critical scenarios) will be approximately 160,000 times (Tynes Bay) and 84,000 (Castle Harbour) within an area of 250 m x 250 m adjacent to the disposal site. No chronic effects should therefore occur outside this area even if the contaminants are not totally evenly distributed. Due to the chosen grid size (250 m by 250 m) used in the mathematical modelling of the dilutions at Tynes Bay and Castle Harbour, only the average resulting contaminant concentrations inside the volume of water corresponding to the source compartment adjacent to the disposal sites can be estimated.

154

Table 7 Calculated resulting maximum excess concentrations of selected trace elements in the innermost compartment of the model (250 m x 250 m) compared to existing average background concentrations at both sites and to acceptance criteria (AC) in terms of trace element concentrations in the water bodies.

SCENARIO

ELEMENT

AVERAGE BACKGROUND CONC.

Pull

CALCULATED EXCESS CONC. P8/ I

ACCEPTANCE CRITERIA (AC)

1(9/1

T m e s Bay

0.000018 0.000001 0.00057 0.000063 0.00033

5 0.1 1 .o 5.6

0.2 < 0.07

0.00073 0.0049 0.0027

0.1 1 .o 5.6

0.03 0.2 < 0.07

0.00001 1 0.00081 0.00019

0.1 1 .o 5.6

0.03 0.2 < 0.07

0.000041 0.000002 0.0013 0.00014 0.00072

5 0.1 1 .o 5.6

1 1 1 1 1

As Cd cu Pb 2n

Scenario 2 scenario 2 Scenario 2

Cd

0.03

cu

Scenario Scenario Scenario Scenario Scenario

Scenario 3 scenario 3 Scenario 3

Pb Cd

cu Pb

0.03 0 .2 < 0.07

C a s t l e Harbour

4 4 4 4 4

AS

Scenario 5 Scenario 5 Scenario 5

Cd

0.03

cu

0.2 < 0.07

0.0014 0.0079 0.0049

0.1 1 .o 5.6

scenario 6 Scenario 6 Scenario 6

Cd

0.03 0.2 < 0.07

0.00001 7 0.0017 0.00033

0.1 1.0 5.6

Scenario Scenario Scenario Scenario scenario

Cd

cu Pb 2n

Pb

cu Pb

Therefore, possible areas or spots within that compartment with concentrations exceeding the acute and chronic toxicity levels cannot be defined. Consequently, with the mathematical model used it is not possible to predict whether or not the emissions may cause an acute or chronic toxicity effect in a limited area (very) close to the disposal site (e.g. within a distance of a few meters from the site). This will depend very much on the disposal scenario chosen (disposal of cement stabilized material causing the least effects) and on the actual design of the disposal site which may have great influence on the initial dilution. In conclusion it may therefore be stated that, given the uncertainties described and the imperfections of the techniques employed, all of the three disposal options at each of the two site locations considered appear to comply with the proposed acceptable load (10% AL) outside a 250 m by 250 m compartment adjacent to the sites. The size of this compartment is determined by the resolution of the model and it is most likely that the area within which there is a risk of exceeding the acceptance criteria in reality will be much smaller. In fact, the data indicate that for the stabilized ash scenarios (1 and 4), the body of water constituting the innermost compartment could probably be reduced to less than 2 % of its present size and still be in compliance with the suggested criteria. For the granular ash scenarios (2 and 5), a similar

reduction to 10 and 20 % of the present size of the innermost compartment appears possible without the 10 % AL being exceeded. Table 8 Calculated emissions of selected trace elements compared to acceptable loads (AL) for each scenario.

ELEMENT

SCENARIO

PREDICTED MAX I MUM EM1SSlON (PME) gfday

ACCEPTABLE LOAD (AL)

SUGGESTED

PME/lO% A t

LIMIT 10% AL

g f day

gf day

%

Tvnes Bay

1 1 1 1 1

AS

Cd cu Pb Zn

0.16 0.01 4.9 0.54 2.8

600 6800 47000

60 680 4700

0.018 0.72 0.011

Scenario 2 Scenario 2 Scenario 2

Cd cu Pb

6.2 42 23

600 6800 47000

60 680 4700

10 6.2 0.49

Scenario 3 Scenario 3 Scenario 3

Cd

0.1 6.9 1.6

600 6800 47000

60 680 4700

0.17 1 .o 0.034

0.16 0.01 4.9 0.54 2.8

270 3100 22000

27 310 2200

1.6 0.025

Scenario Scenario Scenario Scenario Scenario

cu Pb

Castle Harbour

4 4 4 4 4

AS

Scenario 5 Scenario 5 Scenario 5

Cd

5.4

cu Pb

31 19

270 3100 22000

27 310 2200

20 9.9 0.88

Scenario 6 Scenario 6 Scenario 6

Cd cu Pb

0.07 6.7 1.3

270 3100 22000

27 310 2200

0.26 2.1 0.060

Scenario Scenario Scenario Scenario Scenario

Cd cu Pb Zn

Acceptable load (AL):

0.040

Calculated emission which u i l l b r i n g the average concentration o f t r a c e elements i n the uater i n the innermost compartment o f the model (250 m x 250 m) t o the acceptance Level.

10% AL:

10% o f the above mentioned emission (suggested c r i t e r i a ) .

PME/lOX AL:

The Pr edicted naximm m i s s i o n o f t r a c e elements r e l a t i v e t o the suggested acceptable Load value, 10% A t , expressed i n percentages. A value above 100 % indicates t h a t the chosen c r i t e r i a value has been exceeded.

The suggested acceptance criteria are based on toxicity data and are aimed primarily at the protection of fish, shellfish and wildlife in the water body. Other considerations may lead to more restrictive criteria e.g. concerning the emission of Pb. This should not be prohibitive in relation to the ash disposal since the predicted emissions of Pb in no case exceed 1 % of the most restrictive criteria (10%AL). The proposed supplementary requirements that ash leachate having a composition corresponding to the strongest concentrations produced in the laboratory leaching tests should be diluted approximately 100 times to avoid acute toxic effect and

156

approximately 6300 times to avoid chronic effects are based on the results of the bioassays performed on local marine organisms. The criteria and requirements have been conservatively set with respect to toxicity (and existing background concentrations). They do not, however, directly consider potential effects related to long term fate and accumulation of contaminants. The monitoring programme mentioned below should include activities addressing this issue. From an environmental point of view, the most favourable disposal option considered is scenario 1 (disposal of cement stabilized combined ash blocks at Tynes Bay) followed by scenario 4 (disposal of cement stabilized combined ash blocks at Castle Harbour). The least favourable solutions are scenarios 2 and 5 (disposal of granular combined ash by backtipping at either site). It should be noted that a substantial amount of organic material (NVOC) was leached from the granular ash. This could cause some concern and could probably be mitigated considerably in the case of Bermuda if care is taken to ensure a good burnout in the incinerator. Mercury which is particularly undesirable in the environment is leached from the granular ash in minor but measurable quantities, and objects containing mercury (e.g. small batteries and thermometers) should be prevented from entering the feed stream to the incinerator to the greatest extent possible. It should also be noted that there is an existing metals dump at one of the potential locations of the future incinerator ash disposal sites, the Civil Air Terminal at Castle Harbour. This study has shown that the "groundwater" or leachate within the dumpsite is slightly contaminated with organic compounds and trace elementsheavy metals. The bioaccumulation studies indicate that the dumpsite is already having a slight impact on the accumulation of trace elements, particularly lead in mussels deployed in Castle Harbour near the site. The predictions are based on the assumption that good engineering practice prevents the escape of particulate matter from the disposal site. The calculations pertaining to the cement stabilized ash disposal scenarios are based on the assumption that the civil engineering capability to produce mechanically durable 1 m3 cement stabilized ash blocks is available.

12. SAFETY MARGINS AND UNCERTAINTIES The approach of this study has been to attempt to simulate and predict the release and subsequent environmental impact of contaminants from various MSWI ash disposal scenarios. The basic idea is that whereas the release of contaminants cannot be totally prevented, the release may indeed be controlled through the application of appropriate precautions (e.g. cement stabilization) and kept at a rate which is acceptable to the environment. Since environmental acceptability is not a universally well defined concept, the study has included a discussion of acceptability criteria. An actual set of acceptance criteria for Bermuda has been proposed, and the disposal scenarios considered have been evaluated in relation to these criteria. As a consequence of the choice of methodology the conclusions of the study are based on a series of assumptions, choices, theoretical considerations, model calculations, and results of practical tests and field investigations. This adds an element of uncertainty to the study and the results. Since the overall objective has been to achieve an environmentally acceptable and sustainable solution, it has been attempted to adopt a conservative approach in most cases where

157

a choice has been necessary. This means that safety margins have been included at several points of the study. In order to facilitate an evaluation of the conclusions and results, this chapter presents an overview of the major choices made, the major points of uncertainty of the study, and the major safety margins included. In an attempt to further illustrate and somehow quantify the degree of safetyhncertainty associated with the conclusions of the study, the key operationsldecisions have been identified and evaluated for each of the 6 scenarios considered. Each of these key steps of the project has been assigned a safetyhncertainty factor. A factor of 1 means that the operation or decisiodestimation in question is considered realistic and is not expected to contribute any significant degree of uncertainty (nor is it expected to provide any additional safety margin) to the study. A factor higher than unity designates that the operation in question is believed to be on the safe side, i.e. the number is indicative of a certain margin of safety. The size of the factor represents a (rough) quantitative evaluation of the relative degree of exaggeration or conservatism applied at this point of the study. A factor smaller than unity indicates that the operation in question may be associated with a certain degree of uncertainty. The larger the uncertainty is believed to be, the smaller will the factor be. In order to obtain an overall evaluation of the safety marginhncertainty of the study, all the individual factors, including the result of the environmental impact assessment, i.e. the ratio between the suggested acceptable load and the calculated emissions, are multiplied with each other for each scenario. Table 9 summarizes all the individual safetyhncertainty factors and presents the resulting products for each scenario. This exercise exhibits a strong element of subjectivity but it does allow at least a comparison of the degree of safety or the safety margin associated with each of the scenarios. The higher the resulting product, the "safer" are the conclusions in question (from an environmental point of view). If the results are evaluated in absolute terms, a product of 1 indicates a result which is realistic and satisfactory - provided all important (factors) have been accounted for. It is therefore more comfortable to have a resulting product higher than 1 since this would provide some insurance against errors and uncertainty factors which might have been overestimated or overlooked. A resulting product < 1 may be acceptable - it is just associated with a degree of uncertainty which is higher, the smaller the product is. A resulting product of unity or lower could possibly be increased by looking more closely at (and possibly by changing) one or more of the individual steps involved in the procedure and thereby perhaps reduce the uncertainty and increase the size of the factor(s). Using the resulting overall safety factors calculated in table 9, the study of the various scenarios may be ranked in order of decreasing safety or increasing uncertainty: Rank

Option

1

Scenario 1 Scenario 4 Scenario 3 Scenario 6 Scenario 2 Scenario 5

2 3 4

5 6

Resulting safety factor (stabilized ash, Tynes Bay) (stabilized ash, Castle Harbour) (combined solution, Tynes Bay) (combined solution, Castle Harbour) (granular ash, Tynes Bay) (granular ash, Castle Harbour)

325 150 10 4.8

2 1

Table 9

Overview of individual safety/uncertainty factors and resulting products for each diposal scenario.

Safetv or risk factor for each d m s a l scenario Tynes Bay Castle Harbour 1 2 3 4 5 6

KEY OPERATIONS/DECISIONSOF THE STUDY A. Using Jersey & Saugus ash (instead of future Bermuda ash)

1

1

1

1

1

1

B. Selecting only key contaminants for leachate analysis and subsequent evaluation

0.5

0.5

0.5

0.5

0.5

0.5

C. Using accelerated laboratory data instead of actually observed full scale data (not available)

0.5

0.1

0.1

0.5

0.1

0.1

D. Using only the most contaminated initial leachate fmm the column tests for the bioassays

100

20

20

100

20

20

E. Selecting specific organisms and specific test methods for the bioassays

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

G. Lowering the suggested acceptable load to 10 96 of the calculated value

10

10

10

10

10

10

H. Risk of increased contaminant release due to cracking of stabilized blocks

F. Using modified US EPA Water Quality Criteria which only relate to toxicity to organisms living in the water body (but using the criteria for chronic rather than acute toxicity)

0.1

1

0.1

0.1

1

0.1

1.

Safety margin due to the use of constant flux in the calculation of the emission from blocks

10

1

10

10

1

10

I.

Using maximum daily contaminant emissions rather than averaged values in the impact assessment

1

2

1

1

2

1

K. Modelling of dilution

1

1

1

1

1

1

L. The result of the environmental impact assessment (suggested acceptable load/calculated emissions)

130

10

100

60

5

47

A-L The overall safety marein (the Droduct of all safetvlrisk factors) rvnes Bay Scenario 1: Scenario 2: Scenario 3:

Disposal of blocks of cement stabilized combined ash Disposal of untreated (granular) combined ash Disposal of stabilized ash blocks below sea level and untreated ash above sea level

4 R

Castle Harbour Scenario 4: Disposal of blocks of cement stabilized combined ash Scenario 5 : Disposal of untreated (granular) combined ash Scenario 6: Disposal of stabilized ash blocks below sea level and untreated ash above sea level

159

The above ranking is identical to the ranking according to the results of the environmental impact assessment alone (step L).

13. CONCLUSIONS A methodology for assessment of the potential environmental impact of marine land reclamation with MSWI residues has been developed and demonstrated in a study in Bermuda. For various land reclamation scenarios the rate of release of potentially harmful components into the surrounding sea has been estimated by combining the results of laboratory leaching tests on granular and cement stabilized MSWI ash with hydraulic models describing the flow of water through a site. Baseline field studies have been performed to describe the ambient marine environment near the proposed land reclamation sites. Bioaccumulation studies and ecotoxicological tests have been performed on local marine organisms. A set of acceptance criteria for discharge of trace elements into the sea has been developed and proposed for Bermuda. The dilution of the released trace elements in the marine waters surrounding the sites has been predicted using a dynamic mathematical simulation model, and the environmental impact of each scenario has been assessed. The estimated environmental impact of land reclamation with granular combined ash was not surprisingly substantially higher than the estimated impact of land reclamation with cement stabilized combined ash.

Even though the assessment procedure described in this paper is based on a substantial amount of practical experience and dedicated experimental work and modelling, it is still associated with a significant degree of uncertainty. In order to reduce this uncertainty and improve the assessment ability, it is important to monitor new land reclamation sites closely and to review the assessment procedure when actual full scale data become available.

14.

ACKNOWLEDGEMENT

The work described in this paper was funded by the Ministry of Works and Engineering, Hamilton, Bermuda. The views expressed are those of the authors and does not necessarily express the views of the Ministry.

REFERENCES Hjelmar, 0. (1987): Leachate from incinerator ash disposal sites. In: Proceedings of the International Conference on Municipal Waste Incineration, NITEP, Montreal, Canada, October

1-2,1987. Hjelmar, 0. (1989):Characterization of Leachate from Landfilled MSWI Ash. In: Proceedings of the International Conference on Municipal Waste Combustion, Hollywood, Florida, April 1 1-14,

1989. Hjelmar, 0. (1991):Field Studies of Leachates from Landfilled Combustion Residues", Presented at WASCON '91,Environmental Implications of Construction with Waste Materials, Maastricht, The Netherlands, November 10-14,1991.

Hjelmar 0. (1992): Municipal Solid Waste Incinerator Flue Gas Cleaning in Denmark: Residue Properties and Residue Management Options, in Proceedings of ISWA Specialized Conference on Incineration and Biological Waste Treatment, Amsterdam, The Netherlands, September 1-3, 1992. Hjelmar, 0. (1993): Leachate Management at Incinerator Residual Landfills. In: Proceedings of the 9th International Conference: Incineration: The Issues; Cork, Ireland, November 4-5, 1993 (in press). Water Quality Institute: Assessment of the Environmental Impact of Incinerator Ash Disposal in Bermuda. Final Report. Prepared for Ministry of Works and Engineering, Hamilton, Bermuda. Hersholm, Denmark, 1993. Bermuda Biological station for Research, Inc.: Marine Environmental studies to Determine the Impact of the Mass Burn incinerator Proposed for Tynes Bay, Bermuda. Report prepared for Ministry of Works and Engineering, Hamilton, Bermuda. Ferry Reach, Bermuda, 1991. Danish Hydraulic Institute: Bermuda, Ash Disposal. Hydraulic Studies. Hersholm, Denmark, 1989. Jickells, T.D and A.H. Knap (1984):The distribution and Geochemistry of some Trace Metals in the Bermuda Coastal Environment. Estuarine, Coastal and Shelf Science (18), pp 245-262. US-EPA (1984): Estimating "Concern Levels" for Concentrations of Chemical Substances in the Environment. Environmental Effects Branch. Health and Environmental Review Division. Norton, S., M. McVey, J. Colt, J. Durda and R. Hegner (1988): Review of Ecological Risk Assessment Methods. US-EPA, Oftice of Policy, Planning and Evaluation. EPA/230- 10-88-041.

Environmental Aspects of Conshrction with Waste Materials JJ-IM. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) 01994 Elsevier Science B.V. All rights reserved.

161

Quality Assessment of Granular Combustion Residues by a Standard Column Test: Prediction versus Reality M. Janssen-JurkoviEovaa, G.G. Hollmanb, M.M. Nass' and R.D. Schuilingb "KEMA Environmental Services, KEMA, P.O. Box 9035, 6800 ET Amhem, The Netherlands bDepartmentof Geochemistry, Institute of Earth Sciences, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands 'Department of Soil Science and Plant Nutrition, Wageningen Agricultural University, P.O. Box 8005, 6700 EC Wageningen, The Netherlands

Abstract The laboratory leachability tests introduced by the Dutch Standardization Institute (NNI) as draft standards NEN 7341 and 7343 for the analysis of the leaching behaviour of granular materials and/or fly ashes, will play an important role in the near future. Particularly the column test will play a decisive role in the Decree on Building Materials currently in preparation, concerning whether or not to permit the application of these materials in constructional works. In view of the role this test will play, it is important to determine the degree of correspondence between leaching as 'simulated' in the column test and leaching occurring in reality. However, the principles underlying the present column test are not included in the introductory text to draft standard NEN 7343. This lack of information prevents us from understanding exactly which practical conditions are being simulated in this test. The results presented here show that there is a great discrepancy between the leaching of elements in the column test and in a natural environment. Hence, it is necessary first to translate the results obtained in the column test into realistic field conditions. This article will discuss one option by which this could be accomplished. The results also demonstrate that the current availability test (NEN 7341) is not adequate to determine the maximum amount of elements available from a certain material for leaching.

162

1. INTRODUCTION

The Decree on Building Materials currently in preparation requires that all primary and secondary building materials be provided with a quality statement before admitting them to the building market. For most secondary building materials this means that their leaching characteristics should be determined according NEN 7343. The column test described in NEN 7343 is based on the idea that this test simulates leaching of granular materials over a medium-range period of about 30 years, while the cascade test simulates leaching of these materials over a period of several hundred years. It should be possible by means of the so-called availability test (NEN 7341) to determine under natural conditions the maximum amount of elements available from a building material for leaching in the very long term under extreme conditions. The development of standard leachability tests has taken over ten years of efforts from many institutes. These efforts have resulted in the development of tests that are highly reproducible. In view of the ‘simulation function’ that was assigned to the column test in a later stage and the role this test will have to play in the decision whether or not to admit e.g. secondary granular materials to the building market, it is however of great importance to determine: - whether this test is really adequate to simulate leaching over a certain period of time, and moreover - how the test conditions selected affect the intended simulation, if one is to establish whether the simulating (timescale) function ascribed to this test has in fact a realistic or merely an arbitrary value. This article will discuss a suitable test method to determine this. Furthermore, this report will present fairly recent findings resulting from a comparison of leaching values obtained in standard leachability tests with those obtained under field conditions of pulverized fly ash from a power station.

2.TESTlNG OF STANDARD LEACHABILITY TESTS ASCRIBED TO THESE TESTS

FOR THE VALUE

2.1 Full Standard Leachability Test The full standard leachability test comprises a column test, a cascade test and an availability test. In the column test demineralized water (pH4) passes in upward direction through a column containing fly ash. The percolate is collected in seven fractions: after L/S (i.e. Liquid/Solid) 0.1; 0.2; 0.3; 0.5;1.0;5.0;and 10.0. Based on the sum of the fractions an estimate is made of the total amount of elements leached from the fly ash tested in its natural environment over a medium-range period of about 30

163

years. In the cascade test the material is extracted five times at an L/S of 20 in acidified demineralized water (pH4) for a maximum period of 23 hours. The test serves to predict long-term leaching over a period of several hundred years. In the availability test the fly ash to be tested is extracted in demineralized water (L/S lOO),first at a constant pH of 7 and the second time at a constant pH of 4, each time for a period of three hours. The availability test serves to determine the maximum fraction of an element available for leaching in the natural environment.

2.2 The lest Procedure Table 1 lists the total amounts of elements in the fly ash used in the test procedure. Figure 1 represents the procedure for testing the influence of the standard leachability tests on element immobilization and/or mobilization in the granular materials subjected to these tests. This figure demonstrates that the fly ash was subjected first to the standard column test and subsequently to the cascade test.

Table 1 Total amounts of elements in the flv ash sample examined. Amounts of elements in mg/kg As

Mo

Se

27.7

9.3

16.1

Ba 2,166

Fe 61,693

v 332

The availability of elements was determined at the start of the test, after the column test and after the cascade test. Element immobilization in the column test was calculated according to the following equation:

in which ALl = amount immobilized during the column test co = available before column test Abefore = leaching during column test, and L o = availability after column test. Aafter w

164

Q fly ash

availability test

column test

availability test

el-El

cascade test

availability test

Figure 1. Outline for research on the influence of standard leaching tests on the (im)rnobilization of elements.

To determine the influence of the cascade test on the material already subjected to the column test, equation (1) was adapted as follows: AL =

kfter w

L a - Aafter ca

(2)

in which amount immobilized during the cascade test available after column test (i.e. before cascade test) leaching during cascade test, and = availability after cascade test.

Alca

= = =

Aafler

L, Aafter cB

The percentage of element immobilization during the column test was calculated using:

%Aim

=

k x p e c t e d after w

- hetermined after w

-%elore

Wl100

(3)

165

To calculate the immobilization percentage during the cascade test, equation (3) was adapted as follows:

%Aim =

Aexpected afler ca

- betermined afler ca

(4)

-Aafler cn/100 in which Aexmcted afler ca

=

betermined afler w

(5)

-

Findings of the Test Procedure Table 2 contains the data obtained by the procedure represented in Figure 1.

2.3

Table 2 Available and/or leached amounts of elements in the standard leachabilitv tests. type of test in consecutive order

leached and/or available in pg/kg As

Mo

Se

Ba

Fe

v

availability in material at start of test

18,350 10,600 10,200 column test

10

60,700

1,350

5,020

590

9,750

200

76,840 250

"availability after column test" -expected"

18,340

5,580

9,610

50,950

1,150

76,590

-determined

1,720

5,160

7,220 164,340

2,640

19,260

cascade test

420

1,240

6,030

42,160

8,450

6,590

"availability after cascade test" -expected*)

1,300

3,920

1,190 122,180

0

12,670

-determined

7,370

3,440

5,040 260,200

9,760

30,440

as might be expected on the basis of the leaching values found in the column test *) on the basis of kfler cn - L, Table 3 shows the influence of the standard column and cascade tests on element immobilization and/or mobilization calculated with equations (1)and (2). Table 4 gives the percentage values of the amounts of immobilized elements.

166

Table 3 Element immobilization (-) and/or mobilization (+) during the standard leachability tests in pg/kg. tvDe of test

As

Mo

Se

Ba

Fe

V ~~~

’)

column

- 16,620

cascade”

+ 6.070

- 420 - 480

- 2,390

+ 113,390 + 1,490

+ 3,850 +

138,020

- 57,330

+ 9.760 + 17.770

in respect of the column test

Table 4 Element immobilization (-) and/or mobilization (+) during the standard leachability tests in %. type of test column cascade‘’ ’)

As

Mo

Se

- 90

-4

- 23

+ 353

-9

+ 53

+

Ba

Fe

V

187

+ 110 + 370

- 75

+ 84

+ 92

in respect of the column test

Discussion of the Findings Obtained from the Test Procedures 2.4 On the basis of the leaching tolerated by the Decree on Building Materials for Soil Protection, the application of a (secondary) building material as examined in the present study would not be allowed (without any restrictions). The maximum permissible leaching values for Mo and Se would be exceeded. It is the question though, also with a view to the significance of such an observation, if this application restriction (or rejection) would indeed be justified. In other words, a decision on this matter requires that the time-simulating function of the standard leachability tests, and especially that of the column test, should be motivated. Element Immobilization during the Column Test and in Practice Table 3 shows that immobilization of As, V and, to a lesser degree, Se already occurred during the 3-week column test. This means that availability of these elements after the column test is lower than might be expected on the basis of the standard leachability tests. For As as much as 90% of the total available amount is immobilized in the column test and for V this is 75%. The element Se appears to have been immobilized for 23% only, while Mo has hardly been immobilized at all (Table 4). From Figure 2,which represents a comparison between leaching of Mo in a field lysimeter and in the column test [I], it can be derived that immobilization of Mo under field conditions already occurs within a short period. Figure 2 shows that

167

exposure to natural weathering conditions results in a decrease of the cumulative amount of Mo leached in the column test and the field lysimeter; i.e., the decrease in amounts of Mo leached in column tests, carried out at increasing L/S ratio's in the field lysimeter, is greater than the amount of Mo leached during this time in the lysimeter : natural weathering leads to immobilization of a part of the Mo present. Between L/S 2.8 and L/S 4.1 the amount of Mo immobilized according to figure 2 is 0.66 mg/kg. Compared to a fresh alkaline fly ash of similar type, the results indicate an immobilization for Mo of 1.45 mg/kg after 8 years of natural weathering.

0 ' 0

1

I

I

I

2

4

6

I

8 Liquid/Solid

I

1

I

10

12

14

Lysimeter Column t=O Column t=4 Column t=6 Column t=8

I

Figure 2. Leaching of Mo from fly ash under field conditions and from this fly ash in a column test after 4, 6, and 8 years of weathering. The fact that immobilization of the elements stated occurs, under field conditions in fly ash types similar to that used in the examination, and in even higher degrees, is illustrated in the Figures 3 and 4. These figures give concentrations of various elements as a function of the depth in a fly ash deposit where activities were stopped as long as 20 years ago. Figure 3 shows that immobilization of As and Se occurs at the same level as that of the macro-elements Fe, Mg and Ca, while the elements Ba, Mo and V correspond to the levels of the macro-elements Al and Si (Figure 4).

168 Concentration (rng/kg)

Concentration (rng/kg)

200.

a5 150. u)

poo50. O!

I

4

I

10

2.01+

3.0

1 .o

-

0.0’

0 Depth (m)

Figure 3. Concentration of Fe, Mg, Ca, As and Se in the solid phase as a function of depth in a 20 year old fly ash deposit.

.

.

.

.

.

.

. 0,5 1.0 1,5 2,O 2,5 3,O

I

Depth (m)

Figure 4. Concentration of Si, Al, Ba, V and Mo in the solid phase as a function of depth in a 20 year old fly ash deposit.

169

Coprecipitation of trace elements with macro-elements in the environment is a phenomenon known from geology. As an example can be mentioned the high metal content in iron concretions in the Dutch soil [2].The fact that there is a correspondence between leaching of As and of Fe can be corroborated also by findings from our own research [3]. The Influence of the Cascade Test on Leaching The cascade test mainly has a mobilizing effect on the trace elements examined. For instance, the immobilization of As, Se and V that occurred in the column test would be decreased by the mobilizing effect of the cascade test. The mobilization of Fe and Ba that started in the column test would continue reinforced. On the basis of the elements examined it can be stated in general that in a cascade test more leaching occurs than in a column test. Determination of Availability for Leaching As stated earlier, the availability test according to NEN 7341 is assumed to yield the (very) long term emission (in mg/kg) that might occur under field conditions. This means that the availability established at the start of the test i.e. "before the column test" should have the highest value. Leaching in the column and/or cascade test should subsequently reduce the availability, depending on the extent of leaching. Table 2 demonstrates, however, that element availability after the column and/or cascade test does not decrease proportionately to the extent of leaching (e.g. for As, Se and v). The most remarkable finding is the increase of the initially determined availability due to the mobilizing effect of the column test for the elements Ba (factor 3.2) and Fe (factor 2.3). Availability of these elements continued to increase due to the influence of the cascade test: for Fe, which had already been leached for more than the total available amount, nearly 10 mg/kg still appeared to be available. Another remarkable fact is that of a given element a (far) greater amount can be leached in the column and cascade test than was initially leachable according to the availability test (Fe, factor 6.4), whereas the exact opposite occurs in nature.

3. RELATION OF THE L/S RATIO TO A TIMESCALE

The text accompanying draft standard NEN 7343 provides no information on the background of this test. This lack of information prevents us from establishing which practical conditions are simulated in this test. By way of example, this study compares the leaching values obtained in the standard column test and those obtained for a similar fly ash under (semi-)practical conditions (lysimeters with an effective layer thickness of 0.9 m, 1 L/S = 1.7 years). The values in Tables 5 and 6 show that (based on knowledge available so far) no timescale for practical conditions can be assigned to the L/S value of the standard column tests. Thus the amount of elements leached in the column test will not be

170

equal to that leached over a period of 30 years under field conditions. For some elements the amount leached will be smaller, for other ones larger. Previous results [3] indicate that most of the anions, those of Mo being an exception, are less leachable in the column than under field conditions, while for cations this depends strongly on the element itself. This stresses the importance of finding an explanation for the contradictions observed. Table 5 Cumulative leaching of major elements from alkaline fly ash in a column test (mg/kg).

K

Mg

Na

20 0.5 0.25 12.8 0.10 624 0.01 1.0 0.5 12.8 0.17 1235 0.02 35 2.1 1 12.8 0.24 2259 0.03 51 2 12.9 0.32 3925 0.04 100 4.2 5 12.7 0.79 6024 0.17 151 10.4 10 12.7 8.78 7157 0.66 175 20.8

0.14 0.27 0.41 0.59 1.02 1.45

124 220 298 478 596 630

Time L/S days kg/kg

pH

Al

Ca

Fe

P 0.17 0.30 0.43 0.69 0.84 1.00

Si

S

215 215 364 364 630 630 1188 1188 1677 1677 1733 1733

Table 6 Cumulative leaching of major elements from alkaline fly ash in a field lysimeter (mg/kg)'. Time L/S days kg/kg

pH

Al

211 0.429 475 0.782 1202 2.176 1279 2.437 1296 2.542 1489 2.673 2000 3.352 2070 3.457 2269 3.633 2413 3.842 2672 4.039 2798 4.143

10.1 10.9 8.5 7.5 10.1 10.4 8.3 9.9 7.8 7.6 7.5 8.6

15 19 25 25 26 26 27 27 28 28 28 29

~________

*

Ca

Fe

Na

K

-

-

4 13 131 163 1 76 188 295 312 337 376 412 426

144 195 307 322 326 332 353 358 368 379 389 393

0.23 0.27 0.29 0.32 0.32 0.32 0.32 0.32 0.33 0.33 0.33 0.33 ____

0.01 0.02 0.13 0.13 0.14 0.14 0.16 0.17 0.17 0.17 0.26 0.27 ~_______

156 186 234 239 241 243 253 256 262 267 272 274

P

Si

0.08 0.08 0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28

3.9 6.3 9.6 10.1 10.4 10.7 10.8 11.0 11.4 11.7 NA 12.0 NA 12.3 __

= Results obtained from the same type of fly ash as presented in Table 5.

S NA NA NA NA NA NA

> 29

>49 NA NA

> 74

> 88

171

4. POSSIBLE EXPLANATIONS FOR THE DISCREPANCY BETWEEN LEACHING IN THE STANDARD COLUMN TEST AND UNDER FIELD CONDITIONS

The factor time was pointed out as the principal cause of the discrepancy between leaching in the column test and under field conditions. This factor determines the degree in which the influence of the various other factors in a laboratory test or in a fly ash layer is expressed. The duration of a standard leachability test is far too short for certain immobilization processes that are important under field conditions. In the course of decades or even centuries the natural conditions will exert their influence on fly ash leaching by the continuation of such processes as humification, weathering and the formation of secondary minerals. This will result in a modification of qualities such as the pH, Eh, specific surface and the adsorption complex. The findings of this study demonstrated that for fresh fly ashes the parameters specific to fly ash ageing, such as specific surface (0.7 m’/g), pore surface (4.5 m’/g) and cation exchange capacity, CEC (1.4 meq/100 g) did not change during the three-week column test (L/S lo), whereas for fly ash after four years of leaching in lysimeters (L/S approx. 2.7) these values changed significantly, to 19.6 m’/m, 15.2 m’/g and 6 meq/100 g for specific surface, pore surface and CEC, respectively. SEM photographs show that after the column test the fly ash particles are still smooth, while those in the lysimeters are covered with an irregular crust formed by formation of new minerals and amorphous phases (Figure 5).

Figure 5. Left-hand side: ‘fresh’ fly ash; Middle: the same fly ash after the column test (L/S 10); Right-hand side: the same fly ash after a residence time of four years in the lysimeters (L/S 2.7).

172

Due to the high concentrations of elements in solution at the start of the weathering process and the resulting high supersaturation, the precipitation reactions were initially so fast that there was no time to develop clearly marked phases of a certain crystalline structure. Instead, an amorphous crust was formed with the combined stoichiometry of these minerals. The entire process has been documented in a qualitative weathering model as represented in Figure 6. According to this model fly ash weathering will occur in various phases. Phase 1 At the first contact between fly ash and water the oxides (especially CaO) and salts of high solubility that are present at the surface of the fly ash particles, dissolve. Moreover, there is a rapid exchange between ions in solution and ions at or near the fly ash surface. This phase is accompanied by a strong rise of the pH up to values exceeding 11. Phase 2 Due to the high pH value and hydratation, the glass phase starts to dissolve. Cations are detached from the glass network and dissolve. Mg, Al and Si precipitate on the surface of the fly ash particles, where they form amorphous crusts. The pH value decreases gradually. As the fly ash particles are divided into an exterior reactive and an interior, less reactive glass phase [4], the dissolution rate will decrease in time. Phase 3 It still is unclear if and how the crusts formed continue to grow afterwards. It is possible that in-situ conversion into the Mg-AI-Si phase, of which the crusts consist, takes place at the interface with the glass matrix. A probability is that the crusts provide a certain degree of protection against solution of the glass matrix and that the importance of diffusion processes increases. Phase 4 The eventual development of the crusts formed in the course of the ageing process is determined largely by the pH trend. In the pH range from 7 to 9-10 a restructuring takes place whereby O-Si-O-AI-OH chains are formed, materials from which clay minerals such as smectite and kaolinite can be formed. At a pH value exceeding 9 or 10 the formation of clay minerals is prevented by complexation of silica in solution, in which case zeolites are more likely formed. The precise development of these reactions during the ageing process is as yet unknown. Chemical analyses and analyses using a secondary electron microscope (SEM) on samples obtained from experiments carried out at 110, 150 and 200°C to speed up the weathering process, appear to confirm that the formation of zeolites is related to the crusts enclosing the fly ash particles. Results suggest that the formation of zeolites takes place at the interface between solution and crusts, with calcium, potassium, sodium and silicon polymers being taken up from solution and the crusts supplying aluminium, silicon and nucleation sites. When the pH value has become low enough due to the influence of weathering reactions, the formation of zeolites can be replaced by the formation of smectites. Analyses by X-ray diffraction, differential thermal and thermogravimetric analyses and infrared spectroscopy appear to indicate that the crusts indeed possess a structure bearing similarities to that of a clay mineral [5].

173

Phase 1 : Original fresh fly ash: solubilisation of salts and oxides soluble salts and oxides,

Mn*

CaO + H,O = Ca2* + 2 0 H -

H 2 0 , Na+ Phase 2: dissolution of glass phase, formation of crusts

Mg + ySi +zAl = Mg-Al-Si-phase

Phase 3:diffusion, continuing formation of crusts

Phase 4: transformation of crusts a) Ca2+, Na+, K', H,SiO,

pH < 9 a 10: formation of smectites

b) Ca2+,Na', K*, Si,0,(OH),4.

pH > 9 a 10: formation of zeolites

Figure 6. Model of weathering for alkaline fly ash.

174

Fly ashes after seven years of natural weathering in lysimeters show that phases 1 and 2 take place under natural weathering conditions. Whether phase 4 will

eventually be reached depends on the activities of the cations in solution reaching sufficiently high levels. This in turn depends on such factors as permeability and thickness of the fly ash deposit. However, the possibility of the formation of smectites and zeolites is confirmed by saturation indices calculated from the composition of pore water and percolates sampled from various fly ash deposits exposed to natural weathering. Table 7 gives an overview of the minerals calculated to become supersaturated and a comparison with those actually observed to be supersaturated. Table 7 Minerals predicted to be formed, according to calculated saturation indices [6] and data from the literature [7-91, and minerals observed in weathered fly ash [lo-111. Predicted Mineral name boehmite gibbsite Al-hydroxide (amorphous)

Approximate composition

AlOOH AI(W, AI(OH), AIOHS04 Fe-hydroxide (amorphous) Fe(OH), Fe-oxyhydroxide (am.) FeOOH hematite Fez03 magnesiumferrite MgFe,O, calcite CaCO, magnesite MGO, an hydrite CaSO, gypsum CaS0,'2H,O ettringite Cakl2(so,),(OH),,*2sH,O monosulphate Ca,AI,SO,(OH),,'GH,O portlandite Ca(OH), br uc it e MWHh whitlockite CWO,), apatite Ca,(PO,),OH quartz SiO, amorphous silica SiO, Mg-Ca-Na-K-Al-Si phase (amorphous) Al-Si phase (amorphous) proto-imogolite Ca-aluminate Ca-silicate Ca-zeolite CaAI,Si,O,,'yH,O phillipsite NaKAI,S&O,,'ZH,O feldspar (Na.K)AISi,O, halloysite AI,Si,O,(OH), MgAl-phyllosilicate smectite chlorite MgA~,Si,O,,(OH), illite 16,Mg,,kl,,Si,,O,,(OH), prehnite Ca@W,O,,(OH), kerolite Mg,Si,O,(OH), sepiolite MS,SbOtdOH),'WO mica KAI,Si,O,,(OH),

Field

Observed

Column Literature

This Study

Literature

t

t

+

t t

t

+ t

t

t

t t t

t

+

t

+

t

t

t

+

+ t

t

t

t

t

t

t

+

+

+

t

t t

+ t t t t

+

+

+

+

t

t

+

+ + t

+

t

+

+

t

t

+ t t

t

t t t

t

+ +

+

t

+ +

175

5. DEVELOPING A PREDICTIVE MODEL

On the basis of the results obtained it was attempted to develop a predictive model for (long-term) leaching of fly ash and other combustion residues. For the development of this model the approach represented in Figure 7 [9] will be adopted. This approach is based on an estimate of the composition of percolate from the residues, using the following input data: - total element concentrations in the residue and leachability of the element in question; - the different types of solid phase and their solubility; - the kinetics of solution and precipitation reactions; - adsorption and desorption reactions; - pH value, redox potential, ionic strength; - hydrology.

1 FLY ASH

Fly Ash Characteristics Total Chemical Composition Primary and Secondary Minerals and Gasses Extractabllity/Leachabilily(Eh, pH)

-

REACTIONS

THERMOCHEMICAL DATA

Precipitation Dissolution Reactions

Y

Adsorption Desorption Reactions

ADSORPTION

LEACHATE COMPOSTION

Figure 7 . Diagram for predicting the leaching behaviour of combustion residues [9].

176

The modelling results obtained so far [6] demonstrate that the weathering processes in a fly ash deposit probably lead to immobilization of a significant part of the trace elements present. This is partly due to coprecipitation with and adsorption to aluminium and iron (hydr)oxides, smectites and possibly even zeolites. However, there is as yet insufficient information available on a number of input data to enable the development of a predictive model for leaching. This is especially the case for the kinetics of dissolution and formation reactions and for the development of adsorption and desorption reactions. Various literature sources assert that the rate of mineral formation or dissolution in fly ash is so high that it is fair to assume an approach based on thermochemical principles [E, 12, 13, 141. This would mean that the upper limit of the element concentrations in the percolate might be predicted on the basis of data on the solubility of certain solid phases. Our research, however, indicates that a number of major reactions are highly influenced by the factor time and are therefore kinetically determined [6]: - after the relatively rapid dissolution of the exterior reactive glass which reprecipitates into an amorphous crust, the remaining glass, which forms the bulk of the fly ash, dissolves only gradually. Another aspect involved here is that particles are protected by the amorphous crusts. - The amorphous phases formed, such as the crusts, will in time convert into crystalline compounds. - The saturation indices calculated indicate that some minerals (e.g. apatite and nontronite) are extremely supersaturated. Nevertheless, these minerals are not found in the weathered fly ash. This is due either to unknown complexation reactions or to the fact that crystallization of these phases requires more time and is therefore kinetically determined. The kinetics of the weathering processes have so far been insufficiently subjected to scientific analysis. However, these changes over time mean that the adsorption characteristics will also change over time. Desorption and adsorption processes at the surface of solid phases (e.g. iron (hydr)oxides) are highly important in regulating the concentrations of trace elements such as As, Cr, Se and Mo in solution. To be able to predict the leaching of these ecologically significant elements, it is important to be able to accurately predict the leaching behaviour of the macro-elements (Si, Al, Fe, Ca). However, knowledge of the adsorption and desorption processes is also inadequate yet. The development of a quantitative predictive model requires research to be conducted into the effects of fly ash ageing under (semi-)natural conditions on dissolution kinetics, formation of reactive surface and the mutual interaction between these two processes. Moreover, the incorporation of adsorption and desorption reactions into the model requires a better characterization of the surface of the solid phases in fly ash.

177

6. CONCLUSIONS

The findings discussed in this report indicate that the available information on the leaching values for trace elements is not sufficient to relate the L/S ratio of the standard column test to a timescale under field conditions. However, leaching under field conditions differs totally from leaching as expected on the basis of the column test. The principal cause for this appears to be the tests themselves: - the conditions (e.g. time, pH, Eh) under which the standard column test is performed differ considerably from those in the natural environment. This results in different leaching behaviour of elements in the column test and the field; - the column and/or the cascade test may result in an increase of the element amounts initially available in the fresh material (determined according to the availability test); - the amount of an element leached in the standard tests can be significantly larger than was expected on the basis of the availability test; - the availability test does not provide a realistic insight into the maximum amounts available for leaching in practice (under extreme conditions). Assessment of the potential environmental impact of fly ashes used as building materials, but also of fly ashes in (interim) storage requires the development of a model for conversion from leaching in column tests into leaching under field conditions. For this purpose more (quantitative) knowledge is needed about the influence of weathering and soil formation on the leaching behaviour of fly ash. The results from the study presented in this paper show that to predict correctly the leachability of the trace elements present in fly ash, one must also kitow the availability of macro-elements present and their contribution to the immobilization capacity by the formation of minerals. A model based on improved kinetics and considering also adsorption and desorption will enable a more accurate prediction of long-term fly ash leaching under field conditions. Such a model can also be used for an analysis of the correspondence between leachability tests and leaching under field conditions; in this way the model can contribute to the development of quality assessment (certification) of fly ash and similar combustion products. Consequently, the model can also be used to improve the risk assessment of fly ash deposits for the environment.

ACKNOWLEDGMENTS

This research has been funded by the Dutch Electricity Production Sector

178

REFERENCES 1

M. Janssen-JurkoviEova, Electrotechniek, No. 2 (1991) 103-109.

2

F.G.M. Pruissen and B.W. Zuurdeeg, LandtWater, No. 3 (1988)

3

M.H.C. van den Hark and M. Janssen-JurkoviEova, KEMA-report, No. 85560MOZ 89-3308 (1989) 116 p.

4

M.J. Dudas and C.J. Warren. Geoderma, 40 (1987) 101-114.

5

G.G. Hollman, KEMA\UU report MVD-1992-2 (1992) 64 p.

6

G.G. Hollman and M.M. Nass, KEMA\UU\LUW report MVD-1994-1 (1994), in press.

7

EPRI-RAPPORT EA-5176. Inorganic and organic constituents in fossil fuel combustion residues. Volume 1: A critical review, (1987).

8

S.V. Mattigod, Environ. Technol. Let., 4 (1983) 485-490.

9

S.V. Mattigod, D. Rai, L.E. Eary and C.C. Ainsworth, J. Environ. Qual., 19 (1990) 188-201.

10 M.A. Noordewier and M.J. Janssen-JurkoviEova, KEMA report MVD-1992-01 (1992) 62 p. 11 G.G. Hollman, M.A. Noordewier and M.J. Janssen-JurkoviEova, KEMA report 63617-KES/MAD 93-3013 (1993) 52 p. 12 Fruchter, J.S., D. Rai and J.M. Zachara, Environ. Sci. Technol., 24 (1990) 1173. 13 Rai, Dhanpat, S.V. Mattigod and C.C. Ainsworth. In: McCarthy, G.J, and F.P.

Glassner (eds.). Fly Ash and Coal-Conversion Byproducts Characterization, Utilization and Disposal. Mat. Res. SOC. Symp. Proc. Vol. 113 Materials Research Society (1988) 317-324. 14 Talbot, R.W., M.A. Anderson and A.W. Andren, Environ. Sci. Technol., 12 (1978) 1056-1062.

Environmental Aspects of Construction with Waste Materials JJ.J.M. Goumans, H A van der Sloot and Th.G. Aalbers (Editors) el994 Elsevier Science B. K AN rights reserved.

179

Geochemical factors controlling the mobilization of major elements during weathering of MSWI bottom ash C. Zevenbergen" and R.N.J. Comansb 'IWACO BV, P.O. Box 8520, 3009 AM Rotterdam, The Netherlands bNetherlands Energy Research Foundation, P.O. Box 1, 1755 ZG Petten, The Netherlands

Abstract A study of the interactions between the solid and the liquid phase with respect to the major elements, as function of time, POz and PCOz, was carried out using batch experiments with unweathered and weathered bottom ash. The weathered bottom ash has been obtained from a 12-year old, open disposal environment. Mineralogical properties of the unweathered and weathered bottom ash were investigated using powder x-ray diffraction and electron microscopy. The equilibrium solubilities of potential secondary solids were evaluated using the geochemical speciation code MINTEQA2. Possible pathways of weathering sequences, as a function of time and imposed conditions, are hypothesized from the calculated compositional changes in the solid phase and from known natural weathering sequences observed in alkaline soils and soils of volcanic origin. The impact of these processes on contaminant leaching from MSWI bottom ash will be discussed. 1. INTRODUCTION

Municipal solid waste incinerator (MSWI) bottom ash is predominantly composed of high temperature solids. In a natural atmospheric environment many of these solids are metastable and will alter to form thermodynamically stable assemblages of minerals. Recent research indicates that the weathering products of MSWI bottom ash, which has been disposed of in the open are similar to those found in weathered volcanic ashes and scoriae, and that secondary mineral formation has a significant influence on contaminants such as heavy metals [1,2]. It is, therefore, necessary to consider the long term weathering mechanisms of MSWI bottom ash in evaluating the environmental impact of utilization and disposal. Most studies dealing with the environmental impact of MSWI bottom ash have been directed to the determination of the quantities of constituents that can be leached under more or less extreme conditions and have failed to consider chemistry of major elements. Only a few recent studies include an assessment of the geochemical factors that control leaching under field conditions. Systematic leaching patterns from fresh MSWI bottom ash were described by DiPietro et al. [3], and Comans et al. [4]using pH/Eh controlled batch experiments. Both authors found a close correspondence between solubility data for some elements derived from their experiments and known solubility relationships in

180

natural environments. In this study XRD and electron microscopy in conjunction with an equilibrium speciation model was used to identify solubility controlling secondary phases of major elements in long term batch experiments with fresh and weathered MSWI bottom ash. 2. MATERIALS AND METHODS

2.1. Sample description and preparation Two types of bottom ash samples, which originate from the same municipal incinerator, have been used in this study. One was a fresh bottom ash sample taken directly from the storage pile of the incinerator. In the storage pile the temperature may increase up to 40°C as a result of exothermic @io)chemical reactions [5]. The other sample was a 'weathered' bottom ash sample which was obtained from an open disposal environment. The weathered bottom ash sample had been exposed to weathering for over 12 years. The bottom ash deposit was situated above the ground water table. A detailed description of the disposal environment and sampling are given elsewhere [l]. After collection the samples were stored in capped containers at a temperature of 4°C until use. All chemical analysis and leaching experiments were carried out upon the fraction that passed through a 2 mm sieve (fine earth). 2.2. Mineralogical and chemical properties Mineralogical properties of both bulk samples were determined using (unoriented) powder x-ray diffraction (XRD). Total elemental concentration was determined using xray fluorescence spectroscopy (XRF).

2.3. Availability To assess the maximum elemental release on the long term the availability test [6] was carried out. This test consists of two serial extractions, each at a 50:l liquid to solid ratio (wlw) on a crushed sample ( <300 pm) at a constant pH of 7 and 4 respectively. Both extracts were combined for analysis. The availability is defined here as the maximal fraction of the total elemental concentration (XRF) available for leaching. 2.4. Batch leaching experiments Batch leaching experiments were conducted with the fresh and weathered bottom ash sample using a liquid to solid ratio (w/w) of 2.5:1. The extractions were camed out under three different conditions: continuous air purging (saturation with atmospheric O2 and COz), continuous N2 purging (exclusion of Q and CO,), and waterlogging. The air and Nz gas were saturated with water by being bubbled through a gas-washing bottle filled with deionized water before the gas entered the batches. In the closed batches sample contact with air was minimized by completely filling the bottles. The batch experiments were carried out in 1-L Pyrex glass reaction vessels. At selected time intervals an aliquot of 25 ml was removed from the suspension and the pH and Eh was measured. Each extract was filtered through a 0.45 pm Micropore filter prior to analysis. To maintain a constant extraction volume 25 ml of deionized water was added to the batch after each sampling. The elemental speciation in each extract was computed by the geochemical equilibrium computer program: MINTEQA2 [7,8].

181

2.5. Analytical electron microscopy (AEW Following the batch experiments, the <200 pm diameter fraction of the fresh samples was examined using 200 KeV analytical AEM. Electron transparant thin sections were first prepared using an ultramicrotome equipped with a diamond knife. Brightfield and darkfield imaging, lattice fringe imaging, and electron diffraction were used to determine microstructural and crystallographic properties. Energy-dispersive x-ray spectroscopy (EDS) was used to determine chemical compositions. AEM was found to be particulary useful for studying submicrometer precipitates and altered layeres on individual grains, which cannot be detected by (powder) XRD. A more detailed description of the sample preparation and microanalytical procedures is given elsewhere [9].

3. RESULTS A N D DISCUSSION 3.1. Mineralogy X-ray diffractograms of the fresh and weathered sample before leaching are shown in Figure 1. The x-ray diffractogram of the fresh sample is dominated by peaks from quartz, gypsum, magnetite, calcite, feldspar and ettringite. The identity of other phases present in small quantities was very difficult to establish, because the patterns are characterized by a large number of small overlapping peaks. The main difference in the x-diffractograms was the disappearance of the pattern of ettringite in the weathered sample.

Figure 1. X-ray diffractograms of the fresh (A) and weathered (B) sample. Abbreviations: cc, calcite; g, gypsum; mt, magnetite; qtz, quartz; ett, ettringite; fsp, feldspar

182

3.2. Availability In Figure 2 the availability of major elements is given for both samples. For the fresh sample Si, Fe, and A1 have an availability of less than 5 % (w/w). Such low availability suggests that elements are primarily associated with the silicate matrix and/or other poorly soluble mineral phases, for example Fe in iron(hydr)oxides. A higher availability (up to 35 % (wlw)) is seen for Na and Ca and to a lesser extent for K and Mg, which indicates that these elements are distributed between the less soluble matrix and the more soluble fraction. The availability of all elements is significantly lower for the weathered sample than for the fresh sample. A striking decrease is observed for Na. It appears from these data that the major elements are leached substantially from the weathered sample as a result of weathering. 40

tailability (W) wantharod

n

LI_] fresh

30

20

10

0

Si

Fe

Cn

Al

K

Mu

Nn

Figure 2. Availability of major elements from the fresh and weathered sample.

3.3. pH, Eh and elemental release with time The results of the batch experiments are illustrated in Figure 3. High and constant pH values (between 11.O and 11.5) are recorded in the waterlogged and N2purged batch with the fresh sample. The pH values of the air-purged batch with the fresh sample are initially high (pH 9.3), but drop gradually to a constant pH value of 8.2. Similar pH values are recorded in the air-purged batch with the weathered sample. The pH values of the waterlogged batch with the weathered sample gradually decline from 8.5 to 7.5, while the pH of the N2 purged batch stabilizes at pH 8.9. The decrease in pH after waterlogging is probably due to the accumulation of CO, produced by respiration of aerobic bacteria. In the batches with the fresh sample, the Eh decreases during the first few days and reaches a minimum; then it increases and attains constant values. The Eh of the batches with the weathered sample increases, attains a maximum and decreases to fairly constant (positive) values. The initial decrease of Eh is possibly due to the rapid release of reducing substances accompanying oxygen depletion, which is followed by an Eh increase due to a slow buffering by reductive dissolution of oxidizing agents like Mn(1V) and Fe(II1).

183 A steady state for all element concentrations is reached within approximately 20 days with the exception of Si. Silicon concentrations demonstrate either a maximum at about 10 to 20 days or a constant decline as the experiments progressed. These release patterns indicate that the Si concentration is controlled by slow reaction kinetics. Highest Si concentrations correspond with the most alkaline batches. A delayed release pattern followed by a steady state concentration after 20 days is observed for Ca in the air-purged batch with the fresh sample. The rate of calcium dissolution in this batch is presumably determined by the rate of dissolution of CQ(g). The concentration of Ca in the other batches with the fresh and weathered sample reaches almost immediately constant values. The behaviour of Mg and to a lesser extent of SO4 are similar to that of calcium, although steady state concentration levels vary between the fresh and weathered samples. The Al concentrations correlate well with the pH: relative high Al concentrations are found at a pH above 10.5 (e.g in the waterlogged and N, purged batches with the fresh sample), while Al concentrations below detection limit are observed in the batches with near neutral pH (e.g. in the batches with the weathered sample and the air-purged batch with the fresh sample). Fe is only detected (detection limit of 20 ppb) in the waterlogged batch with the fresh sample after 3 days which coincides with a low (i.e. negative) Eh value. In all batches Na, K and CI concentrations attain almost immediately fairly constant values. Their instantaneous release indicate that these elements are controlled by their availabilty in the solid phase. Significantly lower concentrations are observed in the batches with the weathered sample, which is in agreement with the availability data.

3.4. Electron microscopy Direct observations by AEM analysis and intercomparison of the fresh samples (fraction < 200 pm), which have been allowed to weather in the batch experiments under different leaching conditions, revealed changes in the interfacial microstructure and microchemistry and the formation of secondary phases. The most frequently observed secondary phases were those primarily composed of Si, Al and Fe. In all samples evidence was found for widespread decomposition of glassy constituents and growth of clay precursors on glass surfaces. Amorphous or poorly organized layers on the glasses were mainly composed of Si and Al at different relative abundance. In Figure 4a, a typical alteration feature of a silicate glass is given, observed in the sample from the air-purged batch. A rim has developped on the glass particle. The results of EDS analysis show that the rim is depleted in Si and enriched in Al, Mg, K and Fe. The Si/AI ratio of the rim is relatively high. However, Si and hydrolysable elements such as Fe and Al are also found in discrete aluminum and iron (hydr)oxides. Precipitation of aluminosilicates outside hydrolysed silica rims was also observed. Figure 4b shows a typical precipitate of amorphous aluminosilicate with a relatively low Si/AI ratio, found in the sample from the waterlogged batch. Such Al-rich amorphous aluminurnsilicates were not found in the sample from the air-purged batch. In the sample from the air-purged batch small quantities of an amorphous hydrated Al-rich phase were found. A typical example of such a phase is shown in Figure 4c. As discussed in the previous section, the pH of the batches mainly controls the dissolution and precipitation of A l and Si. With increasing pH the Al concentration attains higher values than the Si concentration. The high pH may therefore explain the occurrence of aluminosilicates with low Si/AI ratio in the waterlogged and N2 purged batches. In near neutral conditions much more Si is present in solution than Al, thus promoting the

184

formation of aluminosilicates with high Si/AI ratios. The occurrence of hydrated Al-rich phases in the air-purged batch is probably caused by rapid precipitation of soluble aluminum in the initial stage of the batch experiment. Widespread alteration rims with high Si/AI ratio in the weathered ash sample have recently been documented by Zevenbergen et al. [1,2]. These rims consisted of well ordered clays, exhibiting a basal lattice spacing of 1 nm. The AEM results have established that the glassy material, whether Sior Al-rich, is unstable under the prevailing leaching conditions. The decomposition of these glassy materials leads to the release of silicon and aluminum (and alkali and alkaline earth elements) into the solution followed by precipitation outside the glass, and to in-sifu transformation producing an aluminosilicate rim on the glass. The latter combination may explain the contineous Si decrease in the batch experiments after approximately three to six weeks. pn

Eh Eh lmVl

800,

I

.... ~ . . ... ~ 0.

Ii o

80

40

no

no

IW

no

-400

o

'

an

' 40

'

no

'

'

no

DO

00

80

too

no

day8

Na

K

I o

ao

40

no dY ..

ao

wo

00

*

I " " "

o

20

40

00

days

Figure 3. pH, Eh (mV) and elemental concentrations (mgll) in the extracts of the batch leaching test with the fresh (dotted lines) and weathered (solid lines) sample with time. Symbols: 0 , N2purged; A, waterlogged; x, air-purged (continued on next page)

185 CI

SO4 loooo [mcentratlon ImgAl

t

51 -

loof

...........

x---

~

*ooo

- r g.......

conmratlon lmglll

100

. . . . . . . . . a

I0

t -

0 1

o

ao

40

60

00

IW

J

I

.

,

DO

o

ao

40

,

,

,

80

eo

mo

uo

' 80

' 100

uo

80

mo

uo

day.

day8

A1

SI

concentrationlmplll

concentration Imglll

..........

t

'

0.1' 0

10

' 40

'

80

'

' M

IW

J

110

F

0,lL

o

'

ao

'

40

'

60

days

day8

Mg

Ca

concentrationlmplll

7

loo

f

o

ao

40

60

day8

Figure 3. (continued) Symbols:

0,

N2purged; A, waterlogged; x , air-purged

186

Figure 4a.

I

I

Si

Si

Figure 4b.

Figure 4a-c. Transmission electron micrographs of typical alteration features of a silicate glasses in the fresh bottom ash samples, showing a poorly crystallized aluminosilicate rim observed in the air-purged batch (a), a discrete amorphous aluminosilicate phase with a low W A I ratio observed in the waterlogged batch (b), and a precipitate of amorphous hydrous alumina on apatite (apatite is probably inherited from the parent material) observed in the air-purged batch (c). EDS data show the chemical compositions of the indicated areas.

187

Figure 4c.

Figure 4a-c. (continued)

3.5. Equilibrium modelling The Saturation Indices computed for various minerals in the solutions of the batch experiments at t = lOOd are listed in Table 1. The geochemical speciation code MINTEQA2 (version 3.11) was used for the calculations. The mineral ettringite was added to the standard thermodynamical database, using the solubility product recently determined by Atkins et al. [lo]. Waterlogged and N,-purged experiments were modelled as closed systems (no equilibrium with the atmosphere), using measured total carbonate. Air-purged experiments were modelled assuming equilibrium with atmospheric C02 (PC02 = atm.). Negative SI values suggest undersaturation, whereas values near zero suggest equilibrium and positive values indicate oversaturation. Figure 5 indicates the Ca concentration in the solutions from the batch experiments with the fresh and weathered bottom ash. The solutions from the weathered ash sample and from the air-purged batch with the fresh sample were slightly oversaturated with respect to both calcite and aragonite. The presence of Mg2+and SO:' can inhibit the precipitation of calcite and aragonite because these ions are incorporated in the CaCO, structure [l I]. It is therefore likely that a more soluble CaCO, phase controls the Ca solubility in these batches [ll]. Ca concentrations were highest in the air-purged batch from the fresh sample (Fig. 5 ) , which is consistent with the higher Mgz+and SO:- concentrations.

188

Table 1. Computed Saturation Indices for a number of minerals. mineral

-

fresh

stnrclural formula closed

N,

air

closed

N, mtherec

-

air

AI(OH),-am.

-1,79

-1,76

-0,63

-0.16

-1.04

anhydrite

-1,67

-1,75

-0,25

-1.69

-1.85

-1.69 -0.50

4,50

aragonite

1.84

1,90

0.11

0,16

0,59

boehmite

0.02

0,05

1.17

1,64

0,76

131

brucite

-0,79

-1,04

-4.78

-5,91

-3,86

-5,lO

poltlandite

422

-4,69

-9,25

-1064

-8.46

-9.86

I ,9a

2,oa

0,25

0,30

0,73

4,36

clinoenstatite

-0,33

-0,22

4 ,0 8

-4,21

-2,96

-3.56

basaluminile

-13,09

-12,57

-0,l9

-6,06

-2.30

1,56

I .97

-0.88

-0,50

0.22

-1,78 2.48

calcite

dolomite

-2,Ol

ferrihydrite

-0,16

0,lO

2,45

2,33

2,15

gibbsite

-0,18

-0,15

0,98

1.45

0.57

1,12

gypsum

-1,46

-1.53

-0.04

-1,48

-1,64

-1,48 -I ,92

magnesite

-0,92

-0.61

-1.62

-1,30

-1,oO

quartz

-0.98

-0,73

-0,75

0,26

-0,55

0.09

SO,-am.

-1,97

-1.71

-I ,73

-0.73

-134

-0,90

halloysite

-1,78

-1.21

1,Ol

3,94

0,57

2.94

laumonite

I ,23

I ,a5

-0,53

3,Ol

021

2/44

wairakite

-3.18

-2,56

494

-1.40

-4,20

-1.97

ettMgite

-3.07

-4.63

-1 1.58

-19,15

-14,83

-13,36

sepiolite

1,12

1,39

-6.15

-5,4 1

-3.12

-4,25

analcime

1,lO

I ,22

-0,39

-0,lO --0,lO

-1,25

Saturation Index = lop(lon Activity Product)- log(Equi1ihriurn Solubility Product)

The Ca concentrations in the waterlogged and N, purged batches from the fresh sample are controlled by a more alkaline solid, possibly ettringite. This mineral was identified by XRD in the original fresh bottom ash sample (Fig. 1). Equilibrium calculations by Comans and Meima [12] also suggest ettringite to be the likely mineral controlling calcium solubility at pH> 10. The equilibrium calculations summarized in table 1 indicate, however, that the solutions from the closed and N2purged batch experiments are strongly undersaturated with respect to this mineral. These calculations were performed with the same speciation code and solubility product as was used by Comans and Meima [12]. There is reason to believe that the total-CQ concentrations that were measured in the closed- and N2-purged batches (4 and 4.5 mmoles/L, respectively, using total alkalinity titrations) in the present study may be too high. Especially in the batch which

189

has been purged with nitrogen for 100 days, we would expect total-CO, to be very low. These high carbonate concentrations lower the free Ca” activity at high pH by the formation of strong complexes with the metal ion in solution and, hence, decrease the Ion Activity Product of ettringite. MINTEQAZ calculations with dissolved carbonate < lo5 M indicate that the solution from the N,-purged batch is only one order of magnitude underaturated with respect to ettringite. In view of the fact that ettringite has been identified by XRD and considering the uncertainty in its solubility product, it seems reasonable to assume that the data points around pH 11 in Fig.5 are controlled by ettringite solubility. The presence of ettringite is known to limit the SO4 concentration in solution in contact with alkaline fly ash [13,14]. It is, therefore, likely that this mineral controls SO4solubility at the beginning of the waterlogged and N,-purged experiments. The computed SI values suggest that the SO4 concentration in the air-purged batch is controlled by gypsum. The air and N,-purged extracts from the weathered sample are highly undersaturated with respect to the listed sulfate containing minerals. In these extracts the total available sulfate fraction is presumably insufficient to reach saturation. At a lower pH, however, which is found in the waterlogged batch, the solution is slightly undersaturated with respect to basaluminite (Al.,(OH),,,SO.,). This mineral may control the SO, concentrations in this batch. Basaluminite is a naturally occuring mineral in acid soils that is probably formed by reaction of sulfate with clay minerals [15]. Silicon concentrations are relatively high under the waterlogged and N,-purged conditions in the batches with the fresh ash sample, so that aluminosilicates are stable in addition to the aluminum-hydroxides. It appears from our observations by means of high-resolution electron microscopy that more hydrated and less ordered amorphous aluminosilicate phases begin to form under these conditions. At high Mg concentrations, brucite andlor dolomite and, posssibly, sepiolite are the expected stable Mg-phases. Supersaturation with respect to the latter minerals may indicate that their formation is relatively slow. In the air-purged batch dolomite rather than brucite seems to control the Mg concentration. Analcime seems to remain a metastable mineral in both ash samples, even after the high Na and pH values are lowered by leaching. Halloysite seems to be the stable aluminosilicate mineral at lower pH in both the fresh and weathered ash sample. It is important to note here that the predicted silicate minerals represent mineral assemblages commonly found in alkaline soils and soils of volcanic origin [16-211. In the present study, the lower detection limit of x-ray diffraction (approx. 3-5%) appeared to be too high to reveal any of the silicates possibly formed in this relatively short span of time. The measured iron concentrations, which were all below detection limit in the batch experiments after 100 days, allow no reliable estimation of the Saturation Indices of relevant iron containing minerals to be made.

190 Ca concentration lmg/ll 10000

t

closed. weathered

't

N2, weathered

'

air, weathered

a

closed. fresh

0

N2. fresh

A

air, fresh

- calcite, air

11 7

8

,

10

9

11

12

PH

Figure 5 . Ca concentrations in the solution from the batch experiments with the fresh and weathered ash sample and MINTEQA2 predictions assuming equilibrium with calcite. 3.6. Weathering sequences There is some evidence that the rate of crystallization with respect to amorphous aluminosilicates is inhibited (and probably deviations in stoichiometry) when there is no alternate wetting and drying [22,23]. These phenomena may be of particular relevance in the batch experiments with the fresh sample, resulting in increasing solubility values of silicate minerals. Caution with estimations on mineral solubility and formation on the L-A A.' of themodynariiic equiliorium modelling during experimental bottom ash leaching should be taken. In spt' of tbese shortcomings, relevant information can be obtained about the direction and sequence of secondary mineral formation under different conditions from our experimental data and from known natural weathering sequences observed in tuffs and lavas. Hypothetical weathering products as a result of hydration, hydrolysis, oxidation/reduction and carbonation in relation to some specific environments are summarized in Table 2.

191

Table 2. Hypothetical weathering products of MSWI bottom ash in relation to some specific environments. Environment

Dominant processes

I

Mobility

Waterloerred alkaline reducing low water intiltration rate

hydrolysis of prtlandite formation of ettringite hydration L hydrolysis of glasses formation o f zeolites redoxprocesses

high

QE!! alkaline to neutral oxidizing-reducing high water intiltration rate

carbonation hydration L hydrolysis of glasses formation of 2:l clays redoxprocesses

high : moderate : low :

low

: :

Si, Al, Na, K Ca, Mg, (Fe), SO,

Mineralogy

ettringite Ca-zeolites sepiolite analcime hmcite ~______

Ca, Mg, SO,, Na, K Si. Fe Al

calcite dolomite hasaluminite 2:l clays halloysite gypsum analcime

In the storage pile the initial weathering reactions, including carbonation, hydration and hydrolysis, may progress rapidly due to the prevailing hydrothermal conditions. The subsequent weathering reactions are determined by predominating conditions during disposal and utilization. When bottom ash is waterlogged, gas exchange between ash and air is drastically curtailed. Oxygen and atmospheric CO, can enter the bottom ash environment only by molecular diffusion. The pH of waterlogged, initially fresh, bottom ash is controlled by portlandite. In this alkaline environment the pH is sufficiently high to cause solution of aluminum and precipitation of magnesium and sulfate. Although the formation of zeolites has as yet not been substantiated with high resolution AEM, these conditions provide an ideal setting for formation of zeolites. Migration of atmospheric CO, into the bottom ash environment and microbial respiration producing CO, may cause a gradually decreasing of pH. Carbonate minerals will ultimately control the equilibrium pH of the pore solution in a well drained, unsaturated, bottom ash environment. Under these conditions the solubility of aluminium is relatively low and hence may give rise to the formation of 2:l clay minerals. Indeed, the distinct and extensive neoformation of illite from weathered bottom ash in an open disposal environment has recently been documented [1,2]. It has been long noted that altered (aluminosilicate) layers formed on glasses play a significant role in the retention of trace elements during leaching [24]. In view of the environmental significance, further evaluation of mechanisms of clay mineral formation during MSWI bottom ash is warranted. It must be emphasized that microbiologically mediated oxidation-reduction reactions are probably important as well in controlling element mobility in bottom ash environments [25]. However, very little information is available with respect to these types of reactions during weathering of bottom ash. Low (negative) redoxpotentials were recorded in percolates from waterlogged bottom ash after six months of incubation in large field lysimeters [26]. In a more oxidizing environment, microbiological action was likely to be responsible for the observed translocation of iron in a bottom ash profile, resulting in the formation of an iron pan on the ash-soil interface [ 11.

192

In the present study anaerobic conditions have not been attained in the waterlogged and N2 purged batches, presumably due to slow reaction kinetics. 4. CONCLUSIONS MSWI bottom ash consists primeraly of an assemblage of metastable phases and minerals. Upon weathering these metastable solids will transform into naturally occurring secondary minerals. The experimental observations and the calculations reported here allow the following conclusions to be drawn with respect to the leaching behaviour of major elements during weathering of MSWI bottom ash. The initial stage of weathering is dominated by an extreme solution alkalinity and by instantaneous dissolution of those elements (e.g. Na, K, and C1) that are assiociated with soluble salts. The rate and sequences of consecutive weathering reactions controlling the concentrations of Si, Al, Ca, Mg, S04, and possibly Fe, in the pore solution, is dictated to a large extent by the rate of atmospheric COz entry (andlor production of C02 by microbial respiration). Two factors which are of importance but not considered in this paper are the rate of atmospheric 0, entry and the hydrodynamic conditions. The predicted secondary minerals, which may form on the longer term, represent mineral assemblages commonly found in alkaline soils and soils of volcanic origin. We emphasized that the combination of microanalyses of the solid phase and the geochemical modelling of the processes in solution, followed in this paper, constitutes a powerful approach in revealing the major element chemistry ans secondairy mineral formation in waste materials such as MSWI bottom ash. Knowledge of these processes is mandatory in assessing the long term environmental impacts of these waste materials.

5. REFERENCES Zevenbergen, C., Bradley, J.P., Vander Wood, T., Brown, R.S., Van Reeuwijk, L.P., and Schuiling, R.D. Weathering as a process to control the release of toxic constituents from MSW bottom ash. In: Geology and Confinement of Toxic Waste, Proc. of the Int. Symp. Geoconfine '93, Montpellier, France, 591-595, 1993. Zevenbergen, C., Bradley, J.P., and Van Reeuwijk, L.P. Mobility of heavy metals during leaching of municipal solid waste ash. In: Microbeam Analysis, 2, Proc. of the 27th Annual MAS Meeting, Los Angeles, 1993. Dipietro, J.V., Collins, M., Guay, M., and Eighmy, T.T. Evaluation of pH and oxidation-reduction potential on leachability of municipal solid waste incinerator residues. Proc. Int. Conf. Municipal Waste Combustion, Hollywood, Florida, April 11-14, 2B, pp. 21-43, 1989. Comans, R.N.J., Van der Sloot, H.A., and Bonouvrie, P.A. Geochemical reactions controlling the solubility of major and trace elements during leaching of municipal solid waste incinerator residues. Proc. Int. Conf. Municipal Waste Combustion, March 30- April 2, Williamsburg, VA, J. Kilgroe, ed., AWMA, Pittsburg, PA, 1993.

193

5

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Schnieder, J., Kossl, H., and Pfrang-Stotz, G. Vergleichende Untersuchungen an MV-Schlacken unterschiedlicher Rost- und Reuerungssysteme. VDI Bildungswerk. Seminar Slackenaubereitung, -verwertung und -entsorgung, December 6-7, Dusseldorf, 1993. NVN 5432. Determination of the maximum leachable quantity and the emission of potentially hazardous components from construction materials and stabilized waste products of mainly inorganic character. NNI, October 1992. Felmy, A.R., Girvin, D,C., and Jenne, E.A. MINTEQ--A computer program for calculating acqueous geochemical equilibria, EPA-600/3-84-032, U.S. Environmental Protection Agency, Athens, 1984. Allison, J.D., Brown, D.S., and Novo-Gradac, K.J. MINTEQA2IPRODEFA2, A Geochemical Assessment Model for Environmental Systems: Version 3.0 User’s Manual, EPA/600/3-91/021, U.S. Environmental Protection Agency, Athens, 1991. Bradley, J.P., and Brownlee, D.E. Cometary particles: Thin sectioning and electron beam analysis. Science, 231, 1542-1544, 1989. Atkins, M., Macphee, D., Kindness, A., and Glasser, F.P. Solubility properties of ternary and quarternary compounds in the Ca0-A1,0,-S03-H,0 system. Cement and Concrete Research, 2 1, 99 1-998, 1991. Schramke, J.A. Neutralization of alkaline coal fly ash leachates by C02(g). Applied geochemistry, 7, 481-492, 1992. Comans, R.N.J. and Meima, J.A. Modelling Ca-solubility in MSWI bottom ash leachates. These Proceedings. Simons, H.S., and Jeffery, J.W. An x-ray study of pulverised fuel ash. J. Appl. Chem., 10, 328-336, 1960. Mattigod, S.V. Chemical composition of acqueous extracts of fly ash: ionic speciation as a controlling factor. Environmental Letters, 4, 485-490, 1983. Adams, F. and Z. Rawajfih. Basaluminite and Alunite: Possible cause of sulfate retention by acid soils. Soil Sci. SOC.Am. J., vol. 41,686-692, 1977. Boekschoten, G.J., Buurman, P., and Van Reeuwijk, L.P. Zeolites and palygorskite as weathering products of pillow lava in Curacao. Geologie en Mijnbouw 0016-7746, pp.409-415, 1983. Hay, R.L. Zeolites and zeolitic reactions in sedimentary rocks. Geol. Soc. Amer. Spec. Paper 85, 1966. Baldar, N.A., and Whittig, L.D. Occurence and synthesis of soil zeolites. Soil Sci. Soc. Amer. Proc. 32, pp. 235-238, 1968. Wada, K. Minerals and mineral formation in soils derived from volcanic ash in the tropics. Sci. Geol., Mem., 85, 69-78, 1990. Wada, K., and Kakuto, Y. Embronic halloysites in Ecuadorian soils derived from volcanic ash. Soil Sci. Soc. Amer. J . , 49, (1985), 1309-1319. Tazaki, K., Observations of primitive clay precursors during microcline weathering. Conrrib. Mineral. Petr., 92, (1986), 86-88. Magonthier, M.C., Petit, J.C., and Dran, J.C. Rhyolitic glasses as natural analogues of nuclear waste glasses: behaviour of an Icelandic glass upon natural acqueous corrosion. Applied Geochemistry, Suppl. Issue No. 1,pp. 83-93, 1992.

194 23 Brinkman, R. Clay transformations: aspects of equilibrium and kinetics. In: Soil Chemistry. B. Physico-chemical models. Bolt, G.H. (ed.) Elseviers Science Publishers BV, 1983. 24 Petit, J.C., Dran, J.C., and Trotignon, L. Mechanism of heavy element retention in hydrated layers formed on leached silicate glasses. Mat. Res. Symp. Proc. Vol. 127, 33-40, 1989. 25 Belevi, H., Stampfpli, and Baccini, P. Chemical behaviour of municipal solid waste incinerator bottom ash in monofills. Waste management 8~ Research, 10, 153-167, 1992. 26 Van der Sloot, H.A., and Hoede, D. AVI-bodemas als aanvulmateriaal: migratie van contaminanten uit AVI-bodemas in een isolerende kleilaag en evaluatie van het lange termijn gedrag. ECN-C-91-0441, 1991.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SImt and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. AN rights reserved.

I95

LEACHING BEHAVIOUR OF BUILDING MATERIALS WITH BYPRODUCTS UNDER PRACTICAL CONDITIONS. P.J.C.Bloem, F.L.M.Lamers and L.Tamboer KEMA Nederland B.V.; P.O. Box, 6800 ET Arnhem, The Netherlands ABSTRACT

From sand-lime bricks in which 20 wt% of a mixture of fly ash and S(pray) D(ry) (Absorption) P(roduct) was processed, the leachability was determined by means of a standard diffusion test. Besides a test wall has been built up to determine the leachability under practical conditions. This experiment was started at June 1991 and some provisional results are presented and discussed. The leached quantities from the standard diffusion test meet the U1 values of the draft Dutch Standard involved. Further the amounts of dissolved species in the collected rainwater from the test wall are low up to now. 1. INTRODUCTION

At the end of the eighties all the Dutch coal-fired power stations have been provided with flue-gas desulphurization (FGD) units, producing about 250,000 tonnes/year at the moment. There was some concern, however, that not all the produced FGDgypsum could be applied in that field in the near future. Therefore alternative processes were examined to prevent an excess of FGD-gypsum. The Spray Dry Absorption (SDA) Process might be a good option. This process yields an endproduct (SDA Product) with handling properties similar to those of fly ash; it is primarily composed of calcium-sulphite and -sulphate and an excess of calciumhydroxide and calciumchloride. Application of SDA Products, as a mixture with fly ash, in sand-lime bricks was studied both on laboratory and factory scale. Therefore samples (bricks) were pressed and autoclaved in which sand was partially substituted by a mixture of fly ash and a SDA Product. A big-scale experiment was performed on a sand-lime brick yard (KZI Loevestein). The aim of this was twofold; first to get information about the processing and properties of the bricks with byproducts if the preparation was conducted on production scale. On the other hand it is necessary to determine the leaching behaviour of building materials with byproducts from coal-fired powerplants. First of all a standard test was performed in the laboratory, namely the diffusion test. Some aspects from practise, however, could be hardly simulated by tests performed on laboratory scale, like the changes of the temperature and variations on dry and wet periods. Therefore a test wall has been built up to examine the leaching behaviour of the bricks just-mentioned. The start of this experiment was June 1991.

196

In this paper the provisional leaching results, both from the diffusion test and the test under practical conditions, will be mentioned and discussed.

-

2. SAND-LIME BRICKS WITH (FLY ASH SDA PRODUCT) MIXTURE 2.1. Raw Materials

The conventional raw materials for the production of sand-lime bricks are sand and lime. The chemical compositions of the fly ashes and SDA Products are mentioned in table 1 and 2. Table 1 Chemical composition of fly ash (wt%)

A B C

90,

AI,O,

Fe,O,

CaO

MgO

Na,O

K20

TiO,

SO,

54.9 64.7 51.0

30.2 20.2 24.2

6.0 5.1 7.7

3.2 1.6 2.6

1.0 0.7 1.0

0.32 0.32 0.40

1.49 0.82

1.7 1.1 1.1

0.32 0.22

1.05

LO1

0.91 3.9 0.35 6.9

Table 2 Chemical composition of SDA Product (wt?/b)

1 2

CaS03,0.5H,0

CaS0,.2H20

Ca(OH),

CaCO,

71.8 50.2

3.0 10.0

<0.2 12.6

6.5

0.5

CaCI, 10.6 5.6

2.2. Production

Twelve series of sand-lime bricks were produced; the quantities of the (fly ash-SDA Product) mixtures added to sand and lime was 20%. The compositions of the various mixtures used are given in table 3.

197

Table 3 (Fly ash - SDA Product) mixtures 0%

SDA no fly ash fly ash A fly ash B fly ash C

10% SDA-1

30% SDA-1

II

Vlll Ill IX

SDA-1

10% SDA-2

30% SDA-2

IV

V

X VI XI

60%

60% SDA-2

I XI1

VII

3. LEACHING 3.1. General

The mechanism of leaching depends on the size of the products involved. With regard to grains smaller than 40 mm this is mainly governed by percolation as in building materials (>40 mm) migration of the components take place by means of diffusion. The so called column test and cascade test are designed for measuring the leaching properties of granular products. The results give information on leaching properties within five years and on the long term (> 50 years) respectively. The determination of the leaching properties of the sand-lime bricks was performed by the diffusion test. It consists of submerging a brick in an aqueous solution of pH =4. Further some examinations are being performed in practice. Therefore a test wall has been built up and some provisions have been made onto the wall to collect the rainwater coming from the surface of this wall. The amounts collected were registered automatically and at particular times these aqueous solutions were analyzed. The results of both the diffusion test and the test under practical conditions are compared with the draft Dutch Standard values (Bouwstoffenbesluit). 3.2. Diff usiontest

First of all the measurements of the delivery of potentially harmful components from sand-lime bricks with fly ash and SDA Product were performed by means of the Dutch Standard NVN 7345. According to this a brick is immersed into an acidified aqueous solution (pH 4).

198

After 1/4, 1, 2, 4, 8, 16, 32 and 64 days the liquid is refreshed and then the supernatant analyzed with some components mentioned in the draft Building Materials Act (Bouwstoffenbesluit). The cumulative diffusion is the total amount of a component in all the supernatants determined. The values were corrected for the geometric surface of the brick and expressed as mg.m-’ (cumulative diffusion). It was assumed that the leachability was controlled by diffusion. These cumulative results were compared with the standard values of the draft Building Materials Act. 3.3. Leaching test under practical conditions

A test wall has been set up by means of a part of the produced sand-lime bricks. The wall was divided into four sections; each section consists of one type of the sand-lime bricks (figure 1). So four types of these bricks were subjected to this experiment under practical conditions, namely I, VII, Vlll and XII. The leaching behaviour of these sections is being determined by first collecting the water coming from each section at set times and then analyzing them. Therefore the sections of the wall provided with plastic gutters, sloping down and connected to a vessel.To prevent direct capture of rainwater and contaminations (leaves) a shelf has been placed above the gutters. After removal from the collecting vessels the aqueous solutions has been analyzed with respect to some components mentioned in the draft Building Materials Act.

Fig. 1

Testwall consisting of four sections

199

0

1

mmn mm

AS

BO

Cd

Cr

cu

Mo

Ni

Pb

Se

v

Zn

SO,

Rip.

mmP

m a

AS

Ba

Cd

Cr

cu

Ma

Ni

Pb

Se

v

Zn

o m mmm m!x

As

BQ

Cd

Cr

cu

Mo

Ni

Pb

Zn

Se

SO,

o x mmx m m

AS

BO

Cd

Cr

cu

Mo

Ni

Fig.2 Leaching results from diffusion test o f sand-lime expressed as o fraction of the

U1 limits

Pb

Se

v

Zn

SO'

bricks with fly ash and SDA product

200

From these results the "cumulative diffusion" per unit area of a section was calculated and compared with the already mentioned values of the draft Building Materials Act.

4. RESULTS AND DISCUSSION 4.1. Diffusiontest

The results of the standard diffusiontest of the twelve types of sand-lime bricks are given in fig. 2. They are presented as a fraction with respect to the U1 values of the draft Building Materials Act.If the quantity of a component measured in the supernatant is lower than the detection limit 50% of this limit was introduced into the calculation of the cumulative diffusion. This is an compromise between an optimistic estimation and the "worst case". From these results it may be concluded that all the cumulative diffusion values are far lower than the U1 values mentioned in the draft Building Materials Act except selenium.With regard to the element last-mentioned the quantity dissolved was always lower than the detection limit. 4.2. Test under practical conditions

It was supposed that 10% of the rainwater has been in contact with the wall. This agrees with about totally 180 litres of water during the whole period examined up till now with respect to one section. The amount of water collected is about 33 I. So it may be that the assumption of 10% rainwater being in contact with the wall is too high. Other factors contributing to this figure are evaporation and absorption of water into the bricks. With respect to each period the amounts of collected water of the four sections are of similar order; besides the correlation between these values and the quantities of rainwater that has fallen during these periods is reasonable. The "cumulative diffusion" expressed as the ratio of the U1 values are given in fig. 3-7. After the first periods higher concentrations of some components were found in the collected water. In March '92 higher quantities of some elements were measured. The collected water of November '92 showed increased amounts of elements, whereas in the collected water of January '93 the concentrations of arsenic, barium, cadmium and chromium were comparatively high.

20 1

Fig.3

The r o t i o of cumulative leaching of arsenic and barium from the test wall and the U1 limits

Cd

. -

A m

I

1994""

Fig.4

1992

1993

The ratio of cumulative leaching of codmlum and chromium from the test wall and the U 1 limits

1994

202 (9

lo-')

6.0

r

bl0-21 cu

'.O

r

Mo

Ni

V

Fig 6 The ratio o f cumulatlve leaching o f nickel and vanadium from the test wall and the U 1 limits

203 (.10-~)

c

Zn

a 1

o

m

o m A m

Fig.7

The ratio of cumulative leaching of zinc from the t e s t wall and the U I l i m i t s

This effect may be caused by the (partial) absorption of the rainwater into the pores of the bricks, followed by a period of dryness. During these periods various salts together with the components measured were transported to the surface of the wall. Then during heavy or prolonged rainfall the salts were rinsed from the wall and collected in the vessel. To get more information about the absorption of rainwater followed by migration of the salts the period of rainfall and dryness should be exactly known. Further it is important to determine the humidity of the sections during the whole testperiod. The component concentrations found in rainwater were negligible with respect to the amounts determined in the collected aqueous solutions (RIVM/KNMI; 1991). Fig. 3-7 show that the total quality of the greater part of the components determined till May '93 are much lower than the U1 limit values of the draft Building Materials Act; only the cadmiumconcentration is somewhat higher.

204 It should be noticed that the experiment has not yet been finished, so the results presented are provisional. To examine the effects of evaporation and absorption of the rainwater in the bricks it is decided to build another testwall consisting bricks with a higher poresize and porevolume.The periods of rainfall and dryness will be exactly registered automatically. Further the humidity and dryness of the bricks themselves will be measured.

5. CONCLUSIONS The results of the diffusion test show that the leaching behaviour of all types of sand-lime bricks with 20 wt% of fly ash and SDA Product meet the U1 values of the draft Building Materials Act (Bouwstoffenbesluit). Since limited quantities of fly ash and SDA Product were processed into the sandlime bricks it may be expected that these bricks meet the S1 values of the abovementioned "Bouwstoffenbesluit"too. The results of the collected water from the testwall show that the differences of the leachability between the various types of sand-lime bricks are up to now rather low. Evaporation and absorption of rainwater into the bricks strongly influenced the leaching behaviour. Sometimes the leachability of sand-lime bricks with byproducts is even lower than for conventional bricks (arsenic, vanadium). To examine the effects of evaporation and absorption of rainwater in more detail another testwall consisting of bricks with a higher porosity is being built up.

6. ACKNOWLEDGEMENT

Thanks are due to the Amer Power Station (Geertruidenberg) and Flakt (Sweden) for providing the fly ash and SDA-Product respectively. This study is undertaken by order of the Dutch Electricity Production Sector.

Environmental Aspects of Consmction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) Q1994 Elsevier Science B. K AN rights resewed.

205

FGD GYPSUM DEFINITIONS AND LEGISLATION IN THE EUROPEAN COMMUNITIES, IN THE OECD AND IN GERMANY Franz Wirsching, Rolf Huller, Rainer Olejnik Eurogypsum Environmental Group, 3, rue Alfred Roll, F-75017 Pans 17

Abstract The production of FGD gypsum in a FGD plant has been explained in detail in this paper. This shows that FGD gypsum is produced in a FGD plant as a product with specification and quality standards. The operations which may lead to the recovery of FGD gypum are carried out in the FGD plant itself It has therefore been conclusively proved, both technologically and scientifically, that FGD gypsum is a product. Furthermore, it has been shown that, as a product, FGD gypsum is not included in the European Waste Catalogue, is not included in the OECD lists and is not included in the German Waste Catalogue. 1. INTRODUCTION

In recent years there has been a rapid growth in the area of the law relating to the protection of the environment. Essentially, there are 2 organizations which have taken an active part:

-

EC European Communities (12 Member States, see Table 1)

Table 1 Member States of the EC (State August 1992) Belgium, Denmark, France, Germany, Greece, Ireland, Italy, Luxemburg, Netherland, Portugal, Spain, United Kingdom

-

OECD Organisation for Economic Cooperation and Development (24 Member States, see Table 2)

Table 2 Member States of the OECD (State August 1992) Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Island, Italy, Japan, Luxembourg, Netherland, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, Turkey, United Kingdom, United States In addition to the European States, the following are also Member States of the OECD: Australia, Canada, Japan, New Zealand, United States of America

206

The gypsum industry is also affected by the preparation of the environmental law in one essential point: namely its FGD gypsum product (Flue Gas Desulphurisation Gypsum) It has been found in this connection that the facts relating to FGD gypsum must be considered on a broad basis. The expression "FGD gypsum" was often used for all kinds of residues from FGD plants and led to false conclusions which caused incorrect listing of the FGD gypsum product in the waste catalogue. The fact that FGD gypsum is produced in power stations as a product using operations for recovering the material was completely overlooked. This product from power stations is directly used in the gypsum industry without any further treatment, and is identical with natural gypsum. This paper gives a definition of FGD gypsum, and the recovery operations carried out in power stations to produce FGD gypsum as a product are described and discussed. All the European political and industrial organisations and institutions, e.g. Eurogypsum,, the Working Community of the European Gypsum Industry, ECOBA European association for use of the by-products of coal-fired power stations, EURELECTRIC European grouping of the electricity supply industry, the OECD and the EC, are now agreed in their understanding that FGD gypsum is a product. There are also comments on the EC Waste catalogue and the OECD Waste List. Definitions and translations of important keywords are also given in the three languages, English, French and German. 2 DEFINITION OF FGD GYPSUM

FGD gypsum is defined as follows: Gypsum from flue gas desulphurisation plants (FGD gypsum, desulfogypsum) is moist, finely divided, crystalline, high purity calcium sulfate dihydrate - CaS0i2H20. It is specifically produced in a flue gas desulphurisation process incorporating after lime(stone) scrubbing, a refining process involving oxidation followed by gypsum separation, washing and dewatering. 3 . PRODUCTION OF FGD GYPSUM IN COAL POWER STATIONS

FGD gypsum is produced in power stations as a product with a specification and quality standards. To fulfil these requirements, the flue gas desulphurisation plant (FGD plant) must be designed, built and operated so that FGD gypsum is produced as a product. The individual steps for producing FGD gypsum are shown on the following flow diagram, Fig. 1.

207

Figure 1. Typical flow diagram of a wet flue gas desulphurisation process based on limestone with gypsum as the product. FGD gypsum is produced in 4 stages: Stage No. 1: Desulphurisation In the scrubber, the dedusted flue gas is sprayed with a limestone suspension in counterflow. During this operation the limestone CaC03 combines with the sulphur dioxide SO2 and produces calcium sulphite CaS03%H20. This chemical reaction is represented by the following chemical equation: SO2 + CaCO3 + %H20 -+ CaS01%H20 + CO2 The legal requirements of the desulphurisation system are fulfilled by eliminating the sulphur dioxide SO2 from the flue gas. The calcium sulphite CaS03'%H20 thus obtained appears as calcium sulphite sludge in the quencher of the scrubber. In some power stations this sludge is still drawn off from the quencher and deposited in large ponds near the power station. However, further reaction steps are needed if the calcium sulphite is going to be worked up into FGD gypsum. These operations for recovering the material are described hereafter as stages 2, 3 and 4. Stage No. 2: Forced Oxidation When converting the calcium sulphite into calcium sulphate dihydrate, the calcium sulphite CaSO,'%H20 is oxidized in the quencher with atmospheric oxygen 02. This chemical reaction is represented by the following chemical equation: 2CaS03.1/J120+02+3H20 + 2CaS0;2H20 The calcium sulphite reacts spontaneously with atmospheric oxygen to form first calcium bisulphite and then calcium sulphate dihydrate. The calcium sulphite must be completely oxidised to calcium sulphate dihydrate. This oxidation is carried out in FGD plants by blowing air into the aqueous sulphite slurry in the quencher. During this procedure the gypsum crystals grow by permanent circulation to the required average size of 30 - 70 microns. This 2nd stage is the first operation for recovering the material.

208

Stage No. 3: Gypsum Separation The calcium sulphate dihydrate crystals produced in the quencher slurry have to be separated and refined to remove solid impurities. This is carried out using a hydrocyclone.

Figure 2. Method of operation of a hydrocyclone The hydrocyclone can be classified as a mechanical separation device in which sedimentation takes place in a centrihgal field. In practise, it is a good on-stream classifier for the 5 - 100 micron particle size range. The coarser calcium sulphate dihydrate particles are separated with the underflow and are fed into the fourth stage of the operation. The smaller particles are separated with the overflow and are recycled to the quencher to grow larger. Stage No. 4: Gypsum Washing and Dewatering During this stage of the recovery operations the calcium sulphate dihydrate crystal suspension from the hydrocyclon underflow is filtered into filter cake and filtrate by a filter or centrifuge. The filter cake consisting of moist calcium sulphate dihydrate crystals, is further refined by washing with clear water (of drinking quality) to remove water-soluble substances, especially chloride, sodium and magnesium ions. The dewatered filter cake contains less than 10 % moisture by weight. This moist, finely divided, crystalline, high purity calcium sulphate dihydrate is the "FGD gypsum" product.

209

Figure 3 shows a washing and dewatering station in a flue gas desulphurisation plant. This fourth stage is the last operation for recovering the material. The FGD gypsum obtained is suitable for general use in the same way as natural gypsum.

Figure 3. Washing and dewatering station in a flue gas desulphurisation plant Figure4 shows a typical flow diagram of a flue gas desulphurisation plant for producing FGD gypsum. The four stages of FGD gypsum production are marked with circles No. 1 - 4, showing the desulphurisation (1) and the three recovery operations (2, 3 and 4) of the refining process. It is clear that such a desulphurisation plant producing salelable gypsum will be more expensive - approximately twice as expensive as a FGD plant producing calcium sulphite sludge.

4.

Figure 4. Flow diagram of a flue gas desulphurisation plant for producing FGD gypsum with the 4 operation stages. The specification and quality standards for the FGD gypsum product are shown in Table 3.

210

Table 3 Quality Requirements for FGD Gypsum Property

Requirement

free moisture

:10

M.-YOby weight

Calcium sulfate dihydrate CaS04.2H20

'95*

M.-% by weight on dry basis

Magnesium oxide MgO water soluble

:0,l

M.-% by weight on dry basis

Chloride CI-

:0,Ol

M.-Yoby weight on dry basis

Sodium oxide Na20

:0,06

M.-% by weight on dry basis

Sulphur dioxide SO2

:0,25

M.-% by weight on dry basis

pH value

5 to 9

Colour

white**

Odour

neutral

Toxicity

non toxic***

* ** ***

Reduced purities consistant with acceptable environmental impacts and product performance are allowable, e.g. for the cement industry comparable with natural gypsum conforming to national requirements over the product life cycle

Table 3 shows that the FGD gypsum product is characterized by its: low moisture content of less than 10 % moisture by weight high purity of more than 95 % of calcium sulphate dihydrate very low content of water-soluble substances, such as magnesium at less than 0,l %, chloride at less than 0,Ol % (< 100 ppm) and sodium at less than 0,06 % high level of oxidation, with less than 0,5 % calcium sulphite (or 0,25 % SO*) neutral pH value white colour, comparable with natural gypsum neutral ordour, comparable with natural gypsum absence of toxic substances. FGD gypsum can also be supplied in the form of dry powder or dry lumps to suit different market requirements. Drying and compacting can be carried out at the power station or at a gypsum plant.

21 1

4. FGD GYPSUM IN THE EC LEGISLATION

The legal provisions for wastes in the EC are laid down by the Council Directive of EC, dated 18th March, 1991 (91/156/EEC). These so-called general waste provisions of the EC provide for the drawing-up of a European WASTE Catalogue (EWC). In this Council Directive, WASTE is defined as follows: "WASTE" shall mean any substance or object in the categories set out in Annex I which the holder discards or intends or is required to discard. FGD wastes come under Category Q 9 of Annex I with the following wording Q 9 Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dusts, spent filters, etc.) The FGD gypsum product, as described, cannot be and is not included in the European Waste Catalogue (EWC). All other inorganic residues from thermal processes which are considered as waste are listed under the item 10 of the EWC, as follows (State 20. December 1993). 10 Inorganic waste from thermal processes, Nos. 10 01 00 - 10 01 13

The wastes from FGD plants of power stations are listed under the following items 10 01 05, 10 01 06, 10 01 07 and 10 01 08: 10 01 05

calcium based reaction wastes from flue gas desulphurisation in solid form

10 01 06

other solid wastes from gas treatment

10 01 07

calcium based reaction wastes from flue gas desulphurisation in sludge form

10 01 08

other sludges from gas treatment

As mentioned above calcium based reaction wastes are residues which are not refined by recovery operations. According to the EC definition FGD gypsum is a product, because the following requirements are satisfied: product with specification and quality standards product produced for a specific purpose (used in the same way as natural gypsum e.g. by the building products industry) product with positive economical and ecological value the product use is regulated by delivery contracts FGD gypsum also fulfills the criteria for a product with respect to quantity. At present about 3 million tonnes of FGD gypsum are being produced annually in the Federal Republic of Germany, purchased and used by the building products industry. More than 6 million tonnedyear will be produced and used in Europe in the near future.

212 5 FGD GYPSUM IN THE DIRECTIVES OF THE OECD

The Council decision by the OECD on the Control of Transfrontier Movements of Wastes Destined for Recovery Operations (C(92)39) controls the transfrontier movements of wastes. The following conditions shall apply to transfrontier movements subject to this decision:

-

-

The wastes shall be destined for recovery operations within a facility which, under applicable domestic law, is operating or is authorized to operate in the importing country. The transfrontier movements shall be carried out under terms of applicable international transport agreements. Any transit of wastes through a nonmember country shall be subject to all applicable international and national laws and regulations.

The Organization for Economic Cooperation and Development, in the Council Session on 30 March 1992, essentially adopted the stipulations of the Basel Convention, enriching them by a three-level waste monitoring system: 1. "Green" list "Waste with no hazardous contamination" Wastes destined for recovery operations which are subject to normal controls (,,green tier"); 2. "Amber" Control System and list "Waste contaminated with material, which prevents the recovery in an environmentally sound manner". Wastes destined for recovery operations which are subject to enhanced control including written contracts, specific consent, additional provisions relating to re-export to a third country, provisions relating to recognized traders, and tracking documents (,,amber tier") ; 3. "Red" list "Waste contaminated with or containing hazardous materials" Wastes requiring written consent before transfrontier movement (,,red tier") Initially FGD gypsum was listed on the OECD green list. However, because FGD gypsum complies with the provisions of the OECD for a product, EUROGYPSUM requested the OECD to delete FGD gypsum from the green list, and the OECD have complied with EUROGYPSUM's request. FGD gypsum is thus recognized as a product by the OECD. Therefore, FGD gypsum is not included in the any of OECD green lists. All other inorganic residues from thermal processes, but also gypsum or gypsum containing residues which are considered as waste, are listed in the Green List or in the Amber List, as follows (State 23. July 1993).

213 Green List GG 010

Partially refined calcium sulphate produced from flue gas desulphurisation (FGD)

GG 020

Waste gypsum wallboard or plasterboard arising from the demolition of buildings

Amber List

AB 140

Gypsum arising from chemical industry processes

AB 150

Unrefined calcium sulphite and calcium sulphate from flue gas desulphurisation (FGD)

According to the OECD definition, the following requirements of the OECD are satisfied: FGD gypsum, a product and a secondary raw material, is directly used in the gypsum industry, without any additional recovery operations. Its economic value is comparable with that of natural gypsum, but is also dependent on the freight costs for transportation from power station to gypsum factory. FGD gypsum can be transported by truck, railway or ship without any special provisions. 6 . FGD GYPSUM M GERMAN LEGISLATION

In Germany, differentiation is made between Ruckstande (residues), Sekundarrohstoff (secondary raw material) and Abfall (waste). If residues are properly and harmlessly put to an intended use in accordance with the German Federal Emission Protection Law $ 5 , $9 1, No. 3, they are designated as a product. Only when residues can no longer be utilized and have to be disposed of, are they considered as waste. (State 22. June 1992, 5. Novelle) According to German law FGD gypsum is first designated as a residue. But because it complies with a specification and with quality standards of the Gypsum Industry and because it is properly and harmlessly put to an intended use, the German law therefore considers FGD gypsum to be a secondary raw material. This legal provision has been adopted by other countries. FGD gypsum is also recognized as a product in, for example, the United Kingdom, France, Belgium, Netherlands, Denmark and Austria. It is the intention that in the future the national waste catalogues (e.g. german AbfBestV; Abfall-Bestimmungs-Verordnung) will be brought into line with the European Waste Catalogue and with the OECD lists.

214 7. DEFINITIONSAND TRANSLATIONS OF KEYWORDS RELATING TO FGD GYPSUM

However, some questions still remain unanswered in spite of all the efforts to recognize FGD gypsum as a product and to bring the term "Waste" and the legal provisions governing waste into line in the EC, in the OECD, and nationally. An important and decisive key to answering these questions lies on the exact definition and the correct translation of keywords relating to FGD gypsum. For example: Definitions There is as yet still no uniform definition of the term "Waste" in the EC, in the OECD and on a national basis. Definition of WASTE in the EC (Council Directive 91/156/EEC): Waste shall mean any substances or object in the categories set out in ANNEX I which the holder discards or intends or is required to discard. ANNEX I: Categories of waste Q 9 Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dusts, spent filters, etc.)

Definition of WASTE in Bale Convention for the OECD On the control of the transboundary movements of wastes and hazardous wastes and their disposal Article 2 Definitions Wastes are substances or objects, which are disposed of, or are intended to be disposed of, or are required to be disposed of, by the provisions of national law. Definition of WASTE in Germany (State 22. June 1992, 5. Novelle) Residues ($ 3 (1)) are movable things (substances and objects) in the sense of byproducts from energy processing or from the production, processing and manufacturing or other treatment of substances and products in installations that are regulated by the German Federal Emission Protection Law. Two subdivisions: Secondary raw materials ( 5 3 (2)) are residues submitted to recovery operations as defined in the waste disposal law. Waste (6 3 (3)) are residues for which utilisation as secondary raw materials is not allowed. It can be seen from this that the definitions of "Waste" in the EC, in the OECD and in the national laws are far from consistent. The terms

-

residue secondary raw material by-product

have not yet even been defined.

215

Translations There are, for example, some official translations from English into French and into German, and these also demonstrate how difficult it is to translate the English expressions, which have been defined in the conference, correspondingly and appropriately into French and into German Example 1

Council Directive 18. March 1991 91/156 /EEC (Page 1)

english:

Whereas common terminology and a A n i t i o n of waste are needed in order to improve the efficiency of waste management in the Community II est necessaire de disposer d'une terminologie commune et d'une definition des dechets Fur eine offizielle Abfallbewertung in der Gemeinschaf? sind eine gemeinsame Terminologie und eine Definition der Abfalle erforderlich.

french: german: Example 2

Council Directive 18. March 1991 91/156 /EEC ANNEX I Categories of Waste Q 9

english:

Residues from pollution abatement processes (e.g. scrubber sludges, baghouse dust, spent filters, etc.) Residues de procedes antipollution (par exemple boues de lavage de gaz, poussieres de filtres a air, filtres uses etc.) Riickstande von Verfahren zur Bekamphng der Verunreinigung (2.B. Gaswaschschlamm, Lufifilterriickstande, verbrauchte Filter usw.)

french: german: Example 3

Council Directive 18. March 1991 91/156/EEC ANNEX I1 B R4

english: french: german:

Recycling/reclamation of other inorganic materials Recyclage ou recuperation d'autres matieres inorganiques VenvertungRuckgewinnung anderer anorganischer Stoffe

Example 4

Council Directive 18. March 1991 9 1/ 1 56/EEC ANNEX I1 B

english: french: german:

Operations which may lead to recovery Operations Debouchant sur une possibilite de valorisation Venvertungsverfahren

216

From these few examples it is clear that, in spite of the agreement already reached, there is still much detailed work to be done in the fbture to reach an international understanding in the field of products and wastes. In particular, there must be clear scientific and technical conformity in definitions and translations. It is also necessary to make an exact delimitation between the term WASTE and the term PRODUCT. No such a delimitation has yet been made. 8. SUMMARY AND CONCLUSION

The production of FGD gypsum in a FGD plant has been explained in detail in this paper. This shows that FGD gypsum is produced in a FGD plant as a product with specification and quality standards. The operations which may lead to the recovery of FGD gypum are carried out in the FGD plant itself It has therefore been conclusively proved, both technologically and scientifically, that FGD gypsum is a product. Furthermore, it has been shown that, as a product, FGD gypsum is not included in the European Waste Catalogue, is not included in the OECD lists and is not included in the German Waste Catalogue. These regulations are of great importance, particularly for Europe and Germany. At present a about 3 million tonnes of FGD gypsum are being produced annually in Germany and used as a secondary raw material as well as natural gypsum, and there will be more than 6 million tonnedyear in Europe in the near future. If this FGD gypsum used in Europe and Germany were to be defined internationally as WASTE, this valuable product would become "Abfall" (WASTE) when translated into German. However, the label "WASTE" projects a decidedly negative image everywhere, and the future use of FGD gypsum in Europe would be endangered. FGD gypsum is a product which is identical with natural gypsum and therefore useable in the same way. Elimination of the term "WASTE" (Abfall) for FGD gypsum is essential to ensure its future use as a valuable product.

Environmental Aspects of Consmtction with Waste Materials J J J M Goumans, H A . van der SIoot and l3.G. Aalbers (Editors) 91994 Elsevier Science B.V. All rights reserved

217

In-situ Utilization of Waste Bentonite Slurry Noburu Uchiyama and Sumio Horiuchi Underground Engineering Department, Institute of Technology, Shimizu Corporation, 4-17, Etchujima 3-chome, Koto-ku, Tokyo 135, JAPAN

Abstract The increase in waste bentonite slurry, being discharged through substructural constructions, has become a serious problem because of its negative environmental effects and the decrease in the capacity of disposal sites. This paper describes two methods to utilize the waste slurry: in-situ slurry solidification and cast in place slurry-cement material. Therein the effectiveness of sodium carbonate with respect to viscosity decrease of the mixtures, and higher compressive strength of the solidified slurry are confirmed through laboratory tests and field application. Also, the additions of a retarder and a dispersant make long-distance transportation possible by preventing segregation. This procedure will help in the development of low-cost recycling systems involving collection, processing, transport and utilization.

1. INTRODUCTION The increase in waste bentonite slurry, being discharged through substructural constructions, has become a serious problem because of its negative environmental effects and the decrease in the capacity of disposal sites in Japan. The waste slurry, originally bentonite slurry, is important to prevent trench collapse and water leakage for construction of cast in place piles or walls. Although bentonite is originally an inorganic mineral, properties of bentonite slurry is damaged with cement contamination, and is disposed of by reclamation or sea disposal as an industrial waste material. The reasons for the extended use of the slurry method which causes the waste slurry, are that the driven pile methods can not be used in cities because of their noise and vibrations; and substructural constructions in soft ground are increasing rapidly. Waste slurry amounts to 14,000 ton a year in Japan, but only the 10% has been utilized. The utilization of waste slurry is not promoted due to the following reasons : (1) Slurry state makes its transport and treatment difficult, (2) cost of stabilization exceeds the cost of disposal, and (3) supply and demand of slurries are unbalanced. For increase of the waste slurry utilization, two methods are reported in this paper. One is the in-situ slurry solidification .The other is the use for a cast in place slurry-cement material. In-situ slurry solidification is the method that uses bentonite slurry as the main component, and decreases the discharged waste slurry. Fig.1 shows the conventional procedures, Ground is excavated down to a given depth, filling trench with bentonite slurry

218

(Step 1). Steel as a member of the earth retaining wall, is then installed in the trench, and then vinyl chloride tubing is attached to deliver air (Step 2). While air is blown into the trench to mix the slurry, an additive and mortar are thrown in. The materials can be well mixed for 30 minutes of mixing to develop enough strength for the wall (Step 3). As a result of this application, more than 70% of the waste bentonite slurry can be utilized. In the conventional method, the addition of water glass as a solidifying additive makes the mixture excessively viscous during air-blowing. This high viscosity prevents homogeneous mixing, and splashes the mixture during air blowing. Difficulties for the viscosity control have made this method unpopular.

Excavating

(1) Trench excavation

(2) Installation of steel

(3) Air blowing and materials mixing

Fig. 1. Procedures of conventional in-situ slurry solidification

The first approach of this paper is for the alternative additive. In our past research, it was c o n f i e d that the use of sodium carbonate is effective on strength development of cement-soil mixture without viscosity increase. So, the effectiveness of sodium carbonate was examined the laboratory and field tests. The second approach is for improvement of waste slurry. Fig2 schematically shows the circumstances of waste slurry. The mixture of the waste slurry and cement would be usable for filling, however it is difficult to stock the waste slurry in the same construction site. A new idea consists of a treatment center, where the waste slurry is improved for the use as a cast in place slurry-cement material. The key points to be solved are the prevention of material segregation and the retardation of its viscosity increase that allow long-distance and long-time transportation from the center plant; and the variation of the waste slurry gathered from many construction sites. To achieve these, the effectiveness of a retarder and a dispersant to improve waste slurry is also investigated using eight waste slurries from a waste sluny treatment plant. In this paper, new effective usages of the waste slurry are proposed based on the laboratory and field studies.

219

.

Wastes dealer collection treatment

;' Ouestions

Problems system cost balance

legal regulation properties

treatment plant

-

waste slurry's flow at present waste slurry's

-----) flow proposed

Fig.2. Processing and utilization of waste slurry 2. STUDIES ON EFFECTIVENESS OF SODIUM CARBONATE

2.1.

Laboratory tests

2.1.1. Materials In laboratory tests, 300 mesh bentonite from Gunma prefecture in Japan and three kinds of cement were used. For solidifying agents, water glass, a highly viscous liquid, and sodium carbonate, a white powder, were used. 2.1.2. Test procedure To confirm the influence of the mixing methods, a Hobert-type soil-mixer with two stirring speeds and a hand-mixer were used. Bentonite slumes were mixed with water glass or sodium carbonate for 10 minutes. Next, cement paste with a water/cement ratio of 50% was added to the slurry and mixed together for another 10 minutes. Afterwards, the mixtures were poured into molds and cured in 20 degree water. The unconfined compressive strength (qu) was then measured in accordance with ASTM(D2166-91). 2.1.3. Results (1) Effect of mixing methods Tables 1 and 2 show the effects of mixing methods on qu. In the case of water glass, qu of the high speed mixing and the low speed mixing were 65% and 40%, respectively, the hand-mixer. But in the case of sodium carbonate, qu of the low speed mixing was 68% of that made by the hand-mixer. That means, the use of sodium carbonate decreases the influence of mixing method on qu compared to water glass. (2) Strength changes in compositions Table 3 shows the effect of additives on strength development. The results indicate that

220

the amount of sodium carbonate needed is only 1/3-1/4 of water glass to obtain the same qu. Because the qu developed with sodium carbonate is higher than water glass, especially within the first 14 days, the construction of the vicinal block can be started earlier. Table 1. Unconfined compressive strength using three mixing methods : qu (MPa) Bentonite content : 80 kg/m’, High early strength cement : 200 kg/m’, Water glass : 10 kg/m3. Mixing method

1 day

3 days

7 days

14days 21 days 28 days 70days ~

hand-mixer high-speed soil-mixer low-speed soil-mixer

0.11 0.04 0.03

0.21 0.09 0.05

0.45 0.19 0.12

0.83 0.35 0.20

0.87 0.48 0.29

0.99 0.64 0.40

1.24 0.94 0.60

Table 2. Unconfined compressive strength using two mixing methods : qu (MPa) Bentonite content : 80 kg/m3, Ordinary Portland cement : 200 kg/m3, Sodium carbonate : 4 kg/m3. Mixing method

1 day

3 days

7 days

0.06 0.04

0,15 0.07

0.19 0.13

hand-mixer low-speed soil-mixer

14 days 21 days 28 days 70 days 0.27 0.19

0.31 0.16

0.33 0.26

0.39 0.27

Table 3 Unconfined compressive strength of some compositions : qu (MPa) Cement :Portland blast-furnace slag cement Bentonite content : 60 kg/m3 Solidifying materials cement content water glass sodium carbonate (kg/m3) (kg/m3) (kg/m3)

200 200 200

0 0 0

4 10 20

Curing time 7days

0.16 0.25 0.38

14days

28days

0.36 0.49 0.63

0.56 0.66 0.70

22 1

2.2. Field studies of in-situ slurry solidification 2.2.1 Test procedure The new method using sodium carbonate was applied to a retaining and cut-off wall of a subway construction site in Tokyo. This wall was composed of seven blocks, and the total size was 0.6m thick, 18m wide and 38m deep. Strength required for the slurry wall were 0.98MPa in 28-day qu and O.05MPa in 24-hour qu. During the field mixing, powdery sodium carbonate was poured into the trench, followed by mortar addition. Each mixing time was planned for 30 minutes. 2.2.2. Results Table 4 gives the compositions of the materials in all seven blocks along with the original design. From the observation of the material splashing, it was confirmed that viscosity increasing with time was independent of the volumes of the additive or mortar, and viscosity of the new method after 120 minutes mixing was less than that using water glass. Table 4 Compositions of the solidified material Cement : Portland blast-furnace slag cement Block No.

slurry bentonite cement sodium compressive strength (MPa) density content * carbonate curing time (g/cm3)(kg/cm3) (kdm’) (%) 7days 14days 28days 70days _ _ _ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ ~ ~ ~ ~ ~ ~ Design

1.06

60

225

5.0

1 2 3 4

1.12 1.07 1.06 1.09 1.07 1.10

91 65 57 48 15 57

225 250 260 312 300 270

5.0 5.0 7.5 7.5 8.5 5.0

5 6

0.98 0.23 0.33 0.31 0.49 0.26 0.66

0.53 0.73 0.57 1.05 0.59 1.31

0.97 1.13 0.85 1.61 0.98 1.78

1.54 1.17 1.28 2.07 1.30 2.28

* measured by methylene blue adsorption. Table 4 also shows the qu of the molded samples of the mixtures. All of them exceed the 28-day requirement. Because of the wide variety of the bentonite contents, it was important to know this value prior to the determination of cement content. In Fig.3, the changes in qu of the No. 1 wall are plotted. As the depth increased, qu increases. The average qu at a 35m depth is approximately 1.8MPa, 140% of that at ground level. The distributions of dry density and water content show simple linearly relationship. Because there was no segregation in the molded samples, the tendencies in Fig.3 appear to result from the consolidation of the materials.

or-

222

........... .,.......................................

- 10 ............ .......... >! ............. p .....j ............ .................... .......... ;...

h

-6g-20

EI;"

@.!

j

............. j ..........

.........

_i

........... _/. ........... ............. (...........

3o

I

.......

-4n 1

.

j I ... ,....... . .~..................

...... ..; ....

.o

2 .o

3.0

Compressive

1.3

1.4

1.5

Wet density (g/cm3)

strength (MPa)

100

110 120 130 140 Water content (70)

Fig.3. Properties of boring specimens

3. STUDIES FOR UTILIZATION THROUGH TREATMENT CENTER

3.1.

Materials Waste slurry samples were periodically taken out from the first reservoir in a waste dealer for more than a year. Almost all waste slurry discharged around the Tokyo area is brought to the center. Three retarders and two dispersants were used in the tests. Table 5 shows the main constituents of the agents. Table 5 Composition of agents symbol retarder (A) retarder (B) retarder (C) dispersant (a) dispersant (b)

main constituents sugar hydrooxycarboxylate phosphate sulfonate+carboxylate carboxylate

3.2. T:st procedure First, the physical and chemical properties of the waste slurry were examined before the mixing tests. Each slurry sample was mixed with 50-150 kg/m3 of Portland blast-furnace slag cement, and the strength development of the hardened mixtures was measured. Retarders and dispersants were added to the waste slurries and then the cement was mixed. The PA flow test with ASTM(C939-87), the bleeding test with ASTM(C940-89) and the q u test were conducted on the mixtures.

223

3.3. Results (1) Properties of waste slurry The properties of the waste slurry samples are given in Table 6. There is a wide variety of water content and slurry density; 330-840% and 1.07-1.17 Vm3, respectively. The bentonite content, which is one of the major factors for cement solidification as speculated from Table 4, is low and varies widely. The most significant problem is the high bleeding ratio. Large part of this bleeding water would be segregated after cement mixing, and it makes the direct utilization difficult. Chemical compositions are given in Table 7. CaO contents, which show the cement contamination in the waste bentonite slurries, are higher than the original bentonite slurry. Table 6 Properties of waste slurry Date slurry of density samples (g/cm’)

‘92.3 ‘92.4 ‘92.5 ‘92.9 ‘92.10 ‘92.11 ‘92.12 ‘93.2

1.175 1.132 1.117 1.170 1.165 1.104 1.108 1.072

specific gravity

water bentonite sand content content * content (kg/m3) (%)

( ~ d

326 429 517 327 335 545 708 838

2.723 2.727 2.748 2.769 2.897

22 23 24 36 37 25 15 17

funnel pH viscosity

bleeding (%)

(set)

28

6.0 6.5 3.5 2.7 1.0

25.4 22.6 22.4 21.8 20.9

8.0 10.0 10.5 10.0 10.5

11 11 22 29

35

* measured by methylene blue adsorption. Table 7 Chemical compositions of waste slurry and bentonite slurry

No.

SiO,

&32’

‘92.10 ‘93.2 Bentonite

50.67 48.06 70.80

14.70 14.61 13.05

CaO

Fe2co3

9.35 10.33 2.49

5.7 1 5.87 1.97

(2) Cement solidification of waste slurry Fig. 4 shows the correlation of the slurry density and after 28-day qu. Using the broken lines, qu can be estimated from the slurry density for each cement content. Strength required for backfilling would be more than 0.2MPa in qu. The waste slurries could, therefore, be utilized with 150 kg/m3 cement addition. The strength of a hardened slurry could be controlled by the cement content.

224

1.05

1.10 1.15 Slurry wet density (g/cm3)

1.20

Fig.4. Relation of slurry density to qu

(3) Effectiveness of agents Table 8 gives the components of mixtures, bleeding ratio and qu. Figs. 5 and 6 show the changes in PA flow with time. Table 8 Compositions of mixtures and compressive strength Cement :Portland blast-furnace slag cement 100 kg/m’ waste slurry

‘92.10 ‘92.10 ‘92.10

dispersant sym. content (%)*l a a a

0.5 0.5 0.5

retarder sym. content (%)*2

A A

1.2 2.4

bleeding (%)

1.5 2.0 2.5

compressive strength (MPa) curing time 7days 14days 28days 70days 0.19 0.06 0.03

0.33 0.15 0.09

0.49 0.24 0.18

0.64 0.33 0.27

.......................................................................................................................................................

‘92.11 ‘92.11 ‘92.11

a a a

0.5 0.5 0.5

A B C

2.4 2.4 2.4

6.0 6.5 5.0

0.07 0.03 0.01

0.14 0.10 0.04

0.25 0.17 0.08

0.29 0.20 0.13

’92.11 ‘92.11 ‘92.11

b b b

0.5 0.5 0.5

A B C

2.4 2.4 2.4

4.5 7.0 3.5

0.07 0.03 0.01

0.15 0.08 0.04

0.24 0.14 0.09

0.29 0.16 0.13

* 1. ratio to slurry volume *2. ratio to cement weight

225 As shown in Fig.5, cement mixture of '92.10sample shows a good fluidity even after 6 hours by using 2.4% retarder and 0.5% dispersant, contrasting to an excessive increase in viscosity after 3 hours of mixing without retarder. The retarder addition resulted 28-day qu decrease to 40% , however it might be easily recovered by cement increase. According to Fig.6, PA flow changes for '92.1 I sample, dispersant(a) is more effective on viscosity than (b) without in the bleeding ratio. It was also found that the appearance of qu is determined by a retarder and is not affected by a dispersant. From the Figs.5 and 6, appropriate use of the additives makes the long-distance transportation possible, and will lead to the increase of the waste slurry utilization. 2

0 . .. ... .

8

0

; . ; . : .. : .. : . . . : . .. . .... .... ... ... . .. . .. .. ..

1

I

I

I

I

I

I

2

3

4

5

6

7

8

Passing time (hours) Waste slurry : '92.10 Dispersant (a) : 0.5%

F i g 5 Effects of retarder addition on PA flow

14

13

p

12

g

11

2

10

+Retarder (C)

h

v

6:

.. ...

OO

. .. .,.. .. ,.

,. .. ..

.

.

.

....

.

...

-

+Retarder(B) uRetarder (C)

....... ........... ......... .. .. .. .... ... ,.

d.. .

... .

,

9

U Retarder (A)

Retarder @) ............................

~

,. .. ..

...

:

.......................

.....

.

;

i......

.

-

..

. . . . .

..

. .

,

..

,

..

,

..

,

..

..

1

2

3

4

5

6

7

Passing time (hours) Waste slurry : '92.11 Dispersant (a) : 0.5%

8

O O

1

2

3

4

5

6

Passing time (hours) Waste slurry : '92.11 Dispersant (b) : 0.5%

Fig.6. Effects of dispersant addition on PA flow

7

8

226

4. CONCLUSIONS The superiority of sodium carbonate as a solidifying additive during slurry solidification was verified with respect to viscosity of the mixture and qu of the solidified materials. The mixture with sodium carbonate was less influenced by mixing methods than that with a conventional additive; furthermore, sodium carbonate of only 1/3-1/4 by volume of a conventional additive, was needed to obtain the same qu value. As for application in the field, material splashing decreased, and handling of the

additive became so easy that the operational environment was improved. Waste sluny gathered from many work sites could be used as back filling materials by mixing 150kg/m3 portland blast-furnace slag cement. Adding a retarder and a dispersant to the mixture at the same time made long transportation of the slurry-cement mixture possible without segregetion of the materials.

REFERENCES 1 SHoriuchi, The effects of additives to the strength of soil-cement, Proc. 13th Japan Nat.

Conf. on soil mechanics and foundation engineering, 1393- 1394, 1978. 2 N.Uchiyama and S.Horiuchi, A new in-situ slurry solidification method using inorganic carbonate, Pro. 47th Ann.Conf. of the Japan society of civil engineers, 986-987, 1992. 3 N.Uchiyama, S.Horiuchi and M.Tuyusaki, A recycling method of waste bentonite slurry, Proc. 28th Japan Nat. Conf. on soil mechanics and foundation engineering, 2599-2600, 1993. 4 N.Uchiyama, SHoriuchi, Y.Nakabayasi and M.Matui, The application of a new in-situ solidification method", Proc. 48th Ann. Conf. of the Japan society of civil engineers, 642-643,1993.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Slmt and 7’h.G.Aalbers (Editors) 91994 Elsevier Science B, K All rights reserved.

227

The use of M.W.I. fly ash in asphalt for road construction J.B.M. Hudales Vulstof Combinatie Nederland B.V., P.O. Box 259, 2100 AG Heemstede, The Netherlands

Abstract In The Netherlands several years of experience with the application of M.W.I. fly ash in filler for asphalt for road construction have been obtained. This application is accepted, not only from a technical, but also from an environmental point of view. 1. INTRODUCTION In The Netherlands asphalt fillers are produced on the basis of limestone, calciumhydrate and several industrial waste materials like coal fly ash and M.W.I. fly ash. Limestone and calciumhydrate are specifically gained and worked up for the filler industry in an energy devouring process. From the point of view of protection of nature as well as for conservation of precious natural raw materials it is justified and recommendable to make use of secondary raw materials for the production of fillers on a large scale, although the use of primary raw materials will not be excluded completely. Since the early 1980’s efforts have been undertaken to find useful applications of the waste materials like the bottom ash and fly ash. In an overcrowded country like The Netherlands landfill is never a good solution. In the case of the fly ash we now have about ten years of experience with its application as a raw material in filler for road construction. In The Netherlands about 60,000 tons of fly ash were produced as a result of the incineration of municipal waste in 1993. Although this is only a fraction of the amount of bottom ash produced during the same process, it is much harder to find useful applications for it. Until now the only application is in asphalt filler, which consumes about 40 % of the amount of fly ash produced. For the near future a total amount of 150,000 ton of fly ash is foreseen, of which with a lot of effort only 50 % may be reused depending of course on the demand for asphalt.

228

2. TECHNICAL REQUIREMENTS

Filler is an aggregate for asphalt: in fact, it completes the particle size distribution of the gravel and sand fraction and fills up the pore volume between the sand grains. In priciple, chemically inert it is in asphalt, but it has a positive effect on the viscosity of the binder so that demixing of the asphalt mixture is prevented and the asphalt becomes more stable. Many fillers contain hydrate which is added in the form of slaked lime to enhance the attachment between bitumen and aggregate. This is especially needed in drain asphalt, where the bitumen must achieve the cohesion between the coarse aggregate particles at much smaller contact areas than in the case of dense asphalt because of the lack of a part of the sand and fine gravel fraction. All the fillers have to satisfy many technical requirements to be allowed in road construction, for which purpose they are certified. These requirements are listed in Table 1. They have to be tested according to the dutch draft standards Ontwerp NEN 3975 up to and including 3984 which were jointly published in the booklet "S.V.C.; Normen en Proefvoorschriften" in 1992 [I]. The four filler types only differ in their bitumen binding capacity according to which they are nominated, and air void, except for the class 50 filler and the class 50 filler with hydroxide which differ in the obligatory hydroxide content and therefore in the water solubility. Furthermore, two properties have been added to the list in Table 1 to facilitate the determination of a certain filler. These are the particle density which is also needed for the calculation of the air void and the solubility in hydrochloric acid, both of which are included in the range of draft standards listed above. M.W.I. fly ashes are at the moment only applied in the class 40 and 50 fillers only, but investigations are being carried out for application in small amounts in a class 50 filler with hydroxide which is specially developed for drain asphalt. The properties of the M.W.I. fly ash makes it impossible to use it in class 30 filler. These properties which limit the application to 35 % of the filler, differ from one plant to another, but the ashes used fit in very well in cooperation with the other raw materials. For filler production grinding of the fly ash is necessary to meet the final filler requirement for the particle size distribution (Table 1). Mean values of the relevant properties of several M.W.I. fly ashes used by V.C.N.in 1993 are listed in Table 2.

Table 1 Specifications of the dutch filler types Property

Class 30

Unit

min.

Particle size: Remainder on sieve 2 mm 90 pm 63 pm

5

0 15 25

28

38

% (m/m) % (m/m) % (m/m)

Bitumen binding capacity Air void

%

(vm

28

Loss on heating at 150°C

% (m/m)

Solubility in water

% (m/m)

Susceptibility to stripping

% (m/m)

Swelling

% (v/V)

-

Hydroxide content

max.

% (m/m)

Class 40 min.

max.

5

0 15 25

40

50

-

36 1.5 10

10

3

Class 50 min.

10

3

-

max.

5

5

0 15 25

52

62

52

62

44

10

min.

0 15 25

-

1.5

-

max.

Class 50 with hydroxide

-

44

1.5

1.5

-

10

3

-

-

-

25

10

15 10

3

Reprinted from: 2e Ontwerp NEN 3975 [l] N N \o

230

Table 2 Mean values of fly ashes from two arbitrary dutch M.W.I.’s in 1993 Property Particle size: Remainder on sieve

90 pm 63 pm

Unit

M.W.I. 1

M.W.I. 2

% (m/m) % (m/m)

38.7 f 7.3 48.2 f 7.7

44.2 f 10.4 59.7 f 7.1

53.4 f 5.1

52.3 f 2.8

% (V/V) 46.8 f 3.0

50.2 f 3.1

Bitumen binding capacity Air void Particle density

kg/m3 2586

f 34

2620

f 14

Solubility in water

% (m/m)

20.5 f 3.5

16.8 f 1.7

Solubility in hydrochloric acid

% (m/m)

62.6 f 5.8

67.3 f 2.1

3. ENVIRONMENT There are no sanctioned environmental requirements for fillers, as the dutch Building Materials Decree (B.M.D.) has not yet been accepted; a draft of this decree was published in 1991 [2]. It falls under the responsibility of the filler producers to keep an eye on the environmental aspects of the fillers they produce. M.W.I. fly ash falls under the Toxic Waste Law, unless it is for 100 % used as a secondary raw material, as does the filler industry. By order of the Road and Hydraulic Engineering Division of the dutch Ministry of Transport, Public Works and Water Management TAUW Infra Consult investigated the composition and leaching behaviour according to the dutch leaching test NVN 5432, of asphalt tablets produced with standard fillers some of which containing M.W.I. fly ash [3]. Although a clear difference was measured in the chemical composition of the fillers, this difference was found again only in a limited extent in the composition of the asphalt tablets because of the small amounts of filler in asphalt. Tank leaching tests according to NVN 5432 showed no difference in the leaching of metals between the asphalt tablets with the different fillers. No more a difference in leaching was found between asphalt tablets with differing pore structures like dense asphalt concrete, porous asphalt and poro-elastic alphalt concrete. To check if a filler with M.W.I. fly ash satisfies the above mentioned draft decree filler producer V.C.N.had fillers with standard to high contents of M.W.I. fly ash and asphalt tablets containing these fillers investigated by

23 1

the Netherlands Energy Research Foundation E.C.N. [4].This investigation has shown that the composition of the asphaltic concrete falls within the composition limits set by the government in S1 FORM GIVEN BUILDING MATERIALS of the draft B.M.D. These values also fall within the limits of S l NON FORM GIVEN BUILDING MATERIALS, which means that if the asphaltic concrete is ground down after use it cannot be designated as chemical waste. The leachability of brokedweathered asphaltic concrete is at that stage decisive for the additional work-up. The availability of the metals in the product asphaltic concrete in itself agrees reasonably well with or is lower than that of the separate materials used. The decrease is caused by the bitumen which, due to its hydrophobic nature, has an effect on the degree of contact with water. The possibility exists that after ageing (weathering) of the bitumen the availability will increase; this has to be investigated further. The tank leaching test shows that the leaching of the products easily lies within the U1 limit for FORM GIVEN BUILDING MATERIALS of the current draft B.M.D. (Table 3). The composition can be optimized on the basis of other requirements so that no problems are expected here. Critical components are lead, cadmium and zinc. These three, of which lead and cadmium approach U1 within a factor of 3, originate from the M.W.I. fly ash. One has to keep in mind that in case of the lower M.W.I. fly ash contents this material had to be replaced by other components like coal fly ash, which explains the irregularities in Table 3. The slope in the tank leaching test for the elements antimony, vanadium and zinc is quite sharp (0.67), which may indicate solubilisation. This solubilisation effect is clearly different from the diffusion behaviour of the other elements. On the basis of these results a calculation has been performed on a theoretical filler with 35 % of M.W.I. fly ash, which is considered to be the technical limit. This calculation showed that no problems are to be expected for such a filler according to the draft B.M.D. regarding composition (FORM GIVEN and NON FORM GIVEN BUILDING MATERIALS) and leaching behaviour .

232

Table 3 Measured cumulative release after 64 days mg/m2

M.W.I. fly ash content in filler (% m/m) 5 7.5 10 20

Metals 578 Sodium < 1.1 Copper 24 Zinc Molybdenum < 0.13 Cadmium < 0.16 Tin Antimony < 0.06 25 Lead Inorganic compounds Cyanide Fluoride Chloride 497 Bromide Sulphate 1105 Reprinted from [4]

788 < 1.1 24 0.27

<

662 c 1.1 21 0.20

796 < 1.1 35 0.22

0.16

0.21

0.09 22

0.08 19

0.30 < 1.1 0.10 28

< 2.8 < 24 581

444

1350

064

95 1 < 17 1253

Ul B.M.D. r21

30 125 4 0.7 20 2.5 75 0.9 440 2250 20 5000

4. REFERENCES

1. S.V.C. Normen en Proefioorschriften, Vulstoffen voor bitumineuze mengsels, Stichting Vulstof Certificatie, Kasteel Maurick Vught, 1992 2. Bouwstoffenbesluit, Staatscourant, 26 juni 1991 3. Milieuhygienisch onderzoek vulstoffen en asfaltkernen (Rapportnummer 3 1422868), Rijkswaterstaat, Dienst Weg- en Waterbouwkunde/TAUW Infra Consult B.V., Deventer, 1991 4. D. Hoede & H.A. van der Sloot, Investigation of the environmental proporties of filler in asphaltic concrete (ECN-CX--92-100 CONFIDENTIAL), E.C.N., Petten 1992 (including a supplementary investigation in december 1993)

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) a1994 Elsevier Science B.V. AN rights reserved.

233

Enhanced Natural Stabilization of MSW Bottom Ash: a Method for Minimization of Leaching.

J.J. Steketee & L.G.C.M. Urlings Tauw Milieu bv, P.O. Box 133, 7400 AC Deventer, the Netherlands

Abstract Upon aging, leaching of most contaminants from Municipal Solid Waste (MSW) bottom ash, especially heavy metals, decreases by 50 to 70% within one year. This follows from repeated investigations of large stock piles (practical scale) and from laboratory research (pilot scale). Small scale laboratory research has revealed that the course of this natural stabilization process can be compressed to eight weeks, by manipulating the storage conditions. At the same time, the immobilization of the most important heavy metals is increased; leaching of Cu and Mo decreases with 8045%.

1. INTRODUCTION Leaching is a key-factor in the quality of secondary raw materials, so a proper assessment of leaching behaviour is very important. A much heard question is whether the laboratory leaching tests resemble the practical situation. One aspect of this resemblance is the long term behaviour of a material. Especially in certification schemes, a material is characterized shortly after production while it is still fresh. As a result of physical, geochemical or microbial reactions, material properties can change in the course of time, which may imply a change in leaching behaviour. To gain insight in the long term behaviour of Municipal Solid Waste (MSW) bottom ash, samples taken from MSW materials with increasing age, stored in a stockpile, were analysed. Furthermore, a pilot scale test was performed, in which a quantity of MSW bottom ash was stored for about one year. During this period, several samples were taken and the effect of age on leaching was investigated. The results of both practical and pilot scale research showed a decrease in leaching after aging. This quality improvement is important for the continuation of the use of MSW bottom ash as a secondary raw material. For this use, the preliminary Dutch Building Materials Decree requires lower leaching levels, especially for copper and molybdenum, than nowadays are commonly found in this material. Therefore an acceleration of this "natural stabilization process" would be of great benefit. On laboratory scale, it turned out to be possible to accelerate this process strongly by manipulating the storage conditions. At this moment the process is optimized and experiments on a larger scale are currently carried out.

234

2. MATERIALS AND METHODS Sampling of a stockpile of 15,000 ton MSW bottom ash at the Duiven incineration plant was carried out with a shovel. Shortly after production this bottom ash was sieved over a screen of about 40 mm. Iron had been removed magnetically. Samples of 10-15 kg were taken from different levels in the pile. The same pile was sampled twice, with an interval of two months. Each time, 9 samples were taken. After homogenizing each sample, a subsample of 1 kg was separated and crushed to pass a 3 mm sieve. With the crushed material, a cascade shake test was performed, using demineralized water, acidified to pH 4, as leachant. Each step of this test was executed at a liquidkolid (LIS) ratio of 20, so the final (cumulative) LIS ratio of the test was 100. The leachates of the different steps were mixed and thii sample was analyzed for arsenic (hydride generationlAAS), cadmium, chromium, copper, lead, molybdenum, nickel (ICP or graphite furnace/AAS), zinc (ICP), COD (NEN 6633), chloride (NEN 6476) and sulphate (EPA 9036). The pH and the electrical conductivity (Ec)were measured too. The pilot aging test was executed with a mixed sample of 320 kg bottom ash of the Amsterdam, Den Haag and Rijnmond incineration plants. This sample was stored during one year in a large column with an effective height of 2 m and an inner diameter of 0.4 m. The average annual rainfall in the Netherlands and the course of the temperature in a stockpile were simulated during the storage period. Samples were taken at five different levels in the column, 6, 12, 21, 30, 42 and 54 weeks after the start of the experiment. As described before, cascade shake tests were performed with all samples. For more details, the reader is referred to 111. The accelerated aging tests were performed with samples of 1 kg in small columns. Different storage conditions were realized by pre-treatments (drying, sterilization) and adjustment of the pore gas composition (e.g. oxic with air injection or anoxic with nitrogen injection). Also, an additive was used to accelerate the process. After a storage period of eight weeks, a shake test at L/S 10 was performed with demineralized water, acidified to pH 4,as leachant.

3

RESULTS

3.1 Stock pile investigation In table 1, some results are summarized of the stockpile investigation in Duiven. The fresh material has not been characterized, data from another period suggest that the quality of the 2.7 month old material approaches the average (long term) fresh quality of the Duiven bottom ash.

235 Table 1

Results cascade test, L/S 100. Leaching concentrations and 90% confidence intervals; n=9 at both investigations [3]

age (months) arsenic (pg/l)

2.1

4.8

1.3 f 0.3

4.8 f 0.9

cadmium f u d )

< 1

<

1

chromium &g/l)

11 f 2.6

I f

2.1

copper Olefl)

131 f- 29

31 f

I

< 10

lead

29

f 5

molybdenum &g/l)

14

f 4

18

f 10

f

I

nickel (pg/l)

2

5

f

zinc (pg/l)

49

f 4

7

* 4

chloride (mg/l)

26

f 2

22

f 3

sulphate (mg/l)

15

f I

115 f 13

28

f 7

COD (mg/l)

E.C. (rS/cm)

PH

1

411 10.1 - 11.1

42

I

1

f 8 403

9.3

- 10.9

3.2 Pilot investigation The mean leaching concentrations (cascade test, L/S 100) of five sampling points are summarized in table 2. The same trend as in the stock pile investigation is observed: the pH and the leaching of heavy metals decreases, the leaching of sulphate and arsenic increases. In contrast with the stock pile investigation, the leaching of COD decreases. The course of the leaching of the most important heavy metals is depicted in figure 1. Zinc and copper both show a quick initial decrease in leaching but molybdenum behaves differently and decreases only slowly. After one year, leaching of molybdenum is 40% lower, copper 75% and zinc almost 90%.

236 Leaching concentrations (cascade test, L/S 100) during aging of MSW bottom ash in a pilot scale column. Each concentration is a mean of five samples, taken at different heights of the column

Table 2

week

pH

0

1

6

11.0

CZV '

I

SO.,

As

30

Cd

Cr

Cu

Mo

Ni

Pb

Zn

........ .................(/Lg/l)....... ............,..

........(mg/l) ........ 34

350

I 10.8 I 362

C1

80

0.8

4

13

181

62

8

29

112

32

22

95

0.8

<1

12

145

56

4

<20

7

12

10.5

337

33

41

155

6.6

1.2

4

32

27

1

<20

31

21

10.3

454

40

35

121

1.3

1

19

82

62

6

<20

4

30

10.3

464

19

23

98

1.7

<1

10

55

25

2

3

<11

15

46

118

1.4

<1

7

58

44

2

2

<6

11

34

139

1.5

<1

10

44

37

2

5

12

42

1 54 I I)

EC @S/cm)

9.8 9.5

575')

I 462

I

1

1

mean is 505 if an outlier is excluded Concentration(pg/l)

- Copper +

+

6

12

21

30

42

Molybdenum

Zinc

54

Age (weeks)

Figure 1

Time course of leaching concentrations of copper, molybdenum and zinc during aging of MSW bottom ash. Cascade tests, L/S 100, each point is a mean of five samples out of a pilot scale column.

3.3 Accelerated aging tests Identical subsamples of broken MSW bottom ash (4 < 3 mm) were pre-treated in a different way by drying and sterilization. Also an additive was used and different redox conditions were maintained by storing the samples in air or N2.The leaching concentrations (shake test, L/S 10) of the fresh material and after aging are summarized in table 3.

237 Table 3

Leaching concentrations (shake tests L/S 10) of fresh MSW bottom ash and upon aging during 8 weeks. after different ore-treatmentsand storaee conditions anoxic 11.0 2160 168 295 300 18

1150 8

460

I 4800

61 I) ')

all samples are crushed till 6 < 3 m m all experiments have been performed at a temperature of circa 20 "C

As table 3 shows, storage under aerobic conditions results in a decrease of leaching of most parameters, especially the heavy metals. Sulphate, aluminium and calcium remain more or less constant during the investigated period but chloride shows a marked decrease. The leaching of antimony increases. The above mentioned trends are more or less the same for all experiments, although there are some differences. Sterilization has little effect, although microbial degradation of organic matter is prohibited. Yet a decrease of leaching of COD is measured. A possible explanation is the encapsulation of organic matter by newly formed precipitates. Drying of the material is not favourable: leaching out off pre-dried material is generally higher than leaching out off undried material. The use of an additive, which nature cannot be disclosed yet, gives a further improvement of the leaching behaviour. Especially copper, molybdenum and aluminium are highly immobilized when this substance is used. Leaching decreases with 81-95% in comparison with the fresh material. On the other hand, the leaching of sulphate, zinc and calcium increases. Only the increase of sulphate may create a problem, although this value still complies with the preliminary values of the Dutch Building Materials Decree. Aging of MSW bottom ash in an anoxic atmosphere (of nitrogen) is unfavourable for the leaching of heavy metals but favourable for sulphate and antimony.

238

4 DISCUSSION AND CONCLUSIONS Several laboratory experiments and stockpile investigations revealed that the leaching of especially heavy metals reduced during the aging of MSW bottom ash. This aging process was greatly enhanced by controlling the storage conditions in combination with the use of an additive. The combination of these two treatments results in decreased leaching of copper and molybdenum (80-85% decrease) in 8 weeks. Such a quality improvement, necessary to be able to meet the legal requirements, was not reached in one year under (semi)practical conditions. Probably this "aging" is a complex set of chemical, physico-chemical and microbial reactions, among which: - carbonation, resulting in a decrease of the pH of the material which has directly consequences for the solubility of major and minor elements; - alteration of surface properties due to the decrease of pH (surface-charge!) and precipitation of newly formed minerals; - microbial oxidation of organic matter (this was confirmed by counts of bacteria and moulds, not published results). Because of the complex composition of MSW bottom ash and the different (chain) reactions that take place, it is difficult to judge which processes are responsible for which part of the quality improvement. Most investigations only covered a limited period of time, so the question arises whether this quality improvement holds for the long term. In the stockpile investigations, the oldest bottom ash was about one year [2]. Artificially aged bottom ash was examined again after 1.5 year (not published). In both cases the leaching quality of the samples was comparable or better with regard to earlier investigations. Generally one can say that the aging results in a material that is more in equilibrium with the natural environment than the fresh bottom ash and therefore in a more stable condition. This stabilization, in combination with the isolated application of MSW bottom ash in the Netherlands, i.e. limited contact with rainwater or groundwater, indicates that the quality improvement will hold for the long term. 5

REFERENCES

1. T A W Infra Consult B.V./Zuidelijk Wegenbouw Laboratorium (1988): Veabrin Kwaliteitscontrole van AVI-slakken 1987-1988 Vereniging van Afvalverwerkers, Utrecht 2. T A W Infra Consult B.V. (1986); Milieukwaliteit van slakken AVI Zaanstad. Tauw Milieu bv, Deventer 3. C.R.O.W. (1988): Resten zijn geen afval (meer) - Afvalverbrandingsslakken. Publication 15, C.R.O.W., Ede, the Netherlands

Environmental Aspects of Conshuction wifh Waste Materials JJ,.J.M. Goumans, H A . van der SImt and Th.G. Aalbers (Editors) 01994 Elsevier Science B.K All rights resewed.

239

Immobilization of slag material by foam bitumen

Dijkink, J.H.

R&E Consult, Utrecht, The Netherlands

ABSTRACT With the foam bitumen technique it is possible to coat cold and wet granular materials with bitumen. It is not necessary to heat or dry the materials. With this cold stabilisation procedure a bituminous bound foundation layer can be achieved with the characteristics of a bituminous concrete asphalt layer. The stabilisation is performed by a standard mobile road recycler, equipped with a spccial spray bar system. When hot straight-run bitumen comes in contact with a foam promotor (i.e. de-ionised water and additives) a bituminous foam will result. The original material expands by a factor of 15 to 20 and after a certain period (2 to 3 minutes) it will drop back to its original volume. During this foamy situation particularly fine particles are encapsulated. In slag material that contains heavy metals, mainly the fines are polluted. By using foam bitumen these fines are encapsulated; as a result of which we can speak of an immobilisation procedure. In the past large quantities of zinc slag material have been used as base course materials of small roads in the area around Budel (The Netherlands), where the zinc factory is located. The foam technique has been used successfully on roads in this area. Execution of the works was followed by an intensive research programme. To check the performance in situ, special containers have been installed in the road. The percolate is sampled regularly and chemically tested. The behaviour of the road will be monitored during a period of at least five years.

1.

INTRODUCTION

The surrounding area of Budel, i.e. the "Kempen" in the south-eastem part of The Netherlands has been polluted by zinc slag for many years. These slags and ashes are a residue of the zinc production process by which zinc is being produced out of zinc ore. Budelco, one of the largest producers of zinc in the world, and consequently also of zinc slags, is located in Budel-Dorplein, a small village in the province of North-Brabant. The slags have very good characteristics for a road-building material, which is the reason that this material has extensively been used in a widespread area around Budel. For environmental reasons this material is no longer used now in road-building construction. The material contains a number of heavy metals in rather high concentrations (Cd, AS,

240

Zn,f.i.). Therefore, the material has to be regarded as a chemical waste product according to the provisional Dutch Building Degree. The zincproduction process has been changed in the meantime and the residue material is now stockpiled at the site of the manufacturing plant. Further pollution of the area by the slag material had to be prevented. Pollution by means of percolate affects the ground water quality and wind-blown dust particles affect the shoulder of the road and the adjacent gardens. To prevent this type of pollution the Environmental Department of the Province North Brabant was looking for methods to overcome these problems. Excavation of the slag material and transportation to a special depot are not advisable because of the standard method of execution and because of financial reasons. Since the foam bitumen process has proven that inorganic components in waste materials can be immobilised, the consultancy firm Research & Engineering Consultants b.v. (R&E Consult) was asked to make a proposal for this project; KWS, a major road-building company in The Netherlands took care of the execution of the activities resulting from this plan. 2.

THE PRINCIPLE OF THE FOAM BITUMEN PROCESS

The foam bitumen process is based on the addition of foam bitumen to loose, moist, granular material. Therefore, a modified road-milling machine is used. After the first milling operation - meant to pulverise the construction and to homogenise the crushed materials - a first profile correction is carried out and the treated layer is compacted. Surplus material that cannot be used for correction of the longitudinal profile is excavated. A tanker with bitumen is connected to the road miller. The bitumen pump of the road miller takes care of pumping the hot bitumen to the special spraybar in the milling and mixing compartment of the recycler. Special nozzles will dose de-ionised water as a result of which the bitumen will become foam. The foam is thoroughly mixed with the whirling material. This special technique with intensive mixing results in a homogeneous coating of the material. The process very much depends on the exact quantity of moisture and bitumen. An accurate control of the required quantity is performed by a computerised system. Additives too, are regulated by the computer. The injection system is linked to the working speed of the milling machine. 3.

THE BUDEL PROJECT

In August 1988, a first pilot project based on the foam bitumen process was executed, also in Budel. The aim was to fix the contamination present in the zinc slag material and to give the material enough bearing capacity. After extensive research the results showed that both requirements had been fulfilled. After this pilot project further steps were taken to come to a large-scale project. Again

24 1

Budel was chosen as location for this project. By the end of 1989, the basics for a laboratory test programme were outlined. Special attention was given to the following points: - optimisation of the type and quantity of additions, with the aim to achieve a higher density of the mix; - the influence of a special stabilising agent on the strength and the environmental characteristics; - selection of a laboratory compaction method (preferably dynamic) corresponding with the field process. This research was carried out in the first half of 1990. From the results we learn that: - the cement required needs to be one per cent by mass; - the addition of the special stabilising agent results in a slightly higher strength and a reduction of the percolation behaviour; - compaction with a Kango-hammer (BS-method) gives the highest density; a higher density means a higher impermeability and a smaller amount of percolate; - based on the amount fines (< 63 micron) the required quantity of foam bitumen is five to six per cent by mass. After discussions with the Client and based upon this pre-investigation procedure, the following four variants were chosen: - treatment of roads with foam bitumen, cement and a special stabilising agent: (three variants); - overlaying of the untreated zinc slag roads: one variant.

To check these variables in the mix, execution of the project is followed by several typical research activities: 1. material research to check the composition of the mix and the permeability of laboratory samples (check on the execution activities); 2. environmental tests to check the immobilisation behaviour of foam bitumen (laboratory research); 3. environmental tests to check the impermeability in situ of the foam bitumen construction and to observe the percolation behaviour; 4. road-engineering research to check the bearing capacity of the construction. In October, 1990, KWS started with the project. After intermediate reports of partial test results, the final report was handed over to the Client in December, 1991. The project was financed by the Dutch Ministry of Housing, Regional Development and the Environment P R O M ) .

242

4.

ENVIRONMENTAL RESEARCH

The environmental test procedure can be split in two parts: production control and percolate control. Production control tests During production, a great number of samples of treated zinc slag material was taken with the aim to check the immobilising effect of foam. All samples were tested according to a single shake test (Liquid/Solid ratio US = 20). Based upon the "worst case" results, samples were selected for a complete analysis programme. Therefore, the following tests were performed: - analysis of particle size and total composition; - the determination of maximum leachability; - small column test (US= 10); - large column test (US = 10); - stand test. The column test is meant to simulate the behaviour of a material when the leaching agent percolates through the system. For the small column test material is being crushed to a size smaller than 3 mm. The large column test contains naturally available material. In a stand test, a tablet or cylinder of the compacted material is continuously in contact with a leachate liquid.

4.1

Leachate behaviour in situ To check the quantity and composition of the leachate and the degree of emission of heavy metals from immobilised or isolated zinc slag material to soil and ground water, a special percolate system was adopted. The percolate container had to be designed such that enough percolate could be measured within a certain period. A quantity of a minimum of half a litre percolate in a month is the assumption. Based upon the k-value, the impermeability, of the compacted and immobilised zinc slag material, the average rainfall and the possible infiltration, the required surface of the percolate system can be calculated. Together with the results of quantitative analysis of heavy metals, the real percolate from the immobilised and isolated zinc slag roads can be calculated. 4.2

4.2.1. Percolate container system During the pre-investigation test results of the permeability of Proctor cylinders showed k-values of lo-' to 5*10-6 m/s. Zinc slag covered with a surface dressing will have a k-value of approximately lo-* m/s. The construction of zinc slag overlaid by an asphalt course will have a k-value of m/s (assumption). Based upon these k-values, and the total hours of rainfall and the average rainfall intensity per month, the total amount of infiltrated rainwater can be calculated. Evaporation is not taken into consideration. From these calculations, it can be derived that the total quantity of infiltrated rainwater, depending on the season, rainfall and k-value, varies from 1 1 to a maximum of 60 1 (m2, month). The first figure is based on an average situation, the second figure on a relatively high permeability. With the dimensions 500*500*100 mm3

243 (length*width*depth) a volume of 25 litres means enough capacity to collect percolate during a dry period of two months or more and as well during a wet period in one month at locations with a higher permeability. The container is positioned with a certain fall to the outlet. From there, a stainless-steel tube to the edge of the road collects the percolate when it is connected with a small pump.

The design and lay-out of the container system is given in the drawings of the inset.

244

A few centimetres under the top edge of the container a metal sieve supports a geotextile. This textile has to prevent zinc slag falling into the container. On top of this geotextile another metal sieve is laid to overcome problems during the foam-stab operation. 4.2.2. Positioning percolate containers Figure 1 gives in top view the situation of the various containers in the road. Numbers A are in the centre line, numbers B at the road-side. This has to give more insight in the relation quantity of percolate and container position. To get a good idea of the quantity and quality of the percolate in relation to the type of (treated) material, several containers were installed. The following situations can be described: - in a road treated with foam bitumen and in an asphalt overlaid road; - containers at depths of 200 and 350 mm in both roads; - for both roads, a double percolate container system ( in the centre line and at the roadside); - as a reference two containers are placed in an untreated road. The chosen variants are grouped close together to have more or less the same type of zinc slag material and ground water conditions. At the same location of the containers, piezometric tubes are placed by which means samples of the ground water can easily be collected. 4.2.3 Sampling programme One month after placing the containers, the percolate was collected. These samples were not considered to be reliable and were, therefore, neglected. One month later, the first official sampling was performed. It showed that there was not enough percolate to test. Therefore, another sampling procedure took place after six months. This period of six months will be the standard interval period for the coming years. From every sample the quantity, the acid degree pH and the conductivity are measured

(plus remarks about colour, smell, turbidity, sediment, etc.). Besides, a sample is taken from every percolate quantity and brought to the laboratory for analysis (after acidification). The whole run of tests contains analysis of the heavy metals arsenicum, cadmium, copper, lead and zinc and the organic component PAH's. To avoid any contamination and/or absorption, the materials used are tested in a pre-stage phase. The geotextile is tested by a filtration method to check the resistance against chemical components like heavy metals and acids. Contamination in the percolate collection system is avoided by using a very special quality of manganese steel. Before installation, the containers are flushed and cleaned with acidificated demi water @H=2) and afterwards cleaned with normal demi water.

245 A spare container was used for testing in the laboratory. The percolate from the large column tests was used for treatment of this container. The water was kept in this container for one month. This sample, as well as the original one, were analysed for the same number of elements as described above. The results have shown that there was no corrosion of the container.

5.

RESULTS

5.1

Chemical tests (production control) The results show that: zinc slag material is very heterogeneous. Very often, the C-value is exceeded for Cd, Cu, Pb, Zn, As and Sn. This value is a ranking position in Dutch specifications for soil and means of heavily polluted material; the total quantity of leachate (for the different leachate tests) of the tested parameters is for 90% below 1.0%, for 75% below 0.1% and for 65% below 0.05% of the composition; the best immobilisation effect is reached with foam bitumen without a special stabilizer; no PAH's are found in the percolate of the column tests.

5.2

Percolation behaviour In the period November, 1990 to date several times percolate was collected for analysis. Only the containers in the road overlaid with asphalt were empty. The quantity of percolate is approximately 1-1.5 1 per year. At the same time the ground water has been sampled and analysed. From the results it turns out that: - the components lead and arsenicum are less than the A-value; - the component copper varies between A and B (moderate); - the components cadmium and zinc are above the C-value; cadmium varies extremely widely; - the pH of ground water varies from 4.0 to 5.0; - no PAH's are found in the percolate and in the ground water. The analysis results of the container percolate (L/S = 0.002) are far better than the results of the stand test with Marshall tablets with a US ratio of 10; this situation will occur for the roads after 1500 years.

246 6.

CONCLUSIONS

A general overview of the results of the foam bitumen project shows that heavy metals in zinc slag are very well fixed and the immobilisation effect is very high (more than 95 per cent). Compared to the reults of 1988, the immobilisation is even slightly better. The results correspond with the pre-investigation research in the laboratory. In summary, it may be concluded that: polluted slag material can be solidified and immobilised by the foam stabilisation process; based upon dynamic compaction tests in the laboratory, a resulting higher optimum density was obtained; it could be achieved in the field by closely following the compaction process (control by nuclear density measurements); permeability tests in the laboratory show very low k-values (lo-’ to lo-’?; with the application of a surface dressing the k-value in the field might even be lower; falling weight deflectometer measurements show strength results for a 200 mm zinc slag construction equivalent to untreated slag material with an overlay of 120 mm asphalt; no PAHs are found in percolate and ground water; straight run bitumen is an adequate material to immobilise polluted slag material; a monitoring programme for ten years has to be established in order to monitor the project well; sampling has to take place twice a year.

Environmental Aspects of Constmction with Waste Materials J.J.J.M. Goumans, H A . van der Slmt and 771.G.Aalbers (Editors) el994 Elsevier Science B. K AN rights resewed.

247

Immobilisation of Phenol and PAH by special hydraulic binders P. Vogel, M. Schmidt

Heidelberger Zement AG, Forschung, Entwicklung und Beratung (FEB), 69181 Leimen, Oberklamweg 6, Germany

1. Introduction The utilisation of scarified road material composed of pitch-containing tarviated binders has meanwhile been specified by particular regulations in some of the federal countries in Germany [1,2]. Extensive investigations, both laboratory scale or test track, previously ascertained that recycling is practicable under constructional as well as ecological aspects, when scarified materials a r e consolidated appropriately by means of hydraulic binders or asphaltic emulsion [3,4,5,61. In practice, t h e consolidation by utilization of cement has recently been frequently accepted. This method is easy t o operate with in construction. I t also ascertains a decrease in exchange of phenols and polycyclic aromatic hydrocarbon (PAH) in scarified road materials with a comparably low amount of tarviated components. Even when consolidated with commercial quality cements, several original materials with a higher r a t e of contamination indicated an exchange of phenols and PAH still exceeding the limiting values, part of which are extremely low. In th e following there is a report about t h e consolidation of tarviated scarified road material by means of a hydraulic binder which effects a decisively higher decrease in exchange of phenols and PAH due t o i t s composition and a special additive, compared t o common cements. Thus the special binder also permits a non-polluting and durable recycling of scarified road material with a higher r a t e of contamination in amounts of soluble phenols and PAH for the utilization in hydraullicaly bound bases in road construction.

2. Latest Scientific Findings According t o German standards [7, 81, broken scarified road materials with or without tarviated components may be processed as "mineral aggregate" for bases made of hydraulic binders. This had been ascertained in extensive laboratoryscale examinations [3, 9, 10, 111 as well as in several successful practical applications 13, 4, 121. If th e material contains amounts of pit-coal tar, i t has to be safeguarded tha t those components of t a r with contents of polycyclic aromatic hydrocarbon (PAH) and soluble phenols ar e not permitted t o be released to environment in inadmissible concentrations. A comprehensive description of these compound groups, references t o their solubility and modes of transport for their environmental availability is given in I131 and [141. Today, tarviated scarified road materials are mainly consolidated by means of hydraulic binders [ 5, 131. The consolidation effects a constructional improvement

248 of t h e granulate which obtains the required strength as well as the indispensable weatherproof durability for soil bases. On the other hand, the exchange of PAH and phenols is decisively reduced. Those unwholesome contaminated ultra-fine aggregate particles generated by the scarification are embedded tightly and durably into the mortar in order to achieve a structural impermeability of the building material, so no pollutant-solving water may have any effect 1131. Repeatedly i t had been assumed that the utilization of cement does not reduce the solubility of t h e phenols but results in a formation of e.g. calcium-phenolate, which probably might be more soluble in water [13, 14, 151. Those few actually known investigations mainly deal with the application of portland cements PZ 35 F or sometimes hydrophobic or non-hydrophobic blast furnace cements HOZ 35 L according to DIN ,1164 as hydraulic binders 13, 5, 13, 151. Comparative investigations as in [3] showed nearly no difference in leaching of the used cement types after a maximum setting period of 28 d a y 3 Also the processed cements' quantity (variations from about 50 to 150 kg/m ) had no substantial influence on the solved phenole quantity, determined as phenole index. In some cases i t had been examined whether the exchange of PAH and/or phenole can supplementarily be decreased by the addition of inert auxiliary materials. As shown in [3] a slight reduc ion of phenole leaching could be determined by the addition of up to 60 kg/m of fly-ash from the Rhenish brown coal-mining area. Extensive laboratory-scale and practical examinations [51 by utilization of various cement types and different auxiliary materials however did not result in the determination of a significant immobilization of phenols by use of brown coal fly-ash. This conclusion can also be drawn by the confirming experiments as in [15]. The method of examination selected is of great influence on the r a t e of leaching, determined laboratory-scale [5, 13, 15, 16, 171. In order to standardize the testing and rating for the examination of hardened mixtures of building materials, the practicable trough-method had been described in an informational leaflet [18] by a working group of the Research Society for Road Construction and Traffic Affairs. Hardened test samples are examined after 24 hours' storage in a trough, being washed around by deionated water (solid/water-ratio = 1:lO).

5

3. Laboratow ExDeriments The tarviated scarified road material which had been used for the production of the basic eluates described in chapter 3 of the represented experiments, was derived from a asphalt concrete road base of about 15 years in age. I t had been taken from a job site and then crushed to a grain size 5 32mm in an impact crusher. The strain with eluate determined according to DEV S 4 [16, 191 of the non-set material a t a value of 26,5pg/l was not too high. 3.1 Influence of DH-value on solubility of Dhenol As stated in 1151, the solubility of phenol shall increase as t h e pH-value of the surrounding medium will rise. In the analogous investigations of I181 concerning the solubility of heavy metals i t was revealed that this only happened t o be true partially and only then when the increased pH-value was adjusted solely by addition of hydroxide of calcium or alkaline. By the use of cement grouts, however, a distinctive reduction of soluble heavy metals was noticeable a t identical pH-values of up to pH=13. In order to find out whether a similar behaviour might possibly also be detectable with phenols, crushed and homogenized samples of the tarviated material was leached according to DEV S 4 [16, 191 in some instructive tests. Exceptionally, the eluate was filtered

249 subsequently by means of a 0 . 4 5 ~diaphragm filter, for the sole consideration of th e actually solved quantity of phenol. For t h e purpose of leaching, solutions came into utilization which were presently adjusted in pH-value from 9-13 by addition of sodium hydroxide (NaOH) in various quantities. Up t o a pH-value of 9, t h e determined phenol index approximately coincides with tha t one of the zero sample, as is shown in figure 1. A t a pH-value of 13, however, by a concentration of 70.3pg/l i t nearly exceeded three times the concentration of the zero sample (26.5pg/1) eluated with deionated water. Leaching experiments with reference to DEV S4 Determination acc. to DIN 38409 H16-1 Different elution medium

80 70,3 70 sodium hydroxide

60

cement grout

+ I NHCI-

50 40 30 --26,5-

25,3-

20 10 -

0

Fig.

1: Influence of t h e pH- value

In a second test series the pH-value of t h e eluting medium was changed by the production of a solution composed of lOOOml water and lOOg common portland cement PZ 35 F which came up t o a pH-value of 13.3. Subsequently 1 N hydrochloric acid was added in t h e individual experiments, thus decreasing t h e pH-values down t o 9. The results which are also represented in fig.1 show tha t th e respective phenol index was decisively lower a t identical pH-values than in th e experimenti with sodium hydroxide (NaOH), and even practically did not exceed t h e initial value of the zero sample a t a pH-value of 13.3. With the application of cement-bearing solutions i t may be expected tha t even increased pH-values do not result in a considerable rise in exchange of phenols, compared t o a pH-neutral environment. AbsorDtion of solved phenols by inert ultra-fine a m re ga te particles and bv cements In a further s t e p of investigation i t had been examined, completing the model experiments described in [13], whether t h e addition of inert ultra-fine aggregate particles, various cements or admixtures of ultra-fine aggregate particles with cement may lead t o a decrease in exchange of solved phenols by means of adsorbent and/or chemical action. 3.2

250

3.2.1 Basic Materials Activated bentonite, ultra-fine sealing clay, pit-coal fly-ash (SKFA) with approval of DIfBt and brown coal fly-ash (BKFA) of the Rhenish coal-mining area were used as inert admixtures. The activated bentonite also finds application for the reduction of contamination by heavy metals. The following cements were selected: commercial-trade portland cements PZ 35 F and PZ 45 F according to DIN 1164 produced in plant A, a portland-limestone cement (85% portland clinker, 15% limestone filler) registered by DlfBt and produced in plant B, and blast furnace cements with various quantities of slag (HOZ), according to DIN 1164 produced in the plants C and D. Clay and cements were applied pure and unadultered. Pit-coal fly-ash and brown coal fly-ash came into utilization as admixtures with cements in partially varying proportions of mixture. 3.2.2 Performance of Experiment The tarviated scarified road material had been eluated by deionated water in several individual experiments according to DEV S 4, for a period of 24 hours. The gained individual eluates were joined together and homogenized. Altogether, about 20 1 of eluates were produced in this way. In each case, lOOOml of the eluate were mixed successively with lOOg each of the materials and admixtures. Subsequently, they were kept in motion in a large-neck flask according to DEV S 4, for a period of 24 hours. Afterwards the solutions were filtered by means of a diaphragm filter, type 0.45pm, with the solved quantitiy of phenols determined as phenol index. 3.2.3 Results Figure 2 shows that the addition of the two clays only results in an unsignificant decrease of the phenol index in the starting eluate from 26.5 t o 22.7pg/1. By t h e treatment with portland cements 35 F (columns 3 t o 5 in fig.2) a distinctive reduction of solved phenol to the amount of 15.2-14.3pgh could be determined, almost a bisection of the starting value. The reduction showed t o be independent from the cement fineness, its reactivity and quantity of clinkers. An especially low fjnal contamination of only about 4pg/l, meaning about 15% of the initial value, could be determined on eluates treated with blast furnace cements (columns 6 and 7 in fig.2). The proportional admixture of brown coal fly-ash with cement (columns 8 to 10 in fig.2) only succeeded with the mixture of fly-ash with portland cement (column 10 in fig.2) and led to a considerable reduction from initially about 15 to only about 6pg/l. By this, the same range of effectiveness as realized with pure blast furnace cement could be achieved. The combined application of blast furnace cement and brown coal fly-ash however showed no further reduction, independent from the proportional quantities of cement to brown coal lignite fly-ash selected. Even the combined application of a blast furnace cement and pit-coal fly-ash in various proportions (columns 11 t o 13 in fig.2) did not disclose a phenol reducing effect of the pit-coal fly-ash. The results of the model experiments were utilized for the laboratory scale production of a hydraulic binder optimal for the immobilization of phenols. By this, the composition of the binder and its fineness in grinding as well were optimized carefully. This binder meets the requirements of DIN 18506 "Hydraulische Tragschichtbinder" (hydraulic binders of soil bases). The model experiment resulted in a reduction of the phenol index from 26.5pg/1 initially, to less than 0.5pg/1 - that means less than about 2% of the initial contamination, see column 14 in fig.2.

25 1

Leaching experiments acc. to DEV S4 1000 ml of eluate

+ 100 g of binder

Phenol index [C1g/l]

35

30

inert materials

25

Heidelberger Recyclingbinder TA

20 15

Addition of -

-LFA

10

HOZ 35 L

5

0

PCFA

-

-

v

0

6

7

8

9

Binder Nr.

Fig.

2: Influence of the type of binder

Investigations on hardened comoositions of building materials In order t o screen t h e efficacy of the special hydraulic binder in set and hardened tarviated scarified road material, samples are produced according to t h e german standard TP-HGT for purpose of comparison, made of a portland cement PZ 35 F from plant A and the special binder, by 8 m.-% each. Alter 28 days they were leached by moving deionated water for 24 hours in the troughmethod. The ratio of solids t o water amounted t o 1 : 10. For not only detecting a short-term initial effect, the eluate was removed and examined after 24 hours, while t h e samples were leached again by fresh deionated water immediately afterwards. This succession was repeated a fte r 48, 72, 96 and 168 hours. The phenol quantities evaluated from the concerning eluates a r e represented in fig.3 as total amounts relating to the leaching period. After a period of 24 hours, the summed up phenol index received from PZ 35 F amounted to 67pg/l being twice as high than t h at one received from the sample of special binder (32pg/l). After 168 hours t h e phenol content received from the special binder even amounted only t o about 40%. The efficacy of the special binder in order t o reduce t h e exchange of phenol, detected in t h e model experiments was thus confirmed by experiments on hardened test samples. 3.3

252

Tarviated scarified road material Multiple leaching of unbroken sampels Trough-method

400

---

Type of Binder:

350 300

-

Heidelberger RC-Binder PZ 35 F

cccc

ce-c &c*-cc@-

250

/

200

HH-

150

100 50 I

24

O b

48

72

96

120

144

168

Period of Leaching [h]

Fig.

3: Results of the multiple leaching process

4. $

3

3

)

Scarified road material with a higher tarviated content and a corresponding increased quantity of soluble phenols may additionally be reduced in phenol exchange when the additive "Phenolex" is added for phenol absorption. The method of adding this material together with hydraulic binders for the purpose of consolidation of recycling materials, has been applied for as a patent. To prove efficacy, a crushed tarviated material of 0/32mm particle size was used, being higher in contamination with phenols and PAH than with the experiments of section 3., as detected by the results of leaching of the untreated basic material. I t had been mixed particularly with 8 m.-% of a hydrophobic cement PZ 35 F according to DIN 1164 or the optimized hydraulic Recycling Binder according to DIN 18506, as described in section 3. The admixture of the phenol reducing additive varied in the amounts of 0, 3 and 6 m.-%. They hardened for a period of 28 days wrapped in foil, a t 20°C and 98% relative humidity. Subsequently they were leached by moving deionated water according to the trough method mentioned in section 2. I t is shown in fig.4 that a phenol index of 175pg/l was determined in the eluate of the test sample consolidated with hydrophobic cement. The phenol index of those samples consolidated with the special binder according to section 3 without an additive, amounted to 118pg/I being already reduced for about 30%. The exchange of both binders was again reduced for about 75pg/l each, approximately in proportion to dosage of Phenolex. The phenol index of test samples made of special binder and 6 m.-% of additive only amounted to about 40pg/I, meaning less than 25% of t h e cement value.

253

Tarviated scarified road material Leaching of unbroken sampels Trough-method Phenol index [c1g/1]

200

I

Type of Binder:

180

160

-

140

Heidelberger RCBinder Hydro. PZ 35 F

120 100 80

60 40

20

I O '

0

3

6

Phenolex content [m.-%]

Fig.

4: Influence of t h e additive Phenolex on the leaching of phenol

5. Influence of t h e tme of binder on the exchange of PAH While in t h e beginning of t h e recycling of tarviated scarified road material the immobilization of phenols was considered as an intensified interest, most recently questions concerning t h e efficiency of hydraulic binders for the purpose of PAHimmobilization are spreading. Add t o this, t h at in some federal countries the determination of t h e PAH-content in t h e eluate is not only subject t o 6 PAH according t o t h e ordinance on drinking water, but basing on 16 PAH according t o th e American EPA-list, without corresponding adaptation of the limit levels. For this reason, completing instructive experiments on the immobilization of PAH were performed supplementarily with those binders described in section 3 and 4, at a later moment. For this a leaching process according to the method of DEV-S4 1191 was performed using crushed tarviated scarified road material consisting of a 0/32mm fraction, newly taken and screened t o a fraction of 0/4mm. The total amount of PAH according t o EPA of 370mg/l derived from the initial eluate was determined as a chacteristic value. Test samples of tarviated material (d = 5mm and H = 5mm) had been consolidated by utilization of 10 m.-% of HOZ 35 L, respectively 10 m.-% of Recycling Binder, containing 3 m.-% of t h e additive Phenolex. The leaching process was performed according t o the trough method [ 181 already described, with t h e eluate being replaced after 1, 2, 4, 8 and 16 days of eluation period. The results a r e represented in fig.5 as a total of PAH relating to the period of leaching. Altogether about 1.75,ug/l of PAH were leached from the test samples consolidated with HOZ 35 L during t h e first 24 hours. The one eluate of the samples processed with Recycling Binder and Phenolex only contained 55,ug/l meaning only about one third of this value. Moreover, after already 3 days of leaching, all test samples only slightly released additional quantities of PAH, independent from t h e type of binder applied.

254

Tarviated scarified road material Multlple leachlng of unbroken samples Trough-method PAH sum acc. to EPA bg/1]

Heldelberger Recycllngblnder TA -4

-0

5

10

15

20

25

30

35

40

Period of leachlng [days] VO 1/94 PAWNS11

Fig.

5: Influence of type of binder on the leaching of PAH

Altogether, the instructive experiments demonstrate a decisive decrease in leached PAH by use of special hydraulic binders in combination with decontamining additional components, even in this case of relatively highly contamined tarviated material regarding a prolonged period. This is also confirmed by the investigational results of a research commission 1201. By means of consolidation with Recycling Binder, a reduction in amount of soluble PAH to less than 1/10 of the initial contamination could be achieved in various construcional projects performing the recycling of tarviated material lower in contamination.

6. Summary and Conclusion The following conclusions may be drawn resulting from extensive experiments on reduction in exchange of phenols and PAH out of tarviated scarified road material by means of consolidation with hydraulic binder.

1. As frequently assumed, the exchange of phenols from tarviated granulated material was not increased in spite of the usually higher pH-value. Depending on type and amount of the used binder relating to the extent of contamination of the basic materials, i t will be decreased to sufficient degree so tarviated material may be recycled for HGT compatible t o environment. 2. Phenols and PAH were immobilized especially effectively by treatment with a special binder, which had been developed specifically for the purpose of a non-polluting consolidation of tarviated scarified road material.

The efficiency of this so-called Recycling Binder TA may individually be 3. adjusted to the actually detected amount of phenol and PAH, so a non-polluting recycling may also be achieved a t a higher rate of contamination. This is

255 realized by t h e careful addition of special additives to the binder effecting the immobilization of pollutants. The method was applied for as a patent. 4. The recycling of tarviated scarified road material by utilization of hydraulic binders is applicable for hydraulic set soil bases as well as for the consolidation of the superstructure. The processing of the mixture may be performed by ready-mixed batching as well as mixed-in-place method. Both methods have been successfully applied in several road sections. References: 1 2

3 4 5

6

7 8

9 10 11 12 13 14 15

"Vorlaufige Hinweise fur die Behandlung von pechhaltigem Straknaufbruch", Straknverwaltung Rheinland-Pfalz, July 5th, 1992 Zusatzliche Technische Vertragsbedingungen und Richtlinien fiir die Wiederverwendung von Ausbauasphalt im Stra knba u. Allgemeines Ministerialblatt, Nr.16, August 1990, p.635-639, Bavaria Lewe, H.; Witting, B.: Probleme mit teerhaltigem StraOenaufbruchmaterial. S t r a h und Autobahn 40 (1989), Nr.11, p.426-432 Schulte, H.-P.: Erneuerung einer Betonfahrbahndecke. Verwendung von Recyclingmaterial bei der A7. Beton 38 (1988), Nr.8, p.315-317 Franke, H.-J.; Patzold, H.: Neuere Erkenntnisse bei der Verfestigung teerhaltiger Ausbaustoffe fur hydraulisch gebundene Tragschichten. Betonstrakntagung, 1991. Schriftenreihe der Arbeitsgruppen "BetonstraOen", Nr.20, p.46-52, FGSV, Cologne "Untersuchung zur Umweltvertraglichkeit von Zement und Bitumenemulsion gebundenen pechhaltigen Ausbaustoffen im Rahmen der Versuchsstrecke Wattenheim", Forschungsbericht FE-Nr. 07.144 R89L, Bundesminister fur Verkehr, March 1991 Zusatzliche Technische Vorschriften und Richtlinien fur die Ausfuhrung von Bodenverfestigungen und Bodenverbesserungen im StraBenbau, Edition 1981 (ZTVV-StB 811, editor: Bundesminister fur Verkehr, Bonn 1981 Zusstzliche Technische Vorschriften und Richtlinien fur Tragschichten im StraBenbau, Edition 1986 (ZTVT-StV 86). Editor: Bundesminister fur Verkehr, Bonn 1986 Leykauf, G.: Hydraulisch gebundene Tragschichten aus alternativen Mineralstoffgemischen. S t r a k n - und Tiefbau 41 (19871, Nr.1, p.10-14 Schmidt, M.; Vogel, P.: Stoffeigenschaften von HGT mit Altbeton und Altasphalt. S t r a k n - und Tiefbau 42 (1988) Nr.1, p.5-10; Nr.2, p.19-25 Leykauf, G,; Moos, T.: Laborversuche mit hydraulisch gebundenem Asphaltgranulat und Auswirkung auf die Bemessung. S t r a k und Autobahn 38 (19871, Nr.11, p.412-417 Simm, P.: Die Herstellung einer hydraulisch gebundenen Tragschicht aus Aufbruchasphalt. S t r a k und Autobahn 40 (1989), Nr.6, p.211-214 Schmidt, M.; Spanka, G.: Verwertung von teerhaltigem Ausbauasphalt in hydraulisch gebundenen Schichten - Verminderung des Schadstoffaustrages. S t r a k und Autobahn 41 (19901, Nr.3, p.118-122 Jordan, W.; H. v. Barneveld; 0. Gerlich; J. Ullrich: Phenol. In: Ullmanns Encyklopadie der techn. Chemie, 4th edition (19791, Vo1.18, p.177-189, Basel 1979 W.: Das Eluierverhalten von Phenolen aus teerhaltigem Glet, Straknaufbruch, Bitumen (1991) Nr.4, p.154-161

256

16 17

18 19

20

GStz, D.; W. Gerwinski: Empfehlungen zur Vereinheitlichung der Auslaugbarkeit nach dem DEV S4-Verfahren fiir die Untersuchung von Straknbaustoffen. Strat% und Autobahn 40 (19891, Nr.10, p.387-388 Sprung, S.; W. Rechenberg: Einbindung von Schwermetallen und Sekundiirstoffen durch Verfestigen mit Zement. Beton 38 (1988) Nr.5, p. 193-198 "Trogverfahren zur Auslaugung von Mineralstoffen", Bericht des AK 6.4.1 "Elutionsverfahren fiir Mineralstoffe" der FGSV S t r a h und Autobahn 44 (19931, Nr.5, p.297-300 DIN 38414: Deutsches Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung. Schlamm und Sedimente (Gruppe S) Teil 4, Bestimmung der Eluierbarkeit mit Wasser (S4), Oct.1984. Beuth-Verlag, Berlin - Cologne Eickschen, E.: Tragschichten aus mit hydraulischen Bindemitteln gebundenem teerhaltigem Asphaltgranulat. Vortrag Status-Seminar "Industrielle Nebenprodukte und Recycling-Baustof fe fiir den Strahnbau", December 2nd4rd, 1993, Bochum

Environmental Aspects of Constmction with Waste Materials JJJM Goumans, H A . van der SImt and Th.G. Aalbers (Editors) 01994 Elsevier Science B.V. AII rights reserved.

257

LEACHING OF ORGANIC CONTAMINANTS FROM CONTAMINATED SOILS AND WASTE MATERIALS Wahlstrom, M.’), Thomassen, H.*), Flyvbjerg, J.’), Veltkamp, A.C.3), Oscarsson, C.‘), Sundqvist, J.-0.4)& Rood, G.A.5) VTT Chemical Technology, P.O. Box 1400, FIN - 02044 V l T Espoo, Finland

-

Water Quality Institute (VKI), 11 Agern All& DK 2970 Hnrrsholm, Denmark Netherlands Energy Research Foundation (ECN), P.O. Box 1, NL Petten, The Netherlands

-

Swedish Environmental Research Institute (IVL), Box 21060, S Stockholm, Sweden

1755 ZG

-

10031

National Institute of Public Health and Environmental Protection (RIVM), P.O. Box 1, NL - 3720 BA Bilthoven, The Netherlands Abstract

This paper reviews the activities concerning leaching of organic contaminants from soils and waste at five European research institutes. At present there is very little knowledge of the leaching mechanism and factors affecting the mobility of organic contaminants in contaminated soils and waste. Special test arrangements are often required especially due to adsorbtion and volatilization of the organic contaminants. Leaching of polyaromatic hydrocarbons, volatile BTEX compounds, oil and chlorophenols have been studied. Biological tests can be used as a complement to chemical analysis of the leachates. However, more development and international cooperation work is still needed in this field.

1. Introduction Today the environmental risk assessment of waste materials and soils contaminated with organic contaminants is primarily based on the toxicity of the compounds and the concentrations at which they are present in the waste or soil. The mobility of organic components is usually not taken in account due to lack of proper test methods.

258 Leaching tests are needed for the estimation of environmental risks of residual contaminants in soil or sediments. Informationon the leaching of organic contaminants is also needed when planning remedial actions at contaminated sites. Moreover, leaching tests can be used to estimate the amount of organic contaminants that are available for microbial degradation in soils or waste. Leaching tests can also be used for classifying waste materials as hazardous or non-hazardous. Today there is a fundamental understanding of many of the factors which govern the leaching of inorganic contaminants and standard leaching tests have been developed for this group of compounds. These standard leaching tests can be used as a base for the development of leaching tests for organic contaminants. However, special test arrangements are needed to prevent volatization, adsorption and degradation of the organic compounds. This paper gives a brief description of some of the work on leaching of organic contaminants which has been performed within the past few years at five European research institutes. The institutes are: The Finnish VTT, The Danish Water Quality Institute (VKI), The Swedish Environmental Research Institute (IVL), Netherlands Energy Research Foundation (ECN) and the Dutch National Institute for Publich Health and Environmental Protection (RIVM). 2. Leaching studies

At the five research institutes standard leaching tests for inorganic compounds have been used as a starting point for the studies performed. The test equipment (materials, filters etc.) and test conditions (contact time, leaching medium etc.) have been adapted to the nature of the organic compound of interest. Usually materials like teflon, stainless steel or glass have been chosen to minimize the risk of adsorption of the organic compounds on the equipment. Futherrnore, special precautions have been taken to avoid losses of volatile organics by evaporation. The chemical analysis of the organic compounds may also cause problems. Preconcentrationsof the leachates is often needed due to the very low concentrations. Futhermore, the large quantity of sample needed for the analysis limits the amount of other chemical analysis that can be perfomed on the leachate sample. Usually a choice of analysis has to be made. The degradation of the organic compounds is difficult to estimate. The leachates are therefore recommended to be analyzed as soon as possible. The degradation of organic compounds by e.g. soil microorganisms can be prevented by use of agents that inhibits the growth of micro-organisms. Table 1 summarizes the leaching studies done at the five European institutes. Especially the Dutch institutes RIVM and ECN have experience in leaching of organic compounds, especially polyaromatic hydrocarbons (PAH). The test materials usually

259

Table 1. Leaching studies of organic compounds. Institute

I Organic contaminants

RlVM (NL)

Test materials

Test methods

asphalt, tar asphalt, contaminated soils, clean natural soil, demolition waste, sieve sand, incinerator bottom ash, blasting sand, dredged sediments

column test (LS lo), serial shake tests (LS 20-100)

contaminated soil

column test (LS lo), serial shake tests (LS 20-100)

ECN (NL)

PAH

contaminated soil, incinerator bottom ash, sieve sand, sewage sludge,

batch shaking (LS 20), column test (LS lo), serial shake tests (LS 20-100)

VTT (FIN)

hydrocarbons

contaminated soils, asphalt

batch shaking (LS lo), tank leaching test tank leaching test

VKI (DK)

contaminated soils

column test ILS 0.4) ~

biological tests, serial shake tests (1-5bed volumes)

contained fairly low concentrations of the organic compounds of interest. In some cases the effect of different leaching conditions was difficult to clear out due to the very small amount leached. From the leaching studies it can also be concluded that the leaching from materials spiked with organic compounds does not give a realistic picture of how organic contaminants leach from real contaminated material. In the leaching studies of granular materials, the leached amounts have generally been related to the liquid-solid (LS) ratio. LS describes the ratio between theaccumulated amount of liquid (L in liters) that at any given time has been in contact with the solid (S in kg). 3. Conclusions in the leaching studies

The study on the factors influencing the leaching process is still in its beginning and it is possible that a practical test procedure cannot be developed for all organic compounds.

260 3.1. PAH

A draft test procedure for determination of leaching characteristics of PAH from solid granular waste materials has been prepared at RIVM. The Dutch standard column test and serial batch test has been adapted to these hydrophobic organic compounds. The modifications in the test equipments are the use of teflon columns with KEL-F plungers, teflon or KEL-F capillaries and glass bottles (rinsed with solvent). The use pm) before the membrane filter of a glassfiber prefilter (retentiondiameter 0,75-1,5 prevents the clogging of the membrane filter with small particles. Especially the adsorption on filters has been studied at RIVM. It has been concluded, that the emission of PAH is correlated to the size of the particles in the eluate fraction. Therefore, it is important to standardize the filtration or centrifugation procedure of the leachates (1,2). Leaching of PAH has been studied by ECN using the draft-procedure of RIVM. The main conclusions of the study at ECN are as follows (3):

-

-

-

-

the reproducibility of PAH-determination seems to be satisfactory. However, the results are strongly influenced by the sample preparations method applied, i.e. ultrasonic, soxhlet, and the type of solvents used. the results of PAH determination in the materials as well as in the leachates may be improved by introducing sample clean-up steps in addition to sample preconcentration. This holds true particulary for naphtalene, acenaphtylene, acenaphtene, fluorene and phenantrene. the results obtained are strongly influenced by the type and size of filter used for filtrering the leachates. Figure 1 shows the PAH-concentrationsin the leachates obtained from batch shaking of contaminated soil at pH 4 and LS 20. The leachates were filtered through 1, 0,45or 0,20 pm membrane filters. Results are presented relative to the 1,O pm filter. It is advised to use centrifugation instead of filtration, whenever possible. the leaching of PAH from contaminated soil is enhanced at increasing pH of the leachate (Fig. 2). This may be due to the extraction of humic material from the mineral fraction at high pH (pH 12). Compared to pH 4 leachates, a distinct shift in retention time can be observed in the huge background peak eluting from the HPLC-column after leaching at pH 12. with exception for naphtalene, the leached amounts from contaminated soil were generally quite small (Table 2).

26 1 Table 2.

Leaching of PAH from contaminated soil (batch shaking test at LS 20).

Percentage of content leached relative to the 1 pm filter

*"R

Fig. 1.

The retention of some polyaromatic compounds on 1,0, 0,45and 0,20pm membrane filters. The results are presented relative to the 1,O pm filter. The leachates are from a batch leaching of contaminated soil at LS 20.

262

Uitloging van de lagere PAK's uit vervuilde grond t0.v. de pH

Uitloging van de hogere PAK's uit vervuilde grond t.0.v. de pH.

cutnulatieve

2350E+02r' 2,00E+02

uitloglng (ugkg) 1,50E+O

I,OOE+O 5,00E+O 0,00E+004

Fig. 2.

The influence of pH on the leaching of some polyaromatic compounds. The cumulative leached compounds at LS 100 (serial batch leaching) is expressed as a function of the pH in the intial pH of the leaching medium.

263

3.2. Oil The influence of filtration, mixing systems and shaking time on the leaching of hydrocarbons ("oil components") from two sand soils contaminated with oil was studied at V l T using a batch leaching (LS 10 with destilled water). Only materials of glass or stainless steel (prerinsed with solvents) were used for the leaching tests. The samples and leachates of the samples were analyzed using the UV-fluorescence spectroscopy method (UVF). The UVF-methodcan be used for measuring compounds which emit fluorescent light, e.g. PAH-compounds. A crude oil mixture was used as a standard in the calculations. The UVF-method is very convinient for screening purposes. It is simple and the detection limit is low (e.g. 0,05pg/l for some PAHcompounds). The main conclusions of the batch-leaching study are as follows: the results of the leaching tests were strongly influenced by the method by which the leachate was filtrated. The hydrocarbon-componentswere retained both on a coarse glass microfiber filter (about 12 p.m) and on a layer of reinforced plastic. In Table 3 the results are compared to oil concentrations in leachates which have been centrifugated (5 min. 6000 rpm). the shaking time didn't clearly affect the results. the use of a shaking table or an end-over-end tumbler (30 rpm) for the mixing didn't affect the results (Fig. 3) the leached amounts were relatively high, often over 50 % of the total concentration. This might be due to the weak adsorption of hydrocarbon on sand particles. Table 3.

Comparison of the oil concentrations in leachates which have been filtered and centrifugated. The leachates are from a batch leaching of contaminated soils at LS 10.

I,

II

Content in soil (mgkg)

Soil 1

150

Soil 2

720

Amount leached (mg/kg) After centrifugation

Filtration with a 12 pm glass microfiber filter

Filtration using a layer of reinforced plastics

86

3,6

150

72

43

720

480

100

41 0

91

264

A piece of asphalt beton used in road constructions was also studied using the Dutch tank leaching test without any filtration steps. In the tank leachingtest a specimen was immersed in weakly acidified water (pH 4) and at certain time intervals the water was renewed and analyzed. The leachates were analyzed using both the UVF-methodand the IR-spectrometricmethod for oil determination. The only problem observed was the small air bubbles at the surface of the specimen due to the hydrophobic nature of the asphalt. The leaching test showed clearly that there is a measurable leaching of hydrocarbons. At the end of the test period there was a depletion of hydrocarbons available for leaching. Besides the problem with the wetting of the specimen, it seems that the test protocol worked well.

400 200 0

2h

7h

16 h

24 h

48 h

shaWng time test series 1

shaking table

Fig. 3.

\,,test series 2 \\\\

end-over-endtumble(3Oom)

The influence of shaking time on the leaching of oil from a contaminated soil using a batch leaching test at LS 10.

3.3. Chlorophenols Leaching of chlorophenols from stabilized soil contaminated with chlorophenols have been studied at VTT using the Dutch tank leaching test. Only glass beakers and glass bottles were used in the laboratory work. The soil had been stabilized with binders (e.g. cement) and additives.

265 The adsorption of chlorophenols on a 0,7 pm glass microfibre filter was studied before the performance of the leaching tests. No adsorption on the filter was observed and there was no significant difference between the filtrated and nonfiltrated leachates. The results from one leaching test is shown in Figure 4. The cumulative flux in terms of leached amount per exposed surface area of the specimen is plotted against the contact time on a log-log-scale. The slopes of the lines in the plot indicate that the leaching was diffusion controlled (slopes between 0.4-03). The calculated effective diffusion coefficients of chlorophenols were less than 1O-'* m2/s. The water solutions from the tank leaching test were alkaline (pH between 11 and 12) due to the calcium compounds in the binding agents. About 13 % of the chlorophenols was leached within the testing time (the total concentration of chlorophenols was about 1400 ppm).

Leasching of chlorophenols from stabilized soil cumulative leached amounts (log[mg/mZ])

I

0.25

1.25

2

I

. . I , ,

I

8

16

4

35

64

time (log[d])

----

tritetrapantaTOTAL chlorophenols cholophenols chlorophenol chlorophenols

Fig. 4.

Leaching of tri-, tetra- and pentachlorophenols from a stabilized contaminated soil using the Dutch tank leaching test.

No specific problems arose in the leaching study. The test protocol, which was developed for leaching studies of inorganic compound, seemed to be applicable to chlorophenols as well. Chlorophenols are water-soluble organic compounds and therefore the leaching was easy to study. The leachates were analyzed almost immediately and no degradation was assumed to take place in the leachates.

266

3.4

BTEX

To study leaching of BTEX and other contaminants from polluted soils treated by thermal processes and from soils treated by extraction with dichloromethane (CH,CI,) column tests were performed on these soils in the laboratory. The contents of organic contaminants in the soils are shown in table 4 and 5. The soils were packed into stainless steel columns (diameter = 0.15 m) to a height of approximately 0.4 m and the leaching medium (demineralized water) was passed through in downflow by means of a peristaltic pump. Washed quartz sand was placed at the inlet of each column in order to obtain a good distribution of the inflow. Filter papers (nylon and membrane filter) were placed at both ends of the columns mainly to prevent particles from being carried over with the effluent. Fractions of leachate were collected at the bottom of the columns and analyzed/storedfor analysis (without further filtration). The leaching experiments were conducted in darkness and at 5 "C. The volatile organic compounds were collected on a carbon adsorption tube. The set-up of the column leaching tests in downflow configuration is shown in Figure 5.

The leachate fractions were analyzed for benzene, toluene, ethylbenzene, xylenes, naphthalene, PAH, dichloromethane, total hydrocarbons (THC) and total inorganic cyanide. Leachates were collected in the range from US = 0 - 0.4 (I/kg).The carbon adsorption tubes were analyzed for benzene, toluene, ethylbenzene, xylenes and dichloromethane. In Table 4 the results from a thermally treated soil can be seen, and Table 5 shows the results from a soil treated by extraction with CH,CI,.

267

DESORPTION TEST Set-up

of column desorption test in downflow configurotion.

Stalnloii d.4

Figure 5. Set-up of column leaching tests in downflow configuration.

268

Table 4.

Results from column leaching test on thermally treated soil. The results are shown as contaminant concentrations in the collected leachate fractions and as total amounts of contaminants leached. The numbers in parenthesis indicate the percentage of the soils total content of a contaminant which was leached during the test.

0-0.10

Nil

0.10-0.20

Mil

0.20-0.25

UWl

c0.2

c0.2

<0.2

<0.2

0.6

30

c0.2

20

1

0.6

0.25-0.30

)lgA

c0.2

c0.2

0.30-0.40

Mil

c0.2

<0.2

c0.2

c0.2

c0.05 (
<0.08 (<0.2%)

<0.08 (4%)

c0.15 (4%)

10

50

Total amount leached

z )rmg

Content in soil

Fgkg soil dry matter

soil dry matter

100

50

us

Unit

CN

Phenols

0-0.10

PM

140 180

0.10-0.20

II

<0.2

1.9

5

0.2 0.2

0.25-0.30

Pgfl

29

c1

30

<1

0.30-0.40

.-

39

<1

40

Content In

pgkg soil dry matter

SO11

dry matter

8900

50

<1

X Fglkg soil

c100

140 50

Total amount leached

14

3 16

I

(

57

I

cO.10 (<1%.)

CH,CI, (leachate)

us4

I

90

THC

0.20-0.25

uail

I

0.7

I

I

2

CH,CI, (carbon tube)

I

1 .o

40 (1%)

1.4 (4%)

27 (
(>50%)

3900

30

WOO0

c2

0.6

II

269 3.5. PCB and pesticides

The results of the study of leaching tests for PCB’s and pesticides at RlVM is discussed in another paper at this conference (5). 3.6. Biological tests

As mentioned previously chemical analysis has several limitations. Biological tests such as toxicity tests and tests of the extent of bioaccumulation capacity can be used as a complement to the chemical analysis of the leachates. At IVL a screening test based on the Microtox toxicity test has been developed and a bioaccumulation test is under development. Principle of the Microtox screening test: 1. The leachate is Microtox tested. 2. The leachate is divided into eight subsamples. 3. Each subsample is subjected to a specific treatment, for example filtration ion-

exchange or purging. There is at present eight different treatments that each seeks to interact with certain characteristics of possible contaminants. 4. After the treatment the subsamples are Microtox-tested again. 5. Analysis of the results; if there are a significant difference between the Microtox responses before and after treatment some conclusions can be drawn about the anature of the compound that stands for the toxicity. For example if the toxicity decreases after purging one might suspect that the toxic compound is volatile. After this first screening further analysis may be done. It is possible to continue with fractioning and identification of the toxic compounds and also verification of the toxic effect on Microtox. A serial batch leaching test (based on the WRU-test developed in the United Kingdom) are studied and modified to organic compounds. In the leaching test the volume of the leaching medium is very small (1 bed volume). The contact time needed for equilibrium is determinated in a preliminary test. After the separation of the solid phase in the leaching test, the leaching procedure is repeated with fresh leaching medium. Unit operations that imply an increased risk for adsorption or volatilization, such as filtration and transfer between vessels, are as far as possible avoided by equipment modification.

4. Further work

The development of leaching tests for organic compounds is still in an early stage and there is still a lot of work to be done. The main goal of the work is to develop a tool to estimate the leaching (mobility) in field conditions in the short and long term.

270

The need for standardization of leaching tests for organic compounds has also been addressed at the CENnC 292 "Characterizationof waste". It would be important that the development of leaching tests for organic compounds is carried out in cooperation with research institutes in different countries. Common leaching tests would be very cost effective, overlapping work would be avoided and the results could easily be understood and benefitted. Besides the development of leaching tests for organic compounds there is a need for discussions on acceptable emissions of organic compounds to the environment. The detection limit of the leachate analysis is a relevant question when developing the leaching tests.

References 1. Bauw, D.H., Wilde, P.G.M. de, Rood, G.A., Aalbers, Th. G., A standard leaching test including solid phase extraction for the determination of PAH leachability from waste materials, Chemosphere Vol. 22, no 8, 713-722 (1991). 2. Rood, G.A. et al, Development of leaching tests for PAH in granular materials (in Dutch, summary in English), RIVM-report (publication in preparation). 3. Grapendaal, M., Leaching of Polyaromatics from Contaminated Soils and Waste, ECN, 1993 (in Dutch). 4. Paatero, J., Talling, B., Keppo, M., Wahlstrom, M. & Makela, E., Solidification and stabilization of contaminated soils. 1991 (in Finnish) 5. Rood, G.A. et al, Some developments in leaching tests for organics, These proceedings.

Environmental Aspects of Constmction with Waste Materiols J11.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) 81994 Elsevier Science B.V. All rights resewed.

27 1

Investigating a leaching test for PCBs and organochlorine pesticides in waste and building materials G.A. Rood. M.H. Broekman and Th.G. Aalbers National Institute of Public Health and Environmental Protection (RIVM) P.O.Box 1, 3720 BA Bilthoven, The Netherlands

Abstract The losses of PCBs and organochlorine pesticides during the leaching tests due to adsorption, filtration, volatilization and light were evaluated in this study. The adsorption of PCBs and pesticides on filters made of regenerated cellulose, fibreglass, Teflon, polyamide and glasswool, a tubing of Teflon, a glass bottle and various filtration apparatuses made of glass or Teflon were quantified. It was found that one should not use a polyamide filter but a piece of glasswool. Compared to Teflon the adsorptions on glass were lower. Preliminary findings showed that compared to filtration, centrifugation of the eluates provided better results. In the column test measures were necessary to minimize volatilization of PCBs from the eluates.

1. INTRODUCTION One of the objectives in the National Environmental Policy Plan (NMP) of the Dutch government is to stimulate the reuse of waste materials. An example of the use of waste materials is their application in building. Careful assessment of the impact of waste materials on the environment is therefore important. Nowadays, the assessment of environmental impact of inorganic compounds, like metals, in the Netherlands is based on the leaching of those contaminants determined with standardized leaching tests. However, due to the lack of leaching tests for organic compounds, the assessment of these is based on the concentration of the compounds in the waste material. Research was therefore initiated to develop leaching tests for various organic contaminants. When developing a leaching test for organic compounds, one should consider the specific properties of organic compounds, like the low solubility in water, the high affinity to other particles, volatility, degradability and the analysis of organics in water. In laboratory tests, adsorption on parts of the equipment, volatilization and degradation of the organics influence the results of leaching tests. Our research started with the development of leaching tests for polycyclic aromatic hydrocarbons (PAH) in granular materials [ 1][2][3]. These tests were based on the leaching tests for inorganic compounds. In addition, a limited round robin test was performed to get an indication of the repeatability and reproducibility of the column test for PAH [4]. The leaching tests for PAH were adapted for determining the leaching behaviour of

272 polychlorinated biphenyls (PCBs) and organochlorine pesticides [ 5 ] . Subsequent phases will include a leaching test for products and an availability test for non-volatile organic compounds. Furthermore, leaching tests for volatile organic compounds will be developed in this project. It should be noted that in other European countries there are also activities on the leaching of organic contaminants [ 6 ] . The specific objective of the work reported in this paper was to examine the leaching tests for PCBs and pesticides in granular materials. The losses during the leaching tests due to adsorption, volatilization, filtration and light were evaluated, and from this investigation suggestions for improvement of the leaching tests for PCBs and pesticides were made. 2. RESEARCH DESIGN The column test and serial batch test for PAH were taken as the starting point (Figure 1) [1][2]. In the column test, the sample is leached upflow with demineralized water acidified to pH=4. The eluate leaves the column through tubing and is collected in bottles. In the case of filtration of the eluate in the column, three filters supported by a gauze of Teflon are fitted in the top of the column with two rings (on-line filtration). The three filters are a wide-pore filter, prefilter and membrane filter. For some waste materials it is better to filtrate the eluates after collection to prevent slugging of the membrane filter (off-line filtration). In the case of off-line filtration, only the wide-pore filter is applied in the column.

COLUMN TEST

._ _ _ _ _>--i--

SERIAL BATCH TEST

, us.o.1

filters

US=0.5

\

I

waste material particle size c 4mm duration 5 x 23 hours

i-US=i I

c--

us=2

;--us=3

'.

L--

-*

I

?'

us4

--+

us=20

--+

US=40

--+

us=so

--+

US180

US=lO

waste material particle size < 4mm duration 3 weeks

pump

I water

Figure 1: Column and serial batch test

- - + us-1w

2 73

In the batch test the waste is shaken in a bottle. The eluates of the batch test and of the column test with off-line filtration, are filtered through the prefilter and membrane filter supported by a glass frit in a filtration apparatus. To gain insight into the losses during leaching tests due to adsorption of PCBs and organochlorine pesticides, the following parts of the equipment were tested: filters, supporting gauze, rings, tubing, a bottle and various filtration apparatuses. The adsorption tests were carried out with water solutions in which known quantities of PCBs and pesticides were dissolved (starting solutions, see 3.1). The amount of compound adsorbed reversibly on the investigated part of the equipment was determined and compared with the theoretical concentration in the starting solution. The adsorption in terms of percentages was calculated with the following equation: Aakorption (k) =

amount of compound on investigated part of the equipment amount of compound in starting solution

*

In the adsorption tests also the amount of compound remaining in the water solution was determined and compared with the theoretical amount in the starting solution. The recovery was calculated with the following equation: Recovery (%) =

amount of compound remaining in water solution amount of compound in starting solution

Losses of PCBs and pesticides during collection or storage of eluates due to volatilization or light were also quantified in tests in which the recovery was determined. Because considerable adsorptions of the more-substituted PCBs on the filtration equipment were found, an alternative procedure for separating particles bigger than 0.45 pm from the eluate was investigated. In this investigation the filtration of the eluates was compared to centrifugation of the eluates. Attention was paid to the particle size in the eluates, the concentration and standard deviation of PCBs and pesticides in the eluates.

3. MATERIALS AND METHODS

3.1 Materials The losses due to adsorption, light and volatilization of PCBs and organochlorine pesticides were quantified with solutions of the compounds in demineralized water. Three different starting water solutions of 900 ml were prepared by adding a standard solution in acetone (in solution A 0.5 ml was added, in other solutions 1 ml). The concentrations in the solutions were based on expected concentrations in eluates. Solution A: The concentration of the seven indicator PCBs was 44 ngfl of each PCB in water. The seven indicator PCBs were: PCB-28, -52, -101, -118, -138, -153 and PCB-180. Solution B: The concentration of each of the indicator PCBs, aldrin and y-HCH, is 56 ng/l. Solution C: The concentration of aldrin was 145 pg CIA water. The following parts of the equipment used in the leaching tests were tested for adsorption: -Membrane filter made of regenerated cellulose, 0.45 pm pore (Schleicher & Schuell RC55),

214 -Prefilter made of fibreglass, 0.75-1.5 pm pore (Schleicher & Schuell no.@, -Polyamide filter with 10 pm pore (Pharmacia Biotech Benelux), -Gauze made of Hostaflon* (perfluoralkoxy) (Peter Groenendijk b.v.), -Rings made of polychlorotrifluoroethylene (PCTFE)* (Peter Groenendijk b.v.), -Glass bottle (Duranglass) with a PTFE inlay in cap (Schott), -Glasswool (extra fine, Rhenova), -Tubing made of Tefzel* (Pharmacia Biotech Benelux), -High pressure filtration apparatus made of Teflon (Schleicher & Schuell), -Vacuum filtration apparatus made of glass with a holder of 50 mm diameter and one with a holder of 100 mm (Schleicher & Schuell).

* Hostaflon, PCTFE and Tefzel are materials like Teflon. 3.2 Analytical methods 3.2.1 PCBs and organochlorine pesticides The extraction and analysis were performed according to draft NEN-6406 [7]. The water solution was extracted twice with petroleum ether. The combined extract was dried with anhydrous sodium sulphate. The extract was concentrated in a Kuderna-Danish evaporator and further concentrated with a gentle stream of nitrogen. Clean-up was performed with aluminium oxide. A mix of two internal standard solutions, PCB-155 and PCB-143, was added. PCBs and pesticides were analyzed with a capillary gas chromatograph, equipped with a 63Ni electron capture detector. Carrier gas was helium and the makeup gas was nitrogen. Separation was conducted by on-column injection on a fused silica capillary column, CP-Sil 8 CB. For each compound the linearity of the analysis was determined and the gas chromatograph was calibrated using standard solutions. PCBs and pesticides were preferably identified and quantified with reference to PCB-155. 3.2.2 EOX, Microcoulometric analvsis The determination of the halogen content derived from non-volatile organohalogen compounds (EOX) that are extractable with petroleum ether is described in NEN 6402 [8].

4. EXPERIMENTAL Losses of PCBs and organochlorine pesticides were evaluated on the basis of the results of the following experiments. All experiments were carried out in duplicate (with the exception of the experiment for light). Each of the tests carried out is briefly summarized in the subsequent sections.

4.1 Analytical method In order to validate the analytical method for PCBs and organochlorine pesticides (section 3.2.1) the recovery was determined four times with solution B.

4.2 Adsorption The following parts of the equipment were tested in a shake test: filters, gauze, rings, a bottle and glasswool. The investigated part of the equipment had been shaken with

275 solution B for 16 hours and then rinsed with water and dried at room temperature. The adsorbed organics on the part were extracted in petroleum ether for 24 hours. The adsorption on the part of the equipment and the recovery were determined. The adsorption on the tubing was measured by solution B with a flow of 55 ml/h through the tubing (length 2 m, internal diameter 1.2 mm). The tubing was rinsed with water and dried at room temperature. The tubing was then extracted with 100 ml petroleum ether twice and the petroleum ether extract was analyzed for adsorptions. By means of each filtration apparatus solution B was slowly filtered through the prefilter and membrane filter. The filtrate was analyzed for the recoveries.

4.3 Centrifugation versus filtration 4.3.1 Centrifugation method Suspensions in water were prepared by shaking 150 gram clay with 900 ml water. This was done for two different clays. In ideal situations with clean water and ideal particles (e.g. spherical) an acceleration of the centrifuge of 1950 g for 30 min is just enough for sedimentation of particles bigger than 0.45 pm (d=1550 kg/m3)[9]. In the experiments suspensions were centrifuged at 1950 g for 45 min. A part of each supernatant was filtered through a filter with pore size 0.45 pm. The supernatant and filtrate were analyzed for turbidity by means of UVNIS at k 4 6 7 nm. However, the centrifugation conditions turned out unsatisfactory and the experiments had to be repeated with a centrifugation of 3470 g for 90 min. 4.3.2 Leaching emissions of PCBs Two contaminated soils were leached with water at a liquid to solid ratio of 20 I/kg for 23 hours (first step of serial batch test). One part of the eluate was centrifuged at 3470 g for 90 min in centrifuge glass beakers and the other filtered through a membrane filter by means of the filtration apparatus made of glass with a 100-mm holder. The supernatant and filtrate were analyzed for PCB and pesticide concentrations.

4.4 Volatilization Solutions A in open and closed bottles at room temperature were analyzed after 3 and 10 days, respectively. The opening in the open bottle was about 0.5 cm2. The same experiment had been done with solutions C, in which the aldrin (EOX) content was determined with the microcoulometric analysis after 10 days.

4.5 Light Solutions A in a transparent glass bottle and in a brown glass bottle kept at room temperature were analyzed after 10 days. 5. RESULTS AND DISCUSSION 5.1 Analytical method The recoveries determined for the water solutions did not divert significantly from 100% (within a 95% confidence interval) (Table 1). It turned out that this analytical method was useful for the experiments.

276

Table 1 Recovery and standard deviation Compound

Recovery (a) SD

y-HCH Aldrin PCB-28 PCB-I01 PCB-I18 PCB-138 PCB-153 PCB-180

108 93

14

120

19

102 106

I1 17

15

100

8

105

10

101

10

PCB-52 was not shown because it was interfered with SD = standard deviation ( n 4 )

5.2 Adsorption In theory, the sum of the recovery and the adsorption of one compound should be 100%. In practice, an analytical error, due to extraction and analysis, should be taken into consideration. The error in the experiment was assumed negligible compared to the analytical error. For the various investigated compounds, the average standard deviations for the sum of adsorption and recovery appeared to be between 9 and 18% [ S ] . It was found that 3% of the sums diverted significantly from 100% for inexplicable reasons (ct=O.OS). For the polyamide filter the sums of adsorption and recovery of PCBs were only about 50%, which may be attributable to irreversible adsorption on the filter. The adsorptions of PCBs and pesticides (in terms of percentages) on the investigated parts of the equipment and the recoveries in the remaining water solutions are given in Table 2. Note that the quantified losses in the adsorption tests should be compared to each other and cannot be used for correcting results of leaching tests. Differences are, for example, type of water (demineralized water instead of eluates), duration and means of contact. The adsorptions on the membrane filter of regenerated cellulose and on the prefilter of fibreglass were both less than 15%. In contrast, it was found that the (irreversible) adsorptions of PCBs on the polyamide filter were approximately 50%. As a substitution for this wide-pore filter, glasswool was investigated. For glasswool the adsorptions were low and the recoveries high. In the case of off-line filtration a thin layer of glasswool was also found to prevent material flowing out of the column. In general, the length of the tubing in the column test is approximately 0.5 m. It turned out that, estimated from the results of 2-m tubing, the adsorptions on 0.5-m Tefzel tubing would be less than 10%. However, from the adsorptions on 2-m tubing it is also concluded that it is important to minimize the length of the tubing. Parts of the equipment like the gauze, rings and tubing were made of Teflon or materials like Teflon. It is interesting to note that the adsorptions of the more-substituted PCBs on parts made of Teflon were distinctly higher than on those made of glass, like the bottle, glasswool and prefilter. From the comparison of the recoveries of three different filtration apparatuses, it could be concluded that an apparatus made of Teflon should not be used for the filtration of eluates. In fact, filtration in the Teflon apparatus reduced the concentration of most PCBs to less than

277 Table 2 Comparison of adsorption of PCBs and pesticides on various parts of the equipment (n=2) r-HCH

Aldrin

PCB-

28

101

I I8

138

153

180

Filter. regener.cellulose

3 k0.3

adsorption(%)

recovery (%)

104*1

87 *I

<3

2 *3

9a.3

103 *6

92 *5

94*1

<3

<2

<2

115kO.7

104i3

104io.5

I I io.4

1 1 *O.l

10 io.5

78 *I3

87k0.6

83 *7

Prefilter, fibreglass adsorption(%)

recovery (%)

108io.I

1 io.8

98 *I

421

3*4

10i4

108 i 7

96 *2

91 k0.5

Filter, polyamide adsorption(%)

<3

<2

<2

5 i0.2

3 *2

7i2

recovery (%)

104*28

74i23

66i20

55 i19

42 i15

39 *I3

48 *I5

41 i17

adsorption(%)

<3

<2

<2

<2

I *O.l

14*1

recovery (%)

121 *27

123 *5

I l l *I3

98 i 7

96 i 7

110*15

100+10

110k.9

adsorption(%)

2k0.6

6i3

17i14

44i29

28*18

26*15

36*16

recovery (%)

97

84i0.2

101 i 3

90*14

82 *9

69 5~0.7 6 6 i 0 . 3

55 *I0

6k0.8

12*2

17*3

1622

23*2

1io.9

Glasswool

Gauze, Hostaflon

i1

Rings, PCTfT adsorption(%)

recovery (%)

Ill iI0

88 *I1

116 *8

91 *7

91 *3

75 *3

81 *4

76 26

I *I

15 d . 6

20i0.3

31 *Z

26il

29 k0.2

34*3

adsorption(%)

<3

<2

1i 1

5*1

4*1

13 i 3

recovery (%)

109 *I2

89 i 9

113 27

93 *5

99 *2

89 *8

86 *5

78 *2

Glass, 50-mm

100*30

55 39.7

75 +I0

55 *4

61 *3

49 k0.7

47 *4

36*1

Glass, 100-mm

11Oi30 40 *I0

50 *30

35 i 4

40 *2

29 k0.4

32 *0.7

23 i 5

Teflon

79 * 5

42*3

14*8

14+9

10*4

14*5

1 *2

<3

Tubing, 2-m, Tefzel' adsorption(%) Bottle, glass

Filtration apparatuses Recovery (%)

7*8

PCB-52 was not shown because it was interfered with. * In the column test the length of the tubing is mostly smaller; approximately 0.5 m.

27 8 15% of the starting concentration. Filtration in the glass apparatuses resulted in recoveries of approximately 60 and 45% for the 50-mm and 100-mm holders, respectively. An alternative for filtration was investigated as outlined in section 5.3.

5.3 Centrifugation versus filtration Adsorption of PCBs and pesticides during filtration and also slugging of the membrane filters for some waste materials were reasons to start an investigation into the possibilities of eluate centrifugation instead of filtration through a membrane filter. In the Netherlands particles smaller than 0.45 pm are considered to belong to the ground-water. First, the conditions of centrifugation to separate particles bigger than 0.45 pm from the eluate were investigated. Centrifugation of both clay suspensions at 1950 g for 45 min resulted in higher turbidities compared to filtration (Table 3). However, centrifugation of both suspensions at 3470 g for 90 min showed turbidities of the same order of magnitude as those of filtration. It was concluded that for both clays these centrifuge conditions were satisfactory. Table 3 Results of turbidity 1950 g, 45 min Centr.+ fil.

Eluate of

Centr.

Clay-I Clay-2

0.190 0.227

0.098 0.080

3470 g, 90 min Centr.

Centr.+ fil.

0.086

0.072 0.095

0.108

centr.= centrifugation, fil.= filtration through 0.45 pm.

The centrifugation method found was used to compare concentrations in eluates after filtration with concentrations after centrifugation. For the eluate of soil A, the concentrations of PCBs and pesticides in supernatants are compared to filtrates in Table 4.The particle size in the eluates has not yet been determined, so the influence of the particle size in the eluates on the concentrations of PCBs cannot be excluded for the moment. There was not much difference in concentration for y-HCH, aldrin, PCB-28 and -52; for these compounds the concentration in the supernatant was at the most a factor of 2 higher compared to the filtrate. However, the difference in concentration between centrifugation and filtration increased with increasing substitution of the PCBs. For PCB- 180 the concentration in the supernatant was 25 times higher in reference to the filtrate. The same trend was observed for the eluate of the other investigated soil (results not shown). It was also observed that the yellow colour of both eluates was preserved after centrifugation but disappeared after filtration It is interesting to note that for centrifugation the standard deviations of the pesticides and also of the total of the seven PCBs were lower than for filtration. Preliminary findings indicate that centrifugation of the eluates led to higher concentrations and better repeatability compared to filtration. More research is needed to estimate this for other waste materials and organic compounds. In earlier investigations it was found that the emissions of PAH measured were correlated to the size of the particles in the eluate, so it is important to standardize the filtration or centrifugation procedure of the eluates [ 11.

219

Table 4 Concentration and standard deviations in supernatant and filtrate (soil A) Centrifugation 3470 g, 90 min

Filtration pore 0.45 prn

y-HCH Aldrin

c(W) 0.03 0.68

SD(%) 3.8 14

c (pgfl) 0.03 0.38

34

SD (%) 15

PCB-28

0.32

11

PCB-52 PCB- 10I

2.3 2.7

13

0.20 1.3

18 41

15

0.43

30

PCB-I I8

2.3

PCB- 138

2.2

15 14

0.16 0.14

PCB- 153

1.6 0.51

17

0.09

1.1

27

0.02

9.8

PCB- I80

5.9 2.3

c= concentration, SD= relative standard deviation (n=2)

5.4 Volatilization Table 5 presents the recoveries for the water solutions in open bottles with reference to the recoveries for the closed bottle. Storage for 10 days in an open bottle resulted in an average recovery of about 60%. However, after 3 days no distinct losses due to volatilization were determined in the bottle with an opening of 0.5 cm2. Table 5 Recoveries in tests to quantify losses due to volatilization and light Compound

Volatilization 3 days

-

Light

10 days

Brown bottle

Transparent recov(%)

recov(%)

recov(%)

recov(%)

EOX (Aldrin)

-

PCB-28

95

60 34

101

96

PCB-52

86

46

104

96

PCB- 10 I PCB-I 18

85 88

60 75

97 88

99 96

PCB-138

81

73

86

92

PCB- 153

89

57

87

94

PCB- 180

91

63

92

93

= no data

5.5 Light The concentrations in the transparent glass bottle indicated no significant decrease in concentration when compared to the brown bottle (Table 5). In both bottles the recoveries were more than 85% and of the same order of magnitude.

280

6. RECOMMENDATIONS AND OUTLOOK

* The results of the adsorption tests indicated that for leaching tests for PCBs and organochlorine pesticides the use of glass is preferred to Teflon or materials like Teflon. It was found that for filtration of the eluate a membrane filter of regenerated cellulose, a prefilter of fibreglass and a piece of glasswool may be used in leaching tests. In the column test the length of the Tefzel tubing has to be minimized. * Preliminary findings showed that compared to filtration, centrifugation of the eluates resulted in higher concentrations of PCBs and better repeatability. This has to be estimated for other waste materials and organic compounds. * The volatilization results indicated that for the column test measures are necessary to minimize volatilization of PCBs from the eluates, especially for the last eluate fraction. It is recommended to collect the eluate in a bottle cut off as far as possible for about five days at the most. Splitting up the collection is recommended for the last fraction. The first part of this eluate fraction may be collected for five days and afterwards cut off and refrigerated. After collection of the second part, both parts of the eluate fraction may be mixed and analyzed. * The lack of difference between the concentrations in the transparent and brown bottles implied that light had no considerable influence on the degradation of PCBs in clean water for the duration of 10 days. Early in 1994 a limited round robin test will be performed. An indication of the repeatability and reproducibility of the proposed column test for PCBs and pesticides, including centrifugation of the eluates, will be determined during this limited round robin test. The recommendations will also be applied for estimating the leaching of PCBs and organochlorine pesticides from a number of building and waste materials. 7. REFERENCES 1. D.H. Bauw, P.G.M. de Wilde, G.A. Rood, Th.G. Aalbers, A standard leaching test, including solid phase extraction, for the determination of PAH leachability from waste materials, Chemosphere 22(8): 7 13-722 (199 1) 2. G.A. Rood et al., Development of leaching tests for PAH in granular materials, RIVM report (in preparation in Dutch with English summary). 3. G.A. Rood et al., Development of leaching tests for PAH in granular materials, RIVM report (in preparation in Dutch with English summary). 4. G.A. Rood, M.H. Broekman, Th.G. Aalbers, Limited round robin test with the column test for PAH, RIVM report (in preparation in Dutch with English summary). 5. G.A. Rood, M.H. Broekman et al., Development of leaching tests for PCB and organochlorine pesticides, RIVM report (in preparation in Dutch with English summary). 6. M. Wahlstrom et al., Leaching of organic contaminants from contaminated soils and waste materials, This proceedings, WASCON'94, Elsevier. 7. Draft NEN 6406, Water-Gaschromatographic determination of the contents of a number of organochloropesticides and polychlorinated biphenyls, NNI (1990) (in Dutch). 8. NEN 6402, Water-Determination of the halogen content derived from non-volatile, with petroleum ether extractable organohalogen compounds (EOX), NNI (1991) (in Dutch). 9. U. Rabanda, MTA-journal S(1983) 12.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) 01994 Elsevier Science B.V. All rights reserved.

28 1

~ ~ c a t i o n ~ u r e f o r s o l i ~ c a t i o n ~ J. MBhua, P. Moszkowiczb, R. Barnab, P. Philippec, V. MayeuxC aPOLDEN Insavalor, CEI, BP 2132, 27 Bd du 11 Novembre 1918, 69603 Villeurbanne cedex, France bL.C.P.A.E. Laboratoire de Chimie Physique Appliquee e t Environnement (INSA de Lyon), 20, avenue Albert Einstein, 69621 Villeurbanne cedex, France CADEME, 2 square La Fayette, 49004 Angers, France

Abslxact In the framework of the new French technical and regulatory requirements of industrial waste landfilling, solidificatiodstabilization processes a r e expected to be one of the main tools to render wastes physically and chemically compatible with the Environment on the long term. Consequently, it appears necessary to propose a comprehensive qualification procedure to assess the real performances of the different industrial processes in front of the wide range of industrial wastes to stabilize. This paper presents the main steps of the procedure, proposed by ADEME (French Agency for the Environment and Energy Management) and designed by POLDEN and L.C.P.A.E.(INSA de Lyon). 1. DEFINITION OF AN 'TDEN'ITlY CARD" OF THE PROCESS

The aim of this first step of the procedure is to define an "identity card" for solidification processes. I t is of a purely informative character and no selection will be carried out according to the various criteria used for its definition. Such a n "identity card" could prove useful in two cases : to determine the parameters to be controlled particularly with respect to the techniques involved, and to supply the authorities with an e e n t u a l "safety measure" to be imposed in the case of certain processes which due to their very nature must be used with extreme caution (e.g. obvious pollution transfert). The data to be supplied could be as follows :

- SIS principles involved in the process : - nature of the binders : (hydraulic binders, pouzzolanic binders, organic binders), commercial reactants o r reactants coming from waste recovery. - nature of the additives : mineral or organic

282

-

-

-

nature of treatments prior to solidification: extraction of part of the waste to be treated (extraction of the water soluble salt fraction, extraction with water a t various pH (the pH can be very important for the determination of the relative content of metals extracted o r not), extraction of the heavy or light organic fraction, chemical treatment prior t o solidification strictly speaking (neutralization, oxidation or reduction, with industrial reactants or with other waste), control of the water content (drying, filter pressing, addition of absorbant materials or materials which can be hydrated (lime, clay,...) with industrial reactants or other waste), thermal treatment (temperature, residence time, composition and further treatment of associated Air Pollution Control (APC) residues, mass balance) techniques to implement recipes : (optional) - mixing parameters - quantity of added water - setting and hardening conditions (temperature, time, atmosphere (in the open air, controlled humidity, CO2,...)I techniques for the production of solidified material at full scale, e.g.: - fabrication of blocks (size, casting, control of the surface state) - casting in situ - casting, transport and landfilling after setting sources of different families of waste to be treated: - nature of the family : it will be necessary to find a coherent definition of the set of different waste types to be treated by a given recipe. It is obvious that this definition should not be too restrictive as this would tend to reduce the economic interest of the procedure. On the other hand it must not be too general in order to allow the adopted tests to cover all the potential problems of these wastes. The sets of waste could be: waste incineration residues (APC residues from Municipal Solid Waste (MSW) incineration, APC residues from industrial waste incineration, as well as the two associated types of bottom ash), industrial waste water treatment sludges (which supposes t o include metallic hydroxide sludge as well as organic sludge (such as tannery sludge), residues from metallurgy of non-ferrous metals,...). - disposal scenarios: certain processes can be designed from the beginning to produce materials compatible with certain landfill or valorization scenarios. Without considering the regulatory or technical feasability of this option, it is necessary to be aware of such a possibility in order to implement specific procedures.

N.B. Most of this kind of data is considered as being confidential by the waste treatment vendors. It is however conceivable that such data remain confidential between the authorities, ADEME and the company concerned and that the laboratories involved in these tests do not have access to this particular information.

283

2. SELECTION OF A SAMPLE REPRESENTATIVE FOR ALL THE W A S m TYPESOF THE TARGET SOURCES FOR A GIVEN PROCESS

The selection can be made using available bibliographic data concerning this family of waste. It is necessary to have quasi-statistical knowledge of the total content and of the leaching behaviour (it is not possible to base selection only on analysis of isolated batches). Of course it would be of interest to have a n idea of the speciation of the elements, the chemical sensitivity of the contained pollutants and of the ionic balance in the leachates but these data are rarely available. The international bibliography concerning the treatment of such waste by analogous techniques in order to identify the parameters to be controlled will also be studied. In this area, POLDEN is implementing a specific data base (solidificatiodstabilization, vitrification) which can be interrogated according to waste type or treatment family. From the information obtained it will be necessary to define the scope, and more precisely the limits of the area concerned. These limits can be of two types: qualitative (for example for waste incineration residues : either APC residues from MSW incineration generated by the different treatment options, APC from highly halogenated industrial waste incineration, etc...) and quantitative (the soluble fraction of APC residues from MSW incineration varies from 25% to 55% but that of certain APC residues from industrial waste incineration attains 80%!). Once this preliminary work has been carried out, it will be necessary to select the locations where the most representative wastes in the family are produced, including wastes featuring extreme characteristics. Samples will be made according to a precise protocol defined according to the type of facility involved. After homogenization and sub-sampling, batches can be prepared for analysis and for treatment trials. The minimum requirement is of course three types of waste (two extreme and one medium), but it would be more interesting to have at least five types of waste available (two extreme and three others to represent medium sources). We may recall that the study carried out for the Ministry of Environment on treatment processes of APC residues from MSW incineration (POLDEN 1990)involved five types of waste. 3. CONTROL OF THE FEASABILITY AND QUALITY OF HYDRAULIC

SE3"G

The feasability, speed and quality of the setting of hydraulic binders is a very good criterium to identify eventual problems which may delay or inhibit setting. Two experimental approaches are possible : evolution of resistance to penetration with time or heat release. The first parameter is most commonly used in the cement industry. I t is carried out using what is called "Vicat's needle". The extent of penetration of a metallic needle is measured a t regular intervals. For a normal mixture, setting usually occurs after a few hours or in the worst cases after a few days. For a recipe which has been underdosed or containing inhibitors, setting may take several weeks or may not take place at all. In addition of the presence of

284

inhibitors, this determination can also be useful with regards to storage condition of the product before landfilling which is obviously limited in time. Automatic laboratory setting assessment devices exist which can simplify the manipulations if the normal setting time is known. In this case it would be useful to carry out measurements on a recipe containing only the binders without the waste to determine eventual malfunction due to the presence of waste.

A more scientific approach consists of measuring the heat released during hydration of the binder. This can be measured by calorimetry. However, calorimeters commonly used i n the cement industry are not always well adapted for our purposes, taking into account the fact that the setting times in the area of waste solidification is sometimes longer than with pure cement. A doctoral thesis concerning waste solidification inhibitors and involving such a calorimetric approach of solidified waste setting is being conducted in the L.C.P.A.E. INSA Lyon (France). It is cofunded by ADEME and by Lafarge Coppee Recherche, and started end 1993. The information acquired may later allow a transposition of this technique to process control. However, for the moment we can only recommend the use of the "Vicat's needle". 4.S N D Y OF PHYSICAL AND MECHANICAL PROPERTIESIN THE SHORT ANDLONGTERM This includes the mechanical resistance strictly speaking (compressive strengh, erosion, flexion, ...) as well as weathering effects (wetting/drying, freezingkhawing, ...) and also certain physical characteristics (porosity, water absorption capacity, water transport characteristics,...). The latter group of criteria is crucial. I t can inform us about the future behavior of the solidified materials in several different areas. Firstly, the notion of interface between the porewater and the pollutants in the matrix can be appreciated. This notion can be divided into two parameters: intensity (water absorption capacity, porosity) and dynamics (effective diffusion coefficient of water, permeability). As far a s penetration of water is concerned, there is a competitive effect between permeability (penetration due to a hydraulic load - Darcy's law) and diffusion (penetration due to different water concentrations related to capillary absorption - F'ick's law). The measurement of penetration of water (using an under pressure percolation test for example) is very easy as long a s the permeability of the materials are not below 10-9 or in the worst case 10-10d s . This had been the case for the set of solidified samples tested in the study on APC residues from MSW incineration, but the quality of the solidified samples has since improved and this determination will no doubt become more difficult for high grade solidified materials. It is also possible to study the permeability to gas. It must be noted that this measurement is likely to be relatively costly. Furthermore, in actual condition the materials are more likely to simply come into contact with water and the compactness will favour the phenomenon of diffusion. Consequently, we propose to carry out a test to evaluate the

285

Dynamic Water Absorption Capacity (DWAC) which is an immersion test of a standard specimen (dried at 50°Ck3 until1 constant mass), with water renewal a t fixed regular intervals (lh, 3h, 5h, 15h, 9h, 15h, 24h, 24h). The sample is weighed between each water renewal and the extracted soluble fraction is measured. This will allow us to adjust the DWAC measured and then to evaluate the release dynamics of the soluble fraction. These results should enable us to determine the quantity of water which can be absorbed and also a parameter of the kinetics of the phenomenon. "his determination will also be useful to evaluate the influence of ageing : in fact both tendencies can be observed, an increase in porosity due to physical deterioration or to massive release of a significative part of the solidified sample o r a decrease in porosity due to continuing hydration or due to carbonation.

As far as the mechanical properties are concerned, tests to determine the resistance to compression, flexion, or traction can be carried out. Resistance to flexion or traction in concrete is generally low, about ten times lower than its resistance to compression. For this reason concrete is not used in situations where it is likely to undergo flexion or traction.

There are, however, two exceptions :

- use in structures such as bridges. Resistance to flexion is significant, but it usually relies on the presence of a metallic reinforcement.

-

in road construction (for underlying layers or the top layer for which the resistance to flexion is about 4.5MPa).

Resistance to flexion o r traction is the weak point of hydraulic binders and fissures are liable to appear and expansive compounds may form. It may be added that such resistance tests could be used to detect heterogeneity of the matrix (nodules, aggregations of non treated waste). Compressive strengh is the most widely used test abroad a s in France. Therefore it is natural that we have the most data concerning this test. There is also a greater possibility of correlation with non destructive tests and with formulation parameters (with the waterhinder ratio for example). Consequently, coupling of the two measurements seem to be of interest. The admission acceptance levels remain to be defined. Finally, concerning weathering resistance tests,(e.g resistance to freezekhaw), they are clearly relevant to specific valorization scenarios. For the wetting/drying test, it can supply us with further information, but it does not seem necessary from our point of view to carry it out as a procedure by itself. The essential parameters (loss of soluble mass or not, evolution of mechanical resistance after immersion whatever the considered parameter) can perfectly well be measured within the framework of the DWAC determination which thereby would become a multi-parameter test : physical and mechanical behaviour of the solidified sample in prolonged contact with water.

286

5. ANALYTICAL CHARACTERIZATIONOF THE SOLIDIFJED SAlMPLES

The total content in elements of the solidified samples must be verified in comparison to the initial waste for two reasons :

- to evaluate the mass balance and to control the absence of pollution transfer;

- to verify that the binders and reactants used have not contributed their own pollutants (a problem almost systematically encountered). 6. DETERMINATION OF THE "SENSITM'IY" OF THE PROCESS TO CHEMICAL INTERACTIONS

Chemical interactions may be due to : - diversity of waste in the waste source - storage conditions (acid rains, basic leachates, C02,...). Pollutant retention is of two kinds : - Chemical : incorporation of a pollutant in one of the phases of the hydrates formed o r at least a change i n the speciation of the pollutants towards a less soluble form; - Physical : incorporation of a compound of the waste in the porous structure of the material. Physical retention is evaluated by leaching monolithic standard samples and can be described globally by the diffusion model. Chemical retention and its variations according to the chemical context must be carried out on crushed waste in order to maximize the liquid to solid interface and to separate the "chemical" from the "physical". This determination corresponds to the notion of the maximum available content. This is a very delicate issue. It has been shown that the release of most metallic pollutants is highly dependant on the evolution of the chemical context of the matrix, and it is therefore essential to test the intensity of these phenomena and their limits in the laboratory for the following reasons :

-

in order to determine the evolution of a phenomenon within a limited variation range corresponding to the storage condition, it is necessary to appreciate the evolutionary tendencies over a complete variation range;

-

the real life conditions can vary over a much wider range than expected due to ma1 function of the storage conditions (contact with external water, with the atmosphere, with untreated waste,. ..);

-

a greater severity applied on the constraints, as long a s they act on the same mechanisms, allows us to anticipate and therefore to simulate an accelerated ageing process.

287

We therefore propose the following tests : As the aim is to differenciate the chemistry from the physics of the phenomena, all the tests will be carried out on crushed waste (e.g. 100-200pm) - sensitivity of the wastes to be treated to the chemical context imposed by the matrix (often a high pH). For this, leaching behaviour of these wastes can be studied using the leachate obtained from the leaching of solidified samples without added waste. Analysis of the release and comparison with the release of the waste to be treated using demineralized water. - sensitivity of the matrix to chemical contexts imposed by the wastes. In terms of treatment feasability, this will have been carried out in 3. Here we propose to leach, with demineralized water, the solidified samples containing "extreme" wastes i.e. wastes most likely to induce extreme chemical conditions (in terms of pH and/or redox potential 1. - finnaly concerning the sensitivity of solidified samples to external agents, we propose leaching at four different pH levels about 12.5 (controlled with NaOH so as not to perturb the release of portlandite) about 10 (controlled) demineralized water (not controlled) 5 (controlled) - leaching test on solidified samples using demineralized water can inform us about the eventual reducing properties of the material (with certain precautions : gas stripping of water with nitrogen, low L/S ratio, maintaining the leachate out of contact with the air). If it is the case, the leaching test will be carried out in a highly oxidizing medium. These tests will also allow us to evaluate the maximum extractable fraction in the case of chemical sensitivity of the pollutants and therefore to play the role of the parameter Co for the modeling of long term behaviour. It must be noted that this approach will allow us to assess the solubility of the pollutants at the equilibrium as a maximum solubility. In fact there will be a complementarity between the dissolution and the diffusion both with their kinetics. Sometimes the kinetics of dissolution must be the limitant parameter of the release. French research teams (INSA-CNRS) are going to study these phenomena in the framework of an international joint research program concerning the leaching behavior of solidified wastes, funded by Association RE.CO.R.D. and C.N.R.S for the French part, HSMRC and NSF (New JerseyUSA) for the american part, and CUR (The Netherlands) for the Dutch part. 7. EXPERIMENTAL S " D Y OF LEACHING BEHAVIOUR IN THE MEDIUM TERM

We will not reiterate here, the necessity to carry out medium term leaching tests on monolithic standard samples of treated materials. Use of such processes has already been widely discussed and justified in the bibliography (numerous studies funded or conducted by USEPA, WTC Ontario (Canada), ECN (the Netherlands), studies on the leaching behaviour of solidified nuclear waste, studies funded by Association RECORD,. ..) There is a discussion concerning the geometry and the state of the surface of

288

the standard specimen to be used. Leaching tests usually vary between 64 and 90 days for specimens of a few hundred grammes with a surface of about 150 to 300cm2. This is quite suflicient to observe the depletion of salts but generally not enough for the release mechanism of metals to be explicit (purely diffusional, chemically perturbed or deliberately non diffusional). We therefore propose to carry out tests on smaller specimen of about 40cm2 e.g. a slice of lcm cut in the AFNOR standard cylinder 0=4cm-h=8cm. Thanks to the high surface to volume ratio (SN=3)and the small thickness, an extraction time of 64 days will allow us to observe the release phenomena on a very long time scale compared to those observed on specimens of dimensions @=4cm-h=8cm,and the results on the soluble fraction should be available after the first days of leaching. However, i t must be noted that certain solidified products a re not homogeneous i.e. waste may be present as inclusions or in granular form. Under these conditions, the fact that the S N ratio is high will render the release extremely sensitive to the more or less random presence of such granules on the specimen surface. Cast samples could be a partial solution to this problem, but this poses other problems (heterogeneity of the porosity within the solid which invalidates the application of the diffusion model, formation of a layer of salts on the surface during setting leading to a peak of release in the first extract, probably followed by a lower release than normally observed due to formation of a low porosity surface film, and possibility problems of transposition to industrial blocks). Consequently we recommend the use of cut cylindric specimens 0=4cm in a first phase to be cut out of a block (of about 2 litres) a t the laboratory scale and in a second phase to be taken from an industrial sample. If the results of the DWAC (step 4) conducted on a slice 0=4cm-h=lcm shows a diffusional behavior of the total soluble fraction (and eventually of Na+, Ca+, Cl-1, then this kind of slice can be used for the leaching test.If it appears that the surface effects are too important then we recommend the AFNOR standard cut cylinder 0=4cm-h=8cm N.B. The technical conditions for the disposal of industrial solidified materials have not yet been laid down by the regulation. The recommended procedure corresponds to a classical method i.e. the solidified material is cast into a lagoon. After setting, it is broken up to be transported to a landfill. This is the case for example in the solidification centre in Lihge, Belgium and i n the earlier facilities in France. It is also the approach used for in situ casting. However, it must be considered that in the future a company may propose a procedure on a n industrial scale leading to a particular type of physical retention. We thought it logical that the leaching procedure should take this eventuality into account. For example, i f the solidified sample contains several materials and i f the material is cast under particular conditions, the preparation of the specimens must not degrade or affect the structure of the finished product in any way. Therefore, in a case by case fashion, we propose to study the procedure, and to evaluate with the different partners if it is a determining factor for pollutant retention (in particular, it is necessary to know whether the landfill or storage site is compatible with the various parameters involved), and if this is the case, to take these parameters into account for the definition of the samples to be tested.

289

8. STUDY OF THE INFLUENCE OF AGEING OF THE SOLIDIFIED

SAlMPLESON THE mtopERTIEs OF THE MATERIAL As explained above, we propose to evaluate the evolution in time of the extended DWAC i.e. multi-parameter test concerning the physical and mechanical behaviour of the solidified sample when in prolonged contact with water. This procedure would be repeated on laboratory specimens for up to a year and also in a second phase, on specimens taken from blocks placed in an analagous situation to the actual full scale scenario. In the case of a significant difference, the leaching procedure in the medium term could be renewed on aged samples. A previsional planning of the different phases and experiments can be found at the end of the paper. b

9. SIMULATION AND MODELING TO EXTRAPOLATE RESULTS IN THE LONGTERM

The approach we propose here leads to a critical analysis of the applicability of the diffusion model and, when the diffusionnal proves to be relevant, to the application of a tridimensional numerical resolution to identify the two parameters Co (maximum available fraction) and De (apparent diffusion coefficient). Fick's law gives the equation for the diffusional mass transfer:

-x =D

[

1

d2C d2C d2C

T+T+T

a & a y & where C (x,y,z,t) is the local apparent concentration of the solute (in kg/m3), with the initial condition C = Co and the limiting condition a t the soliUiquid interface C = Ci = 0. The representation log J/log t (where J is the flow rate of pollutant release in mg/m2.s), is useful1 to express the results graphically as i t is more sensitive than the representation log d o g t for judging the validity of the diffusional model. In fact, at the beginning of release, the graph obtained is expected to be a straight line with a slope of -1/2, and as soon as depletion of the solid core is reached, the flow J decreases more rapidly than is predicted by the "semiinfinite" diffusional model.

290

This "depletion" effect is very interesting to consider a s it contains information concerning the kinetics of the process and allows a good simultaneous identification of I>e and Co. By comparison of the experimental results those obtained from a tridimensional simulation, by varying Co and Ge, if the diffusion model is validated, it is possible to determine the optimum couple (Co, De), by minimization of the deviation of the simulated concentrations versus the experimental concentrations (C,, - C,,,,)" , .

c,

The simulation of release in the long term is therefore possible for any predefined geometry. In the case of a cube of lm3, the time for half extraction (m/mo = 0.5) of a species such as sodium, which has a diffision coefficient of about 10-10m2.s-1.would be 984 days i.e. 2 years, 8 months and 2 weeks. The 3D simulation developed, allows to extrapolate results for varying geometries of the specimens (parallelepiped, cylinder, sphere) and of all dimensions. It is also possible to express the results as the time necessary for half extraction or extraction of a given fraction of the maximum potential. This approach is available and directly applicable for all soluble species (including total soluble fraction) featuring a diffusional leaching behavior. Concerning metallic pollutants, several cases can be considered : 1. release is diffusional without chemical interaction but the length of the leaching test has not allowed depletion to be reached and thereby the joint determination by calculation of the coefficients Co and I>e. We therefore propose to use the Co obtained from the test on finely crushed waste leached with demineralized water, 2.

release is diffusional with chemical interaction. The ideal situation in this case would be to carry out a medium term leaching test under chemical conditions for which the interaction has been observed (oxidizing medium, basic leachate,...). The numerical simulation could then take into account the coefficients Co and De as being coherent and representative. An alternative solution to reduce the experimental part would be to use the coefficient Co obtained from the test on crushed waste and a coefficient De readjusted using the coefficient obtained with demineralized water, taking into account the ratio Co (with interaction)/Co(with demineralized water).

3.

release is not diffusional. In this case two situations can be found

- The slope of the curve log of the cumulated quantity releaseflog of time is <1/2 : a modification has taken place in the matrix (blocking of the pores) or in the concentration of the species (precipitation) and in the present state of the available models the behaviour cannot be extrapolated. However, in this situation, the

29 1

diffusion behaviour can be taken as the upper limit and we will be able to use this approach to model or extrapolate the long term behaviour.

- The slope of the curve log of the cumulated quantity releasedAog of time is >1/2 : leaching has given rise to a deterioration of the matrix leading to release which cannot be modelized and whose limits cannot be determined (with the available models). In all cases this indicates a badly solidified material and this criterium should be, according to us, eliminating. 10.PREVISIONAL PLANNING FOR THE VARIOUS PHASES AND ExpERwlENTs: phaseddates 1 2

3 lab. scale industrial scale

before solidification X X

T=h after solidification

T=

T=

to+ 4 mths

to+ 12mths

(XI (XI

(XI (XI

X X

X X

(XI (XI

(XI (X)

X X

4

lab. scale industrial scale 5 lab. scale industrial scale 6 lab. scale industrial scale

X X

X X X X

7 lab. scale industrial scale

a

lab. scale industrial scale 9 lab. scale industrial scale

X X

X X

In addition two different approaches are foreseen but still under discussion according to the type of waste and the disposal scenario: - Experimental assessment of the behavior of solidified waste submitted to conditions of contact with water close to real conditions of storage (e.g. sequential contact and low Liquid to Solid ratio) - Biodeterioration: assessment of direct or indirect (such as bio-leaching) effects of micro-organisms on solidified wastes.

292

11. €mFEFmNcEs 1. D. Hoede, H. A. van der Sloot, P. Moszkowicz, R. Barna, J. MBhu: "Leaching behaviour assessment of wastes solidified with hydraulic binders: critical study of diffusional approach" WASCON94, Maastricht, Pays Bas, 1994.

2. R. Barna, P. Moszkowicz, J. MBhu et H. Van der Sloot: 'Waste solidification: modeling and simulation of sodium chloride release from leached concrete.", Waste Management Symposium, Prague , 1992, p. 65-72. 3. R. Barna, P. Moszkowicz, J. VBron et M. Tirnoveanu: "Solubility model for the pore solution of leached concretes containing solididied wastes", Congr&s International CHISA'93, Prague, 1993.

r:

4. R. Barna, P. Moszkowicz, J MBhu et J. VBron: ''Leaching pattern of hea metals from concrete solidified wastes", Heavy Metals in the Environment, 9t International Conference, Toronto, v01.2, 1993, p.128-131.

5. J. MBhu, P. Moszkowicz et R. Barna: "Evaluation des dkhets solidifibs. Quel cr6dit accorder aux diffbrentes p & m de lixiviation?', Envimnnement et Techniques / Info. DBchets, no 125, avril 1993, p.58-61.

6. Beoordeling van immobilisatenEen vmrstel vmr criteria en testmethoden, Civieltechnisch Centrum Uitvoering Research en Regelgeving, CUR - 1993 7. h p o s e d evaluationprotocol for cemenbbased solidified wastes, Report EPS 3/HA/9 - Environment Canada DBcembre 1991 8. R. M. Bricka, T. Holmes, M. J. Cullinane, An evaluation mlid&atiodstabjlization of fluidized bed incinerator ash, 1988

of

9. R. M. Bricka, M. J. Cullinane, Solidification / stabilization as a Best Demonstrated Available Technology (BDAT) for Resource Conservation and Recovery Act (RCRA) wastes, - USEPA (US Environmental Protection Agency), 1989 10. Robert April, Methodology for developing Best Demonstrated Available Technology (BDAT) treatments standards (draft),USEPA - 1989 11. Technical resources document on solidification/ stabilization and its application to waste materials, Batelle - Columbus Division - Columbus, Ohio, 43301-2693

12. J. MBhu, R. Gourdon, POLDEN INSAVALOR, Etude comparative et critique des normea et p r o d d u mtenuea ~~ au plan internationalpour &valuer le potentiel polluant de dkheta solidifib,AssociationRECORD, 91-302, Juillet 1991 13. P.M Erickson, D.R. Kirk, C.C. Wiles, USEPA, Technical issues on long.

term performanceof solidified/stabi2izedwaste forms,1993

Environmental Aspects of Consbuction with Woste Moteriols J.J.J.M. Goumans, HA. von der SIoot and Th.G. Aalbers (Editors) el994 Elsevier Science B.K AN tights resewed.

293

UTILIZATION STATUS, ISSUES AND CRITERIA DEVELOPMENT FOR MUNICIPAL WASTE COMBUSTOR RESIDUES IN THE UNITED STATES D.S. Kossona, B.A. Claya and H.A. van der Slootb and T.T. Kossona aRutgers, The State University of New Jersey, Dept. of Chemical and Biochemical Engineering, P.O. Box 909, Piscataway, NJ 08855-0909, USA bECN, P.O. Box 1, 1755 ZG Petten, The Netherlands

Abstract Utilization of MWC residues is being considered for a variety of applications in the United States. Currently, there are no federal guidelines or criteria for MWC residue utilization. This paper presents the issues concerning MWC residue utilization in the U.S. and outlines a framework for utilization criteria. Utilization of grate ash as an aggregate substitute in pavement is used as an example to illustrate estimation of lead release in a potential application scenario.

1.

INTRODUCTION

Municipal waste combustion (MWC) has become an important component of municipal solid waste (MSW) management in the United States. The primary motivation for MWC has been a shortage of available landfill capacity and public opposition to siting of new landfill disposal facilities. A secondary motivation for MWC has been the recovery of energy during the combustion process. While MWC typically reduces the volume and mass of waste by more than 70%, MWC residues still require management with approaches that are protective of the environment and economically feasible. The majority of MWC facilities recently constructed in the United States have been mass burn facilities with energy recovery. The principal residues generated by these facilities are bottom ash and air pollution control (APC) residues. Bottom ash is comprised of residues that are discharged from the combustion grates (grate ash) and residues that fall through the grates during combustion (grate siftings). APC residues are comprised of scrubber residue and ash recovered through particulate collection systems (e.g., fabric filters or electrostatic precipitators). Scrubber systems in the US are most frequently

294 semi-dry or dry lime injection systems. of MWC residues generated.

Bottom ash is typically ca. 85% of the total mass

Currently in the US, bottom ash and APC residues are mixed to form combined ash which is disposed of either at a landfill which accepts only MWC residues (referred to as a "monofill") or co-disposed at landfills with municipal solid waste. Co-disposal frequently occurs with the MWC residues being deposited in a separate cell within the landfill. However, the same societal and economic forces which encouraged MWC over direct landfilling of municipal solid waste also make landfilling of MWC residues unattractive. Utilization of MWC residues is being considered for a variety of applications in the United States. Primary applications currently under consideration are use of the MWC residues as (i) an aggregate substitute in paving applications, including as compacted base, or in bituminous pavement, (ii) an aggregate in terrestrial Portland cement applications, including cement block and prefabricated or field erected forms (iii) an aggregate substitute in Portland cement based marine applications such as artificial reefs and shoreline protection, (iv) daily cover for municipal waste landfills, or, (v) granular fill material for embankments. Almost all of these applications would involve some degree of ash treatment, either physical or chemical, either in preparation for or as a consequence of utilization. For example, most applications would require screening of ash to achieve desired particle size gradation or would result in ash encapsulation in another matrix. Currently, there are no federal guidelines or criteria for MWC residue utilization. Individual states have focused on development of utilization criteria to varying degrees. Rutgers University has been working through a cooperative agreement with the U.S. Environmental Protection Agency (USEPA) on identification of the issues associated with MWC residue utilization and the development of recommendations for utilization criteria. This paper presents the issues concerning MWC residue utilization in the U.S. and outlines a framework for utilization criteria. Utilization of grate ash as an aggregate substitute is used as an example to illustrate estimation of lead release in a potential application scenario. 2.

STATUS OF MWC RESIDUE

UTILIZATION AND ISSUES

Many local jurisdictions in the US are pursuing MWC residue utilization research and development programs. Table 1 presents a summary of utilization development and field testing activities in the US (Hoffman, et al., 1993). Most of these programs have been developed independently by the local jurisdiction. MWC residue utilization is of greatest interest in geographic locations of high population density. There is not a clear preference for use of bottom ash or combined ash or for a single utilization scenario. Interest in utilization principally is motivated by (i) the potential for extending existing ash landfill capacity, (ii) the potential for reduced disposal costs, and (iii) replacement of aggregate in some regions where natural supplies are limited. Secondary effects of ash utilization may be (i) reduced environmental impact, (ii) improved ash quality, and, (iii) improved product quality where ash is substituted for natural aggregate. Reduced environmental impact may result because utilization scenarios may have more stringent requirements than disposal. For example, increased contaminant immobilization may occur because of ash encapsulation in asphalt or other materials for utilization. Improved ash quality may result because motivation would exist for reducing contaminant concentrations in ash and maintaining ash quality control to facilitate utilization. This may be achieved through combustion facility operation or separation of specific components from the

295 municipal waste stream or ash. Under most disposal scenarios, no motivation exists to control or improve ash quality. Four primary arguments against MWC utilization have been offered. One argument is that utilization facilitates incineration. This would occur because of avoided disposal costs and siting of MWC residue disposal facilities. The reasons why incineration is considered unwanted include the potential release of contaminants to the environment (atmospheric emissions) and loss of non-renewable natural resources through combustion. A second argument against utilization is that it would reduce emphasis on source reduction and recycling. It is argued that a less expensive waste disposal option would make source reduction and recycling less economically attractive and that they would not be a required for waste management. It is also argued that utilization would decrease public attention on solid waste management issues and the emphasis on changing societal behavior. However, utilization may result in increased source reduction, separation and recycling of specific MSW constituents in an effort to improve MWC residue quality. A third argument against utilization is that ash is classified as a "hazardous" material. Under current US regulation, wastes can be legally classified as hazardous under the Resource Conservation and Recovery Act (42 U.S.C.A. g690l et seq.) in one of four criteria. The four criteria for classification are based on the origin of the waste (the process by which is was generated), ignitability, corrosivity or by failure of the designated regulatory leaching test criteria. Whether or not MWC residues are considered hazardous has focused on the applicability of the regulatory leaching test. Initially, the extraction procedure (EP) toxicity test was the USEPA promulgated leaching test which was subsequently replaced by the toxicity characteristic leaching procedure (TCLP) (USEPA, 1986). Several combined ash samples that have beeii tested have failed the leaching test criteria, primarily based on lead or cadmium leachability. However, RCRA specifically excluded "household waste" from being subject to this test criteria. Household waste was not clearly defined in the legislation and USEPA and the US Court system have had many contradictoty opinions on whether or not MWC residues are subject to this criteria. The applicability of this criteria to MWC residues currently is a case being heard by the US. Supreme Court. While a lot of public attention has been focused on this issue, the outcome of the Supreme Court case may have limited technical impact. Operations at most MWC facilities have been adjusted so that the residues generated routinely pass the TCLP and therefore would not be considered hazardous. The most significant impact on utilization if the court decides the test is applicable may be on the separation of bottom ash from APC residues for disposal. Separation may become less attractive because separated APC residues will not as readily pass TCLP. An unfortunate aspect of the debate surrounding TCLP has been that it has focused attention improperly. The most significant potential impacts from MWC residue leaching are a consequence of high concentrations of soluble salts which may impact groundwater supplies and the leachability of specific elements (e.g., lead) under extremely alkaline conditions. These two issues are not addressed by the TCLP criteria. The forth argument against utilization is the potential for release of potentially harmful MWC residue constituents to the environment. Release of these constituents should be considered for all aspects of residue management and potential releases to the atmosphere, water bodies and soils or sediments. Lead, cadmium and mercury are MWC residue constituents most often cited as being of concern. The framework for utilization criteria outlined in this paper focuses on this last issue. The above arguments for and against utilization have highlighted the need for ash utilization criteria. In general, uniform standards and practices are needed for environmental

296 protection and to provide guidance to states and local jurisdictions. Utilization criteria also will help to clarify liability associated with ash management. In addition, promulgation by USEPA of utilization criteria may be required by pending federal legislation.

3.

A FRAMEWORK FOR UTILIZATION CRITERIA

A comprehensive approach to MWC utilization is needed to assure environmental protection. This section outlines a preliminary framework for envirbnmentally protective criteria. The typical projected life cycle of MWC residues during utilization includes the following stages: 1 . Residue generation (production at the MWC facility): 2 . Physical processing: 3. Stockpiling: 4 . Manufacture; 5. Use in designated application; and, 6 . Post-utilization management and disposal.

Potential MWC residue impacts and considerations are essentially common independent of utilization application from the time of ash generation to the point of manufacturing. Subsequent stages in the life cycle are significantly more application dependent because of the nature of the material in which the ash will be used and the exposure scenario during use. For example, utilization in Portland cement applications will have different effects on contaminant release than utilization in bituminous pavement. Residue generation is defined as the production of the residues to be utilized at the MWC facility. This stage is the most critical for quality control. The intent at this stage should be to produce as uniform a product (defined residue stream) as possible that will permit utilization after subsequent processing. This will minimize the amount of processed material that would be rejected as unacceptable at later stages or require disposal. Physical processing is defined as mechanical processing such as ferrous and non-ferrous metal removal, and, crushing and screening to control the particle size gradation of the material to be utilized. Removal of oversized material is necessary to facilitate subsequent processing into appropriate products (e.g., asphalt paving material or concrete forms) and would be based on the specific utilization scenario. The principal environmental and occupational health impact concerns during this stage would be a consequence of fugitive dust. Removal of fines may be necessary to minimize fugitive dust, and attendant controls, during subsequent stages. Stockpiling of residues is carried out for several reasons. First, during stockpiling, aging reactions occur within the ash which further stabilize the material. These reactions include oxidation, hydration and carbonation (fixation or uptake of atmospheric carbon dioxide) reactions. Oxidation of reduced metals typically result in less leachable forms. Carbon dioxide uptake results in a pH shift of the material from typically greater than eleven to more neutral pH, e.g., less than 9. This process also results in re-speciation of some elements from hydroxides to carbonates. The net result of this process is a shift in the pH domain and speciation of the material to a less leachable regime for metals such as lead and cadmium. Hydration reactions typically result in swelling of the material. These swelling reactions must be allowed to progress prior to utilization to avoid detrimental effects on the structural durability of the final products. Swelling reactions and evolution of hydrogen from the oxidation of aluminum are also reduced at near neutral pH. Exact intervals

291 required for sufficient ash aging have yet to be defined, but preliminary finding indicate a period between three and six months (Oberste-Padtberg, e l al., 1990; Schneider and Vehlow, 1993). A second reason for ash stockpiling is to allow for storage of the material because of seasonal demand. For example, most paving applications will able to utilize the material only six to eight months out of the year depending on local climate. Potential environmental or health impacts from stockpiling can be a consequence of fugitive dust, precipitation runoff, leachate or site access. Manufacturing is defined as the processing of the ash into the final product form. This stage for paving applications would include ash drying and blending with asphalt at the asphalt plant, and placement of the pavement. This stage for Portland cement applications would include mixing with Portland cement, water and natural aggregate and forming into final structures such as blocks. Residue handling requirements at this stage, and during subsequent stages, should conform with standard handling procedures for materials which the ash is replacing to the greatest extent possible. Potential environmental or health impacts during the manufacturing stage could result either from fugitive dust or drying process emissions. Use in the designated application (e.g., pavement construction, cement block, etc.) potentially can impact the environment through particulate release or leaching. Particulate release can occur through erosion or abrasion of exposed surfaces or, in the marine environment, through burrowing aquatic animals. Maintenance procedures also can result in the release of fugitive dust. Finally, the post-utilization management of the material must be considered. Ideally, the disposal of MWC residue containing materials should be compatible with the management and disposal practices used with the standard material which is being replaced. The above potential environmental impact pathways can be summarized as being associated with particulate release, either through fugative dust or erosion and abrasion, or associated with leaching. Standard practices exist to minimize fugative dust. Product durability standards and limitations on utilization applications can be used to control particulate release by erosion or abrasion. Accurate assessment of potential constituent release through leaching and field verification are the most tenatious issues that must be addressed. A two part approach to utilization criteria would maintain environmental protection, permit the greatest degree of flexibility, and avoid unnecessary, repetitive testing and evaluation. The first part of this approach requires determination of acceptable property ranges for characteristic residue types. Thus, a residue stream from any MWC facility that tested within the designated parameter ranges would be classified as acceptable for utilization in previously approved utilization applications. An example residue stream would be grate ash from a mass burn facility. Initially, detailed statistical characterization of a residue stream would be required from any facility seeking to have the residue utilized. This would be followed by routine quality control testing of the residues at regular intervals while being generated. Thus, residues would be certified for approved applications. This concept of certification also was advocated by Steketee and De Zeeuw (1991). The second part of the utilization criteria would be approval of certified residues for utilization in specific applications. Approval of a specific application should consider the potential constituent release pathways and impacts. Two primary routes for environmental impact require consideration for most applications. The first route is through particle

298 transport followed by either incorporation into soil or sediment, or food chain uptake. Food chain uptake is a much greater concern for marine applications. The principal controls over particle transport are through limiting direct abrasion on surfaces containing ash and through product durability requirements. The second exposure route is through leaching followed by impact either on groundwater, surface water, soil or sediment resources. Release through leaching may be either percolation controlled or diffusion controlled. Percolation controlled leaching occurs when the material is granular and used in an application where significant infiltration can be anticipated. Diffusion controlled leaching occurs when the material is either monolithic and durable, or is a compacted granular material with a low permeability or with an overlying barrier preventing infiltration. Contaminant release through leaching can be viewed as being comprised of two components, contaminant release potential and contaminant release rate. Establishing limits on cumulative contaminant release over a fixed time interval is a potential approach for limiting environmental impacts for applications which have a finite use period. The cumulative contaminant release could be projected based on integration of release rate and release potential data for defined geometries. This projection could include application specific information such as mean temperatures, precipitation and pH conditions to provide translation of laboratory data to field scenarios. Cumulative contaminant release would be the most important parameter for elements or species of concern that accumulate in the surrounding environment. Release rate or flux would be the most important parameter for non-accumulating elements or species (e.g., sodium, chloride). Utilization of grate ash as an aggregate substitute in a binder layer for road paving applications is used as the following example. Lead release is used as an example for estimation of release during utilization. A typical pavement consists of the following layers or a subset combinations of layers depending on design (listed from the top driving surface down): a shim/leveling course, a wearingkurface course, a binder course, a base course, a sub-base course, a compacted subgrade, and a natural subgrade. The shim/leveling course is placed on the surface to level ruts and depression and typically consists of a fine grain sand. The wearingkurface course is the top asphalt layer and the binder course is below the surface course. The binder course serves as the bottom portion of the roadbed if the wearing course is less than four inches thick. Otherwise it is placed between the wearing course and the base course. The base course is normally the lower portion of the pavement. However, a sub-base may be required directly below the base. The pavement is built from the bottom to the top on a subgrade that has been prepared by compaction. The entire roadbed is placed on natural subgrade. Contaminant release from the pavement binder layer would be diffusion controlled in this scenario. Minimal percolation through the pavement would be anticipated if it is assumed that the wearing surface is adequately maintained. Particulate release is expected be negligible because the binder layer is not directly exposed to abrasion. Whitehead (1992) and Mammoet Project (ECN) have measured effective diffusion coefficients for contaminant release from asphalt using grate ash as an aggregate substitute. Laboratory observations have indicated effective diffusion coefficients (De) between 10-15 to 10-l8m/s2 depending on product formulation. Figure 1 presents cumulative release from a 45 cm thick road base as a function of PDe and the time the road base is in place (Kosson, et al., 1993). Cumulative release is expressed as the dimensionless variable of quantity released divided by the release potential or availability (R/Rmax). If the useful life of the road is assumed to be 100 yr, the total cumulative release will be less than 5% of the availability. Figure 2 presents an availabilily-pDe plot from leaching tests on untreated MWC residues

299 Road base 45 cm

I""

0.001 0.01

0.1

1

10

100 1000

Time (ycars] Figure 1.

Estimation of fractional cumulative release as a function of time and effective diffusion coefficient (pDe) for 15 cm thick road base. The maximum cumulative release (Rmax) is the mass of the availability of the specific element or species multiplied by the total mass of product. 19 18 17 16

15

g

l4 13

12 11 10

9 1

10

100

1000

10000

Availability (mg/kg) Figure 2.

Availability-pDe plot of release parameters for from tank leaching tests on untreated MWC residues and several product materials containing MWC residues. Diagonal lines represent constant cumulative release [mg/m2] estimated for 100 yrs using the "infinite slab" approximation.

300 Table 1. Summary (partial) of residue utilization projects in the United States by type of MWC residue used, facility source and demonstration type. (Parentheses around terms indicate uncertainty)

MASSBURN Electrostatic Precipitators Scrubber

Proiect (Combined)

Hennepin County, Minnesota Pavement Demonstration Hillsborough County Department of Solid Waste Municipal Incinerator Ash Reuse, Research Development and Demonstration Project, Florida

Combined

McKaynite Demonstration, Acline Street, Florida

Combined

McKaynite Demonstration, Ruskin, Florida

Bottom

Bottom

New Hampshire Bottom Ash Paving Project

Bottom

NYSERDA - Phase Ha, New Jersey

(Bottom, Combined)

CONCRETEKEMENT APPLICATIONS Ash Management Building, OH (Montgomery County)

Bottom

Center for Innovative Technology, VA

(Bottom, Combined)

Commerce Refuse-to-Energy Ash Treatment and Reuse, Los Angeles County, CA. Fly Ash Stabilization Building, OH (Montgomery Cty)

Combined Bottom

Islip, Blydenburgh Landfill, Long Island N.Y.

Combined

Pinellas County, Florida Artificial Reef

Scrubber Bottom

SUNY Artificial Reef Demonstrations

Combined

SUNY Boathouse Demonstration

Bottom, Combined

Combined

30 1 Table 2. Lead content and leachability in MSW, MWC residues and during utilization.

.Pb Total in MSW

-1 kg1Mg MSW

Total in bottom ash

5 kg/Mg ash

7 0Yo

Total in APC residue

12 kg1Mg ash

30%

Available - All residues

150 glMg MSW

15%

100%

Available

- grate ash

45 g/Mg MSW

4.5%

Available

-

grate siftings

70 g/Mg MSW

7 Yo

Available

-

boiler ash

0.3 g1Mg MSW

0.03%

Available

- APC

30 g1Mg MSW

3 Yo

residue

IF GRATE ASH IS USED AS AN AGGREGATE IN ASPHALT BINDER LAYER IN ROAD: 50 wt% ash; availability = 200 mg/kg ash; PDe layer thickness = 45 cm J O O vr - c

Effect on 10 cm depth soil;

=

15;

~ 1 0 0mg/m2 or ~ 1 mg/kg 0 ash

c0.2%

c1 mglkg increase (typical background soil concentrations 50-200 mglkg)

302 and several product materials containing MWC residues. Diagonal lines represent constant cumulative release [mg/m2] estimated for 100 years using the “infinite s l a b approximation described by Crank (1 975). This approximation will over estimate release when depletion of leaching constituents occurs. All of cases for asphalt containing bottom ash are to the left and above the 100 mg/m2 diagonal line indicating that cumulative release over 100 years is estimated to be less than this amount. If released lead is assumed to accumulate within the first 10 cm of soil below the road, this would result in soil lead concentration increases of less than 1 mg/kg. Table 1 summarizes the fraction of lead originally present in MSW that would be contained in different MWC residue streams, released if grate ash were used in binder pavement. and the potential impact on soil lead concentrations. While approximately 70 wt Yo of the total lead originally in MSW is present bottom ash, only 4.5 wt o/o of the lead is available from the grate ash fraction. However, the grate ash fraction represents approximately 80 wt% of the MWC residues requiring management. Estimated release over 100 yr represents less than 0.2 wt% of the original lead quantity and a minimal soil lead concentration increase over normal background levels. These estimates indicate that this application scenario should be environmentally protective based on conservative assumptions. Thus a field evaluation for verification of these estimates would be appropriate. Subsequently, it may be possible to proceed with this as an approved application in the above described framework. 4.

CONCLUSIONS

The following conclusions are made based on the current status and needs for utilization criteria in the US: Utilization of MWC residues may have several environmental and economic benefits. The environmental benefits include the potential for reduced contaminant release and motivation for improved ash quality through source reduction, recycling and separation of MSW components, as well as through MWC facility operation. Economic benefits are primarily reduced MWC residue disposal costs and avoidance of residue landfill siting. Several sociological issues and the need for avoidance of negative environmental impacts are the primary arguments against utilization of MWC residues. The sociological issues require resolution through the public policy process. Avoidance of negative environmental impacts as a consequence of MWC residue utilization can be achieved through development of appropriate technical utilization criteria. Utilization criteria must consider potential environmental impacts through the life cycle of the materials to be utilized, including from the point of generation through ultimate disposal. Two part utilization criteria may be the most effective approach. The first part would certification of MWC residue characteristics and quality control. The second part would be approval of residue utilization in specific application scenarios. The primary routes of impact from utilization are through particulate release and leaching. Particulate release can be controlled through development of standards for materials durability or selection of applications which are not subject to abrasion or erosion. Estimation of constituent release can be achieved through use of an

303 appropriate combination of laboratory leaching procedures, laboratory-to-field translation parameters and field verification. Protocols for evaluation of leaching should be specific to the anticipated exposure scenario. Any single test procedure would provide insufficient information for accurate evaluation. Field evaluations are necessary to verify critical assumptions. Acknowledgment and Disclaimer This approach has been developed to a large extent through discussions in the framework of the activities of the International Ash Working Group (IAWG-IEA) and collaborative efforts between Rutgers University and The Netherlands Energy Research Foundation (ECN) under USEPA cooperative agreement CR818178-01. The views presented in this document have not been peer reviewed by the sponsoring agencies and do imply official recommendation or endorsement.

5. REFERENCES Crank, J. 1975. The Mathematics of Diffusion. Second Edition. Oxford University Press, New York. Kosson, D.S., T.T. Kosson and H.v.d. Sloot. 1993. w t ion of Solidifii ' .. Processes for h$.miciDal Combust ion Residues. USEPA/600/SR-93/167 (NTIS PB93-229 870/AS). Oberste-Padtberg, R. and K. Schweden. 1990. "Zur Freisetzung von Wasserstoff aus Morteln mit MVA-Reststoffen," u a a er. Luft und Boden, vol 34, 61-62. Schneider, J. and J. Vehlow. 1993. unaen zu r Verbesse runa der Um w e l t a w m s c h l a c k e n , Kernforschungszentrum Karlsruhe Laboratorium fur Isotopentechnik. Steketee, J. and J. De Zeeuw. 1991. "Certification of MSW slags as Road Construction Material," in Waste &&r ials in Con s t r u c t i a H. Goumans, H.v.d. Sloot and T.G. Albers, eds., Elsevier, Amsterdam. US Environmental Protection Agency. November 1986. "Hazardous Waste Management System; Land Disposal Restrictions: Final Rule," Federal Reais&, Part 11, Vol 40 CFR Part 261 et seq., Washington, D.C. Whitehead, I.E.. December 1992. An Fnvironmental Fvaluation of bottom Ash Subst itution Pavement Materials, M.S. Thesis, Univ. of New Hampshire (Civil Engineering).

This Page Intentionally Left Blank

Environmental Aspects of Consmtction with Waste Materials JJJ.M. Goumans, H A . van der Slmt and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. All rights reserved.

305

Validation of Dutch standard leaching tests using NEN-IS0 5725 G.J. de Groot and D. Hoede Energy Research Foundation ECN-FB, Soil and Waste Research, P.O. Box 1 , 1755 LE Petten, The Netherlands Abstract The precision of the four leaching tests, to be published as Dutch standards NEN 7341, NEN 7343, NEN 7349 and NEN 7345, was established in terms of reproducibility and repeatability according to the NEN-IS0 standard 5725. The preliminary results for the availability test (NEN 7341) presented here, show a mean standard deviation of the reproducibility (S,) of 5.2% and a repeatability (SR) of 8.6%. These values are corrected for the contribution of the standard deviation of the chemical analysis. The precision is determined in a round-robin with 10 laboratories on 6 types of material (incinerator fly ash, pulverised coal bottom ash, incinerator slag, pulverised coal fly ashkement stabilisation, calcium-silicate bricks with pulverised coal fly ash, and ordinary bricks). The chemical analysis was performed by one laboratory to minimise the contribution of analytical errors. No significant influence of the type of material on the precision was found. Although the influence of the type of element on the precision, for the elements studied here, is small, it cannot be excluded that for other elements this influence is significant. 1. INTRODUCTION

A number of test methods has been developed in the Netherlands for the characterisation of the leaching behaviour of building and waste materials. Over the last 3 years this was done within the framework of the Standard Committee 390 1 1 'Leaching characteristics of building and waste materials' of the Netherlands Normalisation Institute ("I). Four test methods were used: (a) availability test, (b) column test, (c) serial batch test and (d) tank leaching test. In 1988 a pre-standard NVN 2508 has been published, describing tests a, b and c. A year later a concept pre-standard for test d, NVN 5432, followed. Last year a series of four Dutch revised draft standards has been published in which the experiences of 4-6 years of usage of the 4 leaching tests are implemented (NEN 7341, NEN 7343, NEN 7349 and NEN 7345) [l-51. For the final version of these standards the precision of the leaching tests in terms of reproducibility and repeatability are to be established using the NEN-IS0 standard 5725 [6]. 2. OBJECTIVES AND BOUNDARY CONDITIONS

According to the NEN-IS0 norm 5725 the precision is determined using two parameters, repeatability and reproducibility:

306

repeatability: precision under conditions where independent test results are obtained with the same method on identical test material in the same laboratory by the same operator using the same equipment within short intervals of time. reproducibility:precision under conditions where independent test results are obtained with the same method on identical test material in different laboratories with dfferenl operators using different equipment. The precision can be expressed as the standard deviation of the test results obtained under repeatability or reproducibility conditions, indicated by ‘S; and ‘SR’respectively. It should be noted that the precision does not relate to the true value of test result, but depends only on the distribution of random errors. The standard leaching tests are validated while the precision for the chemical analysis in leachates is not yet established. Therefore, the contribution of the chemical analysis has to be minimised. This condition has the following consequences: 1 . The chemical analysis for each leaching test has to be performed by one laboratory. 2. Only chemical components that leach in sufficient amounts can be used for the validation. A guide line for a suitable level is about 10 times the detection limit. At this concentration level the analytical error can be limited in most cases to about 5%. 3 . Each chemical analysis is performed in duplicate for the determination ofthe contribution of the analytical error in the precision of the leaching test results. In principle, for the implementation of the NEN-IS0 procedure, the influence of the leaching level on the precision of the leaching test result should be determined. Different leaching levels for a specific element and material are difficult, if at all possible, to obtain. Instead, the different types of test material will be regarded here as different levels. Because of consequence 2, mentioned above, the validation can only be performed for a restricted number of elements. 3. EXPERIMENTAL 3.1 Layout of the experiments

The precision of the leaching tests is determined using a balanced uniform level experiment [ 6 ] .The test will be performed on q levels (types of material, with expected different leaching

levels). A number of p laboratories will perform the leaching test n times. The experimental scheme is shown in Table 1 . Table 1 . Experimental set-up LEACHING TEST Availability test Column test Serial batch test Tank test

Standard

q

p

n

i

NEN7341 NEN7343 NEN7349 NEN7345

6

10

10

2 2 2 2

6

3 3

10

5 5 5

numbcr oftests 120 60 60 60

fractions per test

3 10 ((I materials, p laboratories. 17 tests per laboratory per material. mean of I elements per test)

1

7 5

8

307 3.2 Leaching tests

3.2.I Availability test ("7341) The purpose of the availability test is to indicate the quantity that may be leach out from a material under environmentally extreme conditions, that is e.g. in the very long term, after disintegration of the material, h l l y oxidised, and complete loss of acid neutralising capacity. The availability for leaching is determined by twice consecutively extracting the finely ground material in demineralised water in a liquid/solid ratio(L/S) of 50 Ukg at controlled pH 7 and 4 respectively. The result of the test to be validated is the leachable amount expressed in mg/kg. 3.2.2 Column test WEN 7343) The purpose of a column test is to indicate the quantity in mg/kg that is leach out in the short to middle long-term corresponding with a L/S range of 0.1-10 Ukg. The ground material (95% < 4 mm) is leached in a column of 5 cm diameter and 20 cm length with a moderate flow-rate (10-15 mUh). Seven consecutive fractions are analysed. The cumulative amount leached at L/S=l and L/S=IO, expressed as mg/kg, are the results to be validated. 3.2.3 Serial batch test ("EN 7349) This test has the same purpose as the column test for the L/S range 20-100 Ukg. Five consecutive extractions are performed with demineralized water for 23 hour at W S 20 each. Two results from this test will be validated: the cumulative amount leached at L/S=20 and L/S=I 00, expressed in mg/kg 3.2.4 Tank leaching lest ("EN 7345) With this test the leaching of components from solid monolithic products is determined by submersing a test piece in demineralised water and refreshing the leachate at 8 fixed times and measuring the concentration in each leachate. The procedure resembles in principle the ANS16.1 procedure [7]. After verifying the diffisive leaching mechanism and determination of the effective diffision coefficient, the cumulative release in mdm2 at 64 days is calculated from this diffision coefficient. For both results, the cumulative release (mg/m2) at 64 days and the diffusion coefficient (m2/s), the precision will be determined.

3.3 Selected materials and elements Table 2 gives a summary of the tested materials and elements analysed. The materials are chosen from different categories based on different morphology, properties and leaching characteristics, These are respectively powders and sludges (AVVH), fine grained materials (<4mm) (MCBA), granular materials (< 40mm) (AVSH), and products/monoliths. Table 2. Materials and elements MATERIAL incinerator fly ash pulvcrised coal bottom ash bottom ash pulverised coal fly asWccinent stabilisation Calcium silicate brick with coal fly ash bricks

SAMPLE CODE AVVH MCBA AVSH VACS KZFH KBAA

ELEMENTS Na, Cd, CI, Pb, SO,, Zn,F, Br Na, As, Zn Na, Ca, C1, Cu, Pb, SO,, F Na, Ba, Cu, Mo, SO,, V Na, As, NI, SO4, V, Se Na, As, V

308 The availability test is applied on all materials and elements in Table 2. The column and serial batch test is done on the 3 granular materials with sample codes AVVH, MCBA and AVSH. On the other 3 materials, VACS, KZFH and KBAA, the tank leaching test is performed. As stated in section 2, only elements are chosen for which it is expected that they will leach in sufficient amounts. If for some chemical components some materials are proved to be inhomogenious (possibly Pb and Cu in bottom ash), the result for that element will not be used. Table 3 . Some physical parameters of the tested materials Sample code

Amount prepared

AVVH MCBA AVSH VACS KZFH

120 kg 600 kg 120 kg 60 proctors 40 bricks 64 bricks

KBAA

Water content (%w/w)" 6OoC 105OC 1.3 2.6 21.6 21.8 2.4 4.3 15.9 20.9 8.8 12.9 0.06 0.14

Dimensions

10 cm 0, 11.6 cm 21x10~8cm 21x10~5cm

' loss of water is measured after drying over night at 60 and l05'C Table 4 . Chemical analytical methods ~~~

Element

Method-1

As Ba Ca Cd cu Mo Na Ni Pb Se V Zn tot-s

HAAS ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES HAAS ICP-AES ICP-AES ICP-AES IC IC IC FI-ISE

so4

Br

c1 F ICP-AES: HAAS: IC: FI-ISE:

DTL-I

Method-2

DTL-2

I

Required DTL* other than Tank Tank leachates 10

0.05 1

80

100 2 2

GF-AAS

0.15

8

GF-AAS

3

40 13 40

GF-AAS GF-AAS

3 3

1.7

17

0.03 13 3

0.05 2.7

2.5

0.01

13 23 0.3

3 7

60 50

100 (SO4) 100-1000** 10- I00 * * 10-100** 10

26500 (as SO4)

~

0.8 5

0.05 7 10

1470 (as SO,)

6

1

10000 180

1000 42

Inductively Coupled Plasma Atomic Emission Spectrometry Hydride Atomic Absorption Spectrometry Ion Chromatography Flow Injection with Ion selective electrode

* Detection limit (3 times the standard deviation of the blank) required to maintain Dutch regulations ** Depends on the presence of nitrate (most critical for Br)

309 3.4 Sample taking and preparation

All materials are obtained from a regular production except for the pcdcement stabilisation (VACS), which was produced in the laboratory and the KZFH bricks, containing 20% coal fly ash, produced during a special production. The sampling and sample preparation was performed by the Materialen Bank Nederland (h4BN). Some information about the materials is given in Table 3, e.g. the amount from the bulk that is used in the sample preparation and the water content of the sample measured after drying at 60°C. This last value is relevant because the leaching test has to be performed on material that has been dried at a maximum temperature of 60°C to prevent loss of contaminants.

3.5 Chemical analysis The chemical analysis methods used for measuring the leachates are shown in Table 4. For the availability test, Method-1 with corresponding DTL-1 is mostly used. To minimise the influence of the analytical error in the determination on the precision, all extracts from one type of leaching test are analysed by the same laboratory. To estimate the analytical error all elements in the leachates are analysed in duplicate. 4. PRELIMINARY RESULTS

Only preliminary results of the validation of the availability test will be presented here as an example of the procedure. The availability in mg/kg of the selected elements in the six materials (see Table 2) is calculated according to the Dutch standard NEN 7341. An overview of the results of the availability test is given in Table 5. 4.1 Standard deviation of chemical analysis

Because of the boundary conditions stated in section 2, it is expected that the influence of

1

10

100

1000

10000

100000

Concentration level (relative to DTL) Figure 1. Relative standard deviation in the chemical analysis of all measured elements as a function of the concentration level in the leachate.

310

Table 5 . Results ofavailability test (NEN 7341) Sample code Element AVVH

Na Cd

c1

SO,

MCBA

AVSH

Pb Zn F Br Na* As Zn Na Ca Cl cu* Pb*

so,

VACS

F Na Ba cu* Mo

so,

KZFH

V Na As Ni

so4 KBAA

V Se Na* As V

Availability (mg/kg)

Factor relative to DTL

11048 195.2 49742 64671 480 8568 2125 189 38.0 0.17 32.3 1070 27979 817 242 112 6745 63.7 68 I I55 7.5 10.3 8308 10.03 264 1.03 13.13 654 3 30 I .OO 48.2 5.90 11.72

1473 887 6066 2683 91 9520 5320 18 6 34 7 324 3292 79 93 1 24 587 236 206 1938 23 10 504 67 71 313 14 46 13 200 8 983 86

S, (YO)

SR (YO) ,,s,

1.9

2.5

2.7

2.7

7.1 1.3 3.3 2.4 25.7 16.5 4.6 3.6 2.9 4.0 19.7 37.6 1.3 9.7 0.6 10.2 19.3

12.1 3.7 7.4 7.5 41.2 20.0 4.6 8.4 11.1 7.5 26.9 53.8 3.5 10.4 2.4 24.2 27.8

0.7 9.6 5.3 8.4

1.4 9.6 7.5 11.3

2.5 3.3 3.8 14.9 7.8 10.5

6.0 6.3 4.4 15.4 15.3 16.3

(%)

2.0 3.2 1.0 2.4 2.9 2.6 1.4 1.5 5.6 5.1 2.7 1.3 1.7 0.7 0.9 3.4 1.3 3.7 1.0 1.0 1.8 4.8 1.4 1.2 1.6 3.3 13.4 I .4 3.2 3.2 6.6 3.8 2.0

Rejected laboratories 2 1

1

2 1 1

2 2 1 1

1 I 1 1 1 1

I

the error in the chemical analysis on the determination of the test precision is minimised. Figure 1 shows the relative standard deviation as a function of the concentration level for all elements measured. For the largest values the name of the element is also displayed. It appears that at the level of about 10-20 times DTL the relative standard deviation is less than 5%. The precision values in Table 5 (S, and SR) are corrected for the standard deviation in the chemical analysis by applying the formula: Test variance (without analysis variance) = Test variance (overall) -

x

analysis variance

where n = number of leaching tests performed per laboratory The effect of this correction is rather small because of the l l n factor. Only for the elements for which a dash is shown in the S, and SRcolumn, the test variance could not be discriminated from the analysis variance (zero or negative value for corrected test variance).

31 1 Histogram h-values per laboratory (indicationof deviation from total mean)

Hlstogram k-values per laboratory (indication for deviation within laboratories)

I

h-values

R

A

D

Figure 2 . Mandels statistics conform NEN-IS0 5725 4.2 Identification and treatment of outliers

Some of the availability test results are discarded on the basis of the following criteria: - Reported error in operation: e.g. malfunction of pH-controller during leaching test -

Mould formation in extract Identified as an outlier by the Cochran criterion or Grubbs tests (1% level)

To facilitate the determination of outliers two histograms are shown in Figure 2 representing the deviation for each laboratory from the total mean (h-values) and the deviation between the duplicate test for each laboratory (k-values). From the histograms of the h-values, which indicate the deviation for each laboratory from the total mean value represented by h=O, it shows that lower results are obtained for laboratory F, while for laboratory D the results tend to be higher than the mean value. From the histograms of the k-values (indication of the deviation between duplicate measurements for each laboratory) it is clear that for laboratory D a different distribution is found than is to be expected (maximum level at k=O and diminishing for greater k-values). By comparing other information ( e g pH-values) the reason for the differences found for laboratory D is traced back to a badly calibrated pH-meter used for a part of the experiments The corresponding results are rejected in Table 5 . The number of rejected laboratories for the leaching test is mentioned in the last column in Table 5. The results of these laboratories are not included in Table 5 for the specified element and material. In all cases a sufficient number of test results per sample per element (p>8) was preserved. 4.3 Dependency of S, and SRon concentration level and type of material

Before a final result of the precision parameters can be calculated, a possible dependency of the type of material and/or concentration level on the result has to be determined. In Figure 3 the precision is plotted as a function of the concentration level. Figure 3 shows generally higher

312 60 50 --

-

s

40

-

~~

Y

0

0

E

30 - -

4oj

20

Na --

.I I cu

Na

1

AWH MCBA A AVSH x VACS

I

x KZFH 0

CU

TAS '

T

Ba

T

100

10

I

KBAA

1000

10000

Concentration level (relative to DTL) Figure 3. Relation between precision parameters S, and SRand concentration level S, and SK values at low concentration levels. This effect should be eliminated after the correction of the variance of the chemical analysis (see section 4.1) if it is caused by the analysis. To examine this effect further, the same type of graph is shown in Figure 4 for two elements that have been measured in more than one material, Na and Sod. The precision is expressed as a percentage of the availability and also as an absolute value in mg/kg. Plotted this way it, becomes clear that the standard deviation of the r and R values, expressed in mg/kg, apparently 50 SO4

40 h

m

i

Y

g, 30

I

C

e

4

20 a

vi 10

0 1

10 100 1000 10000 Concentration level (relative to DTL)

1

10 100 1000 10000 Concentration level (relative to DTL)

Figure 4. Relation between precision expressed as percentage (left) and as mgkg (right) and the concentration level for Na and SO4.

313 25 1

25

I -g 20

15

cn"

10 5

0 AWH

MCBA AVSH

VACS

KZFH

Materials

KBAA

A W H MCBA AVSH

VACS

KZFH

KBAA

Materials

Figure 5 The precision, S, and SR,as a function of the type of material cannot decrease further with decreasing concentration at low concentration levels, and therefore approaches a constant value. This results in an increase of the precision parameters at low concentrations when expressed as a percentage of the availability. Taking into account the above, Figure 4 also show that for Na and SO., no significant influence exists of the type of material on the precision values. This is further illustrated by Figure 5 , in which the mean values of S, and SR of all elements for each material are shown. The only material for which possibly some higher values are found is KBAA. However, the number of elements (As and V) for this material to support this difference is rather small. 4.4 Mean values of the precision

It can be deduced from the above that the precision can be obtained by calculation of the average of the data in Table 5. Only the data for the elements marked with * are not used in the final calculation of de mean S, en SRfor the following reasons: - Low concentration levels for Na in the samples MCBA en KBAA (6-8 times DTL) - Cu en Pb inhomogeneity in sample AVSH - Low concentration levels of Cu in sample VACS These values correspond with the higher values at a low concentration level shown in Figure 3, except for Cu in AVSH. The resulting mean values for the repeatability S, and the reproducibility SR,corrected for the chemical analysis variances, are respectively: S, = 5.2% S, = 8.6%

5. CONCLUSIONS

The precision of the standard leaching tests can be determined by the method in NEN-IS0 5725. For the availability test (NEN 7341) it was shown that a mean value of the S, and SR parameters can be used, independent of the type of material tested. Also, the influence of the different elements on the precision parameters is rather small when the concentration level is

314 higher than about 20 times the detection limit. Therefore, the reported mean S, and SR values can be regarded valid for all measured elements. It cannot be excluded however, that some other elements have a different precision. The same procedure used for the availability test will also be used for the validation of the other 3 Dutch standard leaching tests. 6. ACKNOWLEDGEMENT This work is hnded by the Netherlands agency for energy and environment (NOVEM) and the Netherlands Ministry of Public Health, Physical Planning and Environment (VROM) 7. REFERENCES 1. NEN 7340. Leaching characteristics ofbuilding and solid waste materials - Leaching tests General Instruction. Draft 1993; Netherlands Normalisation Institute; the Netherlands 2 . NEN 7341. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the availability of inorganic components for leaching. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 3. NEN 7343. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the leaching of inorganic components from granular materials with the column test. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 4. NEN 7345. Leaching characteristics of building and solid waste materials - Leaching tests Determination of the leaching behaviour of inorganic components from building materials, monolithic waste and stabilised waste materials. Draft 1993 (previously draft NVN 5432); Netherlands Normalisation Institute; the Netherlands 5. NEN 7349. Leaching characteristics ofbuilding and solid waste materials - Leaching tests Determination of the leaching of inorganic components from granular materials with the cascade test. Draft 1993 (previously part of NVN 2508); Netherlands Normalisation Institute; the Netherlands 6. NEN-IS0 5725. Accuracy (trueness and precision) of measurements methods and results Part 2: A basic method for the determination of repeatability and reproducibility of a standard measurement method. Draft 1990. 7. A N S . 16.1. Measurements of the leachability of solidified low-level radioactive wastes by a short-term test procedure. American Nuclear Society, Illinois 60525 USA.

Environmental Aspects of Consmetion with Waste Materials 1JJ.M. Goumans, H A . vm der S l w t and 771.G.Aalbers (Editors) @I994 Elsevier Science B. T*: All rights reserved.

315

The Laconia, New Hampshire Bottom Ash Paving Project C. N. Musselman('), M. P.KiUeen('), D. Crimi0, S. H a d 3 ) , X. Zhang"), D. L. Gress"), and T. T. Eighmf3)

(')CMA Engineers, Portsmouth, NH, 03801, USA (*)WheelabratorEnvironmental Systems, Hampton, NH, 03842, USA (3)EnvironmentalResearch Group, University of New Hampshire, Durham, NH, 03824, USA

SUMMARY In May, 1993, a 600 meter section of US Route 3, a two lane secondary highway in Laconia, NH,was reconstructed utilizing screened and aged grate ash as a 50% aggregate substitute in base course asphalt paving. A two year monitoring program is underway to assess potential surface water and groundwater quality impacts and the physical performance of the roadway. This paper reports on bottom ash asphalt mix formulations, asphalt plant operating challenges and air testing results, the apparent effect of excluding siftings on bottom ash total composition, and the effect of ash aging on total availability leaching. The initial results of monolith leaching tests designed to further the understanding of fundamental leaching behavior are also reported.

1.0 INTRODUCTION

In the late 1970's and early 1980's, a number of demonstrations were undertaken in the United States to assess the feasibility of utilizing municipal solid waste combustion bottom ash as an aggregate substitute in asphalt paving applications. While those demonstrations were largely successful from a physical performance standpoint, progress in furthering ash utilization in the United States has been hindered by regulatory uncertainty and, in some cases, local controversy. Research and demonstration efforts are now again proceeding and are focusing mostly on utilization techniques which entail encapsulation of the bottom ash in asphalt paving or concrete construction materials. In May, 1993, a 600 meter section of US Route 3 in the City of Laconia, New Hampshire was reconstructed using, in part, grate ash aggregate in a binder course asphalt pavement(1). US Route 3 in this area is a two lane secondary roadway having an average daily traffic which varies seasonally from about 5,000 to 20,000 vehicles per day. Of the 600 m of reconstruction, 350 m was reconstructed as a control section using natural aggregate both in the 5 cm binder course and the 2.5 cm wearing course. The 260 m test section was constructed using a 50% bottom ash/50% natural aggregate blend in the 5 cm binder course pavement. A 2.5 cm wearing surface of 100% natural aggregate was applied over the bottom ash asphalt binder course such that, in this demonstration, the bottom ash asphalt is not exposed to traffic or the environment.

316

317

A plan view of this section of US Route 3 is presented as Figure 1, showing the test demonstration and control sections(2). The binder course pavement for the first 30 m on either side of the transition point between the two pavements was constructed to a 10 cm depth to allow the installation of strain gauges; moisture, resistance and temperature probes; and traffic counters. The wearing course remained at a 2.5 cm thickness through this 60 m transition section. The land use in the control section is commercial, including a resort/conference center, several smaller motels, a restaurant, and retail businesses. In the test section, abutting properties were largely undeveloped. Paugus Bay, a part of the Lake Winnipesaukee system, is in close proximity to the test section. Over a two year research period, the demonstration roadway, including the control and test sections, are being monitored through comprehensive sampling and analysis of both upgradient and downgradient groundwater monitoring wells on each of the roadway sections. Also indicated on the plan are the locations of surface water monitoring stations, roadway runoff collection manholes, and suction lysimeters which were installed 1.5 to 3 meters beneath the pavement surface. These are also included in the comprehensive sampling program. A cross section of the test section pavement is presented as Figure 2. This figure shows the bottom ash binder course with the natural aggregate wearing course above. Below the bottom ash asphalt is a layer of about 8 cm of recycled asphalt consisting of recompacted "cold planings" from the original asphalt surface. The bottom ash asphalt is thus surrounded by relatively impervious natural aggregate materials above and below. The roadway construction entailed utilization of conventional asphalt paving and compaction equipment and procedures. The bottom ash asphalt compacted well to specified densities with some additional non-vibratory compactive effort, and the pavement has performed well through nine months of use. I , , . ,, . 5 l l O cm binder'bourse (507: Grate Ashy I

//

I

0.6-1 2

m

'u -

I 1.5.3

m

I Fiaure 2

-

Pavement Cross Section

318

The environmental and physical performance monitoring data is in the process of being gathered and evaluated and is intended to be reported in future papers. The following sections provide a description of a variety of environmental and civil engineering topics which may be of interest both to those planning further demonstrations and full scale utilization of bottom ash in asphalt paving and to those involved in research in fundamental leaching behavior of encapsulated materials used in construction.

2. BOlTOM ASH ASPHALT MIX FORMULATION Initial efforts to formulate an effective bottom ash asphalt mix design were based on conventional Marshall mix testing procedures. The top line in the graph in Figure 3 presents the relationship between percent bottom ash and optimum percent asphalt content based on the Marshall test procedures(3). Based on these test results, a mix of bottom ash with 9% asphalt cement was manufactured, and a test patch was paved within the footprint of the lined landfill in Franklin, NH. The resultant mix flowed easily and would probably have exhibited rutting failure. Following the first test patch paving experience, additional laboratory work was undertaken utilizing gyratory test methods (GTM), a process which essentially kneads the sample rather than impacting it as in the Marshall mix test. The resulting mix designs using the GTM test were dramatically different, predicting a 7 percent optimum asphalt cement content for a 50% bottom ash/50% natural aggregate blend. A second test paving was completed successfully with this blend, and the same mix was subsequently used in the reconstruction of US Route 3. I

I

% BOTTOM ASH

Fiaure 3 - Optimum Asphalt Content

319

Figure 3 indicates that the optimum asphalt content is about 5 percent for these aggregates when 100% natural aggregate is utilized, using either the Marshall or GTM methods. The two percent additional asphalt required when utilizing a 50% bottom ash blend represents that portion of the asphalt cement which is absorbed by the bottom ash particles. As indicated in Figure 3, asphalt blends with decreased bottom ash percentages would reasonably be expected to require less additional asphalt cement. The additional asphalt cement required is an economic factor which will need to be considered in full scale applications, to be offset by the savings represented by the use of bottom ash aggregate and the costs of bottom ash storage and handling. The use of additional asphalt cement has an environmental benefit in that there is greater assurance that internal pores and vesicles in the ash aggregate are coated with asphalt.

3. ASPHALT PLANT OPERATING CHALLENGES

Although the roadway construction itself presented no significant challenges, the operation of the asphalt plant did present challenges during the manufacture of bottom ash asphalt. The asphalt plant utilized was equipped with a rotating cylindrical drum dryer for drying the aggregate and an air pollution control system consisting of a fabric filter/baghouse. The plant is normally operated at a rate of about 180,000 k g h . During the manufacture of the grate ash asphalt, the plant throughput rate was decreased to 127,000 kg/hr because of the relatively high moisture content in the ash. This helped to avoid extinguishing the flame of the No. 6 fuel oil fired gun used to dry the aggregate. The aged grate ash, after five months of aging, was determined to have a moisture content of 23 percent while the natural aggregate had a moisture content of two percent. The paving demonstration was completed in early spring when the bottom ash moisture content was near its highest level due to spring snowmelt and rainfall conditions. Using a bottom ash asphalt blend of less than 50%, and/or utilizing bottom ash at a lesser moisture content, would allow the asphalt plant to operate at, or close to, its normal operating capacity. The second operating challenge experienced at the asphalt plant pertained to the generation and transport of fines in the aggregate drum dryer. The fines transport system at this asphalt plant was found to be an operating constraint due to the quantity and light weight of the fines produced during ash aggregate drying in comparison to normal natural aggregate operating experiences. A vacuum truck was required to be connected to the plant’s ductwork to periodically withdraw fines. The mix manufactured for the demonstration had about 6% passing the #200 sieve, which was acceptable for the binder course paving. It should be noted that the additional fines did not result in significant increases in particulate air emissions as described below. The fines generated can be reduced in future work by decreasing the bottom ash percentage to a level which does not create material handling constraints, if required. Stack testing was completed at the asphalt plant during the manufacture of both natural and bottom ash aggregate asphalt. The results are presented in Table 4(4).

320

The length of the sampling runs were limited to the amount of time required to manufacture the needed quantity of ash asphalt, and therefore were shorter than the three 90 minute replications which might otherwise be desired for a full air test. The observed opacity was within specified New Hampshire standards for asphalt plants. Particulate levels were somewhat higher when bottom ash asphalt was being processed, but the particulate concentrations for both bottom ash and natural aggregate were within the New Hampshire asphalt plant standard of 91.8 mg/Rm3. The facility was capable of controlling particulate air emissions despite the build-up of fines on the plant side of the baghouse. Emissions tests for multiple metals showed all metals at low levels regardless of aggregate source. Six metals were slightly higher for the natural aggregate runs (cadmium, lead, arsenic, mercury, chromium, and nickel) and four were slightly higher for the bottom ash aggregate runs (beryllium, copper, selenium, and zinc).

-

Table 1 Asphalt Plant Air Testing Results

Number of Sampling Runs Length of Sampling Runs (Minutes) Opacity (NHStandard:<20%) Particulate Emissions (mg/Rm3) (NHStandard: 91.8 mg/Rm3)

Natural Aggregate Asphalt 2 43, 80 <20% 14.8

Grate AsWAsphalt 2 80, 70 <20% 37.9

4. EFFECT OF SEGREGATION OF SIETINGS ON BOTTOM ASH METALS

CONTENT The pavement demonstration was preceded by a two year research effort which included the development of a significant data base to characterize the variation in bottom ash characteristics over time. Hourly and composite samples were taken during 18 days over an 18 month period(5-10). These samples were of bottom ash, consisting of grate ash and siftings. Economizer ash was excluded during the sampling periods. Both siftings and economizer ash were excluded from the grate ash which was subsequently used for manufacturing bottom ash asphalt in the paving demonstration. Total composition data for these two types of bottom ash for silicon, zinc, lead and calcium are presented in Figures 4 through 7. The first column summarizes data for the 18 months' bottom ash samples, including siftings (18 composite sample data points). The second two columns represent pre-aged grate ash (8 data points) and samples from the grate ash pile after a five month aging period, (14 data points), both excluding siftings. In these figures, the boxes represent the 50% confidence interval; the line in the box represents the median value; the short horizontal lines represent upper and lower 90% confidence intervals; and the circles indicate individual outlier

32 1 Figure 6

Figure 4

Total SUkon Composition for M o m Ash. PnAg.d Orate Ash, Aged Orate Ash

Total Zinc Comporltlonfor BottomAsh, PreAged Orate Ash. Aged Orate Ash

m

3.00 g 2.75 -

i

3*00 2.75

5.00

g5.00 c

r

X

2.50

2.50

2.25

2.25

. B 12.00 I-

1 6.00

6.00

1.75 .

1

2.00

Q

f4.00

4.00

13.00

3.00

!I 1.75

I

I-

2.00

to

7.00 1-1 i;i

5

6.00 5.00

j4.00

5

3.00

;2.00

I-

1.00

7.00

I

1

-

6.00

- 5.00

0

1 .oo

Figure 7

Figure 6

Total Calcium Composltlon for Bottom Ash, PreAgad Grate Aeh, Aged Orate Ash

TOWLeadComposition for Worn Ash, PreAgad Orate Ash, Aged Grate Ash

0 0

2.00

12.001 1 1 .oo 9'1 0.00 9.00 8.00 5 7.00 0 ,# 6.00 5.00 - 0

12.00 - 11.00 - 10.00 - 9.00 - 8.00

i

Q

322

data points beyond the 90% confidence level. For the elements presented herein, all showed consistency between the pre- and post-aged samples, indicating both insignificant change through the aging process and limited variability effected by the sampling techniques utilized. For some elements, notably for silicon and zinc presented in Figures 4 and 5, the data from all three ash sampling groups are consistent. However, the data for lead and calcium showed that the grate ash without siftings may be significantlylower in composition than the bottom ash from the earlier 18 month period, which included siftings. Other research work (11) has shown increased concentrations of lead in siftings relative to grate ash. The decrease in lead content indicated on Figure 6, may be due to the exclusion of siftings. The decrease in calcium content is unexplained, and may indicate a difference in MSW composition between the two sampling periods. Siftings were not sampled and analyzed during the paving demonstration project. Although siftings may be enriched in lead relative to grate ash, based on earlier related research work completed as part of this project (9, it is not expected that inclusion or exclusion of siftings would significantly affect lead leaching from bottom ash asphalt; both are expected to be negligible.

5. EFFECT OF GRATE ASH AGING ON TOTAL AVAILABILITY LEACHING

The grate ash used in the paving demonstration was allowed to age for a period of about five months prior to its use as an asphalt aggregate. Aging of the ash was thought to have benefit due to chemical reactions which may tend to stabilize the residue with regard to potential contaminant release and to allow poorly understood but beneficial strength developing reactions to occur. The likely chemical reactions include elemental metal oxidation and H, evolution from the reduction of water, the oxidation of certain metals to stable cationic forms, the formation of metal hydroxides from exothermic hydrolysis, the formation of metal carbonates, and the absorption of metal cations to anionic surface charges on iron oxide@). Results of total availability leaching tests for silicon, aluminum, lead and chloride for pre-aged and aged grate ash are summarized in Figures 8 through 11. No clear patterns are indicated as to the effect of aging on total availability leaching.

6. LABORATORY MONOLITH LEACH TESTING

Laboratory monolith leach testing is being completed to further the understanding of diffusive leaching mechanisms from monolith specimens. The monolith leach test is used to assess the flux of elements from laboratory compacted or field specimens of solidified bottom ash/aggregate/asphalt material. Using gyratory specimens of the same mix design as that used in the paving demonstration (50% bottom ash, 50% natural aggregate, 7% asphalt cement), a partial 33 f 3 factorial experiment is underway to assess leaching parameters for tortuosity (t), chemical retention (R) and effective diffusion (pDe) as a function of cracking, aging and voids. The test follows the draft Dutch procedure (NVN 7349, using 10 cm diameter

323 Figure 8

Figure 9

Total Availability of Lead for ProAgmlGrate Ash V 8 Aged Grate Ash ( M g )

c

TOWAvaihblllty of Chloride for PreAged Grate Ash v8 Aged Grate A8h ( M g )

1400

1400 1200

3.50

1200

3.50

3.00

3.00

=5

63

1000

t 2.50

800

E 12.00

2.00

600

3 1.50

1.50

400

!1.00

4

L

0

0.50

0

0.00

0.00

Figure 11 Total Availability of Aluminum for PreAged Grate Ash vs Aged Grate Ash ( M e )

600

6?

2.00

! 1.50

1.oo

0.50

Figure 10

f

0

200

Total Avallrbiilly of Silkon for PreAged Orate Ash vs Aged Grate Ash (ma/Kg)

+ 2.00

2.50

1.50

-hf 500

r

500

1 400

400

!300

300

I-

200

I

200

324

by 5 cm cylindrical, monolithic gyratory pucks(l2, 13). The bottom asldaggregate is completely asphalt coated. The monolith leach test is being used to investigate the effects of cracking (none, moderate, high), voids (lo%, 7%%, 5%) and aging (fresh, aged and severely aged). This would mimic a range of pavement conditions from new pavement to pavement at the end of its design life. The different degrees of cracking of the specimens are produced by compaction of the specimen using an Instron testing machine. Voids are controlled by varying the compaction of the job mix in specimen preparation. Aging is produced by high temperature treatment of the bitumen. The factorial experiment has center point replication a t mid-point values (n=3) and single point testing at all low and high values. The multiple mid-point values are obtained by conducting tests on three replicate cut specimens from the center point of the experimental design. To conduct monolith leach tests, two procedures are required. An availability leach test is performed to estimate the maximum potential leachable amount, or fraction, of an element present in the monolith that is not tightly and insolubly bound in the mineral matrices. The monolith leach test itself is performed using a second, similar specimen. The specimen is placed in nylon netting and suspended in a 3L container. The container is filled with 2L (5 times the calculated volume of the specimen) of pH 4 type I1 water. After 0.25,1,2,4,8, 16,32 and 64 days, the specimen is removed and placed in a new container of the same volume of new pH 4 type I1 water. Each of the individual leachate samples was analyzed for a variety of elements and the data were statistically analyzed to assess leaching behavior. The initial results of the laboratory monolith leach testing experiments are presented in Figures 12 through 14. Figure 12 presents the relationship between cracking of the specimen and tortuosity (based on Na diffusion). This plot indicates a direct relationship in that the value of tortuosity consistently decreases with increasing cracking. The value of tortuosity for specimens with a high degree of cracking was one to two orders of magnitude less than the tortuosity of specimens not subjected to cracking. The plots of void content versus tortuosity, and aging versus tortuosity, as presented in Figures 13 and 14, respectively, indicate no direct relationship in either case. The information presented herein is preliminary and will be updated as the full factorial experiment is completed. Additional monolith leach testing will be completed on roadway cores taken from US Route 3 after 1%years of road use. These cores will be taken both from the control and test pavements and from rutted (areas subjected to traffic) and unrutted areas of pavement. Thinly sliced sections of wearing and binder course asphalt and the recycled asphalt (RAP) beneath the pavement will be analyzed to determine if any molecular diffusion is occurring in the field. Monolith leach tests will also be conducted on ash asphalt samples treated with various concentrations of phosphate to evaluate the effect of utilizing WES-PHix, a proprietary waste treatment process, on potential contaminant migration. It should be noted that the monolith data gathered to date has uniformly indicated contaminant release rates at levels similar to those for natural aggregate asphalt. The release rates are extremely low with respect to the total potential flux of contaminants. Although the monolith leach test is most helpful in furthering the understanding of fundamental leaching behavior, it should also be noted that the immersion of the solid samples in water is a more aggressive test of leaching potential

325

100000

100000

2 10000 i?

; 1000

I-

- 10000

- w ,0

8

I

I

100 0

-umtdMondnh

10

I

- 1000 - 100 - 10

100000

z

10000

100000 0

-

0 0

A

p

O

1000 -

s r

100

B 0

0

-

0

-

0 - UmvlMOnolnim 10

I

I

- 10000

I

I

1000

- 100 10

-

Figure 14 Log Scale Plot of Aging vs Tortuosity (Na) for Monolith Leach Test

100000

100000

10000

10000

.? 2, =

8

3 1000

z

100

8

6

0

1000

0

100

I

I

I

Nane

Medium

High

Aging

10

326

than is likely to exist in the field, especially in binder course paving applications, where cracks and other pore spaces are not likely to be saturated.

7. CONCLUSIONS

The work completed to date appears to indicate that the utilization of screened grate ash as a 50% aggregate substitute in asphalt binder course paving is acceptable from a physical pavement construction perspective. Gyratory test methods were found to better predict pavement performance, and at a lower percent asphalt content, than would be indicated by Marshall mix design procedures. The generation of fines and associated materials handling requirements at the asphalt plant should be considered in future demonstration and full scale work. The use of bottom ash at less than a 50% blend may be required due to moisture and materials handling related operational constraints. The exclusion of siftings may have the effect of decreasing lead composition in bottom ash to be processed, stored and utilized. Aging of stockpiled bottom ash for five months appeared to have little or no effect on total availability leaching. Preliminary monolith leaching test results appear to establish a direct relationship between cracking and tortuosity. No such direct relationship appears to date to exist between void content or aging and tortuosity. Additional data on both the environmental and physical performance of the roadway will continue to be gathered and analyzed.

8.

ACKNOWLEDGEMENTS

This project has been supported and funded by the 27 member municipalities of the Concord, New Hampshire Regional Solid WasteBesource Recovery Cooperative; by the City of Laconia, New Hampshire; and by Wheelabrator Environmental Systems, Inc. of Hampton, New Hampshire. Additional support and funding were provided by the US Environmental Protection Agency through Rutgers University and by the US Department of Energy through the National Renewable Energy Laboratory. The research is being completed by the Environmental Research Group at the University of New Hampshire with physical performance testing assistance from the US Army Corps of Engineers, Cold Regions Engineering Laboratory.

9. REFERENCES

1)

CMA Engineers, Inc., August, 1992, "Research and Development, NHDES Approval Application for the New Hampshire Bottom Ash Paving Demonstration, Laconia, NH," Portsmouth, NH.

327

Musselman, C.; Eighmy, T.; Gress, D.; Killeen, M; Presher, J.; Sills, M. (1994), "The New Hampshire Bottom Ash Paving Demonstration, US Route 3, Laconia, New Hampshire," in Proceedings of the American Society of Mechanical Engineers, Solid Waste Processing Division; Boston, MA, pending publication, May, 1994. Zhang, X., August, 1993, "The Utilization of Municipal Solid Waste Incineration Bottom Ash as Paving Materials", Ph.D. Dissertation, University of New Hampshire, Durham, NH. Rojac Environmental Services, Inc., July, 1993, "Research Emissions Test Report, Pike Industries, Inc., Asphalt Batch Plant P-700, Pembroke, New Hampshire", Hartford, CT. Eighmy, T.; Gress, D.; Zhang, X; Tarr, S.; and Whitehead, I., May , 1992, "Interim Report, Bottom Ash Utilization Evaluation for the Concord, New Hampshire Waste-to-Energy Facility", Environmental Research Group, University of New Hampshire, Durham, NH. Gress, D.L., Zhang, X., Tarr, S. Pazienza, I., Eighmy, T. (1992) "Physical and Environmental Properties of Asphalt-Amended Bottom Ash." Trans. Res. Record 1345: 10-18 Gress, D.L., Zhang, X., Tarr, S., Pazienza, I., Eighmy, T.T., 1991 "Municipal Solid Waste Combustion Ash as an Aggregate Substitute in Asphaltic Concrete", p. 161-175. In (J.J.J.R. Goumons, H. A. van der Sloot & Th.G. Aalberts, eds.) Waste Materials in Construction Elsevier, 134510-18. Tarr, S., January, 1993, "The Characterization of Municipal Solid Waste Incinerator Bottom Ash Physical Properties and Use in Emulsified Asphalt Mixtures", Master's Thesis, University of New Hampshire, Durham, NH Whitehead, I., December, 1992, "An Environmental Evaluation of Bottom Ash Substitution in Pavement Materials", Master's Thesis, University of New Hampshire, Durham, NH. Whitehead, I., Eighmy, T.T., Gress, D.L., & Zhang, X., 1993, "An Environmental Evaluation of Bottom Ash Substitution in Pavement Materials", p. 356-370. In Municipal Waste Combustion, Proceedings of the International Specialty Conference, Williamsburg, Virginia, AWMA, Pittsburgh, PA. Sawell, S.E; Chandler, A.J; Rigo, H.G; Hetherington, S.; and Fraser, J. March, 1993, "The Waste Analysis, Sampling, Testing, and Evaluation Program: Effect of Lead and Cadmium Spiking of Municipal Solid Waste on the Characteristics of MSW Incinerator Residues," In Municioal Waste Combustion, Air & Waste Management Association, Pittsburgh, PA.

328

12)

de Groot, G.J. and H.A. van der Sloot (1992) Determination of Leaching Characteristics of Waste Materials Leading to Environmental Product Certification. In Hazardous, Radioactive, and Mixed Wastes, 2nd Volume, pp. 149-170. T.M. Gilliam and C.C. Wiles, eds., ASTM, Philadelphia, PA.

13)

van der Sloot, H.A., 1991, "Systematic Leaching Behaviour of Trace Elements from Construction Materials and Waste Materials" In Waste Materials in Construction,pp. 19-36. J.J.M.M. Goumans, H.A. van der Sloot, Th.G. Aalbers, eds., Elsevier Science Publishing Company, Amsterdam, The Netherlands.

Environmental Aspects of Constmction with Ware Materials J11.M. Goumans, H A . van der SIoot and n.G.Aalbers (Editors) 01994 Elsevier Science B. V. All rights reserved.

329

Application of fly ash and other waste materials for the construction of an off shore island opposite the coast of Tel-Aviv Y. Zimmels,* G . ShelefX and A. Boas**

* **

Department of Civil Engineering, Technion IIT, Haifa 32000, Israel Private Consultant

Abstract The prospects of high volume utilization of fly ash for the construction of a n offshore island opposite the coast of Tel Aviv are considered. Preliminary results of a feasibility study of the project are outlined. This study shows that the construction of a 810,000 m2 surface area artificial island, in the region 1to 2 km off the shore of Tel Aviv, can be one of the largest and most economically feasible national projects. The study indicates a potential high rate of return on investment. This is based on alternative designs and uses of the island . The fill material required for the island exceeds the expected availability of fly ash. This indicates that the ash surplus can turn from a status of waste to that of a commodity. The limited availability of ash facilitates its use as fill layers above sea level where its environmental impact is controllable best.

1. INTRODUCTION

Due to the demographic and geographic situation of Israel and the agglomeration of the population and of the commercial and industrial activities in its coastal Mediterranean strip, the reclamation of land from the sea, in the form of shore extensions andor off-shore artificial islands is only a matter of time. It seems that the trend is to form a vast dense "Megalopolis" extending from Naharia in the North to Ashkalon in the South.

330

Because of already existing development plans and previous rights to the shore line, as well as the prevailing geological and sediment patterns, the potential of shore extensions is rather limited to a few cases. Off-shore artificial islands provide a more realistic answer for the future. The Israeli Mediterranean Coastline has geological and bathimetrical advantages for off shore projects due to the moderate slope of the sea bottom. This is particularly true in a strip extending 2-3km from shore. This strip is known to have a relatively good geomechanical stability. In view of the above considerations, an off shore island opposite the coast of Tel Aviv is now the subject of a feasibility study being carried out jointly by Israeli and Dutch engineers. The study is funded by the S. Neaman Institute for Advanced Studies in Science and Technology a t the Technion, Israel Institute of Technology in Haifa, the Israel Electric Corporation, the Israel Land Authority and the Dutch Ministry for Economic Affairs. A Dutch Advisory Committee was formed t o provide guide lines for the feasibility study (1,2). The Tel Aviv area was chosen as the most promising location for construction of the first island. Tel Aviv is enclosed by fixed boundaries with surrounding satellite cities of the Dan Region and by its shore line in the west. The city developed into a typical self-densifying metropolitan with a n ever increasing quest for land. This resulted in a steep increase in prices of land and only recently a relative small plot off the center of Tel Aviv was allocated t o a developer a t a price of approximately $20 million per hectare ($2 million per dunam). The prime land along the shore line, where and if available, is expected to fetch substantially higher price levels. The shoreline of Tel Aviv is the site of many hotels and other tourist facilities. This shore line is a n asset to the commercial life of the city and hence a twin development of an off-shore island opposite the coast of Tel Aviv and the on-shore area should offer substantial opportunities. The construction of an artificial island about 1 km off shore should be part of a master plan to expand the city limits. The combination of a commercial island opposite the shore of a city which is a center for economic activities has been known to boost its commercial activities. Furthermore such an island can be designed as a separate entity with different building codes. This can evolve into a scheme which is similar to known city centers such as in New York, Tokyo, Hong Kong and Singapore. The construction of an artificial island is a complex engineering and economic enterprise, which calls for an inter-disciplinary effort of different engineering

33 1

disciplines. It requires the implementation of appropriate technologies and environmental safeguards (3). In this paper data about the economical and commercial viability of the island project will be considered first, and then the utilization of fly ash as fill material and its uses for other constructional purposes of the island will be discussed.

2. ECONOMICAL AND COMMERCIAL VIABILITY OF THE ISLAND In order to arrive a t the optional range of costs of reclamation per square meter, various shapes and sizes of the island were considered. In the early stage of the study it was decided that the island should be located a t a distance not closer than 800 meters and preferably not further away than 2000 meters from the shore line, where the depth of the sea is between 9 meters and 20 - 22 meters, respectively. The environmental impact of the island in changing the coastal drift and sedimentation of sand depends on the ratio of the width of the island t o the distance from shore of the section where this width is measured. The smaller this ratio the smaller the environmental impact is expected to be (43). Therefore an island shaped as an inverted trapezoid (i.e. with its smaller base toward the shore) was considered. The environmental impact of the island on the transportation of sand along the coastline has been studied by a morphological computer model. A t this stage of the feasibility study, the work revolved around rectangular islands but preferable shapes are yet to be determined. This will be done as more research is completed. Cost estimation for a fixed 810,000 m2 surface area of the island (which corresponds to 1,000,000 m2 base area a t sea bottom) were obtained for square and rectangular shapes. The cost was also calculated as a function of the distance of the island from the shore line, between 800 and 2000 m. Typical construction costs of the island ranged between $650/m2 to $85O/m2 depending on the size, shape and distance from the shore h e . The economical and commercial viability of the project, was assessed using a preliminary architectural modular design. This modular design can be adopted to different shapes of the island. Some design features of the island are shown in figs. 1 to 4. Fig. 1 shows a cross section in the region of the western sea wall of a caisson retained island.

332

0 0 0 0 0 0 0 0 , 000000001 1-1 0 0 0 0 0 0 0 , L 1 0 000 000 ,

0 0 0 0

0 0 0 0

0000 000 0 0000 0000

0 0 0 0 0 0

9 I

3

333

The caissons are protected against the action of the waves by rubble mound and concrete blocks (6,7). The caisson wall forms the perimeter of the island up to a level of +11 m above sea level. This level is required for protection against the highest waves expected in the region. Fig. 1 shows a design that incorporates underground open spaces in order to reduce the volume of fill material below sea level. This scheme also increases the added value of the land. The use of underground open spaces is expected to decrease the volume of the fill material by about half and concomitantly i t increases the share of fly ash in the total amount of fill required. Fig. 2 shows a conceptual architectural plan of a square island of 810,000 m2 surface area. The architecture of this island involves a terminal and central commercial complex, recreation and tourism buildings, hotels and lodging facilities, apartment towers, commercial and parking facilities, a marina and open spaces. A perspective view of the conceptual square island is shown in fig. 3. The highrise buildings are built on multi-level large complexes that occupy large portions of the island. The access to the terminal is via a bridge and the terminal is connected to the complexes by underground tunnels. Fig. 4 shows a typical section in the island where the layers of fill material between and below the complexes are clearly seen. The fill material below sea level is sand or other appropriate and durable fill. Above this layer a nearly 5m thick layer of fly ash is placed. A drainage blanket separates the sand and fly ash a t sea level. The fly ash is covered with a 0.5 thick layer of soil. The business opportunities of the development of such an island were considered by a team of an architect and town planner, land surveyor, civil engineers, and industrial economic engineers. This team evaluated different proportions for land allocations according to the type of commercial commodity involved. In each iteration, the number and value of housing estates and apartments, hotel, ofice and parking spaces, shopping centers and other commercial facilities were estimated. In compliance with municipal regulations, 34% of the area were allocated t o public buildings, green and open spaces and roads. It was assumed that the remaining 66% of the area which amounts to 533,000 m2 a t ground level could be utilized on the basis of 200% "building percentage", i.e. 1,066,000 m2 of construction floor area. This level of floor area can be achieved by building the multi-level complexes and high-rise buildings of 25-30 storeys on top of them.

334

OFFSHORE ISLAND PRELIMINARY ARCHITECTURAL DESIGN

Fig. 2. A conceptual architectura plan of a square island.

D

TERMINAL k CENTRAL COMPLEX RECREATION & TOURISM MARINA COMMERCIAL k PARKING

G H

APARTMENT TOWER OPEN SPACE

A

B C

BRIDGE

AREA FOR DEVELOPMENT : SIZE O F ISLAND O N SEABED :lo48 DUNAM Fig. 3. A perspective view of the conceptual architecturalplan

of the island

I!

WIDTH OF BUILDING PIT 270111I 540m

80

II

C

E

W AREA

200m I 200-

It

1

I/ II

I

5

II

I

I I

OFF SHORE ISLAND SECTION C - c 1 : 250

Fig. 4. A typical section in the island.

w w

VI

336

The areas below street level, are mostly allocated as parking lots and for their smallest part to shopping centres and other commercial facilities. In this particular design, total saleable property, including areas below street level is about 2,100,000 m2. Based on prices recently obtained for property along the shore of Tel Aviv and for property near the recently constructed marina of Herzlia, about 10 km from Tel Aviv, the total value of all saleable property is estimated at $1,610,780,000 or nearly $2000 per m2 for the total reclaimed area of 810,000 m2. This is up to three times the construction cost. In view of the continuous rise in the cost of apartments in the Tel Aviv area, and the expected boost in the nation's economy if peace prevails, a 20% increase of the total saleable property can be justified. In addition a building percentage of about 200% is relatively low for a project of this kind. A denser building utilization up to 350% should probably be allowed on the island. This can make the project even more attractive by offering a high rate of return on investment.

3. UTILIZATION OF FLYASH

3.1 Introduction When the project was initiated, one of the main concerns was to identify economically feasible sources for fill material. The large volume of fill material required suggests the use of sand. The cost of sand depends on its availability and on the distance of its source from the construction site of the island. Sand dunes exist along the shore in the southern part of Israel but due to their rapid depletion, this source will be hard to come by. Sand is relatively abundant on the north beaches of the Sinai peninsula and the possibility to import i t from there should be explored. Deposits of sand exists in the sea bottom along the Israeli shore line. Sand is continuously drifting from south to north along this shore line. Most of the sand is concentrated in the 3 km strip which is bordered on the east by the shore line. The sand content and its particle size decrease with distance from the shore line. Dredging of sand in a manner that would be environmentally acceptable can provide the necessary fill material for the island. The currently available dredging technology and equipment is capable of operating at water depth of over 30 m. Since the slope of the ses bottom in the

337

southern part of Israel is 1%and less, dredging operation can be readily done across the full 3 km strip that runs parallel to the shore line. Nevertheless any dredging operation must be subject to approvals of local and national authorities. Such approvals depend on an appropriate plan that will minimize potential damage to the environment. This potential risk to the environment depends on the amount of dredged sand. Therefore it is desirable to use other alternative fill materials. The use of fly ash as fill material for the construction of the island was considered as a technically and economically viable option. This potential high volume utilization of fly ash promotes the policy of turning a refbe material into a commodity. This statement is commensurate with the expected shortage of fly ash in view of the expected high demand for fill material. The Israel Electric Corporation will be faced in the coming years with increasing quantities of fly ash which cannot be absorbed by the cement and building industries. Therefore high volume utilization of the ash in the island can be a preferred solution to the disposal problems of the fly ash. In this context one of the guidelines of the island project was to incorporate as much waste material as possible within the framework of technical and environmental feasibility.

3.2 Availability of fly ash A large part of the fly ash generated by the coal fired power stations of the Israel Electric Corporation Ltd. is currently utilized in the cement industry. The quantities of fly ash which are not absorbed by this industry at the moment and probably will not be utilized for any practical purpose in the near future, were estimated for the next decade. For this forecast, the coal fired power units in operation a t the beginning of 1994,those under construction, and those in the design stage were taken into account. The forecast is based on the following data: Atqthe lvl near Hadera, 4 production units of 350 MW generate annually about 350,000ton fly ash and 40,000 ton bottom ash. At the erg Power Station near Ashkelon, 2 production units of 550 MW generate annually about 270,000 ton fly ash and 30,000 ton bottom ash. In 1996, the completion of 2 additional 550 MW units at the Maor David Power Station will add about 270,000ton fly ash and 30,000 ton bottom ash annually. A t the turn of the century the completion of 2 additional 550 MW units at the Rutenberg Power Station, will contribute to the total ash output about 270,000ton fly ash and 30,000 ton bottom ash annually. Approximately in the year 2005 two

338

additional units will come on stream a t a site yet to be designated, probably a t the Haifa Power Station. From 1994 about 425,000 ton fly ash is expected to be utilized in the cement industry and from mid 1995 about 150,000 ton per annum of fly ash is designated to be processed into Aardelite light weight gravel in a future plant a t Modiim. From mid 1994 about 50,000 ton may be exported. I t is expected that total utilization will increase from 620,000 ton in the year 1995 to about 800,000 ton in the year 2005. The estimated tonnage to be utilized and the estimated surplus tonnage is summarized in table 1and shown in Fig. 5. The bottom ash is not included in the table. It was assumed that nearly all the bottom ash will be used as a building material, replacing either sand in the block industry or after the ash has been graded and its larger particles have been crushed, it may be used in road works. Table 1and Fig. 5 show a trend of increasing production, utilization as well as ash surplus which totals 3,260,000 ton in the 10 years period of the forecast. Note that if one of the ash consuming projects will not materialize or for some reason its demand by the current consumers will decrease the surplus figure can be significantly higher. Table 1. Production and Utilization Forecast of Fly Ash Year 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Production ton

Utilization ton

Surplus ton

620,000 740,000 890,000 890,000 890,000 1,010,000 1,160,000 1,160,000 1,160,000 1,160,000 1,280,000

600,000 620,000 640,000 660,000 680,000 700,000 720,000 740,000 760,000 780,000 800,0,00

20,000 120,000 250,000 230,000 210,000 310,000 440,000 420,000 400,000 380,000 480,000

10,960,000

7,700,000

3,260,000

339

3.3 Quantities of fill required and the application of fly ash The fill required for the conceptual island, 810,000 m2 surface area, a t a location between 800 and 1800 meters from the shore, where the depth of the sea is between 8 and 20 meters, was estimated to be in the range of 12,000,000 m3 to 15,000,000 m3. Therefore, the total surplus fly ash forecasted in the next decade amounts only to 22%-27% of the total fill required. This indicates that the island project can provide a good solution for any surplus fly ash that may be available from the power plants. Because of this limited availability of the fly ash, i t can be applied in preferential sites where the potential environmental impact of this material will be controllable and minimized. Consequently, the fly ash is to be placed above sea level in accessible layers. Consolidating the fly ash above sea level will not pose any technical and maintenance problems. The embankments constructed around the Hadera Power Station and those now being constructed near the Hadera River, set a good example to the potential use of the fly ash in the island. Previous investigations showed that fly ash can be placed and consolidated without causing any problem also under water. This applies in confined spaces, irrespective of their being in an off-shore island or in a shore extension. Thus, the use of fly ash is not expected to have any harmful effect on the marine environment. Typical related examples can be found in Denmark and in Scotland.

3.4 Method of application of the fly ash (8,9) As shown in fig. 6, the fly ash is to be placed in compacted layers in the spaces between the building pits on top of a drainage blanket. This blanket consists of two layers of granular material, which are separated by a plastic foil. The drainage blanket is located about 0.50 meter above sea level. The purpose of the upper drainage layer is to remove all surplus water, which may percolate through the fly ash. The extent of such percolation through the fly ash is expected to be minimal. The compaction of the fly ash is expected to decrease its permeability t o the range of 3 - 5 x 10-5cdsec. The lower drainage layer will absorb and remove water which may rise through the capillary action from the submerged layers of sand. A t 5-6 meters above sea level, the fly ash fill is topped off by a layer of fertile soil, grassed or planted with trees. The upper surface of the soil layer will have a dip towards a surface water drainage system. This surface water drainage

340

system consists of side drains and a grid of collector drains. The collector drains are not required in those places where the top of the fill is covered by asphalt. The drainage system is designed to take care of all run off water, so that the quantity of water left to percolate through the fill, will be minimal. Should this small quantity reach the surrounding sea, its virtually infinite dilution in the sea will prevent any significant ecological impact. Previous research showed that the concentrations of trace metals in typical fly ash leachate obtained from deionized and tap water are generally smaller than the concentrations of the same trace metals in the surrounding sea. For the purpose of calculating and designing the drainage system of a n off shore island only rain water is deemed relevant. No allowance is considered to be necessary for floods, or storm water from outside sources. Since there will be no sweet water aquifers below the island, pollution of such aquifers is irrelevant.

UTILIZATION of FLY ASH ISRAEL ELECTRIC CORPORATION A

I

1400 1200

r a

u)

1000

>

G'C

2

-

600

0 0

400

DUCED D

200

I

n " I

1995 '1996 '1997 '1990 '1999 '2000 '2001 '2002 r2003 r2W4 r200S

YEAR

Fig. 5. Forecast of production, utilization and surplus of fly ash in the forthcomingdecade.

34 1

The amount of fly ash which can be applied in the upper layers of a 810,000 m2 off-shore island was estimated to be in the range of 2,150,000 ton. This quantity is to be placed during the last phase of the actual construction period of about 5 years, out of a total 10 years period that includes the design and preparatory stages. Storage of approximately 1,000,000 ton, during 3-4years a t a suitable and environmentally acceptable site, will therefore be required. The site should preferably be located adjacent to, or within the work area on shore, which will be designated for the construction operations. As hydraulic conveyance will not be economical for the quantities involved, the fly ash will be transported by large dump trucks which will carry it from the depot over the bridge to the island. Consolidation of the fly ash will be done by normal road construction equipment. 3.5 Fly ash aggregates The products of a factory processing about 150,000 tons of fly ash annually into 185,000 tons of light weight aggregates, can be used for the construction of the high-rise buildings on the island. The use of light weight aggregates will decrease the load on the foundations of the buildings as well as the required quantities of reinforced steel and iron beams. Production of aggregates has to start already in the preparatory stage of construction, so that during the actual construction operations sufficient supply of material will be available.

3.6 Depot for fly ash storage and extension of island in the future After the completion of the island, preparatory steps toward its extension can be made. These steps involve the enclosure of an area adjacent to the island for storage of fly ash. The fly ash will be dumped and consolidated in this area and for most of this operation, no effect will be noticed a t the sea level. Such storage area can for example accommodate an additional 2,000,000 tons of fly ash which will be produced as a surplus over a number of years. This area can be developed according to the needs of the island and its future can be decided a t a later stage.

342 I I I

NO OVERFLOW

l l l

l l l

IRAIN 1I

1l

1l

I

!

!

FERTILE SOIL GRASSED OR PLANTED

BUILDING MODULE

SEA LEVEL 0.00

z

Fig. 6. Details of drainage systems.

343

This fly ash storage depot will have some similarity to the shore extension Slufter project near Rotterdam. In this project a large amount of polluted silt, dredged from the bottom of the Rotterdam harbour and its access waterways, is disposed off.

4. OTHER WASTE MATERIALS Building refuse is another waste material that has a potential use in the project. However this type of waste must be carefully selected and processed before use. Furthermore the inclusion of hazardous materials that may pollute the fill or soil must be absolutely prevented. This calls for a careful consideration on the option and feasibility of using such wastes. 5.

CONCLUSIONS

1. The preliminary engineering economic evaluation of the feasibility of construction of an artificial island, opposite the coast of Tel Aviv, suggest that this project can be one of the largest and most profitable enterprises in the future development of Israel. 2. The construction of the proposed island requires adequate sources for fill material. These sources can be sand dredged from the sea bottom, sand from beach and inland sources and solid wastes such as fly ash. 3. In the next decade the forecasted surplus in fly ash production by power stations in Israel and which can be used a s fill material in the island, is estimated a t 3,260,000 ton. This amount covers only 22 to 27% of the expected demand for fill material. 4. Because of the limited availability of fly ash, it is to be applied as fill layers above sea level where its potential environmental impact is controllable. 5. The utilization of fly ash is combined with appropriate drainage systems. This system is designed to minimize penetration of rain fall into the compacted fly ash layers. Because of the low permeability of these fly ash layers, the rate of leachate formation and its release is expected to be negligible. 6. Future extension of the island can be done in conjunction with the development of a storage depot adjacent to the island. This storage basin can be used to accommodate, mostly undersea level, the surplus of fly ash after the island has been completed.

344

REFERENCES 1. Zimmels, Y.,Shelef, G. and Boas, A. "Utilization of fly ash for land reclamation from the sea and offshore islands", presented a t the Coal Ash Conference, Orlando, Florida (1990), paper 66-1-15. 2. Zimmels, Y.,Shelef, G. and Boas, A. "Application of fly ash for the construction of an off shore island in Israel", presented a t the Coal Ash Conference, Orlando, Florida (19931,paper 27-1-16. 3. Raviv, R. "Movement of sand along the Israeli coast" (1973). 4. Waterman, R.E. "Towards integrated coastal policy via building with nature" (1991). 5. Nir, Y. "Offshore artificial structures and their influences on the Israel and Sinai Mediterranean beaches" (1982). 6. Frankel, E.G."Artifical island port technology development", Massachusetts Institute of Technology (1980). 7. "The history of Caisson construction", Hollandsche Bouwgroep (1977). 8. Boas, A. Coastal development project. Feasibility study on behalf of the Israeli Ministry of Energy and Infrastructure (1984). 9. Boas, A. "Ash disposal schemes in operation in Europe and the USA.Paper presented a t coal Technology Europe, Copenhagen, Denmark (1982).

ACKNOWLEDGEMENTS The authors are indebted to Mr. A. Lavie of the IEC for his promotion of this work and to Architect M. Wertheim for his part in the architectural design.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) 81994 Elsevier Science B.V. AN rights reserved.

345

Fly Ash Utilisation in Civil Engineering J G Cabrera and G R Woolley

Civil Engineering Materials Ihit, Department of Civil Engineering, University of Leeds, England

Abstract Fly ash production in the UK amounts to approximately 10 x lo6 tons per year. The major part of this material is deposited in lagoons or is placed on disposal sites. The new EEC directives regarding disposal of industrial wastes requires that materials like fly ash should be disposed of either encased or on sites where there are provisions for controlling the release of trace harmful chemical elements which could contamimte phreatic and run-off waters and could eventually contaminate agricultural products. For this reason, it is necessary to study means of intensifying the use of this material, o r at least to develop economic methods for safe disposal. Fly ash is currently used as a pozzolan to substitute part of the cement in concrete, it has been used in embankments for motorways and in minor applications, for example as a filler for plastics. It is also used for the production of light weight aggregate. Large volume utilisation is not made in the UK since the use for embankment constructim may potentially be the source of environmental Contamination via leached trace elements. In this paper we discuss the potential large volume utilisation of fly ash and give data on the properties of high volume fly ash concrete for dams and pavements; hot rolled asphalt using fly ash as a fffler and high volume fly ash concrete for coastal protection; fly ashbentonite and fly ash-colliery spoil liners for waste disposal sites.

1.

INTRODUCTION

The fine particulate materials recovered by electrostatic or mechanical means from the t h e gases of coal burning furnaces has traditionally been disposed of in ground lagoons or deposited above ground (see Figure I). The lagoons. generally the result of mineral extraction, are often water-filled and when subsequently fffled with fly ash the water level rises within deposited material to that of the surrounding natural ground, suggesting interaction with natural ground water. When fly ash is placed above ground, natural run-off during the tipping phase, water percolation through the material and fluctuations of the phreatic levels within the material may cause contamination of natural ground water. New EEC directives for controlling the disposal of materials like fly ash in these traditional ways are resulting in demands for more effective encasement of the materials and provision for the control of leaching of trace chemical elements to reduce the possibility of contamination with ground and surface water sources.

346

Figure I. Fly ash generation at a typical thermal power station. An ideal way to reduce the environmental problems which promoted the introduction of new EEC directives is to ensure, as far as practically possible, that all fly aqh is encased. Ideally the most efficient way of disposing of fly ash is to use it as a constituent of a composite material where the aqh reacts chemically with other constituents of the composite and binds any trace elements which could be harmful. It is clearly not practical to expect all of the collected tly ash to be contained in this controlled way and there is room for the argument thst the material is made safe for economical disposal. Ln this paper we will introduce and discuss five possible ways of including more fly ash in the construction industry. Each in its own way contributing through the product to greater environmental protection and enhancement.

2. HISTORICAL

2.1

Fly ash in Concrete:

The typical range of composition of a low calcium fly ash (class F) obtained from modern coal burning furnaces is given in Table I. Early furnaces, coal milling plants and extraction methods gave a coarser, more variable aqh with significantly higher loss on ignition in the form of unburnt carbon as shown in Table 1. These early ashes were found to have pozzolanic properties and were used to replace a small proportion of cement in concrete placed in massive dam structures in order to reduce heat generated by the hydration of cement in concrete (I). In 1937 (2) it w a reported that fly ash had been used in the construction of the Hungry Horse dam in the United States of America where 20% of cement by volume had been replaced. Research into the properties of fly ash in the UK during the late 1940's and 1950's led to the use of the material in a number of dam structures, as in the USA replacing a proportion of cement with fly ash by volume. The replacement by volume method extended into a small amount of structural work at the Newman Spinney and High Mamham power station sites where 20% by volume of cement was replaced (3).

347

Introduction of batching by weight provided the threshold to an increase, albeit small, in the amount of tly ash replacement thought to be technically possible. Indifference by the Generators and co-ordinated resistance by the powerful cement lobby largely prevailed until the energy crisis of 1973 whereupon interest became focused on the conservation of fuel. More economic realism induced a renewed interest in the use of fly ash, it being recognised that significant savings were possible through the introduction of the material to replace cement. Contemporary research and the analysis of structures built with fly ash concrete in the 1950's combined to demonstrate that hardened concrete which included fly ash showed excellent strength and durability properties hitherto thought only to exist with a l l cement concrete, often with high cement contents. Extending this research with particular attention to the reduction of heat of hydration coupled with a demand for greater durability has led to the expectation that proportions of up to 50% by weight of cement may be replaced in structural concrete with higher replacement levels in the larger sections of structures. Perhaps more pertinent is the understanding that only a modest amount of cement is truly required to stabilise fly ash into a hardened mass capable of containing trace elements against decay (4).

2.2

Fly ash in Fill

The lower density of fly ash compared to natural materials identifies it as a suitable product with which to form load bearing structures on poor ground. Three types of ash have been used for fill purposes namely: I . Conditioned ash, material taken directly from the plant to which water has been added to m i s t with delivery and subsequent compaction on site.

2. Lagoon a s h , material which has been hydraulically placed in lagoons where it has been allowed to settle and drain. Re-excavation recovers this drained material for use on site. 3 . Stockpiled ash, previously conditioned ash which has been placed in a stockpile and has to be recovered for use elsewhere.

348 Fly ash has lower density than granular materials and clays resulting in lower tonnages and lower haulage requirements. Figure 2 gives a comparative example of the density of clay said and fly ash.

Fly ash (1)

Fly arh (3)

Moisture content

(X)

Figure 2. Compaction curves for clay, sand and lagooned fly aqhes. The shear strength of well compacted fly ash is adequate for structural fill.*, and embankments. Values of effective cohesion vary from 0 to 55 kN/m2 and the effective angle Of shearing resistance varies from 30" to 40". These values are affected by the degree of compaction and the age at which the tests are carried out. Coefficient of consolidation values range from 20 to 60 m2/year, therefore settlement% within saturated fly ash occur rapidly and do not present long term problems. Age hardening can reduce the compression index of fly ash from 0.3 for fresh ash, to 0.03 after curing for 4 months (6). Compacted fly ash is significantly less compressive than dense sand, therefore construction of fills and embankments does not exhibit secondary consolidation or structural weakness.

1.25

Permeability ( X

m/s)

Figure 3. The effect of dry density on the permeability of fly ash.

349 The permeability of fly ash depends on its dry density (Figure 3). Values of the coefficient of permeability vary from d s e c . These values place fly ash in the classification of to low to very low permeability (7). Thus, water movement and leaching of ions is very small, nevertheless, there is need to provide cut off systems to avoid potential contamination of ground water by the small proportion of soluble material which tly ash contains, mainly the trace elements found in fly ash which are shown in Table 2.

2.3

Other uses of fly ash

2.3. I Grouting: Mixtures of varying proportions of cement and fly ash are used in the provision of grout to inject fissures, fill voids and cavities to improve structural capacity. The process may also be used to close internal rubble filling in masonry structures and to grout the overbreak behind tunnel linings. Fly ash-lime mixtures are used for the same application described for cement fly ash mixes. Fly ash-cement or fly-ash lime tend to bleed. In these cases small amounts of clay, usually Kaolinite or sodium bentonite, are added to the mix to improve its stability and viscosity (9). 2.3.2 Building blocks and bricks: As partial replacement for cement, and to replace tine aggregate, tly ash is used in the manufacture of concrete building blocks. It is a major constituent in the manufacture of lightweight building blocks for use internally in domestic structures. Mixtures of clay and fly ash are also used to fabricate structural bricks (10). Approximately 20% of ash produced by a modem furnace is a coarser ash than fly ash and is removed from the bottom of the furnace. Typically it is of similar chemical composition to fly ash. This bottom ash is much in demand for the manufacture of lightweight building blocks and may be combined with a proportion of fly ash and cement to provide a stabilised road base or areas of hard standing. 2.3.3 Aggregates: There are processes for the manufacture of lightweight aggregate from fly ash, a composition used in the production of lightweight building blocks and for the making of lightweight concrete (1 I). 2.3.4 Fillers: Between I % and 2% by weight of fly ash consists of hollow spherical particles, known as cenospheres, with a specific gravity less than unity. This inherently lightweight material is used in the production of plastics, paints, vanishes and refractory applications which make use of its insulating properties (12, 13).

350 3.

RECENT DEVELOPMENTS

3.1

Fly ash-bentonite containment walls

Diaphragm containment walls using mixtures of bentonite, cement and fly ash are used to isolate areas polluted by leachates and landfill gas. This mixtures normally has the consistency of a slurry and can be pumped easily. It has been shown that this s!uny can withstand attack m/s. from pollutants and be self-hardening. Its insitu permeability is not greater than 1 x The compressive strength of this materials is not greater than 1.5 MPa at 2X days and is able to stand a strain (if 5% without failure by cracking. During excavation the slurry has sufficient density and caking ability to provide stability to the trench walls. Field trials indicate that the material hardens to the consistency of clay hi about 12 hours and that strength gain md consequent reduction in permeability continues for about 90 days. The use of tly ash in the mix enables the material to meet the required permeability without exceeding the low compressive strength and stiain capacity required to avoid cracking. The rheological improvemena that fly ash addition gives to a bentonite mix are very noticeable. An example of a slurry trench leachate barrier is given in Figure 4 (14). Ground level

I

I

Low perrnoabllity d r d o

Figure 4. An example of slurry trench leachate barrier.

3.2

Colliery spoil and fly ash as landfill liners

The University of Leeds (15) has carried out comprehensive investigations into the use of unburnt colliery spoil as an alternative material for landfill liners. The Liquid permeability of colliery spoil is on average greater than 10-9 d s e c and therefore fails the maximum specified by current UK specifications. Mixtures of colliery spoil and fly ash have shown potential for use as landfill liners. Fly ash improves the compaction characteristics of colliery spoil and the composite mix exhibits lower permeability. It also shows good short term attenuation potential. Mixtures of fly ash and small amounts of bentonite exhibit desirable characteristics landfill liners.

35 1

1.30 0 h

E

2 I

1.25

v

-

z r

a

1.20

-

1.15

-

C

4

t. 0 100% FA

I 22

24

26

so

28

Moisture content

1

32

(X)

Figure 5. Variations of density and moisture content with the addition of bentonite to fly ash. Figure 5 chows the changes of dry density caused by the addition of bentonite to fly ash. The density increases and the optimum moisture content decreases with the addition of 10% to 15% of bentonite, but most importantly, the permeability of fly ash which ranges from 5 x to 1.5 x lo-’ d s e c is improved to specified values with the addition of 10% to 15% bentonite. This increase depends on the fly ash used as it is shown in Figure 6. The major attraction of using blends of tly ash and bentonite is that the uniformity of the material can be easily controlled and the construction procedure, i.e. mixing handling and compacting is easy and does not require special measures or special equipment. Furthermore, the attenuation potential is adequate in the long term (16).

Bentonite

(X)

Figure 6. The effect of bentonite on the permeability of various fly ashes.

3.3

High Volume Fly Ash Concrete for Dams and Pavements

Development of the concept of roller-compacted concrete for dam construction raised the proportion of fly a s h replacement of cement in this material to as high as 80% by volume (70% by weight). Fundmientally different to place. roller-compacted concrete has been used

352 successfully world-wide. There are however, some restrictions to the use of this technique in respect of transportation and the placing/compaction process. To offer similar high proportions ot fly ash in concrete for conventional placing mix designs have been developed. In a joint project the Universities of Leeds (United Kingdom) and Cantabria (Spain) have investigated the use of high volume tly ash concrete and, following successful apprhisal demonstrated the successful use of this material in a series of gravity dams built in Spain (17, IX, 19 and 20).

Compressive strength (MPo)

Figure 7. Relation between porosity and compressive strength for mortars made with various proportions of fly ash (from 0% to 70% by weight of cement). The major advantage of high volume fly ash is its low porosity and low long term permeability. Figure 7 shows a typical example of the effect of fly ash on the porosity compressive strength relationship. This figure shows clearly that for the same compressive strength increased quantities of fly ash decrease the porosity of the concrete substantially.

0

Figure 8. The effect of fly ash on the permeability of mortars.

353 Figure X shows the relation between oxygen permeability and age of concrete. Although the mix containing 70% fly ash by weight exhibits 6 times more permeability than an ordinary portland cement mix at the age of 3 days. at 90 days the 79% fly ash mix has a permeability i 0 times less than the ordinary portland cement mix.Another very noticeable advantage of high volume fly ash concrete is its ability to resist chloride penetration. Measurements which are typical of the values obtained when using the induced electrical gradient chloride test (21) a1.e shown in Table I , these values were obtained from measurements of cores obtained from thr first dam constructed in Bayona, Spain using the design developed by the Universities of Cantabria and Leeds (19). The results of Table 3 show clearly that high volume tly a%h concrete shows far better chloride resistance than ordinary portland cement concrete. Another interesting property of high volume fly ash concrete is its relatively high strain capacity which is a desirable property when used in road and airf7eld pavements. Although the early strength is low, this can be improved substantially by the use of superplasticisers which on the whole allow placement by conventional methods and reduce the high early porosity of the material substantially.

Core No.

Chloride Permeability (Coulomb)

70% Fly Ash Concrete

3.4

2 3 4 5 6 7 X Average Standard Deviation

695 760 590 710 685 724 590 673 59

Portland Cement Concrete Average Standard Deviation

2500 767

Low Energy Hot Rolled Asphalt

The influence of fly ash on the workability of hot rolled asphalt has been evaluated in the laboratory. A design and development study was made to establish the energy benefit$ resulting from the substitution of conventional fillers with fly ash in bituminous mixtures. An assessment was undertaken to determine the influence of fly ash on the workability of hot rolled asphalt and to quantify possible energy savings by its use as a filler in the asphalt composite. Initially there was a laboratory evaluation of eight conventional hot rolled asphalts made with aggregate/sand/filler combinations currently used in practice in the North of England and Scotland (22). using the Leeds Design Method, mixes were designed using fly ash as the til!er. This design method lays particular emphasis on the effect that fly ash has on the workability of hot rolled asphalt. Workability is measured in a way developed by Cabrera using a Gyratory Compactor (23). Successful completion of the laboratory stage confirmed the original development. The second stage, a field trial was then planned and undertaken. Construction of a trial pavement using one (if the mixes designed during the laboratory study

354 was completed. Asphalt was produced in a conventional asphalt plant at four different temperatures ranging from 110 "C to 140°C. The material was laid at placement temperatures ranging from X S O C to 125°C. During placement, air, bituminous mix and suiface rolling temperatures were recorded together with wind speed measurements to determine wind chill factor. Monitoring was carried out to assess performance and durcbility of the hot rolled asphalt. Periodic tests include examination of core samples for density, porosity, strength and measurement of surface deformation. The project was successful and after 3 years of monitoring and inspection it was handed to Cltveland County Council for continuing control and performance assessment. The trial section was laid on a trunk road in the County of Cleveland, England. Energy saving resulting from the decrellse in temperature of mixing, laying and compaction is of the order of 14%. This does not take into account indirect savings from the rejection of material which hlis cooled down and does not include the saving due to better performance of a properly placed and compacted material. The annual tonnage of laid bituminous mixes in the UK is 2X million tonnes and therefore, the net and indirect savings of energy are considerable.

4.

POTENTIAL FOR DEVELOPMENT

4.1

High Volume Fly Ash for Coastal Protection

Protection against coastal erosion and tlooding is a world-wide problem for maritime states. Traditionally reinforced concrete structures with sheet piles, timber piles and groynes of o m e t i e s in combination have been used. Reinforcement to rising ground un shore with selected natural rock or complex shapes produced from concrete is also commonplace. An alternative to these so called hard reinforcements, more recently promoted, is the formation of off-shore islands. These artificial structures are generally constructed with natural stone, but islands of old vehicle tyres have also been tried. Placed off-shore at locations designed to intercept the natural tide surge, the islands are completely submerged and may be upto one kilometre in length with height and width determined by coastal protile and construction material. Clearly the quantities of cc~nsuuctionmaterial required are massive. This h a s promoted the idea that waste materials should be considered for their constructioii. Work is in progress on the design of a family of large irregular shaped boulders manufactured from a basic 90/95% fly ash in combination with cement, lime and admixtures (24). The boulders are to be formed within a constraining inert fabric during the manufacturing process, the fabric to remain on completion. A novel but simple production process is planned which will allow a continuity of manufacture commensurate with provision of constituent materials, adequate hardening of lifting for transportation. The majority of electricity generating stations are positioned on main rivers with water access to the sea. Transportation to site by bottom opening ship/barge will secure the least expensive mode of carriage and allow placing off-shore with minimal interruption. The family of boulders will vary in mass from I through 50 cum., the optimum physical shape determined by transport and manufacturing plant provision. Density of the material will approximate to 1750 kg/m3, low when compared to natural materials but, the irregular design of boulders, family of shapes and mass of completed structure should combine to firm a stable and viable off-shore structure. Bound in combination with cement any concern for the loss of trace elements from the fly ash should be unwarranted and the inclusions of original fabric envelope will prevent early surface erosion. Polypropylene fibres are an option if found to be necessary to improve mechanical strength. With time, this dense. homogeneous ma hould continue to develop further strength.

355 Successful trials with formation of an artificial reef with blocks of flue gas desulphurisation gypsum, fly a s h and cement are on-going. The trial in Poole Bay, Dorset, UK has shown that the blocks have good durability and impoitantly are being coionised by ciustaceans and other species. This suggests the environmentally friendly nature of the trial and bodes will for the major proposal outline above. In every aspect the manufacture of off-shore boulders outlined suggests a major contribution to the use of waste materials in coiistruction.

5.

CONCLUSION

There is a plethora of data on the performance of cmcrete where tly ash has been included as part of the cementitious content. Similarly records exist of fly ash use as a part replacement of sand in concrete mixes, in particular where the normal sand fraction is coarse or gap graded. Through this experience and evaluation of service life fly ash concrete has been shown to have high qualities of durability especially when placed in hostile chloride and sulphate environments. The use of fly ash to replace a proportion of sand has effectively increased the proportion of fly ash available as cementitious content and in this way observers have been able to note and record the advantageous effect produced particularly in reducing water content and giving durable concrete in the long term. Using this advantage mix designs have evolved which utilise and extend the increased volume of fly ash in mixes wherein dense packing and low porosity are specific features. In combination with cement and bentonite, fly ash has been shown to he an effective extender for sluiry support walls. Utilising the early age aspects of tly ash behaviour ui combination with cement, the slurry design development proved effective in supporting the ground during excavation and insitu provided an homogeneous mixture with low permeability and acceptable strain features. Landfdl liners made of fly ash-bentonite mixtures show much potential due to their permeability characteristics, ease of placement and uniformity of the mix. Fly ash in combination with colliery spoil offers the possibility c:f producing an acceptable waste disposal tip liner at an extremely attractive cost. Given that ccilliery spoil is perhaps the most prolific of all mineral wastes and the present dumping in spoil heaps so commonplace. successful development using a cornbination of both materials will he extremely attractive. As a replacement for filler in the formulation of hot rolled asphalt tly ash had produced a material which adequately met the specification demands and did so with an energy saving approximately to 149. Successful development of a high fly ash family of boulders for use in off-shore sea defences will open up a valuable opportunity for large scale use of the material. In combination with a simple manufacturing process and the cheapest form of transport there is real promise for high volume use of fly ash world-wide. Stabilised within a "containment" to reduce the possibility of early erosion and any loss of surface trace element$, environmental acceptance by marine creatures and fauna is favourable.

Acknowledgement Professor Cabrera, holder of the Chair of Civil Engineering Materials at the University ot Leeds gratefully acknowledges the support given by National Power plc.

356

4.

1. 2. 3. 4.

5. 6. 7. X. 9.

I0 I I. 12. 13. 14. 15. 16.

17. 18. 19.

20. 21.

22. 23. 24.

REFERENCES Cabrera J G and Woolley G R. Proc. ICE, Part 2, 79( 19x5) 149-165. Davis R E. ICI Mag. Proc, 33, No.5 (1937) 577-612. Howell L H. CEGB (19%) I No. 36 and 11,37. Electric Power Research Institute of Canada. Research Project TR- 103 I5 I , ( 1993). RP 3 176-00. Cabrera J G, Braim M and Rawcliffe J. Proc. Ash Tech X4 (19x4). 529-533. Brackley I J A and Smith E. Proc 8th Int Ash Utilisation Symposium 1 (1987). Waslinstum, USA. Head K H. Manual of Soil Lab. Testing 2 (1982) Pentech Press, London. Lumb P. Geotechnique (1965) London. Bradbury H W. Proc. Ash Tech X4 (19X4), 513-517. Anderson M and Jackson G. Journal of British Ceramic Society X2, No.2 (19x3). Bijen J. 1st Int. Conf on the Use of Fly Ash, Silica Fume, Slag and other Mineral By-products (19x3) Canada. Kaas R L Plast. Des. Process. 18, No. 1 1 (1978) 49-53. Forestal T A and Moon E L. 34th Ann. Tech. Conf. Reinforcement PlasVComp. Inst. SPI (1979) Section 19-A, 1-3. National Ash. Case Study 5. National Power (1990). Cousens T W and Studds P G. Final Report for the Department of the Environment Contract No. 7/10/245 (1992) University of Leeds. China Light & Power Co. Review Report. Refuse Tip Management (19x9). CL & P. Ash Marketing. Polanco J A. Roller Compacted Concrete for the Construction of Dams. Doctoral Thesis (19x9) University of Cantabria, Spain. Cabrera J G and Lee R E. Proc. 7th Int. Ash Utilisation Symp. (1985) Vol. 1. 34760. Diez-Cascan J, Cabrera J G and Polanco J A. Cement and Concrete Composites (1994). To be published. Cabrera J G, Diez-Caszon J, Polanco J A and Garcia R. Concrete International (1994). To be published. Cabrera J G and Lynsdale C J. Proc. Measurements and testing in Civil Engineering ( 1 ) ( 1988) 279-29 I . Cabrera J G and Zoorob S. Final Report ETSU Contract No. E/CS/3580/2669 ( 199 I ) University of Leeds. Cabrera J G. Highways and Transportation No. 1 1 (199 I). Woolley G R and Cabrera J G . Coastal Protection Project (1994). University of Leeds (in progress).

Environmental Aspcts of Conshcction with Waste Materials JJJM Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN rights reserved.

351

HIGH PRESSURE MIXING: A NEW TECHNOLOGY TO RE-USE WASTE MATERIALS CONTAINING CaO AND/OR MgO R. Haverkort", W. Dekkerb and J. Senden'.

"KZH, Kalkzandsteenfabriek Harderwijk bv., p.0. box 97, 3840 AB Harderwijk, the Netherlands. bConsultant Company Dekker, Bakkersweg 35, 3781 GN Voorthuizen, the Netherlands, 'Novem, Netherlands Agency for Energy and the Environment, p.0. box 17, 6130 AA Sittard, the Netherlands.

Abstract Large amounts of waste materials contain CaO and MgO. Due to the high temperatures at which these materials were burnt, the CaO and MgO hydrate very slowly under atmospheric conditions. This phenomenon obstructs the use of these residuals in many constructing materials. At the calcium silicate work in Harderwijk a pilot plant employing a high pressure hydrating technique was constructed. Because of high pressures and temperatures (lobar, 150°C), this technique allows hydration of over burnt CaO- and MgO-oxide particles. This paper describes the high pressure hydrating technique and presents results from tests in which building products were produced containing up to 40% of fly ash.

1. INTRODUCTION Large amounts of waste-materials contain oxides of Si, Al, Fe, Ca and/or Mg. To use these oxides as raw material in high quality construction materials, such as calcium silicate bricks, a good hydration of CaO and MgO is essential. Due to high temperatures at which the oxides were burnt, MgO and CaO hydrate very slowly under atmospheric conditions. KZH (Calcium Silicate work Harderwijk), with financial support of Novem, started a demonstration project based on a high pressure hydrating and mixing technique. With this technique it is possible to hydrate over burnt CaO- and MgO-particles. In the project a pilot plant was built at the KZH. The pilot plant was connected to the main production plant. This makes it possible to produce building bricks and blocks from mortars produced by the pilot plant. Calcium silicate bricks usually are made of sand, lime and water. In the conventional mixing system these three materials are mixed in one step. After mixing, the CaO is allowed to hydrate in a reactor, To ensure complete hydration, a retention time of 2 to 3 hours is needed. The temperature in the reactor reaches about 60°C. After slaking, the hydrated mix is transported into the factory. Often more water is added to regulate the moisture content of the mortar. In the factory the mortar is pressed into bricks, blocks or large elements. These products are

358 transported into the autoclave, where they are hardened by means of steam. The slaking behaviour of lime is very important in this process. If lime slakes too fast, it will cause dust problems while mixing it with wet sand and water. If it slakes too slow, not all CaO particles will be hydrated after 2 to 3 hours. These particles however will hydrate during autoclaving. This causes the bricks to expand, thus loosing their predefined geometry. It can even lead to cracks in the bricks. This last situation occurs when materials containing over burnt CaO or MgO particles are used. In the high pressure mixing technique the slaking behaviour of lime is of less importance, as will be explained in this paper. First the high pressure mixing technique itself will be described, followed by the application of powder coal fly ash in the system. In paragraph 4 results form tests with powder coal fly ash will be presented. Finally some future possibilities of the high pressure mixing system will be discussed.

2. THE TECHNIQUE The high pressure mixing system (HP system) is divided into three mixing stages. One dry stage and two wet stages. The hart of the system is the first wet stage. In this stage all CaO containing materials, sand and water are mixed in the high pressure mixer (HP mixer). When CaO reacts with water, Ca(OH), is formed and energy is released. In the HP mixer this energy heats up water and eventually forms steam. Because the HP mixer is a closed vessel during mixing, the pressure increases. It is this pressure which makes it possible to hydrate over burned CaO and MgO particles, and ensures a complete and quick hydration [l]. In figure 1 the flow scheme of the high pressure mixing technique is presented. In the figure the three stages are represented by three mixers; the powder mixer (dry stage), the high pressure mixer and the atmospheric mixer. The powder mixer is used to make premixes of powders with different CaO contents. A maximum of three different powders can be mixed into one premix. The premixes are stored in the silos " R l " and "Low Grade Lime". From these silos the premixes can be dosed into the HP mixer. Apart form the CaO-containing materials sand and water are dosed into the HP mixer. In order to be able to control the hydrating process, sand and water are the first components to be dosed. After a short time of mixing sand and water, the CaO containing premixes are added. Immediately after this all valves are closed. Now the HP mixer is a closed vessel. As soon as mixing is started again, pressure starts to increase. Within 40 seconds peak pressure is reached. The temperature of the mix does not start to rise until peak pressure. Maximum pressure reached during mixing depends mainly on three factors: water content, CaO content and degree of filling. Because CaO content is equivalent with the amount of energy released, this is the most important one. When, for example, a mixture is made with 15% CaO, 1% free water after slaking and 300 kg in the mixer, the maximum pressure is about 5 bar. With 20% CaO this is almost 10 bar. The maximum temperatures that go along with these pressures are 142°C and 153°C. After peak temperature the pressure is lowered by allowing the steam to flow out of the mixer into a water vessel. By doing so, the steam heats up the water in the vessel. This hot water is used as reaction water in the HP mixer. Using hot water instead of cold water improves the hydration.

359

When the pressure in the HP-mixer has dropped to 0.3 bar, the valve at the bottom of the mixer is opened and the hydrated mixture is unloaded into the atmospheric mixer (AT-mixer). In the AT-mixer more sand and water are added. There is also a possibility to add a fine and a coarse aggregate (silos "Fl" an "Cl" in figure 1). After mixing in the AT-mixer the mortar has reached its final composition, it can now be used for the production of calcium silicate bricks. For this purpose the production plant of the KZH is used. The connection between the pilot plant and the production plant is made by a closed conveyor belt. The content of the AT-mixer is unloaded into this belt, and subsequently transported into the factory. From this point on the mortar is processed like a normal mortar. The use of a closed conveyor has two major advantages. First of all it prevents the formation of dust. Secondly it keeps constant the moisture content of the mortar. The HP mixing system, including the transportation of mortar, is completely PLC controlled. The time needed to make one complete cycle, i.e. from the first mixing stage to the point that the mortar reaches the production plant, takes about twenty minutes. Because the system can handle several tasks at one time, a production of one charge per 7 minutes can be reached. With a standard recipe this is about lotihour. The mixing system, as it is applied in the pilot plant, and the products that result from it are patented under the European patent nr. EP 90 20 2688 (Schalij and Broekhuis) [2].

3. THE APPLICATION OF POWDER COAL FLY ASH There are two possibilities to test an alternative raw material in the high pressure mixing system. 1 2

The material can be added in the atmospheric mixer. This way the new material will not be a part of the high pressure mix. Usually this option is used for non reactive products. The material can be added solely or mixed with other components in the high pressure mixer. This is done with materials that are expected to be reactive, e.g. materials that contain CaO.

In the experiment with powder coal fly ash, option 2 was used. The fly ash was first mixed with a high grade lime, before being added to the HP-mix. This way the application of a low grade lime is simulated. The way fly ash is applied in the system is schematically drawn in fig. 1. The thick lines show the route of the fly ash in the system. The thin lines show the route of the other components that were used during the experiment. The dashed lines show the possibilities that were not used during the test. As can be seen from the picture, the mortar was produced in three stages. In stage 1 fly ash and lime are mixed in the powder mixer to form a low grade lime. In stage 2 the low grade lime is mixed with sand and water in the HP-mixer, to hydrate the lime. In stage 3 the content of the HP-mixer is unloaded into the atmospheric mixer. Here the final composition of the mortar is reached by adding more sand and water. After the last mixing stage is completed, the mortar is discharged into the closed conveyor belt and transported into the production plant. The exact compositions of the stage 1 mix (low grade lime), the stage 2 mix (HP-mix) and the stage 3 mix (mortar) are given in table 1.

360

- -I 4

>

k

H

36 1

While designing the recipes, three conditions had to be met: 1 2 3

The fly ash content of the mortar had to vary: lo%, 20% and 40%. The CaO-content of the mortar had to be 6.6%. This is the standard CaO-content of the mortar of the KZH. Fly ash had to be a part of the HP mix.

With these conditions the composition of the mortar (conditions 1 and 2) and the composition of the premix (conditions 1, 2 and 3) are defined. The CaO-content of the HP-mix can vary between an upper and a lower boundary, being the CaO-content of the premix and the CaO content of the mortar. In this experiment the researchers chose for 18.9% CaO in the HP-mix for the production of the 10% fly ash mortar. 18.9 % was the standard percentage at that time. For the 40% fly ash mortar, the maximum CaO-content in the HP-mixer is 14% (see table 1). We chose for a percentage close to this maximum: 13.2%. The CaO-content in the HP-mixer mainly determines the pressure that will be reached during mixing. Since pressure is of great importance for the hydration, the CaO-content in the HP-mix could influence the quality of the bricks. In order to determine this influence, the mortar containing 20% fly ash was produced in two different ways. Once with 18.9 % CaO and once with 13.2% CaO in the HP-mix (see table 1). Table 1 Composition of the mixes Stage 1: Premix CaO (%) Fines (%) Fly ash (%) Sand (%)

38.4 3.6 58.0 0.0

24.3 2.3 73.4 0.0

24.3 2.3 73.4 0.0

14.0 1.3 84.7 0.0

18.9 1.8 28.6 50.7

18.9 1.8 57.1 22.2

13.2 1.3 40.0 45.5

13.2 1.3 80.0 5.5

6.6 0.6 10.0 82.8

6.6 0.6 20.0 72.8

6.6 0.6 20.0 72.8

6.6 0.6 40.4 52.8

Stage 2: High Pressure Mix CaO (%) Fines (%) Fly ash (%) Sand (%) Staee 3: Mortar ~~

CaO (%) Fines (%) Fly ash (%) Sand (%)

Fines = non reactive fine particles in the lime Since the CaO-content of each mortar is constant, the fly ash can be seen as a sand replacer. In calcium silicate materials sand is not only a filler, it is also a reactive component.

362

4. THE EXPERIMENT The raw materials used to produce the fly ash mortars were sand, lime and fly ash. The sand and the lime used, are the standard raw materials of the KZH. The fly ash originated from a powder coal fired power plant in the Netherlands. A short chemical analysis is given in table 1 L.

Table 2 Chemical analysis fly ash Oxides

SiOz

A1203

Fq03

CaO

MgO

NazO

KzO

Mass %

66.10

22.40

5.57

1.67

0.70

0.24

1.17

The application of powder coal fly ash in the HP-system was examined by producing four different recipes, resulting in three different mortars. Each recipe was taken into production for one day. The bricks produced with the resulting mortars, were sampled and tested according to the Dutch standards for calcium silicate bricks [2]. Furthermore, samples were taken from the mortars and subsequently tested in the laboratory. Results from these laboratory experiments were compared with results from experiments in which the conventional mixing system was simulated in the laboratory. The mortar with the best results regarding quality and feasibility was selected for a longer test (10 days of production). From the produced bricks two qualities were determined, the compressive strength (CS) and the density (RHO). The samples and the mortars made in the laboratory, were used to make laboratory specimens. The specimens were tested upon: 1 2 3 4

Green strength (GS) Compressive strength (CS) Density (RHO) Expansion

Green strength is the tensile strength of a specimen before hardening. This quality is important in terms of handling bricks before hardening. Compressive strength is the strength of the hardened brick. Density is the specific mass of the hardened brick after drying. During autoclaving calcium silicate bricks tend to expand a bit due to the formation of CSH crystals. This expansion is small and will not cause the bricks to loose their geometry. A brick made of poorly hydrated lime expands far more; expansion can be used as an indicator for the hydration degree of lime. 4.1 Results

The quality of the produced bricks will be discussed in the paragraph "Technical quality". Here the results of the laboratory tests will be presented. For compressive strength and density the laboratory results will be compared with the results obtained from the bricks. As stated before, the mortar with 20% fly ash was produced in two different ways. The differences in green strength, compressive strength, density and expansion were small and often not statistical significant. Therefore the results of the 20% fly ash mortars will be combined. The results will be presented graphically. In the graphs curves marked with represent the

"+"

363

specimen of the HP-mixing system (HP-specimen) and curves marked with "0" represent specimen of the conventional mixing system (C-specimen) and curves marked with "*" represent the results of the bricks (HP-bricks). In figure 2 green strength is shown as a function of the percentage fly ash in the mortar. From this graph it is clear that fly ash has a positive influence on green strength, regardless the way of mixing. In figure 3 the relative increase of green strength is shown. The relative increase is calculated by subtracting the 0%-value from the actual value and expressing this value as a percentage from the 0%-value. From this graph it is obvious that, looking at green strength, fly ash is most effective in the conventional mixing system. The maximum increase in the conventional system is 126%, in the HP mixing system this is only 25%. GS [kPal

7.51 1 I 15?J

12.5

5

O

F

__-- _--

_-

-a

~

~

P

/ __t -

10-

4 ~ ~

~

7.5[-

t -

_i

5

Figure 2. Green strength (GS). (0) = Cspecimen, (+) = HP-specimen.

Figure 2. Relative increase green strength (GSr). (0) = C-specimen, (+) = HP-specimen.

In figure 4 the compressive strength is shown as a function of fly ash content. In the conventional mixing system compressive strength decreases sharply due to the adding of fly ash. In the HP mixing system maximum strength is measured at 20% fly ash. In the conventional 5oCS IMPal

-1

I

/

/

40

I -------------(7

15'

0

I

10

20

30

40

% FLY ASH

Figure 4. Compressive strength. (0) = Cspecimen, (+) = HP-specimen, (*) = HPbrick.

-50'

0

10

20

30

40

% FLY ASH

Figure 5. Relative increase compressive strength. (0) = C-specimen, (+) = HPspecimen, (*) = HP-brick.

364 mixing system maximum relative increase is -32.2% (see figure 5). Comparing this with the +33.3% increase in the HP mixing system, it is clear that the combination of HP mixing and fly ash is a better one than the combination of conventional mixing and fly ash. Note that the relative increase of the HP-bricks and HP-specimen are almost identical. In the conventional mixing system, density reaches maximum at 10% fly ash (see fig. 6). In the HP system density increases with increasing fly ash content. For the specimen maximum density is measured at 20%., the HP-bricks show a linear increase in density. The difference in density between specimens and bricks can be explained by differences between the laboratory press and the press in the production plant. Furthermore, the pressure needed to shape a brick had to be increased by 20% to be able to produce bricks containing 40% fly ash. The maximum relative increase in the HP system, is 7.0% for the specimen and is 7.9% for the bricks. In the conventional system maximum increase is only 2.8%. Note that at 40% fly ash HP-specimen show an increase of 5%, whereas C-specimen show a decrease of 10%. RHO (kg/m3) 19001

I

\

\ \

1650

\\

1600'

0

0

10

20

30

,

40

% FLY ASH

Figure 6. Density (RHO). (0) = C-specimen, (+) = HP-specimen, (*) = HP-brick.

-51

-10'

0

10

20 30 % FLY ASH

",

40

Figure 7. Relative increase density (RH0)r. (0) = C-specimen, (+) = HP-specimen, (*) = HP-brick.

None of the specimens, neither in the HP system nor in the conventional system, showed expansions higher then 1 %o; slaking the low grade limes was not a problem. 4.2 Technical Quality The technical quality of the bricks has been determined according to NEN 3836, the dutch standard for calcium silicate bricks. In this standard the bricks are divided into four qualities being "NORMAL", "IUINKER", "GEVEL" and "HOGEDRUK". The latter two are special qualities. The first two are qualities for normal construction purposes. These two qualities are based on the compressive strength of the bricks. A minimum mean value and a minimum value are defined (see table 3)

365 Table 3 Technical quality of calcium silicate bricks

NORMAL KLINKER

M a Compressive Strength (MPa)

Minimum Compressive Strength (MPa)

Number of samples

15.0 25.0

13.5 22.5

10 10

From: NEN 3836, Kalkzandstenen en kalkzandsteenblokken, 1978 [3] The quality of the bricks produced during the ten day test are summarized in table 4. In the last column of this table the quality of the brick according tot NEN 3836 is given. Table 4 Technical quality bricks experiments

10% Fly As 20% Fly Ash 20% Fly Ash 40% Fly Ash

MG3ll CS (MPa)

Minimum CS (MPa)

Standard deviation

Quality acc. to NEN 3836

17.0 23.4 25.5 19.2

15.8 19.5 22.8 16.8

2.24 2.57 1.66 1.62

Normal Normal Klinker Normal

CS = Compressive Strength Though the best results were obtained at 20% fly ash, the recipe leading to a mortar containing 10% fly ash was chosen for the ten day test. The reasons for this were the formation of dust in the production plant and stoppages in the HP-system, while producing the 20% mortars. These problems will be discussed in more detail in paragraph 4.3 Feasibility. During the ten day test the produced bricks were also tested according to the standard. Results from these tests are given in table 5. As in the previous table the technical quality is stated in the last column. Table 5 Technical quality bricks ten day test

1 2 3 4 5 6 7

M a CS (MPa)

Minimum CS (MPa)

Standard deviation

Quality acc. to NEN 3836

21.9 25.4 24.8 22.0 26.1 25.7 22.7

16.4 22.9 21.5 19.2 18.6 22.8 19.5

3.31 2.15 1.75 1.92 5.60 3.26 2.74

Normal Klinker Normal Normal Normal Klinker Klinker

CS = Compressive Strength

366 The bricks produced during the ten day test and the bricks denoted "10% Fly Ash" in table 4, originated from the same recipe. Nevertheless, the strengths measured during the ten day test are far higher. This difference might be related to two factors. First the moisture content of the mortar was increased in the ten day test to prevent the formation of dust. This leads to a better compaction, resulting in higher strengths. And second the adjustment of the press was better during the ten day test. After producing several mortars containing fly ash, it was easier to find the correct setpoints for the press. This also improves the quality of the bricks.

4.3 Feasibility Apart from the technical quality of bricks, problems encountered during the production of mortars is also an important factor while judging a recipe. The two main problems that occurred during the experiment with fly ash were dust formation and stoppages. During the production of all fly ash containing mortars the formation of dust in the production plant was a problem. At 10% fly ash this problem could be solved by increasing the moisture content. At higher percentages this was no longer sufficient. Since the HP-system is a closed system, dust was not a problem in the pilot plant. Stoppages mainly occurred during the production of HP-mixes with high percentages fly ash (40% - 80%). Stoppages occurred in pipes between the HP-mixer and the water vessel, and between the water vessel and the AT-mixer. They were caused by fine particles like fly ash and hydrated lime that flow out of the HP-mixer while letting off steam. The frequency of stoppages increased with increasing fly ash content in the HP-mixer. At percentages higher then 40% the stoppages became so frequent that it was not possible to have a continuous production for one day. Only recently the system has been improved at this point. In our opinion the stoppages will no longer be a problem. Apart from the problems mentioned above, a third problem arose during the production of the 40% mortar. Though the technical quality of the resulting bricks is good, it was very difficult to shape the mortar into bricks. Even after increasing the pressure, the non hardened bricks had to be handled with great care in order not to break them. Looking at feasibility, producing the 10% mortar is not a problem. When precautionary measurements are taken to prevent the formation of dust, 20% is also a possibility. To produce a mortar with 40% fly ash, a HP mix with 94.5% powders (13.2% CaO, 1.3% fines, 80.0% fly ash) is needed. With these amounts of fines, stoppages will occur. Therefore producing mortars containing 40% fly ash in not a viable option. 4.4 Conclusions

Based on results from laboratory experiments, the combination between fly ash and high pressure mixing proved to be a better one than the combination between fly ash and the conventional mixing system. In the HP system the maximum increase in compressive strength is 33.3%. In the conventional system this is -32.2%.

In the HP system the best results were obtained with the recipe that resulted in 20% fly ash and had 13.2% CaO in the high pressure mix. For the specimen the green strength increased by 24.8%, the compressive strength by 33.3% and the density by 7.0%. The compressive strength of the bricks was 25.5 MPa, the density 1833 kg/m3. The production of these bricks requires precautionary measurements regarding the formation of dust. The results from the experiments with fly ash are summarized in table 6

367 Table 6 Summary of results Mixing system

Scale

cs

GS (Wa)

(MPa)

RHO (kg/m3)

++ +

__ +++ + + ++ GS = Green Strength; CS = Compressive Strength; RHO = Density; + = positive influence; ++ = strong positive influence; - = negative influence; -- = strong negative influence; +- = positive influence at low percentages., negative at high percentages Conventional High Pressure High Pressure

Specimen Specimen Brick

All fly ash containing bricks were tested "NORMAL" or "KLINKER" according tot NEN 3836.

5. FUTURE POSSIBILITIES In the experiments fly ash from a powder coal fired power plant was used to replace sand. Other residuals can also be used for this purpose. One possibility is to use materials from a FBC-oven. The filler from this unit could be used in the same way as fly ash. The coarser aggregates (FBC sand) could replace more sand. A mixture of filler, FBC sand and CaO would then be the HP mix. Depending on the quartz content of the filler and the FBC sand, some quartz containing powder might be necessary. Quartz is needed for the formation of CSH crystals during autoclaving. By adding more sand the atmospheric mix would be obtained. Possible compositions of the mixes are given in table 7.

Table 7 Possible composition of mixes ~~

FBC Filler FBC Sand CaO Sand Quartz Powder

Premix

HP mix

Mortar

73.4 0.0 24.3 0.0 0.0

40.0 44.5 13.2 0.0 2.0

20.0 22.3 6.6 50.1 1.o

Since the pilot plant is connected to the production plant of the KZH, its mortars can be used to produce building materials. The mixing system however can also be used to produce other products, e.g. artificial gravel. In fact small amounts of artificial gravel were made accidentally during a cleaning operation. Due to its flexibility the pilot plant can produce hydrated mortars of entirely different compositions in a short time. This makes the installation very suitable for contract research, or the production of half products. The composition of the half products can be adjusted according to the wish of the client.

368

Recently another feature was added to the pilot plant. Now it is also possible to dry granular materials. These materials can either be used in the mixing system, or be stored in silos from which they can be dosed into trucks. The dryer uses hot air to dry materials. The energy needed to heat up this air, is supplied by steam originating from the autoclaving process of the KZH. In this process, an amount of steam once used to heat up an autoclave, is re-used for this purpose until it is so polluted with other gases, that it can no longer be used for the hardening of CSbricks. However, the temperature of this steam is still f 130°C. By using the remaining energy stored in the polluted steam to heat up air, instead of using energy stored in natural resources, energy is saved. At the moment the dryer produces dried sand for a glass fibre reinforced cement producer.

In the near future the HP system will be tested as a production unit. Until now, the unit was mainly used for experimental purposes. A test will be done in which the plant will produce mortar for 24 hrs/day at a rate of f 10tlhour. Furthermore a test will be done with limes containing high grades of MgO. After this the pilot plant will be available for contract research and for the production of hydrated or non hydrated half products.

6. REFERENCES 1

Dekker W.D., Waste Materials in Sand-Lime Brick, Environment and Technology 3, 1991.

2

Schalij J. and Broekhuis J., Method for preparing a mortar of lime and sand, sand-lime bricks produced thereof and apparatus for the preparation of the mortar of lime and sand, European Patent Office, Publication nr. EP 0 422 741 Al, Bulletin 91/16, 1991

3

NEN 3836, Kalkzandstenen en kalkzandsteenblokken, 1978.

Environmental Aspects of Consmction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) @I994 Elsevier Science B.V. All rights resewed.

369

ENVIRONMENTAL COMPATIBILITY OF CEMENT AND CONCRETE S. S p r u n g , W . Rechenberg and G . Bachmann

Forschungsinstitut der Zementindustrie P.O. Box 301063, D - 4 0 4 1 0 DUsseldorf, Germany

Abstract Concrete prisms 4 x 4 ~ 1 6c m w i t h 300 k g c e m e n t / m 3 concrete and water cement ratios from 0.50 to 0.70 w e r e produced and stored up to 4 0 0 d i n drinking water and i n aggressive carbon dioxide. A n ordinary Portland cement (OPC), a fly a s h c e m e n t , and a Portland pozzolana cement were used. The highest amount of chromium leached f r o m a porous concrete w a s l.exp.-4 g i n 10 P water after 7 d caused by a w a s h - o f f effect. The released amounts decreased w i t h time and density of concrete, approaching the limit of determination. The coefficient of diffusion also decreased f r o m l.exp.-ll cmZ/s to approx. 2.exp.-13 cm2/s after 4 0 0 d . The time to reach the drinking water limit i n a water reservoir w a s calculated to be about 2 300 a .

1. INTRODUCTION

According to the German waste materials l a w [l] the generation of w a s t e shall be more and more minimized or re-used i n the same or i n other industries. As far as the cement industry is engaged i n the utilization of residues i t has to be assured that the emissions of the clinker burning process are not raised, the quality of the cement is n o t impaired and the environmental compatibility of the concrete is n o t affected [ Z ] . The partial utilization of secondary i n exchange of natural materials i n the burning or grir.ding process - as a rule - does not lead to higher contents of heavy metals i n the cement compared to a n exclusive utilization of natural r a w materials [ 3 ] . Despite these findings it seems to be necessary to discuss the question of a potential risk and the influences o n the environmental compatibility of concrete o n the basis of investigations. I n this context the environmental compatibility should be understood as a requirement o n the property and quality of cement and c o n c r e t e , taking the effects o n human h e a l t h , soil and water into consideration as well. The range o f heavy metal contents i n cement meets the range found i n natural soils [ 3 - 5 1 . The ecological evaluation of cement o n the basis of the total content of heavy metals is only of secondary interest. The binding capacity of the hydrated cement and the mobility of heavy metals i n the concrete are of

370 greater importance. The binding capacity of hydrated cement in the concrete structure can only be evaluated by the leachability behaviour. Earlier findings have shown that the leachability of many heavy metals in waste materials may already be drastically reduced only by stabilization with cement [ 6 - l o ] . Test procedures destroying the dense structure prior to the elution and thus enlarging the leachable surface [ll] or dissolving the dense structure of hydrated cement by strong acids [12] have proven not to be suitable for the judgment of the long time stability of the fixation [6. 8 . 9 , 1 3 1 . The elution from compact specimens is diffusion controlled. Test procedures, therefore, have to consider the surface of the test specimens [ 1 4 ] and the fact that leachability is a diffusion controlled process [ 1 5 - 1 9 1 . This paper deals with investigations of the long time stability of the binding of soluble compounds of the elements chromium, mercury, and thallium in hardened concrete.

2. TEST SPECIMENS

2.1 CEMENT The contents of chromium, mercury, cements used are given in table 1.

and

thallium

in

the

Table 1 Contents of chromium, mercury, and thallium in Portland cement, Portland fly ash cement (CE I I / B - V ) and Portland pozzolana cement (CE II/A-Q), according to ENV 1 9 7 , part 1 [ Z O ] in g / t Cement OPC CE I I / B - V CE I I / A - Q

Chromium

Mercury

Thall ium

79 137 227

< 0.02

< 0.2

< 0.02 < 0.02

< 0.2

0.4

Portland fly ash cement C E I I / B - V contained 2 5 % by w t . of siliceous fly ash and the Portland pozzolana cement C E I I / A - Q about 20 % by wt. of a nonferrous slag as industrial pozzolana. The chromium content of the OPC was 79 g / t , which is somewhat above the mean o f German OPCs [ 4 , 2 1 1 . The fly ash cement contained 137 g C r / t (CE I I / B - V ) and the pozzolana cement 227 g C r / t (CE II/A-Q). The concentration of mercury and thallium was with one exception lower than the limit of determination of the AAS method [ 2 2 ] . 2.2 AGGREGATES

As aggregates for the concretes a mixture o f fine quartz ( 0 1 0 . 2 mm), quartz sand ( 0 / 2 mm), and Rhine gravel ( 2 / 8 mm) was applied. The grading curve of the aggregate mixture complied with a composition in the upper part of the range between the grading curves A and B of figure 1 i n DIN 1 0 4 5 [ 2 3 ] . I n table 2 the total concentration of Cr. H g , and T1 in the single grain

371 fractions and the water soluble portion of the heavy metals are given. Table 2 Total contents of C r , H g , and T1 [ 2 2 ] as well as w a t e r soluble portion [ l l , 211 i n grain fractions of the aggregates G r a i n Fraction in mm

Chr omium i n glt

Mercury i n glt

Thallium i n glt

Total Contents < 0.01 < 0.01 < 0.01

2.2 15.6 5.9

0.03

62.8

Water S o l u b l e Portion < 0.01 < 0.01 0.01 < 0.01 < 0.01 < 0.01

010.2 012 112 218

0.01

< 0.01

< < < <

0.2 0.2 0.2 0.2

< < < <

0.01 0.01

0.01 0.01

The total contents o f Cr and T1 have been determined after total digestion. For the determination of the Hg the solid powders have been atomized directly [ 2 2 ] . The w a t e r soluble portion of the elements w a s determined i n a leachate [ l l , 2 1 1 . The total contents of the heavy metals i n the concrete may be calculated f r o m the total contents i n the starting materials. Characteristic is that the water soluble portion of the heavy metals i n the aggregates is extremely l o w , mostly below the limit o f determination. 2.3 F R E S H C O N C R E T E

Table 3 contains the composition and the curing conditions of the t e s t specimens. Table 3 Composition and curing conditions of test specimens Concrete Mix Cement Cement Content Grading of Gravel Water Cement Ratio

OPC 300 k g / m 3 ConcreLe A/B 8 0 . 5 0 - 0.70

Doped Concrete Mix Doped w i t h Doped Amount

Cr, H g , T1 100 mg/P Mixing W a t e r

Concrete Specimens 2a d

4 x 4 x 16 cm 2 0 O C , 100 % r.H.

372 The concretes were uniformly mixed with 3 0 0 kg c e m e n t / m 3 concrete and w i t h different amounts of water to give water cement ratios ( w / c ) of 0 . 5 0 to 0.70. The concretes w i t h C E I I I B V and C E I I / A - Q cements were produced only with a w / c of 0.60. I n one series of tests OPC concretes were doped w i t h 100 mg of the heavy metals per P of mixing water from the w a t e r supply of the city of DUsseldorf. All fresh concretes w e r e completely compacted. TEST SPECIMENS For the investigations 3 concrete prisms 4 x 4 ~ 1 6c m w i t h measuring plugs were produced. The test specimens w e r e cured 1 d in the mould and 2 7 d i n a fog chamber with 2 0 OC and 100 X r.H. They were protected against dropping water (table 3 ) . 2.4

3.

INVESTIGATIONS

For each series of test 3 prisms from one mould w e r e eluted after curing i n a plastic trough with water from the supply of the city of DUsseldorf. The total surface of the prisms was 864 cm2, the total weight 1.8 kg. Each trough contained 18 0 water. The surface to volume ratio was around 0 . 0 5 cm”. This condition corresponds to the instructions of the German Health Authority [ 2 4 ] . The mass to volume ratio corresponded to 10. This meets the requirements of DIN 3 8 4 1 4 , part 4 [ l l ] . Drinking water was used because it should not be spoiled during processing, transport and storage. The same kind of water is used normally f o r the production of concrete for drinking water pipes and reservoirs as well 2 s for concrete foundations in drinking water catchment areas. The drinking water i n the laboratory test was partly enriched with carbon dioxide. This rendered it possible to investigate a dissolving attack by aggressive carbon dioxide for example in ground water [ 2 5 - 2 9 1 . 3.1 ELUTION OF H E A V Y METALS I n figure 1 a n equipment for the elution of heavy metals w i t h water enriched i n carbon dioxide is schematically reproduced. Gaseous carbon dioxide is introduced into the water i n an enrichment vessel. The water is then pressed through a pipe by a pump into the trough. The mean upward velocity of f l o w in the trough w a s 4 , e x p . - 5 c m / s . This condition means a slowly flowing water according to the definition of the DIN 4 0 3 0 [ 2 8 ] . After this the water flows back to the enrichment vessel. Immediately after filling the trough the carbon dioxide content increased to 1 4 0 mg/e and decreased approximately after one w e e k to 100 m g / e . The mean carbon dioxide c o n t e n t , therefore, was considered to be 120 mg/e. According to D I N 4 0 3 0 [ 2 8 ] this is a very strong chemically attacking water. The Concrete Standard D I N 1 0 4 5 [ 2 3 ] under such conditions gives the advise to protect any concrete against the immediate contact.

373

I 0

0

0

0

0

0

0

0

0

1

0

0

Figure 1. Device for testing the leaching of concrete by water enriched w i t h aggressive carbon dioxide

The photograph of figure 2 shows a rack which w a s used as a holder for the specimens. The plugs of the specimens rest i n notches of a n U-shaped plastic tub with holes i n the bottom. The water passes through the holes without streaming directly to the surface of the specimens. T h u s , a n additional mechanical abrasion is avoided [ 2 9 ] and the specimens a r e brought into contact w i t h the water o n all sides. For the elutions with drinking water without additional chemical attack similar tanks have been used w i t h o u t a gas enrichment vessel. I n this case the water flows directly from the trough to the pump. The water i n these troughs w a s changed at the same schedule as the water with aggressive carbon dioxide.

314

Figure 2. Rack for the storage of 4 x 4 ~ 1 6c m prisms w i t h plugs

SAMPLING A N D ANALYSIS The contents of the heavy metals i n the fresh drinking water have t o be considered. While filling the troughs water samples were taken and analysed. Table 4 shows the extreme values and means of the determinations. 3.2

Table 4 Concentrations of c h r o m i u m , mercury, and thallium drinking water used. Extreme values and means in mg/P Element

Lowest Value

C hr omi um Mercury Tha 1 l i u m

< O.l.exp.-3 < O.l.exp.-3 < 0.5.exp.-3

Mean 0.5 .exp.-3

0.25.exp.-3 < 0 . 5 .exp.-3

in

the

Highest Value 2.l.exp.-3 1.9,exp.-3 < 0.5.exp.-3

For the determinations of the eluted heavy metals samples were taken immediately before changing the water i n the troughs and then analysed. The results were corrected for the concentrations in the original drinking water.

375 4. RESULTS

4.1 ELUTION OF CHROMIUM BY DRINKING WATER The corrected quantities of eluted chromium are given in figure 3 . The different cements and w / c ratios are marked by different signs. The 3 test specimens of the OPC-concretes contained uniformly 2 0 mg Cr/kg concrete. The chromium concentrations i n the other concretes w e r e 31 mg C r / k g concrete ( C E I I / B - V ) and 5 2 mg C r / k g concrete ( C E II/A-Q). The concretes showed different d e n s i t i e s , distinguished by different w / c ratios.

O D W

A

c 01

!i 10-6

0

7 142128

56

100

200

300

400 484

lime of elution in d (root scale I Figure 3 . Amounts of chromium leached from concrete by drinking water in dependence of time and water cement ratio First of all it emerges from the figure that the leached quantities of chromium up to 4 0 0 d in tendency depend o n the wlc ratios of the concrete. That means that they depend o n the density o f the concrete structure. The highest amount of 1 . exp.-4 g Cr w a s found i n the leachate of the concrete w i t h the highest w / c ratio of 0 . 7 0 (triangles). Lower w / c ratios and a correspondingly higher density o f the structure decreased the leached amounts. I n addition the eluted quantities decrease w i t h the time of elution. After approximately 4 0 0 d the highest value is lower than 8 . e x p . - 6 g. I n most cases the leached amounts approach the l i m i t of determination of the AAS m e t h o d , w h i c h is

376 about l.exp.-6 g under these circumstances. The upper and the lower data points mark a field into which all marks fall. This field also includes all leaching results from the cements with fly ash and pozzolana additions, respectively. Inside the field the results scatter noticeable, especially in the middle part (100-200 d). The correlation between the density of the concrete and the eluted quantity, therefore, becomes visable only i n tendency. Nevertheless, the decreasing elution by time is perceptible. Additional the investigations have shown that the elutions during the first time space of 7 d , in some cases also during 14 d , showed the typical wash-off effect from the surface of the specimens. The wash-off effect was noticed in all eluates from all test specimens independent from the type of cement, the time of curing and the W / C ratio. The initially leached quantities decreased, however, rapidly and approached values near the limit of determination. These results as well as results from the literature [ 1 4 , 29-33] indicate that the leaching process following the wash-off effect is diffusion controlled. 4.2 ELUTION OF CEROMIUM B Y AGGRESSIVE CARBON DIOXIDE The leached amount of chromium increases when water containing about 120 mg of aggressive carbon dioxide per liter instead of drinking water is allowed to react with concrete. The increased elution is caused by additional chemical attack. The results of the leaching experiments with aggressive carbon dioxide are shown in figure 4 . The composition of the concrete and the curing conditions correspond to those of the specimens stored in drinking water. I n the diagram the amount of released chromium is applied with the leaching time. The resulting area is limited by upper and lower boundary lines. The results on concretes from different cement types or varying w / c ratios are indicated with different symbols. The range of the values referring to the figure 3 is also illustrated for comparison with a hatched area. First of all it may be outlined that the elution of chromium decreases with leaching duration. This behaviour indicates an elution of chromium by a diffusion controlled process submitted to the influence of aggressive carbon dioxide. In addition to this it can be noticed that the boundary lines compared with the hatched area are raised. This fact is due to the additional influence of the chemical attack. A s a result the lower boundary line deviates only by a small amount from the lower line of the hatched area whereas the upper boundary line is clearly exceeding the hatched area. This gives evidence for the fact that dense concretes show a stronger degree of resistance against aggressive water than concretes with a higher porosity. Beyond this fact it can be concluded from the test results that the cements with additions, causing a remarkable elevated chromium content, fall into the area of the ordinary Portland cement with a lower chromium concentration. This clearly indicates that the elution within a normal concentration range mainly depends on the density of the concrete and not on the heavy metal content.

377

7 142128 56 100 200 Time of elution in d ( root scale 1

0

300

COO 484

Figure 4. Amounts of chromium leached from concrete by water enriched w i t h aggressive carbon dioxide i n dependence of time and water cement ratio

Summarizing the individual results of each cement leads to a linear correlation between the leached amount and the leaching time from w h i c h the coefficients of diffusion may be calculated. 4 . 3 COEFFICIENTS OF DIFFUSION 4.3.1 G E N E R A L

The coefficients o f diffusion of chromium i n concrete have been calculated o n the basis of the measured values according to equation (1) for drinking water and aggressive c a r b o n d i o x i d e , respectively. The w a s h - o f f effect w a s not considered i n this calculation. 6 ’ V

- D = -

A . t . P n

C

max C

- c

ma x

Where: D effective coefficient of diffusion i n c m 2 / s 6 thickness of the boundary layer: 0.01 c m V volume of the eluent i n cm’: 18 000 cm3 A surface o f the specimens i n cm’: 8 6 4 c m 2

378 t time of elution in s : 86 400.d cmax chromium concentration in the pore solution of concrete in g / p : l.l.exp.-Z g / p [ 3 4 ] c chromium concentration in the eluent at time t in g / p

4.3.2 COEFFICIENT OF DIFFUSION OF CHROMIUM FOR DRINKING WATER LEACHING The coefficients o f diffusion of chromium resulting from the measured values of the elution with drinking water are illustrated in figure 5 . The diagram contains a l s o additional informations about the cements and the w / c ratios.

g 0

u

0

7 1L2128 56 100 200 300 Time of elution in d (mot scale 1

COO C8L

Figure 5 . Coefficient of diffusion for chromium leached from concrete by drinking water in dependence of time and water cement ratio The course of the measured values shows that the coefficient of diffusion decreases with time. Obviously that is due to the fact that the pores of the concrete are closed w i t h increasing hydration time of the cement. Accordingly the diffusion is hindered and a s a result the coefficient of diffusion will diminish. This process will not be finished even after 400 days, provided the concrete is kept under humid conditions. Nevertheless, it can b e estimated that the coefficient of diffusion will decrease to a value smaller than l . e x p . - 1 3 cm2/s. Additionally the results show that all coefficients of diffusion

379 are situated w i t h i n a n a r r o w band between a n upper and a lower boundary l i n e , respectively. The coefficients of diffusion of the dense concretes with lower w / c ratio are to be found mainly nearby the lower boundary l i n e , whereas the coefficients of the somewhat porous concretes are located near the upper boundary line. Therefore, the density of a concrete is the most important factor for the elution behaviour of heavy metals. I n this context the coefficients of diffusion of concretes, containing higher amounts of the heavy m e t a l , are situated i n the area between the boundary lines although their chromium content exceeds clearly that of Portland cement concrete. I n relation to the density of structures it can be stated that the elution of this element depends essentially on the density o f the concrete w i t h i n a range known from experience - n o t o n its and concentration i n the concrete.

-

4.3.3 COEFFICIENT OF DIFFUSION OF CHROMIUM FOR CHEMICALLY AGGRESSIVE W A T E R LEACHING The summarized results of these leaching tests w e r e used as well for the calculation of the coefficients of diffusion for chromium according to equation (1). The coefficients are shown as a function of the leaching time i n figure 6.

g u 0

0

56 100 200 300 Time of elution in d Iroot scale 1

7 142128

COO 484

Figure 6. Coefficient of diffusion for chromium leached f r o m concrete by w a t e r enriched w i t h aggressive carbon dioxide i n dependence of time and water cement ratio

380 The diagram also shows a hatched area which corresponds to the results in figure 5 for the elution with drinking water. The figure demonstrates that the coefficients of diffusion decrease with time also in an aggressive medium with its damaging influence [ 2 6 , 2 7 , 2 9 1 . This is due to the fact that the growing amount of hydration products of the cement in the concrete structure is not affected by a dissolving attack on the surface of the concrete. The coefficient of diffusion can be fitted as well in an area between upper and lower boundary lines. The lower boundary line represents the data points of dense concretes ( w / c of 0.50; open circles), whereas the upper boundary line w a s drawn through the data points of l e s s dense concretes ( w / c of 0 . 7 0 ; open triangles). Comparing the position of the data points with those of the hatched a r e a , however, it seems to be obvious that the elution with chemically aggressive water leads to higher coefficients of diffusion than the elution with drinking water. The fact is that a higher coefficient of diffusion will be deceived by a dissolution process at the concrete surface. Because of the mass l o s s due to chemical attack also the chromium content increases in the leaching solvent. This increase, therefore, depends not on a change of the chromium coefficient of diffusion in concrete but only from the extent of chemical attack which, however, is diffusion controlled [ 1 3 , 29-31]. A s a result and in accordance to the requirements of the German Standard DIN 1045 [ 2 3 ] it can be concluded that water with " a very strong aggressive property" [28] is not allowed to come into direct contact with the concrete surface because i t leads to complete deterioration of the concrete with time. This restriction also comprises that mineral water with a comparable or even higher content of carbon dioxide is not a l l o w e d t o be stored in non-protected concrete reservoirs. But this will not be further discussed in this article. 4.4

LEACHING BEHAVIOUR O F MERCURY AND THALLIUM

Mercury could be released only i n very small portions by drinking water from the specimens with natural base materials containing only very low amounts of this element (tables 1 and 2 ) . With chemically aggressive water containing carbon dioxide the amount was only insignificantly higher. Neither i n drinking water nor in aggressive carbon dioxide thallium could be detected for the same reason. Therefore, doped concretes (table 3 ) were included i n this investigation for comparison. The specimens ( 3 prisms) contained after artifical addition by mixing water 11.5 mg of the respective elements. The result of such a comparison is indicated in figure 7 . The graph shows the accumulated amounts of the three heavy metals which could be leached from Portland cement concretes ( w / c of 0.50) during 4 0 0 days. The left group of the columns shows the results of the elution with drinking water whereas the group on the right represents the results with water containing aggressive carbon dioxide. The results from concretes with a natural heavy metal

38 1 content are indicated i n the front line. The eluted amounts of the doped concretes are represented i n the back line.

/I

1

0.5

Doped

Concrete

o,,;q,tl,==

Cr TI Drlnklng

I II

Hg Water

nnn-r

Cr TI Hg Aggr. C02 ln Water

c""-O'O"'

Figure 7 . Totals of leached heavy metals from base and doped concretes w i t h a water cement ratio of 0.50 in dependence of the leaching media Figure 7 demonstrates that the leached amounts after 4 0 0 days accumulate to 0.10 mg C r , to l e s s than 0.01 mg T1 and to merely 0.002 mg Hg w h e n drinking water was used as eluent. Chemically aggressive w a t e r raised the eluted amount of chromium to a value of 0.13 m g , w h e r e a s the values for thallium and mercury remained unchanged. I n the case of the artifically doped concretes only 0.13 mg C r , 0.002 mg T 1 and only 0 . 0 0 2 m g Hg have b e e n leached from the 3 prisms. The additional dissolving attack by aggressive c a r b o n dioxide led to a release of 0 . 5 5 mg Cr. 0 . 4 0 mg T 1 and 0.007 m g Hg from the doped concretes. The results with drinking w a t e r show that i n fact the leached amounts may increase slightly w h e n concretes are doped with higher amounts of water soluble trace elements via the mixing water. But the increase i n the leachate does not correspond to the amounts a d d e d , because the heavy metals are bound chemically i n the cementitious material of the concrete.

5.

EFFECT ON DRINKING UATER

I n Germany the heavy metal content of drinking water is imposed by the Drinking Water Act [35]. For comparison the total amounts of the leached metals have been calculated i n relation to the volumes used for the steps of the leaching procedure. The results for drinking water are shown in table 5 and for aggressive carbon dioxide i n table 6. respectively. Table 5 Concentrations of the totally eluted amounts of elements i n the total drinking water volume after 4 0 0 d i n mg/P Line

Element 0.50

1 2

3 4 5 6 7

a 9

Water Cement Ratio 0.60

0.70

Concretes w i t h Natural Contents Chromium 4 .exp. - 4 5.exp.-4 6 .exp. - 4 Mercury < 2.exp.-6 4 .exp. - 5 1 .exp.- 4 Tha 11 i u m < 2,exp.-5 < 2.exp.-5 < 2.exp.-5 Doped Concretes (100 mg/P Mixing Water) Chromium 3 . exp. - 4 4 . exp. - 4 a . exp - 4 1.exp . - 5 Mercury 1 .exp.- 4 l,exp.-4 < 2,exp.-5 < 2.exp.-5 1 . exp. - 4 Thallium

.

Table 6 Concentrations of the totally eluted amounts of elements i n the total volume of aggressive carbon dioxide after 4 0 0 d i n mg/P Line 1 2

3

4 5

6 7

a 9

Element

Water Cement Ratio

0.50 0.60 0.70 Concretes with Natural Contents Chromium 5 .exp.- 4 6 . exp, - 4 7 . exp. - 4 Mercury 6 .exp.- 6 7 * e x p ,- 6 2 .exp.- 4 Thall i u m < 2.exp.-5 < 2.exp.-5 < 2 . e x p . - 5 Doped Concretes (100 mg/P Mixing Water) Chromium 1 .exp.- 3 2 .exp.- 3 3 .exp. - 3 Mercury 3 .exp.- 5 7 .exp.- 5 3 .exp. - 4 Tha 1 1 iurn 2 . exp. - 3 4 .exp. - 3 5 . exp. - 3

I n both tables the first line indicates the w / c ratios of the concretes. The heavy metal concentrations found i n the leachates of the undoped concretes are presented i n lines 3 - 5 . Lines 7 - 9 show the corresponding details of the doped concretes,

383 respectively. For comparison information is g i v e n o n limiting values of the Drinking Water Act [ 3 5 ] i n table 7 .

the

Table 7 Limits of the G e r m a n Drinking Water Act [35] Line

Element

Limit i n mg/P

1 2

Chromium Mercury Thallium

5 .exp.- 2 1 .exp.- 3 unl. ( 4 , e x p . - Z ) *

3

*)Unl: Unlimited (lead limit instead) The highest concentration of chromium i n the leachate ( 3 , e x p . - 3 mg/P) appears for a concrete w i t h w / c of 0.70, w h i c h has been stored i n chemically aggressive w a t e r (table 6. line 7). This c o n c e n t r a t i o n , however, is about a factor of 1 7 lower than the limiting value of 5 . e x p . - 2 mg/P (table 7 , line 1). The highest mercury concentration of 3 . e x p . - 4 mg/P is given i n line 8 (table 6) for concretes w i t h a w a t e r cement ratio of 0.70. This value is about 3 times lower than the limiting value of l , e x p . - 3 mg/P (table 7 , line 2). The highest thallium concentration of 5.exp.-3 mg/P (table 6 , line 9 ) was leached from a doped concrete w i t h a w / c of 0.70 after 4 0 0 d storage i n aggressive COz containing w a t e r . I n the G e r m a n Drinking W a t e r Act exists no limiting value for thallium. For comparison the limiting value for lead is indicated i n line 3 (table 7 ) instead. Under this precondition the maximum thallium concentration is 8 times smaller than the limiting value of lead. It is w o r t h to note that identical limiting values for C r and Hg are also mentioned i n the Drinking Water Act of the Netherlands [36] as well as i n the European Drinking Water Act [37]. The tables also demonstrate that the element concentrations i n the leachates decrease with decreasing w / c r a t i o , e v e n i n the case of leaching w i t h water containing very high amounts o f aggressive c a r b o n dioxide. The heavy metal concentrations i n the leachates are extremely l o w if only drinking w a t e r of quite normal composition is used for elution and if the concretes are n o t artificially doped w i t h remarkably higher heavy metal concentrations.

6 .

CONCLUSION

From these experimental results the conclusion m a y be drawn that the utilization of concrete i n the sensible field of drinking w a t e r is harmless a n d , therefore, compatible w i t h the

3 84 environment and human health. The leaching of heavy metals depends i n the first line on the density of the concrete structure, given by the water cement ratio and the curing conditions. W i t h i n a concentration range for C r , H g , and T1 w h i c h is known f r o m experience with the utilization of different kinds of additives the leaching is - besides a first surface wash-off effect - diffusion controlled and within a fairly wide range independent from the heavy metal concentrations or from the amount per m 3 of concrete. Taking into account the calculated coefficients of diffusion e.g. for chromium the time to pass for leaching the limiting value of 5.exp.-2 mg/9 i n a stationary concrete reservoir for drinking water will take about 2 300 years. This calculation is based on the assumption that the concrete is impermeable to water and the penetration depth of moisture is 2 c m , utilizing the highest diffusion coefficient value of l . e x p . - 4 cm2/s. Under practical conditions with a steady exchange of water from the reservoir the actual Cr-concentrations are. therefore, far below the chemical detection limit. Similar results can be expected for other, still l e s s soluble heavy metal compounds i n the cement c l i n k e r , interground pozzolanas and granulated blast furnace slag as well.

7. REFERENCES 1

Gesetz Uber die Vermeidung und Entsorgung von Abflllen (Abfallgesetz-AbfG) v. 27.8.1986, BG B1. Teil 1 , 1410.

2

S. Sprung, Zement-Kalk-Gips, N o .

3

S. Sprung and W. Rechenberg, Verfahrenstechnik der Zementherstellung, Proc. VDZ-Kongress '93, DUsseldorf. 27.9.-1.10.93, i n press

4

S. Sprung, Zement-Kalk-Gips, No. 5 (1988) 251.

5

Forschungsinstitut der Zementindustrie, Tltigkeitsbericht 1 9 9 0 - 1 9 9 3 , DUsseldorf (19931, 3 7 .

6

S. Sprung and W . Rechenberg, beton, N o .

7

S. Sprung and W. Rechenberg, Zement und B e t o n , N o . 2 (1989) 54.

8

W. Rechenberg and S . Sprung, Abwassertechn.. No. 3 (1990) 24.

9

W. Rechenberg and S. Sprung i n B. Bohnke (ed.) GewPsserschutz, W a s s e r , Abwasser. Bd. 118, G e s . Ford. Siedlungswasserwirtschaft, Aachen, 1 9 9 0 , 178.

5 (1992) 213.

5 (1988) 193.

385 10

W . R e c h e n b e r g , S . Sprung and H . - M . S y l l a , Proc. I n t e r n . Conf. Environm. Implications Constr. Waste Mater., M a a s t r i c h t , The Netherlands, 1 0 . - 1 4 . 1 1 . 1 9 9 1 , 3 0 1 .

11

DIN 3 8 4 1 4 , Teil 4 ( 1 0 . 8 4 ) . Deutsche Einheitsverfahren z u r W a s s e r , Abwasser- und Schlammuntersuchung. Schlamm und Sedimente (Gruppe S): Bestimmung der Eluierbarkeit n i t Wasser ( S 4 ) , Berlin-KOln.

12

H . G r u b e r , G I T Fachz. L a b . , N o . 7 ( 1 9 8 4 ) 6 0 3 .

13

W . R e c h e n b e r g , G. Spanka and G. T h i e l e n , beton, No. 2 ( 1 9 9 3 ) 7 2 and No. 3 ( 1 9 9 3 ) 1 2 2

14

W . Rechenberg and G . Spanka in: 6sterr. Bundesmin. U m w e l t , Jugend und Familie (ed.); Proc. RILEM-Workshop, Mittlg. Forschungsinst. VSZ 4 2 , W i e n ( 1 9 9 2 ) , 21.

15

American Nuclear Society (eds.), American Standard M e a s u rement of the Leachability of Solidified Low-Level Radioactive Wastes by a Short-Term Test Procedure, Amer. Nucl. S O C . La Grange P a r k , It, 1 9 8 6 .

16

G. D i d e r i c h , C . K i r p a c h , N. Kirsch. R. Schmit and A. W a g n e r , VGB Kraftwerkstechn., No. 11 ( 1 9 8 9 ) 1 1 3 2 .

17

E.D. H e s p e , Atom. Energy R e v . , No. 1 ( 1 9 7 1 ) 1 9 5 .

18

W.A. R o s s , J.H. W e s t s i k , F.?. Roberts and C.C. H a r v e y , Ceram. Bull., No. 9 ( 1 9 8 3 ) 1 0 2 6 .

19

S . S p r u n g , W. Rechenberg and G. Bachmann, Verfahrenstechnik der Zementherstellung, Proc. VDZ-Kongress '93. D U s s e l d o r f , 27.9.-1.10.1993, i n press.

20

E N V 1 9 7 . Teil 1 ( 1 2 . 9 2 ) : Zement. Zusammensetzung, Anforderungen und Konformitltskriterien. Teil 1: Allgemein g e brluchlicher Zement. German version ENV 1 9 7 - 1 : 1 9 9 2 . Berlin-KOln.

21

H. P i s t e r s , Z e m e n t - K a l k - G i p s , No. 10 ( 1 9 6 6 ) 4 6 7 .

22

VDZ-Arbeitskreis "Analytische C h e m i e " , Bestimmung v o n Spurenelementen in Stoffen der Zementherstellung, Schriftenreihe der Zementindustrie, H. 5 5 , Dlisseldorf, 1 9 9 3 .

23

DIN 1045 ( 0 7 . 8 8 ) , Beton und Stahlbeton. Bemessung und A u s fUhrung. B e r l i n - K O l n , 1 9 8 8 .

24

N.N. Mitteilungen aus d e n Bundesgesundheitsamt, Bundesgesundh.-B1. No. 9 ( 1 9 7 7 ) 1 2 4 .

386 25

F.W. Locher, beton, N o . 1 (1967) 17 b e t o n , No. 2 (1967) 47 and Betontechn. Ber. 1 9 6 7 , Beton-Verlag DUsseldorf 1 9 6 8 , 19.

26

F.W. Locher and S. S p r u n g , beton. No. 7 (1975) 241 and Betontechn. Ber. 1 9 7 5 , Beton Verlag, DUsseldorf 1 9 7 6 , 9 1 .

27

F.W. L o c h e r , W . Rechenberg and S. Sprung, b e t o n , No. 5 (1984) 193 and Betontechn. Ber. 1 9 8 4 / 8 5 , Beton V e r l a g , DUsseldorf 1 9 8 6 , 41.

28

DIN 4 0 3 0 , Teil 1 (06.91), Beurteilung betonangreifender W l s s e r , BOden und Gase. Grundlagen und Grenzwerte, Berlin-KOln.

29

H. Grube and W. Rechenberg, beton No., 11 (1987) 4 4 6 , beton, No. 1 2 (1987) 4 9 5 and Betontechn. Ber. 1 9 8 6 - 8 8 , Beton Verlag, DUsseldorf 1 9 8 9 , 117.

30

W. Rechenberg, in: 6sterr. Bundesmin. Urnwelt, Jugend und Familie ( e d . ) ; Proc. RILEM-Workshop, Mittlg. Forschinst. VbZ 4 2 , Wien (1992) 26.

31

R.H. Rankers and I. H o h b e r g , Waste Mater. Constr., Proc. Intern. Conf. Environrn. Implic. Constr. Waste Mater., Maastricht 1991.

32

Inst. f . Bauforschung, Forschungsbericht "Umweltvertrlglichkeit v o n zernentgebundenen Baustoffen", Sachstandsbericht F 366. RWTB Aachen, Aachen 1991.

33

W. J o s t , Diffusion i n Solids, Liquids, G a s e s , 2 . Ed. Academic P r e s s , Publishers, New Y o r k , 1955.

34

W. Rechenberg and G . S p a n k a , in preparation

35

Verordnung Uber Trinkwasser und Uber Brauchwasser fur Lebensmittelbetriebe, Fassung BGBl., Teil 1 , Nr. 2 2 ( 1 9 8 6 ) 7 6 0 , gelndert BGBl., Teil 1 , Nr. 6 6 , Bonn, 1990.

36

Besluit v a n 2 april 1 9 8 4 , hondende wijziging van het waterleiding besluit (Stb. 1 9 6 0 , 345). Staatsblad van het koninkrijk der Nederlanden, Jaargang 1 9 8 4 , 2 2 0

37

Richtlinie des Rates v o m 15.7.1980 Uber die Qualitlt von Wasser fur den menschlichen Gebrauch. Arntsbl. Europ. G e meinsch. No. L 2 2 9 / 1 1 - 2 9 v. 30.8.1980.

Environmental Aspects of Consbuction with Waste Materials JJJ.M. Goumans, H A . van der SImt and Th.G.Aalbers (Editors) 01994 Elsevier Science B.V. AN rights resewed.

387

LEACHING PROPERTIES OF CEMENT-BOUND MATERIALS

I . Hohberg, R. Rankers Institute for Building Research, Aachen University of Technology, Germany

ABSTRACT Only limited knowledge of the potential environmental impacts of construction materials with or without so-called "secondary raw-materials materials" is available. In order t o evaluate the environmental impact from the use of secondary raw materials in cement-bound materials it is necessary t o aquire an understanding of the leaching properties of the contaminants. These data can be obtained only by means of leaching tests carried out in the laboratory. The aim of our study is t o gather information on the leaching properties of cement-bound materials. For this purpose hardened cement paste and mortar specimens were prepared using different coal fly ashes approved as concrete addition. The elemental compositions of cement and fly ashes were determined. Various leaching tests were subsequently performed on the fly ashes, hardened cement pastes and mortars, t o determine the influence of test method and concrete technology parameters on the leaching rate.

1

INTRODUCTION

Potential environmental pollution from cement-bound building materials with and without industrial by-products is linked mainly to the leaching of heavy metals and/or harmful salts by water, e.g. rainwater or groundwater, possibly leading to environmental pollution. To prevent environmental impact, information on a product's time-dependent leaching behaviour is required before it is used. These data can be obtained only by laboratory leaching tests. Leaching tests attempt to reproduce natural conditions and simulate specific influencing variables. It is then possible t o assess long-term leaching behaviour by elucidating the leaching mechanisms. Numerous leaching methods are currently in use 141. Methods o f chemical analysis have also become simpler and more accurate, allowing contaminants t o be detected at any desired low concentration. This often leads to results with no common basis of comparison, causing public confusion. In order t o achieve a standardized, reproducable and practice relevant test method reflecting the leaching behaviour of cement-bound building materials, a closer study of the influence of test and technology parameters on leaching rates is required.

388 The following parameters influence the leaching rates of heavy metals and salts from cement-bound materials /4,2/:

-

-

kind of used test method (investigation of specimens with real dimensions or o f ground up samples) grain sizelspecimen size, liquid/solid ratio ( = L/S), leaching rate -L/S, pH value of the leachate, composition of the leachate, leaching time, temperature.

The choice of test method plays a significant role. Depending on the purpose different methods should be used. Leaching tests with ground up material are only useful to examine the chemical fixation o f a material but not in order to judge lond-term leaching behaviour under practice relevant conditions. In this case practice related leaching tests, with specimen dimensions close to reality must be performed. The grain size of ground material or the specimen size, and particularly the surface/volume ratio, influence the leaching rate to the extent that the greater the surface available t o the leachate, the greater will be the contaminant concentration in the eluate. The differing distributions o f the trace elements at different grain sizes also play a significant role. The leaching rate in batch tests (with ground material) is directly proportional to the liquid/solid ratio ( = L/S). This means a time axis can be represented by variation of the L/S ratio. The pH-dependence of the leaching rate is due to the different solubilities of the heavy metal ions at different pH values. The leaching rate is, however, affected not only by the pH value of the leachate but by the buffer capacity of the solid material (e.g. hardened cement paste) itself, which changes the pH value of the leachate; the chemical composition of the material to be leached is therefore significant. The composition of the leachate is particularly important if leaching media other than the usually used demineralized water or synthetic acid rain are employed. Buffer solutions and leachates with differing redox potentials require attention in this context. Temperature has a great influence on the leaching rate, since the reaction rate increases exponentially with temperature.

In cement-bound materials, the following technology parameters have a particular impact on the leaching rates: - waterkement ratio (w/c ratio),

389 - degree of hydration, - degree of carbonation.

As shown above different testing conditions lead inevitably to strongly differing results. For example results from ground up samples will differ considerably from results obtained under practice relevant test conditions. Leaching tests with parameter variations were performed to allow more detailed investigation of the effects of the various parameters on the leaching rate in cement-bound materials. Initial attention was concentrated on the method-relevant parameters rather than the concrete technology parameters. A report describing the influence of concrete technology parameters will be issued shortly.

2 2.1

TESTS General

In the first stage of the investigations ground material was studied. Main emphasis was layed on the first stage of the test programme determined the influence of leaching time and of the pH value and grain size of the leached material on maximum leaching rates. Maximum leaching rates were determined in accordance with the Netherlands standard NEN 7341 131, maintaining a constant pH value of the leaching medium throughout the leaching time. Details of the method employed and evaluation of the analyzed data are described in 141. All eluates were examined for their Cr, Co, Ni, Cu, Zn, Cd, Pb, Hg, As and TI content. Results are illustrated by selected examples. First results of practice relevant leaching tests from the second stage of the test programme will be shortly presented in section 2.6.

2.2

Materials

On the basis of chemical analyses, a cement with medium trace element content was selected from various Portland cements for the test programme. Different fly ashes with the attestation of conformity were analyzed for trace element content and t w o fly ashes were selected for the programme. Three hardened cement pastes were made up The w l c ratio or w/(c+O.5 f) of the hardened cement pastes was 0.5, fl c = 0.25 in each case. The binder content was equal for all samples. T w o mortar mixes were also included in the test programme. Table 1 shows the designation and table 2 indicates the trace element contents of the selected materials.

390 Table 1;Designation of materials

Table 1: Trace element contents of materials used in the test programme

22 MO

M1

2.3

61 11 69

504 194 259

2.4 0,4 1,2

141 42 53

13 9 21

300 79 185

66 5 17

78 10 18

21

30 35

0,4

< 0,4

< 0 , 1 <0,4

0.3

< 0,4

Influence of Leaching Time

To determine the influence of leaching time on the amount of leached trace elements, the fly ash with higher trace element content (FA 1I was studied. The material was sifted to a grain size < 125 p. The following leaching times were selected: 1 h, 2 h, 3 h, 4 h, 5 h and 24 h. The pH value was kept constant a t pH = 4 throughout the leaching time. Fig. 1 shows test results for arsenic, zinc and chromium.

391

60 40 20

0

Fia. 1: Influence of leaching time on the amounts of leached trace elements FA 1 Generally, the highest amount of each trace element has been leached out already after a short time (after 1 or at latest 4 hours). Unlike the rates for the other trace elements, the leaching rates for arsenic fell sharply with increasing leaching time. Arsenic appears to form insoluble compounds with other salts leached over the course of time. On the basis of the results, leaching time in subsequent tests was limited to one hour.

2.4

Influence of pH on the leaching results

To check the influence of the pH value on the amounts of trace elements leached out of the samples, the material was ground to a grain size < 125 p, the leaching method was carried out at the following four pH values: pH pH pH pH

= 2, = 4, = 7, = 12.

The PC 35 Portland cement and the t w o fly ashes FA 1 and FA 2 were investigated first. Fig. 2 shows the percentage of the amounts leached after one hour from the total content of trace elements for the t w o fly ashes. The percentage gives the leachable (or soluble) fraction of the elements under given conditions. As expected, the highest percentages were attained at pH = 2. The leaching amounts declined with increasing pH value; only very slight leaching amounts were detected for the various elements at pH = 12. Significant quantities of arsenic and zinc are, however, still detected at pH = 12, due to the relatively

392 good solubility of these elements a t high pH values (amphoteric behaviour).

Fly ash FA 1

Fly ash FA 2

Fia. 2: Influence of pH on the leachable fractions (leaching time 1h) The pH-dependence of maximum leaching rates for the hardened cement pastes Z 0, Z 1 and Z 2 got investigated next. Results (percentage of amounts leached after one hour from total content) for arsenic, chromium and zinc are shown in Fig. 3. Generally, for the three elements arsenic, chromium and zinc, at pH = 2 high amounts of the different elements were leached out. Specially for Chromium and zinc the leachable fraction are high in relation to the fly ashes. This indicates that most of the leachable chromium and zinc comes out of the cement. For arsenic the leachable fraction is greater than expected from the values of FA 1 and 2 0. Probably a chemical reaction took place, which mobilize the arsenic from previously insoluble compounds. With increasing pH the leachable fractions decrease extremely caused by chemical fixing / I '6'71, due to the forming of insoluble salts. This is not valid for chromium. The percentage of leachable chromium is relatively high a t pH-values from 2 to 7. The most of the chromium seems to come from the chromium content of the cement. The fly ash has a rather positive effect on the leached chromium amounts of the hardened cement paste. The results indicate that fixing by a cement matrix as well as chemical reactions in the hardened cement paste can be assessed to some extent by comparing the leaching rates for the elements in a hardened cement paste matrix and in the non-bound state. Comparing the leachable fraction from FA 1 and hardened cement paste 2 1.

393

% of

con

100 80 60 40

20 0 Hardened cement paste Z 0

Zn

%

% of total

C

content

I

100 80 60 40 20

H=2 4

0 Hardened cement paste Z 2

Hardened cement paste Z I

Fia. 3: Influence of pH on leachable fractions (leaching time 1h)

2.5

Influence of Grain Size

In order to determine the influence of grain size on the maximum leaching rate, studies were made at a constant pH value of pH = 4 and a leaching time of 1 hour. The hardened cement pastes 2 1 (hardened cement paste with fly ash FA 1) and 2 2 (hardened cement paste with fly ash FA 2) were investigated. The w/c ratio or w/(c 0.5 f) was 0.5. The hardened cement pastes were ground at an age of 28 d and the following grain size fractions classified:

+

0.500 - 1.OOO mm, 0.125 - 0.500 mm, 0.063- 0.125 mm, 0.000 - 0.063 mm. Fig. 4 shows the test results for arsenic, zinc and chromium.

394

100 -

50 -

r

hardened cement paste 2 1

0,5-1 rnm

0,125-0,5 0.5-1

hardened cement paste Z 2

mm

Fia. 4: Influence of on grain size on the leaching rates (leaching time 1 h) As expected, leaching rates rise with decreasing grain size. Only in the case of arsenic there was a fall in leaching volumes with declining grain size. This correlates with the test results for the time-dependence of leaching. Arsenic appears to form insoluble compounds during the leaching time, causing a fall in the leaching volume with increasing leaching time. These compounds are apparently formed more rapidly at smaller grain sizes, explaining the behaviour of the arsenic.

2.6

Concluding Tests

As reported in 141, the dominant leaching mechanism with cement-bound construction materials is diffusion. Apart from determination of maximum leaching rates, practice-oriented leaching tests (tank tests) are required when studying cement-bound materials, in order to reflect practical conditions. In tank test mortar or concrete specimen with real dimensions are placed into a container which is filled with the leachate so as to allow direct contact with the leachate on all sides. The leachant is renewed at several intervals (s. 141).The tank tests allow t o determine the influence of concrete technology parameters. Tests of this nature will be performed in the second stage of the research programme. Results will be published shortly 151. Different leaching methods were compared in preliminary tests, to obtain an impression of their effects on the leaching rate. Fig. 5 shows results for the mortar M 1, Details of the method are given in 141.

395

mgl

200 I00 3tal content ed amounts after 1h at pH = 4 (ground material) leached amounts after 40 days)

0 Mortar M 1

Fia. 5: Comparative results with different methods

As will be evident, leaching volumes determined in practice-oriented tests are much smaller than maximum leaching volumes. This is due to the very small available surface, reflecting real conditions during use of a structure. Maximum leaching rates typify the case after demolition of a construction (and possible treatment of the concrete) or conditions during storage of the constituents of concrete (like aggregates or additions). 3

CONCLUSIONS

The tests presented in the paper confirmed the pronounced influence of the test parameters (leaching time, pH value of the leachate, grain size of the material) on leaching rates. Results are applicable to other leaching tests. These test parameters should be specified precisely in a standardized universal method. The influence of concrete technology parameters on leaching rates (w/c ratio, hydration age, degree of carbonation) will be investigated in further tests. The dominant leaching mechanism for cement-bound construction materials is diffusion of compounds out of the building material to its surface. This mechanism should be taken into account in describing the leaching behaviour of cementbound materials under practical conditions, i.e. investigation should be mainly by means of tank tests. Determination of maximum leaching rates will remain necessary, since the leaching behaviour of the construction materials during storage on the construction site and following demolition of the structure also need to be allowed for. A standardized test method determining the leaching behaviour of cement-bound materials should therefore consist of a system combining the following tests: - determination of the total content of environmental-relevant materials, - determination of maximum leaching rates on the ground building material, - practice-oriented leaching tests.

396 4

REFERENCES

/I/

Bishop, P.L. ; Gress, D.L. ; Olofsson, J.A.: Cement Stabilization of Heavy : Annual Arbor Science Metals: Leaching Rate Assessment. M i c h i g a r " Publication, 1982- In: Proceedings of Mid-atlantic Industrial Waste Conference 14th, S.459-467 /2/ Hohberg, I. ; Rankers, R.: Bestimmung der Umweltvertraglichkeit von zementgebunden Baustoffen - Methoden und Mechanismen. Dusseldorf : VDI-Verlag. - In: VDI-Berichte (19931, Nr. 1060, S. 193-204 /3/ NEN 7341 (Draft): Leaching Characteristics of Building and Solid Waste Materials : Leaching Tests : Determination of the Availability of Inorganic Components for Leaching /4/ SchieRl, P. ; Rankers, R . ; Hohberg, I.: Umweltvertraglichkeit von zementAachen : lnstitut fur Bauforgebunden Baustoffen - Sachstandsbericht schung, 1991. - Forschungsbericht Nr. F 366 /5/ SchieRI, P. ; Hohberg, I.: "Umweltvertraglichkeit von zementgebundenen Baustoffen : Untersuchungen zum Auslaugverhalten von sekundaren Baustoffen. Aachen : lnstitut fur Bauforschung, - Forschungsbericht Nr. F 414 (Veroffentlichung in Kurze) 161 Sprung, S ; Rechenberg, W: Einbindung von Schwermetallen in Sekundarstoffen durch Verfestigen mit Zement. In: Beton 38 (19881, Nr.5, S.

-.

193-191 171 Uchikawa, H ; Tsukivama, K. ; Mihara, Y.: Uber die Binduna schadlicher Elemente durch einen hochwertigen Spezialzement. In: Zemgnt Kalk Gips 31 (19781, Nr. 4, S. 195-203

Environmental Aspects of Construction with Waste Materials JJJM Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) 61994 Elsevier Science B. K All rights reserved.

397

European standardization of additions for concrete J.M.J.M. Bijen Professor of Materials Science, Delft University of Technology, P.O. Box 5045, 2600 GA Delft, The Netherlands President of Intron, Institute for Materials and Environmental Research, P.O. Box 5187, 6130 PD Sittard, The Netherlands

Abstract The development of the European standards and Technical Approvals for the use of additions (mineral admixtures) in concrete is described. In the European standards current practices in various European countries will be harmonized. European Technical Approvals will make accessible markets for special application of concrete containing additions.

1. INTRODUCTION The European Community is aiming at one market. Harmonized standards all over the community are regarded mandatory for such unified market. The European Standard Organization CEN (Comiti europten de Normalisation) has a mandate of the Commission of the European Community to draft such a harmonized system of standards. According to the Construction Products Directive (1989) products, when incorporated into permanent works, have to meet six so called "Essential Requirements". These requirements relate to health, safety and energy economy, depending on the intended use of product. Standards have to be focussed on these requirements. Products which meet the European standards will in future get the CE mark. The CE mark can also be obtained for products with a European Technical Approval. European Technical Approvals can be granted to products by notified bodies approved by the European Technical Approval Organisation (EOTA). This relates to specific products, often newly developed, for which the drafting of standards is too cumbersome and whose characteristics are beyond the limits of the existing standards. The paper describes the standards and Technical Approvals developed for additions (mineral admixtures) in concrete and presents the present practice in the various states of the European Community.

398

2. FRAMEWORK FOR STANDARDIZATION OF ADDITIONS The European standardization aims at harmonization. That means that it will not change the common practice in the various member states but rather harmonize the current procedures in countries to arrive at that practice. With respect to additions in concrete there are two crucial points: the drafting of a product standards for additions as a constituent of concrete and the production of the standard for concrete itself. The latter concerns the way the additions are taken into account in the concrete composition. In 1989 a prestandard was approved, EN 206 - concrete, performance, production, placing and compliance criteria. This prestandard is not mandatory; existing relevant national standards need not be withdrawn, but stay valid. At present CEN TC104 SC1 is working on the definitive standard which will be mandatory in the European Community Countries. It has been decided that the present prestandard for concrete will be split up into separate standards for execution and for concrete technology. In ENV 206 the use of additions (mineral admixtures) is allowed but it leaves open to national rules the way these additions are taken into account in the concrete composition, notably in the minimum cement content and the maximum waterlcement ratio; these are the boundary limits in the ENV 206 for various environmental classes. To cope with this specific point CENT TC104 SC1 has appointed a taskgroup (TGS) which had to submit proposals on how to take fly ash and other additions (mineral admixtures) into account in the minimum cement content and waterlcement ratio. The taskgroup has formulated its recommendations recently. The standard for fly ash as a constituent for concrete EN 450 "fly ash in concrete" has been finished and is expected to be approved shortly. The standard for micro-silica is ready as a draft.

3. SURVEY OF USAGE ADDITIONS IN VARIOUS EUROPEAN COUNTRIES An estimate of the annual tonnages of additions to concrete used in the participating countries is given in Table 1. It is clearly seen that fly ash from bituminous coals combustion is most widely used in Europe. Ground granulated blast furnace slag is only used in substantial quantities as an addition to concrete in the U.K., but is incorporated on a massive scale in composite cements in other European Countries, notably Germany, the Netherlands, Belgium and France. In France ground limestone filler is used not only for composite cements but also as an addition to concrete. Micro-silica is used particularly in the Nordic countries. In general four methods exist for taking additions into account in the determination of the cement content and waterkement ratio. These are: a fixed equivalence value (k-value) (i) on top of a fixed value a higher value is allowed if test results prove the e(ii) quivalence in particular applications (iii) an addition is allowed to a certain amount as long as tests are made proving the equivalence between concrete compositions with additions and those without additions. In this performance concept, compressive strength equivalence is commonly used as the criterion

399

(iv)

equality for additions against cement if the combination complies with the appropriate composite cement standard (only UK).

Table 1 Estimate of the annual tonnages of additions to concrete in various European countries (exclusive of utilization in composite cements) (1992) country

natural pozzolans

Austria Belgium Denmark Finland France Germany Italy Netherlands Norway Portugal Spain Sweden UK

* occ.

fly ash

microsilica

slag

80,000 100,000 100,000

occ . 25,000 50,000

limited

200,000 340,000

17,000

1

occ. *

30,000-

50,000

lime-stone filter

5,000 450,000

1,800,000

limited

100,000 35,000 95,000 900,000 10,000 1,040,000

occ . 17,000

25,000 1,000

,

1,000 900,000

I

= occasionally

A number of European countries use fixed compressive strength based equivalence factors, also called efficiency factors or k-values. These factors express the cement equivalent part of the addition with respect to its contribution to compressive strength development. For cement content it may be read:

cement

+ k * addition

and for the waterkement ratio

water/(cement

+ k * addition)

The amount of addition to be taken into account is restricted.

4. THE WAY FLY ASH IS TAKEN INTO ACCOUNT IN VARIOUS COUNTRIES In Table 2 a survey is given of the way fly ash is taken into account in the various European countries.

400

Table 2 The way fly ash is tal en into account in vari, i s Europe in countric i :ement :lass

maximum waterlcement ratio

Greece

I? not allowed

Netherlands

I k'=0.2

I

ENV197

?

not allowed

-

k=0.2

CE-I

I Norway

k=0.3

no requirement

CE-I

Portugal

not allowed

not allowed

-

Spain

not allowed

not allowed

-

Sweden

L k=0.3

maximum amount to be taken into account** f/c +f

maximum amount total f/c+f

wing

?

?

?

232.5

25%

232.5

same as in standard for Portland fly ash cement BS6588 or BS6610

1

rules

extra curing time not rewired

no requirements minimum cement con-

United Kingdom

no requirement

no requirements minimum cement content

* **

= efficiency, also called cement equivalence factor cement type adjusted to pr EN 197 cement

k

In a number of countries fly ash is not allowed to be taken into account. However, other countries use the k-value concept, e.g. Belgium, Denmark, Germany, the Netherlands, Norway and Sweden. In the UK and Finland, where there are no requirements regarding minimum cement concrete or maximum waterlcement ratio in the national concrete standards, the way fly ash is taken into account is different. In Finland up to 40% of the

40 1 cement can be replaced and the allowable concrete composition is dependent on strength only. In countries where the k-value is used this varies between 0.2 and 0.5. In analysing the backgrounds for these differences it becomes clear that differences in fly ash quality and the type of cement are the reasons, e.g. in Denmark (k = 0.5) only cement similar to CE-I class 42.5 - rapid hardening Portland cement according to draft ENV 197 Cement (1991) - is used, while in the Netherlands (k = 0.2) also CE-I class 32.5 (ordinary Portland cement) is involved. It is known that with rapid hardening cements pozzolanic activity develops faster than with slower hardening cements of the same type, as shown in figure 1 [l]. In Germany prolonged curing of concrete is required when fly ash is taken into account relative to plain concrete of the same 28-day strength in order to compensate for the retardation in early strength development. In the Netherlands the k-value is based on 7 days compressive strength and no prolonged curing is mandatory. The maximum amount of fly ash to be taken into account varies between 20% and 40% of the total of cement fly ash. In the UK concrete compositions are allowed if the rate between Portland cement and fly ash corresponds to that of the British standard for Portland fly ash cement, provided these fly ash-cement compositions meet the requirements in these cement standards (BS 6588 or BS 6610). In the UK this is tied up with a technical approval and certification system.

+

- OPC

----.

RHPC

........-

OPBFSC

currd lor 7days

undrr watrr f20 'Cl

fly ash A PFAK

0-33

:

Figure 1. Efficiency factor of fly ash A as a function of the waterlcement ratio [ l ] RHPC = rapid hardening Portland cement OPBFSC = Portland blast furnace slag cement (65 % slag).

402 5. THE WAY OTHER ADDITIONS ARE TAKEN INTO ACCOUNT IN VARIOUS COUNTRIES 5.1. Micro-silica

The usage of micro-silica (silica fume) is most developed in the Nordic countries. Kvalues of 1.0 (Norway-Sweden)up to 2.5 (in Finland) are used. Table 3 shows a survey.

5.2. Ground granulated blast furnace slag Ground granulated blast furnace slags are used as an addition to concrete in: Finland : same rules as for fly ash : very limited use Sweden United Kingdom : same procedure as for fly ash but with BS 146 "Portland Blast Furnace Cement" as a reference In other countries there is a substantial use of portland blast furnace slag cement but no use of ground granulated slag as an addition to concrete.

5.3. Natural pozzolans In Germany trass is used as an addition to concrete. Natural pozzolans are not taken into account regarding maximum water-cement ratio and/or minimum cement content. 5.4. Limestone filler

Limestone filler is applied in substantial amounts in France, but up to now it has not been taken into account regarding waterlcement ratio.

F

Table 3 The wav mic .osilica is taken into account in various EuroDean coun :ies (1991) increase of maximum waterlcement ratio

Austria

I reduction of maximum maximum minimum cement amount to be amount content taken into total account

Belgium

Denmark

k=0.2

for minimum cement content I

I

I

I

can be used together with other additions

403

increase of maximum waterkement ratio

reduction of maximum maximum curing minimum cement amount to be amount content taken into total account

remarks

for max. w.c.f.

no requirement for minimum cement content

k-value of 2.5 is applied

k=O.O

not allowed

France

Italy Netherlands Norway

k= 1 .O or higher no requirement for minimum if proved cement content

Portugal

-

Spain

I-

higher kvalue has to be documented

Ino requirement for minimum cement content

United Kinedom

6. EUROPEAN STANDARDS FOR FLY ASH, MICRO-SILICA AND CEMENTS The standard for fly ash as a constituent for concrete EN 450 will be approved shortly. The standard covers fly ash from flue-gasses of furnaces fired with pulverized anthracite or bituminous coal. The various requirements are summarized in Table 4.

test standard

LO1

1 5 . 0 % by mass

EN 196-2

CI

50.10% by mass

EN 196-21

404

Table 4 continued Requirements of EN 450 fly ash for concrete

5 3.0%by

5

mass

EN 196-2

1.0%by mass

EN 451-1 EN 451-2 EN 196-1 EN 196-3

by mass fly ash 50% by mass reference

A specific requirement is the activity index. This is the ratio of the compressive strength of standard mortar bars, prepared with 75 % reference cement plus 25 % fly ash by mass, to the compressive strength of standard mortar bars prepared with reference cement alone, when tested at the same age. The cement is a Portland cement of type CEM-I, strength class 42.5, conforming to pr ENV 197 Cement. Fly ashes meeting EN 450 will be allowed to be used in concrete manufactured in accordance with EN 206. For silica fume a standard is drafted. This standard will essentially be similar as the Norwegian standard. The European prestandard ENV 197 Cement defines the various cements. Table 5 shows a survey. A vast amount of cements is used in Europe and most are covered by this prestandard. Obviously the performance of fly ashes can be quite different form one type of cement to the other. With some cements hardly any pozzolanic reaction will occur. Most data with fly ash relate to the combination with Portland cements, CEM-I. Limited data are available for other cement types. Some countries have experience with blends of fly ash and slag cement, CEM-IIIA-S and B-S and CEM-IIIIA and B (see Table 5). 7. EUROPEAN TECHNICAL APPROVALS

Construction products in the European community must meet fundamental requirements concerning health, safety and energy economy. Apart from European standards The Construction Products Directive also accepts products which have a European Technical Approval. Such an approval is a declaration that the product is fit for its purpose. The approval can be awarded for a specific product from a specific manufacturer. To get such an approval the product must meet the requirements specified in an Technical Approval Guideline. The approval can be granted by a notified Technical Approval Body which has been approved by the European Technical Organization, EOTA. Standards and Technical Approval Guidelines can be seen as two parallel routes; one for a generic range of products and the second for specific products from specific manufacturers.

405

8. PROPOSALS ON HOW TO TAKE ADDITIONS INTO ACCOUNT IN CONCRETE COMPOSITIONS ACCORDING TO EUROPEAN CONCRETE STANDARDS ENV 206 defines additions of type I1 as one with latent hydraulic or pozzolanic properties.

Table 5 . Cement types and composition: Proportion by mass') pr ENV 197 Cement

TG 5 was charged with developing a scheme based on additions could be considered andlor taken into account. So far, the task group has been concerned mainly with fly ash. The general objective behind the scheme for calculating additions based on their waterkement ratio and minimum cement content is to obtain a concrete made with those additions that will match the performance of the relevant standard concrete types for a

406 given environmental exposure class. For this, TG 5 has provided two different concepts. Concept A contains the k-value method as used in many European countries for fly ash and micro-silica. Concept B provides that only certain cornerstones are to be established in EN 206 and that the actual technical details are to be left to the European technical approvals or separate standards. In concept A, the addition content is multiplied by the k-value and is then integrated into the appropriate formulas for the waterlcement ratio and the minimum cement content. 8.1. k-value

With respect to concept A (the k-value) it is recommended for fly ash to consider only the CEM-I cements (Portland cements). For other cements, national rules valid in the place of use of the concrete should be used. EN 206 shall refer to these national documents. The range of values considered for CEM-I is 0.2-0.6. A fiied k-value has to be decided upon. The amount of fly ash to be taken into account shall meet the requirement: fly ash/(cement

+ fly ash) 50.25

With respect to the cement content it is suggested to replace the term cement in ENV 206 by cement

+ k * fly ash

or a fixed maximum reduction of the minimum cement content (X) should be applied min. cement - X With respect to the waterlcernent ratio this should be replaced by water/(cement

+ k * fly ash)

For silica fume k-values are considered for CEM-I cements varying from 1 to 2. 8.2. Cornerstones in equal performance procedures Although the k-value concept is simple and easy to be used in practice, it is not very discriminative between the better concrete-addition composites and the lesser ones. Especially there appears to be a very broad band with respect to the contribution fly ash makes to the development of concrete properties [as illustrated e.g. in figure 1. The kvalue ranges in this case from higher than 1 for a low waterlcement ratio and rapid hardening portland cement to 0.2 for a water cement ratio of 0.6 and higher. Other important influencing factors are the cement source, especially with respect to alkalinity, the fly ash source and the temperature. Therefore in practice a very much better performance of fly ash could be found as is suggested by a general k-value of say 0.3. To cope with this aspect the taskgroup has proposed comer stones which are the basis

407 for further standards and/or technical approvals. The cornerstones are applicable to specific fly ashes (meeting EN 450) with specific cements (meeting EN 197) of which manufacturing source and characteristics are clearly defined and documented. They provide the basis to assess the equivalence of performance based on a comparison of characteristic values or properties. This assessment should be made following procedures laid down in either CEN standards, annexes to EN 206 or European Technical Approval guidelines which refer to these cornerstones. The equal performance has to be approved by notified Certification or Technical Approval Bodies. The production of concrete compositions according to these procedures shall be subject to continuous quality assessment. Two methods are distinguished. Cornerstones of both of these methods are recommended to be implemented in EN 206.

Method I . Concrete properties equivalence (A) Test@) shall be carried out which demonstrate(s) that the concrete containing the specific fly ash (in accordance with EN 450) and the specific cement (in accordance with EN 197) meets the requirements for the relevant exposure class. These requirements are: - a characteristic compressive strength at 28 days of cubes or cylinders cured according to EN .. . of at least X, (cubes) respectively Y, (cylinders) for plain concrete and of X, respectively Y, for reinforced and prestressed concrete; - for reinforced and prestressed concrete a characteristic carbonation resistance according to EN ... not less than P. For concrete compositions of fly ashes with CEM-I cements according to ENV 197 tests for carbonation are not required; - a frost thaw deicing salt resistance according to EN ... at least as good as Z. N.B. X,, X,, X,, X,, P and Z are &ed values, to be defined. The range of compositions for which this (sub) procedure is applicable is restricted as follows: - The total amount of blending agents (in the cement and added to the mix) shall be within the limits given in EN 197 for the corresponding cements to be used according to EN 206 for the relevant exposure class. - The sum of fly ash and cement shall be at least as great as the minimum content according to table 3 of EN 206 for the relevant exposure class(es). - The water/(cement + fly ash) ratio shall not be greater than the maximum watedcement ratio for the relevant exposure class(es). Method 2. Cement properties equivalence Testing according to EN 196 shall be carried out on a combination of the specific EN 197 cement with the specific EN 450 fly ash against the requirements of the corresponding EN 197 cement type and strength class permitted by table 3 of EN 206. The total proportion of fly ash in the total of fly ash and cement clinker shall be within the limits given in EN 197 for the specific type of cement. The testing procedure shall provide the user with a similar degree of protection against non-conformity as for factory - made cements tested in accordance with EN 197. These cornerstones concern only recommendations to CEN TC 104 SC1, which is

408

drafting EN 206 and the principles could be changed. Method 1 follows in outline the Dutch Technical Approval System for fly ash in concrete, method 2 concerns the current British practice. 9. CONCLUSIONS A variety of methods exists in Europe with respect to the way additions are taken into account. The differences appear to be due mainly to the way the national concrete standards have been formulated. In countries where a minimum cement content and a maximum water cement ratio have been defined often a fixed cement equivalence factor is used. In countries where this is not the case other systems prevail. To arrive at a harmonized system of standardization is not an easy task, but experience shows that Europe is slowly but steadily on its way towards harmonization for fly ash in concrete as well.

10. REFERENCES

1 Fly Ash as Addition to Concrete, CUR-report 144 ed. CUR, Gouda, The Netherlands (1991), ISBN 90 376 00123.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SImt and Th.G.Aalbers (Editors) 81994 Elsevier Science B. T.: AN rights reserved.

409

STATE OF THE ART OF WASTE CHARACTERIZATIONON EUROPEAN LEVEL A. TukkeP, M. van den Bergb and H.A. van der Sloot' a Study Centre for Environmental Research TNO, P.O. Box 6013, 2600 JA Delft, the Netherlands; present adress: TNO Institute for Policy Research, P.O. Box 541, 7300 AM Apeldoom, the Netherlands

Dutch Standardization Institute (NNI), P.O. Box 5059, 2600 GB Delft, The Netherlands

' Netherlands Energy

Research Foundation (ECN), P.O. Box 1, 1755 ZG Petten,

The Netherlands Abstract In November 1991 the European Standardization Institute (CEN) established a Technical Committee on Characterization of waste ( C E W C 292). This TC coordinates the development of standardized test methods for waste for EC- and EFTA-countries. A State of the Art document on waste characterization forms the basis of its work programme. Making use of this State of the Art document, this paper reviews the relation between waste management, legislation and standardization work. Important conclusions are:

-

1

the need for close contact between the CEWC's, responsible for work on measurement tools, and legal authorities like the EC, responsible for defining limit values that have to be complied with; the need to discern different test levels and use as much existing information as possible in test procedures; the need for horizontal coordination of work of TC 292 on waste and work of other TC's on products, since the same material can be a waste or re-used as a secondary raw material in products. INTRODUCTION

In November 1991 Technical Committee 292 (TC 292) was established by the Technical Board of the Comite Europeen de Normalisation (CEN). The title of this TC is 'Characterization of waste'. The TC coordinates the development of standardized test methods for waste characterization on EC- and EFTA-level. Until December 1993, The TC established five Working Groups (WG's):

-

WG 1 on sampling of waste; WG 2 on the development of a compliance leaching test; WG 3 on the analysis of leachates;

410 2

WASTE MANAGEMENT AND INFORMATION NEEDS

2.1 Waste as a part of the substance cycle Figure 1 gives a general description of material cycles in society, including production, consumption, waste generation and waste treatment [2]. In general environmental policies aim to minimize emissions and waste production out of the economic system (i.e. to close valves 2, 3 and 4 as much as possible).

Waste management policy, as a part of the source-oriented environmental policy of the EC and most of its member states, in general aims to minimize waste production (close valve 3), to promote recycling (open valve 6) and to ensure proper treatment that minimizes dispersion of toxic substances (close valve 4). The ultimate goal is to meet stricter environmental requirements. Treatment methods improving residue quality may facilitate re-use or lead to disposal in less strict disposal regimes. The figure shows that several routes can be chosen to manage a waste. These routes include several treatment options, but also re-use (line 6). The actual route that can be chosen depends on the characteristics of the waste, the acceptation criteria of the treatment technique or application (wether for disposal or re-use) and limit values set by legislators. In fact these criteria define the actual structure of the valves in figure 1. Next paragraph discusses in more detail what kind of characteristics can influence the flows and directions through the valves. 2.2 Waste management options and information needs In general waste properties and characteristics that have to be known in order to make well-founded choices on the right treatment or recycling technology can be divided in the following groups [3]: 1 2

3 4

Process-technical criteria; Environmental criteria; Health and safety criteria; Waste management preferences chosen by the competent authorities. These types of criteria will be discussed in more detail below.

. .

Process-technical cntem From a process-technical point of view waste management firms need information on the characteristics of a waste in order to ensure a controlled operation of the applied waste management technique. For instance, when waste is incinerated in a rotary kiln information on characteristics like alkali metal content is needed because these elements can affect the kiln.

. .

Eoyironmental mkna The emissions to air, water and soil from a waste management plant in general are related to the characteristics of the waste that is treated. From an environmental point of view information is needed in order to ensure the emissions from the applied waste management technique are within the limit values. Therefore in most countries the leaching characteristics of a waste play a role in

41 1

-

WG 4 on terminology; WG 5 on a group of parameters like organic sulphur, organic chlorine and lipophilic substances.

WG 6 on a full-characterization leaching test is planned to be established in June 1994. Apart from these WG's, the TC established an Advisory Group (AG) that advises the TC on its working programme. As a basis for the working programme insight was needed in the state of the art on waste characterization within EC and EFTA countries. Therefore a State of the Art document on waste characterization has been drafted [I].It includes topics like waste management strategies, relevant legislation and its consequences for standardization. It also lists waste characterization methods and research programmes in each CEN member state. The objective of the document is to provide facts, figures and practical information. The document states and analyzes the differences between waste management systems and test protocols, but does not present choices and does not speak out any priorities or preferences. As such, the document can provide a basis for the consensus process on technical work in C E W C 292. On the basis of the State of the Art document, this paper reviews the relation between waste management and legislation and shows the importance of standardization work. It summarizes the state of the art in waste characterization and gives a possible outline of a programme for the development of standardized methods. Conclusions are drawn with regard to the implementation of a standardization programme. Figure 1 : The closing of material cycles in a sustainable society Emissions

2

Production

Consumption Products

1

u

1 Secondary raw

materials

I

1

Waste management

Extraction of raw materials 1. Purification valve 4. Disposal valve 2. Reduction valve 5. Product valve 3. Prevention valve 6. Recycling valve

I

Final waste

*

c4!

Disperison and immobilization

412 the decision which kind of landfill is suitable for a certain waste. Health and safety c W Information on health and safety aspects are of importance to ensure a sufficient protection of the personnel involved in the waste management plant. Examples of important characteristics are danger of explosion, self-ignition, skinirritation, etc.

..

Dreferences chosen bv authorities Wastemanaaement Apart from these three aspects, the legislator or permitter might have preferences for certain treatment routes. In those cases the legislator might forbid to accept wastes with certain characteristics in waste treatment plants, that are in principle suitable to treat the waste in question. An example is the Dutch policy on incinerable municipal waste: within a few years, landfilling of waste with a certain organic material content most probably will be forbidden.

The kind of information that is needed depends on the specific waste management technique or re-use option. E.g., when waste is intended to be landfilled, leaching characteristics are important; when the same waste is intended to be incinerated information on its sulphur content and caloric value can be important. Table 1 gives a non-limitative list of characteristics that in practice are felt to be of importance to assess the suitability of a waste treatment technique or re-use options. In general only a limited amount of these characteristics is mentioned in permits or legislation. In several cases the characteristics of a waste are well enough known on the basis of experience and testing is not always found to be necessary (e.g. incineration of municipal solid waste).

2.3 Limit values in legislation Some EC and EFTA countries have developed an extensive set of environmental limit values and rules with regard to waste management. The EC is developing similar legislation. Quite a few countries follow these EC initiatives. Some countries are behind this 'average' group. This situation is also reflected by the differences in the waste management systems between EC member states. Some countries rely for a great deal on landfilling, whereas other countries have a policy to promote re-use and have set regulations accordingly. In the UK codisposal is regarded as a qualitative good disposal method, where in other countries this is forbidden. For practical reasons this paragraph will be limited to a discussion of relevant EC-legislation. Directive 911156 and 911689 play a central role in the Community legislation on waste. Directive 911156 is known as the Framework directive on waste. It specifies a definition of waste' and defines disposal and recovery operations.

1

The criteria for the definition of 'waste' are, however, sometimes defined in such a way that they can not be measured by (standardized) methods.

413 Table 1: Waste treatmenure-use options and information needs TECHNIQUE

C H A R A C T E R IS T I C S MENTIONED IN (PROPOSED) EC-LEGISLATION

OTHER CHARACTERISTICS OFTEN MEASURED IN PRACTICE

Incineration

non-bumablematerial contents, pH, CI, S. heavy metals (informative annex proposed Incineration directive 9ZC 130/01)

F, Br. I, flash point, PCBs, caloric value, dry material content

COD, EOCI, VOCI, Cd. Cr, Cu. Ni, Pb. Zn. Hg, As, N-Kjehldahl, aromatic compounds, phenol. respirationtest

Industrial waste water treatment

pH, TOC, As, Pb, Cd, CdV, Cu, Ni, Hg, Zn, F, CI. CN. SO4 (in leechate; in proposed Landfill directive 9WC 21Z02))

Landfill

Quite often composition of the waste is assessed as well

con-

Heavy metals, PAHs, EOX, VOX. mineral oil, aromatic compounds, CN (depending on technique/contamination)

Physical-chemical treatment

Pilot treatment on lab-scale, GC-scan. pH, Cd, Cr, Cu, Ni. Pb, Zn. Hg, As. free CN, phenol, nitrite, EOX emuant;

Distillation

Pilot treatment on lab-scale, GC-scan, cormsiontest on distillate (part of product quality control)

Treatment of taminated soil

Waste oil recycling

PCB (EC87/101)

EOCI. flash point, sediment, S, ash content. water content

Re-use of sludge as a soil improver c.q. fertilizer

Cd, Cu, Ni, Pb, Zn, Hg, Cr (EC 86/278)

PAHs, PCB's. dry matter contents (...)

Re-use as a building material

Cd, Cr. Cu, Ni, Pb, Zn, Hg, As (leaching characteristics and composition), TOC, dry matter contents (...)

Directive 91/689 is the revision of Directive 78/319 on hazardous waste. The Directive lists characteristics of waste that render them hazardous*. For transfrontier transport of these wastes Regulation 259/93gives a notification system. Other Directives are in development on landfill of waste, incineration and re-use as a fertilizer/soil improver. Several product oriented directives give criteria that have to be met by primary (or secondary !) raw materials. These Directives mainly

2

The hazard criteria are, however, sometimes defined in such a way that they can

not be measured by (standardized) methods. The criteria are taken from Directive 67/548 on the notification of hazardous substances; the related OECD test methods are developed for pure chemicals and not for testing waste.

414

are meant to ensure a high and equal level of protection of the environment in EC member states and to ensure that waste treatment and recycling takes place on the same quality level. E.g., the proposed Landfill directive gives classes of wastes according to leaching characteristics and relates them to the required level of protection (permeability of the soil, etc.). The most important characteristics for which limit values exist in (oncoming) EC legislation are indicated in Table 1. Several countries, like Germany, the Netherlands and Sweden have developed or are developing a more elaborated legislation, e.g. limit values for the re-use of secondary materials. In general, legislation in these countries gives limit values that have a different scientific basis and mentions different tests to be used. Apart from this, for quite a few characteristics the actual value measured is influenced by the test method used. This means that at this moment both limit values and test methods differ from country to country. These points can form a serious obstacle in the standardization process in CEN/TC 292. 2.4 Conclusions It is very important to be aware of the fact that almost the same kind of material, depending on its characteristics, could be regarded as a waste (that may have to be treated) or a secondary raw material (that can be used in products). It is also very important to be aware of the fact that test criteria (and thus test methods) for materials used in production processes will be similar for primary materials and secondary raw materials. Figure 1 shows that a material can be regarded as a waste on one moment, but used as a raw material on another moment. This implies that close cooperation between TC's dealing with waste and TC's dealing with raw materials that could be replaced by waste is vital to facilitate re-use and the associated standardization needs.

Table 1 makes clear that it is impossible to characterize the whole range of the mentioned parameters in every individual shipment that arrives on a waste treatment plant or is re-used. This means in practice that the number of parameters that is measured has to be minimized or simple test and measurement methods have to be used. If information is available about research results from the past, previous samples with the same background, etc., a simple test can provide the information necessary for a decision. In fact this approach optimizes the use of available information before performing a full characterization or making efforts for performing an indivi-dual analysis or test. Research on the similarity in the behaviour of specific contaminants leaching from different wastes holds promise for the future of waste characterization. The right test level has to be chosen on the basis of a StNCtUred, decision tree approach.

415 3

WASTE CHARACTERIZATION AND STANDARDIZATION

3.1 Introduction In the characterization of materials different steps can be distinguished. This chapter describes the State of the Art in waste characterization in modular formats, according to Figure 2. 3.2 Characterization steps

a) Characterizationstrategy Paragraph 2.4. states a clear need for a decision-tree approach to testing of waste. The right test level has to be chosen on the basis of existing knowledge on the characteristics of a waste. On partial aspects a decision tree approach to waste characterization has been developed in e.g. sampling. For leaching, C E W C 292iWG 2 has made the choice to distinguish between three levels of testing:

-

characterization tests (for full material characterization); compliance tests (on key variables before shipment of previously full characterized materials); and on-site verification tests (on-site tests at the gate on well-known wastes).

The characterization tests can help to define the test conditions required for compliance testing. Compliance tests are the generally short tests to evaluate materials with respect to regulatory limits focused on key parameters and most relevant test conditions. In the compliance tests the chance for false positives and false negatives must be minimized. Examples exist of conditions where minor variations in release controlling parameters such as pH, redox, complexants and US ratio may cause substantial changes in the amount leached from a waste. These conditions should be identified and proper measures taken to avoid erroneous decisions. Clear standards on overall characterization strategies are lacking. Research is needed on characterization strategy, also in relation to sampling strategy (b) and data interpretation (9). The leaching example shows also that research programmes to make available basic information on behaviour of materials could be necessary to obtain workable compliance and verification tests. b) Sampling Most EC and EFTA countries (e.g. Germany, Italy, the Netherlands, the UK) have standards on sampling of waste. Most of these standards were inspired by ASTM D 4057. WG 1 of C E W C 292 is developing a European Standard for sampling of waste, at first dealing with sampling techniques. On this point consensus seems easy to achieve. For sampling strategy the situation is more complex. Specifically the sampling of a static, inhomogenic bulk stream causes problems. Several countries have chosen a different approach to obtain a workable sampling strategy, so a difficult consensus process may be expected.

416

, Terminology

WASTE MATERIALS

CEN/TC 230

waste water

solids

A

E

WG

4

liquids

sludge

Characterization strategy

New WG's

S a w l i n g Strategies/Techniques

UG 1

WG 1 ?

Sanple Pretreatment o f phases, homogenizing) l i q u i d s s o l i d s sludge

F I

leaching t e s t s for inorganic compounds

Monolithic Materials

Granular Materials

I

leaching t e s t s f o r organic compounds F Monolithic Materials I Granular Materials

tests

tests

Characterization tests

tests

tests

tests

Verification tests

Verification tests

Characterization tests - new

WG 2

BCR

Reference Materials

,

G 1

tests

Reference Hateri a l s

Data Handling and I n t e r p r e t a t i o n

,

61

New UG o r work f o r Legislator

Figure 2: Technical work needed for standardization of characterization of waste (A-G refer to the relevant text in paragraph 3.2)

WG's

- BCR

417 c) Storage and sample preparation (1nter)national standards have been developed for water samples and soil samples. A check of applicability of the water and soil standards for waste has to be carried out. Several national standards on sample preparation exist for soil and products. CEN/TC 292NVG 1 has been asked to deal with this item. Possible work items are mainly of technical nature. If the existing standards for soil and products are found to be applicable on waste, the consensus process is expected not to be too difficult. d) Physical and biological properties Physical properties in general are assessed to choose the right characterization strategy or to decide on the right pretreatment or test procedure. E.g. the particle size of a material has to be known because it influences the minimum sample weight in sampling. Other tests could involve e.g. ecotoxicity etc. Tests for these kind of properties exist for water, soil and products. A check of applicability for solid and liquid waste and leachates is needed. e) Chemical composition For analysis of metals in waste Italy, Sweden and the Netherlands have developed or are developing specific methods. Mostly these methods are adoptions of existing standards for water or soil analysis. An important point of discussion within CEN/TC 292 might be whether water standards are applicable for waste and/or leachates and whether for the determination of the contents of metals a complete sample digestion is required, such as applied in Sweden, or whether a milder digestion method, such as the Dutch method, is sufficient. Eventually C E W C 292 could decide to standardize both methods and leave the choice to the user. For m n i c components very few countries have developed specific methods for the analysis of waste. Most countries use methods developed for water, (sewage) sludge or soil. The same applies for inorganic halogens and other inorganic compounds. For wastes or leachates with a matrix very similar to (waste) water, sludge or soil probably existing standards and analytical methods can be used with minor adoptions or modifications (as is currently proposed by CEN/TC 292NVG 3) For other matrices, specifically when organic compounds have to be determined, most probably research is needed before standardized methods of analysis can be developed. f)

Leaching characteristics Worldwide several leaching test methods have been developed in the last decade. Leaching test methods can be grouped in different ways. Tests can be grouped in terms of an equilibrium or a kinetic approach or in terms of level of testing (characterization tests, compliance tests and on-site verification tests). For some wastes the influence of several parameters on leaching behaviour is reasonably well known. A more quantitative insight in relations between lab testing and field conditions could help to define or optimize test methods. The understanding of processes controlling leaching behaviour of organic contaminants is still in its infancy and needs more research.

418 CEN/TC 292NVG 2 is developing a compliance leaching test for granular waste (mostly inorganic components). The standard is based on a synthesis of German, French, Dutch and Scandinavian leaching test procedures. A compliance test for monolithic materials will be the next item in the work programme. WG 6, that will develop characterization tests, is planned to be established in June 1994. Factors that are important to consider in the standardization process are the differences in existing tests in relation to existing limit values (specifically with regard to characteristics as pH and US ratio). Adaption of a test method (e.g. when a country has to replace its own test for a CEN test) in practice means adaption of limit values. Due to this close link between legal aspects and technical work the consensus process is affected and made more complex. Another important choice to be made is to which extent a relation between laboratory results and leaching behaviour in practice is felt of importance. One could argue that a test should predict as good as possible leaching behaviour in practice; however, in general this means a more complicated test. The decision tree approach described under a) is suggested by the AG to solve this conflicting situation.

g) Data interpretation National standards on data interpretation are lacking. Research on partial aspects is in progress; however, a total, systematic approach on data evaluation (a.0. in relation to the decision tree approach on waste characterization) is not available yet. Statistical methods for evaluation of uncertainities could be a work item for the TC. Due to the close relation with legal aspects it is doubted if interpretation and comparison with legal standards should be a work item for the TC rather than a task for legislators. 3.3 Outline of a working programme for TC 292 In view of above mentioned aspects an overwhelmingly large working field may be laid open for CEN/TC 292. On the other hand a great many organizations including other CEN-committees cover part of the area of interest. Figure 2 presents the most relevant relations between existing Working Groups and other organizations. An appropriate form of cooperation should be looked for.

In order to obtain a manageable number of topics to be treated within a reasonable time frame priority setting is a must. According to the general CEN strategy on environmental standardization [5],TC 292 could focus their primary attention on standardization related to EC legislation and to needs of TC 292 or existing Working Groups. Thus the work programme could be split up into two parts:

-

First-term activities related to immediate needs as derived from current preparation of European legislation. These activities are mainly related to the EC directives on landfill and incineration. Second-term activities within a more comprehensive program for TC 292 for the longer term. These activities are related to general information needs in waste management.

419

For topics like sampling techniques, physical and biological properties and chemical composition it is suggested to use as much as possible the results of work of TC's on water, soil and products. CEN/TC 292 could concentrate on testing the applicability of these tests for waste. Liaisons with these other TC's can be a help on this work. On topics like a characterization leaching test, a compliance leaching test and sampling and testing strategy the work requires an extensive effort of TC 292. 4

CONCLUSIONS

The following conclusions can be drawn with regard to standardization of waste characterization: 1

the need of close cooperation in work in legislative circles and technical standardization work.

The practical level of legal limit values is often determined by the technical measurement method chosen to assess the value. Also the definition of a limit value in legislation can be of influence of the difficulties that arise in the technical standardization work. 2

the importance of horizontal coordination between Technical Committees working on standardizationon waste and products.

It is very important to be aware of the fact that almost the same kind of material, depending on its destination, could be regarded as a waste (that may have to be treated) or a secondary raw material (that can be used in products). In case the characteristics to be tested for re-use as secondary raw material are similar to those for treatment, the same test method should be applicable. If no coordination exists between the work of the TC on waste and TC'S on products making use of recycled waste different standardized test protocols will be developed. The same material would have to be tested differently on the same characteristics. Without this horizontal coordination standardization work does not lead to standardizationbut to chaos.

3

the need for priority setting for work items for the CEN/TC related to EC-legislation. In principle an overwhelmingly large working field may be laid open for C E W C 292. In order to obtain a manageable number of topics to be treated the TC could focus on standardization needs as a result of EC legislation, which are mainly related to the proposed directives on landfill and incineration.

4

the importance to discern different test levels and the usage of existing information on waste characteristics

In practice the number of parameters that is measured is minimized or simple test and measurement methods are used. If information is available about research results from the past, previous samples with the same background,

420 etc., a simple test can provide the information necessary for a decision. The right test level has to be chosen on the basis of a structured, decision tree-like approach.

5 the need for research on items like measurement strategy, leaching of organic materials, and data evaluation. Research is needed on characterization strategy, also in relation to sampling strategy and data interpretation. Research programmes to make available basic information on behaviour of materials could be necessary to obtain workable simple tests compliance and verification tests. Another area that still needs research is leaching of organic materials.

Acknowledgements The authors had support of mr. J. Wolsink, mr. E. Mulder and mr. M. van Son of TNO in drafting the State of the Art document. Though the authors have full responsibility for the text of this article and the State of the Art document, they also wish to give special thanks to the members of CEN/TC 292 and the AG. They provided information, material and parts of the texts for the document. This publication has been made possible by financial support of the Stimulation Programme for Standardization work of the Dutch Ministry of Economic Affairs.

References

[I] A. Tukker, M. van den Berg. H.A. van der Sloot, 'State of the Art document waste characterization CENlTC 292', NNI, Delft, concept November 1993 [2] TNO, 'The closing of material cycles', Delft, 1992 [3] TNO-SCMO, 'Acceptation procedures hazardous waste permit holders', Waste Management Series 1994/.., Ministry of Housing, Physical Planning and Environment, the Hague (in press) [4] Document N16 of CEN/TC 292/AG 2, Secretariat NNI, Delft, the Netherlands, 1993 [5] CEN Consultation document: 'Environmental standardization by CEN proposal for a general outline of activities', Brussels, November 1992

-

A

Environmental Aspcts of Consmction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) el994 Elsevier Science B.K All rights resewed.

42 1

Leaching behavior assessment of wastes solidified with hydraulic binders: critical study of diffusional approach P. Moszkowicza, R. Barnaa, J. Mehub, H. van der Slootc and D. HoedeC aLaboratoire de Chimie Physique Appliquee et Environnement (INSA de LYON), 20 avenue Albert Einstein, 69621 Villeurbanne Cedex - France bPOLDEN INSAVALOR, CEI - BP 2132 - 27 boulevard du 11 Novembre 1918,69603 Villeurbanne cedex - France CEnergieonderzoek Centrun Nederland (ECN), PO Box 1, 1755 ZG Petten Netherlands

- The

Funded by l3E.CO.R.D (French cooperative network for waste research), CEI 2132 - 27 boulevard du 11 Novembre 1918,69603 Villeurbanne Cedex, France

- BP

Abstract Leaching procedures of wastes solidified with hydraulic binders are expected to allow the assessment of the safety of the long term storage. The Dutch procedures (Availibility Test and Tank Leaching Test) or the Canadian one (close to ANS 16.1) are based on diffusion model and determine the two parameters De and Co from two different experiments : one on crushed materials and the other one on a monolithic sample. The present study, jointly conducted by a Dutch team (ECN) and a French one (POLDEN, LCPAE INSA Lyon), has been funded by RE.CO.R.D. Its two main aims were : - to point out the influence of the chemical properties of the binders and the wastes upon the release of the pollutants. - to define the application field of the diffusion model in order to predict the long term leaching behavior of the solidified products.

1. AIM OF THE STUDY The aim of the study was twofold :

- to demonstrate the influence of the physicochemical properties of the binders and the wastes on the release of pollutants during leaching of the solidified samples ; we particularly focused on the acidic-alkaline and redox characteristics of the different constituants of the solid matrix. - to develop a model based on the obtained experimental results in the laboratory in order to predict the long term leaching behaviour of the solidified material. The generally accepted model to describe the release phenomenon for each species is as follows : assuming that the porous medium is saturated with water and after a washing off of the soluble species present on the surface of the block, the migration in the pore water of the soluble species towards the liquid solid interface

422 can globally be described as a diffusional transfer. The kinetics of the phenomenon is characterized by an effective diffusion coefficient De (in m2.s-1). The intensity of the release is also related to the available content in the block. The block is considered to be homogeneous initially and that no physical or chemical alteration will take place to hinder diffusion. Compared to the complexity of the actual physicochemical processes involved, such a model is necessarily simplifying. The limits of its field of application must be verified carefully. Both Dutch and French teams studied the leaching behaviour of eight solidified samples obtained from two different wastes, and with four hydraulic binders of different compositions. 2. SOLIDIFIED WASTE TESTED

The two wastes were chosen according to the following criteria :

- highly soluble content, - presence of amphoteric heavy metals, - industrial relevance.

The choice was as follows : Dry air pollution control residues from MSW incineration, Lead secondary smelting slag Four different recipes were selected after preliminary trials to obtain the required mechanical qualities, by using different binders (Portland cement CPA 55, and blast furnace slag cement CLK 45)and additives (metakaolin, sand, caustic soda). The chemical analysis of the total content of the studied elements is resumed in the table 1. The table 2 gives the mass concentrations of the analytes in the mortars. Table 1 Content of wastes in soluble elements (mg/kg)

1

Elements

Sodium

Arsenic

Lead

Cadmium Chlorine

Sulfur

APC MSW

18400 16400

20.9 20.8

2292 2281

151 148

159100 161300

21700 22000

Slag

105600 110560

1058 1138

116100 105900

272 258

17700 15100

105000 100400

I

423

Table 2 Composition of the eight solidified samples (mg/kg) Elements

Sodium

Arsenic

Cadmium Chlorine

Lead

Sulfur

1s 2s 3s 4s

38000 38600 38000 38000

390 320 390 390

93 102 93 93

5800 5750 5800 5800

41000 37000 41 000 41 000

38000 40000 38000 38000

1R 2R 3R 4R

6200 6700 6200 6200

13 10 13 13

53 53 53 53

56000 56000 56000 56000

800 800 800 800

9600 10000 9500 8800

3. LEACHING PROCEDURES Four leaching procedures were used in the experimental program. Two of them aim to evaluate the maximum quantity of pollutants released and the two others are to determine the kinetics of the phenomenon in the medium term (64 days). The following tables resume the main characteristics of the procedures. Table 3 Tests to evaluate the maximum quantity of pollutants released Test carried out

Mass of us the ratio sample

NVN 2508

89

DW mass

100

Availibility test

lo0g

NF X31-210 Leaching test

I

Number Time oi Leaching of contact solution intervals

95 % of mass < 125 pn

2

3 hours then 4 hours

100 %

10

waste Raw

Crushing

of mass c4mm

3

3 x 16 hours

pH : 7 controlled using 4N HNOj Demineralized water pH approx. 6.5 not controlled

424 Table 4 Leaching tests to evaluate the dynamics of release

Test carried out

ECN Tank Leaching Test INSA Flow around test

Size

a 70 m m

us

Nature of Stirring the water

10 by volume

pH : 4

ratio

(not controlled during extraction) None

4 cm

10 by mass

pH = 6.5 demineralized water

Number of intervals

Time of contact

8

0.25 h., 1, 2, 4, 8, 16,32 and 64 days

Mechanical 3 stirring then < > 8 60/mn

________

accordins the TLT

4. INTERPRETATION OF THE RESULTS The leaching behaviour of the eight solidified samples was studied according to the Dutch approach (Availibility Test + Tank Leaching Test) and to the French approach (X 31-210 + prolonged flow around test over 64 days). Each sample was doubled. The leachates were analysed according to the following criteria : pH, conductivity, redox potential, sodium, chlorine, lead, arsenic, cadmium. The Dutch approach is based on the determination of the two parameters of the diffusional model Co and De : Co is obtained by the Availability test, under rigorous extraction conditions (finely crushed waste, pH 4 controlled by addition of acid). De is identified from the Tank Leaching Test results based on the unidimensional resolution of the diffusional model, which does not take into account the depletion of the solid core. At the beginning of the leaching process, and as long as the leachable concentration of the solid core remains equal to Co, the flow rate of pollutant release J(t) can be expressed as follows :

J(t) = CO (m/zt)”’ The cumulated quantity released m(t) can therefore be expressed as : m( t) = s co (4m/ z)’”t’’’ where S is the contact at the solid/liquid interface From the graph of the experimental results and by determining the position of the most “representative“ straight line with a slope of 1/2, the value of De can be identified as it is the only unknown parameter.

425 The French approach has led to a critical analysis of the field of application of the diffusional model and to the use of a tridimensional numerical resolution to identify Co and De. Fick's law gives the equation for the diffusional mass transfer: -dc =

[a x a y a z 1

a2C+ a2CT2+ c T DT

where C (x,y,z,t) is the local apparent concentration of the solute (in kg/m3)), with the initial condition C = Co and the limiting condition at the solid/liquid interface C = Ci = 0. The representation log J/log t is usefull to express the results graphically as it is more sensitive than the representation log m/log t for judging the validity of the diffusional model. In fact, at the beginning of release, the graph obtained is expected to be a straight line with a slope of -1/2, and as soon as depletion of the solid core is reached, the flow J decreases more rapidly than is predicted by the "semi-infinite" diffusional model. This "depletion" effect is interesting to consider as it contains information concerning the kinetics of the process and allows a good simultaneous identification of De and Co. By comparison of the experimental results with those obtained from a tridimensional simulation, by varying the parameters Co and De, and if the diffusional model is valid, it is possible, to determine, the optimum couple (Co,De), by minimization of the deviation of the simulated concentrations versus the experimental concentrations c , ( C c x p- C,,,)2. The figures 1 and 2 show the good agreement between experimental and calculated values obtained in the case of sodium and chloride release:

h

1

? N

O

E

' c n

-1

E -2

v

-

0

3

4

5

6

7

log t ( s ) Figure 1. Experimental and simulated Na release results

-3!-. -4

3

4

5

6

7

log t (s) Figure 2. Experimental and simulated CI release results

426

The simulation of release in the long term is therefore possible for any predefined geometry. In the case of a cube,lm3, the time for half extraction (m/mo = 0.5) of a species such as sodium, which has a diffusion coefficient of about 1010.m2.s-1,would be 984 days i.e. 2 years, 8 months and 2 weeks. The 3D simulation developed, allows to extrapolate results for varying geometries of the specimens (parallelepiped, cylinder, sphere) and of all dimensions. 5. MAIN RESULTS

The following two tables resume the results obtained by the Dutch team : Table 5 Maximum extractable quantities (Co) (in mg/kg) Samples

Arsenic

1s 2s 3s 4s

5.3 5.8 5.2 5.9

1R 2R 3R 4R

Chlorine

Lead

36033 40571 39848 37186

6000 5600 3700 5700

5894 2848 2752 1248

5054 6452 7427 5073

56000 68800 67500 61500

293 108 273 326

Cadmium Sodium

55 48 62 56

Table 6 Apparent diffusion coefficients (pDe) Samples

Arsenic

1s 2s 3s

10.94 10.53 11.08 11.37

4s 1R

2R 3R 4R

Cadmium Sodium

18.82 17.99 18.72 18.99

I Chlorine

1

Lead

10.51 11.15 10.41 10.69

10.75 10.97 10.32 10.90

17.88 18.01 16.91 15.95

10.34 10.39 10.48 10.32

10.55 10.67 10.66 10.76

14.87 14.66 14.89 16.42

Concerning the results obtained by the French team, two cases can be distinguished as follows :

427

For the soluble species (sodium, chlorine) and for the soluble fraction as a whole, the tridimensional diffusional model is validated and the parameters Co and De can be determined from the flow around procedure (64 days), taking into account the depletion part of the phenomenon. The table 7 shows the values of the effective diffusion coefficient De, and the maximum leachable content Co. for sodium and chlorine. Table 7 Identified leaching caracteristics of soluble species Chlorine

Sodium De (m2.s-1)

CO (kg.m-3)

1s 2s 3s 4s

3.15.10-11

44.7

2.96.10-11 4.17.1 0-11 4.15.1 0-11

44.0 44.9 58.4

4.68 1.75.10-1 1 7.82 6.0.10-1 1 5.1 1 11.4.10-11 6.91

1R 2R

18.4.10-11 20.3.1 0-11

9.8 9.7

11.8.10-11 87.0 11.4.10-11 73.8

3R 4R

22.9.10-11

12.9

14.1.10-11

18.9.10-1 1

B.9

7.28.10-1 1

De (m2.s-1) 1.o. 10- 11

CO ( k g . n ~ - ~ )

76.2 74.0

For the other studied species, the diffusional model can not be validated. The behaviour of lead varies according to the waste concerned. In the case of dry APC residues from MSW incineration, the pollutant release is immediate and depends on the type of binder involved and the induced pH : Ill (CPA + NaOH) > I (CPA) > IV (CPA + 40 % pouzzolanes >I1(CLK) After 200 to 400 hours, release decreases. Considering the theoretical solubility of lead and the results obtained from the X 31-210 test, this decrease cannot be attributed to depletion of the leachable content. Figure 3 and figure 4 show the behaviour of lead from 1 s and 2 s leached samples. It is probable that, according to the evolution of the physicochemical conditions of the pore water, pollutant release can again take place and increase. In the case of solidified waste prepared from lead secondary smelting slag, an increase in the phenomenon of release is observed with time. In this case also, the levels of pollutant released are dependant on the pH induced by the type of binder used. Results obtained from 1R and 2R samples are represented by figures 5 and 6. The behaviour of arsenic present in the slag is extremely significant : after an initial washing, there is a period when no apparent release can be observed for up to 200 hours. Release then begins, with no apparent depletion effect during the rest of the experiment. The values obtained are greater than those obtained from the X 31-210 test on crushed waste (figures 7 and 8). In contrast to the case of lead, the levels of release observed and the pH induced by the binder do not seem to be related in any obvious way.

428 h

O Y

lo1

E

v

E

I]

n

m

loo

l

"

I I

0 7

10- 1

loo

IOI

10-1-

l o 3 lo4

lo2

10'

IOO

lo2

l o 3 lo4

l o g t (h)

l o g t (h)

Figure 4: Lead release from 2R sample

Figure 3: Lead release from 1 R sample

Figure 5: Lead release from 1S sample

E El

El

cn 6

El

cn

El

v

El

6 m

E

El

v

PElQEl

El

10-1:

10-1:

EI

ElElEl

c

0 7

10-2

..''.'.I

."'".I

'""'.I

-

l o g t (h) Figure 7: Arsenic release from 1s sample

10-2

-...-.- ..."."

....."l

I

I

-

o4

log t (h) Figure 8: Arsenic release from 2s sample

429

ECN has observed an influence of the Redox potential on the release of metals, for the couple, waste/conditions of contact with water. Globally, the results obtained for lead and arsenic demonstrate the fact that release is highly "sensitive" to the chemical context in the pore water, which can evolve during leaching of the specimen. At the beginning, the pH is greater than 12, but then changes due to decalcification of the mortar (release of soluble lime), at least in the region near the solidliquid interface. The solubility of amphoteric metals, sensitive to pH, can therefore vary greatly, and more intense dissolution, or on the contrary, reprecipitation in the pores, can alter the diffusional transfer process to a great extent. 6. CONCUSIONS

6.1. Role of the leaching tests in the evaluation of solidified waste

Among the procedures studied, three types of test can be defined according to the required aim. Leaching procedures on crushed waste, the aim being to extract the pollutants in order to determine the maximum leachable fraction. Successive leaching procedures on monolithic waste to evaluate, over a period of two to three months, the leaching dynamics in the relatively long term, in order to understand the phenomenon and to develop a model corresponding to the release process. A French procedure on monolithic waste over a limited period of a few days, in order to control solidified waste prior to landfill. Each of these three types of procedure has therefore its own specific interest. The first two are necessary to evaluate long term release and could no doubt be regrouped into one test over a long period of time. In fact, it is effectively difficult to obtain coherent results from the two procedures. Shorter procedures, would also seem to be necessary, but in order for them to be interpreted in terms of pollutant release, they should be preceded by tests, over a longer period, on the same category of solidified waste, in order to obtain sufficient knowledge concerning the process involved during release. 6.2. Influence of different operational parameters

The liquid to solid ratio generally conditions the level of extraction, particularly as far as only slightly soluble compounds are concerned for which saturation may be a limiting factor. However, it can be noted that a high US ratio leads to lower concentrations of such compounds, possibly below the detection limits, which leads to an underestimation of release. Furthermore, by a cumulative effect, this can lead to important relative errors concerning the release per unit mass of waste. The interpretation of the concentration of the leachates is mainly based on the liquid volume to solid surface ratio during the first phase of release due to diffusion. In the second phase, the liquid to solid mass ratio then determines the possible extension of the maximum pollutant release. The physicochemical context generated by the leaching procedures is the result of the simultaneous presence of soluble compounds coming from the waste and solutes from the leaching solution which can enter the solidified waste specimen by diffusion. According to the buffering capacity of one or the other, the physicochemical

430 interactions, reponsible for leaching, will be more highly influenced, either by the waste composition or by the leaching solutions used. It follows that the use of demineralized water offers a minimum buffering capacity and therefore the physicochemicalcontext will be governed by the waste itself. The use of acid or salt solutions will involve a complex situation of physicochemical interactions, which, according to the pollutants, can either inhibit or enhance the release process. Only a sound knowledge of the actual preponderant interactions in sifucould justify the use of non demineralized water. It could be of interest to develop tests with parameters according to specific disposal or reuse scenarios especially concerning pH and the US ratio. 6.3. Questions concerning the notion of "maximum extractable quantity": From studies carried out in parallel by INSA and ECN, the notion of the maximum extractible quantity Co, defined as the quantity present initially in the solidified specimen which can be released if the test time tends towards infinity, must be considered with great caution : In the case when release of the species is apparently not sensitive to the chemical context of the pore water (solubility is not the limiting factor), Co can be defined and measured by a short test on a crushed sample (in this case, the pH of the leaching solution must not influence the result of the test), or by identification from the flow around test in the medium term, on condition that the phenomenon of depletion of the solid core is taken into account and that 3D resloution of the diffusional model is applied. In the case where the solubility of the species is sensitive to the chemical context (diffusional transfer is not the limiting factor ), for example to pH, it is obvious that the Co determined by the short test will depend on the pH of the leaching solution used. This is systematically the case for the release of lead and arsenic for the samples tested. Furthermore, if the pH of the pore water of the solid changes during leaching in the medium or long term (which is in fact the case when leaching a mortar with an acid or neutral solution), the variable solubility of the species will modify the leachable fraction during the flow around test. As a result, in this case, we must reconsider the notion of the absolute maximum leachable quantity, measured by a specific test with completely different chemical conditions to those of the solidified waste specimens It is however possible to envisage the determination of Co related to chemical contexts corresponding to given situations i.8. specific disposal or reuse scenarios. 6.4. Limits of the application field of the diffusional model with regards to pollutant release

This question is of course related to the previous one. The distinction between the species whose solubility is apparently not sensitive to the chemical context and the other species present is of importance.The diffusional model is a perfect fit as far as the most soluble species are concerned. The release of sodium, chlorides, and even the soluble fraction as a whole, is perfectly described by the diffusional model. In this case, the flow around test in the medium term on a block of reduced dimensions allows us to obtain, over a relatively short period, the beginning of the phenomenon of depletion, which allows precise identification of the two parameters Co and De of the diffusional model. The values of the effective diffusion coefficient are then between l o l l et 10-10.m2.s-1 for the set of cases studied.

43 1

However, the set of results obtained has shown the importance of the physicochemical interactions on the release of only slightly soluble metal pollutants , even if the form of the curves obtained is compatible with the diffusion process. To predict the behaviour in the medium term, it would seem necessary to take into account the coupling of the diffusion transfers towards the leaching solution with the phenomenon of physicochemical interactions which are preponderant (solubilisation, precipitation, oxydo-reduction, equilibium in solutions...). 6.5. Possibilities to predict the long term behaviour?

The simulation obtained by 3D numerical resolution of the equations of the diffusional model enables the prediction of the long term behaviour of solidified waste (of any form and any size).if it undergoes contact with pure water infinitely renewed. To apply this result to the case of a species contained in a solidifed block, it is necessary to have established beforehand with certainty that the diffusional model well describes the phenomena. This is the case for the "soluble" species using the flow around test in the medium term (64 days on specimens 4 x 4 x 8 cm, or less on smaller specimens). Another precaution must be considered to ensure the validity of the prediction of the long term behaviour as based on the diffusional model : the integrity of the physical structure, and in particular the porosity, must be ensured. The evolution of the pore size due to the release of a highly soluble fraction can lead to an increase in the effective diffusion coefficient which must be taken into account. For the "slightly soluble" species, the insensitivity of pollutant release to the chemical context must be verified by means of short term tests on crushed waste with several leaching solutions corresponding to different chemical contexts. If chemical insensitivity is established, a test on the crushed waste will allow the determination of the total leachable content Co and the flow around test in the medium term will allow the identification of the effective diffusion coefficients De. If sensitivity to the chemical context is established, the available models do not allow the prediction of the long term behaviour. We suggest therefore to carry out couples of tests (short term tests on crushed waste and medium term tests on monolithic waste) in fixed and controlled chemical contexts, and relevant to specific disposal and reuse scenarios. In this way, the parameters of maximum extractable fraction and release dynamics will be coherent. 6.6. Subsequent research subjects

Effort must be focused on the pollutant species which are sensitive to the chemical context when released. Two approaches can be carried out in parallel, corresponding to different aims : A behavioural approach and an approach concerning the phenomena involved (medium term aim : to evaluate the performance of the processes). This would involve the clear definition of the disposal or reuse scenarios of the solidified waste (plausible scenarios or the "worst case") and to identify the behaviour of the different pollutants from two points of view : leachable potential and release dynamics. This pragmatic approach will have to be carried out on several couples, waste/processes, before an evaluation of the long term behaviour will be possible. A more scientific approach to understand the intimate mechanisms of dissolution and release. Furthermore, the variation of the chemical conditions in the porewater needs to be studied in greater detail, in order to include this parameter in the model. In the solid blocks elaborated using a cement, the lime is sufficiently soluble for it to be released

432

as such during leaching. The induced variations in pH will have an influence on the solubility of numerous species (amphoteric metals, for example). An experimental study on the release of lime and the pH variations in the porewater of the solid block should be carried out for certain types of wastes and hydraulic binders. The development of a model of the release of species whose solubility is related to the pH of the pore water must be carried out, and then validated experimentally. The case of lead release, present in different forms (oxide, sulfide, chloride...) in the solidified waste obtained using different cements, could be the subject of an interesting study. Other phenomena, related to the nature of the leaching solution, should also be the object of studies : - the influence of carbonation of lime by dissolved carbon dioxyde gas ; - the influence of the oxydizing role of the dissolved oxygen ; - the influence of an acidic leaching solution (acid rains). These subjects of research would aim to study the behaviour of solidified blocks in real storage conditions. 7. REFERENCES

American National Standard. Measurement of the Leachabilityof Solidified Low-Level Radioactive Wastes by a Short-Term Test Procedure, ANSVANS-16.1-1986 Barna, R., Moszkowicz, P., MBhu, J., van der Sloot, H. Leaching pattern of heavy metals from concrete solidified wastes. In: Heavv Metals in the Environment, 9th International Conference Toronto, v01.2. Edinburgh: CEP Consultants, 1993, p. 128131. NVN 5432. Determination of the maximum leachable quantity and the emission of potentially hazardous components from construction materials and stabilized waste products of mainly inorganic character. Amsterdam, 1991 van der Sloot, H. A., de Groot, G. J. Determination of leaching characteristics of waste materials in relation to environmental product certification. Proceedings ASTM Symposium on Solidification Stabilisation of Radioactive and Hazardous Wastes, Williamsburg Virginia, 1990 34 p.

Environrnental Aspects of Conshuction with Waste Materials J.J.J.M. Goumans, H A . van der SIoot and TI1.G. Aalbers (Editors) el994 Elsevier Science B.E All rights reserved.

433

Burning of Hazardous Wastes as Co-Fuel in a Cement Kiln Does it Affect the EnvironmentalQuality of Cement ?

-

Kllre Helge Karstensen The Foundation for Scientific and Industrial Research SINTEF SI, P.O.Box 124 Blindern, N-0314 Oslo, NORWAY,

SUMMARY In Norway liquid organic wastes is commanly used as a supplementary fuel to coal in the production of cement. Studies during several years has proven that this is an environmental sound practice. The organic compounds in the waste are safely destructed and the heavy metals are to a high extent retained in the clinker. This paper evaluates if any additional content of heavy metals causes any enhanced leaching compared to clinker produced without waste fuel and compares results from different regulatory leaching test to see if they are in accordance.

1

INTRODUCTION

Cement kilns offer an excellent alternative for destruction of hazardous organic waste. The advantages of a cement kiln are the high temperature (14OOOC - 20WC) and long residence time in the rotary kilns (1, 2, 3). Furthermore, when burning halogenated organics, a large mass of alkaline cement clinker absorbs and neutralizes the acidic stack gases. Because of the high energy requirement of cement production, the combustion of hazardous waste containing a high calorific value (i.e. waste oil and solvents) results in significant fuel savings. So far much attention has been given to assess the potential environmental impacts of this practice, i.e. emission studies from cement production plants. Stdies during several years has proven that this is an environmental sound practice (4, 5). The organic compounds in the waste are safely destructed and the heavy metals are to a high extent retained in the clinker. There is therefore considerable interest in whether the use of wastes as a supplementary fuel has any effect on the environmental quality of cement. So far has this usually been evaluated by performing the US TCLP test (6). There is, on the other hand, performed studies which has been focusing on leaching from different materials stabilized or mixed with cement (7, 8,9, 10). This paper presents results from studies were different hazardous wastes was used as supplementary fuel together with coal. The cement kiln was operated in a dry process mode. The studies includes also investigations from normal cement production using coal only. The

434

wastes, constituted about 15 % of the total fuel consumption, was pumped into the cement kiln as a liquid or a suspension and contained chlorinated organic compounds, as chlorinated benzenes and polychlorinated biphenyls (PCB), and heavy metals. Several earlier studies has indicated that heavy metals in fuel and raw materials will be retained in the clinker, i.e. the product of the cement plant (11, 12, 13), and not discharged from the plant. The aim of this study was in two parts; firstly to evaluate if any additional content of heavy metals in clinker causes any enhanced leaching compared to clinker produced with coal only, and secondly, to compare the results from different regulatory leaching test to see if they were in accordance. 2

EXPERIMENTAL

Several full scale trial burns were performed in this project, with and without waste fuel. Emission samples and samples of solid process solids were continuesly collected over several days in each trial, and process parameters were monitored. To evaluate the fate of the constituents in the waste fuel, samples of raw-materials, fuel batches, coal, precipitator ash, stack-outlets and klinker were thoroughly analyzed for organic and inorganic constituents. 2.1

CHEMICAL ANALYSIS OF PROCESS SAMPLES

All the elements were analysed with ICP-AES after high-pressure acid decomposition (14), with the exception of mercury which was analysed with AAS cold wapor technique. Some of the samples were also analysed with XRF. ICP is not adequate with regards to the detection limits for several of the trace elements and further investigations will be perfomed with more appropriate techniques. In table 1 are the samples which were tested with different leaching tests listed. Table 1 Summary of samples tested with leaching tests

..

escption D147

Mortar specimen made of cement produced with coal only

D148

Mortar specimen made of Cement produced with coal and waste fuel

5/5

Clinker made of cement produced with coal only

1915

Clinker made of cement produced with coal and special waste fuel

2215

Clinker made of cement produced with coal and PCB-waste fuel

6B

Electro precipitator ash produced with coal and waste fuel

435 Two of the clinker samples, produced with and without waste fuel, were prepared as mortars according to EN 196-1 (15), i.e. 450 gram of cement (approximately 430 gram of grinded clinker is mixed with approximately 20 gram of gypsum), 1350 gram of sand and 225 gram of water were mixed and cured for 24 hours under 95 % relative humidity at 200C. prior testing. the specimens was stored for 28 days under 100 % relative humidity at 200C. Table 2 lists the characteristics of the mortar specimens. Table 2 Characteristics of mortar specimen Dimensions (cm)

4x4~16

Curing time (days)/conditions

1 /200c, 95% RH 1 /200c, 95% RH 28 /200c, 100% RH 28 /200c, 100% RH

Compressive strength (MPa)

50,3

493

73

7,6

Bend strength (MPa) Composition

4x4~16

450 gram of cement, 1350 gram of sand and 225 gram of water

The mortar specimens are both in the normal range with regards to compressive strength and bend strength, and there is no significant difference between the specimens. The other four samples, two clinker samples produced with coal and waste fuel, one clinker sample produced with coal only and one electro precipitator ash produced with coal and waste fuel, were tested without further preparation. The elemental composition of the samples are listed in table 3. As can be seen from table 3, is the difference in composition in the mortar samples D147 and D148 marginal, with the exception of Cr, Cu and Zn which are statistical significant higher in D148. This mortar is made of clinker produced with coal and special waste fuel, and the additional elemental content is probably due to enriched in these elements in the waste fuel compared to coal. Table 4 list the elemental composition of fuels and raw material. This tendency is even more pronounced in the clinker samples. The difference in composition between the precipitator ash 6B and the other samples are marginal, although we can see some tendencies to enrichment of volatile elements like T1 in the ash. The more volatile species will condense on dust and ash particles further out in the plant and is trapped in the elctro precipitator (16).

436

Table 3 Elemental composition of samples (listed in table 1)

2.2

CHEMICAL ANALYSIS OF SAMPLES OF FUEL AND RAW MATERIAL

The elemental composition of fuel samples and raw material are listed in table 4. The samples are so far only analysed with ICP-AES and XRF. As can be seen from the table is the difference in sample composition marginal, with the exception of 0, Cu, Hg, and Zn which is significant higher in the waste samples, and Tl and V which is higher in the coal. When wastes are used as a supplementary fuel it constitutes maximum 15 % of the total fuel consumption, the rest is coal. That implies the additional heavy metals in the wastes will to a high degree be diluted in the process.

437

Table 4 Elemental composition of fuel and raw material

138 1110

cu

200 300

0,082

Mg IMn

Na Ni P

F

c1 S

2.3

I

14

0,050

17001

12001

11001

I

900 34 300

41 I 2600 22 3 in

1800 15 450

2150 15 154

202 160 7720

90 6375 2885

71 14800 1740

489 90 4240

<4

211 I

10400 <4

I

LEACHING TESTS

As can be seen from table 3 is the additional content of heavy metals in the samples produced with waste as fuel small because of dilution in the process. To evaluate if this small additional content of heavy metals in clinker causes any enhanced leaching compared to clinker produced with coal only several regulatory and standard test were performed. To get

43 8

a basis of knowledge with regards to future applicability of any of the tests, is it necessary to compare the results from different regulatory leaching test to see if they were in accordance. Following leaching tests were performed on the samples listed in table 1: the Dutch NVN 5432 tank leaching test, NVN 2508 column test, NVN 2508 serial batch test and NVN 2508 availability test, the German DIN 38414 S4, the American EPA-TCLP and a modification of the German DIN test. In table 5 is the test scheme listed. Table 5 Test scheme Lea&&

test

D 147

Mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar

NVN 5432 Tank leaching test NVN 2508 Column test NVN 2508 Serial batch test NVN 2508 Availability test Modified DIN test DIN 38414 S4 PA-TCLP

8 7 5 1 4 1 1

D 148

Mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar Crushed mortar

NVN 5432 Tank leaching test NVN 2508 Column test NVN 2508 Serial batch test NVN 2508 Availability test Modified DIN test DIN 38414 S4 EPA-TCLP

8 7 5 1 4 1 1

Clinker Clinker Clinker

NVN 2508 Availability test DIN 38414 S4 EPA-TCLP

1

Clinker Clinker Clinker

NVN 2508 Availability test DIN 38414 S4 EPA-TCLP

1 1 1

Clinker Clinker Clinker

NVN 2508 Availability test DIN 38414 S4 EPA-TCLP

1 1

Precipitator ash Precipitator ash Precipitator ash Precipitator ash Precipitator ash Precipitator ash

NVN 2508 Column test NVN 2508 Serial batch test NVN 2508 Availability test Modified DIN test DIN 38414 S4 PA-TCLP

1 5 1 4

6B

1

1

1

1

1

The tests uses different amounts of sample mass and generates leachates with different W S ratio, and in order to compare the results between the tests, one have to take this into account. Those elements which are not detected in the leachates, are omitted in the tables, but is

439 mentioned in the text in each case. In table 6 is the detection limits for the actual elements listed. In each test, blind samples were run and analysed in the same way as real samples, and the results were taken into account. Table 6 Detection limits (ICP-AES) of trace elements in leachates ( m u ) Ag

As B Be Cd

<0.008 ~0,026

Co

~0,025
Cr

<0,010

cu

Pb

Fe Hg

~0,005 <0,0001

Sb

Mn

Mo

~0,006

Ni

~0,019 <0,090

Sn Ti Ti

P

sc Se

<0,040 ~0,042 <0,002 <0,050

~0.036 <0,002 <0,15

2.3.1 The Dutch NVN 5432 tank leaching test

In the NVN 5432 tank leaching test diffusion controlled (and surface wash off) leaching is measured. The mortar specimen is immersed in acidified demineralized water (5 times the volume of the specimen) without any stirring or agitation (17). The solution is renewed all together 8 times, i.e. after 0.25, 1, 2, 4, 8, 16, 32 and 64 days respectively. The solutions are filtered, pH and conductivity are measured. The solutions are finally conserved and analysed. The results are listed in table 7 and 8. On the basis of the results, diffusion coefficients can be measured (9). This can, under certain conditions, give a picture of the leaching process over time. Table 7 Tank leaching test of sample D147

Ag, As, B, Be, Cd, Co, Cr,Cu,Fe, Hg, Mn, Mo, Ni, P, Pb, Sb, Sc, Se, Sn, Ti, TI and Zn was below the detection limit in alle the leachates.

440

Table 8 Tank leaching test of sample D148

Ag, As, B, Ba, Be, Cd,Co, Cr, Cu,Fe, Hg, Mn, Mo, Ni, P. Pb, Sb, Sc, Se, Sn, Ti, T1 and Zn was below the detection limit in alle the leachates. As can be seen from tables 7 and 8 is it first of all the alkali metals Li, Na and K and the alkaline earth metals Ca, Mg and Sr, together with A1 and Si, which is mobilised with time during the leaching test. This correlates well with the increase in pH and conductivity. There is almost no difference in leachability between the two samples, and the different content of heavy metals seams to have no significance.

2.3.2 The Dutch standard leaching test NVN 2508 The Dutch standard leaching test consists of three main parts: 1) a column test, 2) a serial batch shake test and 3) a test for the determination of the availability of elements for leaching under natural conditions (18).

2.3.2.1Column test

In the column test approximately 800 grams of crushed sample (<3 mm) is percolated with water from the bottom to the top. 7 fractions are collected (L/S 0,l-lo), the solutions are filtered, pH and conductivity are measured. Finally the leachates are conserved and analysed. The results are listed in table 9-1 1. The column test is used to assess short- and medium-term leaching, i.e. 4 0 years (8).

44 1 Table 9 Column test of sample D147 (crushed)

Ag, As, Be, Cd, Hg, Mn, Mo, Ni, P, Pb, Sb, Sc, Se, Sn, Ti, T1 and V was below the detection

limit in alle the leachates. Table 10 Column test of sample D148 (crushed)

442

Ag, As, Be, Cd, Hg, Mg, Mn, Mo, Ni, P, Pb, Sb, Sc, Se, Sn, Ti, T1 and V was below the detection limit in alle the leachates.

As can be seen from tables 9 and 10 are the alkali metals leached out first, together with some heavy metals. The concentration of Cr,Cu and Zn is higher in leachate from D148, but if this can be ascribed the higher content, is uncertain. The alkaline earth metals has another leaching pattern, with low mobility in the beginning, increasing to a maximum at L/S 1-2, and then decreasing. Table 11 Column test of sample 6B

Ag, As, Be, Cd,Hg, Mn, Ni, P, Sb, Sc, Se, Sn, and Ti was below the detection limit i n alle the leachates. The leaching of T1 will be further investigated. The electro precipitator ash, sample 6B, shows the same picture as the crushed mortars, with the exception of lower concentrations of the alkali metals. We can also some leaching of Pb and Mo. If have to be noted that this precipitator ash is continuously feeded back into the process.

2.3.2.2 Serial batch test

In the serial batch test approximately 40 grams of crushed sample (c3 mm) is extracted 5 times with demineralized water at L/S ratio 20 for 24 hours each. 5 fractions are collected o./S 20-loo), the solutions are filtered and pH and conductivity are measured. Finally are the

443 leachates conserved and analysed. The results are listed in table 12-14. The serial batch test is used to get an impression of long-term leaching behaviour 50-500 years (8). Table 12 Serial batch test of sample D147 (crushed)

Sr pH C mS/cm

2,4 13 6,7

0,86 12,6 3,M

0,43 12,2 13

0,29 11,4 0.3

0,40 12,2 1.7J

Ag, As, B. Be, Cd, Co, Cu, Hg, Mn, Mo, Ni, P, Pb, Sb, Se, Sn, Ti, T1 and Zn was below the detection limit in alle the leachates. Table 13 Serial batch test of sample D148 (crushed)

Ag, As, B, Be, Cd,Co, Cu, Hg, Mg, Mn, Mo, Ni, P, Pb, Sb, Se, Sn, Ti, T1 and Zn was below the detection limit in alle the leachates.

444 As can be seen from tables 12 and 13 increases the Al-concentration with time, to a higher extend than in the column test, in spite of the large dilution. Both alkali metals the alkaline earth metals decreases with time, which also correlates well with the decrease in pH and conductivity. Also in the batch tests are Cr higher in the leachates of D148. Table 14 Serial batch test of sample 6B

Ag, As, B, Ba, Be, Cd,Co, Cu, Fe, Hg, Mn, Mo, Ni, P, Pb, Sb, Se, Sn, Ti, T1 and Zn was below the detection limit in alle the leachates.

In the leachate of sample 6B we can see the Al- and the Si-concentration is decreasing with time, in contrast to sample D147 and D148. This correlates well with the decrease and lower concentration of alkali metals and the alkaline earth metals, and also with the decrease in pH and conductivity.

2.3.2.3 Availability test

In the availability test 8 grams of crushed and sieved sample ( 4 2 5 um) is added 800 ml acidified (the pH is kept at pH 7 by adding 1 M HNO3) demineralized water and stirred for 3 hours. The solution is then filtered, and the sample is added 800 ml acidified (the pH is kept at pH 4 by adding 1 M HNO3) demineralized water and stirred for another 3 hours. The two extracts are combined and analysed. The results are listed in table 15. The availability test is assumed to give a picture of the maximum leachability under natural conditions (8).

445

Table 15 Availability test of all samples

Ag, As, Be, Cd,Hg, Mo. Ni, P, Pb, Sb, Se, Sn, Ti, Tl and Zn was below the detection limit in alle the leachates.

2.3.3 Modified DIN test In the modified DIN test 100 grams of crushed and sieved sample (c4 mm) is added 200 ml acidified (the pH is adjusted to pH 4 by adding HNO3) demineralized water and rotated for 6 hours. The solution is then filtered, and the sample is added 800 ml acidified (the pH is adjusted to pH 4 by adding HNO3) demineralized water and rotated for another 18 hours. The solution is then filtered, and the sample is added 4OOO ml acidified (the pH is adjusted to pH 4 by adding HNO3) demineralized water and rotated for another 23 hours. All the fractions (LlS 2-50) are filtered, pH and conductivity are measured, and the leachate is conserved and analysed. The sample is then added lo00 ml acidified (the pH is kept at pH 4 by adding HNO3) demineralized water and stirred for 4 hours. The leachate is filtered, conserved and analysed. The results are listed in table 16-18. The modified DIN test is assumed to give a more detailed picture of the leachability with time than the German DIN test.

446 Table 16 Modified DIN test of D147 (crushed)

Ag, As, Be, Cd,Cu, Hg, Mo, Pb, Sb, Se, Sn, Ti, T1 and V was below the detection limit in alle the leachates.

Table 17 Modified DIN test of D148 (crushed)

0,Sl

Zn

0,41

441 Ag, As, Be, Cd,Hg, Mo, Pb, Sb, Se, Sn, Ti, T1 and V was below the detection limit in alle the leachates. We can clearly see the effect of keeping pH at 4 in table 16 and 17,especially for Al, Ca, Mg, Si and Zn. Otherwise are the results quite in accordance with L/S 2 and L/S 10 in the column test and L/S 50 in the serial batch test. On the other hand are the Cr-figures in the modified DIN test quite the same, in contrast to the column test. Table 18 Modified DIN test of 6B

I

I

LS2

I

LS10

I

LS50

[

p

Ag, As, Be, Cd, Hg, Sb, Se, Sn,Ti, and T1 was below the detection limit in alle the leachates. The results of sample 6B in table 18 is also comparable with the earlier leaching tests, as it was for sample D147 and D148.

2.3.4

DIN 38414 S4

In the DIN test 100 grams of crushed sample ( 4 0 mm) is added loo0 ml demineralized water and agitated for 24 hours. The solution is then filtered, pH and conductivity is measured, and the solution is conserved and analysed. The results are listed in table 19. The DIN test was originally developed for testing of sludges (19).

448

Table 19 DIN 38414 S4 test of all samples

Ag, As, B, Be, Cd, Hg, Mn, Ni, P, Pb, Sb, Se, Sn, Ti, T1 and Zn was below the detection limit in alle the leachates in the DIN test.

If the results of the German DIN test is compared with the modified DIN test (at W S 10) it is quite obvious that there is an effect of the initial acidification in the modified DIN test. In the German DIN test pure water is used.

2.3.5 Toxicity Characteristic Leaching Procedure In the Toxicity Characteristic Leaching Procedure test 100 grams of crushed sample (43 mm) is added 2000 ml acidified (to pH 2.88 with 5.7 ml glacial acetic acidflitre) demineralized water and rotated for 18 hours. The solution is filtered, pH and conductivity is measured, and the solution is conserved and analysed. The results are listed in table 20. The Toxicity Characteristic Leaching Procedure test is originally developed for testing leaching in a mixed landfill (20).

449

Table 20 EPA TCLP test of all samples

Ag, As, Be, Cd, Hg, Mn,Ni, P, Pb, Sb, Se, Sn,Ti, Tl and Zn was below the detection limit in alle the leachates. In the TCLP test there is obvious an pH effect of the more stronger acidification than in the L/S 20 of the serial batch test, but this has no measurable dramatic effects with regards to leaching of heavy metals from this type of samples. 4

CONCLUSION

This study has so far shown that waste fuel used as supplementary fuel in the production of cement is enriched with regards to heavy metals. The heavy metals are to a high extent retained in the clinker but the dilution factor in the process is great. The additional content of heavy metals in clinker caused by the waste fuel is small for most elements and not measurable for some. Performance of different leaching tests has shown that the leachability are quite the same in all the samples, regardless if its produced with waste as fuel or not. The results from the different tests seems to be in accordance, but it will be performed additional analysis with more sensitive techniques to confirm this also for the trace elements.

450

ACKNOWLEDGEMENT I gratefully thanks The Norwegian Research Council and Norcem FoU Brevik which have financed the project and Ingegerd Rustad at SINTEF SI which have performed the chemical analyses.

REFERENCES Ahling, B., Destruction of chlorinated Hydrocarbons in a Cement Kiln, Environmental Scientific Technology, 13 (1979) 1377. lee, C.C., Huffman, G.L. and Oberacker, D.A., An overview of hazardous toxic waste incineration, JAPCA, 36 (1986) 922. Oppelt, E.T., Incineration of hazardous waste - A critical review, JAPCA, 37 (1987) 558. Benestad, C., Incineration of hazardous waste in cement kilns, Waste Management & Research, 7 (1989) 351. Karstensen, K.H. and Benestad, C., Buming of hazardous wastes as co-fuel in a cement kiln - Norwegian experiences. Conference proceedings of KilnbumP2, September 10-11, Brisbane, 1992. Mantus, EX., All fiied up - Buming hazardous waste in cement kilns. Report from EnvironmentalToxicology International Inc. & The Combustion Research Institute, Seattle, 1992. Sloot van der, H.A., Systematic leaching behaviour of trace elements from consauction materials and waste materials, Waste materials in construction, Studies in environmental science 48, Elsevier, Amsterdam, 1991. Sloot van der, H.A., Hoede, D. and Bonouvrie, P., Comparison of different regulatory leaching test procedures for waste materials and construction materials. Report ECN-C-91-082, Petten, 1991. Rankers, R.H. and Hohberg, I., leaching tests for concrete containing fly ash evaluation and mechanism. Waste materials in construction, Studies in environmentalscience 48, Elsevier, Amsterdam, 1991. Rechenberg, W., Sprung, S. and Sylla, H.M., A test method for the determination of leachability of trace elements from wastes bound with cement. Waste materials in construction, Studies in environmental science 48, Elsevier. Amsterdam, 1991.

45 1

Branscome, M. and Mournighan, R.E., Hazardous waste combustion in industrial processes - Cement and lime kilns. Report EPA 600/2-87-095, Cincinnati, 1987. Sprung, S., Technological problems in pyroprocessing cement clinker - cause and solution. Beton - Verlag GmbH, Dusseldorf, 1985. Seebach von, M. and Gossman, D., Cement kilns - sources of chlorides. Conference proceedings of AWMA conference on waste combustion in Boilers and industrial furnaces, April 18-20, Kansas City, 1990. Karstensen, K.H. and Lund, W., Multielement analysis of MSWI reference sample - BCR 176, Journal of Analytical Atomic Spectrometry, 4 (1989) 357. European Standard EN 196 Part 1, Methods of testing cement - Determination of strength, May 1987. Karstensen, K.H. and Lund, W., Multielement analysis of city waste incineration ash and slag by ICP-AES, The Science of the Total Environment, 79 (1989) 179. NVN 5432 Dutch pre-standard. Determination of the maximum leachable quantity and the emission of potentially hazardous components from construction materials, monolithic waste materials and stabilised waste products of mainly inorganic character. May, 1991. NVN 2508 Dutch pre-standard. Determination of leaching characteristics of coal combustion wastes. February, 1988. DIN 38414 S4 German standard procedure for water, wastewater and sediment testing - sludge and sediment. Determination of leachability. Institut fur Normung, Berlin, 1984. Toxicity Characteristic Leaching Procedure. Federal Register No 261, March 29, 1990.

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der Slmt and Th.G.Aalbers (Editors) 01994 Elsevier Science B. K AN rights resewed.

453

APPROACH TOWARDS INTERNATIONAL STANDARDIZATION:A CONCISE

SCHEME FOR TESTING OF GRANULAR WASTE LEACHABILITY. H.A. van der SIoot ', D.S Kossonb, T.T Eighmy', R.N.J. Comama, 0. HjelmaP.

Box 1, 1755 ZG Petten, The Netherlands. 'ECN, P.O. bRutgers University, Dept. of Chem. and Biochem. Engineering, P.O. Box 909, Piscataway, NJ 08550909, USA

' University of New Hampshire, Environmental Research Group, Durham, NH 03824, USA Water Quality Institute, 1 1 Agern Alle, DK-2970 Horsholm, Denmark

Abstract A series of short and relatively simple leaching tests is proposed for rapid compliance testing of granular (waste) materials. The test conditions selected are based on results obtained from extensive testing programs that have identified several critical factors influencing leachability of a particular granular (waste) material. These factors include specific element solubility and availability or release potential. Solubility can be influenced by pH, complexation by inorganic species or dissolved organic matter, and reducing properties of the waste. The sum of all of these factors reflect the chemical speciation of constituents in the material. Most current regulatory protocols do not explicitly consider these hndamental waste properties during evaluation. The proposed testing protocol includes two serial batch extractions with deionized water, first at liquid to solid ratio of 2.1 followed by L/S 10; and two static pH extractions at L/S 50, first at pH = 8 and then at pH = 4.The entire procedure can be completed within 32 hours and is designed to be simple, concise and reliable. Some typical examples of test results are presented in comparison with more extensive test data.

1. INTRODUCTION

The leaching behaviour of wastes is important for assessing the environmental impact of waste utilization, requirements for treatment, recycling or disposal options for waste materials. Many regulations, both existing and under development, use leaching test results to evaluate the potential for environmental and health risks associated with a given material. However,

454 leaching is a complex phenomenon where many factors may influence the release of specific constituents from a waste over prolonged time intervals. These factors include major element chemistry, pH, redox, complexation, liquid to solid ratio (LS), contact time and biological activity. A distinction between leaching tests for waste characterization, (detailed assessment of leaching behaviour), compliance and on-site verification has been made in the framework of CEN standardization [ 13. This recognizes that the properties of wastes that govern release of potentially harmful substances is too complex to be evaluated by a single leach test. Classification of current leach tests leads [I-41 to a limited number of generic tests that can be used to quantify the majority of factors controlling leaching. Prior classification has been based on specific disposal scenarios rather than from an integrated waste management perspective. The waste management perspective indicates that initially detailed information is required to evaluate the properties of a material and potential management options. Subsequently, simpler testing protocols (compliance tests) can be selected based on knowledge gained from detailed characterization for quality control purposes and comparison with regulatory thresholds. The maximum acceptable time interval for completion of testing increases from less than one hour for on-site verification to 48 hours for compliance testing, and up to several weeks for detailed characterization. An alternative classification of leach tests is from the perspective of controlling physical and chemical release mechanisms. This approach differentiates between equilibrium (batch extraction and controlled pH tests) and dynamic tests (column tests, tank leaching or diffusion controlled tests). The following selection of characterization tests would cover almost all aspects of leaching based on the identification of the properties assessed by the different leaching tests in use. This selection is given below: Material Granular (waste) materials

Stabilized waste, construction materials and other monolithic materials

Test method pH controlled test Availability test Column test Reducing capacity test Availability test

Tank leach test Reducing capacity test

Conditions pH 4 - 13, LS*=5, d, < 4mm pH =7, 3 hrs, LS=50, LS=4, 3 hrs, LS=50, d,< 125 pm LS = 0.1 - 10, d, < 4mm

1

pH =7, 3 hrs, LS=50, LS=4, 3 hrs, LS=50, d,< 125 pm Leachant renewal (8 cycles: 6 hrs up to 64 days), LV=5 , dmin > 40 mm I

Practical routine testing protocols must be able to be completed in less than two days if they are to serve as the basis for immediate decision making. The approach advocated in this paper is that management decisions are made based on a combination of simple and rapid tests for which results are evaluated in conjunction with background information provided by initial detailed characterization of typical waste samples. This approach statistically establishes

455

"characteristic" waste leaching behaviour for categories of similar waste streams and compares quality control and on-site verification results to the defined characteristic behaviour. Thus the question being asked is "is this waste sample the same as the defined waste stream?" This approach permits the development of a range of management options for different waste characteristics and relatively easy site-to-site transference of prior knowledge. Application of this approach calls for a good understanding of the underlying mechanisms and parameters controlling constituent release. This allows the selection of an optimized combination of simple tests which allow more profound conclusions with respect to environmental consequences than just a pass or fail criterion on an arbitrary test. The aim of this work is to provide a first approach towards a concise, but at the same time comprehensive test covering as many relevant aspects as possible with a minimum of effort. 2. EXPERIMENTAL

2.1 Characterizationtests Based on the summary of test methods by Environment Canada [2],Wallis et al [3] and Van der Sloot et a1 [4] the following test procedures are considered most appropriate for characterization: 2.1.1 Capacity oriented Availability test r5l. This test assesses the fraction of the total concentration that under extreme environmental conditions could become available for leaching. Solubility contraints are minimized in this test by using a high dilution (Liquid to solid ratio (LS) = 100) and a maximum particle size of 125 him(). The data obtained with the pH static test at pH=4 may come close to the quantity determined with this test. Redox capacity test 161. A proper test for this property is not yet avialable. COD measurements [7] lead to too high values due to the fact that carbon and chloride are reactive as well. The test result is needed to evaluate how long a material may remain reducing upon exposure to atmospheric conditions to decide whether a material should be tested under reduced conditions or whether prior oxidation of the material leads to a better estimate of the possible release.

2.1.2 Equilibrium oriented pH static test and Acid Neutralization Capacitv testL8.91. These tests cover the leachability of a material over a large pH range, which may not be relevant entirely for the environmental assessment but will give information on the chemical speciation of the constituents considered. Many regulatory and other tests produce data that are consistent with the results of the pH stat test [4,10]. The pH static test or ANC test have succeshlly been used for geochemical modelling of the leaching process. Dissolved Organic Carbon (DOC) and Total Organic Matter (TOC). DOC and TOC are important parameters to assess the possible complexation of constituents - inorganic and organic- with dissolved organic substances like humic and hlvic acids. DOC is the actual property as measured in a leachate, whereas TOC is the potential property that may lead to the formation of DOC.

456 2.1.3 Dynamics oriented:

Column testsrl 11. In a column test the dynamic aspects of leaching that may occur due to slow transformation processes, sequential release and depletion of species may be reflected. The release is usually expressed in m a g leached against the LS ratio. This latter property is related to a time scale through the cumulative infiltration rate. Serial batch test[ 1,2,3]. This procedure provides almost the same information that a column test provides but in a shorter time span and with less resolution with respect to the low LS ratios. Tank leach test112.131. This test is relevant for monolithic specimen, where the release is mostly diffision dominated. Provided the monoliths are sufficiently durable size reduction of such materials would lead to a significant overestimation of the actual release to the environment. The aspect of leaching from stabilized materials and construction materials is not hrther addressed here, but covered in other studies [ 14,15]. ComDacted granular leach test [16J This test focusses on release by diffision from granular materials. Some fine grained materials in a surrounding of coarser material or those compacted to a low permeability during placement show a release which is governed by diffision rather than by percolation. A test has been developed to assess similar release controlling properties (physical retardation and chemical retention) as in the tank leaching test. 2.2 Concise tesr The relevant aspects to be addressed in assessing the environmental properties of waste materials are the changes that take place at the longer term, which can be derived from testing at different LS values, when it is realized that in most applications of granular materials slow percolation is the prevalent transport process. The actual release is controlled by sorption and solubility of specific phases, which is very much controlled by the chemistry of major elements in the wastes. Important leaching controlling factors are the pH, the redox situation, the presence of complexants- inorganic such as chloride and organic substances, such as DOC, and the presence of active sorption sites. Apart from the actual pH it is important to know how long a material is likely to maintain a given pH. As the pH is known to be an important parameter controlling release, changes in pH with time are important for the long term leaching behaviour of wastes. At present the role of reducing properties of wastes or applications under reducing conditions are not addressed in the regulatory framework. Such changes may lead to order of magnitude differences between the laboratory test and the actual situation in the field [ 171. From all this it is clear that a single extraction giving just one number to compare with a regulatory threshold is quite inadequate and likely t3 lead to many erroneous decisions- both as false positives (e.g. reducing materials in an oxidizing environment) and false negatives (e.g. materials with metal leachability due to the high pH showing a much lower pH under actual field conditions). The proposed concise protocol consists of a optimized serial batch extraction with as wide an LS range as practical in a batch procedure and two pH-controlled conditions in accordance with the unified approach of leaching for characterization purposes [10,18]. In the leachates some additional measurements are carried out to fill in some other crucial properties (Redox potential - EH, Dissolved Organic Carbon, Total Dissolved Solids). The duration of the serial batch extraction has been designed such that the whole procedure can be carried out within two days. In this paper we will focus on granular waste materials. A

457

similar approach is possible for stabilized waste, contruction materials and other monolithic materials, but will not be addressed here. 3. RESULTS AND DISCUSSION

3. I Examples of clzaracterization test data Data obtained from a column study on a neutral reacting coal fly ash [ 191, as shown in figure 1, illustrates some of the typical release profiles as observed in column leaching studies. AII results are expressed as cumulative release in mgkg. For comparison the total composition (straight line) of the respective constituents in the ash as well as the availability (dotted line) are included as relative assymptotes. From the graphs it is clear that a fraction of the Ca is being washed out rapidly, followed by a more slowly dissolving phase as reflected by the difference in the K values (measure for matrix retention; for hrther description see below). In the case of Cr and Mo all of the fraction available for leaching is released. At the end of the experiment (combination of a column experiment up to LS=lO and a serial batch procedure up to LS=lOO) V, Ba, Pb and Zn start to approach the available fraction indicating a release largely controlled by solubility. Contrary to Ca, Ba release is slow at low LS and increases more strongly at LS > 5 . This is most likely related to Ba - solubility control by sulfate, which is released initially in high quantities. The more leachable Ca fraction may well be the gypsum phase present in fresh coal ash. The element Cu features a very slow release, which even at the end of the experiment has not by far approached the available fraction. This is an example of very strong matrix retention. Similar observations have been made for other coal ashes and for other materials. These examples also illustrate the need to include analysis of major- and release controlling species (e.g. Ca, sulfate) during testing, not only the elements of regulatory significance. 3.2 Exaniples of release ns a function of LS Based on the column data given in figure 1 a few general types of release from column experiments can be identified (figure 2): fast (A, wash-out), intermediate(B) and slow release (C; solubility/dissolution control); a decrease in availability due to slow mineral formation or sorption reactions (D); an increase in release due to depletion of a solubility controlling phase (Barium) or changes in chemical conditions, such as pH (oxyanions) redox potential, with time (F); a decrease in release due to changes in chemical conditions or initial release of a different, more mobile, species (E ;Ca , DOC complexed metals). When solubility is the main controlling factor and changes in major element chemistry are limited, a Continuously Stirred Tank Reactor model (CSTR) can be used for initial evaluation of release. Subsequent model refinement would include evaluating the column as aplug flow reactor with dispersion. Use of a CSTR model leads to a description of release (E in mg/kg) from the column by:

E = AVB * ( 1 - e -LsK) + Co with AVB: the availability in mg/kg, LS: the liquid to solid ratio in Vkg, K: a retention factor for the constituent in the matrix in f i g and CO: a constant.

45 8 so00

30000

Total

1000

10000

Ba

100

Available

10

1000

1 0.1

100

Cr

10

1

0.1

LO

0.01 0.001

100

I

10

1

0.1 0.01 I

100

K-200

0.1

1

10

100

0.01 0.1

I

10

100

Liquid to solid (LS) ratio

Figure 1. Column leaching data for coal fly ash with retention data obtained from modelling release.

459 2 1

I

Availability 01

01

0 01

0 MI 0 OMS 01

A 0 OMS

I

10

100

01

I

10

100

2 I

01

0 01

u 001

due to changes in chemical conditions

0 001 0 woI

0 wO5 01

I

IU

IM?

,

01

.

,

I

,

10

I (M

2 ,

2 I b 01

0 01

0 WI 0 wos 01

o1

I

10

Decrease in release rate due to change in chemical/mineralogical conditions or presence of dillererent

101)

Figure 2. Examples of release patterns as a function of the liquid to solid ratio and identification for possible changes in the long tern).

In figure 1 this relation has been used to quantie the matrix retention parameter K. In a support document for the development of a new European leaching test for waste [ I ] a comparison of column studies with batch leaching tests of the same material was carried out on a wide range of materials to demonstrate that in many cases the proposed serial batch procedure matches well with the more eleborate column procedure. In table I a comparison of K values for column and serial batch are given for a few different materials.

460 Table I. Comparison of modelling parameters for evaluating matrix retention

* MSWI FA = MSW incinerator fly ash, FGD = flue gas desulhrization residue. 3.3 Reducing conditions When materials contain reducing substances, either due to the fact that reducing substances were introduced in the materials (e.g. stabilization with sulfides) or the materials were produced in oxygen starved conditions (industrial slags), the leaching behaviour will be significantly different from normal oxygenated conditions[20]. In addition, disposal or utilization in reducing environments will have consequences for the evaluation of material behaviour. Materials containing organic degradable matter can turn reducing due to biological Demineralized water 1000 900 800 700

s a v

w"

0 2

Coal Gassification Slag

600 500 400

Blast Furnace

Slag

300 200 100 0 -100 -200 -300

Coal fly ash

MSWI Bottom ash 2

3

4

5

6

7

8

9 1 0 1 1 1 2 1 3

PH Figure 3. Redox potentials measured in lcachates from wastes as a function of pH to indicate reducing properties of materials.

Phosphate Slag

46 1 degradation. transformations of sulfate to sulfide and reduction of FeIII to Fe I1 are important in this respect. Metals will be retained as their sulfides, Ba mobility will increase due to the decrease in sulfate concentration. The leachability of Fe and Mn will increase as well, since the reduced forms - FeII and MnII- are more mobile than the oxidized forms. This can mobilize trace elements associated with Fe and Mn sorptive sites. To be able to address the issue of reducing materials and materials in reducing environments, it is important to know which materials exhibit reducing properties and what circumstances in the field are relevant. The reducing capacity is an important property, in this connection, which has to be known in order to define how long a material will maintain its reducing properties. Figure 3 shows the redox potential of a range of materials measured in batch extractions in a closed vessel relative to the stability lines of water. For comparison the redox potential measured in demineralized water used in the extractions at different pH values is given as well. Coal fly ash is obviously oxidized, but all slags exhibit reducing properties. Upon exposure to the air both oxidation and neutralization (COz) will take place simultaneously. 3.4 p H dependence of Ienclring

Many studies have pointed at the relevance of pH as one of the most important controlling factors of leaching [ l - 4,10, 21, 22, 231. It is important to realize that the major element chemistry largely dictates the leachate composition and should therefore not be neglected [21,22]. The leaching behaviour of an individual element as a function of pH has been shown to feature generic and systematic characteristics to the extent that a baseline leaching characteristic can be identified for an element, which will deviate as a function of elementspecific interactions. In figure 4 the leaching behaviour as a function of pH is given for Cu from four different wastes. The coal ash reflects the Cu leachability curve governed mainly by inorganic Cu species. In the case of MSWI bottom ash the Cu is strongly complexed with DOC [24]. The modelling by MINTEQA2 [25] indicates the differences between inorganic solubility control and DOC complexation [10,22]. In car shredder waste the large organic fraction leads to a qualitatively predictable high leachability of Cu. Similar generic pH dependent leach curves have been established for other element as well [I, 101. It leads to the conclusion that for each element a limited number of parameters can be identified as the most crucial ones, which tends to make the task to characterize waste more manageable.

3.5 Description of the concise test procedure and its interpretation The proposed test consists of a two step serial batch extraction and a two step pH controlled batch extraction at pH = 8 and pH = 4, respectively. It complies with the unified approach to leaching as developed in the framework of the IAWG work[ 181. The serial batch test is carried out in a closed bottle using degassed water. Agitation in the serial batch test is achieved by test placing the bottles on a rollertable at about 10 rpm. The pH static extractions can be carried out in an open vessel and agitation by strirring is adequate. The four extracts obtained are analysed separately. The material to be tested should be size - reduced to 95% less than 4 mm for the serial batch and to 95% less than 300 pm for the pH controlled test. The serial batch and the pH controlled test can be run in parallel, which implies that the entire procedure can be completed within two days. In the extracts generated by the batch tests relevant major- and trace elements, pH, EH,TDS, conductivity and DOC are measured. In the pH controlled test

462

_I 6

0.01~

0.0011 4

o'li L$

0.01

MSWI fly ash "

5

6

"

7

8

"

I

4Y

0.001

4

1 0 1 1 1 2 1 3

5

6

1

8

9

1 0 1 l I 2 1 3

I000

1000

MSWI bottom ash 100

,

+

"

9

Coal fly ash

1

100

10

10

1

1

0. I

0.1

0.01

0.01

Y

\

CU-DOC complexation

I Shredder waste

0.001

0.001

5

6

7

8

9

10

I1

I2

13

PH Figure 4. Leaching behaviour of Cu from MSWI fly ash, MSWI bottom ash, Coal fly ash and Shredder waste as a function of pH. Geochemical modelling data is included for MSWI bottom ash.

the acid or base consumption is recorded. This combination of extractions allows several relevant conclusions on the properties of a material, which go well beyond a statement as to pass fail in relation to a regulatory limit value. When a material has been characterized extensively and shown to behave quite sytematically, part of the protocol may prove sufficient for quality control purposes (compliance testing). The following aspects can be addressed on the basis of the test results: - For each constituent an indication is obtained on the retention in the waste matrix and consequently the potential risk for short term release. Wash-out (no retention) and depletion of a mobile species can be distinguished from solubility-controlled release. - The release under low infiltration conditions can be derived from the LS=2 data as well as an estimate of the pore water concentrations for constituents that are not retained in the matrix.

463 MOBLLIZATION A N D WASH-OUT EFFECTS

Available for lencliing (long t e r m b

Wash-out/deplet ion of soluble species

0 ,

High retention I

.._..... K-Z OOM ) 10

I

0

I .s

20

LS

m

SERIAL BATCH TEST 1LS=2; 6 hrs; closed vessel LS=2-10; 18 hrs; closed vessel pH CONTROLLED TEST LS=50; pH=8 control; 4 hrs LS=50-100; pH=4 control; 3 hrs Record pH, E,, DOC, TDS and Conductivity.

r

REDOX PROPERTIES OF WASTES

Acid consumption in pH=8 and pH=4 test + alkalinity of L S = 2 and L S = 2 - 1 0 +Acid Neutralization Capacity

Fig 5. Concise testing protocol for the leachability of granular (waste) materials.

I

464

- Based on the deviation from CSTR behaviour a distinction can be made between changes leading to decreased release on the long term (remineralization, slow sorption kinetics) and increased release at the longer term, which depending on the level at which this occurs, requires further action to identify the causes for this behaviour and the potential risk at the long term. - In combination with the data from the serial batch extraction procedure the pH controlled test will allow a comparison with existing pH dependent leaching behaviour of the same waste or the same category of wastes. From this a conclusion can be drawn whether the material fits the pH pattern or deviates significantly from it. A deviation can often be related to element specific chemical speciation aspects, e.g. increased leachability of Cd in the pH range 4 to 9 due to a higher CI concentration or increased Cu leaching in the pH range 6 to 12 due to complexation with DOC. Abnormal deviations require further evaluation of its cause to minimize unexpected leaching behaviour in the long term. - The pH controlled test will give a measure for the fraction available for leaching and the acid neutralization capacity, which is a useful property to assess how long a material may be expected to maintain its own equilibrium pH when exposed to acid rain or carbon dioxide from the atmosphere or from biological activity. - By measuring the total dissolved solids (TDS) and conductivity in the leachate of the serial batch extractions an indication of the quantity of soluble salts can be obtained, which will have consequences for leachate analysis and may trigger more detailed analysis of soluble salts, which are generally not considered hazardous but may pose a serious threat to groundwater quality. - The Eh measurement will allow an identification of materials exhibiting reducing properties, when the redox potential in the leachate is compared with a &-pH relation for oxygenated demineralized water. A value of more than 50 mV lower than the value for oxygenated water at the corresponding pH value is considered to indicate reducing properties. This deviation has been chosen because of the uncertainty associated with this type of measurement and can only be regarded as indicative. If the material is considered to be reducing a reducing capacity needs to be determined (to be developed). Based on the destination of the material the material may have to be oxidized and tested again to represent the conditions to which it will be exposed. - By performing a DOC measurement in the leachate generated in the serial batch test an indication of possible mobilization of metals and organic contaminants can be obtained. The information generated with this concise protocol will help focus on key issues to improve environmental quality of (waste) materials. In the process of recycling, treatment of wastes, use as secondary materials and in disposal, this information is essential for proper management. 4. CONCLUSIONS

The proposed concise protocol for testing of (waste) materials has been developed on the basis of a number of integrated activities in the field of waste leaching and as such forms a synthesis of many existing leaching tests around the world . With a test duration of less than two days it meets the requirement of fast turn around needed for control purposes in industrial processes. The integrated approach that has been chosen to cover many aspects of leaching allows one to deal with time-dependence of leaching, initial leaching behaviour of materials, pH dependence, occurrence of reducing properties, aspects of chemical speciation and retention in the (waste)

465 matrix. Observations derived from the test may require hrther action to allow a better judgement of potential environmental effects. Parts of the test may be used in compliance testing, when the most crucial factors governing the leaching of constituents from a given waste material are known. This implies that optimization in terms of test use for specific applications is feasible. An optimization of the analytical effort is also possible based on previous knowledge of constituent behaviour.

Acknowledgement This approach has been developed following discussions in the framework of the activities of the Int. Ash Working Group (IAWG-IEA), discussions with colleagues from Working Goup 2 of CEN TC 292 “Characterization of Waste” in relation to the development of leaching test methods for waste characterization and compliance testing, activities in the Dutch standardization committee on leaching of Contruction Materials and Waste Materials and through collaboration under US-EPA Cooperative Agreement CR 8 18178-01. The financial support by the Netherlands Agency for Energy and the Environment under contract 222.3.6600.10 is gratefully acknowledged.

5. REFERENCES

H.A van der Sloot, 0. Hjelmar, Th.G. Aalbers, M. Wahlstrom and A.-M. Fallman. CEN TC 292 WG2 document: Proposed leaching test for granular solid waste. February, 1993. 2. Compendium of waste leaching tests. Environment Canada. Environmental Protection series. Report EPS 3/HA/7. May 1990. S.M. Wallis, P.E Scott and S. Waring. Review of leaching test protocols with a view to 3. developing an accelerated anearobic leaching test. AEA-EE-0392. Environment Safety Centre. 1992. 4. H.A van der Sloot, D. Hoede and P. Bonouvrie. Comparison of different regulatory leach test procedures for waste materials and construction materials. ECN-C-91-082, 1991. NEN 7341, Determination of the leaching behaviour of granular materials. Availability 5. for leaching. “I, 1993. H.A van der Sloot, D. Hoede en P. Bonouvrie. Invloed van redox condities op het 6. uitlooggedrag van reststoffen. ECN-C-93-037, 1993. NEN 323 5.3 Determination of the Chemical Oxygen Demand. ”I, Delft, 1976. 7. J.V. DiPietro, M.R. Collins, M. Guay, and T.T. Eighmy, Proc. International Conference 8. on Municipal Waste Combustion, Hollywood, 1989. Test methods for solidified waste characterization, Acid Neutralization Capacity test, 9. method #7, Environment Canada and Alberta Environmental Center, 1986. 10. H.A van der Sloot, Leaching aspects of MSWI residues. Special session on MSWI residues properties. This conference. 11. NEN 7343. Determination of leaching behaviour of granular materials. Column leaching I1993. test, “ 12. A N S 16.1 American Nuclear Society, Lagrange Park, 11, 1986. 1.

466 13. NEN 7345. Detemination of the leaching behaviour of construction materials and I1993. monolithic materials. Diffusion test. " 14. Proc. Sec. Int. Symp. Stabilizatiodsolidification of Hazardous, Radioactive and Mixed wastes. Williamsburg, Virginia, May, 29 to June 1, 1990. 15. H.A van der Sloot, G.L van der Wegen, G.J. de Groot and D. Hoede. BCR intercomparison of leaching tests for stabilized waste. This conference. 16. D.S.Kosson, T.T.Kosson, H.A. van der Sloot.,"USEPA Program for Evaluation of Treatment and Utilization of Municipal Waste Combustor Residues", Cooperative agreement CR 8 18178-01-O.USEPA/RREL,Cincinnatti, September 1993. 17. Several papers at this conference. 18. T.T. Eighmy and H.A. van der Sloot. A unified approach to leaching behaviour of waste materials. These proceedings. 19. H.A van der Sloot, G.J de Groot and 0.Hjelmar, EC contract EN3F-0032 NL . ECN-R91-008, 1991. 20. H.A van der Sloot, D. Hoede, R.N.J. Comans. The influence of reducing properties on leachingof elements from waste materials and construction materials.These proceedings. 21 T.T.Eighmy, D. Domingo, J.R.Krzanowski, D. Stampfli and D. Eusden. 1993. Proc Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania. 1993. 457 -478. 22. R.N.J.Comans, H.A.van der Sloot, P.Bonouvrie. Proc. Municipal Waste Combustion. VIP 32. Air & Waste Management Association, Pittsburg, Pennsylvania. 1993. 667 -679. 23. C.S. Kirby and DXmstedt. 1993, Proc Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania. 1993. 479 - 51 1. 24. H.A. van der Sloot, R.N.JComans,T.T.Eighmy, D.S.Kosson., Ruckstande aus der Mullverbrennung, Ed. Martin Faulstich, EF-Verlag fiir Energie und Umwelttechnik, GmbH, Berlin, 1992. 331-346. 25. A.R. Felmy, D.C. Girvin, and E.A. Jenne, MINTEQ--A2, EPA-600/3-84-032, U.S. Environmental Protection Agency, Athens, 1984.

Environmental Aspects of Consttuction with Waste Materials J.J.J.M. Goumans, H A . van der SImt and l3.G. Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

467

SPECIATION OF AS AND SE DURING LEACHING OF FLY ASH Eline E. van der Hoek and Rob N.J. Comans Netherlands Energy Research Foundation, P.O. Box I , 1755 ZG, Petten, The Netherlands

Abstract The most important mechanisms which control the leaching process of (hazardous) elements from combustion residues are dissolutiodprecipitation and sorption processes. In this study these processes are discussed as far as the leaching of As and Se from coal fly ash is concerned. We have found that arsenate and selenite are the most important redox species in fly ash leachates. The leaching of As and Se from acidic fly ash is controlled by sorption on amorphous iron oxide and can be modelled using a simplified surface complexation model. The As and Se leaching from alkaline fly ash is probably controlled by sorption on a Ca-phase, possibly ettringite or portlandite. Arsenate is sorbed much less reversibly than selenite on different matrix minerals of fly ash (especially iron oxides). This property can explain the lower availability of As for leaching from fly ash.

1. Introduction Combustion residues are subject of environmental concern [ 1,2]. For example, coal fly ash and municipal solid waste incinerator residues (MSWI) contain high concentrations of hazardous elements [2]. These residues must be stored under environmentally safe conditions and this storage is expensive. An alternative is to use these residues for example in construction materials. In both cases (disposal or usage) it is necessary to quantify the potential release of hazardous substances under different environmental conditions. Leaching tests have been applied to quantify the release (leaching) of contaminants from combustion residues. Single batch leaching tests are often used because of their simplicity, but the results of these tests depend on the experimental conditions [3]. We can obtain better predictions by using more extensive tests, such as the dutch standard leaching test (a combination of column and batch leaching tests at different Us and pH-values; [3]). Fig. 1 shows the schematic framework of the leaching processes of combustion residues. The leaching behaviour of combustion residues is controlled by the elemental composition (Fig. I ) . Although there is a high variability in the elemental composition of combustion residues, all these residues are composed of high-temperature solids and are metastable at low temperatures in water [4]. A systematic leaching behaviour has been observed for coal

468 fly ash [5], MSWI bottom ash and also for waste products [6]. The systematic leaching behaviour shows to be a function of major element concentration, pH [5,6] and the redox potential (Eh) as is shown by Comans et al. [7].

I

COMBUSTION RESIDUES

I

However, it is difficult to translate the results of leaching tests (also of the more extensive tests) into the actual release of (hazardous) elements in the environment. A number of processes that influence the actual release have often been neglected: e.g. the redox-potential [6] and weathering processes such as carbonation [8,9] and clay formation [lo,] I]. These underlying processes have to be known in order to obtain a better judgement regarding the (long-term) chemistry of combustion residues. This knowledge can be applied to all types of waste under Fig 1 . Schematic framework of leaching different environmental conditions. processes from combustion residues In Fig 1 the mechanisms which determine the composition of leachates from combustion residues are shown. The geochemical reactions which describe the processes between the solid and the aqueous phase are dissolutiodprecipitation and adsorptioddesorption. These geochemical reactions depend on the pH, Eh and the speciation reactions. The observed dependency for leaching (above paragraph) is in accordance with the dependency of the geochemical reactions. The precipitatioddissolution reactions of the major elements can be calculated using thermodynamic data, viz. complexation and solubility constants (Fig. 1). In a number of studies it was observed that major element leaching is generally controlled by dissolutionprecipitation reactions: In a column leaching experiment Warren and Dudas [I21 show the dissolution and precipitation of a number of solid phases from a alkaline fly ash. Fruchter et al. [I31 modelled the major element concentrations in leachates of coal fly ash by solubility reactions. Comans et al. [I41 also succeeded in modelling the major element leaching in MSWI bottom ash with solubility reactions. For example, both modelling studies observed that the Al concentrations in the leachates seemed to be in equilibrium with amorphous AI(OH), at low pH and with gibbsite at high pH. Trace element leaching can sometimes be modelled by precipitation reactions: the leaching of Cd in MSWI bottom ash could partly be described in equilibrium with otavite [14]. For other trace elements, such as As and Se, leaching cannot be modelled by solubility relations. It is more likely that adsorption and desorption reactions control the leaching behaviour (Fig 1.; [12-14]). In order to model the leaching process, these sorption

469 processes have to be identified and the parameters of the reactions have to be known. In combustion residues the sorption reactions are still not identified. In sediments and soils sequential extractions have been used to obtain qualitative information about the type of sorption process [ 151. The sequentid extractions have an operational character and, therefore, no sorption parameters, required to model the reactions, can be obtained. On the other hand single step extractions can be useful in obtaining model parameters [16]. In our study we focus on the leaching of oxyanions from coal fly ash. Coal fly ash is produced worldwide and in enormous amounts. In 1986 over the 5,000million tons of coal fly ash were produced [17]. Oxyanions, such as As and Se, are leaching in high amounts [ 181. To model the leaching of oxyanions, the speciation of these elements during leaching has to be known. The term speciation refers to the distribution of As and Se among different chemical forms (species) in the aqueous phase and on the solid: the speciation indicates which (redox) species of As and Se are present in solution and in which solidstructures As and Se are present on the fly ash matrix. As indicated above, the leaching of trace elements, such as As and Se, is mainly dependent on sorption reactions. Therefore, the sorption reactions controlling the oxyanion leaching from fly ash must be identified. The results of this study can be used to reveal also the leaching behaviour from other combustion residues, because of the fundamental approach and the systematic leaching behaviour of combustion residues in general. In this paper we will first discuss the major chemistry and mineralogy of coal fly ash Secondly, we will briefly review the environmental chemistry of As and Se. Finally the behaviour of As and Se in fly ash is described.

2. Coal fly ash The composition of coal fly ash depends on the composition of the coal, the type of boiler, the precipitator and the FGD (flue-gas desulphurization) installation [20]. The greatest part of coal fly ash is produced by pulverizedcoal plants [21]. In these boilers the temperatures rise to 1500°C,while in fluidized bed boilers, also frequently used, temperatures are approximately 850°C [22]. Fly ashes from fluidized bed boilers have a different composition and structure than fly ashes from pulverized-coal boilers, because of the different temperatures and the different grain size of the coal. In order to bind SO,, additions are sometimes made to the coal while burning. Obviously, additions alter the fly ash composition. In the Netherlands, FGD is mainly camied out with scrubbers [23] after precipitation of the fly ash and, therefore, the

Table 1: Major element composition of coal fly ash

Element

reported range [ 181

range of 50 Dutch coal fly ashes [I91

Al (%)

0.1-20.9

7-18

Ca (%)

0.1-22.2

0.5-6.0

Fe (%)

1-27.6

2.5-8.0

K (%I

0.17-6.7

0.4-3.6

Mg

0.04-7.7

0.25-2.3

Na (%)

0.01-7.1

0.08-0.96

s

0.04-6.4

0-0.7

Si (%)

1 .O-31.8

19-23

470 fly ash composition is not influenced by FGD. Coal may be divided in different ranks, ranging from peat, brown coal, lignitic coal, bituminous coal to anthracite. These ranks refer to the degree of coalification [21]. The mineralogy of the coal controls which minerals are formed in the fly ash [18]. The dominant presence of phyllosilicates and quartz in coal is reflected in the observed predominance of glass, mullite and quartz. The frequently reported Fe-sulphides, Fecarbonates, Fe-sulphates and Fe-oxides in coal account for the presence of Fe-oxides in fly ash. Also, the presence of alkaline earth carbonates in coal is reflected in the presence of Ca- and Mg-oxides in fly ash [18]. The major element composition of coal fly ash is given in Table 1. The range of Al, Fe and Ca concentrations in the fly ashes are within the range of the concentrations found in soils [18]. In our study we used mainly fly ash of bituminous coal of pulverized-coal plants, because this fly ash is the most produced fly ash in the Netherlands [24]. The range in composition of 50 different fly ashes produced in the Netherlands [I91 is also included in Table 1 . Fly ash from bituminous coal consists of 70-80 % of an amorphous A1,Si glass phase. The most important minerals are quartz, mullite, magnetite and hematite [25]. The trace elements, such as As and Se, are preferentially associated with smaller fly ash particles and are, therefore, probably enriched at the surface [20,26]. Surface enrichment can be explained by the condensation of elements, which are volatilized during combustion, onto solid particles at different rates and in varying amounts as combustion gases cool [4]. In a submicroscopic model Dudas and Warren [27] described coal fly ash particles as hollow and solid spheres. These spheres consist of an internal amorphous glass layer with minor and trace elements and an external glass layer with more available salts and trace elements. The amount of trace elements present in the internal glass layer is probably not available for leaching.

3. The environmental chemistry of As and Se In the natural environment, the partitioning of trace elements between the aqueous phase and the solid phase is determined by the speciation of these elements [28]. Very similar processes are likely to take place during the leaching of combustion residues because, similar to soils and sediments, these materials can be seen as an assemblage of different minerals [4,18]. The behaviour of oxyanions in the natural environment has been extensively studied, as shown below, and can tell us more about the leaching behaviour of oxyanions from fly ashes: As and Se can appear in a number of valence states. The valence state influences, among other things, the toxicity of the oxyanions. For example, the toxicity of As(II1) is higher than that of As(V) [29]. During the formation of fly ash, high amounts of oxygen are present and the fly ash leachates are, therefore, probably oxic. In the oxic natural environment As and Se are generally present as oxyanions [30] which dependent on the pH can be protonated (Table 2). In sediments and soils As and Se are often associated with (iron) hydroxides [16,32,33]. At pH-values above 8, it has been shown that clay minerals and calcium carbonates are important for the retention of As and Se in soils [34,35].

47 1 Table 2: Oxvanionic species of As and Se in oxic environment ~

Arsenate ASO,'-

+ H'

HASO:-

tf

- 1 1.5

HASO:-

+ H' e H,AsO,

-6.94

HZASO,

+ H'

-2.24

tf

H,AsO,

Selenate Se0,2' HSeO;

+ H' + H'

+ H' tf HA SO,^. HA SO,^. + H' tf H2AsO; H,AsO,' + H' tf H,AsO, As0;'

-12.71 -12.13 -9.23

Selenite tf

HSeO;

tf

H,SeO,

1.91 - 1.97

+ H' tf HSeO; HSeO; + H' tf H,SeO,

Se0,'-

-7.3 -2.57

The mobility of oxyanions in soils and sediments depends also on the valence state. Arsenate is more strongly retained than arsenite, while selenite is more strongly retained than selenate [36]. This effect can be explained by the fact that the sorption processes also depend on the valence state. For instance, Pierce and Moore [37] observed a lower sorption affinity for arsenite than for arsenate on amorphous iron oxide. Hayes et al. [38] observed a much lower sorption affinity for selenate than for selenite on goethite.

4. Speciation of A s and Se in fly ash leachates As stated above, the valence state influences the toxicity, the mobility in the environment and the sorption behaviour of the oxyanions. Therefore, it is necessary to determine their valence state in fly ash leachates. In order to measure the valence state of As and Se, we have tested a number of analytical methods and these methods were optimized [39]. In many studies the speciation of As is determined by hydride generation (as reviewed in van der Hoek et al. [39]). We found that this method gives unreliable results in fly ash leachates. It is possible, however, to obtain the total-amount of As by hydride generation. Coprecipitation of As(II1) with dibenzyldithiocarbamate appears to be a reliable method to determine these species in fly ash leachates. The precipitation of Se(IV) with ascorbic acid was found to be the best speciation method for Se. Total-Se was determined after reducing Se(V1) to Se(IV) in 6 M HCI. From these methods it appeared [39] that only small amounts of As(II1) (< 24 pg/l) and Se(V1) (< 50 pg/l) were present in the fly ash leachates after 24 hrs of leaching. We conclude that arsenate (As(V)) and selenite (Se(1V)) are the most important species in fly ash leachates. Only in leachates from brown coal fly ash, more selenate (Se(V1)) than selenite was present. Since we found no precipitatioddissolution processes that controlled As and Se concentrations in fly ash leachates, sorption reactions were studied for their possible role in controlling As and Se leaching. As a first attempt to find the possible sorbents, the leaching process was compared with the sorption of As and Se on important matrix minerals in fly ash [40]. Figs. 2 and 3 illustrate the leaching from acidic fly ash and alkaline fly ash, expressed as the percentage of As and Se remaining on the fly ash particles as a function of pH. The highest percentage of As and Se is released from acidic

412 100

t

.*.*t

100 A

8

A

e

A:

8

0

P

P g

50 ._ C

f

*::

0

& 4 4

50

._C

z

t

8

AS

A s e

z 0

0 2 '

4

6

8

10

12

14

2

4

6

8

10

12

14

PH

PH

Fig. 2: Percentage of As and Se remaining on the solid during leaching of acidic fly ash.

Fig. 3: Percentage of As and Se remaining on the solid during leaching of alkaline fly ash.

fly ash at pH 12, while the highest release from alkaline fly ash is at low pH (pH 4). Figs. 4 and 5 show the sorption of arsenate and selenite on different matrix minerals. Hematite is one of the principle iron-bearing minerals in fly ash. Mullite is an important crystalline Al-silicate. Portlandite and ettringite may be formed during leaching of alkaline fly ashes. By comparison and interpretation of the sorption and leaching results we conclude [40]that the leaching of As and Se from acidic fly ash (Fig 2) can be described by sorption on iron oxide (Figs. 4 and 5). The leaching from alkaline fly ash seems to be controlled by sorption on an Ca-phase [MI. This sorbent may be portlandite (at pH > 12; Figs. 4 and 5) or, possibly, ettringite (Figs. 4 and 5 ) . Mullite may be important at neutral pH, but only when there is no iron oxide at the fly ash surface (Figs. 4 and 5 ) . 100

-$

-4-

-

g

-E

50

-e

-+

0

2

4

6 8 10 12 14

PH Fig. 4: Sorption of As on different matrix minerals as a function of pH.

2

4

6 8 10 12 14

PH Fig. 5: Sorption of Se on different matrix minerals as a function of pH.

473

It was shown above that sorption on iron oxide is important in controlling the leaching of As and Se. In a subsequent study [41] an attempt was made to model this process in the fly ash. Leaching experiments were followed by selective extractions of iron oxides from the leached fly ash, in order to obtain model parameters. Both a crystalline and an amorphous iron oxide extraction were performed, because only crystalline iron oxides (hematite and magnetite) are present in dry unweathered fly ash, while amorphous iron oxide can arise as a secondary precipitate during leaching of the fly ash [lo]. Amorphous iron oxide proved to be more important than crystalline iron in controlling the leaching of As and Se [41]. A simplified surface complexation model [41] was applied to the leaching and extraction data (Figs. 6 and 7). In Figs. 6 and 7 it is shown that it is possible to describe the leaching of As and Se (pH c 10) from acidic fly ash by using a simplified surface complexation model for the sorption on amorphous iron oxide. Se leaching above pH 10 is probably controlled by another (still unknown) mineral [41]. 7

0 0

a

6

2 0

0 -

5 4

3 2

4

6

8

10 12

14

PH

Fig. 6: Apparent overall equilibrium constant (KA) of As during leaching of fly ash (0) and of As model experiments ([37, 381 lines 1,2 and 3) on amorphous iron oxide.

2

4

6

8

10

12

14

PH

Fig. 7: Apperant overall equilibrium constant (K,) of Se during leaching of fly ash (0) and of Se model experiments ([38,42] lines 1.2 and 3) on amorphous iron oxide.

As the reversibility of the sorption processes is important for the actual release, we also studied the reversibility of the sorption processes of arsenate and selenite on the different minerals. There is a difference between the sorption of arsenate and selenite on mullite, portlandite and hematite [40,43] in that arsenate sorption was in general less reversible, especially on hematite (Fig. 8). This may explain the lower availability of As relative to Se leaching.

5. Conclusions The leaching of As and Se from coal fly ash can be described by sorption processes. In this study we have identified a number of relevant sorption reactions. We found that

474

E'

arsenate and selenite are the most important redox species in fly ash leachates. The leaching of arsenate and selenite from alkaline fly ash is likely to be controlled by sorption on a Ca-phase. Possible sorbents are portlandite and/or ettringite. The leaching 0 8 .S 0 40 from acidic fly ash is controlled by sorption 0 0 P on iron oxide. Selective extractions have f P 20 . shown that amorphous iron oxide is the most important sorbent during leaching of acidic 0 fly ash. It is possible to model the leaching of 0 10 20 30 As and Se from acidic fly ash using a time (days) simplified surface complexation reaction for Fig. 8: Desorption of As and Se from amorphous iron oxide. It is important to know hematite at pH 12 o.3. Prior to the reversibility of the sorption reactions in desorption, As and Se were adsorbed for order to be able to quantify the actual release weeks at the pH values indicated in the Of these oxyanions from fly ash. The sorption reversibility of arsenate on the studied legend. sorbents is different from that of selenite. Especially on iron oxide, arsenate is sorbed much less reversibly. This property can explain the lower availability of As relative to Se, for leaching from fly ash. The results of this study can be used to reveal also the leaching behaviour from other combustion residues, because of the fundamental approach and the systematic leaching behaviour of combustion residues in general.

T

loo

L

6. References 1. Carlson, C.L. and Adriano D.C. (1993) Environmental impacts of coal combustion residues. J. Environ. Qual. 22, 227-247. 2. Theis, T.L. and Gamer, K.H. (1990) Environmental assessment of ash disposal, C.R.C. Crii. Rev. Environ. Conirol. 20, 21-24

3. van der Sloot, H.A. (1988) Leaching procedures for waste materials and waste products. Hazardous Waste: Deieciion conirol, Treatment, (Ed) Abbou, R., Elsevier Science Publishers B.V., Amsterdam, 637-649. 4. Eary, L.E., Rai, D., Mattigod, S.V. and Ainsworth C.C.(1990) Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: 11. Review of the minor elements. J . Environ. Qual. 19, 202-214. 5. de Groot, G.J., Wijkstra, J., Hoede, D. and van der Sloot, H.A.(1989) Leaching characteristics of selected elements from coal fly ash as a function of acidity of the contact solution and the liquidsolid ratio. In Environmental aspects of stabilization and solidiJicaiion of hazardous and radioactive wastes (eds. P.L. CBtC and T.M. Gilliam) ASTM STP 1033 pp. 170-183, American Society for Testing and Materials, Philadelphia. 6. van der Sloot, H.A. (1991) Systematic leaching behaviour of trace elements from construction materials and waste materials. In Wasre materials in construciion, Proceedings

of ihe iniernaiional conference

on

environmenial implicaiions of

475 construction with waste materials, Maastricht (eds) Goumans, J.J.J.M., van der Sloot,

H.A., Aalbers, Th, G. Elsevier, Amsterdam, 19-37 Comans, R.N.J., van der Sloot, H.A., Hoede, D. and Bonouvrie, P.A. (1991) Chemical processes at a redox/pH interface arising from the use of steel slag in the aquatic environment. In Waste materials in construction, Proceedings of the international conference on environmental implications of construction with waste materials,

Maastricht (eds) Goumans, J.J.J.M., van der Sloot, H.A., Aalbers, Th, G. Elsevier, Amsterdam, 243-255 Schramke, J.A.( 1992) Neutralization of alkaline coal fly ash leachates by C02(g) Applied Geochem. 7 , 481 -492. Sakata, M. (1987) Movement and neutralisation of alkaline leachate at coal ash disposal sites, Environ. Sci Technol. 21, 771-777. 10. Warren, C.J. and Dudas, M.J. (1984) Weathering Processes in relation to leachate properties of alkaline fly ash , J. Environ. Qual. 13, 530-538. 1 I . Zevenbergen, C., Bradly, J.P. Van der Wood, T., Brown, R.S., Van Reeuwijk, L.P., and Schuiling R.D. (1993) Weathering as a process to control the release of toxic constituents from MSW bottem ash. In Geology and Confinment of toxic waste, Proc. of the Int. Symp. Geoconfine '93, Montpellier, France, 591 -595. 12. Warren, C.J. and Dudas, M.J.(1985) Formation of secondary minerals in artificially weathered fly ash. 1. Environ. Qual. 14, 405-410. 13. Fruchter, J.S., Rai, D. and Zachara, J.M.( 1990) Identification of solubility-controlling solid phases in a large fly ash field lysimeter. Environ. Sci. Technol. 24, 1173-1179. 14. Comans R.N.J., van der Sloot, H.A., and Bonouvrie, P.A. (1993) Geochemical reactions controlling the solubility of major and trace elements during the leaching of municipal solid waste incinerator residues. In VIP-32 Municipal Waste Combustion Proceedings of an international specialty conference, Williamsburg, Virginia, 667-680. 15. Salomons, W. and Forstner, U.: Metals in the hydrocycle. Berlin, Springer verlag, ( I 984). 16. Belzile, N. and Tessier, A.( 1990) Interactions between arsenic and iron oxyhydroxides in lacustrine sediments. Geochim. Cosmochim. Acta 54, 103-109. 17. Manz, O.E., Faber, J.H., Takagati, H. (1989) Worldwide production of fly ash and utilization in concrete. In third CanmetlACI international conference on j i y ash, silica fume, slag & natural pozzolans in concrete, supplementary papers, Trondheim. 18. Mattigod, S.V., Rai, D., Eary, L.E. and Ainsworth C.C.(1990) Geochemical factors controlling the mobilization of inorganic constituents from fossil fuel combustion residues: I. Review of the mayor elements. J. Environ. Qual. 19, 188-201. 19. van der Sloot, H.A., Weyers, E.G., Hoede, D., Wijkstra, J. (1985) Physical and chemical characterization of pulverized-coal ash with respect to cement-based applications, ECN-I 78, Netherlands Energy Research Foundation, Petten. 20. Natusch, D.F.S. and Taylor, D.R.(1980) Environmental effects of western coal combustion. Part IV. Chemical and physical characteristics of coal fly ash. U.S. Environmental Protection Agency Rept. EPA 60013-80-094. 21. Helmuth, R. (1987) Fly ash in cement and concrete, Portland Cement association, Skokie, Illinois. 22. Tauber, C ( 1 987) Spurenelementen in flugaschen: Kohle-Kraftwerk-Umwelt, Verlag TUV Reinland.

416 23. Personal Communication R. Meij, KEMA, Arnhem, The Netherlands. 24. van der Sloot, H.A., Zonderhuis, J. and Meij, R. (1983) Spoorelementen in steenkool en steenkoolas. Energiespectrum 7 , 3 18-325. 25. McCarty, G.J., Manz, O.E., Johansen, D.M. and Steinwand, S.J. (1988) X-Ray Diffraction Analysis of fly ash. In Advances in X-ray Analysis. 31 (eds) Barrett, C.S., Gilfrich, R.J., Russ, J.C., Richardson, Jr, J.W. and Predecki, P.K. Plenum Publishing Corporation, 331 -342. 26. Meij, R. (1989) Tracking trace elements at a coal-fired plant equipped with a wet fluegas desulphurisation facility. Kema Scientific & Technical Reports 7 ,267-339. 27. Dudas, M.J. and Warren, C.J.(1987) Submicroscopic model of fly ash particles. Geoderma 40, 101-1 14. 28. Buffle, J. (1988) Complexation reactions in aquatic systems: An analytical approach, Ellis Horwood Limited. Chichester, England. Joint group of 29. Gesamp ( 1 986) (IMO/FAO/UNESCO/WMO/WHO/IAEA/UN/UNEP experts on the scientific aspects of marine pollution) Review of potentially harmful substances- arsenic, mercury and selenium, Rep. Stud. GESAMP 28. 30. Cutter, G.A. (1992) Kinetic control on metalloid speciation in seawater. Marine Chem. 40, 65-80. 31. Parfitt, R.L.(1978) Anion adsorption by soils and soil materials. Adv. Agron 30, 1-50. 32. Maher, W.A. (1984) Mode of occurrence and speciation of arsenic in some pelagic and estuarine sediments. Chemical Geology, 47, 333-345. 33. Neal, R.H., Sposito, G., Holtclav., K.M. and Trana, S.J. (1987) Selenite adsorption on alluvial soils: I. Soil composition and pH effects. Soil Sci. SOC.Am. J . 51, 1161-1 165 34. Goldberg, S., and Glaubig, R.A.(1988a) Anion sorption on a calcareous, montmorillonitic soil-selenium. Soil. Sci. SOC.Am. J . 52, 954-958. 35. Goldberg, S., and Glaubig, R.A.(1988b) Anion sorption on a calcareous, montmorillonitic soil-arsenic. Soil. Sci. SOC.Am. J . 52, 1297-1300. 36. Masscheleyn, P.H., Delaune, R.D. and Patrick, Jr, W.H. (1991) Arsenic and selenium chemistry as affected by sediment redox potential and pH. J. Environ. Qual. 20, 522527. 37. Pierce, M.L. and Moore, C.B.(1982) Adsorption of arsenite and arsenate on amorphous iron hydroxide. Water Res. 16, 1247-1253. 38. Hayes, K.M., Papelins, C. and Leckie, 5.0.(1987) Modeling ionic strength effects on anion adsorption at hydrous oxide/solution interfaces. J . Colloid Interface Sci. 125, 7 17-726. 39. van der Hoek, E.E., van Elteren, J.T. and Comans, R.N.J. (to be published) Determination of As, Sb, and Se species during leaching from fly ash. 40. van der Hoek, E.E., Bonouvrie, P.A. and Comans, R.N.J. (submitted) Sorption of As and Se on mineral components of fly ash: relevance for leaching processes. 41. van der Hoek, E.E. and Comans, R.N.J. (submitted) Sorption of As and Se on iron oxide in acidic fly ash as a model for the leaching process. 42. Balistrieri, L.S. and Chao, T.T. (1990) Adsorption of Selenium by amorphous iron oxyhydroxide and manganse dioxide. Geochim. Cosmochim. Acta 54, 739-75 1 43. van der Hoek, E.E., Boots, B. J. and Comans, R.N.J. (to be published) Sorption reversibility of arsenate, selenite and molybdate on hematite and amorphous iron (hydr)oxide.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) 01994 Elsevier Science B.V: All rights resewed.

411

Measurement of redox potential during standardized column tests J. Keijzer and A.J. Orbons IWACO B.V., P.O. Box 8520, 3009 AM ROTTERDAM, The Netherlands

Abstract A method for continuous measurement of the Eh during the column test as described in the Dutch standard NEN 7343 has been developed. This method has been used on a variety of waste materials such as MSW bottom ash and fly ash, phosphorous slag, lavalite and various kinds of (contaminated) soil. The reproducibility of the method was satisfactory (* 50 mV). The observed redox changes during the column test give an indication of the redox capacity of waste materials and provide important information about (microbiologically mediated) leaching processes within the column. By taking into account redox potential this column test method enables a more accurate prediction of the actual leaching behaviour of reducing waste materials in field situations. 1. INTRODUCTION

The first Dutch standard describing leaching tests N V N 2508 [l] does not take into account the redox potential. Nowadays it is widely accepted that redox behaviour is an important factor influencing leaching of contaminants from waste materials [3, 41. The importance of measuring the redox potential is also recognized in the column test described by the recently published Dutch standard NEN 7343 [2]. However, a method to determine this parameter is not described in this document. The experimental setting for this column test is a waterlogged system, in which the uptake of atmospheric O2 (and COJ by the material is very limited. Therefore, if reducing materials are placed in the column, they may impose reducing conditions on the system, depending on their actual reducing capacities. This paper reports on monitoring data with respect to the redox behaviour during the column test leaching of different waste materials and soils, using a newly developed continuous method for measuring redox potential. Redox potential in waste material environments is largely a function of only a limited number of redox reactions. The most common reactions are those of nitrates, manganese (IV <-> 11), iron (111 < - > 11) and sulphates [ 5 ] . The redox conditions during column test leaching are controlled by the actual redox capacity of the sample being investigated. Decay (oxidation) of organic matter and microbiological activity are also factors influencing this parameter, and subsequently redox potential [6]. The redox potential in leachate samples can change very fast when exposed to air [3]. For this reason it is necessary to

478 measure redox potential in-situ in order to get a reliable description of redox changes occurring in the column. In the method newly developed the redox potential of the leachate is measured directly after leaving the column, without being exposed to air. 2. EXPERIMENTAL

All column tests were performed on a variety of waste materials using the apparatus shown in figure 1. In accordance with NEN 7343 demineralized water acidified with HNO, was used as influent. The oxidant NO< might have some influence on materials with low reducing capacity. With the continuous flow applied L/S=10 was reached after three weeks. Contact of the sample with atmospheric air is virtually absent under these circumstances, and the material investigated will control the value of the redox potential in the column. A flowcell (k 3 ml; zero headspace) with a built-in electrode was placed directly after the column (length 3060 cm, internal diameter 5 cm). Redox potential of the leachate was continuously measured with a platinum electrode to a calomel electrode (+244 mV vs. S.H.E.). Data were recorded digitally. Electrodes were validated using a buffer solution containing 0.1 M (NH,),Fe(SO,), and 0.1 M (NH,)Fe(SO,), in 0.1 N H2S04 (Eh +430 Figure 1: Apparatus used for mV) to correct for drift, caused mainly by leaching and redox test measurements sulphide uptake of the platinum surface [7]. 3. RESULTS The reproducibility of the experimental procedure proved to be satisfactory. Variations between duplicate measurements on waste materials were limited to 50 mV (in ranges +/100-300 mV). The redox potential of waste materials measured during the column test was reasonably constant. In most cases variations did not exceed 100 mV over the time period of three weeks. In figure 2 the variation of the Eh during the column test for four waste materials is given as an example. In figure 3, Eh/pH positions measured during the column test for these waste materials are shown. Figure 4 shows Eh/pH positions for four types of soils. The variation in redox potential during the column test was substantially larger, as shown in figure 5.

479

A

B

-E

c

9Qo-

D

300

100 -100 3 9w-

Figure 2. Redox potentials measured during column tests of demolition waste (A), phosphorous slag (B), MSW fly ash (C) and MSW bottom ash (D)

Figure 3. Eh/pH positions measured during column test leaching of waste materials. The solid line represents the redox potential as function of pH in demiwater.

480

"

-m400-

Figure 4. Eh/pH positions measured during column test leaching of four types of soils. The solid line represents the redox potential as function of pH in demiwater.

Figure 5. Redox potentials measured during column tests on different soils with 5.9 wt% (A), 7.5 wt% (B), 7.0 wt% ( C ) and 4.1 wt% organic matter (D)

48 1

Figure 6. Eh measured during elongated column tests on phosphorous slag (A), MSW fly ash (B) and MSW bottom ash (C)

5. CONCLUSIONS Using a continuous method to measure Eh during the column test, different waste materials investigated could be categorized as creating either a stable negative redox potential (reducing) or a positive redox potential in the column. Eh during the column test (L/S 10, 3 weeks) was fairly stable with these wastes (k 100 mV). Four soils investigated were harder to categorize. Reducing capacity in soils is associated with organic matter, and the soil sample used in this study containing less than 2.5% organic matter showed virtually no reducing capacity. The variations in Eh during column tests on soils were larger than for the (inorganic) waste materials. The results reported can help to understand leaching processes in the column, and may provide an extra tool to extrapolate laboratory results to actual leaching in field situations. 6. REFERENCES

1 NVN 2508. Dutch Standardization Institute NNI, 1988. 2 NEN 7343. Dutch Standardization Institute NNI, 1993, 3 H.A. van der Sloot, D. Hoede and P. Bonouvrie. Invloed van redoxcondities op het uitlooggedrag van reststoffen. Taakstellend Plan Uitloging, Activiteit V6, ECN, Petten 1993. 4 C. Amrhein, P.A. Mosher and D.A. Brown. Soil Science Vo1.155, No.4, April 1993, pp. 249-255. 5 D.J. Greenland and M.H. Hayes. The chemistry of soil processes. Wiley & Sons, New York 1981. 6 C. Zevenbergen, W.F. Hoppe. Leaching tests and the influence of oxidation-reduction processes. In: Waste materials in construction, J.J.J. M. Goumans, H.A. van der Sloot and Th.G. Aalbers Eds., Elsevier, Amsterdam 1991, pp. 369-370 7 T.S. Light. Anal. Chem. 44, 1972, pp. 1038-1039. 8 R. Bartlett and B. James. Soil SCi. SOC.Am. J. 44, 1980, pp. 721-724.

482 4. DISCUSSION

From figure 3 it appears that the waste materials investigated can be divided in two different categories according to their redox behaviour in the column. Phosphorous slag, MSW bottom ash, MSW fly ash and to a lesser extent coal fly ash create (slightly) reducing conditions during the experiment, indicating that these materials have enough reducing capacity to create a negative redox potential in the column. This is in accordance with the findings of van der Sloot et a1.[3] about the reducing capacities of these materials. Lavalite, demolition waste, asphalt and blaster grit show a distinctly higher Eh. All waste materials showed a reasonably constant Eh (* 100 mV) during the column test. In order to investigate the duration of this Eh stability column tests were elongated up to 4 months (L/S=50). Figure 6 shows the Eh measured during elongated tests on phosphorous slag, MSW bottom ash and MSW fly ash, wastes with a relatively strong reducing capacity. All wastes show the same type of curve: Eh slowly rises from negative values (reducing conditions) to values of 0 to +50 mV, while pH slightly falls. Apparently the actual reducing capacity of the wastes diminishes in time. This can be explained by the leaching of the available reducing agents, which lowers the reducing capacity of the waste. The soils investigated are much harder to categorize than the waste materials, as can be seen from figure 4. The soil with low organic matter content ( < 2.5%) has virtually no reducing capacity, which suggests that the redox behaviour of soils is associated with organic matter. The progress of Eh during the column test of soils is quite different from the waste materials discussed previously. Eh is always positive at the beginning of the experiment. The rapid initial decrease of Eh in soil A is probably due to the release of (mobile) reducing substances, accompanied by oxygen depletion. Eventually oxidizing agents are mobilized (a process with comparatively slow kinetics), and the buffering capacity is restored. Microbiologically mediated processes could account for the decrease of Eh at high L/S ratios [8]. In measuring redox behaviour during column tests on soil, special care should be taken to avoid artifacts caused by pretreatment of the sample. If a soil sample is dried and rewetted, a sharp initial decrease in Eh (up to 800 mV) was observed. This sharp dip in Eh is caused by an explosion of microbiological activity induced by the previous drying, and can be avoided by storing soil samples with preservation of their original moisture content [8]. The importance of measuring redox potentials during the column test is twofold. Monitoring of Eh can provide an explanation for seemingly anomalous results, such as a sudden release of arsenic (whose solubility is particularly sensitive to sudden changes in redox conditions). Eh measurement provides an additional tool to help understand processes taking place within the column. Most of all, insight in redox behaviour is essential to help predict actual leaching in field situations. In the case of reducing wastes that are stored in an oxidizing environment a modification of the column test is required to assess redox behaviour in order to predict the actual leaching under field conditions. However an additional test (for example determination of chemical oxygen demand) is needed to quantify the reducing capacity of the waste material.

Environmental Aspects of Construction with Waste Materials J J . M . Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) a1994 Elsevier Science B. V. AN rights reserved.

483

THE INFLUENCE OF REDUCING PROPERTIES ON LEACHING OF ELEMENTS FROM WASTE MATERIALS AND CONSTRUCTION MATERIALS. H.A. van der Sloot , D. Hoede, R.N.J. Comans. ECN, P.O. Box 1 , 1755 ZG Petten, the Netherlands

Abstract In testing waste materials and construction materials for their leaching properties none of the existing regulatory tests take reducing properties of materials or application of materials in a reducing environment into account. This omission can lead to mismanagement of wastes because results of leaching tests of short duration fail to show the potential leachability of initially reducing materials after oxidation in a certain utilization or disposal scenario. Nor do they reflect the behaviour of oxidized materials, when brought in a reducing environment. It is clear that a range of constituents feature highly different leachability under oxidized versus reducing conditions. Typical examples of potentially critical situations are discussed. A procedure to identify whether a waste or a construction material possesses reducing properties is presented, as well as a method to assess the reducing capacity of materials, which can be used to determine how long a material may stay reducing or will be able to impose reducing properties on its environment. Implementation of the assessment of reducing properties of materials in decisionmaking on waste handling, utilization and disposal is discussed. 1. INTRODUCTION

The application of secundary materials in construction usually takes place under oxic conditions due to the permanent contact with the atmosphere. Some materials, such as slags from industrial processes, possess reducing properties as a result of the prevalent oxygen starved conditions in the furnace. This material property is not addressed in the evaluation of materials with current regulatory test procedures (TCLP or EP tox[l], DIN 38414 S4[2], Afnor X-3 1-210[3], Swiss TVA[4], NEN 7300 series[5,6]). When the material imposes reducing conditions on the leachate that will have consequences for the release of several constituents. The question arises whether the release measured in a test properly reflects the actual release that may occur under the conditions of the application. A few situations can be identified in which reducing properties may play a major role - reducing materials exposed to the atmosphere. - oxidized materials exposed to reducing conditions imposed by its surroundings (e.g. material in contact with reducing soil or sediment) - materials with latent biological activity (e.g. material rich in organic degradable matter) turning anoxic with time.

484

For a proper assessment of release in these specific circumstances additional information is needed. First it is crucial to identie whether reducing conditions will play a role in the application aimed for. To be able to address that issue it is necessary to know whether a material has reducing properties. Once that has been established the reducing capacity needs to be determined to be able to assess how long a material will feature reducing properties and impose reducing conditions on its environment. Finally the consequences for the leaching behaviour of several constituents under oxic and anoxic conditions needs te be addressed to allow an evaluation of the critical nature of the occurrence of changes in redox conditions with time on release of constituents of concern. As examples studies on steelslag [7], blast furnace slag, phosphorus slag, lead slag will be discussed, that have revealed the common characteristics of these materials due to the release of reduced sulphur species, which are the main carriers of reducing capacity affecting the surrounding. Studies on Municipal Solid Waste Incinerator bottom ash has shown the relevance of developing reducing conditions upon degradation of residual organic matter on the leaching behaviour of Cu. The oxidation of stabilized waste containing reducing substances to retain constituents of concern and stabilized reducing wastes are discussed in light of the management of such wastes.

ZEXPERIMENTAL 2.1 Identification of reducing properties of niaterirrls. The procedure that is applied to identi@ whether materials exhibit reducing properties consists of a comparison of the redox potential (Eh in mV) measured in the leachate obtained after extraction for 24 hours at a liquid to solid ratio (LS) of 1 in a closed vessel and the redox potential of normal oxygenated water at the final pH of the leachate. When the Ee value of the leachate, exposed for 24 hours to the waste or a crushed waste product, proves to be lower than that of the demineralized water at the same pH by more than 50 mV, then the material can be considered to exhibit reducing properties and the reducing capacity has to be determined as described below. 2.2 Deterntination of reducing potential For the determination of the reducing capacity of a material a cerium titration is applied [8,9]. The procedure for the determination of the reducing capacity of extracts consists of an extraction at liquid to solid ratio (LS) is 1 for 24 hours with 0.1 N Ce4' solution in 1 M HzS04. The reduced fraction of the Ce added is back-titrated with Fe2'- solution. The amount of Ce converted to Ce3' is calculated as mMol Oz/g of material. The procedure for the determination of the reducing capacity of solid materials is based on the same principle at a LS of 10 at for 2 hours only. The data need to be corrected for the moisture content, as drying samples prior to the determination may affect the reducing capacity. The carbon content of the material can contribute to the measured reducing capacity. In slags of melting processes the carbon content is usually not relevant, which means no additional corrections are needed. In combustion residues a fraction of unburnt material is common. In case the carbon content of the sample is not marginal (> l%), a correction is needed. The correction is a function of the carbon content and the specific surface area. When the specific surface area is smaller than 50

485

m2/g and the carbon content is below 5 %, the contribution of carbon is marginal and can be omitted. In many combustion residues this condition is fulfilled. The detection limit of the reducing capacity measurement is 0.02 mMol 0 2 /g (or 0.6 mg 0 2 /g). 2.3 Redox stntic test. A redox static setup has been developed using hydrogen as the redox controlling constituent [lo]. Based on the experience gained it has been possible to maintain the redox ofthe leaching medium at a stongly reducing condition. Other forms of redox control are based on applying reducing substances (e.g. sulfides, hydrochinon, hydrazine). Only in systems where sulfur species are the redox controlling species addition of a mixture of sulfur species rather than sulfide only is a suitable option. 2.4 Suljiur specintion In many cases it is important to know the distribution of the individual sulfur species as they have different chemical properties with respect to their interaction with other constituents. The following constituents are relevant: sulfate, sulfite, thiosulfate, polysulfides and sulfide. For a given redox potential a specific ratio of the sulfur species may be found. The measurement of the individual species requires sophisticated separation techniques. In this work HPLC was applied [ 111.

3. RESULTS AND DISCUSSION

-B ? .

3.1 Materials with reducing properties

15

1

B

'W

Industrial slags, such as phosphate slag, c blast furnace slag, steel slag and metal Q I2 -0d slags from several metal processing plants G 9 (e.g. Pb slag, Zn slag) exhibit reducing 5 v properties. The data in figure 1 show the m relation between the availability of S and 2 6 $ the total S content for blast furnace slag (circles), phosphate slag (triangles) and 3 steel slag (squares). There is no direct 9 correlation between S content or 0 availability and the the reducing capacity 500 1M)I) 1500 IMO 25W according to the method described before. Available S (mg/kg) The relatively high reducing capacity of Figure 1. Relation between available S, steelslag is caused by the high Fe I1 content of steel slag. S-species are total S and the reducing capacity of slags. important for imposing reducing conditions. Much more so than reduced Fe or Mn species, which are only released from slags in relatively low dissolved concentrations. A substantial fraction of S in fresh slags can be considered to be speciated as sulfides. In the case of slags, a low redox potential is usually associated with a high pH. In figure 2 the change in EH - pH condition upon exposure to air is indicated.

-

Y

486 1000 It leads to a combined oxidation/ neutralization. In contact with biologically 800 active environments with CO2 - production 600 and not directly in contact with the air, the v lower curve reflects the changes with time. 3 400 * In the case of application of industrial slags c Q 200 as hydraulic binder or subbase in road n construction, the importance of placing such x o 0 a construction at least 0.5 m above -200 groundwater level on a sandy soil (good aeration) is illustrated in figure 3. The -400 oxidation of reduced S-species, the 2 3 4 5 6 7 8 9 10111213 neutralization of leached alkalinity and the PH formation of calcite prevents uncontrolled spreading of reducing sulhr species. Thus Figure 2. Changes in redox behaviour of preventing adverse effects on the reducing slags in different applications. environment. In addition, release of reduced Fe- and Mn- species (FeII and MnII) will lead to formation of hydrated Fe(II1) and manganese oxide phases upon oxidation, which act as a sorption barrier for several metals and oxyanions. h

$

3.2 Dimerenee in leaching behaviour under oxidized and under reducing conditions

ROAD CONSTRUCTION

3.2.I M S W bottom ash

The leachability of Cu from MSWI bottom ash can be used as Subbase with an hydraulic slag mi an illustration of the magnitude of the effect of reducing conditions on metal release. Under oxidized conditions Cu is complexed with Dissolved Organic Carbon leading so: so: so: CaCO,$ to release of about 1 mg/kg at neutral pH. Upon heating the ash $ 4 4 Groundwater to 550 C for 6 hours the release is substantially reduced (almost two Figure 3. Oxidationheutralization reactions occurring ii A orders of magnitude). verification of the effect of the construction of a roadbase with reducing materials. reducing conditions on Cu release using a recently developed " Redox stat"[ 101 based on H-2 purging has shown a reduction in leachability of at least an order of magnitude. It is clear that the occurrence or absence of reducing conditions has a drastic effect on metal release and can not be neglected.

487

3.2.2 Availability tinder oxidized and reducing conditiotis. The availability has been measured for a reducing material and three oxidised materials under oxidized and reducing conditions. In the case of the oxidized materials the reducing conditions were enforced by using a Sspecies mixture as derived from blast-furnace slag leaching. From the availability data a clear difference amounting up to a factor of several thousands for some metals is noted between oxidized and reducing conditions. The difference for anionic species is less pronounced.

50

f

I

I

10

v

XI

40

I

6

0. I

0.01

3

4

5

6

7

8

9 1 0 1 1 1 2 1 3

PH Figure 4. Influence of reduction and removal of DOC on Cu leachability from MSWI bottom ash.

3.3. Sulphur speciation under reducing conditions.

In an experiment blast furnace slag was placed in a layer at the bottom of a large cilindrical vessel, which was subsequently filled with degassed water. The vessel was closed at the top to prevent uptake of 02 from the air. The S-speciation was followed at different levels in the cilinder at different contact times. The ratio of S-species relative to total S are given in figure 5 as a function of pH. In the bottom of the cilinder the solution turned yellow, indicative of the presence of significant concentrations of polysulfides. Thiosulfates are the most abundant S-species in BFS extracts, whereas polysulfides can amout to 10 % of the total S. Both polysulfides and

Table I. Availability data (in mg/kg) under oxidized and reducing conditions. Material

Cu

Mo

Zn

As

V

0.1

0.3 7.5 1.6 2.4

1.2 2.2 4.7 0.3

0.8 11.5 0.3 22.3

166.9 46.8 3.6 1.3

85 107 615 9420 65

105 5 505
~

Reducing Steelslag ECVN AVSA AVVA ~

Oxidized 1121 Steelslag ECVN AVSA AVVA HOS

0.1 0.1

0.1 ~

~

46 325 675 2135 27

02 84
129 06 45 <02

*ECVN=neutral coal fly ash, AVSA = MSWI bottom ash, AVVA = MSWI fly ash

488 thiosulfate can complex metals to form soluble species. This may lead to mobilization in the soil rather than in the low metal containing slags. 3.4 Release from stabilized reducing wastes When a reducing waste is stabilized the short term results (24-48 hrs) may look very promising and erroneously lead to the conclusion that performance criteria are met. However, when such materials are exposed to air oxidation, a redox front will develop that moves into the stabilized waste product leaving a highly alkaline, oxidized outerlayer at the surface[l3]. In this zone Pb is highly mobile due to its amphoteric nature. As shown in figure 6 after a slight initial wash-off Pb leachability is low. However, upon hrther oxidation the leachability of Pb increases drastically until ultimately

50000

10000

1000

r

I

11

cn

0 .-*

2

0.001 950

10.00

10.50

11.50

PH

,

,'

Total

/

6

Available (ox)

due to oxidation

Surface wash-off +

1

+

+

+

+.

?

*

reducing conditions 0.1

1

10

100

Time (days) Figure 6 . Pb release from a stabilized reducing waste due to contact with air (+: cumulative release;

0:release

12.00

Figure 5. S-species in blast furnace slag leachate as a function of pH.

j

100 7

11.00

per interval).

489 all of the leachable Pb is depleted. In current regulatory testing this aspect is as yet not taken into account. A management solution for stabilized reducing wastes is t o ensure encapsulation/coverage/isolation in such away that exposure t o the atmospheric oxygen is minimal. The important lesson here is that one has t o be aware o f the fact before a solution can be offered. 4. CONCLUSIONS

In the evaluation of environmental properties of wastes and stabilized wastes the aspect of redox conditions that may occur in materials exhibiting reducing properties or affect materials exposed to reducing conditions in the final destination of the waste or stabilized waste need more emphasis than currently practised. In this work a simple identification of possible reducing conditions is described. A method t o determine the reducing capacity of a material, which is important t o be able t o assess the time during which a material may exhibit its reducing properties is described.

Acknowledgement Part of this work was carried out in projects funded by NOVEM on preparation for standardization of leaching from construction materials and waste materials.

5. REFERENCES 1 Toxicity Characteristic Leaching Procedure(TCLP). Federal Register Vol 5 1 No 114, Friday, June 13, 1986, 21685-21693 (proposed rules). Federal Register, Vol No 261, March 29, 1990 (final version). EPA Toxicity Test Procedure (EP-tox), Appendix 11, Federal register, Vol 45(98), 1980,33127 - 33128. Government Printing Ofice, Washington D.C. 2. DIN 38414 S4: German standard procedure for water, wastewater and sediment testing - group S (sludge and sediment); determination of leachability (S4). Institiit fin Normung, Berlin, 1984. Dechets: Essai de Lixiviation X 3 1-2 10, 1988. Association FranGaise de Normalisation 3. (AFNOR), Paris. 4. Fderal de I'lnterieur. Switzerland. NEN 7343 and NEN 7341 (formerly NVN 2508) Determination of leaching characteristics of 5. inorganic components from granular (waste) materials. "I, Delft, 1993. NEN 7345 (formerly draft NVN5432). Determination of the maximum leachable quantity and 6. the emission of potentially hazardous components from construction materials and stabilized waste products of mainly inorganic character.NN1, Delft, 1993. 7. Waste Materials in Construction; Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials,Eds. J.J.J.M. Goumans, H.A. van der Sloot, Th.G. Aalbers, Elsevier Science Publishers, Amsterdam, 1991. M.J. Angus and F.P. Glasser. Proc. Materials Research Society Symposium. Vol 50, 1985, 8. 547-556. H.A van der Sloot, D. Hoede en P. Bonouvrie. 1993. lnvloed van redox condities op het 9. uitlooggedrag van reststoffen. ECN-C-93-037. 10. R.N.J.Comans, H.A.van der Sloot,P.Bonouvrie. Geochemical Reactions Controlling the Solubility of Major and Trace Elements During Leaching of Municipal Solid Waste Incinerator

490

1I . 12.

13.

Residues. Proceedings Municipal Waste Combustion. VIP 32. Air & Waste Management Association Pittsburg, Pennsylvania. 1993. 667 -679. R. Streudel, Holdt, and Gobel. J. of Chrom., 475, 1989, 442-446. C.W. Versluijs, I. H. Anthonissen and E.A. Valentijn. Mammcet 85 project, RIVM 738504008, June, 1990. J. Mehu, H.A van der Sloot, P. Moscowitz, R. Bama and D. Hcede. Research Association RE.CO.R.D, 1992.

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) @1994Elsevier Science B.V. AN rights reserved.

491

HYDROLOGY AND CHEMISTRY OF PULVERIZED FUEL ASH IN A LYSIMETER or THE TRANSLATION OF THE RESULTS OF THE DUTCH COLUMN LEACHING TEST INTO FIELD CONDITIONS Ruud Meij and Harald P.C. Schaftenaar KEMA Environmental Services, P.O. Box 9035, 6800 ET Arnhem, The Netherlands Tel.: +31-85-562225, Fax.: +31-85-515022

Abstract In the leaching process two steps can be considered: percolation and dissolution of various water-soluble compounds. Only through the combination of these two processes can compounds be leached out of the waste and enter into the environment. The two steps in the leaching processes require water. Since there were strong indications from a four-year trial storage project of pulverized fuel ash with no cover layer at the Amer power station that the initial moisture level did not increase over the years, it was decided to study this subject more closely. Lysimeters were built and filled with pulverized fuel ash produced by Dutch coalfired power plants. In these lysimeters the moisture content was monitored and the vaporization of the moisture determined. The hydrology was modelled. In order to gain more insight into the chemical processes, the pore water in the lysimeters and the percolate was monitored as well. In this paper the results of the first year are given, together with leaching test results. This project will provide information for the translation of the results of the Dutch column leaching test into field conditions. 1. INTRODUCTION In the Netherlands electricity is nowadays mainly generated using natural gas and coal. In the eighties the contribution of coal increased from about 10% to about 40% (from about 2 million metric tons to about 9 million metric tons). Only imported bituminous coal is fired. Typical values for the coal are presented in Table 1. Coal is imported from all over the world. Major suppliers are Australia and the USA. Other suppliers are Colombia, Poland, Indonesia, South Africa and China. Today mostly blends are fired. In the Netherlands the only boilers installed are pulverized coal-fired dry bottom types. The flue gases are cleaned by high-efficiency cold-side electrostatic precipitators (ESPs) and in all large coal-fired power plants they are also cleaned by flue-gas desulphurization (FGD) installations of the

492 lime(stone)/gypsum process. Table 1 shows some typical values for a 600 MW, coal-fired power plant in the Netherlands. The by products are bottom ash, collected ash, gypsum and sludge of the waste-water treatment plant. The collected ash from the electrostatic precipitators (ESP's) will thereafter be called pulverized fuel ash (PFA). An integrated coal gasification plant, based on the Shell gasification process, was built at Buggenum, the Netherlands. This demonstration plant, with a net capacity of 250 MW,, will start operation at the beginning of 1994. An extensive research programme will be performed by DEMKOLEC. If experience with this plant turns out positive from a viewpoint of the environment, economy, reliability and availability, it can be expected that more units will be built towards the end of the century. The by-products are CG slag, CG fly ash, sulphur and sludge of the wastewater treatment plant. The applications of these by products are discussed in a separate KEMA paper by Beekes et a/. [I]. In Table 2 the elemental contents of the by-products are presented [2,3,4]. The weighted average of coal composition for coal imported and fired in the Netherlands in 1992 is also provided [5]. The policy in the Netherlands is in principle not to produce waste, but to produce usable residues. The electricity generating companies in the Netherlands founded a special firm for the marketing of the coal-firing residues: 'de Vliegasunie' (Dutch Fly Ash Corporation). This firm also stimulates research of and experiments with applications. Long-term disposal of coal-firing residues is currently impossible. So far the Dutch Fly Ash Corporation has realized almost 100% utilization of all byproducts. The Dutch Decree on Building Materials, currently in preparation, will be decisive for the application of the by-products. For this Decree standards are in preparation for leaching behaviour for elements and compounds [6,7].The leaching behaviour at US=IO has to be determined by the Dutch Column test [El. If the byproducts fail to meet the standards there are two options: immobilization or storage. The results of the Dutch Column test at US=1 is also decisive for the way of storage. Accordingly, the translation of results of the Dutch standard leaching tests into field conditions is important and therefore a major research area at KEMA. For 10 Table 1 Averaged mass flows at a modern coal-fired power plant of 600 MW, description net capacity full load hours thermal efficiency energy demand coal demand coal, ash content coal, sulphur content desulphurization efficiency collection efficiency ESP

unit MWe h d %

MJea'' t0n.a" %(Wh) % (w/w) % %

600 6,000 40

3.2.10'' 1.2.10' 11 0.7 90 99.8

descrbtion ratio bottom ash/PFA bottom ash PFA gypsum sludge coal, caloric value fly dust emission process water FGD limestone demand

unit ton*a" tond tond t0n.a" MJ-kg-'

tows.' m3*h' t0n.a.'

12/88 16,000

11 0,000 41,000 1.000 27 el00 100 24,000

493

Table 2 Typical elemental concentrations in solid streams at Dutch coal-fired power plants coal b-ash') macro-elements (in %): Al 1.65 15.0 C 73.2 2.2 Ca 0.14 1.2 CI 0.06 0.004 Fe 0.51 4.7 K 0.17 1.5 Mg 0.08 0.7 N 1.6 Na 0.04 0.3 P 0.01 0.04 S 0.7 0.1 Si 2.82 25.7 Ti 0.08 0.8 trace elements (in mgokg"): As 3.7 2.5 B 43 141 Ba 158 1,116 Be 3.3 22 Br 5.4 0.5 Cd 0.10 0.4 Ce 17 147 co 5.8 35 Cr 14.4 131 cs 1.o 9 cu 16.6 73 Eu 0.4 4 F 80 55 Ge 2.0 0 Hf 1.2 11 0.16 0.10 Hg I 2.2 0.6 La 7.6 69 Mn 46 415 Mo 3.0 13 Ni 11 73 Pb 8.5 42 Rb 9.2 04 Sb 0.8 2 sc 3.3 30 Se 2.2 0.2 Sm 1.8 16 Sr 107 971 Th 2.9 26 TI 1.o 3 U 1.5 8 v 29 183 w 1.o 7 Zn 24 109 ') b-ash=bottom ash

pf a

15.0 4.3 1.2 0.004 4.7 1.5 0.7

qvpsum

0.06 0.02 23.7 0.01 0.08 0.02 0.02

0.3

<0.01

0.4 0.10 0.1 25.7

0.13 <0.03 0.002 0.22 0.01

0.8

34 163 1,438 29 1.6 0.9 151 52 131 9 151 4 127 18 11 0.23 0.6 69 415 27 98 77 84 7 30 13 16 971 26 9 13 262 9 21 8

2 <3

sludqe

1-16 0.41 23.6 0.1-12 0.6-10.5 0.13 0.1-12 <0.07 0.15 0.4 18 2.5-9.9 0.1

20-40 60-4,000 181 <1 2.7 <0.2 <27 ~0.1-0.3 0.1-12 25 <0.4 10 4 - 10 20-85 c0.4 1 0.6-9 26-65 <0.2 0.6 100 2,300-15,000 <5 8 <0.3 ~0.5-1.3 5-35 6 0.9 12 <2 509 <2 6 <0.5-13 10-90 6-21 34-200
494 years at the KEMA premises leaching of PFA is studied in lysimeters. This item is discussed for vitreous residues in a KEMA paper by Janssen-JurkoviEova et a/. [9] and for sand-lime bricks in a KEMA-paper by Bloem et a/. [lo]. In this paper another leaching project of pulverized fuel ash in high lysimeters will be discussed. 2.

LEACHING BEHAVIOUR OF PULVERIZED FUEL ASH IN LABORATORY TESTS

By order of the Dutch Fly Ash Association KEMA is testing the leaching behaviour and radioactivity of the pulverized fuel ash as produced during the firing of blends in 1993 and 1994.The leaching behaviour is tested by the Dutch Column test [8] and the Dutch Availability test [Ill. The column test is performed with an US (liquid/solid) ratio of 10 and the availability test with an US ratio of 100. The column test should predict the leaching behaviour for 50 years and the availability test should predict the maximum potential leachability (worst case). The leaching behaviour of one sample of PFA is studied in detail at the laboratory. This sample originates from a batch that was used in the lysimeters (see next paragraph). Besides the Dutch Column test and the Dutch availability test, the Dutch Cascade test (US=lOO simulating a leaching behaviour up to hundreds of years) and US EPA test (US=20) were carried out as well. The availability test was carried out three times: at the original sample, after the column test and after the cascade test. The consideration of performing the availability test at different stages is discussed in detail in a paper by Janssen-JurkoviEova et a/. [9]. Some characteristic parameters of each leaching test are given in Table 3. The Dutch leaching tests and other tests are discussed in detail by Van der Sloot [12]. The elements and compound which are studied are Al, Ca, CI, Fe, K, Mg, Na, Si, As, B, Ba, Be, Cd, Co, Cr, Cu, F, Ge, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V, W, Zn and SO,". These elements are clustered into three groups. Group I, II and 111 elements are leached out for less than 0.1 %, between 0.1 and 10% and more than 10% respectively. Some preliminary results are presented in Figure 1. In general, elements which show a relatively high leaching behaviour are As, B, Ca, Cd, CI, F, Mo, Sb and Se. Except for Ca and Cd, all elements are anions. The cumulative leaching behaviour obtained from the various tests is plotted as a function of the US ratio in Figure 2. The released amount is expressed as mg-kg-' per amount of solid (PFA). The results of only the major elements Ca, Fe the oxyanions As, Mo, V and the cation Cu are given in Figure 2. It appears that the leachability amount depends on the type of ions. As can be seen in Figure 2 the leachability increases in the following order: for cations: column test -+ cascade test + €PA test + availability test for anions: column tesf + EPA test -+ cascade test + availability test An exception in this specific example is the cation copper. The leachability of copper by the EPA test is lower with respect to the cascade test.

495

Column last PFA (LIS-10)

Figure 1. Leaching behaviour of elements in pulverized fuel ash as produced in Dutch coal-fired power plants in different leaching tests. Group I, II and Ill elements are leached out for less than 0.1 %, between 0.1 and 10% and more than lo%, respectively.

496 Fe

V

cu

Figure 2. Cumulative leaching behaviour of PFA as used in the lysimeters, obtained from the various leaching tests, as a function of the US ratio (in rngmkg-'). Column test, cascade test, availability test after column test, availability test after cascade test, availability test and EPA test.

497

’)

column test

cascade test

EPA test

availability test

10

5~20=100

20

2 x 50

initial pH=4

constant pH=5

constant pH=7 and pH=4

equilibrium-

alkaline equilibrium pH

process

upward flow <2 cm*h-’

shake test 5x refreshment

shake test

shake test 2x refreshment

time

3 weeks

5x23 hours

24 hours

2x3 hours

the pH is adjusted by adding HNO,; for the EPA test this is a deviation from the prescribed acetic acid; for some ashes the equilibrium pH is acid, but those ashes are not taken into consideration in these experiments, because they are hardly produced any more.

U Figure 3. Cross-section of the lysimeters with tubes for the neutron sonde, heat pulse meter (right) and pore water sampling equipment (left).

The leachability strongly depends on the pH and Eh and also on the US ratio (or the solubility) and contact time. Leaching test results by Van der Sloot [ 12,131 generally show a minimum leachability in the pH range 7 to 10 for metals such as Cd, Cu, Pb and Zn. Oxyanions such as As, Mo, Se and V show a maximum leachability in this pH range. An important difference between the cascade test and the EPA test is the equilibrium pH: for the EPA test this was forced at pH=5 and for the cascade test, for the samples studied in this project, this was alkaline. Consequently, the cations show higher leachability in the EPA test as compared with the cascade test and the anions show higher leachability in the cascade test as compared to EPA test. Accordingly, for most elements the highest leachability is found by the availability test because this test is performed at a high US ratio and at a constant pH of 4 and7. The lowest leachability is found in the column test. This is due to the low US ratio and in this case the solubility is the dominating limitation.

498

3. LYSIMETERS 3.1 Experimental Five lysimeters were built, (0 = 2m, four of about 4 m in height and one of about 1 m in height), filled with pulverized fuel ash produced by Dutch coal-fired power plants (see Figure 3). During the filling at several heights samples were taken for determining the bulk density (1006 kgmm3 on a dry basis) and the initial moisture content. From two grab samples the chemical composition, particle size distribution (MMD = 15pm), proctor test (density as a function of the moisture content: the maximum dry density is 1184 kg*m3at a moisture content of 30.3 %), specific gravity (2200 kg*m3), water retention characteristics (see Figure 4) and shrink [14] were determined. The moisture content is measured weekly with a neutron probe at various heights. At various heights (see Figure 3) pore water can be sampled by means of a membrane. This sampling system is given in Figure 7. On line the pH, Eh and conductivity can be measured in the pore water. Secondly, percolate can be collected and analysed. Furthermore the following meteorological parameters are monitored: precipitation, ambient air temperature, sun radiation and wind velocity.

+ Bull

Run

- A - ' Colbert

Q

0.1

0.00

0.20

0.40

0.60

0.80

1.00

saturation of moisture

Figure 4. Water retention characteristics of the pulverized fuel ash as used in the lysirneters and other published pulverized fuel ashes form the USA.

499 3.2 Aim of the lysimeter experiments In the leaching process two steps can be considered. The first step is transport of water along the pores. This is called percolation. The second step is the dissollution of various water-soluble compounds. Only through the combination of these two processes can compounds be leached out of the waste and enter into the environment. In leaching tests there is always a good contact with water, and actually only the dissolving and precipitation process is tested. The question arises what the percolation is under field conditions and how much rain water will be evaporated. Since there were strong indications from a four-year trial storage project of fly ash with no cover layer at the Amer power station that the initial moisture level did not increase over the years, it was decided to study this subject in detail. The height of the lysimeter is an important parameter, therefore lysimeters were built with a height of about 1 m and about 4 m. The lysimeter of 1 m can be compared with other 10 year old lysimeters with a height of 1 m at the KEMA location. The percolate will be monitored in order to compare the results of the laboratory test with the results obtained with the lysimeters under field conditions. To get more insight into the mechanisms of dissolution and precipitation, the pore water is monitored as well: elemental composition, pH, Eh (redox), Ec and chemical speciation of As, Cr and Se. 100

I

100 +moisture +tot.

200 DAYS

content (%)

+cum.

300

400

precipitation x 10 (mm)

moisture content x 10 (mm)

Figure 5. Averaged moisture profile in % and mrn of four high lysimeters (height about 4 m.) after the first 360 days, together with the cumulative precipitation.

500 3.3 Hydrological results after one year of operation The bulk density of the PFA in the lysimeters approximates the maximum as obtained in the proctortest. This bulk density is also in agreement with those in a actuel storage. The bulk density is an important parameter for the hydrology. From Figure 4 it can be deduced that the waterretention characteristics (desorption) are comparable to those of other pulverized fuel ashes, as produced in the USA [15], and that they are comparable to coarse sand [14]. However, the critical pressure head for coarse sand is about 1 m and for PFA it is about 3.5 m. Theoretically, moisture at depths up to 3.5 m can be transported and evaporated. Therefore, it is vital that the lysimeters are higher than 3.5 m. The high lysimeters were in full operation during the whole of 1993. 1993 was an extreme year with more rain (total of annual precipitation of 870 mm) and few sunny spells, as averaged. However, percolation did not occur. The results are presented in Figure 5. The averaged moisture contents increased in 1993 from 21.8% (787 mm) to 38.1% (1452 mm). This means that about 24% of the precipitation was evaporated. The evaporation is lower than expected, probably due to the extreme meteorological year. The differences between the four lysimeters are small. The small lysimeter was in full operation from 27th May 1993. The results are presented in Figure 6. The averaged moisture content increased from 27.1% (220 mm) to about 50% after 120 days and was then completely saturated. 80

70 -~

60

2 50

6

40

2

30

5

20 10

0

150

100

50

0

200

250

DAYS +moisture +cum.

content (%)

cum. precipitation * 10 (mm)

+

percolate (rnrn)

Figure 6. Averaged moisture profile in Yo of small lysimeter (height about 1 m.) after the first 220 days, together with the cumulative precipitation and percolate.

501

r-----

---+

I

mllrl

T I;-

J

three way valve

redox

Data Acquisition

perislallic pump

1 -@

gas-liquid separator

a 1

& lellon tubing0 0.5 mm allificial root sampling points in duplicate

1

flow-through conduclivity cell

1 ‘Ifi

y&id

separator

pH-electrode flow-through redox-electrode

I

Figure 7. Sampling system and measuring apparatus of pore water. Subsequently, percolate has been collected. The precipitation during operation of this lysimeter was in 1993 728 mm. 3.4 Chemical results after one year of operation Pore water was sampled after 9 months. The conductivity, pH, Eh and moisture content are presented in Figure 8 as a function of depth. It appears that the pH increases from 11.3 at a depth of 0.5 m to about 11.8 below 1 m. The Eh-value indicates an oxidative environment, which becomes slightly less oxidative below 1 m. The chemical composition was measured for the same elements as was done in the standard leaching test. The macro elements Al, Ca, Fe, K, Mg and Si are selected to be presented in Figure 9, the trace elements As, Cr, Cu, Mo and V and the compound sulphate are selected to be presented in Figure 10. The released amount is expressed as mgokg-’ per amount of solid (PFA), assuming an US ratio of 0.4 (moisture content 30%), allowing comparison with the column test (see Figure 2). Depending on the element, the composition of the pore water is comparable to the column test for US ratios between 0.1 (Ca) and

502 Ec I

0

I

1

3

3

4

4

::I j

.2

-100

--

-50

0

50

100

150

110

200

112

114

I20

0

C

1

1

-i

2

4 -100

IIU

Moisture content

Eh

--f,

118 PH

Es (rnSh1

-50

0

50

Eh lmV1

100

150

200

1

-c D

.2

3

3

4

4 0

10

20

40

30

moimre c m l m l lvol

50

%I

Figure 8. Conductivity, pH and Eh in pore water and the moisture content as a function of depth in the lysimeter after 9 months. exceeding 10 (Mo). Four different elemental concentration profiles can be distinguished in Figure 9, see Table 4. For further interpretation of these profiles the geochemical module MINTEQA2 will be applied. The first percolate of the small lysimeter corresponds with an US ratio of about 0.01. The observed elemental concentrations are generally comparable to those of the pore water as obtained at a depth of 0.5 m.

503 Al

Ca

.. Fe

Si

Figure 9. Elemental composition of pore water as a function of depth in the lysimeter after 9 months: macro elements.

504 As

Cr

I

I

I I I

MO

V

P

Figure 10. Elemental composition of pore water as a function of depth in the lysimeter after 9 months: trace elements and sulphate.

505

Table 4 Concentration-profile characteristics of the measured elements of the pore water in the lysimeter

decrease: 0.35-=1 m constant: =1-3.5 m

Ca, Mg, SO:

increase, maximum: =1-2 m decrease: =2-3.5 m

Fe, Ba, Cu, Sb, V

increase, maximum: =1.5-2 m constant: =2-3.5 m

K, Na, Cr, Mo, Se, CI, F

increase, maximum: =3 m constant: =3-3.5 m

Al,

Si,As, B

3.5 Conclusions So far the results are very promising. At the moment the results of the pore water samples are being studied. The interpretation will require considerable efforts. Further chemical and physical measurements have to be performed in order to translate the results of the leaching tests into field conditions.

4

ACKNOWLEDGMENTS

This research has been funded by the Dutch Electricity Production Sector and the Dutch Fly Ash Association. The students Bas van Straaten, Corien Cuijpers, Adri Roovers, Michel Kars, Karin ter Maat, Jolt Andela, Christien Hillenaar and Jan van Driel are thanked for the enthusiastic contributions. Thanks are also due to the following coworkers: Hans Erbrink for making the lay-out, Peter Jansen for the modelling of the hydrology, Harry Slangewal for developing the pore water sampling equipment and for writing the computer programs, Wilfried Elfrink for developing the heat diffusion meters, Bennie Stortelder for the general supervision of the construction of the lysimeters, Leo van Hulst for his assistance at the determination of water retention characteristics, Hans Overbeek for performing the moisture content measurements, Geert Melchers for the general supervision, Henk te Winkel for the chemical sampling, the analytical department of KEMA for the chemical analyses, Ronald van Wijk (FUGRO) for civil technical measurements and finally mr G.J Veerman and mr J.H.M. Wosten (DLOStaring Centrum, Wageningen) for the determination of the water retention and conductivity characteristics.

506

5

REFERENCES

1

M.L.Beekes, J.W. van den Berg and A.J.A. Konings. Applications of by-products from coal gasification power plants: Quality and Environment-related aspects. These proceedings (1994). R. Meij and G.D. Krijt. Databank Spoorelementen. Dee1 2 Bodemas (Database trace elements. Part 2 Bottom ash). KEMA report no. 63597-KESMIBR 93-3114 (1993). R. Meij and G.D. Krijt. Databank Spoorelementen. Dee1 3 Poederkoolvliegas (Database trace elements. Part 2 Pulverized fuel ash). KEMA report no. 63597-KESMIBR 93-

2 3

3113 (1993). 4

R. Meij, R.H. Hadderingh and F.W. van der Brugghen. Environmental Aspects of CoalFired Power Plants in the Netherlands. Water and Waste Issues. In: Proceedings of The Second World Coal Institute Conference held in London, UK, 24-26 March 1993. Published by World Coal Institute, London, United Kingdom, pp. 237-244. ISBN 0-

-

5 6 7

8

9520005-1-2. R. Meij and G.D. Krijt. Databank Spoorelementen. Dee1 1 Steenkool (Database trace elements. Part 1 Coal). KEMA report no. 63597-KESMIBR 93-3115 (1993).

Ontwerp Bouwstoffenbesluit Bodem- en Oppervlaktewaterbescherming (Draft Dutch Decree on Building materials). Staatscourant 121 (26 June 1991). Th.G. Aalbers et a/., Milieuhygienische kwaliteit van primaire en secundaire bouwmaterialen in relatie tot hergebruik en bodembescherming (Environmental quality of primary and secundary building material in relation to reuse and soil protection). RlVM report no. 771402005 (20 June 1992). Draft NEN 7343 Leaching characteristics of building and solid waste materials Leaching - Determination of the leaching of inorganic components from granular building and waste materials, Netherlands Normalization Institute (NNI), Delft, October 1992

9

10 11

12

13

M. Janssen-JurkoviEova, G.G. Hollman, M.M. Nass and R.D. Schuiling. Quality assessment of granular combustion residues by a standard column test: prediction versus reality. These proceedings (1994). P.J.C. Bloem, F.L.M. Lamers and L. Tamboer. Leaching behaviour of building materials with byproducts under practical conditions. These proceedings (1994). Draft NEN 7341 Leaching characteristics of building and solid waste materials Leaching - Determination of the availability of inorganic components for leaching, Netherlands Normalization Institute (NNI), Delft, October 1992. H.A. van der Sloot. Systematic leaching behaviour of trace elements from construction materials and waste materials. In: Waste Materials in Construction, J.J.J.R. Goumans, H.A. van der Sloot and Th. G. Aalbers (editors), Studies in Environmental Science 48, Elseviers Science Publishers B.V. (1991), ISBN 0-444-89089-0 pp. 19-36. H.A. van der Sloot. Leaching behaviour of waste materials; characterization for environmental assessment purposes. Waste Management & Research (1990) 8, 215-

228. 14 G.J. Veerman and J.H.M. Wosten. Bepaling van de bodemfysische eigenschappen van

twee soorten vliegas (Determination of soil-physical properties of two types of pulverized fuel ash). Dienst landbouwkundig onderzoek, Staring Centrum, lnstituut voor onderzoek van het landelijk gebied, Wageningen, the Netherlands. Report no. 261 (1993). 15 S.C. Young. Physical and hydraulic properties of fly ash and other by-products from coal combustion. EPRI-report TR-101999 (1993).

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der SIOOI and Th.G.Aalbers (Editors) @I994 Elsevier Science B.V. All rights resewed.

507

Role of facilitated transport in the emissions of secondary raw materials

J.J. Steketee', J.C.M. de Wit', G.J. van Rossumb & L.G.C.M. Urlings" 'Tauw Milieu bv, P.O. Box 133, 7400 AC Deventer, The Netherlands bKEMA Nederland B.V., P.O. Box 9035, 6800 ET Amhem, The Netherlands

Abstract Binding of contaminants by colloidal particles or macro-molecules may significantly enhance their leaching and dispersion in the environment. These particles naturally occur in groundwater and surface water but probably also in secondary raw materials. Standard leaching tests may underestimate the emission of colloid-bound contaminants. In laboratory experiments, humic substances and a ferrihydrite sol were added to demineralized water and cascade shake tests with bottom ash of Municipal Solid Waste (MSW) and pulverized coal fly ash were done. The leaching of Zn, Pb and As increased by 1.5 to 3 fold. Theoretically, stronger effects are possible. Factors like pH, and the recovery of the added particles, were relatively unfavourable in the experiments. 1. Introduction

Facilitated transport is the phenomenon of poorly soluble contaminants being transported through binding by mobile macro-molecules and colloids, i.e. carriers such as humic substances and iron oxide particles. In the past decades, research on buried radio active waste and other contaminated sites, has revealed that the binding by colloidal particles may greatly enhance the transportation of inorganic and organic contaminants [l]. However, very little is known about the role of colloidal particles in the leaching of common secondary raw materials like bottom ash from Municipal Solid Waste (MSW), pulverized coal fly ash, demolition debris etc. Colloidal particles may already be present in such materials, if not, they sometimes are formed through biological or geochemical processes. In time, such internal colloidal particles will be released and thus facilitate the transport of the contaminants bound by them. Furthermore, the material may come in contact with humic substances or metal (hydr)oxides present in soil water. Binding by these external carries will result in additional leaching of contaminants. Standard leaching tests do not account for facilitated transport as far as external particles are concerned. The effect of internal particles is measured, if the particles are smaller than 0.45 pm (the standard membrane filter which is prescribed for all Dutch leaching tests). From field measurements it is clear that also larger sized particles can be transported, e.g. in surface water [2] or in sandy soils. The internal carriers that are formed during aging of the waste materials are also not accounted for by the standard leaching test.

508

Apart from an underestimation of leaching emission, facilitated transport can give rise to an underestimation of the mobility of contaminants. In soil, neutral or negatively charged colloids are transported quicker than positively charged metal ions. The possible role of facilitated transport in the leaching of secondary raw materials was investigated by means of a literature search and laboratory experiments [3], [4]. In this article, emphasis is placed on the laboratory experiments and the modelling of leaching. 2. Materiais and methods

MSW bottom ash and pulverized coal fly ash were selected as model materials. With both materials, cascade shake tests were performed at cumulative Liquid/Solid (L/S) ratios 3, 5, 10, 20 and 40 (L/S-ratio 3 was only used with fly ash). Three different leachants were used: demineralized water (to be called demiwater), demiwater plus a humus extract (30 ppm C) and demiwater with ferrihydrite sol added until 10 ppm Fe was reached. The humus was extracted from a Moor-podzol, following the directives of the International Humic Substances Society. The ferrihydrite sol was prepared by a reaction of Fe(NO), with NaOH, followed by dialysis and filtration over a 10 pm membrane filter. Analytical-grade reagents and demi-water were used throughout all experiments. After each step of the cascade test, parallel samples were filtrated over membrane filters of 10 pm (Millipore, LCWP), 0.45 pm (S & S RC55) and 0.15 pm (S & S RC57). The samples were analyzed for antimony (MSW bottom ash), arsenic (fly ash) as well as calcium, copper, lead, zinc, iron, Total Organic Carbon (TOC) and 16 EPA PAH (MSW bottom ash) and the principal macroelements. Furthermore, the &-values (i.e. organic carbon based partition coefficients) of a number of PAH (fluorene, anthracene, pyrene, chrysene and benzo(a)pyrene) in the humics/ water system were measured with a dialysis method. Conditional stability constants were determined of the humics extract with copper and lead in 0.003 molar calciumnitrate solutions. For this determination three acid-base titrations are performed, namely: - known amount of the humics extract in 0.003 molar calciumnitrate is titrated with a sodiumhydroxide solution from pH = 2 up till pH = 11, using a glass and a saturated calomel electrode for detection; - a known amount of the metal ion in 0.003 molar calciumnitrate is titrated with a sodiumhydroxide solution using a glass, an ion-selective and a saturated calomel electrode for detection; - a mixture of known amounts of the metal-ion and humics extract in 0.003 molar calciumnitrate with a sodiumhydroxide solution using a glass, an ion-selective and a saturated calomel electrode for detection. The surface complexation constants of the ferrihydrite sol with arsenic and zinc in 0.003 molar calciumnitrate solution have been determined too, by means o f - an acid base titration of a known amount of the ferrihydrite sol in 0.003 molar calciumnitrate with a sodiumhydroxide solution from pH = 2 up till pH = 11, using a glass and a saturated calomel electrode for detection; - adsorption experiments of mixtures of known amounts of ferrihydrite sol and the metalion in 0.003 molar calciumnitrate.

509

Details of these determination methods of the conditional stability constants and the surface complexation constants will be published elsewhere [9].

3. Results Leaching experiments The leaching emission of contaminants, Fe and TOC are summarized in table 1 and 2. Table 1 shows that the leaching of Pb and Zn increases by 150 to 200% if iron particles are added. The addition of humics to MSW bottom ash has no significant effects, probably because this material already contains a lot of leachable organic components. The leaching of TOC in the humics experiment is only 8% more than the blank. Table 1 Influence of potential carriers on leaching emissions MSW bottom ash. Cascade stir tests, cumulative LIS 20. leaching medium filtrated over 10 Cm membrane filters

Antimony Copper Lead Zinc Iron

TOC

unit

blank

(mglkg DM) (mglkg D M )

0.54

0.55

0.50

( m g h DM)

7.7 0.32

7.8 0.34

(%kg D M ) (mglkg D M ) (%kg DM)

0.7 3.8 650

0.6

7.7 0.99 1.7 4.7

humics

700 10.7-10.9

10.7-10.9

PH

Fe

10.9

Table 2 shows that especially arsenic is sensitive to the addition of carriers. It increases leaching with 35 to 53%. The leaching emissions of copper and lead remains undetectable but zinc also increases. This increase of zinc is partly a consequence of impurities in the humics extract that was used in the experiment. Table 2 Influence of potential carriers on leaching emissions pulverized coal fly ash. Cascade stir tests, cumulative L/S ratio 40. leaching medium filtrated over 0.45pm membrane filters ~

Arsenic Copper Lead Zinc Iron TOC PH

~

unit

blank

humics

Fe

(mglkg D M )

4.7 $0.1

7.2 <0.1 <0.2 4.5

6.3

(mgQDM) (mglkg DM) (m@g DM) (mglkg D M ) (mgkg D M )

40.2

c2.0 1.1

78 7.5-8.1

<0.1 <0.2 2.2 3.9

790 8.48.5

8.0-8.7

In general, the effect of carrier addition is moderate. There are several reasons to explain this. Firstly, the recovery of the carriers is no more than 2% for iron and 20 to 25% for

5 10

humics, measured as TOC (mean of the different steps of the cascade test). This means that the majority of the carriers is adsorbed onto the solids. Secondly, MSW bottom ash already contains a lot of leachable organic components, probably also with complex-forming properties. Thirdly, the leachability of the examined fly ash sample is relatively low and finally, a proper filtration procedure is essential for the recovery of colloidal particles. However, due to technical problems, it was not possible to perform this procedure correctly for all fly ash samples. Furthermore, it should be noted that the range of conditions examined is limited. It is possible that the effect of carriers is greater at different pH-values or higher L/S-ratios. The effect of increasing L/S-ratios is illustrated in figure 1. The effect of the addition of carriers on the leaching of copper from MSW bottom ash was enhanced at higher L/S-ratios. However, the leaching of arsenic from fly ash only increases until L/S 10. The latter example is representative for the behaviour of most elements. Therefore, only in some cases, raising the L/S-ratio results in a stronger carrier effect. One would expect this to be more common because effects like (1) the binding of carriers by solids, (2) competition with elements like Ca and (3) destabilization due to high salt concentrations are likely to have less influence at higher LIS-ratio. During the cascadetest, the leaching medium is repeatedly refreshed, so soluble salts are removed and with each refreshment new carries are added, resulting in a saturation of adsorption sites. Leaching carrier/blanc 3-

Leaching canierblanc

-

.

~~

1 B.

I

~

- Blanc - Hurnics *Iron

1

0'

0

5

10

20

40

US cum

L/S(cum)

Fieure 1 Relative effect of added carriers as a function of the LIS-ratio. Ratio concentration in carrier experiment to concentration in blank. A: Leaching of copper from MSW bottom ash; B: Leaching of arsenic from pulverized coal fly ash. I

511 Separation of the particle fractions of the leaching media revealed that the distribution of elements differed widely over the fractions. Copper, antimony and arsenic were mainly present in the fraction <0.15 pm, which means they were mainly in solution or bound to fine colloids. Zinc and lead from MSW bottom ash were mainly leached with particles in the range 0.45 to 10 pm. Generally speaking, the addition of carriers had a limited effect on the distribution of the elements. In table 3, some results of the measurement of PAH leaching from MSW bottom ash and the humics & determination are presented. In the experiment with humics, a slight increase in leaching of some PAH was measured, e.g. 33% for pyrene. Probably the effect of humics addition is moderate because the leaching of total DOC is much higher than the added humics-C. Therefore, some calculations were done, based on measured blank concentrations, measured humics K, values, assumed humics concentrations of 3 ppm C and 15 ppm C and assuming a linear relation between humics and PAH mobilization. The most hydrophobic PAH like perylene, were hardly detected in our experiments. For the sake of completeness, a blank leaching level of 0.1 pg/l perylene was assumed and a literature & value of 106 was used to calculate the effect of humics on the mobilization. The calculations indicate that at &-values 5 10’. the effect of the humics is limited, unless the humics concentration is fairly high ( > 15 ppm C). More hydrophobic compounds (& lo6) show a more pronounced effect. At a humics concentration of 3 ppm C (i.e. 10% of the amount added in the experiment) the leaching of perylene increases by 4 fold. At a humics concentration of 15 ppm (as TOC), the perylene concentration increases by 16 fold. Table 3 Leaching of PAH from MSW bottom ash. Measured r6. values, measured concentrations (shake tests LIS 5) and calculated concentrations, based on assumed humics levels and measured &-values

phenanthrene pyrene perylene (1)

(2) (3)

1% K,

measured concentrations in leachates blank humics

(lk)

(Mfl)

Wl)

4.1 (1) 4.9 (1) 6 . 0 (2)

0.10 (1) 0.045 (1) 0.10 (3)

0.10 (1) 0.06 (1) <0.01 (1)

calculated concentrations (pgfl) at humics levels: 3 p p m C 15ppmC 0.10 0.06 0.4

0.12 0.10 1.6

experimental values; ref. [51; theoretical value.

Conditional stability constants of the humics extract The determined conditional stability constants, in 0.003 molar calciumnitrate, of the humics extract with the copper-ion and with the lead-ion are given in table 4. Additional determinations of the conditional stability constants of the humics extract with the copperion has been performed in a 0.003 molar sodiumnitrate solution. Qualitatively it has been shown that the conditional stability constants of the copper-ion with the humics extract in a sodiumnitrate solution is several orders in magnitude larger than in a calciumnitrate solution

PI.

512 Table 4 Conditional stability constants of the humics extract with copper-ion (K[Cul]) and with the lead-ion (K[PbL]) in 0.003 molar calciumnitrate PH

K[CuL]

pH

2.2 3.0 4.0 5.1 6.1 7.3 8.3 9.2 10.0

1.41E 04 2.51E + 04 5.11E 04 7.788 + 04 9.978 + 04 1.12E 05 1.16E 05 1.76E 05 4.20E + 05

K[PbL]

___

+ +

2.11E + 02 3.868 02 1.06E + 03 1.888 03 2.738 + 03 3.70E 03 8.30E 03 3.42E + 04

3.5 4.0 5.3 6.4 7.2 8.1 9.2 10.3

+ + +

+ + + +

Surface complexation constants of a ferrihydrite sol The acid-base properties of the ferrihydrite sol in 0.003 molar calciumnitrate was determined. In the literature the following surface protonation constants of a ferryhydrite sol are given [lo]:

iFeOH" =FeO

+ H+ + H+

+

=FeOH,

log K, 7.29 f 0.08

(1)

+

=FeOH"

log K, 8.39 f 0.06

(2)

The results obtained in this study for the surface protonation constants of the ferrihydrite sol in a 0.003 molar calciumnitrate solution are log K, 2.72 f 0.16 and log K, 5.90 f 0.10. These results differ very strongly from the literature values. The main reason is that our values are determined in 0.003 molar calciumnitrate. The surface protonation constants of ferrihydrite sol, determined in 0.003 molar calciumnitrate, were not published before. Very important in the explanation of the results obtained are the surface complexation constants of the ferrihydrite sol with the calcium-ion: =FesOHo

+ Cazt

=Fewma+

+ H+

log K3 4.97 f 0.08

(3)

+ Ca2+ log K., 5.85 f 0.15

(4)

+

=FeOHCaZ+

+

=FewOH"

and the studies of the hydrolysis of ferri-ions, which have established that Fe(OH)'+, Fe(OH),' and the dimer Fq(0H);" are formed in solution [7]:

+ H+ Fe'+ + H,O Fe(OH),' + 2H+ Fe3' + 2H,O F%(OH);+ + 2Ht 2Fe3' + 2H,O Fe(OH),+

--+

+

+

log

a,

2.56

(5)

log

a6 6.19

(6)

log 8,2.85

(7)

513

After a careful examination of the results obtained from the determination of the surface protonation constants of the ferrihydrite sol, it can be concluded tentatively that the K, 2.72 0.16 is probably the stability constant of reaction (5) and not the surface complexation constant of reaction (1) Furthermore, log K2 5.90 0.10 is probably the surface complexation constant of reaction (4) and not the surface complexation constant of reaction (2).

*

The following surface complexation constants of the ferrihydrite sol with arsenic have been determined [lo]: =FeOH" =FeOH" =FeOH"

+ As0:- + 3H+ =FeH,AsO," + H,O + As0:- + 2H+ -. =FeHAsO, + H,O + As0:- + H+ =FeAs0,2- + H,O

(8)

+

(9)

-

(10)

The results of the determination of the surface complexation constants of the ferrihydrite sol with arsenic, in 0.003 molar calciumnitrate are given in table 5, together with the published values [ 101. Table 5 Surface complexation constants of ferrihydrite sol with arsenic in 0.003 molar calciumnitrate surface complexation constant

experiment I

reaction (8) reaction (9) reaction (10) reaction (11)

29.6 22.9 16.4 10.0

1%

Y

cxperirnent 2 1%

Y

29.0 22.6 16.5 10.5

log Y values from the literature [lo] 29.3 23.5

____

10.6

The following surface complexation constants of the ferrihydrite sol with zinc have been determined [ 101: eFe'OH" mFe'OH"

+ Zn2+ + Zn2+

+

+

=FeSOZn+ =Fe"'OZn+

+ H+ + H+

(12) (13)

The results of the determination of the surface complexation constants of the ferrihydrite sol with zinc, in 0.003 molar calciumnitrate, are: experiment 1: log K = -2.7 experiment 2: log K = -2.5.

514

When these determined surface complexation constants of the ferrihydrite sol with zinc-ions, in 0.003 molar calciumnitrate, are compared with the published values [lo], than it can be the concluded that the here determined values are at least two orders of magnitude smaller than the published values. 4. Modelling the binding of contaminants by carriers

To get an impression of the potential effects of humics on metal leaching, model calculations were done for the humicsCu and the hurnics-Pb systems. The binding of the metal-ions is described with the measured conditional constants (table 4), assuming a free ligand concentration of 0.01 M. The hydrolysis species of the metals only were considered (CuOH+, Cu(OH),). In figure 2 the ratio's of organically bound metallfree metal and totalinorganic metal/free metal are plotted. The figure clearly illustrates that at pH values > 10, the organic-ligand bound fraction is small compared with the total fraction of inorganic ions. However, the opposite holds when pH is neutral. Under these conditions, facilitated transport may therefore result in an important increase in leaching due to the binding, by humics, of Cu and to a lesser extent of Pb. Results of modelling the surface complexation of copper and arsenic to the ferrihydrite sol with the MUSIC model [8],are illustrated in figure 3. For the Cu-cation, similar trends as mentioned above were apparent. A weak binding at high pH values is combined with strong binding at neutral pH values. For pH < 6 , the binding decreases again due to competition with protons for the adsorption sites and due to the variable-charged character of the ferrihydrite sol. At low pH values, the surface charge becomes increasingly positive, thus suppressing the binding of cations. For anions like arsenic, the charge effects are reversed. 5

-4

-5 2

0,3

2 0

0

$2

2 m

-1

0 2

3

4

5

6

7

8

9

1

0

1

1

PH Figure 2a Log (Cu-"bound/Cu-free) as a function of pH. Cu "bound" by humics is calculated from K' given in table 4. at a [CuOH+] + [Cu(OH),]. free ligand concentration of 0.01 M. Cu "bound" inorganically = [Cu*']

+

515

1 I

4

m

2 c Li

!k3 '0 2

0

n n 2

a,

0

2

3

4

5

6

7

8

9

10

11

PH

Figure 2b Log (Pb-"boundlPb-free) as a function of pH. Pb "bound" by humics is calculated from K given in table 4. at a [PbOH'] + [Pb(OH),]. free ligand concentration of 0.01 M . Pb "bound' inorganically = [Pb"]

+

Enhanced anion-binding at low pH values is due to the positive surface charge while the negative surface charge suppress anion binding at high pH values. This is illustrated by figure 3: again a limited effect of facilitated transport at high pH holds true. It is therefore concluded that the high pH of the MSW bottom ash that was used in the experiments was a major reason for the limited facilitated transport that was observed. 5. Conclusions

Considering literature, laboratory experiments and model calculations, it is concluded that facilitated transport can play an important role in the leaching of contaminants from secondary raw materials. In preliminary laboratory tests with MSW bottom ash and pulverized coal fly ash, increased leaching was measured for some elements when carriers were added. This increase varied for As, Pb and Zn by 1.5 to 3 fold (emission at cumulative WS-ratio 20 to 40). Model calculations show that higher increases are possible, roughly estimated between 5 to 15 fold. For inorganic components, increases are only expected to occur when pH is between 4 to 8 for humics and 6 to 11 for ferrihydrite. Secondary raw materials often show a high initial pH ( > 11) but upon aging, the pH can decrease to 8 - 9. Another key factor in facilitated transport is the stability of the colloid particles: are the colloidal suspensions stable or are the colloids readily precipitated, adsorbed etc. The recovery of added particles in the experiments varies between 0 to 2% for Fe and 0 to 25% for humics. It is therefore concluded that the nature of the particles is very important.

516

Also the separation procedure, which was not always optimal has an important effect on the measured values. Furthermore, the initial presence of carriers in the material itself is of major importance. For a good understanding of facilitated transport, characterization of these material-borne carriers is necessary. The results of this investigation show that, in addition to standard leaching tests, specific tests for the quantification of colloid-bound emissions may be necessary to accurately evaluate the quality of secondary raw materials. ---n----ro, l

.o 0,80 P c

-

.-C

I

0,60

0

-m I

D

0,40

s

an

0,zo

0,oo 3

4

5

6

7

8

9

1

0

1

1

12

11

12

.-C 0,

r

C

p

-z

0,60

m

c

0

0,40

~

c

3

0

n

g 0,zo C (u

2

0,oo 3 4

5

6

7

8

9

10

PH

Figure 3 Fraction of bound copper (3A) or arsenic (3B) by ferrihydrite (HFO); 2 to 20 ppm HFO. 600 pgfl Cu, 150 pgfl As. Model constants derived from [El.

517 Acknowledgement This research was carried out in the framework of the target orientated research program on leaching characterization of construction and waste materials, under a contract with NOVEM (Netherlands Organization for Energy and the Environment).

6 . References 1 J.F. McCarthy & J.M. Zachara: Subsurface Transport of Contaminants, Environ. Sci. Techn., 23 (1986) 496.

2 D. Perret et al.: Submicron Particles in the Rhine River - I, 11. Wat. Res., 28 (1994) 91. 3 T A W Infra Consult B.V. (1992): Role of Facilitated Transport in the Dispersion of Poorly Soluble Components. Phase 1, Literature Search (original title: Rol van drager gebonden transport bij de verspreiding van relatief slecht in water oplosbare componenten. Fase 1, Literatuur onderzoek) . 4 T A W Infra Consult B.V. (1993): Role of Facilitated Transport in the Dispersion of Poorly Soluble Components. Phase 2, Preliminary Laboratory Experiments (original title: Rol van facilitated transport bij de verspreiding van relatief slecht in water oplosbare componenten. Fase 2, orienterend laboratorium onderzoek). 5 M.A. Schlautman & J.M. Morgan: Effects of Aqueous Chemistry on the Binding of Polycyclic Aromatic Hydrocarbons by Dissolved Humic Materials. Environ. Sci. Techn., 27 (1993) 961.

6 De Wit, J.C.M. et al: Analysis of Ion Binding on Humic Substances and the Determination of Intrinsic Affinity Distributions. An. Chim. Acta, 232 (1990) 189. 7 J. Kragten, Atlas of Metal-Ligand Equilibra in Aqueous Solution, Ellis Horwood Limited, Chichester, Sussex, England, 1978, ISBN 85312-84-6.

8 T. Hiemstra & W.H. van Riemsdijk (1990): Adsorption Modelling of Cations and Anions at the Solid/Solution Interface of Metal(hydr)oxides: A New Mechanistic Multisite Approach. I: Model Description. 11: Evalution of Intrinsic Constants. Dep. of Soil Science and Plant Nutrition, Agricultural University, Wageningen, The Netherlands. 9 G.J. van Rossum and B.H. te Winkel, to be published. 10 D.A. Dzombak and F.M.M. Morel, Surface Complexation Modelling - Hydrous Ferric Oxide, John Wiley & Sons, 1990, ISBN 0-471-63731-9.

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials J..I..I,M. Goumans, H A . van der Sloot and 7h.G.Aalbers (Editors) @I994 Elsevier Science B. K All rights resewed.

519

Immobilization of heavy metal ions by the alkali activated slag cementitious materials J. Malolepszy and J . Deja Academy of Mining and Metallurgy, Cracow, Poland

Abstract The granulated blast furnace slags or nonferrous slags are the main component of the alkali activated slag cementitious materials. The calcium silicate hydrates (C-S-H type) of low basicity, hydrogarnets and sodium zeolites form as the alkali activated slag hydration products. Their structure and properties indicate that they can play an essential role in the immobilization of some elements. The microstructures of alkali activated slag pastes shows a higher gel pores content as compared with OPC pastes and simultaneously, significantly lower capillary pores fraction. The properties of alkali activated slag pastes in the presence of Zn, Cd, Cr and Pb ions were studied. The leaching and tank procedure were used to evaluate the level of immobilization of particular elements in the paste.

1. INTRODUCTION The problem of heavy metals immobilization becomes more and more significant with l Several technologies will develop only when increasing contamination of ~ t u r a environment. the heavy metals containing by-products are sufficiently and safely well separated. In many research centers the studies are carried out to solve this problem. The cementitious materials play an important role in the heavy metals immobilization. They can be used not only in the construction of waste dumps and concrete shields but also as immobilizing agents forming a matrix incorporating the heavy metals in a physical or chemical way. Cements are particularly useful in the wet wastes processing; it is important in view of the fact that the wastes occur predominantly as slurries (e.g. galvanic wastes containing Cr+6). The efficiency of the heavy metals immobilization is strongly related to the hardened paste microstructure, particularly to the pore size distribution and porosity. It is commonly known that the large pores of diameters > lOOnm influence decisively the paste tightness and permeability. The microstructure and properties of hardened paste depend on the C-S-H phase content and properties [6]. These features, in turn, are often related to the presence of pozzolanic admixtures. Such materials as silica fume, natural pozzolans and granulated blast furnace slags give the hydration products as a result of pozzolanic reaction thus influencing the porosity of paste. The admixtures listed above bring about the gel pores fraction increase and capillary pores decrease [5, 71. The advantageous changes accompanying the occurrence of

5 20

pozzolans give, as a consequence, the significant decrease of permeability attributed to the hardened cement matrix in concrete [8]. The pH values in the pastes are very high (about 12) because of the basic Ca(OH), formation. The heavy metal salts are neutralized at the presence of Ca(OH), and, as a result, the heavy metals hydroxides of very low solubility precipitate. The calcium zincates or chromates can also form [9]. Therefore the immobilization of heavy metals in the hardened cement matrix is the consequence of the significant C-S-H phase content and high pH value. The properties of alkali activated slag concretes have been studied in our laboratory for many years [lo-131. lt have been found that the alkali activated slag matrix would produce the idealized conditions for immobilization of heavy metals. The slag hydration products consist mainly of the gel-like C-S-H phase, zeolites and hydrogarnets [12, 141. The pastes are very compact. The pores of diameters less than lOnm predominate; these pores do not take a part in the filtration of water throughout the paste [12, 151. The high pH values resulting from the presence of alkaline activators, ensure the neutralizing properties of pastes. Such phases as sodium zeolites and hydrogarnets can incorporate the heavy metals to the structure [ 161. The alkali activated slag cementitious materials have been also applied in heavy metals immobilization by the other author as it is reported in some works [ 17,181. The results of the studies on the C P 6 , Zn 12, Pb+* and Cd+*immobilization in the alkali activated slag mortars will be presented hereby.

2. EXPERIMENTAL

2.1. Materials The granulated blast furnace slag, standard sand (strength determination), alkaline activators and compounds of heavy metals such as Zn(NO,),, Pb(N03),, CdCI, and Na,CrO, have been used. The blast furnace slag was ground to the specific surface 3500cm2/g as measured by Blaine method. The chemical composition of slag is given in Table I . Table 1 Chemical composition of slag Component CaO SiO, '41203

MgO Fe20s

so3

+

Na,O K,O residuum

wt (%) 41.10 38.10 9.60 8.40 0.40 1.10 1.20 0.10

521

In Poland this slag is used in the metallurgical cement production. The sodium carbonate and water glass have been used as alkaline activators. The mortar was prepared at water to cementitious material ratio equal to 0.36. The proportion between slag and sand was 1:3. The heavy metals compounds were dissolved in water. The mortars denoted as A-I were prepared using the sodium carbonate and alkaline activator whereas those denoted as J-S were activated by water glass. The samples denoted as 1 and J were prepared as a control alkali-activated slag pastes without heavy metal compounds addition. The mortars were mixed in the standard laboratory mixer, cast into the moulds for IS0 40 X40 X 160mm bars and shaken on a laboratory shaker. The samples were domoulded after 24 hours. The mortars prepared with water glass as an activator were stored for 28 days at 20°C, 100%RH.The mortars activated by sodium carbonate were subjected to the steam curing at 85°C for 4 hours and subsequently stored at 20"C, IOO%RH. The characteristics of mortar specimens are shown in Table 2. The total concentration of Zn, Cd, Cr and Pb ions in the mortars is presented in Table 3. Table 2 Characteristics of Mortar Specimen Type of mortar

Density (glcm') A

Na,CO, activation

B C D E F G H I J

K L Water glass activation

M N 0 P R S

Compressive strength (N/mm*) 3 days

28 days

2.31 2.38 2.37 2.34 2.37 2.38 2.36 2.31 2.37

34.0 25.4 35.4 39.1 45.0 39.2 37.4 31.5 33.8

36.2 28.9 38.5 38.4 46.0 40.4 38.4 39.0 38.6

2.38 2.36 2.28 2.31 2.35 2.38 2.38 2.36 2.37

74.5 48.3 48.4 40.2 28.0 69.0 57.2 68.0 50.9

82.2 52.1 52.1 41.7 29.0 74.4 72.5 70.5 62.4

522

Table 3 Concentration of Zn, Cd, Cr and Pb ions in the mortars Type of activator

Na2C03

Water glass

Ions concentration (mg/kg) Martar

Zn

Mor-

tar

Cd

Mortar

Cr

Mortar

Pb

A B I

787 397 7

C D I

1384 2767 <2

E F I

749 1475 <23

G H I

1432 2841 <23

K L

397 202 7

M N J

1384 2767 <2

0 P J

749 1475 < 23

R

1432 2841 <23

S J

2.2. Leaching tests [21] The leaching method similar to the german EDV-S4 test was used. The following procedure was applied: 100s samples were ground and the fraction 2+4mm was selected for the tests. The samples was subsequently treated with 0.51 distilled water in 11 polyethylene bottles (mortar to water ratio equal to 1:5) and shaken within 24 hours at room temperature. The suspension were filtered and the liquids thus obtained were subjected to the chemical analysis. The chromium (VI) and total chromium content after the Cr(II1) to Cr(V1) oxidation was analyzed by the following methods: - spectrophotometrically , as red-violet complexe of chromium with benzocarbazide (Xw=545nm at 5cm thick cuvette), - impulse polarography using sodium hydroxide or sodium hydroxide and triethanolamine as basic electrolyte [20]. Table 4 Results of the leaching test Type of Ions concentration (mg/l) p~ zn activator pH

Cd

pH

Cr

pH

Pb

A 12.1 0.06 Na2C0, B 11.9 0.05 I 12.1 0.05

C 12.1 0.24 D 11.9 0.56 I 12.1 0.02

E 12.2 0.37 F 12.2 6.52 I 12.1 0.03

G 12.0 H 12.0 I 12.1

0.24 0.44 0.09

K 12.0 0.05 L 12.0 0.04 J 12.1 0.03

M 12.0 0.06 N 11.9 0.19 J 12.1 0.02

0 12.1 0.28 P 12.1 6.06 J 12.1 0.03

R 12.0 S 11.8 J 12.1

0.11 0.21 0.09

Water glass

523

The cadmium, lead and zinc content was determined by the atomic absorption spectrometry using the air-acetylene flame or by the emission spectroscopy with the plasma flame. Alternatively, the traces of zinc were analyzed by derivative impulse polarography in the basic solution of acetate buffer. The result of leaching tests are presented in Table 4. At some simplified assumption (among other things that the leaching process is of linear character, irrespectively of the concentration in the solution) the following "degree of immobilization" has been found: a) about 99.9% Zn, b) about 99.8 Cd at Na,CO, activator and about 99.95% Cd at water glass activator, c) about 9 9 3 % Cr at 1 % Na,CrO, addition and about 95.5% Cr at 2 % Na,CrO, addition to the mortar, d) about 99.8% Pb.

3. CONCLUSIONS The results thus obtained have confirmed the assumption that the alkali activated slag cementitious materials could be very useful as the heavy metals immobilizing agent. The highest values of immobilized elements content have been established for the slag cementitious materials activated by water glass. This fact is the consequence of the lower total porosity and higher gel pores content in the water glass activated pastes as compared to those prepared with soda [12, 151. In the former pastes a higher amount of CSH phase type 111 and IV according to Diamond classification was observed. Therefore, because the microstructure of alkali activated slag pastes can be controlled in a wide range, there is always a possibility to produce a special, alkali activated slag cementitious material with aim to immobilize the heavy metals.

Acknowledgement This work is supported by the Polish Scientific Research Committee under Grant No 18.160.248PB0764/S2/93/05

4. REFERENCES 1 2 3 4 5 6

C.M. Jantzen, F.P. Glasser, E.E. Lachowski, Journ. Amer. Ceram. Soc. 67 (1984) 668. C. Tashiro, K. Akama, J. Oba, Cement and Concrete Research, 9 (1979) 303. F.P. Glasser, Cement and Concrete Research, 22 (1979) 201. W. Kurdowski, Cement Wapno Gips, 6 (1992) 185. P.K. Mehta, Supplementary Cementing Materials for Concrete Editor V.M. Malhotra, Canada, 1987. S . Diamond, 8th I.C.C.C., Rio de Janeiro 1986, 2/2 1 .

524 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21

G.F. Massara, G. Obertii, Proc. Durability of Concrete 2nd Int. Conf., Montreal 1991, I1 1259. R.E. Davis, Technical Memo, Amer. Concr. Pipe Assoc. 1954. P. Longuet, G. Bellina, 7th I.C.C.C., Pans 1980, IV 617. A. Derdacka, J. Maiolepszy, Cement Wapno Gips 10 1975 291. J. Malolepszy, J. Deja, Silic. Ind. 53(11-12) 1988 179. J. Malolepszy, Hydration and properties of alkali activated slag cementitious materials, Zesz. Nauk. Akad. G6m. Hutn., Ceramika 53 1989 1-126 (in polish). J. Maiolepszy, 9th I.C.C.C., New Delhi 1982, IV 118. W.D. Gluchowski, Gruntosilikatni wirobi i konstrukcji, Budiwilnik, Kiev 1967. P. Kriwienko, Tsement, 11 (1990) 2. D. Breck, Zeolite Molecular Sieves, New York 1974. R.F. Runowa, Proc. Int. Conf. on Blended Cements in Construction, Sheffeld 1991. Wux Yen S., Shen Tang M., Yang L., Cement Concrete Research, 21 (1991) 16. 0. Bian, M. Zhange, Z. Chen, 4th Int. Conf. on Fly Ash Silica Fume Pozzolans in Concrete, Istambul 1992, Supl. 601 A. Bobrowski, B. Barchadska, Chem. Anal., 24 (1979) 857 R.H. Rankers, I. Hohber, Int. Conf. "Wascon 91" Studies in Environmental Science, 48 Elsevier 1991 275.

Environmental Aspects of Consttuctioti with Waste Materials JJJ.M. Goumans, H A . van &r SIoot and Th.G. Aalbers (Edtors) el994 Elsevier Science B. V. AN rights reserved.

525

Integrated treatment of MSWI-residues Treatment of fly ash in view of metal recovery B. Laethema, P. Van Herckb, P. Geuzensa, C. Vandecasteeleb aFlemish Institute for Technological Research, Department of Environment, Boeretang 200, 2400 Mol, Belgium buniversity of Louvain, Department of Chemical Engineering, de Croylaan 46, 3001 Heverlee, Belgium

Abstract To minimize the production of residues in municipal waste incineration, concepts are developed, which link fly ash extraction and inertizing at metal recovery To facilitate the possibility for metal recovery an extended study has been performed on the leaching behaviour of the fly ash in function of pH, liquid to solid ratio and time Additional interventions, both on the leaching process and the total concept of fly ash treatment, are examined in order to optimize leaching efficiency and final concentrations

1. INTRODUCTION

Up till now the focus within the environmental research field on municipal solid waste incineration (MSWI) has been laid at first on the maximal reduction of toxic components in the flue gas. Because of a more stringent emission-regulation new flue gas cleaning techniques have been developed. As a consequence higher amounts of residuals are produced. To minimize the amount of residues new concepts of gas cleaning in waste incineration are needed. MSWI-fly ash is one of the most critical products produced during the flue gas cleaning process. Due to the high concentration and mobility of several heavy metals the reuse of MSWI-fly ash as a secondary building material is prohibited in Flanders. At this moment only disposal in a covered landfill is allowed. Within the scope of a project on the treatment of MSWI-fly ashes, by order of the Public Waste Company for Flanders (OVAM), a concept is proposed for inertizing fly ash and metal recovery. The basic concept for the treatment of fly ashes is similar to the German 3Rprocess (3R-proces = Rauchgas-Reinigung mit Ruckstandsbehandlung, which means flue gas purification including residue treatment) [I]. In this process, developed by the Nuclear Research Centre in Karlsruhe, an acid extraction is carried out by which the soluble heavy metals 2re leached from the fly ashes to a certain extent, using the acid flue gas scrubbing solution. The contemporary method for the removal of the heavy metals from the extraction solution is a hydroxide precipitation. In the following text the leaching behaviour of fly ash is discussed in function of the development of a concept which integrates the recovery of heavy metals from the extraction solution.

526 2. LEACHING PROPERTIES OF MSWI-FLY ASH

The basic principle of the 3R-process is the extraction of fly ash with the solution from the acid flue gas scrubber. In addition the recovery potential of the metals is examined. To this goal different leaching procedures can be used. To optimize the leaching procedure an extensive study on the composition and the leachability of the fly ash has been carried out. First priority has been given to the influence of pH, extraction time and the liquid solid-ratio on the leaching behaviour of the fly ash. 2.1. Material and methods Samples of MSWI fly ash were obtained from the Houthalen Waste Incineration Facility, a municipal solid waste facility with a annual capacity of 98 000 ton. The fly ash was collected by a classic electrofilter. The chemical composition of the fly ash was measured by inductively coupled emission spectrometry (ICP-MS) after destruction with aqua regia. The extracts obtained from the leaching tests were analyzed by the same method. Simple batch extractions on lab scale were used to characterize the leaching properties. To simulate the acid flue gas scrubber solution, and since the main input of acidity into the scrubber unit is represented by absorbed HCI, synthetic solutions of HCI were used as extraction medium. 2.2. Results of elemental analysis Table 1 shows results of the elemental analysis on the incinerator fly ash samples. Results

are compared with literature data of the elemental analysis of the fly ash used during experiments with the German 3R-process [I]. We note a generally good agreement among the element composition of the fly ash used in both experments with the exception of Ca, Fe, Cr and Sn. Especially the difference in the amount of Ca in the fly ash is important since Ca is the most important element with respect t o neutralization capacity and leaching behaviour. Table 1 Composition of the fly ashes (mg/kg d.m.) Parameter This work Ref [I] Parameter Al 85 000 a2 000 Cr Ca 187 900 cu 89 000 Fe 11 250 30 000 Ni 13 000 Pb 16 700 Mg As 115 100 Sn Cd 305 280 Zn

This work 120

Ref [I] 810

810

1100 140

215 3 250 500 1 1 970

5 300

1800 16 000

2.3. Results of the leaching tests

2.3.1. Leachability in function of pH Influence of pH on the leaching of several elements has been measured during a set of extraction procedures with different additions of acid. Each extraction is carried out at a liquid solid ratio of 10 (L/S=lO Vkg) during 3 hours.

527

Figure 1 shows the evolution of the final pH after extraction. Figure 2 and 3 show the leaching eficiency in hnction of the "acid dose". Acid dose (AD) is the ratio of added Hfions to the amount of fly ash (mol H+/kg fly ash)

0

,

,

I

1

,

,

,

2

4

6

8

10

12

14

@ , * ~ ,, 16

1E

20

acld dose (mol/kg)

Figure 1: Final pH in function of the acid dose (molkg), L/S=10 Vkg, time=3hrs.

Between acid dose 0 and 4 mol/kg the pH decreases rapidly. Between acid dose 4 en 12 mol/kg the pH decreases slowly. The added acid is neutralised by the dissolution of basic metal salts. During the strong decrease between acid dose 0 and 4, there is only little dissolution of metal salts. The added acid is not neutralised, so the pH decreases.

60

60

40

40

Pb I

20

20

0

2

4

6

8

10

12

14

16

Acld dose (rnollkg)

Figure 2 Leaching efficiency (%) of Pb, Cu, Cd and Zn in function of the acid dose (moVkg)

18

I0

2

0 0

L

1

,

,

,

,

,

,

I4

16

18

0

2

4

6

8

10

12

jzo 0 20

A d d do80 (rnollkg)

Figure 3 Leaching efticienq (YO) of Al. Ca, Fe, Mn and Mg in function of the acid dose (moVkg)

Both Zn and Cd have a good leaching efficiency even at low acid doses. Pb and Cu however can only be leached out at high acid doses.

528

The chloride saltsof both Cu and Pb have a low solubility, but at high CI--concentration both metals can form complexes resulting in a higher solubility. The CI-concentration is only at high acid doses high enough for the complexation. Also the lower pH gives a better solubility. Ca ,Al and Mn leach gradually until almost complete removal is established. Mg and Fe only leach for 50%. These 5 metals are not important for neither toxicity nor possibility for recovery, but they play an important role in the leaching process because of their high amounts in fly ash. In general the metals can be divided in 3 groups according to their leached amount (mg leached/kg fly ash): 1. Ca, Al, Na, K 2. Zn, Mg, Fe, Pb 3. Mn, Cu, Cd An optimal acid dose for a maximum leaching efficiency of Pb, Cu, Zn and Cd with a minimal cost is situated at 6 moVkg for a liquid solid ratio of 10 Vkg. This means a leaching solution with a HCI concentration of 0.6 mol/l. 2.3.2. Leachability in function of liquid to solid ratio

The influence of the liquid solid ratio is measured by changing the volume of the leaching solution while the acid dose is kept constant. This means that the same amount of acid is added to a changing volume of water. This experiment is carried out for several acid doses. The leaching time was 3 hours. Figure 4 shows the final pH and figures 5 and 6 show the leaching efficiency in fimction of the liquid solid ratio.

0' 0

' 10

2

20

"

30

40

"

50

60

'

70

'

80

"

90

100

ilquld solld ratio (Vkg)

Figure 4 :Final pH in function of the liquid solid ratio (mg) for different acid doses (moVkg).

The final pH stays constant for acid doses 0, 2 and 6 moVkg. Acid dose 10 moVkg gives an increasing pH in fknction of the liquid solid ratio. The most abundant metals present are almost completely leached out at an acid dose of 10 which results in some unused acid. The resulting pH increases therefore with increasing liquid solid ratio and depends on the composition of the used fly ash.

529

11 0

"

10

10

"

30

40

"

50

60

"

70

80

' 90

0' 0

1.1 100

"

10

llquld solld rallo (I/kp)

10

"

'

1

1

'

30

40

SO

I0

70

80

' 90

10 100

llquld solld ratlo (I/kg)

Figure 6 :Leaching eaciency (YO) of Zn, Pb, Cu and Cd in function of the liquid solid ratio (vkg) for an acid dose of 10 movkg.

Figure 5 :Leaching efficiency (%) of Zn, Pb, Cu and Cd in function of the liquid solid ratio (vkg) for an acid dose of 0 movkg.

The metals can be divided into 2 groups. The first group comprises the metals that show a constant leaching efficiency in function of liquid solid ratio. The concentration of the metals in the leaching solution decreases because of the dilution at higher liquid solid ratios. A second group of metals possesses an increasing leaching efficiency in function of the liquid solid ratio. The concentration decreases but not so fast as the concentrations of group 1. The increasing leaching efficiency points to a solubility restriction. When the volume of the leaching solution increases, more metal can be dissolved before the solubility product of the metal salt is reached. Table 2 shows the distribution of the metals over both groups in function of the changing acid dose. Table 2 Distribution of the metals over 2 groups in function of the behaviour of their leaching efficiency in function of the liquid solid ratio.( l=constant leaching - efficiency in function ofL/S, i=increasing leaching kfficiency in function of US)

I

Na AD=OIl A D = AD=61 D = l 1

K 1 2 1 1

Mg Mn 2 2 1 1 1 1 1 1 1

Cd Pb 2 2 1 1 1 1 1 1 1

Al 2 2 1 1

Ca 2 2 1 1

Fe 2 2 1 1

Co 2 2 1

Ni 2 2 1

Zn 2 2 1

Cr 2 2 2

1

1

1

1

Cu 2 2 2 2

If one wants to remove as much heavy metals as possible, a high leaching efficiency is needed, thus a high liquid solid ratio. When recovery of heavy metals is in view, a high concentration is recommended, thus a low liquid solid ratio. Most of the time a compromise between recovery and removal of heavy metals is needed. Table 3 shows the optimal liquid solid ratio for Zn as a function of the used acid dose. Each time an acid dose is searched where both the concentration and the leaching efficiency are as high as possible. Also the concentration of the leaching solution is included. Table 3 Optimal liquid solid ratio (Vkg) for various acid doses (movkg). AD (rnoVkg) L/S (vkg) concentration (moVI) 2 13.6 0.15 9.1 0.65 6 10 6.5 1.50

530 2.3.3. Leachability in function of the extraction time During this experiment the extraction time varies from 1 minute to 24 hours with a constant acid dose and liquid solid ratio. The experiment is repeated for different liquid solid ratios and acid doses. Figure 7 shows the final pH for an acid dose of 0 moYkg and figure 8 for an acid dose of 2 moVkg

'i : 7l 8

+

..

f

.

::I:::

.

10

100

x US=100 1000

10000

100000

llrne (sac)

Figure 7 :Final pH in function of the extraction time (sec.) for various liquid solid ratios (Ukg) and for an acid dose of 0 moykg.

1 :I 10

i, 100

,

,

1000

10000

1

x USrlOl 100000

Urns (800)

Figure 8 :Final pH in function of the extraction time (sec.) for various liquid solid ratios (Ukg) and for an acid dose of 2 moUkg.

For acid dose 0 moVkg the final pH increases until a maximum is reached after 3 hours. At short extraction times the pH increases also with increasing liquid solid ratio. This increase disappears when the maximum pH is reached. For acid dose 2 moVkg the final pH increases in function of the extraction time and stays constant in function of the liquid solid ratio. The experiments of the previous paragraphs were carried out during 3 hours, thus the combined influence of extraction time and liquid solid ratio is eliminated. The metals can be divided into 3 groups according to the behaviour of their leaching efficiency and concentration in the leaching solution in function of the extraction time. The first group holds the metals with a constant leaching efficiency in function of the extraction time. The concentration decreases in hnction of the liquid solid ratio while the leaching efficiency remains constant. Fot these metals there is no solubility restriction and the decrease in concentration is only caused by dilution at higher liquid solid ratios. The second group holds the metals with a decreasing leaching efficiency in function of the extraction time, as shown in figures 8 and 9. This evolution is the strongest with a liquid solid ratio of 5 I/kg. The concentration decreases in function of the liquid solid ratio while the leaching efficiency increases. The metals are influenced by a solubility restriction.

53 1

. us=s + LIS-25

-

* U6=50

. . . .. US=50

lo

6tmUS=75

x L/SIlOO 0 10

1,

,+

I

,

i

-i

+++++++

us-75

+

A

100

1000

10000

100000

lime (sac)

Lima (sac)

Figure 8 :Leaching efficiency (%) of Zn in function of the extraction time (sec.) for various liquid solid ratios (lkg) an for an acid dose of 0 mol/kg.

Figure 9: Concentration (mmol/l) of Zn in the leaching solution in function of the extraction time (sec.) for various liquid solid ratios (lkg) and for an acid dose of 0 molikg.

The last group contains the metals which show an increasing leaching efficiency, as shown in figures 10 and 11. Several metals have a minimal solubility in function of pH. Because the pH increases during the process, the metal salts reach a minimum solubility. When the pH increases hrther, more metal salts can dissolve which results in an increasing leaching efficiency. Table 4 shows the distribution of the metals over the three groups,

00"cmd.IIWI

'

5

(nmol I)

I]

us=5

'+ us=x

5-X.

LlS-50

-2

x x

us-100

#

3-

21-

LIS=50

xx xu(

US176

.I#*

.

i

+A+++++. .

..

*.

+

1+

0.02

.

m

a

n

.

x

1

0.01 0

0

ia

i , 100

i

. ..

l

..

:*tat*::

j

;

1000

10000

~oopoo

lime (sac)

Figure 11 :Concentration (mmoUI) of Cr in the leaching solution in function of the extraction time (sec.) for various liquid solid ratios (l/kg) and for an acid dose of 2 moUkg.

AD=O molkg AD=2 moUkg

I Na, K, Fe

Ca, K, Na, Ni, Fe, Cr

I1 Mg, Ca, Mn, Ni, Cu, Zn, Cd, Pb Zn, Cu, Al, Pb, Cd, Co, Mn

I11 Al, Cr

Mg

532 3. ADAPTION OF THE PROCESS FOR FLY ASH TREATMENT IN FUNCTION OF METAL RECOVERY 3.1. Introduction The concept for the treatment of fly ash by acid leaching has to include the possibility for metal recovery from the leachate. First priority is given to the recovery of Zn, Cd, Pb and Cu. One of the parameters that effects the potential for recovery is the concentration of the metals in the solution. Table 5 shows the concentration of the 4 mentioned metals after optimization of the one step leaching procedure in hnction of pH and liquid to solid ratio. Except for Zn we notice too low concentrations of dissolved metals to perform metal recovery with sufficient efficiency by most methods. Many more recovery technics with high efficiency are available when the concentration of the metals exceeds a treshold of 0.5 g/l.

Table 5 Concentrations of metals in the leachate (AD = 6 mol/kg, L/S = 9.1 Vkg) Parameter Concentration mgll 806 Zn Cd 21 Pb 18 cu I To facilitate the metal recovery there is a need for additional interventions to increase the metal concentration. Two possibilities have been examined. A first possibility is the addition of additives to improve the leaching efficiency. Secondly, one can increase the concentration by recirculating the leachate 3.2. Increasing of the leaching efficiency by means of EDTA addition

.it

+

+ '

+

+ +.

+

00

+ + + +

+

+

l.1 +

t

i

101

20

+: : I .+. +. .+ 10

. . . .

. '

0 g EDTA

+ lopEDTA

0 0

2

4

6

1

.p + lo 0 EDTil

10

Add do..

Figure 12 :Leaching efficiency (%) of Cu in function of the acid dose (molkg) with and without the addition of EDTA

12

14

16

11

10

(rnollkp)

Figure 13 :Leaching efficiency (%) of Pb in function of the acid dose (molkg)with and without the addition of EDTA

533 A difficulty in the leaching process is the restricted solubility of some metal salts. Pb and Cu for example can only leach out at high acid doses. A possibility to increase the solubility is the addition of a complexing reagent. EDTA is a good example and is used in this research. The addition of EDTA gave for most of the metals an increase in leachability. Especially the results for Cu and Pb are good and they can now be leached out at low acid doses as shown in figures 12 and 13. However more research is needed.

3.3. Influence of recirculation on the metal concentration A second method to increase the metal concentration is the re-use of the leachate in successive extraction steps. The number of successive extraction steps, and so the extent for the increase of the metal concentration is determined by the recirculation factor. The parameters that influence this factor depends on the process principle. Recirculation factors have been calculated for two different concepts.

3.3.1. Concept 1 The flow sheet ofthe first concept is shown in Figure 14. The leachate is directly recirculated to the extraction unit after acidification with fresh acid scrubber solution. In this case the recirculation factor depends on both the amount of acid scrubber solution needed to reach the required acid dose for extraction and the solubility of the metals in the chloride-solution.

Flu. G u I

flue G u

Figure 14 Process flow of the first concept

534 In this concept the pH value in the acid scrubber circuit has to be kept as low as possible. In practice the pH value of the acid flue gas scrubber solution is limited to pH 0.5 -0.3 due to corrosion problems [2]. By using NaOH in the acid scrubbing unit for partial neutralization (and minimization of water consumption) pH-control of the acid scrubber solution is possible. When assuming an initial pH for the extraction equal to 1 (0.1 mol H+/I) and considering a minimum acid dose of 4 mol H+/kg fly ash to reach sufficient leaching efficiency (although AD = 6 is better) , the liquid solid ratio must be equal to 40. From the leaching test we learned that in this case the pH of the extraction solution is equal to 4. Using the following equation we can calculate for this concept a recirculation factor between 3 and 5.

with Ca Ci Cr

: : acid concentration (mol H+/I) in the acid flue gas scrubber solution : initial acid concentration (mol H+/I) of the extraction step : final acid concentration after extraction (mol H+/I)

The effect on the metal concentration in the solution for the metal recovery is shown in Table 6. As a result we notice a rather small effect on the concentration. Table 6 Effect of direct recirculation of the leachate on the metal concentration Parameter Leachability in one Recirculation factor Final concentration step extraction L/S = 40, initial pH = 1 final pH = 4 3-5 15 - 25 mg/l cu 5 mg/l Pb 13 mg/l 3-5 39 - 65 mg/l Zn 960 mg/l 3-5 2 880 - 4 800 mg/l Cd 12 mg/l 3-5 36 - 60 mg/l

3.3.2. Concept 2 Minimizing the water consumption in the scrubber unit is possible by recirculation of the scrubber solution. Since the pH value in the unit is limited to 0.5 - 0.3 partial neutralisation is required. The recirculation factor is in this case determined by the chloride concentration. In some incinerators (e.g. MSWI Iserlohn, Germany) the water consumption in the acid scrubber unit kan be restricted down to 100 Vton waste by neutralisation with sodium hydroxide. This corresponds to a maximum chloride concentration of 100 gA. In a second concept the extraction of fly ash is totally integrated in the scrubber unit. By using the fly ash basicity, the consumption of neutralizing agent can be minimized. No additional neutralization is needed in a concept which integrates fly ash extraction and electrolytic chlorine recovery in one process (see Figure 15).

535

I

I

L

Ll

Figure 15 Process flow of the second concept

Experiments in a bench-scale electrolyzer performed at the Karlsruhe Nuclear Research Centre proved the technical feasibility of this electrochemical recovery process [2]. Critical factor for the recirculation in this concept however is the solubility of the metal chlorides. One must avoid precipitation in the scrubber solution due to accumulation of the metals during the recirculation. Most critical elements are Cu and Pb. The recirculation factor in function of the solubility of these two elements has been calculated for two different process conditions. In the first example pH value in the acid scrubber circuit is kept on 0.3 which corresponds with a concentration of 0.5 mol HCIA In the second example the pH-value is kept on 1 . To reach sufficient leaching efficiency a minimum acid dose of 4 mol Hf/kg fly ash is required (final pH after extraction equal to 4). The results are shown in Table 7. In both situations different parameters are most critical. Solubility of PbC12 is limiting the recirculation if the pH value in the scrubber unit is kept equal to 0,3. In the second situation (pH = 1) Pb becomes more soluble due to the decrease of the chloride concentration. Cu, however becomes less soluble, since solubility of Cu is mainly depending on the formation of chloride complexes. As a consequence the recirculation factor of the second process is depending on the solubility of Cu.

536 Table 7 Calculation of the recirculation factor as a function of solubility Example 1 Parameter Maximum Leachability solubility LIS = 10 initial pH = 0.3 [HCl] = 0.5 M final pH = 4 Pb 423 mg/l 31 mg/l cu 3 llOmg/l 6.5 mg/l Example 2 Parameter Maximum Leachability solubility LIS = 40 initial pH = 1 [HCI] = 0.1 M final pH = 4 Pb 1 378 mg/l 13 mg/l cu 410 mg/l 5 mg/l

Recirculation factor

13.6 478 Recirculation factor

106 82

Effects on the metal concentration in the solution are summerized in Table 8. We notice a significant increase of the concentration, which gives much more perspectives in view of recovery potential. However more research is needed to examine the chlorine recovery from this specific solution. Table 8 Influence of the integration of fly ash treatment in the acid scrubber unit on the metal concentration in the solution prepared for recovery Metal concentration in solution prepared for recovery Parameter Example 1 Example 2 Recirculation factor = 82 Recirculation factor = 13.6 1 066 mgll Pb 423 mg/l 410 mg/l cu 89 mg/l Cd 313 mg/l 984 mg/l Zn 11 000 mg/l 79 000 mg/l

4. CONCLUSIONS

In view of the reduction of municipal waste incineration residues concepts are developed which link fly ash extraction, using the acid flue gas scrubbing solution, at metal recovery. To reach this goal the leaching process must be optimised in terms of leaching efficiency and final concentration of metals in the leachate. One of the most important factors of the leaching process is the solubility of the metal salts. This is shown by examining the role of pH, liquid solid ratio and extraction time. Especially the experiment with varying liquid to solid ratio showed the importance of the solubility. When the liquid solid ratio increases the leaching efficiency increases since more metal salts can dissolve before solubility restriction is reached. By decreasing the pH, the solubility and so the leaching efficiency of the metal salts are increased. Several metals show a decreasing leaching efficiency as a function of the extraction time due to a increasing pH value.

531

Since the process links extraction at metal recovery a high concentration of dissolved metals is also needed. First priority is given to the recovery of Zn, Cd, Pb and Cu. Especially Cu(I1) and Pb give problems in view of potential recovery because of the limited solubility of their salts. The solubility of these elements can be improved by the use of complexing reagents. Positive results are noticed with EDTA. The increase of the final metal concentration in the solution can also be obtained in a total different way By using the fly ash extraction as a neutralising step in the acid scrubber unit and in combination with an electrolytic chlorine recovery process the leachate can be recirculated several times. During the recirculation metals are accumulated. The recirculation factor depends on the solubility of the metal salts. Using this concept the metal concentration of the most critical metals (Cu and Pb) can be increased up to 0.5 - 1 g/l which facilitates their metal recovery. 5. REFERENCES

1 Vehlow, Braun, Horch, Merz, Scneider, Stieglitz and Vogg, Semi Technical demonstration of the 3R-process, Waste Management & Research No. 8 (l990), 461-472. 2 Volkmann, Vehlow, Vogg, Improvement of flue gas cleaning concepts in MSWI and uti-

lization of by-products, Studies in Environmental Science 48, Waste Materials in Construction, Elsevier (1991), 145-152 3 Laethem, Elslander, Kinnaer, Geuzens, Geintegreerde venverking van reststoffen van huisvuilverbrandingsinstallaties,VITO (l993), 120.

This Page Intentionally Left Blank

Environmental Aspects of Consmcnon with Waste Materials JJJ.M. Goumans, H A . van der Sloot and 7'h.G. Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

539

Life Cycle Assessment of a Road Embankment in Phosphogypsum Preliminary Results 1.W. Broers, Road and Hydraulic Engineering Division, Ministry of Transpod, Public Works and Water Management, Delft, Holland' F. E. T. Hoefnagels, H.L. Roskamp, CREM Consulfancy and Research for Environmental Management, Amsterdam, Holland

Abstract: The Life Cycle Assessment (LCA) method developed by the University of Leiden has been used to quantify the environmental interferences caused by a road embankment built of phosphogypsum, a waste material of the fertilizer industry. It is taken into account that the gypsum must be dumped or discharged if it is not re-used. This article gives a global view over starting-points and assumptions, which sometimes had to be quite arbitrary. Also, some preliminary results are presented. It seems that dumping is least attractive. The LCA study can not decide between discharging the gypsum and building an embankment of it. 1. Introduction

In the Netherlands, more than two million tons of phosphogypsum. a waste product of the fertilizer industry, is yearly discharged into surface water. To prevent this wasting, and to reduce the use of primary materials like sand, research is made into using phosphogypsum in construction. Several applications are possible. Application of stabilized phosphogypsum in a road embankment is one of the most promising options. However, the application in a road embankment has some environmental disadvantages, e.g. leaching out of impurities. The Road and Hydraulic Engineering Division has taken the initiative to apply the Life Cycle Assessment method (LCA), as developed by the University of Leiden [I], to a road embankment built of phosphogypsum. The main object of this project is to try using, and to learn from using, the LCA method in the working field of road building. A subsidiary object is to compare the LCA method to other environmental assessment methods, like the Environmental Impact Assessment (EIA, in Dutch: Milieu-Effect-Rapportage). The result obtained from the LCA study, the quantitative evaluation of the environmental interferences caused by the road embankment, is of secondary importance in this study. 2. Object of the LCA study The object of the LCA study is to compare the road embankment in phosphogypsum to a road embankment in sand. Three options are compared: A. an embankment built of stabilized phosphogypsum; B. an embankment built of sand, and continuing to discharge the phosphogypsuminto surface water; C. an embankment built of sand, and dumping the phosphogypsum at a controlled dump site on land. The production of the phosphogypsum and the use and maintenance of the road are not taken into account, as they are equal for all three options. The functional unit of the LCA is " A road embankment of one kilometre length during a period of 60 years, and the processing of 78 kiloton phosphogypsum". 78 kiloton phosphogypsum is the amount that in the design that is used - can be stored in 1 km of road embankment.

-

'

Correspondence: Road and Hydraulic Engineering Division, P.O. Box 5044. NL-2600 CA Delft, Holland, tel. (+3 1)I 5-699111.

540

3. Starting-points and assumptions As pure phosphogypsum does not satisfy the mechanical demands for road building, it is stabilized with fly ash and cement or quicklime (CaO). It is assumed that the phosphogypsurn is used in the form of briquets, consisting of 65% gypsum, 25% fly ash and 10% quicklime (on mass basis).

~

/

<

~

28 m

---Sand ~ (cappin concrete layer) ~ -Sand bentoni e --fhosphogypsum briquet - - - S a n d (drain layer) -Sand

9,

>

Figure 7. Outline of half of the road embankment in phosphogypsum (to scale). The design used in the study is shown in figure 1. It is a four-lane road with hard shoulders. The width at the top is about 30 m, the height of the embankment is 6.4 m before consolidation. A 1.5 m thick capping layer of sand is needed to prevent that the sand bentonite layer is perforated by lighting poles, etc.. A 25 cm thick layer of sand bentonite is used to reduce water infiltration. A 1.5 to 2.5 m thick layer of sand is applied below the phosphogypsum briquet layer, to prevent contact between gypsum and ground water. This layer is necessary, since it is assumed that the embankment is built near the fertilizer factories in Rotterdam, where the soil is very soft and the ground water level high. Because of these safety layers, the phosphogypsum briquet layer has a height of only two metres. Though the technical life span of a road embankment may be infinite, is it is clear that the economical life span must be shorter. Future building activities may require moving the embankment. Furthermore, environmental problems like the greenhouse effect and the limited oil supply will have their influences on transportation, which might shorten the economical life span of road embankments. Therefore, the economical life span of the road embankment is arbitrarily fixed on 60 years. A further arbitrary assumption is that 90% of the material resulting from the demolishing of the embankment in phosphogypsum can be re-used. Most of these assumptions will be subjected to sensitivity analysis. 4. Preliminary results At the moment this article is written, a final concept of the LCA report is ready. Some changes will probably be made before the report is published [2]. Fourteen environmental effects are distinguished in the Leiden LCA method, which are shown in table 1. Radiation is added to this list since phosphogypsum is slightly radio-active. For many of the effects it is not possible to quantify the data or the classification factors.

The preliminary results of the LCA study are shown in figure 2. As was expected, option B where the phosphogypsum is discharged, leads to high scores on nutrification and ecotoxicity, due to emissions of phosphate and heavy metals to surface water. Options A (building the road embankment in phosphogypsum) and C (dumping the gypsum) score high on most other effects. This is due mainly to the use of fossil energy sources for building machines (road-roller, transport materials for both road and dump construction), to quicklime production and to the water purification unit of the dump site. Detail analysis of the results of option A makes it clear that the most important contribution to the ecotoxicity is not the soil contamination by leached out impurities, but the emission of oil in the energy production chain.

541 Table I. Environmental effects in the LCA study. Environmental effect

Status

depletion of abiotic resources depletion of biotic resources enhancement of the greenhouse effect depletion of the ozone layer human toxicity ecotoxicity photochemical oxidant formation acidification nutrification waste heat odour noise damage to ecosystems and landscapes victims radiation

not enough classification factors not relevant in this case study quantified not relevant in this case study quantified quantified quantified quantified quantified hardly any data quantified no data no quantitative data no data no classification factors

m A embankment

Enh. grwnhouse Mest

0

B discharging

Human toxkiiy

C dumping Photochem oxydant form Aciddication Nutrdication Odour

0

20

40

80

80

100

relative effectscore [%]

Figure 2. Comparison of the effect scores for various environmental effects (preliminary results). For every environmental effect the effect score of the highest scoring option is fixed on 700%. From the results it seems that option C (dumping) is least attractive. It should, however, be noted that dumping might have the lowest effect score for radiation. Furthermore, the sensitivity analysis makes it clear that the relatively good score for option A is caused by the assumed re-usability of the road embankment material. If the phosphogypsum briquets are not re-usable and should be dumped after one life cycle, it would be better to dump the gypsum at once. 5. Discussion As the technical research on phosphogypsum as embankment material is still going and some data are unknown, it is necessary to make several assumptions. This will have its effects on the quality of the results. In a case like this, the sensitivity analysis is an essential part of the LCA study. No standard LCA data are available for road building processes, unlike other sectors like package manufacturing. Such data would be very convenient for applications like this.

542 A major reason for using waste materials in construction is the fact that depletion of resources is avoided. However, no classification factors have been established for resources like sand, bentonite and limestone, since the world supply is sufficient for more than 100 years. The depletion of such resources tends, therefore, to be forgotten in LCA studies. The unknown, but rather long, life span of constructions is a special point of attention in LCA's of constructions. Much of the environmental interferences depend on processes which take place in the future. The environmental interferences caused by a construction built of waste materials can be attributed to the construction (road embankment) or to the product of which the waste is a by-product (fertilizer). This attribution step can be a difficult step in a LCA like this, but it can be avoided by assessing alternative ways to process the waste material. The Leiden LCA method is location-independent. This has some disadvantages when the method is applied to road building cases: roads are designed for a specific location and the transport towards that location significantly contributes to the total of environmental interferences [this study,3,4]. When using the method on specific road cases, the location independency should be released slightly. 6. Conclusions As was expected, it is not possible to decide which option is best. This is partly due to the inability to classify some important interferences (like radiation) and partly to the impossibility to compare environmental effect scores as different as nutrification and greenhouse effect. The LCA method appears to be quite well applicable to road building cases. Some special points of attention exist however, which are listed under 'Discussion'. Local environmental effects were not included in this LCA study. It showed no overlap with a local assessment method like Environmental Impact Assessment. EIA and LCA could be used side by side. A LCA study should be executed in two phases: (1) establish the relevant processes, subprocesses, starting-points and assumptions, (2) determine the environmental effects in a systematic way. These phases are mixed in this study, which appears to be inconvenient. A final remark: the most 'sustainable' solution to the phosphogypsum problem is probably not a change in the way the gypsum is processed. In a perfectly sustainable society fertilizers are extracted from living nature and not from mineral resources.

Contributors to this study The LCA study is executed by H.L. Roskamp and F.E.T. Hoefnagels of CREM Consultancy and Research for Environmental Management. C. Huppes and A. Wegener Sleeswijk of the State University of Leiden are advisors to this project. J.W. Broers, P.M.C.B.M. Cools, M.B.C. Ketelaars, G.J. Laan, J.A.M. Mank, H. Rietveld, M. de Soet and E. Vos of the Road and Hydraulic Engineering Division established the starting-points and assumptions and learn from the project. 11terature 1. Environmental Life Cycle Assessment of Products. I. Guide and II. Backgrounds, R. Heijungs (red.), Centre of Environmental Science, Leiden (1992). Published by order of the National Re-use of Waste Research Programme (NOH). NOH-reports 9266 and 9267. 2. H.L. Roskamp and F.E.T. Hoefnagels, Levenscyclusanalyse van drie mogelijke bestemmingen van fosfogips, publication in preparation. 3. F. Hoefnagels and V. de Lange, De milieubelastingvan houten en betonnen dwarsliggers, CREM by order of Nederlandse Spoomvegen, Amsterdam (1993). 4. Personal communication R. van Selst, Intron, Sittard.

Environmental Aspects of Conshuction with Waste Materials JJJ.M. Goumans, H A . van der SImt and Th.G.Aalbers (Editors) 91994 Elsevier Science B. V.All rights reserved.

543

CO-COMBUSTION OF COAL AND WASTE WOOD, CONSEQUENCES FOR THE BY-PRODUCT QUALITY

M.L. Beekes, C.H. Gast and A.J.A. Konings KEMA Nederland B.V., P.O. Box 9035, 6800 ET Arnhem, the Netherlands

Abstract The co-combustion of coal and waste wood has been experimentally investigated in a 1 MW,, pilot plant. The amount of coal replaced varied between 0 and 8% on a calorific basis. The consequences for the emissions to air and the by-products, fly ash and bottom ash were monitored. Cd, Pb and Zn concentrations in the fly ash increase significantly.

1. INTRODUCTION

The total amount of waste wood in the Netherlands is 1-1,3 million ton per year, of which around 770,000 ton is difficult to process. In the near future the disposal of waste wood in landfill sites will be no longer allowed. The contamination with environmentally harmful components is one of the main causes of the problematic processing. In principal incineration in special waste boilers is an option but the capacity of those installations is limited and the efficiency of electric power generation low (20-25%). The relatively high heating value of waste wood makes it an interesting fuel for cocombustion in existing coal-fired power plants. The advantages are a high efficiency of electricity generation (> 40%) and the formation of reusable by-products (fly ash, bottom ash and gypsum) compared with conventional waste incineration plants. A research program was defined to investigate the technical feasibility of cocombustion of coal and waste wood in Dutch power plants. The main objectives of the project were: demonstrate the co-combustion of powdered coal and waste wood determine the consequences for the emissions, such as NO,, SO,, heavy metals and dioxines

544

determine the influence on the by-product quality, such as heavy metal content. The paper will give an overview of the project with in-depth discussion of the influence of co-combustion of wood on the quality of the by-products.

2. WASTE WOOD CHARACTERIZATION

The particle size of fine and coarse waste wood and reference wood has been determined by sieve analysis. The results are given in Table 1. The Drayton coal used has been milled to a particle size of 90% < 60 pm. Table 1 Sieve analysis of fine and coarse waste wood and reference wood sieve width (mm)

fine waste wood % within range

reference wood % within range

sieve width (mm)

< 0.50

62

57.9

< 0.21

6.4

0.50 - 0.85

27.9

40.6

0.21 - 0.50

9.6

0.85 - 1.00

4.1

1.25

13.7

1.00 - 1.25

3.4

0.1 1

1.25 - 1.60

1.7

0.13

> 1.60

0.9

- 1.00 1.00 - 3.00 3.00 - 4.00 4.00- 5.00 5.00 - 8.00 0.50

> 8.00

coarse waste wood % within range

13.0 53.8 2.5 0.45 0.55

Waste wood and coal have been analyzed with respect to combustion parameters and heavy metals. The results are presented in Table 2. Drayton coal can be regarded as representative for the average values with respect to physical (ash, volatile, LHV) and chemical parameters (macro and trace elements) of the total mix of coal types fired in Dutch power plants.

545

Table 2 Analyses of Drayton coal and the fine and coarse fraction of waste wood (as received) parameter

unit

fine waste wood

coarse waste wood

Drayton coal

total water

6.0

bounded water

5.02

6.31

2.10

ash

2.13

1.87

9.63

volatile matter

75.20

75.18

34.55

LHV

17.10

18.63

29.08

C

48.61

17.28

75.1

N

0.44

1.53

S

0.02

0.81

H

6.33

4.94

0

36.4

6.1

As

9.5

10.9

Cd

1.13

0.07

Cr

10.9

25

cu

37.6

23

Hg

0.07

0.23

Pb

980

14.0

Sb

9.1

< 1

Sn

2.2

< 2

Zn

870

19.8

797

426.5

546 3. REACTIVITY MEASUREMENTS

Waste wood has to be reduced in size to ensure complete burn-out in the boiler. The energy necessary for size reduction increases rapidly below a certain point. Therefore the maximal allowable size has to be determined.

1m7,J

supply of coal

Furnace furnace length: 1.5 m rnax. temperature: 1600 "C capacity: 30 g l h

Collector

Figure 1. Drop tube furnace set-up.

The experiments are performed in a so-called drop tube furnace, see Figure 1, in which wood particles fall through a heated tube filled with air. The residence time can be varied within the range representative for coal-fired boilers in power plants. The ash is collected and the amount of carbon can be determined. From the results it appeared that waste wood has to be reduced in size to below 1 mm.

4. PILOT PLANT EXPERIMENTS

KEMA has a 1 MW,, powder coal-fired test installation at its disposal. Figure 2 shows a simplified flow-diagram of the installation.

547

natural gas

r-1,

flue-gas cooler

P; -

pulverized

low. pressure cooling system

/’

primary air

//

’

combustion chamber

ash disposal

cooling system

3

‘test zone HT-pipes

6

to ash disposal system

Figure 2. Simplified flow-diagram of the powder coal-fired test installation.

Experiments have been performed in which 2.5-8% (calorific value based) waste wood has been co-combusted with Drayton coal. Operational parameters, furnace temperatures, emissions and by-product compositions have been measured. 4.1 Emission measurements

During the experiments the concentration of NO,, SO,, C,H, CO, CO, dust, Hg, Cd, Pb, and Zn in the flue gas has been determined. The results are shown in Table 3. The measurements have been conducted in the flue gas ducting behind the bag filter. The oxygen concentrations measured varied between 4.7 and 8.7% suggesting excess air levels of at least 20%. However it appeared that air had leaked into the bag filter house. The actual excess air levels were much lower than those calculated from the measured flue gas values. Dioxin concentrations have been measured in duplicate during run 1 and 3. Only one measurement gave a concentration of 0.01 ng TEQ/m3, the three others were below this detection limit.

548 Table 3 Analytical results of emission measurements during co-combustion waste wood experiments

SO, (mg/m3)'

0,(% v/v)

co,

(% v/v)'

run 1

run 2

run 3

run 4

run 5

0

2.7

5.6

8.0

6.0

1.2

1.3

2.2

6.2

0.8

16.4

2.9

< 2.5

< 2.8

< 3.1

8.5

30

36

63

87

24

53

62

100

93

121

74

78

115

117

40

260

179

173

39

<2

16

a

10

<2

483

320

569

368

587

1420

1400

1440

1390

1450

5.0

4.7

5.1

5.2

8.7

12.4

13.2

13.1

13.2

13.1

concentration calculated in dry flue gas 0 "Cand 6% 0,

4.2 Fly ash and bottom ash analysis

Fly ash The carbon, As, Cd, Pb, Sb, Sn and Zn concentrations have been analyzed and are given in Table 4. The carbon content appeared to be high. Due to the control of combustion air on flue gas oxygen content and the air leakage in the baghouse filter unit, the excess air levels during the experiments were lower than anticipated. The selection of the metals analyzed is based on the composition of the coal and the waste wood. It appears that these metals report mainly to the fly ash. The composition limiting values for unformed building materials according to the 'ontwerp Bouwstoffenbesluit, juni 1991' (the Dutch 'Decree on Building Materials, June 1991') may be approached or exceeded, depending on the content of especially lead and zinc in coal as well as waste wood. Since the fly ash is used almost completely in formed building materials, the percentage fly ash in the products has to be determined in order to assess a possible exceeding of the

549 composition limiting values for products. It is also important to determine the leaching behaviour of heavy metals in products in which fly ash from pulverized coal/ pulverized wood co-combustion is used. Dioxin concentrations have been measured for fly ash from run 1 and 3. Only octachlorodibenzodioxin and octochlorodibenzofuran was measured. The other component concentrations were below the detection limit of 10 ng/kg. The total 2,3,7,8 congeners (TEQ ng/kg) amounted 0.038for run 1 (coal only) and 0.026for run 3 (5.6% waste wood co-combustion).

Table 4 Fly ash compositions of co-combustion waste wood experiments run 1

run 2

run 3

run 4

run 5

%waste wood co-cornbusted

0

2.7

5.6

8.0

6.0

% carbon

18.3

33.4

26.9

28.4

17.6

As @g/g)

90

120

120

100

90

Cd @s/g)

1.1

2.2

2.4

2.8

3.1

Pb @s/s)

151

930

970

1300

1740

Sb @g/g)

8.3

17.4

17.6

22.2

25.5

Sn @g/g)

7

12

15

12

14

200

990

990

1340

1400

Zn

hala)

Bottom ash The bottom ash contains particles which could be identified as unburned waste wood. Especially in run 5, where the course waste wood was co-combusted, the amount of unburned wood was high (85%).

5. CONCLUSIONS

Waste wood has to be reduced in size to below 1 mm in order to get a satisfactory burn-out of the particles. This is important for the energy efficiency of the installation as well as for the utilization of the by-products. The latter needs special attention due to the present practice of low-NO, burning techniques, which already presents a problem with respect to keeping unburned carbon in fly ash below 5%.

550

Waste wood may contain high concentrations of heavy metals such as cadmium, lead and zinc, which report mainly to the fly ash. The increase in heavy metal content of the fly ash can be predicted on the basis of waste wood and coal analysis. The leachability of these metals from the fly ash and from products in which the fly ash is used, can also be predicted, provided that the ash contribution from the waste wood is small compared to the ash contribution from the coal. Thus the maximum amount of waste wood that may be co-combusted, to produce fly ash that still complies with the 'ontwerp Bouwstoffenbesluit' from June 1991 can be determined.

SECTION 3: Technical Aspects

This Page Intentionally Left Blank

Environmental Aspects of Conshuction with Waste Malerials JJJ.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) 01994 Elsevier Science B.V. All rights resewed.

553

Use of demolition concrete to produce durable structural concrete P J Wainwright and J G Cabrera

Civil Engineering Materials Unit, Department of Civil Engineering. University of Leeds. England

Abstract The results presented in this paper form part of a current programme of research o n the use of recycled concrete as an aggregate for the manufacture of new structural concrete. Emphasis is placed on durability related properties rather than engineering properties. Durability is assewed in terms of permeability, porosity and strength. The paper examines the relation between strength porosity and permeability and presents numerical relationships obtained by statistical afialysk. Partial fly ash substituticin of recycled fines increaqes the strength of concrete but does not improve long term permeability.

1.

INTRODUCTION

The demands of modern technology have affected land use and placed great pressure for the optimisation of expensive land in large cities. Building structures are required to become taller for maximum land utilisation, bridges are required to carry ever increasing load traffic and the rapid growth of populations all over the world result in far shorter useful life of structures. This modern pace has resulted in ever increasing demolition waste. In the European Community alone it is estimated that by the year 2000 broken concrete waste will reach 100 million tonnes per year. Regulations and restrictions on disposal sites wdl require greater recycling of this industrial waste. The developmenn in the technology of recycling demolition concrete started in 1940- 1950. Nixon (1978) and Hansen (1986, 1992) have presented comprehensive reviews of the state of the art. They have shown that the major thrust of the research on the use of demolition concrete for use as an aggregate in new structural concrete has been the study of the engineering properties and structural behaviour. Researchers in this field agree that concretes of satisfactory strength can be produced using recycled coarse or fine concrete aggregates. However, when coarse and fine recycled aggregates are used together there is considerable reduction in the quality of new concrete. This Ls understandable since aggregates from concrete made by crushing will exhibit the sanie relatively high porosity associated with the original concrete, in comparison with the porosity of natural

554

aggregates. Economic use of recycled concrete aggregates should include the use oi' the fines to replace natural sand, since the amount of tines generated is approximately 40% to 50% cif the total weight of the recycled concrete. It i;, also interesting to point out that the weight percentage of the mortar adhering to the mineral aggregates with which the recycled concrete is made, varies from 5% in the coarse fraction to 40% in the fine sand size fraction (Wainwright et al 1992). Data on the performance and durability of concrete made with recycled concrete aggregates is not easily found. Therefore, in this paper data is presented on the use of recycled coarse and tine aggregates to make concrete. Properties measured include strength, porosity and permeability. Statistical methods are used to propose models for assessment of the performance of these concretes for use in environments which are typical of aggressive road environment% Fly ash and superplasticizers are also used to niodifj, the properties of the concretes and their potential improvements are assessed using the same parameters.

2. MATERIALS Recycled aggregates: Although it will be ideal to use as recycled aggregates "denolition concrete" recovered from a concrete structure, for the purpose of this work it was decided to use simulated laboratory "demolition concrete". One mix was therefore assigned to realistically simulate properties of a good concrete with adequate performance properties and another mix was designed to exhibit average performance properties. Therefore, two sources of aggregates for recycling were produced in the laboratory from two concretes made with different mix compositions. The mix compositions were designed to provide concrete mixes with nominal cement contents of 380 kg/m3 and 220 kg/m3; both mixes were made to a nominal slump of 50 mm and the resulting watedcement ratios were 0.41 and 0.7X Izspectively. Cubes and slabs were cast from each mix and specimens were kept in a mist room at 20°C rt 2°C for 2X days. The slabs were broken down to provide the aggregate for the new concrete and the cubes tested for compressive strength the values of which were 43.0 and 78.0 MPa for the low and high cement content mixes respectively. It is generally acknowledged that the performance of concrete is closely related to its total porosity and permeability and that a good concrete should exhibit an intrinsic permeability of not more than 2.5 x 10-17 mz. The source concretes designed in the laboratory had total porosities of 12.5 and 10.0% with intrinsic permeabilities of 3.85 x lo-" and 2.41 x m2 and therefore complied with the "good" and "average" performance requirement. Concrete mixes made with recycled aggregates: A number of different mixes were made with the recycled concrete aggregates and their properties compared with that of a control mix made with natural aggregates from the same source as those used to make the original concretes. All mixes were made to a nominal cement content of 280 kg/m3 using a computer package to proportion the mixes. In the fust instance three mixes were chosen for investigation: one in which the coarse aggregate was replaced with the recycled materials, one in which only the tine aggregate was replaced and one made completely from recycled material; these three mixes were repeated for the recycled aggregates made from both source concretes.

555

I n addition, a number of mixes were later made to assess ways of improviiig the performance of concrete made with the rzcycled fines. Using the mixes made froni all recycled materials as the controls, modifications were made to the mix proportions in the following w a p : I.

Replacing 25% and 50% by weight of the recycled tines with natural sand.

2.

Replacing I(,% and 30% by weight of the recycled fines with tly ash (fa). The fa used w u an unclassified ash obtained from Drax Thermal Power Station in North Yorkshire, England.

3.

Use of a superplasticizer to enable the watedcement ratici to be reduced to achieve constant workability.

The specimens made from all mixes were stored at 20°C k 2°C and 1000/0 RH until required for testing. Information on the mix designations and proportions are given in Table I and the properties of the hardened concrete are given in Table 2. Table 1. Mix :tails for recycled aggregate c( cretes. Mix Source Concrete Mix Description Designation (see Table 2) 3A, 3B R U 100% NF 12 RU100% W 4A, 4B 12 RC/50% RF/50% NF 5A, 5B I ,2 .^ RC/75% RF/25% NF hA, 6B RC/90% RF/I 0% FA 7A, 7B XA, 8B RC/70% RF/30% FA 9A, VB NC/ 100% RF RC/IOO% RF + SP IOA, 108 Control All natural aggregates

Plastic Density (kg/in3) 2390,2360 2250,2290 2320,2320 2290,23 I5 2290,233 1 2290. 232X 23 I!), 2350 2290, 2320 2450

RC = Recycled coarse; RF - Recycled fines; NC = Natural coarse; NF = Natural fines; FA = Fly ash; SP = Superplasticizers; A = Recycled aggregates from 43 MPa concrete; B = Recycled aggregates from 78 MPa concrete. Concrete performance was assessed in terms of strength, porosity and permeability. Strength was measured on 100 mm cubes in accordance with BS I X X 1 (19x3). and porosity was determined by measuring the weight of the specimens in saturated and dry conditions using a vacuum saturation technique. The specimens used for this test were the same as those used for oxygen permeability. Permeability to oxygen waq measured using the equipment and procedure developed by Cabrera and Lynsdale ( 1988). The specimens used were 50 mm in diameter by 4X-50 mm in height cored from 100 nim cubes. After coring, the specimens were placed in an oven at 105°C k 5°C for 72 hours. They were then placed in an air-tight container until they reached room temperature before the start of the test.

556

2.1 Compressive strength porosity relationship The development and long term strength of the concretes studied in this paper have been reported by Wainwright et al 1993. In this paper the writers are concerned with the relation between compressive strength and performance related parameters. It is well known in materials science that the pore volume of a composite is related to the strength of it by a logarithmic decay function (Mehta and Montero, 1993). The result$ of the laboratory study of this project are used to find this relationship. Figure 1 presents this relationship which numerically is expressed as:

- (j9.22.e

fC -

Where: fc = P =

-0.03P

(1)

Compressive strength (MPa) Porosity (96)

This equation includes all concretes listed in Table 1. The correlation coefficient r is 0.7 I which at 99% confidence limits is statistically valid. However, another more important indicator of high performance and durability is the permeability of the mixes, therefore, in the next section permeability strength relations are explored. 60

h

0

a I

v

50

f m C r

40 0

.VI

ea

E

50

0

20 0

10

20

SO

1

Pororiiy (%)

Figure I . Relation between compressive strength and porosity.

557

I

Table 2. Properties of recycled aggregate concretes.

I

Mix

Compressive streueth (MPa)

w/c

Porosity f%)

liltrillsic

x

JA

0.62

3n

0.69 0.65 0.66 0.60 0.62 0.69 0.69 0.68 0.65

4A 4B 5A

5n 6A

6n 7A 7H XA XU YA

9n I 0A

1on Coot.

(1.SK 11.57 0.7 I 0 71 0.58 0.56 0.62

7d . 28d 32.5 44.2 32.2 42.3 .;0.0 22.9 29.6 37.0 2h.2 35.2 31 I 38.6 27.4 35.0 283 38.9 29.6 19 Y 32.4 5.37 727 48.3 37.5 55.9 28.0 36.3 37.9 38.9 32.3 39.1 35.6 47.5 40.8 49.8

-

S6d

16&! 50.0 44.7 34.6 44.0 40.9 46.4 39.1 45.1 55.0 63.4 62.7 76.0

46.5 44.0 32.0 40.3 37.4 44.2 36.4

39.1 47.4 51.9 59.3 65.9 37.8 42.6 41.7 51.5 52.7

7d

32 17 39 19 36 19 37

21 21 19

23 I6

39.5 44.2 42.9 53.2

55.9

17 I6

2Xd 14 14 22 19 18 16 21 18 21 15 17 13

22 19 11

17 10

IhXd 14 14

?n

17 I7 14 II 15 12

16 7-0 13 16

I9 15 19

S6d 14 13 22 17 18 16 20 17

15 19 16

9

21 I6 18 13 20

I5

IX 14 8

711 12.0 9.7 17.4 16.3 13.4 10.2 14.1 9.2 31 6 16.0

59 X2 13 7 15.4 9 .(I

8.5

-5.5

penneahi!ity

1o.n (Ill')

18d 5.7 3.9 10.5 10.0 (3.4 5.2 9.4

5611

.16Xd

5.1

6.9

7.6 8.6 7c h.7 5.7 6.3 7.0 5.5

4.2 2.8 6.7 5.0 5.2 2.2 4.8 5.9 6.6 6.4 5.0 4.7 55 13 4.7 3. I 2. I

10.5 7.8 54 4.8

x.x 7.3 6.3 8.6 4.3

3.2 8.2 7.0 5.6 4.2

9.3

5.7

-

2.4

-

2.2 Strength Permeability Relationship Figure 2 shows a cloud diagram of the suength permeability relationship. The statistical correlation is poor, however eliminating some of the values which correspond to the values higher than 50 MPa a statistical correlation can be found. The expression is:

Log10 K = 1.794 - 0.025 fc S L = 95% p = 0.83 Where:

K = Oxygen intrinsic permeability (m2) SL = Significance level

.. .:.. ' 9

-9

'

0 20

SO

9

40

.

50

so

70

Cornprassive strength (MPo)

Figure 2. Relation between Log oxygen permeability and compressive strength.

558

Figure 2 alsci shows that permeability cannol be related to strength unless pore size distiibution i. taken into account (Cabrera et id 19x9). because the mixes studied vary widely in pore structure due to their different compositions, permeability strength relations should be studied and compared only between mixes which have similar pore structure compositions. In this study, pore size distributions were not measured, therefore the interpretation of results is based on the permeability effects caused by replacement of coarse or fine or both recycled aggregates and also on the effect that superplasticizers and fly ash make to the permeability strength relationships. Ln the following section, data is presented to elucidate these aspects. I’he strength permeability relationships for each mix was obtained by statistical regression analysis. The best tit was obtained by a decay function of the following form:

KO

= a

+

I()&

(2)

Where:

KO

=

fc a, b

=

=

Oxygen permeability (m2) Compressive strength (MPa) Coefficients dependent on the mix composition.

Ths va!iies of the coefficients a and b are given in Table 3.

Table 3. Values of comtantq and correlation coefficients of equation ( 2 ) . MiX Coefficients of equation ( 2 ) a b correlation coefficient r 3A 3B 4A

98. I 7 215.73

-0.028 -0.042

0.997 0.994

48

192.22 75x3 163.29 136.00 19.60

-0.036 -0.030 -0.038 -0,035 -0.0 1 I

0.9X8 0.960 0.913 0.799 0.934

4 1 .00

-0.0 13

0.922

12.29 109.72 13,300.3 1 s9.07 45.07 85.7 1

-0.006 -0.032 -0.0x0 -0.025 -0.0 I 9 -0.02x

0.694 0.92 1 0.765 0.9XO 0.506 0.x50

5A 5B 6A

6B 7A 7B XA 8B OA 9B

IOA 1 OB Control

559

2.3 Effect of mix composition on the permeability strength relationship Recycled coarse and recycled tine aggregates: Figure 3 shows ihat the effect ot substituting natural coarse aggregate by recycled concrete aggregate depends (111 thc nature of the source ot concrete. 67

5

100

n.

._ 0

M

c .I

Compressive strength (MPa)

Figure 3. Permeability-strength relationship for the mixes shown in the figure.

High strength concrete recycled aggregate produces a concrete which above 25 MPa has lower permeability than a concrete made with recycled coarse aggregate from a weak concrete (mixes 3A and 3B). When comparing with the control mix, 3A composition gives a higher value of permeability than the control for all strengths. However. mix 38 gives lower values of permeability than the control mix above approximately 32 MPa. Figure 3 also shows the effect of replacing the natural fine aggregate with the recycled tines from the source concrete (mixes 9A and 9B). The effect of substituting natural fines with recycled fines is that changes of strength cause large changes in permeability, i.e. when using recycled fines, care should be taken with the changes on pemieability. However, at high strengths, permeability appears ti) be lower for the concrete with 100% recycled fines than for the ccintrol concrete.

2.4 Partial replacement of coarse and fine aggregates Figure 4 shows the effectq on the permeability strength relationships of the replacement of coarse aggregate and the partial replacement of fine aggregate with recycled materials. The results show that the strength permeability relationship is not unduly modified by this change.

560

Compressive strength (MPo)

Figure 4. The relation between permeability and strength for mixes containing a blend of natural and recycled fines. With the exception of mix 6B, there is little difference between the control mix and mixes 5A, 5B and 6A. Within the range of strengths measured, mix 6B (45 MPa maximum) also falls in the same category. Therefore, it is apparent that total replacement of coarse aggregate and

partial replacement of fuie aggregate up to 75% does not affect the potential performance of the concrete mixes.

2.5 Effect of partial substitution of fly ash Mixes 7 and 8 were made with partial substitution of recycled fines by fly ash (see Table I). Its effect on the permeability strength function is shown in Figure 5. Mix 8B which was used to illustrate the fly ash effect does increase in strength considerably but, the permeability does not show reductions related to the strength increase. Although there is no clear explanation for this imusual trend, it is hypothesised that the large volume of fly ash reduces the volume of recycled fines to an extent which k not shown by the percentage expressed as weight substitution and this results in a considerable increase in strength, but not in a reduction of total pore volume. This effect is also shown with mix 7B. Further work is being carried out to elucidate the fly ash effect on the permeability strength function. h

J c

100

I

0 x

g 5

$

lo

0

-.c

'C

c c

63

0 20

30

40

50

60

Cornpresslve strength (MPa)

Figure 5. Permeability-strength relationships for mixes containing fly ash or superplasticizer.

70

80

2.6 Effect of superplasticizers Although the addition of a supeiplasticizer resulted in a considerable reduction in w/c ratio, its effect on the permeability strength function did not appear to be noticeable. In fact mix 10A gives statistically the same results as the control mix. Mix 10B on the other hand gave higher values of permeability than the control mix when the strength was equal to or greater than 40 MPa.

It seems clear that when using recycled aggregates the effect of superplasticizers is not as predictable as when using them with natural aggregate concretes. Again these explanatory results are being investigated.

3. CONCLUSIONS The limited results presented in this paper allow us to offer the following conclusions: 1.

The strength of the concrete source of the recycled aggregates has a marginal effect on the strength of the rccycled aggregate concrete, but it does not noticeably affect the porosity strength function or the permeability strength relationship.

2.

Accepting that performance is quantitatively evaluated by the porosity strength and permeability strength relationship, recycled concrete aggregates do not reduce the performance of concrete.

3.

Partial tly ash substitution of recycled fines increases the strength of concrete, but it does not reduce the long term permeability.

4.

The use of superplasticizers allows the reduction (if w/c ratio but it does not seem to improve the permeability strength relationship.

5.

Intrinsic permeabilities of <10-'h m2 are considered to be the lower Limit acceptable to ensure adequate long term performance. The concretes tested, with few exceptions, comply with this requirement and therefore, they are suitable for use in mildly aggressive environments.

562 4.

I. 2. 3.

4. 5.

6.

7. X.

9.

REFERENCES British Standard BSIXXI: pt 116. 1983, British Standard Institution, London. Cabrera J G and Lynsdale C J. 40, No. 144. (1988) 177-182. Cabrera J G, Cusens A R and Lynsdale C J. IABSE Symposium: Durability of Structures, Volume 57/1, (1989) 249-254, Lisbon. Hansen T C. Materials and Structures (RILEM), 19, No. 1 I I , (1986) 201-246. Hansen T C. RILEM, Report No. 6, (1 992) E & F N Spon. Mehta P K and Montero P J M. p 44 (1993) 2nd Edition. Prentice Hall, New Jersey USA. Nixon P J. RILEM TC-37-DRC. Materials and Structures (RILEM). 65, (197X) 37 1-37. Wainwright P J, Yu J and Wang Y. Proc. Int. Conference on Fracture and Damage of Concrete and Rock, (1992) Vienna, Austria. Wainwright P J, Trevorrow A, Yu Y and Wang Y. Int. Conf. on Demolition and Recycling of Construction Waste (RILEM) (1 993) Odense, Denmark.

Environmental Aspects of Construcfion with Waste Moterials JJJ.M. Goumans, H A . van der SImt and l3.G. Aolbers (Editors) 01994 Elsevier Science B.V. All rights reserved.

563

Improvement of Portland cement/fly ash mortars strength using classified fly ashes Paya J., Borrachero V., Peris-Mora E., Aliaga A. and Monzo J. Departamento de Ingenieria de la Construcci6n. Universidad Politecnica de Valencia. Camino de Vera s/n 46071 Valencia (Spain).

Abstract The effect of replacing 30 % of portland cement by Spanish fly ash (class F according to ASTM C-618) and their sized fractions, obtained using sieves on compressive and flexural strength of mortars was studied. The study reveals an enhancement of RJR, and R,/R, ratios when finest fly ash fraction is used due to pozzolanic effect. This pozzolanic effect is related with fly ash fineness, but not in the same way for compressive and flexural strength.

1. INTRODUCTION The use of fly ashes in mortars or concrete modifies technological properties as workability, compressive and flexural strength, etc. In addition, the utilization of fly ash also avoids the disposal of large amounts of them contributing to solve big-waste management problem. The fineness of a fly ash is one of the parameters which has a decisive influence on fresh or hardened mortar and concrete properties. One of these properties modified by fly ash addition is the workability of Portland cement mortars. This property mainly depends on fineness, shape morphology and particle size distribution of the fly ash used [1,2]. On the other hand, the particle-size and crystalline/amorphous ratio play an important role in their reactivity towards lime, due to the pozzolanic reaction takes place mainly on the surface of the particles [3].

564

Fly ashes with different fineness can be obtained directly from various steps by the electrostatic precipitators of the coal power plant, or, alternately, in the laboratory using: a) horizontal or helicoidal-shaped air current separator or b) sieves; so, sized fractions obtained show no significant differences in chemical composition, but, in general, glassy content is greater for the finest fractions [4-61. This communication presents the influence of different fly ash sized fractions on two important properties of Portland cement/fly ash mortars: compressive and flexural strengths.

2. EXPERIMENTAL Materials: Mortars were prepared using ordinary Portland cement P-450. Fine aggregate: natural sand with 2.94 fineness modulus was used. Fly ash: the source of this material was the thermoelectric power plant of Andorra (TeruelSpain), that mainly use lignites; this fly ash has a low calcium content (class F according to ASTM C-618). Original fly ash was separated in several sized fractions using sieves: the original fly ash (0)was dried at 105 QCfor 24 hours and, when cold, sieved using sieves of 149 pm, 53 pm and 40 pm. Fraction retained on 149 pm sieve was discarded, and three sized fractions were collected: coarsest fraction (C), (retained on 53 pm sieve), medium-size fraction (M) (retained on 40 pm sieve) and the finest (F) one (no retained on sieves). Each sized fraction was homogenized before preparing mortars. Chemical data of initial fly ash and sized fractions are given in Table 1. Additionally, granulometric distributions of fly ashes are shown in Figure 1. SEM microphotographs of the coarsest (a and c) and the finest fractions (b and d) are showed in Figure 2 . Microphotographs a and b were taken practically at the same magnification, which permit an easy size comparison.

Apparatus and procedures: Particle size distributions were recorded using Sympatec Helos Analyzer. Preparation of mortars was carried out according to ASTM C-305 test, mixing 450 g of Portland cement, 1350 g of natural sand and 200 mL of water for control mortars and replacing a 30% of Portland cement by fly ash (original or sized fractions) for the rest of mortars. Mortars were put in a mold for obtaining 1 6 x 4 ~ 4cm specimens, which were stored in a moisture room (2021 QC)for 24 hours. Afterwards, the specimens were demoulded and stored under water at 2021 QCor at 4021 QCuntil testing.

565

Table 1. Fly ash chemical composition Fly ashes %

Original

Coarse (22%*)

Medium(46%*)

Finest(29% *)

SiO,

41.40

42.77

42.05

43.34

A1203

26.22

24.62

21.42

22.21

IR (**)

7.70

4.55

5.60

4.16

CaO

6.10

5.91

6.43

5.84

MgO

1.11

1.09

1.29

1.37

K2O

0.53

0.31

0.23

0.39

LI (***) 2.20 3.86 2.99 1.88 (*) Fly ash percentages obtained by sieving (**) Insoluble Residue (***) Loss on Ignition

16

YQ

14

12

1

.

.

10

8

+ x -8-

6

4 2

0 1

10

100

diameterhm)

Figure. 1 Granulometric distributions of original fly ash (0)and sized fractions obtained by sieving

566

Figure 2. Scanning Electronic Microscopy microphotographs a(2663) and ~(266.5)coarsest fly ash fraction b(2660) and d(2661) finest fly ash fraction 3. RESULTS AND DISCUSSION Two experiences were developed, both study the variation of Ri/Rcemen, versus curing time (Figures 3 to 6) . First experience curing temperature was 20 2 1 *C and long-term curing periods ( until 270 days). Second experience curing temperature was 40 2 1 QC and short time curing periods (3 to 28 days). Compressive and flexural strength were measured in both experiences, the results for both experiences are discussed separately below.

567

RVRc

1.25 1

0.75 0.5

t (days) 0

C

m

M

mF

Figure 3. Long-term Rim, ratios development for mortars cured at 20

?

1 QC

Ri/Rf

1.4 1.2 1 0.8

0.6 90

28

180

270

t (days1 0

c

~M

DF

Figure 4. Long-term Rim, ratios development for mortars cured at 20

f

1 QC

568

RVRc

1.2 1 0.8

0.6

t (days)

C

0

m

M

m

F

Figure 5. Early age Ri/R, ratios development for mortars cured at 40 f 1 QC

RVRf

1.a 1.6 1.4 1.2 1 0.8 0.6 7

3

28

14

t ( days1 1

0

C

m

M

m

F

Figure 6. Early age RJR, ratios development for mortars cured at 40 * 1 QC

569

Compressive strength (RJ:Little differences among R,/R, ratios for different fly ashes were observed at 28 days aged experiences (Figure 3). In all cases R,/R, ratios were el. These little differences increased markedly when curing time increases (90, 180 and 270 days). For these last curing times Rim, order was: Finest > Medium Original >> Coarsest.

-

Finest and Medium fly ash fractions presented RJR, ratios larger than 1 and close to 1 respectively, which makes clear pozzolanic reaction. As expected, coarsest fraction produce a decrease of compressive strength respecting "only cement" specimens (Ri/R, << 1). Some experiences were carried out at 40 QC trying to increase fly ash pozzolanic reaction rate. The results show similar tendency that experiences at 20 QC(Figure 5). In short time curing periods (3 days) no significant differences among Ri/R, ratios for different fly ash fractions tested were observed, and these ratios were in all cases less than one. Larger 40 QCcuring times (7, 14 and 28 days) yield significant differences among Ri/R, ratios following similar tendency that 20 QC experience. Largest R,/R, ratios were obtained for specimens containing the finest fraction.

Flexural strength (RJ:Long term experiences (90 to 270 days) show for Original fly ash and Medium and Finest fraction a significant increase of R,/R, ratios (all of them larger than one), making clear that these fly ash addition have a positive influence on flexural strength (Figure 4). There are not observed significant differences among original fly ash, medium and finest fraction for each curing time. From 90 to 270 curing time days coarsest fraction yielded R,/R, ratios < 1 and less than ratios for the rest of fly ashes. Figure 6 shows the results obtained from 3 to 28 curing time days at 40 QCcuring temperature. The tendency observed is the same that observed at 20 QC long term curing time experience.

4. CONCLUSIONS The results show a positive effects on RJR, and R,/R, ratios on mortars containing fly ash due to their pozzolanic effect. The R,/R, ratios increases when fineness particles increases. This tendency was not so clear for R,/R, among, Original, Medium, and Finest fly ashes. The increase of temperature produce a pozzolanic reaction development that makes strength to increase.

570

5. REFERENCES 1. P.K. Mehta. Proc. CANMET/ACI First Int. Conf. Montebello, 1 (1983). 2. E. Peris Mora, J. Payti, J. Monzb. Cem. Con. Res., 23, (1993) 917 3. M.P. De Luxan, M.I. Sanchez, M. Frias Cem. Con. Res., 19 (1989) 69. 4. J.A. Campbell, J.C. Lad, K.K. Nielson, R.D. Smith. Anal. Chem., 50 (1978) 1032 5. E. Peris Mora, J. Paya, J. Monzb. Mat. Con., 41 (1991) 29. 6. K. Ukita, S. Shigematsu, M. Ishii. Proc. CANMET/ACI Int. Conf. Trondheim 1, 219 (1989).

Environmental Aspecrs of Consbuclion wirh Wusre Materials JJJM Goumans, H A . van der SIoot and l3.G. AaIbers (Edirors) BPI994 Elsevier Science B.K AN rights resewed.

571

Ground Fly Ashes: Characteristics and their Influence on Fresh and Hardened Mortars. J. Paya, V. Borrachero, J. Monzb, E. Peris-Mora and A. Aliaga Departamento de Ingenieria de la Construccibn. Universidad Politecnica de Valencia. Camino de Vera dn, 46071 Valencia (Spain).

Abstract A fly ash was mechanically treated by grinding, yielding ground samples with different fineness. During grinding, calcium carbonate formation was observed. Workability of mortars containing 30% ground fly ash replacing Portland cement is similar (10 minutes-grinding sample) or less (20-60 minutes-grinding samples) than "as received" fly ash one, due to loss of spherical shape of particles; however, in all cases, they showed greater workability than "only Portland cement" mortars. Compressive and flexural strength development at early ages of specimens cured at 20 QCshowed that there is an important influence of fly ash fineness: compressive and flexural strengths increased with grinding-time.

1. INTRODUCTION Studies on characteristics of fly ashes are necessary for their adequate use in concrete and mortar production. These characteristics of fly ashes can be modified in order to influence on quality of fresh and hardened concrete and mortar; additionally, new "directions for use" of these materials can be promoted modifying some parameters of fly ashes. The behaviour of fly ashes in Portland Cement mixtures could be modulated by means several procedures, namely: a) Chemical procedures (attack with chemical reagents as acids, bases, etc ...); b) Physical procedures [1,2,3]

572

(classification methods as sieving, flotation and air separation); c) Thermal procedures [4] (heating and cooling treatments); and d) Mechanical procedures [3] (grinding methods using mill or air current). This paper reports on preliminary results of investigation to analyze the influence of ground fly ashes on fresh and hardened mortar containing 30% of fly ash replacing Portland cement; obviously, the firs step will be an adequate physico-chemical characterization of original and ground fly ashes.

2. EXPERIMENTAL SECTION

Materials: An original low-calcium fly ash (namely TO) from thermoelectric power plant of Andorra-Teruel (Spain) was used as received. Analytical data (dry sample): LO1 2.44%, Fe,O, 16.0%, Al,O, 26.2%, S O , 41.4%, CaO 6.1%, MgO 1.1%, Na,O 0.1% and K,O 0.5%. Mortar mixes were prepared using ordinary Portland Cement (OPC) P-450 (Turia II-S/35A). Fine aggregate: natural sand, 2.93 modulus fineness. Analytical data for water used for preparing the mortars and curing the specimens: the content in chloride was 93 mg/L, calcium and magnesium 480 mg/L (expressed as CaCO,), sulphate 298 mg/L, pH 7.88 and conductivity 0.939 mS. Apparatus and Procedures: Samples of TO fly ash were ground using laboratory ball-mill (Gabbrielli Mill-2) for several times: 450 g of original fly ash TO were introduced into the bottle-mill containing 98 balls of alumina (2 cm diameter) and were ground during 10, 20, 30, 40 and 60 minutes, yielding the ground fly ashes namely T10, T20, T30, T40 and T60 respectively. Granulometric distributions were performed using Sympatec Helos Particle Size Analyzer; X-ray powder diffractogramms were recorded on a PW1710BASED Cu-anode; and infrared spectra were recorded on a Perkin Elmer 781 Spectrophotometer as KBr pellets. Preparation of mortars were carried out mixing 450 g of OPC, 1350 g of fine aggregate and 200 mL of water for control mortars, and replacing a 30 % of OPC by fly ash (original or ground fly ash). Preparation of specimens: mortars were put in a mold for obtaining 1 6 x 4 ~ 4cm specimens, which were stored in a moisture room (2O+lQC)for 24 hours; afterwards, the specimen were demoulded and stored under water at 20+1 QCuntil the test age. Flow table was designed as ASTM C-109 and UNE-83.452-88 tests indicate. Freshly prepared mortars were placed into a conic mold [5] which is centered on the flow table. Mortar was put on two layers and compacted with a wooden tamper (10 times). Afterwards, the mold was removed and the table was dropped 15 times (one per

573

second). Flow table spread (FTS) was given as a mean of maximum and minimum diameters of the spread mortar cone. Control mortars were prepared varying the water volume (200, 208, 216, 225 mL) and test mortar containing 30 % fly ash replacing OPC were also prepared varying the water content in the same way.

3. RESULTS 3.1. Physico-chemical characterization of ground fly ashes. Chemical composition: After grinding process chemical composition of fly ashes may remains unchanged. In general, this fact can be accepted, and we have observed that contents in mainly components remain constant. However, loss on ignition value increases when fly ash is ground. A more detailed study on ground samples revealed the formation of calcium carbonate during the grinding process. IR spectra of TO and T60 samples (Figure 1) showed the increasing of signal corresponding to carbonate anion (1430 cm-') when fly ash is ground. Additionally, X-ray powder diffractometry also revealed a little amounts of CaCO, (peak at 29.36Q).

ToT60

---

Figure 1. Infrared spectra for TO (original) and T60 (ground) fly ashes.

574

There are two possibilities to explain this fact: the first reason is the carbonation of free CaO with atmospheric CO, into the bottle-mill:

CaO (s) t CO, (g) ===> CaCO, (s) and the second one is the oxidation of unburned carbon with atmospheric 0, and further acid-base reaction with free calcium oxide: C (s) t 0, (g)

+

CaO(s) ===> CaCO, (s)

Granulometric data: Particle distribution, particle mean diameter and calculated specific surface are given in Table 1.

Table 1 Granulometric data for fly ashes Fly Ash

Percentage of particles with diameter greater than

Mean diameter

Specific surface

TO

60

20

6

32.19

2400

T10

43

5

0

13.48

4020

T20

35

0.7

0

9.96

4640

T30

30

0

0

8.49

4900

T40

25

0

0

6.73

5410

T60

23

0

0

5.93

5959

Granulometric data indicated that for short-grinding periods (10-20 minutes) nearly all of coarsest fly ash particles (greater than 45 pm) were crushed; additionally, hollow fly ash particles (cenospheres) are easily crushed and they can release smaller spheres (pherospheres). When grinding time increases finest particles (diameter less than 45 pm also were crushed as indicates the decreasing of percentage of particles with diameter smaller than 10 pm. However, effectiveness of grinding is reducing as the particle size is being smaller. So, we can observe that the decreasing of mean diameter is not linear because the loss of effectiveness of grinding. Crushing produced particles with irregular shape as was observed by

575

electronic microscopy; these new particles were covered with fine needless and flakes which were originated in the grinding process.

3.2 Applications in mortar production Test Workability: It is extensively accepted that partial substitution of Portland cement by fly ashes enhances workability of mortars, concretes and pastes [5,6,7] and in the same way it is found that the role of fly ashes is related with their fineness, shape morphology of particles, vitreous character and, even, chemical composition. Obviously, when fly ashes are ground, two of their properties are dramatically modified: fineness and shape morphology. Crushing fly ash by grinding yields samples with larger fineness than "as received" fly ash (see granulometric data) which would contribute to enhance workability. On the other hand, crushing original particles, mainly spherical or spheroidal, increases the percentage of irregular particles (mainly flake, needle or splinter shape, sometimes semispherical or semispheroidal morphology) and, so, their lubricant effect in Portland cement mixtures is limited. The behaviour of fresh mortars containing ground fly ashes has been studied using a flow table and following already reported procedure [5]. Flow table spread values (FTS) have been measured (see experimental section) for mortars containing 30 % of fly ash replacing Portland cement and varying water con tent. Figure 2 shows the results obtained for "only Portland cement" mortars (PC) and mortars containing original fly ash (TO) and ground fly ashes (T1O T60). We can observe that mortars containing ground fly ashes yielded FTS values greater that corresponding PC ones.

On the other hand, significant differences among fly ash series are observed: so, workability of mortar containing short-time grinding sample (T10) is similar than mortar containing "as received" (TO) fly ash ones. For higher grinding-time fly ashes a clear decreasing of FTS values is found. Flexural and compressive strengths: The fineness of fly ashes, specially that of its glassy phase is found as a crucial parameter in strength development of concretes and mortars containing fly ashes, and direct correlations between fineness of fly ashes and strength development have been reported [8].

576

_c

+

-

--sC

+ + -

PC TO T10

145 135

T20 T30

-+-

T40

-4-

T60

125 115 105 I 200

I I

205

I

I

210 215 water (mL)

I

220

225

Figure 2. Flow table spread (ITS) values for prepared mortars. Grinding process of fly ash increases its fineness, and possibly, enhances reactivity towards lime. So, pozzolanic reaction rate will be different depending on the grinding time, and strength development may be influenced. Mortars containing 30% ground fly ashes (T10-T60) replacing Portland cement have been prepared and their early age strengths compared with "only Portland cement" mortars and mortars containing ''as received" fly ash (TO). Compressive and flexural strength developments of specimens cured at 20" C are showed in Figures 3 and 4 respectively. We can observe that for compressive strength value (RJ of fly ash containing mortars always are lower than "only Portland cement" ones. However, a significant difference is observed among fly ash series; so, we note that R, values increase from TO to T60 and differences among them are greater for 28-days test. Similar tendency is obtained for flexural strength development (RJ. In this case, 28-day R, values for mortars containing from T20 to T60 ground fly ashes are equal or greater than "only Portland cement'' ones. Both facts indicate that, even at early ages, there is an important influence of fineness on strength development, probably due to pozzolanic reaction rate is favored when fly ash particle size is mechanically reduced.

571

50

PC

45

+

TO

40

*

Ti0

-+-

T20

_c

+

T30

+

T40

-A-

T60

Rc(MPa)

35 30 25

20 15

0

7

14 t(day)

21

28

Figure 3. Compressive strength development for prepared mortars.

a

R f ( MPa) PC

+ TO

7 6 5

4

*

T10

*

T20

--x-

T30

-4-

T40

&

T60

3 0

7

14 t(day)

21

28

Figure 4. Flexural strength development for prepared mortars

578

4. CONCLUSIONS 1. 2. 3. 4. 5.

6. 7.

Grinding fly ashes produced the formation of litle amounts of calcium carbonate. The rest of components remained unchanged. Fineness of ground fly ashes depends on grinding-time, and it is easy to obtain samples with mean diameter less than 10pm. Grinding process crush fly ashes particles, yielding new particles with irregular morphology. In general workability of mortars containing fly ashes is reduced when ground fly ash are used, but, for short grinding time samples, FTS values are not specially affected. In all cases, mortars containing ground fly ashes showed better workability than only "Portland cement" mortars. Compressive and flexural strengths of mortars containing fly ashes are improved when ground samples are used, and in general, they increase when grinding time is increased Flexural strength for mortars containing finest fly ashes, are equal or greater, at 28-day age, than "only Portland cement" specimen at the same age

5. REFERENCES 1 2 3 4

5 6

7 8

W.B. Butler, M.C. Mearing, MRS Symposia Proceedings: Fly Ash and Coal Conversion By-products; Characterization, Utilization and Disposal 11, 65 (1986) pp.11 E. Peris Mora, J. Pay& J. Monz6. Materiales de Construccih 41 (1991) 29. R. Hardtl, Studies in Environmental Science 48, Waste Materials in Construction Proceedings: Environmental Implications of Construction with waste materials, Maastricht (1991) 399. E. Anakura, H. Fujinawa, T. Nishida, Y. Fukada. Jpn. Kokai Tokkyo Koho,41,137,1991 E. Peris-Mora, J. Paya and J. Monzo, Cement and Concrete Research, 23 (1993) 917. E.E. Berry and V.M. Malhotra, Fly Ash for Use in Concrete: A Critical Review, ACI Journal, March-April, American Concrete Institute (1980). U. Costa and F. Massazza, I1 Cement0 (1986) 397. Fly Ash in Concrete: Properties and Performance, Riley Report 7, Ed. K. Wesche, London, Chapter 3 (1991) 62, and references therein.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editon) 91994 Elsevier Science B.V. AN rights resewed.

579

Development of cementitious products using industrial process wastes as sources of reactive sulfate and alumina G. Belz a, J. Beretka b, R. Cioffi C, L. Santoro d, N. Sherman b and G.L. Valenti e aENEL Direzione Studi e Ricerche, Centro Ricerca di Brindisi, Via Dalmazia 21/C, 72100 Brindisi, ITALY. bCSIRO Division of Building, Construction and Engineering, P.O. Box 56, Highett, Victoria, AUSTRALIA. CUniversita degli Studi di Napoli "Federico 11", Dipartimento di Ingegneria dei Materiali e della Produzione, Piazzale Tecchio, 80125 Napoli, ITALY. dUniversitA degli Studi di Napoli "Federico 11", Dipartimento di Chimica, Via Mezzocannone 4,80134 Napoli, ITALY. Wniversita degli Studi della Basilicata, Dipartimento di Ingegneria e Fisica dell'Ambiente, Via della Tecnica 3,85100 Potenza, ITALY. Abstract Two series of mixtures containing up to 90% waste materials have been tested to assess their potentialities for the manufacture of ettringite-based building materials. One series of mixtures is useful for the manufacture of preformed building elements by hydrothermal reaction between a chemical gypsum and reactive oxides or hydroxides of calcium and aluminium. Curing temperatures in the range 55-85OC have proved to give adequate mechanical properties. The other series of mixtures has been used to produce a clinker by firing at about 1200OC. The resulting binder contains calcium sulfoaluminate and sulfosilicate as well as anhydrite. Upon hydration it gives mechanical strengths well above those of ordinary portland cements. The wastes used in the present work are phosphogypsum, fly ash and blastfurnace slag. 1. INTRODUCTION Calcium sulfoaluminate hydrates 4CaO.A12036@,.12H20 (monosulfate) and 6CaO.Al203.3S03.32H20 (ettringite) are compounds characterized by good binding properties and water resistance. Hence systems able to generate them upon hydration behave as cementitious products [l-131. Such systems belong to two different categories: (a) blended compositions containing calcium sulfate and sources

580 of reactive lime and alumina, and (b) hydraulic binders based on anhydrous calcium sulfoaluminate, 4Ca0.3A1203SO3, which can be obtained by high-temperature synthesis of raw mixes containing the required oxides. The mixtures in the first category generally require elevated curing temperatures and are suitable for the manufacture of preformed building elements [14-171. The source of sulfate can well be hemihydrate instead of gypsum, in order to exploit the contribution to the hardening given by the hydration of plaster of Paris. Moreover a further increase of early strength can be achieved if portland cement is incorporated in the mixes. The hydraulic binders based on calcium sulfoaluminate rapidly generate ettringite by hydration at room temperature and are therefore termed rapid-hardening cements [18-241. These binders are important inasmuch as they can be produced at temperatures considerably lower (1100-1300°C) than those required by ordinary portland cements. Most importantly, both categories of cementitious products can utilise large amounts of industrial wastes as sources of reactive sulfate and alumina. 2. EXPERIMENTAL

2.1 Materials

Except for analytical grade CaC03 the materials used for the experiments and their principal chemical components are indicated in Table 1. The composition of the systems investigated is shown in Tables 2 and 3 . Table 1 Principal chemical components of materials used (wt%) Material

CaO

SiO2

A1203

Fe2O3

MgO

SO3

H20

Bauxite Blast furnace slag Clay Fly ash Hydrated lime Natural gypsum Phosphogypsum Portland cement n.a. = not analysed

0.02 41.13 1.30 4.80 72.80 32.60 32.60 63.80

4.70 33.17 46.80 56.80 n.a. 3.33 0.05 22.22

51.50 14.15 34.50 25.50 n.a. 0.35 0.23 4.52

15.30 1.57 1.33 4.20 n.a. 0.22 0.02 3.60

0.04 7.00 0.12 1.50 0.71 0.06 0.22 1.72

n.a. 2.58 0.10 0.40 ma. 43.40 49.00 2.43

25.40 0.15 14.69 0.40 24.39 20.70 20.50

--

Table 2 refers to six blended compositions (BL) containing calcined phosphogypsum, fly ash or blast-furnace slag, portland cement and/or hydrated lime. Six additional compositions containing calcined natural gypsum instead of phosphogypsum and the same amounts of the other components were prepared and used as reference terms. Calcined natural gypsum was prepared by heating in a laboratory oven at 140-145°C for 16 hours, followed by conditioning for 1 day at 21OC

58 1

and 67% R.H., in order to obtain complete conversion to hemihydrate. Phosphogypsum was calcined in a kettle and conditioned as above. Table 2 Blended compositions (wt%) System Calcined Fly ash p hosphog ypsum BL-1 28.5 43.0 BL-2 26.0 43.3 BL-3 30.0 50.0 BL-4 28.3 47.2 BL-5 18.5 -BL-6 20.0 --

Portland cement

--

17.4 10.0 10.0 20.0 10.0

Hydrated lime 28.5 13.3 10.0 14.5

-1.0

Blast furnace slag

---__

61.5 69.0

Table 3 Calcium sulfoaluminate-based compositions (wt%) Material Bauxite Blast furnace slag CaC03 Clay Fly ash Phosphogypsum

FA

BS

CL

22.14

23.30 17.24 25.23

18.97

-34.72

--

Total

---

--

35.40 12.01

--

9.60 33.54

34.23

33.62

100.00

100.00

100.00

Table 3 refers to three calcium sulfoaluminate-based compositions, labelled FA, BS and CL, according to whether fly ash, blast furnace slag or clay, respectively, was used in the raw mix. The compositions indicated in Table 3 were calculated to give a fired product containing C4A3SI C2S and CS in the weight ratio of 1.5:l:l (cement chemistry notation: C=CaO, A=Al2O3, S=SO3, S=SiO2 and H=H20, is used). 2.2 Procedures Blended compositions were pre-cured for 16 and/or 24 hours at 55,70 and 85OC, then allowed to dry at 21OC and 67% R.H.. For hydration studies small (2g) samples were mixed with water (water/solid ratio w/s=0.5) and, at the end of the curing period, ground in acetone to stop the reaction, dried with ether, stored in a dessicator, then analysed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Measurements of compressive strength were made after 1, 7 and 28 days of post-curing at 21OC and 67% R.H. on paste specimens (25 mm cubes). Calcium sulfoaluminate-based compositions were prepared by blending the previously sieved ( d 5 0 pm) raw materials, then firing in an electric kiln for 8 h at

582

1220OC. After firing, the sintered products were crushed, ball-milled and sieved to pass a 53 pm screen. These compositions were paste hydrated (w/s = 0.4) and cured at room temperature and 100% R.H. from 1 to 90 days. Small samples and cubed specimens, as described before, were submitted to DTA/XRD and compressive strength tests, respectively. XRD was also used for studying the mineralogical composition of fired products. 3. RESULTS AND DISCUSSION 3.1. Blended compositions

In these systems, at any pre-curing temperature, the main hydration product is ettringite. No calcium monosulfate forms. Typical thermograms are shown in Fig. 1, relative to specimens of composition BL-1 pre-cured 16 hours at 55,70 and 85OC. The presence of neoformed ettringite as well as unconverted gypsum and hydrated lime is revealed by the endotherms at about 120, 160 and 47OoC, respectively. Furthermore, at 70 and 85OC, the formation of calcium silicate hydrate is evidentiated by a shoulder on the rising slope of the ettringite peak.

Figure 1. Thermograms of specimens of composition BL-1 pre-cured 16 hours at 55, 70 and 85OC.

583

The compressive strengths for all the blended compositions pre-cured 24 hours at 55, 70 and 85OC are shown in Figures 2 and 3, which are referred to 1 and 28 day

m

Q

z

i

E" g

i

.-

3

I

I--

20.0

0.0 50

I

I

I

1

60

70

80

90

1 0

Temperature, "C

Figure 2. Compressive strengths, at 1 day post-curing, of blended compositions precured 24 hours at 55,70 and 85OC. 28 days

2

EL- 5

-

40.0

EL- 2

z

i

p

BL- 6 EL- 4 EL- 3

30.0-

f? c

u)

2!

'B In

20.0-

8

10.0-

ii

0.0 50

EL- 1

60

70

80

90

1 0

Temperature, "C

Figure 3. Compressive strengths, at 28 day post-curing, of blended compositions precured 24 hours at 55,70 and 85OC.

5 84

The results show that a great increase of compressive strength is obtained when precuring temperature is raised from 55 to 70°C. The effect of further increasing the precuring temperature to 85°C is much less favourable. Comparing Figures 2 and 3 shows that, at 55"C, the increase of post-curing time from 1 to 28 days has a positive effect on the development of compressive strength. On the other hand, at 70 and 85"C, the systems develop within 1 day most of their attainable strength. As far as the effect of composition is concerned, the most relevant observation is that mechanical strength increases with portland cement content. Additional data, not reported here, have shown that replacing phosphogypsum with natural gypsum has no relevant effect on the mechanical properties of the blended compositions. 3.2. Calcium sulfoaluminate-based compositions

The mineralogical compositions of the fired materials fired varied only slightly for the three systems listed in Table 3. Fig. 4 shows a typical XRD trace for system CL.

30

40

"28.C O k a

Figure 4. XRD diagram for the composition CL fired at 1220°C.

585

Although the composition of the systems was designed to contain C4A3SI C2S and C S, all the fired materials consisted mainly of C4A3S, C5S2S (2C2S.CS ) and C S. C2S did not form in the firing conditions tested as a major phase. Traces were only present in the system CL. Furthermore, traces of C3A were also present in all

the three systems. When hydrated, the three calcium sulfoaluminate-based compositions generate ettringite and hydrated alumina gel, according to the following reaction:

Fig.5 shows the thermogram of the specimen of composition FA hydrated for 28 days. Thermal dehydration of the two products, ettringite and hydrated alumina gel, is evidentiated by the two endotherms at about 120 and 250°C, respectively.

I

I

I

I

I

200

400

600

800

1000

T e m p e r a t u r e , 'C

Figure 5.Thermogram of the specimen of the composition FA hydrated for 28 days.

5 86

The compressive strengths of the hydrated specimens of the three compositions tested are shown in Fig.6. It can be seen that all the compositions, particularly FA and CL, develop very good early (Id) strength. Increasing the curing time up to 90 days makes the strength increase further to values ranging between 60 and 90 MPa.

h I

80.0

0

I

I

I

I

25

50

75

100

Time, days

Figure 6. Compressive strengths of hydrated specimens of the compositions FA, BS and CL.

4. CONCLUSIONS

This study has shown that systems containing up to about 90% waste materials are of interest in the field of building materials manufacture. Blended compositions containing wastes such as phosphogypsum, blast furnace slag and fly ash, are suitable for the manufacture of preformed building elements. For all the blended compositions and under the most favourable curing conditions, it is possible to achieve compressive strengths higher than 20 MPa with a maximum of 44 m a . Phosphogypsum, blast furnace slag and fly ash can also be employed in raw mixes for the synthesis of calcium sulfoaluminate-based cements at about 1200°C. Compressive strengths ranging between 35 and 50 MPa at 1day, 58 and 76 MPa at 28 days, 61 and 90 MPa at 90 days, have been obtained. These values are higher than those achievable by ordinary portland cements.

587

Part of this investigation was carried out with natural gypsum instead of phosphogypsum and no relevant differences were found. The extension to other chemical gypsums, in particular desulphogypsum which is usually generated together with fly ash within coal-fired power plants, seems worthy of consideration and is being carried out. 5. REFERENCES 1 2 3

4 5 6 7 8 9 10 11 12 13 14 15 16 17

T.Azuma, Kkhimaru, T.Murakami and K.Tateno, Calcium aluminate monosulfate hydrate, Ger. Offen. No. 2 551 310 (1976). T.Azuma and Kkhimaru, Calcium aluminate sulfate-based inorganic hardened product, Japan Kokai No. 76 62 826 (1976). P.K.Mehta, World Cement Technol., May (1980) 166. K.Ikeda, Proc. 7th. Int. Congr. ChemCement, Paris (1980) 31, Vol. 2, Theme 111. GSudoh, T.Ohta and H.Harada, Proc. 7th. Int. Congr. Chem.Cement, Paris (1980) 152, Vol. 3, Theme V. Deng Tun-An, Ge Men Win, Su Mu-Zen & Li Xiu-Ying, Proc. 7th Int. Congr. Chem. Cement, Paris (1980) 381, Vol. 3, Theme V. L.Santoro, G.L.Valenti and G.Volpicelli, Thermochimica Acta, 74 (1984) 35. G.L.Valenti, LSantoro and G.Volpicelli, Thermochimica Acta, 78 (1984) 101. L.Santoro, R.Garofano and G.L.Valenti, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 389, Vol. IV. L.Santoro, 1.Aletta and G.L.Valenti, Thermochimica Acta, 98 (1986) 71. L.Santoro, R.Garofano and G.L.Valenti, Thermochimica Acta, 116 (1987) 145. J.Beretka, L.Santoro and G.L.Valenti, Proc. 4th Int. Conf. on Durability of Building Materials and Components, Singapore, (1987) 64, Vol. I. G.L.Valenti, R.Cioffi, L.Santoro and S.Ranchetti, Cement and Concrete Research, 18 (1988) 91. G.L. Valenti, L.Santoro and J. Beretka, Proc. 2nd Int. Symp. on Phosphogypsum, Miami, 2 (1988) 167. J.Beretka, R.Cioffi, LSantoro and G.L.Valenti, Proc. 3rd Int. Symp. on Phosphogypsum, Orlando, (1990) 417. J.Beretka, R.Cioffi, LSantoro and G.L.Valenti, Proc. 3rd NCB Int. Seminar on Cement and Building Materials, New Delhi, 3 (1991) 110. RCioffi, M. Marroccoli, L.Santoro and G.L.Valenti, J. Therm. Analysis, 38 (1992) 761.

W.Kurdowski, C.M.George and F.P.Sorrentino, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 292, Vol. I. 19 G.A.Mudbhatka1, P.S.Parmeswaran, A.S.Heble, B.V.B.Pat and A.K.Chatterjee, Proc. 8th Int. Congr. Chem. Cement, Rio de Janeiro, (1986) 364, Vol. 4. 20 G.L.Valenti, L.Santoro and R.Garofano, Thermochimica Acta, 113 (1987) 269. 18

588

21 22 23 24

A.K.Chatterjee, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992) 177, VOl. 1. Su Muzhen, W.Kurdowski, and F.P.Sorrentino, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992)317, Vol. 1. J. Beretka, L. Santoro, N. Sherman and G.L.Valenti, Proc. 9th Int. Congr. Chem. Cement, New Delhi, (1992) 195, Vol. 3. J. Beretka, B. de Vito, L. Santoro, N. Sherman and G.L.Valenti, Cement and Concrete Research, 23 (1993) 1205.

Environmental Aspects of Constnrcfion wifh Waste Materials JJJ.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) G.1994 Elsevier Science B.V. AN rights reserved.

589

Potentials for utilisation of PFBC ash J. Rogbeck and P. Elander Swedish Geotechnical Institute, S-581 93 Linkoping, Sweden Abstract Pressurised Fluidised Bed Combustion (PFBC) is a coal combustion technique commercialised during the last ten years. Development of PFBC has been carried out for more than 20 years and has resulted in a combustion technique with low emissions to the atmosphere, producing ashes with favourable properties concerning utilisation. Two types of ash are produced, fly ash and spent bed material. For utilisation, a mix of the two ashes and water has been found to be of the greatest interest. In this paper, laboratory investigations and field tests carried out to clarify significant properties of PFBC ash mixtures in different utilisation objects are presented. It is concluded that the ash has excellent potentials for utilisation regarding mechanical properties as well as environmental effects. The paper is based on research kindly supported by ABB Carbon AB, EFO Coal & Oil AB, Sweden and Stockholm Energy AB.

1. THE PFBC TECHNIQUE Pressurised Fluidised Bed Combustion (PFBC) is a coal combustion technique which has been commercially developed by ABB Carbon AB. The development of PFBC has been carried out for more than 20 years and has resulted in a combustion technique with low emissions to the atmosphere and solid residues with favourable properties concerning utilisation. The PFBC technology uses a combined cycle, involving generation of electricity by a gas turbine and a steam turbine. This ensures high efficiency, giving something like 15 % lower fuel consumption than with conventional technologies. Combustion takes place in the fluidised bed at elevated pressure, 5-12 bar depending on load. The combustion temperature is about 820O to 880° C. This means that the nitrogen oxide emissions can be kept down, since thermal NO, is only formed at higher temperatu-res. Prior to combustion, the coal is crushed to a maximum size of about 5 mm and is then mixed with a sorbent (limestone or dolomite). During combustion, the sorbent will capture released sulphur to form calcium sulphate. Residues from a PFBC plant are created in three streams; as granular bed material, as fly ash captured by the cyclones and as filter catch from the final back end filter. The ratio between spent bed material and fly ash varies, but is normally between 50/50 and 30/70, with fly ash dominating. The amounts of ash from the back end filter are very small, less than 1 to 2 %, and are normally added to the fly ash from the cyclones. Regarding the grain size distribution, the fly ash can be characterised as sandy silt and the bed material as coarse sand.

590

2. MECHANICAL PROPERTIES The results from laboratory investigations and field tests presented in this paper are mainly based on a comprehensive study carried out in 1988 on ashes from the pilot plant at ABB Carbon in Finsping (I). The results have then been complemented with recent tests on ashes from the commercial Vartan PFBC plant in Stockholm. The bed material in the tests is mainly based on limestone as sorbent, althoug dolomite ashes have also been investigated. At an early stage in the investigations it was found that, even if spent bed material and fly ash can be used separately, a mix of them is of the greatest interest. If these ashes are mixed with water and vibro compacted, a concrete-like material with high bearing capacity and compressive strength is obtained. The results presented below refer accordingly to mixes of the ashes. Although the mixing ratio between bed material and fly ash has been varied in the investigations, the most common ratio has been 50/50 or 30/70 with fly ash dominating. In the tests, bed material and fly ash have almost always been mixed in a dry state before adding water. The amount of water varies, depending on whether the intention is to obtain a wetted mixture or a slurry. The samples are then vibro compacted. Curing normally takes place under high humidity (RH about 90 %) at a temperature near +20° C. Some test series have been cured under other conditions, such as under water or at a high (+50° C) or low ( - 1 8 O C) temperature. Curing times up to one year have been investigated. An important factor when estimating the potential for utilisation of fine grained combustion residues is their strength properties. For ashes, the strength is usually determined (at least in Sweden) as the unconfined compressive strength. This is normally assessed from samples with varying curing times so that a time strength relation can be achieved. The growth of compressive strength concerning PFBC ash mixes is relatively fast and values of over 5 MPa are achieved within a few days. The final strength is normally between 20 and 45 MPa, even if values over 50 MPa have been measured. Figure 1 presents examples of the development of strength of ash mixtures. In this case, has the ratio been 30 weight-% bed material and 70 weight-% fly ash (Polish coal, limestone as sorbent). Other results have shown that when dolomite is used as sorbent, the compression strength may decrease (2). Maximum measured values so far for dolomite based bed material vary between 15 and 25 MPa. However, the test series in this case are too small to be statistically significant.

Strength properties 100

Compression strength (MPa)

10

1

"I'

1

10

100

1000

Curing time (Days)

Figure 1. Examples of the development of strength of PFBC ash mixtures (70 %fly ash and 30 % bed material). Polish coal, limestone as sorbent.

591

To clarify the long term durability of the compression strength, one test series based on limestone as sorbent was cured for 28 days and then placed in pressurised cell permeameters. Water under high pressure (170 Wa) was forced through the samples for up to 8 months. The unconfined compression strength was then determined. The results indicated no decrease in strength compared with samples cured in the normal way. However, it should be observed that the high strength properties are very dependent on curing the mixture can be cured above freezing temperature until the hardening process is completed or at least has progressed for a certain time. In some laboratory and even full scale tests, the ash mixture has been exposed to temperatures below 0 C from the beginning or only after a few days of curing, which has resulted in almost no increase in strength. Results from freeze-thaw tests also show that the ash mixtures are sensitive if the curing time is too short before freezing. As a result of the concrete-like material obtained, the permeability of the ash mixtures is very low. Test results show that the permeability after 28 days curing is less than 1 0 1 0 d s . Se Figure 2.

Permeability 1OE-09

Permeability (m/s)

1OE-10

1OE-1 1 .___

I OE-12

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100

Time (days) -50/50 bed ashhyclone ash *30/70 bed ash/cyclone ash --Swedish clay

Figure 2.

Permeability ofPFBC ash mixtures (Polish coal, limestone as sorbent, curing time 28 days).

In addition to the above mentioned parameters, a large number of laboratory tests have been carried out, for example to clarify the properties of synthetic aggregates produced from PFBC residues. These tests included compacting characteristics, degradation of aggregates, Swedish flakiness index and Swedish impact value. In general, the results have shown that after curing and crushing, PFBC ash mixtures are well suited for use as synthetic aggregates in fills and road building. 3. LEACHING CHARACTERISTICS

Like coal ash, PFBC ash mostly consists of a mixture of amorphous glass and crystalline phases and some unburnt material. The main components of the ash are compounds of silicon (Si), calcium (Ca), aluminium (Al) and iron (Fe). The desulphurisation process in a PFBC results in capture of sulphur as (CaSO,), while calcium surplus is obtained as calcium carbonate (CaCO,). The chemical composition of the ashes may vary to a certain extent, depending on the type of coal burned and the type of sorbent used (limestone or dolomite). If dolomite is used as

592

sorbent, the ash will also contain a certain amount of magnesium. In the 1988 study, a 50/50 mix of fly ash and bed material was analysed. The content of different trace elements in the mixture was generally less than 200 mgkg and for most of the elements less than 30 mgkg. In general, the environmental consequences of utilisation of residues are associated mainly with the release of contaminants, in particular trace elements, with percolating water. The possible release of contaminants from PFBC ashes were evaluated by means of leaching tests according to the Swedish ENA-method. This test is a serial batch test with four of leachings at the L/Sratio 4 (accumulated L/S-ratio 16) and with 24 h agitation by horizontal oscillation. Leaching at the L/S-ratio 1 is also determined. To achieve this build-up in L/S ratio concentration is used in the same procedure as above, but the material is renewed instead of the leachant. The particle size of materials used in ENA-tests should be <20 mm and the sample mass should be 125 g. Demineralized water adjusted to pH 4 by means of sulphuric acid is used as leachant. Centrifugation and 0.45 m filtration are used for leachate separation. The leachates in question were analysed for a considerable numbers of elements by means of ICP-ES. AAS were used for analysis of some leachates in order to achieve lower detection limits (for lead, mercury and cadmium). Leaching tests on PFBC ash were performed with 70/30 mixtures of fly ash and bed material (samples No 1-3) and 50/50. For the 70/30 mixture, tests were performed both with untreated samples and with samples that were cured and thereafter crushed to a gravel-like material (synthetcic agglomerates). For the other mixtures, tests were performed only on synthetic agglomerates. The ash showed a high buffering capacity and the pH was high in all the leachings, between 10 and 13, with the lower value in the leachates with higher L/S-ratios. In Figure 3, the accumulated leaching of Cr, Mo and Pb is given as a function of the L/S-ratio as determined in the successive leachings L/S 4 to L/S 16, and compared to results from identical leaching tests with ordinary pulverised fly ash, references (3) and (4), and a normal Swedish moraine (4). It should be mentioned that the L/S 12 leachate was not analysed in the tests, but the leaching in this step was estimated as the mean of the L/S 8 and the L/S 16 leachings. From the results, it appears that leaching from the synthetic agglomerates was in the same range as leaching from the untreated sample (No. 1). Neither were any significant divergences observed between samples with different mixing ratios. Possibly, the leaching from sample No. 3, which originated from combustion with ammonia in order to reduce the emissions of nitrogen oxides, was somewhat higher than from other samples. However, it is difficult to draw any firm conclusions as many elements in the leachates were below the detection limits. It was concluded that the leaching of chromium and molybdenum was higher than leaching of other trace elements from PFBC ash. From Figure 3, it can be seen that leaching of chromium was higher than from a normal moraine, but leaching of Cr as well as of Mo was lower than from the pulverised fly ash. Leaching of lead was in the same range as from PFA, but considerably lower than from the moraine. The reason for the high leaching of Pb from the moraine is not clear, but has been noticed for several samples from different places in southern Sweden (4). Leaching of other elements from the PFBC ash was low or very low. In Sweden, leachate levels from the L/S 1 leaching test have often been used for calculating leaching from various end-products in landfills and thereby estimation of the environmental consequences of disposal and utilisation. In Figure 4, maximum levels of some elements in leachate from PFBC are compared to results from identical tests with other materials. Data for pulverised coal fly ash (PFA) and coal bottom ash (BA) are taken from references (3), (4) and (5), and data for moraine from (4). Also normal background levels in unaffected fresh water, as suggested by the Swedish National Environmental Protection Agency (6) to be used in environmental impact assessments, and drinking water criteria in Sweden are shown in the figure. The elements shown are considered to be the most critical for PFBC ash from an environmental

593

Cr ---

PFBC 1

--O-

PFBC 2

--*-

PFBC 3 PFBC 4

--

PFBC 5 PFA

1

10

100

-O-

LIS

Moraine

Mo

--

PFBC 1

/

PFBC 2

+

--c

PFBC 3

--

PFBC 4 PFBC 5

1

10

100

-*-

PFA

L/S

Pb

-

11

PFBC 1 PFBC 2

--

---

PFBC 3 PFA Moraine

1

10

100

LIS

Figure 3. Accumulated leaching of chromium, molybdenum and lead as afirnction of the USratio for the PFBC ashes, a fly ash fiom pulverised coal combustion (PFA) and a normal Swedish moraine.

594

point of view, taking into account the leachate levels compared to background levels. For the elements shown, the leachate levels from the investigated PFBC ashes are in the same range as that measured in leachates from pulverised fly ashes. For other elements, the leachate levels have been generally low and in many cases not detected at the detection limits used (established for most elements by the ICP-ES technique). AS

i

.

PFBC

PFA

BA

Moraine

Cd

-I

PFBC

PFA

BA

Moraine

BA

Moraine

Cr

Moraine

- -

_-

Pb

-2

1000

I

0,l

- BACKGROUND LEVEL

-DRINKING WATER CRITERIA

-I

PFBC

PFA

Figure 4. Leachate levelsJEomPFBC ashes, other coal ashes and moraine, compared to background levels and drinking water criteria..

595

4. POTENTIALS FOR UTILISATION

The residues from PFBC, in particular hardened mixtures of spent bed material and fly ash, have proved to be one of the important competitive edges of this valuable technology. Mechanical properties such as high strength, high bearing capacity and low permeability combined with a low environmental assessment, make PFBC residues well suited for a range of utilisation purposes. Some examples of commercial exploitation are; till material road construction material stabilising agent 4.1. Fill material

Due to their mechanical properties, residues from PFBC are well suited for a range of fills. By adding water to a mixture of spent bed material and fly ash and then vibro compacting the material, a monolithic fill with high strength can be obtained. Half-scale tests have demonstrated that this is possible even directly into water, as would be necessary for extending a harbour area for example. In the test, a mixture of spent bed material and fly ash was mixed in a dry state and poured into a basin filled with fresh water. The mixture was then vibro compacted under water. After one week of curing, standard penetration test (SPT) was performed on the fill. The results showed a coefficient of elasticity modulus of more than 300 MPa. Investigations are in progress both in Sweden (the Viirtan plant in Stockholm) and in Japan (the Wakamatsu plant) to clarify the possibilities for using PFBC ashes for land reclamation. Another way of using PFBC ash mixtures as fill material is to first produce synthetic aggregates from the material. This can be done by casting large slabs which are cured a certain time, after which the slabs are crushed in a conventional rock crushing plant. It is also possible to produce synthetic aggregates by manufacturing paving stones. This has already been performed on an industrial scale test. The brick-sized pieces obtained can be used either directly as fill material, or as synthetic gravel after crushing. One of the advantages is that production can take place during the firing season (normally the winter months), after which the bricks can easily be stored (cured) until the summer season when demand is greatest.

Casting of PFBC ash.

Brick production.

596

4.2. Road construction material In the same way as mentioned above, synthetic aggregates produced from PFBC ash mixtures can be used as road construction material. Various full scale tests have already been performed. In one case, a mixture of spent bed material and fly ash was cast into a homogeneous slab which, after curing, was crushed to a coarse gravel. This was then used for an embankment and sub-base for an industrial road. The road was built in 1989 and the results so far are very good.

Test road in Linkoping, Sweden, uses synthetic gravel madefrom PFBC ashes.

In a similar full-scale test, synthetic aggregates were used as road-base material on an industrial site at ABB in Finsphg. Above the road-base, a mixture of fly ash and conventional crushed bedrock was used as a sealing layer. The sealing layer was allowed to cure for about six weeks. All of the goods transports in the area were then made to cross the test area. Also in this case, the results proved very good even after a couple of years and no damage could be found on the surface. 4.3. Stabilising agent Due to their self-binding properties, PFBC residues, especially fly ash, are well suited as a stabilising agent. A project financed by the Swedish National Road Administration (7) showed that fly ash from PFBC can be of interest as a stabilising agent in the construction of embankments on soft andor fine grained soils, e.g. clay or silt. In the project, different stabilising agents were mixed with natural silt. The results showed that when adding 10 weight-% of pure PFBC fly ash to silt, the shear strength increased from 30 kPa to about 140 Ha. An additive of 15 weight-% fly ash resulted in a more than ten times higher shear strength (450 H a ) than for the natural silt. Consequently, the results indicated that using PFBC fly ash as a stabilising agent in embankments either increases the quality of the road or allows the thickness of the sub-base andor roadbase layers to be reduced. Similar tests have been performed to demonstrate the use of PFBC fly ash as a stabilising agent in mining with back filling. Due to the demands for a fast hardening time, the fly ash in this investigations was mixed with small amounts of cement. The results showed that PFBC fly ash increased the shear strength, Figure 5. This means that the conventional addition of cement can be reduced, resulting in lower costs for the back filling. Another interesting result from the laboratory investigations was that an additive of PFBC fly ash give a more plastic shear failure than conventional cement admixtures. This allows the fill to accommodate rock movements better before the mixture fails.

597

-

2Ora cyklon 3% lOra cyklon 3% 2Ora cyklon 6% eee%E 1Ora cyklon 6% _ _Reference _ _ . (1 0s m-s++.a

6000Y

v

cement cement cement cement cement)

5 cn 5000 c

?!

% 4000 C

.-0

$ 3000 -

! ! a

gu 2000lJ .-g 1000L

C

8

0

I

,

15

I

I

I

30

I

I

I

45

I

I

I

60

Figure 5. Increase in shear strength as a function of time for mining backfill using PFBC jly ash as stabilising agent. A similar use of PFBC fly ash as stabilising agent is in lime columns. Fly ash can then be used as an additive to lime or cement, which will reduce the costs. However, before this is done on a commercial basis, complementary laboratory tests, especially concerning long-term durability, are required. Since PFBC residues can be used to produce a material which has a compressive strength comparable to that of concrete, it should be possible to use them as an additive in the manufacture of cement and concrete. One limiting factor when using ordinary coal fly ashes in the manufacture of concrete is the amount of unbumt carbon. Comprehensive measurements of fly ashes generated in Stockholm VWan indicate that during normal operation the unbumt carbon content is less than 3 %, which is well below the requirement for Sweden. The possibility of using PFBC residues in this way, although variable according to the feedstocks, would seem to be very high.

4.4 Environmental aspects If the ash is to be used in aggregates such as gravel, results from the leaching tests mentioned above may be used for environmental impact assessments. From the leaching tests, it can be concluded that the leaching of trace elements from PFBC ash is generally low. However, the results in relation to background levels indicate that leaching of chrome possibly could be problematical and should be observed. This can be illustrated by an environmental impact assessment performed for a planned utilisation object in Sweden, a fill for a reclamation harbour in Stockholm (8). The projected fill is small, about 10 000 m3. For conservative reasons, the leaching was calculated assuming a relatively high permeability, such as for silt, even if the hardening could lead to a much lower permeability. Calculations of the leaching from the fill, based on the leachate levels from the L/S 1 tests, showed that the leaching of chrome should be in the same range as the wet deposition on the surface of the close recipient (7 square kilometres), and that 520% of the discharge with urban run-off in the neighbourhood led directly to the recipient.

598 For the same fill, also a more probable scenario was calculated, on the assumption of a hardened fill of low permeability. For estimation of the leaching, tank tests were performed with ash from the VSirtan PFBC plant in order to determine leaching by diffusion from a monofill. An environmental assessment based on these assumptions showed a considerably lower leaching of chrome, about 5 % of the wet deposition on the close recipient and less than 1 % of the urban run-off in the area. The lower calculated leaching of chrome was probably related mainly to different leaching properties of the tested ash sample, compared to the ash samples investigated in the 1988 study, and not only to the different test procedures. A simple batch test on the same sample, performed with L/S ratio 2, resulted consequently in a chrome level considerably lower than that from L/S 1 tests as well as from L/S 4 tests in the 1988 study. The relatively high leaching of chrome calculated for the first case is a consequence of the high permeability of an unhardened fill in combination with changing water levels, causing frequent pore water exchanges in the fill. This effect would be even more pronounced if the fill were constructed with synthetic agglomerates, because of the higher permeability of such a fill. Leaching of a permeable fill constructed on land would be considerably lower, since the amount of water flowing through the fill decreases, and the release of chrome would consequently be less important in relation to other sources. Recent leaching tests indicate also that leaching of chrome may not be of the same importance for all ashes, but can vary. Varying leaching properties may, for instance, depend on the type of coal burned and the combustion conditions. Finally, it should be emphasised that leachate levels measured in laboratory leaching tests should be used with caution when predicting leachate levels and environmental impact from real fills. For instance, Figure 4 shows that also leaching tests on conventional filling materials, such as normal moraine, result in leachate levels in the same range or higher than the tested PFBC ashes, disregarding chrome. Taking this into account, the summarised test results indicate that PFBC ash in most utilisation objects causes only a limited impact on the environment. 6. REFERENCES

1 Rogbeck, J. (1988). Utilisation of residues from PFBC. Swedish Geotechnical Institute Dnr. 1-227/88. In Swedish. 2 Rogbeck, J. (1991). Investigation of strength of PFBC ash from VSirtaverken. Swedish Geotechnical Systems AB, No 9107. In Swedish. 3 Hartlkn, J. Elander, P. Kullberg, S. Lundgren, T. & RosCn, B. (1986). Residues from semi-dry flue gas desulphurisation. REFORSK FoU nr 10. In Swedish. 4 Nilsson, C. (1987). Residues from fludised bed combustion - properties in disposal and utilisation. Stiftelsen for v h e t e k n i s k forskning, No 276. 5 The Swedish Coal Health Environment Project (1983). The Swedish State Power Board. 6 Swedish National Environmental Protection Agency (1990). Basis for forming estimates for lakes and watercourses. SNV AllmSinna Rid 90:4. In Swedish. 7 Elander, P. (1991). Soil stabilisation for road construction. Laboratory study on the effects of some stabilising agents. Swedish Geotechnical Institute, Dnr 1 -366/89. In Swedish. 8 Elander, P & Rogbeck J. (1992). Filling with ash in Stockholm harbour. Swedish Geotechnical Systems AB, No 9107. In Swedish.

Environmental Aspects of Construction with Wuste Materials JJJ.M. Goumans, H A . van der Slmt and Th.G. Aalben (Editors) el994 Elsevier Science B.V. AN rights resewed.

599

Recycling of Magnesium Slags in Construction Block Form M. Courtial a ,R. Cabrillac b and R. Duval b a Laboratoire d'Artois MBcanique et Habitat, Universitk dArtois, Rue de l'UniversitB,62408 BBthune, France

b Laboratoire dEnergBtique, MBcanique et Sciences des Constructions, Universitk

de Cergy, 1,AllBe des Chgnes Pourpres, 95014 Cergy-Pontoise, France

Abstract Magnesium slags are silico-aluminates compounds of lime, that are waste products of the "Magnetherm" magnesium french industrial process. After considering the stability of the slags, experimental procedures for the improvement of physical and mechanical characteristics of hydrated slags are proposed, and further industrial trials carried out. The aim of this paper is to show the feasibility of the recycling of the whole slags production in the form of construction blocks. This requires a good stability of the by-products, the processing of the hydrated slags, suitable strength and a good durability of the end product. It is shown, that despite the presence of unfavorable mineralogical composition, the recycling of magnesium slag wastes is feasible.

1. INTRODUCTION

During the "Magnetherm" industrial process, the production of a single ton of magnesium is accompanied by six tons of waste by-product. After vaporisation of the magnesium from the furnace, the remaining molten by-product material is poured into a crucible [ll and quenched in water, and a granulated slag (W3 of the production) is obtained. The material remaining attached to the crucible is removed by air-cooling and produces an additional powdered slag. Because of their difference of granulometry ranges, the granulated (0.5-5mm) is considered as a sand and the powdered (20-80pn) as a cement. As they originate from the same molting bath, both materials have the same chemical composition, but despite their metallurgical origin, they differ clearly from the usual blastfurnace slags and are closer from cement chemical composition.

600

However, mineralogic composition of the slags is slightly different from that of cements, their mechanical properties are poor. This is due to a n unfavourable mineral composition explained by the absence of C3S and the presence of: - unreacted y CzS, rare ClzA7 aluminate and crystallized MgO in the powdered slag - CzS p, C f l S and MgO in the granulated slag. In this work, we describe how the compressive strengths of the by-products can be improved by adjunction of additional products. The fluctuation of the wastes is first described. Then the feasability of the industrial block process is discuss. In order to do so, unhydrated compounds were first studied, then industrial trials were performed and the possibility of industrial processing of these wastes in the form of construction blocks discussed. 2 RESULTS AND DISCUSSION 2.1 Stability of the unhydrated slags

The stability of a by-product is the first problem to overcome it. Materials without reproductible properties cannot lead to reproductible mechanical strength. A statistical study of the chemical composition of the slags yield (measured by X-ray fluorescence) obtained after nine months of production is first carried out (Table l),small standard deviations values were found. Table 1 : Compound Average Standard

Average and atandard deviation of the chemical compounds of the magnesium slags Lime CaO 57.7 % 0.87%

Silica Si02 25.85% 0.72

Alumina A1203 Magnesia MgO 11.6% 4.8% 0.66 0.76

In fact, in the "Magnetherm" process, the characteristics of the magnesium is controlled indirectely by the chemical composition of the slag. So from this point of view the stability of the slags from an industrial production to a n other is carried out. The hydraulic properties of the slags comes from their mineralogical composition and from the glass content. The absence of mineral variations between two slag productions (measured by quantitative XRD) but rather a difference in crystallinity correlated to the powdering of each cooling stage is pointed out. C1zA7 is crystallized in the middleprocess and in a parallel fashion, reactive flCzS is produced [21(this phase exists at normal temperature when stabilized by impurities). The crystallinity of the unhydrated powdered salg is directely correlated to the compressive strength of

60 1

the hydrated product. This last property is enhanced with time. This requires to homogenize the whole powdered slag at the end of each powdering in order to obtain a good reproducibility of its hydraulic properties. In the case of the granulated phase, the glass content depends on quenching kinetics [2]. When quenching factors are stable (water flow rate, pouring speed, dimensions of reception pipe and pit), the granulated phase is stable from a mineralogical point of view as for its granulometry.

No other variation at the collection of unhydrated slags.(every week) was observed. But care is needed for storing as for other hydraulic materials. The granulated slag contains water (10 to 17%),thiswater further reacts with it, to the extent the slags are fully hydrated within a fourteen and forms a block. So, it must be employed short after reception. The powdered slag reacts as a cement. It loose of its hydraulic power after a few months at the condition to be stored in nonhumide conditions. In order to avoid these drawbacks, the powdered slag was blended at the end of each production (by Pechiney Company) and sent to the laboratory in close containers. Both slags were used within a week after reception.

2.2 Experiments on the hydrated slags 2.2.1 Experiments performed in the laboratory In order to obtain samples corresponding t o the french block fabrication standards, experiments were first carried out in the lab. By studying the setting time with the Vicat method, the very short setting time value of 7 minutes (not compatible with the industrial fabrication of construction blocks) was increased to an half an hour. In order to improve the strength shown at the beginning of the study, slags various compositions of powdered and granulated slags were tested 131. In the present paper, the mixture related to the magnesium industrial process are described (2/3G-l/3P,i.e. W3 of granulated slag and 1/3 of powdered slag). The mortars were mixed for three minutes, poured into 4x4~16cm3 test pieces, vibrated and stored at 20°C in air until the compressive strength test were carried out. XHA and silica fumes and CPA 55 were included to the mortar composition. Finally a solution to the periclase (crystallized MgO) swelling during the later hydration is prosed. The absence of swelling of periclase is important for the durability of hydrated end product.

Setting time of the 2/3G-l/3Pmortar 2/3 G-1/3 P mortar behave in the same way as alumina cements. Due to their relative high lime aluminates content and especially C12A7 C41, they posses flash setting time (7 minutes). As industrial processes requires at least 30 minutes, low concentrations of retarders were added in the giichage water. Retardations effects are obtained by the addition of 1%of sugars [5]. Setting times of 37 minutes are obtained by saccharose and 60 minutes with glucose. An addition of 1% of a of a product called Chrytard (Chryso Company) containing glucose and calcium

602

lignosulphonate retards the set up process up to 53 minutes. Similar setting times were found when retarders were added to XHA and silica h e s pastes. As in the case of the other hydraulic compounds, the effects of the retarders depend both on the amount added and on the stage of the addition 161. As opposed to what was said before [l], gypsum does not retard the set, as can be explained by the very composition of the slags -relatively high calcium aluminate content with respect to the calcium silicate content, which reacts slowly. Improvement of slags compressive strength The values of compressive strength of 2/3G-l/3P mixtures are presented here. After a 7 day period (the delay after which the construction blocks are sold), a minimum value of compressive strength of 8 MPa is required by the French standards for the test samples prepared in the Lab. The 28 day test period is used in the cement community, as it corresponds to the time when the increase of compressive strength is slowed down. But compressive strength measurements were made after longer period of time on the magnesium slags because of their slow reactive calcium silicates constituents. The hydrated powdered alone, follows the same increase of compressive strength as classical cements (it is twice as weak as CPJ 451, while the granulated shows low resistance values. This shows that the C2S phase is hydraulic (as opposed to what is said by most other workers), as the presence of C2S cannot explain the high strength values obtained. The first results were obtained from 18.33 % waterlsolid ratio, the 28 day-old samples had a compressive strength value of 6 MPa while a value of 12.4 MPa was obtained after 6 months. As the values obtained were not up to required standards, we have undertaken to improve them by the addition of CPA, XHA and silica fumes (S) (Fig.1). The only adjunction that permitted to reach the required values of 8 MPa after 7 days is XHA. Other adjunctions do not provide such short term improvement. CPA has no effect. Silica fumes multiply by a factor of two, the 28 days strength values. These are constituted by grains a hundred times finer than the powdered grains, which decreases the paste porosity. Furthermore, silica fumes react with C2S in order to produce CSH. On the other hand, the hydration of C2S gives less portlandite than the hydration of C3S. These simultaneous effects lead to a low porosity paste with relatively high compressive strengths. Because of cost, the percentage of silica fumes used was kept to 2.5%, and 10%XHA was added to it. This proportion of adjunctions yielded similar results as the adjunction of 5% of silica fumes, a t least up to a three month period. The simultaneous effect of retarders and adjunctions on the compressive strengths was then carried out. Chrytard and glucose were added to the 5% XHA and to the 5% silica fumes mortars mixtures. Compressive strengths superior to 8 MPa at 7 days, and to 13 MPa at 28 days were measured. As for usual cements lignosulphonates adjunctions increase short term compressive strengths [6].

603

Compressive strength in MPa

5%CPA

3 months 6 months Time Figure 1: Compressive strength versus time of the mix 2/3 granulated slag-1M powdered slag with additions of silica fiunes (S),XHA and CPA 55. 0

Durability considerations About, 5% magnesium dioxide remains in the slags after the magnesium fabrication process. When crystallized, as it is in the powdered slag, it reacts with water after a few months, is transformed in Mg(0H)z and swells. This swelling induces dramatic cracking of the material. As a n example, one laboratory sample out of three had broken up after five months. This problem was overcome by separating the periclase clusters, in order to reduce the stress within the material. To do so, the powdered was sieved and the unhydrated material was mixed, and the operations optimized. No failure of the hydrated powdered slag samples was observed for a 0.350 mm sieR and three minutes mixing times of the unhydrated slag. In fact, the swelling behaviour can be simulated by autoclaving tests, but in the conditions of these tests, the hydrated powdered samples are transformed into powder. Nevertheless, not a single failure was observed in a single sample out of the 500 prepared.

2.2.2 Industrial trials French standards state that usual mortar samples possessing compressive strengths ranging between 8 to 12 MPa after 7 days, full construction blocks corresponding to these samples show strengths superior to 8 MPa. As we obtained such values in our Lab., industrial trials were carried out, and no particular problem were encountered during this process.

604

Table 2 : Results of compressive strength on different combinaisons construction replete blocks at 7 and 28 day

Mix

waterlsolid ratio

2/3G-Y3P 2/3G-l/3P4.4% XHA 2/3G-l13P8.8% XHA-2.7%S

17.5 18.2

Strength (MPa) 7 days 4.4 6.8

Strength (MPa) 28 days 4.2 8.2

18.5

10.6

11.95

In the abscence of adjunctions other than retarders, the mortar has already shown 4.4 MPa compressive strength a t 7 days (Table 2). The presence of 4.4% XHA increases this value up to almost 7 MPa. With the further addition of small quantities of silica fumes (and 8.8% XHA), much higher mechanical performances were obtained. Industrial optimization can now be undertaken. 3. CONCLUSION In this paper, the study of the hydraulic wastes of the magnesium industrial process is performed. After examining the production stability, their properties were improved. After reaching the french standards in the Lab., one industrial process was carried out and a possibility for the recycling of the whole magnesium french production proposed.

ACKNOWLEDGEMENTS This work was supported by the "Agence Nationale de Valorisation et d'Aide A la Recherche", the "Agence De 1'Environnement et de la Maitrise de 1'Energie" and Pechiney Electrometallurgie Company. The industrial trials carried out in the SOPREFA Company. 4 REFERENCES [l]M. Courtial, R. Cabrillac and R. Duval, Waste Materials in Construction, Proceedings of the international Conference on Environmental Implications of Construction with Waste Materials, Maastricht, 10-14 November 1991. p.491. [2] M. Courtial, R. Cabrillac and R. Duval, accepted in Materials engineering, RILEM Italian Groupe. [3] M. Courtial, Thesis, Reims oct. 1992 [4] A. Capmas, D. Menetrier-Sorrentino and D. Damidot, Calcium Aluminate Cement, Ed. by R.J. Mangabhai, p.65 [5] C. Laval and F. Durrieu. Rapport de recherche no 16. LCPC. Paris. Dec. 1971 16lH.F.W.Taylor, Cement chemistry. Academic Press. London. 1990

Environmental Aspects of Construction wirh Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) @I994 Elsevier Science B. V. AN rights reserved.

605

Improving the MSWI Bottom Ash Quality by Simple In-Plant Measures J. Schneider, J. Vehlow and H. Vogg Kernforschungszentrum Karlsruhe GmbH, PO. Box 3640, D-76021 Karlsruhe, Federal Republic of Germany

Abstract Bottom ashes from two German MSWI characterizedby different combustion and bottom ash dischargetechnologieswere tested for their leaching stability in the as-discharged state and after simple treatment procedures. The treatment included washing, sintering at 850 and 1 OOO "C, and melting at 1300 "C. Main conclusions drawn from these tests are: washing removes substantial portions of chlorides and other soluble components; thermal treatment reduces the TOC substantially; sintering at temperatures of 1 OOO "C and even below improves the fixation of heavy metals; melting causes further improvement, but the increase in stabilityis low compared to the energyconsumption.On this basis recommendations can be made to improve the bottom ash quality by simple in-plant measures: modifying of the quench tank to establish simplewashing and taking care for adequate sintering of the bed material at the end of the grate.

1.

Introduction

The recently issued German technical gudeline residential waste, the so-called 'TA Siedlungsabfall' [Bundesministerium19931,follows the line not to displace our problems to future generations. Preventionofwasteand utilizationof unavoidable residues rank highest in priority and only inert materials are allowed to be disposedof on a landfill. Especially the limitsof total organic carbon (TOC) - 1% for landfill categoryI, 3 %for category I1 - can be interpreted as a strong demand for thermal treatment of residues prior to their disposal. Utilization is also preferred for bottom ashes from municipal solid waste incineration. The standardsto be met - aside of burnout and soluble matter especially leachingstability - are comparablewith or even more stringent than those for landfilling.Hence quality control and quality assurance of bottom ashes are most important in order to guarantee a low pollutant and environmentallycompatible management of this mass stream - either by adequate utilization or by safe disposal. The degree of technologicalmeasures installed to comply with all regulations has to be considered carefully against the expenditures in order to balance the implemented strate-

606

gies with respect to both, the resulting environmental impact as well as the economical constraints. Intelligent technology tries to solve problems at their sources and passes only stepwise, if there is a need, over to more complex - and expensive - measures. From theoretical considerationstwo simple options to improve the bottom ash quality by in-plant measures can be deduced: 0 adjustmentof high temperatures in the fuel bed in order to achieve an excellent burnout as well as to volatilize and/or immobilize heavy metals by sintering or vitrification, and 0 washing in the quench tank at low liquid-solid ratios (US)to remove soluble salts. In 1992the KernforschungszentrumKarlsruheGmbH and the MiillheizkraftwerkKarlsruhe GmbH launched a research program to test simple annealing and washing of bottom ashes taken from two modern German municipal solidwasteincinerators (MSWI) in a laboratory scale. The properties selected to evaluate the effects of treatment with respect to environmental compatibility were burnout, total soluble matter and leaching stability. The leaching behavior has been tested by means of two regulatory tests, the German DEV S4 [DIN384141andthe SwissTVAprocedure[Bundesamt 19911. Inorder togetmore detailed informationabout the leaching potential as well as the underlyingmechanisms the more elaborated Dutch availability and column leaching test [”28081 has been run on all materials, too.

2. Description of Facilities 2.1. Criteria for Selection The bottom ashes were taken from two modern German MSWI whch represent the state-of-the-art. Both facilities differ in grate as well as in combustion chamber design and are known for good combustion practice. Almost the entire bottom ash stream of both of these facilities is normally utilized after pretreatment in road construction. The TA-Siedlungsabfall, the packaging ordinance enacted three years ago and the recently installed DSD (Duales System Deutschland) for separate collection and sorting of packaging material are going to change the waste quality significantly.The municipalities being served by the two MSWI have already installed activities for separate waste collection. Hence the waste actually burnt during bottom ash samplingshould more or less reflect future German residual waste composition.

2.2.

WWA

The facility Ais equippedwitha modern middle flow furnace comprisinga reciprocating combustion grate and a travelling grate as feeder. The name plate throughput is 12 Mg/h. The quench tank of this facility is operated using a moderate surplusof water. At first glance this procedure represents a simple washing of the bottom ash. The washing medium, however, is taken from the boiler water regeneration containing already high salt concentrations. Hence this process can be expected to result in only limited removal efficiencies for soluble salts. A scheme of the combustion part of the MSWI A is given in Fig. 1

2.3.

MSWI B

The facilityB is characterized by a modern uniflow combustion chamber in combination with a roller grate. A hydraulic ram feeder is used for charging the waste. The nominal

607

Fig. 1: Combustion chamber of MSWI A throughput is 12Mg/h. Since the rolls of a roller grate are only during 30 % of their rotation covered by the hot fuel bed, it can be expected that this grate type allowshigher combustion temperatures in the fuel bed to be established than other grates. This is supported, moreover, by the gas temperatures in the sampled MSWI B which is usually operated at approx. 1050 "Cthus exceeding the typical 900- 950 "Cin other German MSWI. Ascheme of the furnace of tlus facility is depicted in Fig. 2.

Fig. 2 Schematic design of the furnaceof MSWI B

608

3. Sampling and Qsting 3.1. Sampling and Sample Pretreatment Both facilities were operated at normal conditions when the bottom ash sampling was done. In facility A the actual combustion gas temperature was 820 "C, in facility B approx. 1 050 "C were measured. No data of fuel bed temperatures were available at all. The bottom ashes were sampled according to the recommendationsof the International Ash working Group [Chandler 19921. Increment samples of approx 5 kg each were taken every 10 min for a total collection time of 3 h. The increments were combined to a gross sample which was immediately shipped to the laboratory for further treatment. At facility A the increments were taken as full cross-section cuts directly from the bottom ash discharge conveyer in front of the storage bunker. Agross sample of 95 kg was collected. At facility B the bottom ash had to be sampled by means of a special gripping device from the bottom ash stream falling into the storage bunker. The gross sample was 72 kg. Pure metals and oversizematerials (< 40 mm) were removed by hand in the laboratory. Subsamples of approx. 2 kg each were obtained by means of a riffle box. Subsamples intended for analysis or thermal treatment were dried at 105 "C. The samples chosen for washing or for elution tests were stored in a refrigerator without drymg.

3.2.

Thermal Peatment and Mhshing

Dried subsamples of 2 kg each were annealed for 30 min in a laboratory muffle oven using ceramic crucibles. The annealing temperatures were 850,l OOO, and 1300 "C, the last one resulting in total melting of the material. After cooling the sintered ashes were easily removed from the crucibles and subjected to analysisand to the leaching tests. The molten products, however, could only be separated by crushing the crucible using a hammer. The residues of the cruciblewere carefully separated. The grain size distribution formed by this procedure was directly used for the leaching tests. The washing was performedwitha US of 1Wg. Distilledwater at a temperature of 60 "Cwasused aswashingsolution.The residence time was 1 h. No extra shaking or stirring took place.

3.3.

Leaching Tests

Since all German regulations are based on results of the DEW S4 test [DIN 38 4141 this had to be the standard test procedure. A second regulatory test widely used in Central Europe is the Swiss TVA test [Bundesamt 19911which was also applied. Both tests give only limited informationabout leaching mechanisms and the time-dependent leaching behavior. To get more detailedknowledgeabout these parameters the Dutch column leaching test 25081 was conducted in addition. in combination with the availability test

3.4.

Digestion and Analytical Methods

Since all analytical methods applied use liquid samples, all solids required some pretreatment. At first they were sub-divided to a subsample size of approx. 100 g using riffle boxes. Further sub-dividing was performed in a rotating sample divider. For analpng heavy metals about 100-300 mg of each sample have been digestedusing a HNQ/HCl/HF mixture in a Teflon bomb at 200 "C. For analpng anions the materials were extracted by superheated steam in a glass set-up. Total Reflecting X-Ray Fluorescence Analysis (TRFA) was used for metal analysis. All anions were analyzed by Ion Chromatography (IC).

609

parameter sample size metal fraction fraction > 40 mm

unit

MSWIA 95.0 12.4 11.0

kg % %

humidity LO1 TOC PCDD/PCDF

% % %

ng(WQ)k

cl

%

%

Cu Zn

I

mg/kg m.fdkn

I

msh

29.3 3.2 0.8 1.8 0.29 4.4

MSWIB 72.0 13.1 14.0

I

I

730 3800

I

2100

24.3 1.6 0.7 2.0 0.32 3.4

I

1800 2 700

I

1600

I

LO1and even more the TOC are important parametersboth inview of utilization as well as landfilling.The regulations for utilization in road construction in the German state Hessen set a limit of 2 %of unburnt matter (that means LOI) pessisches Mnisterium 19881. The German TA-Siedlungsabfall sets a limit of 1 % of TOC respectively3 % of LO1 for landfill category I. As can be seen from Table I the bottom ash B is capable of meeting all limits discussedabove whereas ash Aexceeds the LO1limits and is closer to the TOC limit. Both MSWI, nevertheless,have to be ranked among the top-burnout facilities. The PCDDPCDF levels found in both bottom ashes are very low and compare to the background levels in natural soils reported to be approx. 1 ng(I/TEQ)/kg [Hagenmaier 19891. These values, too, characterize the excellent burnout of both incinerators. Since no

610

PCDD/PCDF formation is to be expected during all further treatment procedures no respective analysis has been carried out on the samples after treatment. The heavy metals Cr, Ni, Zn, Mo and Cd show uniform distribution,but even the values of Cu and Pb are within the range of typical concentrationsfound in bottom ashes prunner 1986, Eighmy 1987, Sawell 1988, Lahl1992 Schneider 1992, Faulstich 1993, Dalager 19931.

Changes during lleatment

4.1.2.

All thermal treatment experiments improved the burnout of the ashes as can be seen from Fig. 3. After sintering at 850 "C the TOC is already dunhished sigmficantly and the loo0 "C samples were designated by data which guarantee the easy compliance with the limit of 1 % for landfill category I. 0,900 0,800

0,700

E8

.3

0,500

c-c

0,400 0200

8

0,200 0,100

0

untreated 850°C 1ooO"C 1300°C Fig. 3: TOC in untreated and annealed bottom ashes No other analyticalparameter, neither the heavy metal concentrations nor those of chloride were changed sipficantly by any thermal treatment. Only sulfate was removed to a certain extent at 1300 "Cdueto the limited thermal stabilityof many metal sulfates including gypsum.

E8 .¶

G

untreated washed Fig. 4 Chloride concentrations in untreated and washed bottom ashes

61 1

Aside from chloride removal no significant changes in metal concentration and TOC were found after washing of the bottom ashes. Fig. 4 demonstratesthat the extraction of CI is more effective for bottom ash B than it is for k Bottom ash A, as described above, has been subject Bundeslandto a kind of washing already in the plant which might already have removed a certain fraction of the original chloride inventory.

4.2. Leaching Test Results 4.2.1. DEV S4 Test In all test solutions pH values of approx. 11.5were established. In this environment most heavy metals form low-soluble compounds like hydroxides or oxyhydrates. Hence the differentiationof this test with respect to heavy metal mobility is only moderately pronounced. Fig. 5compiles normalized DEV S4 results of the untreatedbottom ashes for some heavy metals and other parameters regulated by the TA-Siedlungsabfall. For easier comparison all given data are normalized to the respective limits of the TA-Siedlungsabfall.

E pJ

MSWIA

. a2

a

I

E

1

c1

M 0,100

c1

n

0,010

B

R ~

Cr Ni cu Pb sol cond EOXphenols Fig. 5: Untreated bottom ash DEV S4 test results of metals, soluble matter (sol), electric conductivity (cond), extractable organic halogens (EOX), and phenols (normalized to the TA-Siedlungsabfall limits for landfill category I) The most obvious result is the compliance of all normalized results with the respective limits of the guideline. This once more demonstrates the excellent quality of both of the original ashes. The fixation of heavy metals seems generally to be slightly better in bottom ash A than it is in ash B. This is in contradiction to the expectedproperties sinceon one hand the facilityB should have the superior sinteringcapabilityand on the other hand it was operated at combustion temperatures approx. 200 "Chigher than those in facilityA There is no way, however, to interpret these trends due to the lack of valid data of waste quality as well as of fuel bed temperature and residence time. To evaluate the effects of thermal treatment the test results of Ni, Cu,Zn, and Pb will be used The respective normalized data are presented for both materials in fig. 6. The bar plot indicates a certain improvement of leaching stability by annealing. The lithophilic metal Ni shows only very small changeswhereas the properties of the more volatile ones are altered more significantly.The DEV S4 test results do not allow to distingush between the annealing temperatures. That implies a first conclusion to be drawn: the melting of the ashes causes no significantchanges in fixation compared to the sintered samples.

612

10,oooo

3-.1,oooo 3 0,1OOo I

a

0,0100

0,0010

Zn Pb MSWIB Fig. 6: DEV s4 test results of annealed bottom ashes for Ni, Cu,Zn, and Pb (normalized to the TA-Siedlungsabfall limits for landfill category i) N i C u Z n P b

Ni

Cu

MSWIA

To get a feelingof the degree of leaching stability results of the natural building materials gravel and quartz sand obtained by the identical test procedure have been included in fig.6. Obviously the data prove the annealed bottom ashes to be approximately as stable as the natural materials. Major deviationsare only noticed for Zn which belongs to the most common metals in bottom ashes and which is characterized by its high mobility. Special attention has to be directed to Cr. In the untreated ashes and in the samples annealed under nitrogen or flue gas atmosphere the results compare in most cases to those of Ni. If the thermal treatment, however, is performed in an oxidizing atmosphere often a significant increase in mobility is found, The effect might be explained by partial oxidation of trivalent Cr species into the hexavalent state. The generallyreducing flue gas atmosphere in the combustion chamber seems to prevent this reaction since during our recycling of 3R products into the furnace of a full scale MSWI Cr behaved exactly like a lithophilic metal [vehlow 19931. The limit of hexavalent Cr set by the TA-Siedlungsabfall for the landfill category I ( 0.05 mg/l) is extremelylow. Therefore it must stronglybe recommended to take care that any potential oxidation taking place during thermal treatment is avoided. Washing of bottom ashes does not remove substantialamountsof heavy metals due to the pH regime adjustingin the washing solution.Asignificantvariation in total concentrationas well as in DEV s4 test results could not be observed. The process is yet intended to remove soluble species the most important being CI. The chloride concentrations in the DEV S4 test solutions after different washing procedures are compiled in Fig. 7. The TA-Siedlungsabfall sets no c1 limit but some regulations for utilization do. In the German state Baden-Wiirttemberg the respective value is 100 mgil for recycled road construction materials [verwaltungworschrift 19911. Fig. 7 points out that both of the untreated bottom ashes have difficultiesto meet this limit. The ash B exceeds it even by 25 %. One singlewashing step at US=1l/kg reduces the c1elution alreadyto values far below 100 mgll. Repeated washing improvesthis effect. in regard to compliance with the regulations, however, this second step can be saved. Recommendationshave been made to age bottom ashes prior to washing [Lahl1992].In order to prove this concept 20 kg of bottom ash B have been stored outside in a pile (height

613

Fig. 7: Chloride concentrations in the DEV S4 test solutions after direct washing and washing after aging of 3 months

25 cm)for three months. From the precipitation a US of 0.5 l/kg could be calculated Fig. 7 points out, that the Cl release out of this material is reduced by the same order of magnitude than it is by washing. A subsequent washing of the aged ash causes only minor reduction in the Cl leaching. Hence aging prior to washing has no significantlybeneficial effect. Full scale aging is not performed in thin layers, but by piling the ashes up to several meters in height. Thls will reduce the US to values in the order of 0.1 Vkg and thus deteriorate the Cl removal. The appropriate treatment of the Cl rich washing solutions,furthermore, is easier performed inside a MSWI - e.g. as feedingsolution of the wet scrubber - than it is at the storage site. These considerations in combination with the experimental findings give reason not to recommend aging prior to washing. 10,oooo

3 1,oooo

. .3 I

+ 0)

0,lOoo

CI

M

CI

0,0100 0,0010

Zn W Ni Cu Zn W MSWIA MSWIB Fig. 8: TVA test results of annealed bottom ashes for Ni, Cu,Zn, and Pb (normalized to the TVA limits for residue landfills) Ni

Cu

614

4.2. 2.

TVATest

The SwissTVA test procedureestablishesa weakly acid environment (pH approx. 5.5) in the test solutionby CQ permanentlyblown into the system. Many heavy metals are characterized by an increased solubility in this pH regme. The results of this test, too, do not allow a modelling of the long-term behavior of materials. Misleading effects can be caused by the formationof insoluble carbonates (e.g. PbCQ) as well as highly soluble bicarbonates (eg. Zn(Hcq7)2). Fig.8 compiles all test results for Ni, Cu,Zn, and Pb. The data are normalized to the limits set for Swiss residue landfills [Bundesamt 19911. The results of the TVA test indicatethe same trends as those of the DEV S4 test, but generally in a less pronounced manner. Ni shows no effect of the thermal treatment as it did already in the DEV S4 test. Acertain improvementof stabilityis seenfor Cu where the meltingseemsto produce a higher increasein fixation than in the DEVS4 test results. The trends concerningZn and Pb are less pronounced than in the DEY S4 test results. This is presumably due to the above mentioned limitations of the TVA test.

4.2.3. Column Leaching Test 4.2.3.1. pH Values and Alkalinity This more elaboratedtest procedure results in more detailed information includingthe adjustingpH, buffer capacity,the elution behavior as a function of the US - which can be interpreted as a time relation -, and the availabilityof single components under the most severe environmentalconditions.The column test has also been run on small pieces of concrete from a demolished German highway bridge to bring the results into perspective to common building materials.

Fig. 9: pH values in the column leaching test solutions after US = 20 An important and simply available information is the pH value in the solution. Fig 9 compilesthe pH values found after a US of approx. 20. The sinteringdecreasesthe pH only slightly in the case of ash A but significantly for ash B. In the molten productsboth ashes end up with a pH of approx. 10.5. Washing does not alter the pH. In many of the test solutions pH values exceeding even 12 were found. In this environment amphotericmetals like Pb are starting to be noticeably dissolved. The effect can be

615 A A A

untmted + + + 850 'C I m washed

v v v 1300 "C

1OOO "C

a

cr

a

.I

0.100

U

e

.L

a

3

0.010

rn 0 . 0 0 1 , . . . . . . . . . , . . . . . . . . . , . . . . . . . . . ) 10 11 12 13

pH value Fig. 10: Elution of Pb in mgkg of tested product as a function of pH

seen from Fig. 10.The graph compilesdata representing all investigatedUS ratios at all different treatment options. Below a limiting pH value of approx. 11.5 the concentration is more or less constant. Above this pH a strong increase with increasingpH is observed Ths pH control of Pb is confirmed in literature [van der Sloot 19921. Generally the establishingpH influencesthe actual leachingbehavior. The long term behavior dependsstronglyon :he changesin pHwith time and that means on the buffer capacity of the material. A measure of this value, a kind of acid neutralization capacity (ANC),is obtained in the availability test where the acid consumptionduring stabilizingthe pH of the solution is recorded. The sum of protons needed to stabilize a pH of 4 during 3 h has been found to be 2.7 meqg for the bottom ash A and 2.1 meqg for bottom ash B.

Fig. 11: ANC (end point pH = 4) measured in the availability test Fig. 11 depicts the ANC of all materials obtained by the availability test. This parameter distinguishesto a greater extent betweenboth ashes than the pHvalues do. The alkalinityin

616

theashAwiththehigherbuffercapacityislessaffectedbyannealingupto 1OOO "Cthanthat in the ash B. In both of the molten products, however, the same amount of approx. 65 % is removed The washing process dissolves about 25 % of the alkalinity of both ashes. From a theoretical standpointof view a high buffer capacity keeps the pH for long times in the alkahe range even in an environmentcharacterizedby acidrain and the actual leaching rates of most metals of concern are low. Hence the addition of alkaline components to the bottom ash was recommended in order to enhance its buffer capacity Phl19921. Such action has yet to take care that the pHis limited tovaluesnot mobilizing amphotericmetals.

4.2.3.2. Availability and Release As an example of column leaching test results Fig. 12 compilesthe total concentration, the availability,and the actual release of Zn from bottom ash B. The concentrationof Zn does not vary beyond statisticaltolerance in all tested materials.The availabilitiesform two groups, untreated and washed ashes being characterizedby high values up to about 10 % of the total inventory, and all annealed samples showing numbers in the order of 1 % of the inventory and below. This picture is typical for lithophilic as well as for volatile metals.

10

i1 a

Ir

0

1 10 100 L/S Fig. 12 Total concentration,availability,and elution of Z n in bottom ash B 0.01

0.1

Just the same applies to the elution behavior. If treatment has an effect, it can be discerned already in the early beginning of the elutionprocess, whereas the slopes of the elution curves generally prove to resemble each other. This indicates the removal of small amounts of soluble species already in the initial phase of the leachingwhile the subsequent release is controlledby the same mechanisms in all materials. In the case of annealed samples the removal can be caused by volatilization and/or by immobilization. The washed ashes show about the same availabilitiesas well as leachingproperties as the untreated ones, although with a trend to slightly decreased values for most heavy metals. For that reason they will not separatelybe discussed. The samplesannealed at 850 "C, too, will not be includedsince they behave similar to the 1 OOO 'Cones. Furthermore all results obtained from both types of bottom ashes are in good agreement and that is why averaged data only will be presented.

617

100,oooO

't

f!

*a

109-

l,m

0,lOoo 0,0100 0,0010

Ni Cu Zn Mo Pb Ni Cu Zn Mo Pb availability release Fig. 13: Availability and total release after US=20 for selected metals

Availability and total release after L/S=U) of some metals are shown in& 13.For comparison data of concrete from a highway bridge are included in the graph. As mentioned before the availabilitymodels the ultimate release obtained in an amessiveenvironment.Itisperformedonfinelygroundmaterial.The test is not controlled by any diffusion. Hence it represents a sensitiveindicatorof chemicalor mineralogicalchangesin a substance. The availabilitiesof next to all metals are at least by one order of m a p tu d e higher than the actually leached quantities. Both parametersfollow the same trends as can be deduced from the graph. The differencescaused by thermal treatment are still more pronounced in the case of availabilitiesthan they are for the leaching rates. 'Especiallyfor metals designatedby a certain volatility in waste incineration like Zn, Pb, and Cu the annealing reduces the availabilityat least by a factor of 10. The leaching is also dirmnished,the factor, however, is less than 10. The molten products tend to show slightly lower values for availabilityand release than the sintered ones, albeit the respective parameters of all thermally treated ashes are generally close to each other. The availablefraction of the annealed products represents in most cases less than 1%of the total inventory.Their leaching rates are close to those of the additionally tested concrete. Lithophilicmetals like Cr, Mn, Fe, or Ni are already tightly fixed in the oxide or silicate matrix of the original bottom ashes and suffer only minor changes in mobility by thermal treatment. In the annealed samples about 1 %or less of the original inventoryof thesemetals is available for leaching. Again the leaching rates compare to those of concrete. A third group of elements characterized by high availability, intense leaching, and approximatelyno response to thermal treatment is that of oxyanions formingmetals, in the graph represented by Mo. There is indication that Sb behaves similar. The availability of Mo is in the order of 5 %, most of it leached in short term.

4.2.3.3.

Leaching Parameters and Thermal 'keatment

The combination of all results obtained by the availability and column leaching test forms a coherentbasis to identify main parameter variationsin bottom ashesby the applied

618

treatment procedures and allows recommendationsto be made for future ash management options. In general the conclusionsdrawn out of these findingssupport the trends indicated by the results of both regulatory tests.

3

10,Ooo

?a

j

CI

l,Oooi

.4

siII

3 I z

0,100

rn untreated AIOoo°C

-

01300°C

0,010

I

1

10

100

1(

availability in mg/kg of product Fig. 1 4 Total elution at US=Bversus availability

In order to interpret the relation between availability,release, and thermal treatment in fig. 14the total release of 4 typical metals is depicted as functionof availabilityand thermal treatment. In the case of the lithophilicelement Ni the sintering at 1OOO "Creducesthe availability but does not alter the leaching process significantly. Whether volatilization or immobilization reduces the amount of availableNi speciescan hardly be substantiated. The statistical error of total concentrations allows no precise decision. The fixation seems more likely since the availability is already reduced at 850 'C and volatile Ni compounds like NiF2 or NiCl2 have sublimationpoints around 1 OOO "C. On top of that the concentrationsof F or Cl ions in the ashes are very low. The leaching behavior is not varied due to the diffusion control of the process. The pore structure of the material is not altered to a great extent by the sintering.Thls interpretation is supported by the dirmnished leachmg rate of the molten ashes. The constant availability indicatesno chemical or mineralogical transformations,the high densityof the matrix, however, acts as a d i h i o n barrier. Bothvolatile metals Zn andPb have more intensivelybeen affectedby the thermal treatment. The sinteringdecreases the availabilityas well as the actual leaching rates drastically. Again the total concentrationsdo not support a considerable evaporation of Zn or Pb compounds. It could be suspected that minor quantities of chlorideshave beenvolatilized.Substantial fractions of available compounds still must have been immobilized. Additional changes in availabilitycaused by melting can be neglected. The leaching, too, varies by not more than a factor of 2, again due to the dense structure of the molten product. Mo is a typical representative of oxyanions forming elements and does not react to any treatment at all, neither to annealing, nor to melting, nor to washing. It is characterized by high availability and fast leaching. It can not be volatilized during combustion, its crystal

619

radii prevent a fixation in silicate lattices and the diffusion coefficient in sintered materials is high [vehlow 19931. The only effective measure to minimize its leaching out of bottom ashes points out to be source separation prior to combustion.

5.

Evaluation and Conclusions

Intense investigationsof the changes in quality of bottom ashes by simple treatment procedures intended for future in-plant processing have been performed on materials taken from two modern German MSWI. The program aimed for the development of measures which guarantee the production of bottom ash qualities enabling these residues to be utilized as secondary building material in road construction or to be at least disposed of on a category I landfill according to the German TA-Siedlungsabfall. Gross parameters, results from two regulatory leaching tests and the combination of findings of an availability test and a time resolving leaching test were used to characterize the effects of the different treatment processes. The following conclusions can be drawn: 0 One simple washing step of bottom ashes at a US of 1, which could be performed in a modified quench tank, diminishes the chloride inventory and thus reduces the leaching of Cl down to about 50 mg/l. Agmg prior to washing did not reduce the Cl release substantially. 0 Thermal treatment dunhishes LO1 and TOC to a great extent. By sintering at 850 to 1OOO "C a TOC in the order of 0.5 % and less could be achieved. 0 If bottom ashes are brought in contact with water the pH should be kept well below 12 to avoid mobilization of amphoteric metals like Pb. This should be considered if alkaline matter is added in order to enhance the buffer capacity. 0 The sinter process improves the fixation of heavy metals of concern like Ni, Cu, Zn, and Pb considerably.The investigations indicate an important contribution of chemical and mineralogical transformations to this stabilization. The leaching rates of annealed bottom ashes compare to those of commonly used construction materials like gravel, sand, or concrete obtained under equal test conditions. 0 An annealing under oxidizing atmosphere must be avoided due to the potential formation of hexavalent Cr. Melting of bottom ashes results in only minor improvement of quality factors like burnout and leaching stability and should be considered carefully against the sipficantly higher energy consumption. Evaluating all findings there is reason to recommend the fuel bed temperature at the back end of the grate to be kept high in order to get well sinteredbottom ashescharacterized by low burnout and high leaching stability. A simple washing in the quench tank is recommended for removal of soluble matter, especially chlorides. Bottom ashes produced this way will have a great potential for utilization.

6.

References

Brunner, PH. & Monch. H.. (1986), WasteManagement & Research, 4, 105

620

Bundesamt fiir Umweltschutz (1991), Entwurf zur Vernehmlassung einer Technischen Verordnung uber Abfalle P A ) , Bern, August 1988, revision 1991 Bundesministerium fur Umwelt, Naturschutz und Reaktorsicherheit (1993), Dritte Allgemeine Verwaltungsvorschrift zum Abfallgesetz (TA Siedlungsabfall), Bundesanzeiger Jahrgang 45, Nr. 99a Chandler, AJ., Eighmy, TT, Hartlen, J., Hjelmar, O., Kosson, D., Sawell, S.E., van der Sloot, H A & Vehlow, J. (1992), WasteManagement International, (%mi-KOmu'ensky, K J , ed),Berlin: EF-Verlag, Vol. 2, 115 Dalager, S. (1993), hnference om affaldsforbrmdingunder nye betingelser; September 6, 1993, Kobenhavn, DK DIN 38 414 (1984), Teil 4, Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung;Schlammund Sedunente (Gruppe S), Bestimmungder Eluierbarkeit mit Wasser (S4), Berlin: Beuth-Vertrieb Eighmy, TT, Guay, MA, McHugh, S.A,Thompson, EH., Kmner, N.E. & Ballestero, TF? (1987),Municipal WasteIncineration,Boceedings, October 1 - 2,1987, Montreal, Quebec (Environment C a d , ed.), 349 Faulstich, M. ,Hey, G. (1993), EntsorgungsPraxis4/93,211 Forschungsgesellschaftfbr StraBen- und Verkehrswesen (1986), Merkblatt fur die Verwendung von industriellen Nebenprodukten im StraBenbau. Teil: Miillverbrennungsaschen (MV-&he), Mull-Handbuch (Hiisel, G., Scknkel, W & Schnurer; H., e d ) Berlin: Erich Schmidt Verlag, Kennzahl8667, Lfg. 5/91 Hagenmaier, H. (1989),Halogenierte organische Verbindungenin der Umwelt, I/'DI-Bericht NK 745, 939 HessischesMmisterium fur Umwelt und Reaktorsicherheit(1988), Merkblatt uber die Verwertung von Schlacken aus Hausmdherbrennungsadagen, Staatsanzeigerfw dasLand Hessen, Nx 28, 1514 Lahl, U. (1992), Verwertung von MV-Schlacken - durch Optimierung konventioneller Aufbereitung, Mull undAbfall,24,619 NVN 2508 (1990), Determination of Leaching Characteristics of Inorganic Components from Granular (Waste) Materials, Neth. Standardization Institute ("I) Sawell, S.E., and Constable, TW (1988), Environment C a d Report, Manuscript Series, IP-82 Schneider,J., Kossl, H. & F'frang-Stotz, G. (1992), SchhckeauyWeitung -venvertungund -entsorgung: Handbuch zum Seminar;Miinchen, 16 - 17.Marz 1992,Diisseldorf:VDI Bildungwerk, BW- 141711 Schoppmeier,W (1992), Zentrale Schlackenautbereitungaus mehreren MVAs nach dem System der Container Company, VDI-Bildungswerk, BW 43-76-01. S. BW 1379 van der Sloot, H A , Comans,R.N.J., Eighmy, TT & Kosson, D.S. (1992), WasteMnagement International, (%me'-bzmiemky, K J , ed.), Berlin: EF-Verlag, Volume 2,99 Vehlow, J. & Geisert, H. (1993), 3rdInt. ConferenceonMunic@alWasteCombustion, March 30 - April 2, 1993, Williamsburg,VA Verwaltungsvorschrift des Verkehrsministeriums und des Ministeriums fur Umwelt uber vorlaufige Lieferbedingungen fur aufbereiteten StraBenaufbruch und Bauschutt zur Verwendung im StraBenbau Baden-Wiirttemberg vom 15. November 1991, Az.: 46-8982.31/114 (UM)

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and 7h.G. Aalbers (Editors) el994 Elsevier Science B.V. AIl rights reserved.

62 1

Potentials in Quality Improvement of Processed Building Rubble by Demolition and Treatment Technics. J.O.V. Trankler" and I.Walkerb ' Bavarian Institute for Waste Research, Am Mittleren Moos 46B, D-86167 Augsburg, Germany, Institute for Water and Waste Management, Aachen Technical University, D52056 Aachen Germany

Abstract Demolition waste is an important factor for the waste management of most industrialized countries, both in terms of quantity and quality. Demolition waste consists at a high extent of mineral building materials, but includes up to 15% refuse and even small amounts of hazardous substances. Today the composition of building rubble mainly originates from the time before 1955 and is dominated by demolition waste from industrial sites. The application and use of building materials have changed within the last decades. This will affect the composition of the demolition waste of the future and the relevant treatment technics. Nowadays the plants for building rubble treatment provide a technology that decisively improves practical criteria. But the efficiency concerning environmental compatibility is of lower significance, because only some 30-50%of the product is subjected to an intensive treatment. According to the change in waste composition and higher specifications the treatment process and the demolition technics have to be optimized. 1. WASTE MANAGEMENT FOR BUILDING RUBBLE

With an estimated rise of about 150 Million Mg pa in the EU and 30 Million Mg pa in Germany the treatment and the disposal of building rubble represent a significant factor for waste management both in terms of quantity and environmental aspects. On a medium-term basis, no decrease of building rubble is anticipated, since the demolition of buildings is also a consequence of limit supply of real estate. In the western part of Germany, new buildings are rebuilt on two-thirds of all demolished real estate. For mass waste such as building rubble, the declared objective of the government is to achieve a drastic reduction of residues to be dumped on landfills.

622

2. COMPOSITION OF BUILDING RUBBLE TODAY AND TOMORROW

If the range of current building rubble composition is considered (fig. 11, it does not become evident that the first starting point is to be sought in demolition techniques. The following description characterizes the situation in Germany, but can easily compare with other industrial countries. Exclusively lowcost demolition technics are namely being applied, by which an inhomogenous material mixture is obtained. This is composed of mineral building materials, materials from furnishing and fixtures like glass, ceramics, wood, plastics, light composite materials and materials in connection to the building that are related either in a functional or nonfunctional way. A separation of the former material groups by means of suitable selective demolition processes would be conceivable and would relieve processing measurably, however, this is currently still the absolute exception.[3]

[“A1 80 60

40 20

0

glass caramlcs stc.

bituminous matsrial

Mnd, soll piamtsr

bricks masonry

concrste

Figure 1.Fluctuation ranges of building rubble composition expressed as percent by weight. 2.1 Use of building materials in the past On the other hand the composition has to be regarded under the viewpoint that now primarily buildings built before 1955 accounts for the main proportion of the demolition waste. The amount of building rubble is dominated by demolition waste from industrial sites. Whereas the actual lifetimes of domestic buildings come out 70 to 90 years, the factory buildings attain less than 50 years and their lifetimes are still decreasing. Actually the demolition waste from industrial and domestic sites figures a ratio between five to one (fig.2) A chronological survey shows the use of building materials in Germany from 1949 to 1989. During this time the building industry was subjected to several interactions best recognized by the relative distribution of the main fractions used as building materials. This influence is characterized by an increase of concrete and a decrease of masonry.

623

1979

1981

1983

1985

1987

1989

.

Figure 2.Loss of domestic (left-hand side) and industrial buildings from 1979 till 1990 in Germany [3,4].

1949

1959

1969

1979

1989

Figure 3.Use of building materials in Germany from 1949-1989 \ 1\ ready-mixed concrete, \ 2 \ concrete (insitu or prefabricated), \ 3 \masonry, \ 4 \ plaster, mortar, screed, \ 5 \ miscellaneous. Special interest should be focused on the miscellaneous. In figure 3 it was impossible to figure out which materials are concentrated under this term. It is obvious that 5 to 10% of the building materials are not of inferior bearing. The importance is best explained by a double image of these materials. A description in detail is given by weight and volume. Especially the lightweight materials will cause frequently problems for treatment of demolition waste.

624

1949

1959

1969

1979

1989

1949

1959

1969

1979

1989

Figure 4.Use of specific building materials percent by volume (above) and by weight (below) \ l \ roofing ; \ 2 \ bitumen ; \ 3 \ lagging; \ 4 \ lumber and timbers; \ 5 \ plasterboard ; \ 6 \ constructional steel. In addition chemical substances,e.g., coatings, seals and bonding agents are today excessively used in the building industry. Compared with the production and use of common building materials their part seems negligible. However, this statement is only valid in concern to the quantity but not found out for environmental-related criteria. These small amounts of building chemicals affect the environmental compatibility even today and will increase in future. A strategy in combination with selective demolition technics is absolutely necessary to avoid the foreseen problems.

625 2.2 Source Separation

Some practical investigations showed that source-separation effect the potential recycling rate. A specific survey of a factory building showed that only 0,3% of the total mass consisted of hazardous waste. A part of 3,9% was not applicable for treatment and the remainder of 95,8% could be directly reused or recycled. This part consisted not only of mineral building materials but also of glass, rubber and so on [l]. The recycling potential of a domestic building by selective demolition figured out the same magnitude. Therefore an amount of 89% could be submitted the recycling and only a small part of 6%was not applicable [2]. The manual work for the selective demolition compared with the common demolition is expensive but with increasing dumping charges it is an incentive to gain a high-quality product with low treatment efforts. 3. TREATMENT EFFICIENCY

Currently, building rubble recycling is designed to produce a secondary mineral building material from heterogeneous materials. These are used primarily for earthworks and road construction. For the corresponding quality criteria to be fulfilled, organic components and the material that impair the resistance to shock and the frost susceptibility has to be removed. Stationary processing-plants use for the elimination of interfering and bulking materials a dry (air classifying) or wet process step (washing). Concerning this objective, such processes reveal high efficiency (fig.5 ). The processed mineral fraction of the particle size range 0 - 45 mm generally reveal clearly less than 1%by wt. of foreign or interfering materials resp. no measurable organic contamination. That is to say, the processing steps named enable a considerable improvement of technical product quality.

[“A1 80 70 60 50 40

30 20 10 0 WCondaW bulldlng material 0-6mm

tine traction mm

, ,.

scrap

wooden

refuse

material

Figure 5.Result of building rubble recycling in percent by weight.

626

3.1 Environmental compatibility of treated material Apart from the construction-oriented requirements, increasing emphasis is being placed on the environment-related steps due to the heterogeneous composition. When using of secondary building materials, a leaching of the processed materials could endanger water and soil. The uncertainty prevailing at this time concerning how and by which standards this risk potential is to be rated has meanwhile been regulated by different specification of limiting values sometimes even with a respective tolerance range and rules of application. Thus it is not only the practical but the environment related criteria that restrict the scope of the recycled materials. However this should not be a place for discussing limits neither values nor necessary and sufficient condition are argued. An overview of many parameters of leachate from building rubble is given in table 1.

Table 1 Properties of leachate characteristics from processed demolition waste [3] Parameter

range of values

below detection

min [mg/ll

max [mg/ll

90% percentile

[mgill

[%I

Calcium Magnesia Chloride Sulfate

31 0,02 295 990

424 11,l 50,O 1540

230 6 $0 24,7 470

0 0 0 0

COD Ammonia Nitrate Fluoride Cyanide Tot .Phenol AOX CH

13 0,03 091 0,2 0,Ol 0,Ol 0,Ol 0,05

77 5,5 26,O 0,24 0,04 0,17 0,07 0,20

43 171 2,3 0,17 0,03

18 0 62 0 60 15 20

Cr Fe Ni cu Zn Cd Hg Pb

0,004 0,Ol 0,002 0,03 0,Ol 0,0001 0,0001 0,001

0,074 570 0,06 0,lO 0,14 0,002 0,0005 0,200

0,08

0,04 0,20 0,037 0,84 0,018 0,09

0,05 0,0012 0,00048 0,028

11 19 45 63 0 10 81 69 57

627 4. EFFICIENCY OF SPECIFIC PROCESSES

While the effect of the wet and dry processing steps on product quality is indisputable, there has been a lack of information on possibilities on how to improve the product quality concerning criteria of environmental compatibility. Especially the wet treatment should compel leaching and wash out soluble fractions. In comparison with a dry treatment, advantages could occur since with a dry process step only relevant fines fractions can be discharged. Using typical examples, investigations on this complex topic are presented and discussed in the following. Assessments of current position were made using a plant with air classifying and a plant with wet processing. These processes are familiar with the treatment of sand and gravel. 4.1 Dry processing

The plant for dry treatment consists of a preliminary screening, a single-stage crushing and a connected air classifying installation. Before air classifying, the product is separated into five closely adjoining particle size fractions, since a classifying of heavy mineral and light interfering and ballast materials will otherwise not can be accomplished. For the fines fraction 0 - 4/8 mm, no air classifying is possible, consequently the fraction sized 4/8 - 45 mm is treated accordingly. Since besides the crushing process, too many fines are obtained, about fractions from the dedusting of the air flow. The processed product available represents about 65% of the original feed material.

in, -

air

m

s

c

r

a

p

B - 45

I@

0-8

0 \\\

+

iz-

-

0

dust and light weight material

--

0-4/B -----

/me rac ion

Figure 6.Building rubble treatment with an air classifying system \ 1\ screen; \ 2 \ impact crusher; \ 3 \ magnetic separator; \ 4 \ manual sifting; \ 5 \ air classifier; \ 6 \ filter.

628

2-5 % of these are removed, while the remaining 24% of the total throughput pass untreated the air classifying, i.e. 46% are separated by air classifying. Besides fines of about 26% (this is about 2% of the throughput) from the air classifying residues are additionally obtained. The residual material also contains the dust. 4.2 Wet Processing

The wet treatment represents a plant where the feed material, after screening, is crushed through a multistage crush in a combination of jaw- and impact crusher and 1.An intermediate screening relieves the second crushing stage. Subsequently, the partial fraction 16-45 mm or 35% of the total throughput is subjected to the wet treatment. Only some 50% of the final processed product is treated. The wash-water is fed into the circuit. About 6% of the total throughput is added to the mass flow as wash-water. About 15% of this wash-water remains in the treated material. In relation to the total throughput, besides about 65-70 % of the product, about 25-35% occurred as fine fraction 0 - 8 mm and also about 3% as residues and slurry.

flne fraction

processed rubble

Figure 7.Building rubble treatment with an Aquamator \ 1\ screen; \ 2 \ jaw crusher; \ 3 \ manual sifting; \4 \ magnetic separator; \ 5 \ impact crusher; \ 6 \ Aquamator (wet processing),

629

4.3 Investigations The investigations concerning the treatment efficiency included, at the plants presented, the entire mass flow during an operation day: At all points where product flows are separated or converged and/or partial flows are diverted, a mixed sample was taken from the respective mass flow. The sample taking and analysis have been repeated for several times. Leachate was obtained according the German standard test method DIN 38414S4. Since untreated building rubble is unfit for this kind of leaching test, the inputloutput relationship is figured out. The corresponding yields from processed or separated partial flows are added and the total yield obtained from the input represents the leaching-potential, which among others is created even by processing, eg during crushing. However, such a procedure was impossible for organic trace substances or heavy metals because of partially falling below detection limits. Ascertained dependencies are presented for sulfate, chloride, chemical oxygen demand (COD) and total phenol. The specification of by absolute values was dispensed with since these values were governed by various feed materials and thus did not appear suited for a process comparison.

4.4 Results of dry processing In dry processing, relevant materials were removed from the system by the low mass flow of the filter dust. As shown in Figure 8 4% of chloride also 5% of sulfate were discharge from the entire input of air classifying. In comparison with anions, the COD and total phenols revealed a better performance with elimination rates of 9 resp. 11% (Fig.9). However, the total elimination rates seem low. One third of the input bypassed untreated the air classifying. Based on the partial flow, efficiencies of 12 and 15%for chloride and sulfate, considered relatively, were obtained. Even clearer results yielded the consideration for COD and the total phenols with relatively high rates of 25 resp. 28%. Furthermore, apparently the mass flow corresponds with flow of leachate only to a limited extent. Clearer deviations to the throughput of 35 to 65% are found out for chloride, COD and total phenols with a ratio of untreated partial flow of 55 to 45 for chloride and COD, resp. 45 to 55 for the total phenols. This again means that the untreated material, at least for these parameters, clearly affects the leaching rates of the processed material. A similar observation that there was only a partial parallelism of mass flow and leaching-potential can be made for the preliminary screening. While most parameters corresponded approximately with the mass flow or exceeded it by a maximum of 20%, a discharge rate about twice as high was figured out for the sulfate. Thus, the product was relieved effectively through the preceding screening of sulfate.

630

Dry Processing: Air Classifier

Wet Processing: Aquamator

32 %fine fraction

25 % fine fraction

processed

66 %

64 %

filter dust 4 %

wastewater

46 Yofine fraction

processed material 49 %

100%

filter dust 5 %

60 % fine fraction

processed material 33 %

100 %

wastewater

Figure &Balance for the leaching characteristics of chloride and sulfate by dry resp. wet treatment. 4.6 Results of wet treatment In comparison to dry processing with air classifying, similar conditions are observed for wet treatment. Here only partial flows were obtained through these processing steps. Thus the throughput and the respective material contents agree only partially. For the investigated plants, this was already evident for the preliminary screening, where this was due to the composition of the feed material. In comparison to mass flow, some 10% more phenols, 25% more chlorides, 65% more COD and eventually 200% more sulphate was separated by preliminary screening. Thus the amount of these content materials had also decreased so that the relative efficiency of wet treatment had to be considered. For wet treatment, a high elimination rate occurred for sulfate and phenol compared to a dry treatment. For the chloride the efficiency was naturally higher for a wet treatment. If the partial flow passing through wet classifying is considered, the elimination effect must be rated higher. However, it is also evident that the relative values in comparison with dry processing revealed a doubled efficiency for chloride and sulfate. A change of elimination effect was not observed to this extent for COD and total phenol, here the two different processes resemble one another. The imbalance between the distribution of the throughput and the relevant leachate parameters was not that significant as for dry classification. However, one half passes through the wet treatment, while the other half bypassed this processing untreated. For dry classification this ratio was 2 to 1.

63 1

Dry Processing: Air Classifier

Wet Processing: Aquamator

29 %fine fraction processed

100 %

33 %fine fraction

slurry, 9 % wastewater

filter dust 9 %

30 % flne fraction

100%

tot. phenol

&DS9.

filter dust 1 1 %

processed material 58 %

oo %

processed material

22 % flne fractlon

loo%

processed material

fT) tot, phenol

slurry, 13 % wastewater

65 %

Figure $).Balance for the leaching characteristics of COD and tot. phenol by dry resp. wet treatment. 5. DISCUSSION

A wet treatment of demolition waste, like dry processing with air classifying, is a complex system. Only a part can pass through the classifying dry resp. wet stage. Since these processing technics are related to many problems for the fine size fraction 0-4/8 mm resp. 0-16 mm. Wet treatment is quite able to affect product quality. This applies for the soluble shares especially chloride and less clearly for sulfate and phenol. However, attention must here be drawn to the fact that for circulation control of wash-water, a superimposing of elimination and contamination does not occur. The investigations revealed that most of the efficiency is based on the separation of fine fractions. Even when based on extensive investigations of end products, it cannot be confirmed which process would be better since no clear trend was observed [5]. An isolated consideration of the efficiency of treatment steps for a process appraisal has totally neglected the problem of residues also. Residues from dry classifying are filter dust from the dedusting unit, which is mixed with the light materials separated by air classifying. For the residues from wet treatment, double problems arise for waste treatment for wash-water and slurry. Dry processing is to be preferred for here only the filter dust is to be disposed of and only an exhaust air has to be dedusted.

632

6. CONCLUSIONS

The plants for dry and wet treatment of building rubble provide a proven technology that can decisively improve practical criteria. Considered generally, this effect seems of subordinate significance for environment-related criteria. The critical parameters only apply for low concentrations and only some of 30 - 50% of the product is subjected to a wet resp. dry treatment. To what extent the optimization is still possible by a respective processing of untreated fractions is to be figured out in detail. Besides source separation at demolition sites the treatment process has to be improved. Solutions are likely found by improvement of - the screening using this step as first step for classifying by mass acceleration of heavy parts, - the screening of fine sizes, - the crusher technics using a multistage crushing avoiding too much fines and cut composite materials, - the air classifying or wet treatment of the fine sizes and - recycling of air and water at a high extent by air classifying or wet treatment. The results are to be seen with the view that now primarily buildings from industrial sites built before 1955 accounts for the main proportion of building rubble and consequently the composition of building rubble originates from building material application and technology of the time before 1955. After 1950 the building industry was subject to several interactions that are characterized by an increased use of concrete, less brickwork also an increase of lightweight materials, insulating materials and building chemicals. Mineral processing techniques too have to adapt to future changes of building rubble composition resulting from this, so that the ambitious objectives of a maximum degree of recycling are achieved under consideration of both technical also possibly dominating environment-related criteria. 7. REFERENCES 1 M. Ruch et al, Vermeidung, Verwertung und Entsorgung von Baurestmassen bei Abbruchmahahmen, B. Bilitewski (ed.) Recycling von Baureststoffen EF-Verlag, Berlin (1993) 189 2 K. Marek, Recyclinggerechter Abbruch - kontrollierter Ruckbau, B. Bilitewski (ed.) Recycling von Baureststoffen EF-Verlag, Berlin (1993) 177. 3 J. Trankler, Bauschuttentsorgung - Entwicklung und kunftige Bedeutung unter besonderer Beriicksichtigung von Umweltbeeintrachtigngen, Abfall-RecyclingAltlasten 2 ,Aachen (1991). 4 J. Trankler and I. Walker, Zukiinftige Venvertbarkeit von Bauschutt, Proceedings of the workshop: Forschungsnetz Abfallwirtschaft und Altlasten des Landes NordrheinWestfalen, LWA, Dusseldorf (1992) 31. 5 H. Martens, Neue Verfahrenstechnik in der Bauschuttaufbereitu, B. Bilitewski (ed.) Recycling von Baureststoffen EF-Verlag, Berlin (1993) 239.

Environmental Aspects of Construction with Waste Materials J.I.I.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) el994 Elsevier Science B. V. AN rights resewed.

633

QUANTITIES AND QUALITIES OF MUNICIPAL WASTE INCINERATOR RESIDUES IN THE NETHERLANDS

J.G.P. BORN Waste Processing Association, P.O. Box 19300,3501 DH Utrecht (The Netherlands)

ABSTRACT With an annual combustion capacity of 2.6 Mt the Dutch Municipal Waste Incinerators (MWls) produce some 570 kt of bottom ash, 90 kt of fly ash and some 6 kt of residues stemming from Air Pollution Control (APC) devices. With the government policy on Municipal Solid Wastes (MSW) aiming at incineration of the combustible fraction rather than land-filling, the production of MWI-residues will almost double by the end of this decade. As the quality of these residue determines whether (and in what way) they can be applied usefully or have to be disposed of, much attention is paid to its physical and environmental properties. Knowledge of (fluctuations in) quality also provides a basis for choosing the best technique for quality improvement, which may be imminent due to tighter legislation in the near future.

INTRODUCTION The Waste Processing Association (Vereniging van Afvalverwerkers) is the branch organization in the Netherlands in the field of waste incineration, landfilling and composting. The aim of the Association is look after its members’ interests with regard to an ecologically-sound waste disposal in the broadest sense of the word. This aim is achieved, among other things, by consultations, promotion of research, collective pursuit of quality improvement, exchanging knowledge and experience, and also by initiating training etc. 1.

The Waste Processing Association came into existence in order to approach the problems in the field of final waste processing collectively. The Association reached its present form at the end of 1991, when VEABRIN, the association of waste incineration installation operators, was broadened to include operators of landfilling sites and composting facilities. All Dutch MWls are member of the Waste Processing Association. The objective of the Waste Processing Association with respect to MWI-residues is to have them re-used in a responsible way as a replacement for natural materials; thereby reducing the need for excavation of natural resources and limiting the space for land-filling. As a result already > 90% of the bottom ash and 25% of the fly ash have found a useful application in earth and road construction in the Netherlands. This paper gives an overview of the Dutch situation with respect to the quantities and qualities of residues of Municipal Waste Incineration.

634 QUANTITIES OF INCINERATED WASTE In 1992 a total amount of 2.6 Mt of MSW has been combusted in the Netherlands using the 10 MWls that were in service by that time. The tonnage of incinerated municipal waste has gradually decreased over the years 1988 - 1992. Partly this is due to the closure of several MWls. In addition there has been an continuous increase of the calorific value of the MSW in that period, resulting in decreasing effective capacities of the MWls. It is generally accepted that the increase in calorific value is caused by the increasing amounts of separately processed fruit, vegetable and garden (FVG) waste, resulting in a relatively dry remaining fraction to be combusted. Graphically the contribution of these two effects on the amount of incinerated waste is shown in Fig. 1. 2.

With respect to the future, the total combustion capacity in the Netherlands for municipal waste will increase to an expected level of 5.5 Mt/y by the year 2000. This number is based on known initiatives for new MWls to be constructed in this decade to comply with the Dutch policy to avoid landfilling of combustible waste. In 1993 the new MWI of Amsterdam has replaced the smaller old one. At the moment three other MWl’s are under construction. Finally several older MWl’s will be retrofitted with a concomitant increase in capacity. Summation of these initiatives results in the forecast given in Fig. 1.

TOTAL MWI CAPACITY (STATUS 1992)

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

IN SERVICE

YEAR CLOSED

=TO

BE BUILT

Fig. 1 Quantities of incinerated waste in the Netherlands. In general combustion of Dutch MSW results in ca. 22% ( m h ) of MWI bottom ash, 2.5% (m/m) of scrap metal, 3% (mlm) of fly ash and varying amounts of APC-residues depending on the type of APC-devices that are installed (wet scrubbers: 0.2% - 0.8% ( d m ) filtercake; (semi-)dry lime-injection: 2% (dm)).

63 5 QUANTITIES AND QUALITIES OF MWI BOlTOM ASH Quantities of Dutch bottom ash In the Netherlands raw bottom ash is treated prior to useful application. This treatment (upgrading) consist of magnetically removing scrap material and subsequent sieving to remove all components with a diameter larger than 40 mm. Usually the uncombusted material present in the fraction > 40 mm is recycled into the incinerator. At most MWls large inert parts of this fraction are crushed and consequently sieved again. The scrap is recycled in the steel industry. At some MWls the non-ferrous metal fraction is removed and recycled as well. Throughout this article the word bottom ash refers to the residues resulting from the treatment as denoted above. 3. 3.1

Since over the last years the relative amount of bottom ash per ton of waste has remained essentially the same at 22 - 23 % (m/m), the absolute production figures have diminished parallel to the declining quantities of combusted waste (vide supra). From Fig. 2 it can be inferred that the production dropped from some 720 kt/y in 1988 to 570 kt/y in 1992.

MWI BOTTOM ASH PRODUCTION, APPLICATION AND DISPOSAL I I I

1989

o DISPOSAL

1990

1991 1992 YEAR APPLICATION I IPRODUCTION

Fig. 2 Quantities of bottom ash in the Netherlands. As Fig. 2 visualizes, on average more than 95% of the bottom ash finds a useful application in the Netherlands. Typical applications are earth and road construction as bottom ash is suitable for use as a roadbase stabilization layers and/or as an embankment material. Given the size of several embankments - up to 500,000 metric tons - prepared with MWI bottom ash, it sometimes appears to be necessary that one or more MWls keep large amounts of bottom ash in stockpile until the (next) year in which delivery is required. This phenomenon occurred in 1989 and in 1992 and explains the irregularities in the bardiagram presented in Fig. 2.

636 Certification of Dutch bottom ash Quality control and quality assurance of the produced bottom ash, in recent years awarded by certification of 55% of the Dutch bottom ash, can be regarded as the basis for its present successful useful application. The physical properties of certified bottom ash are specified based on guidelines given by the CROW (abbreviation for: "Stichting Centrum voor Regelgeving en Onderzoek in de Grond-, Water- en Wegenbouw en de Verkeerstechniek) in 1988. An independent laboratory (KOAC) carries out the regular test to see whether the MWI bottom ash meets these specifications. The environmental specifications (i.e. leaching behaviour) are inspected by another independent laboratory (Intron) and should comply with the present Dutch regulations ("IPONROM-richtlijn", 1986). Samples are taken 1-2 times a day during a production period of two weeks, directly after removing the scrap and the components larger than 40 mm. Depending on the throughput of the incinerator and - hence - the production of bottom ash, sampling is performed continuously or intermittently. 3.2

Apart from specifications for the bottom ash itself, the operation of the installations must obey certain rules. With respect to the environmental quality of the bottom ash the following rules have to be obeyed: The MWI must be operated according to the present regulations and authorizations Only municipal solid waste or comparable wastes are accepted for combustion Chemical wastes are excluded from the process (except for one installation, which is allowed to process a limited number of wastes, submitted to tight regulations). MWI bottom ash should be stored for at least 6 weeks The Bottom ash should be free of fly ash The environmental quality of the MWI bottom-ash is periodically monitored by an independent laboratory which reports the results to the certifying authority. Concerning the physical quality of the bottom ash it is required that: Uncombusted material is segregated from the MWI bottom ash and recycled into the oven Components larger than 40 mm are removed by sieving The majority of the iron scrap material is removed The physical properties of the bottom ash are periodically monitored by an independent laboratory which reports the results to the certifying authority. Irregular inspections of the certifying institute (KIWA) make sure that these specifications are met at all times.

-

-

-

Qualities of Dutch bottom ash Table 1 gives an overview of the average, maximum an minimum values of the physical parameters relevant for certification. As the quality control of MWI bottom ashes is performed for several years now, an ever growing set of data is being generated. By presenting some of these data concerning the physical properties of MWI bottom ashes it is shown that this material can be characterized as well defined.

3.3

63 I Table 1

Physical properties of Dutch bottom ash.

CERTIFICA I N LIMITS NONCEMENTBOUNDED 0% 0 - 10% 10-

40%

40 - 70% 92 - 100%

MEASURED VALUES AVERAGE MINIMUM MAXIMUM

20.5%

562

1 0 - 40% 40 - 70%

92 - 100% > = 0.65

>= 0.65 c 5% c 6% c 2%

PARAMETER

I

c 2%

In 1986 the federal government formulated the so-called "IPONROM-directive" in which guidelines for the useful application of MWI bottom ash were given. The IPONROMdirective uses leaching behaviour as a criterion to decide whether bottom ash is to be applied usefully. The limiting values have already been listed in section 3.2.Examination of the actual leachability of the bottom ash relative to these values is performed by means of the cascade leaching test (NEN 7343). This test implies a fivefold sequential extraction; each step at US = 20, resulting in a final US = 100. As for most elements the highest leaching occurs in the first step, Table 2 presents the results at US = 20 only (note that the obtained leachate concentrations obtained by every separate step have to comply with the limits of the IPONROM-directive). Table 2

Leaching behaviour of Dutch bottom ash (cascade test).

3,5 2,O 245 1620 1250 90 850

491 491 491 491 491 491 491

The Dutch environmental legislation concerning building materials is currently under review. A decree concerning the minimum environmental quality of building materials as well as guidelines with respect to application is in preparation for some years now ("Bouwstoffenbesluit"). Although still not definitive, it has become clear that the principal criterion for the environmental quality of building materials will be their leaching behaviour, to be established using the column-test at US = 10 (NEN 7343). Faced with this imminent change in leaching test and criteria, the Waste Processing Association embarked in an

63 8 additional quality control programme, parallel to that already in progress. Table 3 summarizes the results of these leaching test, relative to the expected limits. Table 3

Leaching behaviour of Dutch bottom ash (column test).

i

From Table 3 it can be inferred that in particular the leachability of Copper (Cu) and Molybdenum (Mo) deserves attention in terms of quality improvement. Anticipating on an enacted Building material decree by 1997, the Waste Processing Association aims at quality improvement in order to reach the N,-status (cf. Table 3) for the majority of the bottom ash by that time. The level of inorganic micro-constituents in building materials is not an issue any more in the Netherlands as far as legislation is concerned. However it still is the criterion to discriminate between hazardous and non-hazardous waste. Furthermore, systematic knowledge of the composition of bottom ash is an valuable tool for choosing a appropriate quality improvement technique. Therefore, the level of some micro-contaminants in MWI bottom ash is monitored systematically for several years now (Table 4). Table 4

Levels of micro-contaminants in Dutch bottom ash. COMPOSITION OF EOlTOM ASH (AQUA REGIA, NEN 6465) MEASURED VALUES AVERAGE MINIMUM MAXIMUM

6 4 124 21 69 12 105 1312 37 1858 13092 2867

0,5 0,l 53,O 480,O 3.7 22,o 35,O 3,O 550,O 3865 1600

-

-

13 25

-

5500 470 5200 21100 5720

n 76 76

-

76

33

639 Note that generally speaking MWI bottom ash is not a hazardous waste. Only in some rare cases the hazardous waste limits (as stipulated in the Dutch decree called "BAGA") are exceeded. A closer examination of the speciation of the relevant metal in those cases has shown that the speciation is mainly at zero valence (metallic). Metallic phases are usually exempt of the hazardous waste composition criteria and - as bottom ash imposes high pH at the leachate - do not leach substantially.

QUANTITIES AND QUALITIES OF MWI FLY ASH Quantities of Dutch flv ash Parallel to the decrease in the tonnage of combusted MSW over the last years, the production of fly ash has diminished from almost 100 kt in 1989 to slightly over 80 kt in 1992. The relative amount of fly ash per ton MSW has remained constant at 3.2% (mlm).

4. 4.1

MWI FLYASH PRODUCTION, APPLICATION AND DISPOSAL

-3 110 100 90 25 80

70 60 0 50 2 40 I-

5

a

30 20 10 0 1989

1990

1991 YEAR 13APPLICATION 0DISPOSAL

1992

PRODUCTION

Fig. 3 Quantities of fly ash in the Netherlands. Apart from the above mentioned decline of production Fig. 3 also visualizes, the extend to which fly ash has found an useful application in the Netherlands. On average over 25% of the fly ash is used as a filler in asphalt for road construction. Lacking other application routes, the remaining fraction of the fly ash is landfilled. Leqislation concerninq fly ash related to its environmental quality Dutch legislation designates MWI fly ash as a hazardous waste. Only in case no other treatment is available the direct useful application of fly ash as a raw material in an industrial process is allowed. The use as a filler in asphalt for road construction fulfils these requirements. The Dutch decree concerning hazardous waste (BAGA) designates all residues of 4.2

640 MSW combustion as hazardous, an exempt has been made for bottom ash, justified by the composition of bottom ash (cf. section 3.3).lmmobilisation of waste to reduce its leaching behaviour is still not legitimate in the Netherlands. Therefore, the only law-abiding option to produce a (raw) building material from hazardous waste is to reduce the levels of contaminants below the relevant limits. Hence it is of interest to monitor the levels of micro-pollutants in MSW fly ash. In 1993 the Waste Processing Association commenced a quality control programme for MSW fly ash. Results are not yet available, however. Gathering of the data from previous years resulted in the overview as listed in Table 5.

-

-

Table 5

Levels of micro-contaminants in Dutch fly ash.

35 236 260 244 1 21 114

-

-

1 200 -

9000 337 1270 3218 1909 430 983 11414 6500 59 2500

83 122 83 122 83 39 122 122 122 122 44

In the absence of sufficient options for useful application MSW fly ash has to be disposed of by means of landfilling. Quite recently the federal government defined criteria for landfilling hazardous waste based on the leachability of the contaminants present in these waste materials. The higher the leachability, the more stringent isolating measures have to be taken. For MWI residues three relevant categories of hazardous wastes and landfilling sites are accessible: C,-Category: Strongly leaching waste materials which can only be processed under strict regulations and by means of special landfilling facilities. In practice the regulations are interpreted by handling and landfilling the waste material dryly to prevent percolate being formed. Nevertheless a C,-landfill is provided with facilities for the collection and purification of the percolate (if any). C,-Category: Medium leaching waste materials which can be processed simultaneously with other industrial waste on monitored landfills. The protective measures at the C,-landfill consist of double top and bottom liners and facilities for the collection and purification of the percolate. C,-Category: Slightly leaching waste materials and industrial waste which are to be

64 1 processed simultaneously with MSW using existing monitored landfills. In principle this category is only of a temporary nature. The C,-landfill is equipped with top and bottom liners and facilities for the collection and purification of percolate. Leaching behaviour of the residues is the main criterion that determines whether residues are to be landfilled under C,-, C,- or C,-conditions. In Table 6 the leaching limits (U, and U,) that discriminate between the hazardous waste categories are listed, together with the measured leaching behaviour of Dutch MSW fly ash. Once the leachability of at least one component in the waste exceeds the U,-limit, it is to be disposed of under C,conditions. Similarly, medium (> U, but < U,) leachability requires disposal using at least C,-conditions, whereas mild leachability (< U,) allows C,-conditions.

Table 6

20,OO

25,OO

Leaching behaviour of Dutch fly ash.

60,OO 3,727 C2

0,0026

-

2,543 C3

0,9956

-

19,484

13

0,0003

8

280,OO N.D. -

From Table 6 it can be derived that the majority of MWI fly ash, based on its leaching characteristics should be disposed of under C,-conditions. However, the only C,disposal available in the Netherlands does not accept more than 5,000 ton/y of a specific waste stream of one client. Hence, MWI fly ash is landfilled at other sites using interim measures to ensure the integrity of the environment.

QUANTITIES AND QUALITIES OF MWI APC RESIDUES Quantities of Dutch APC residues In 1989 the federal government formulated stringent federal limits (Richtlijn verbranden '89) to air emissions by MWls in the Netherlands. These limits were to be met 5. 5.1

642 by November 30th, 1993; later to be postponed to January 1st 1995. As a result all Dutch MWls that planned to continue business after that date invested massively in new installations or retrofitted existing MWls with additional APC-devices. Consequently, the amount of APC-residues increased rapidly over the last years (Figure 4) and will continue to do so for the next several years. Whereas in 1988 2 MWls produced a total of 230 tons of APC-residues, this number has risen to 5,600 kt in 1992, produced by 5 MWl’s. In 1993 3 additional major MWl’s have started up their APC-devices. Hence, the anticipated production of APC-residues in the Netherlands for 1993 will mount to 30 kt.

MWI FGC RESIDUES PRODUCTION, APPLICATION AND DISPOSAL

Fig. 4 Quantities of APC-residues in the Netherlands. After having solved the air emissions against considerable costs the members of the Waste Processing Association are now faced with the challenging task to dispose of the APC-residues in an economical way whilst preventing unaccepted contamination of the Dutch soil and/or groundwater. To date no useful application of APC-residues has been established, implicating that the entire Dutch production is landfilled. 5.2

Environmental uualitv of APC-residues Dutch legislation with respect to MWI APC-residues is similar to that concerning MWI fly ash, i.e. APC-residues are defined as hazardous waste. Before relating the actual composition of Dutch APC-residues to the threshold values of the Dutch decree concerning hazardous waste (BAGA), the several types of APC-residues are discussed briefly. The majority of the APC-devices that are installed at Dutch MWls consists of a double wet scrubber. In the initial acid scrubber (pH = 1) most of the heavy metals are trapped together with HCI and HF. The second scrubber is kept basic (pH = 8) by adding Ca(OH), or NaOH as to trap most of the SO, and those heavy metals that passed the

643 initial scrubber. In all cases both waste water streams are combined and neutralised, usually with Ca(OH),. Subsequently, after adding a flocculation and precipitation agent, the precipitate (containing the hydroxides of the heavy metals) is separated from the filtrate (containing the bulk of the soluble SO,= and (21.). The precipitate is dehydrated to about 40% dry weight and commonly known as "filtercake". Filtercake is produced by the MWls 4, 5 and 10 as listed in Table 7.

Table 7

Levels of micro-contaminants in Dutch APC-residues.

26667 > BAGA

14270 > BAGA

6500 > BAGA

34402 > BAGA 6286 > BAGA

5650

448 > BAGA

MWI 1 of Table 7 uses the so-called semi-dry lime injection technique. After having removed the fly ash using an electrostatic precipitator a slurry of water, Ca(OH), and active carbon is injected into the flue gas. The resulting dry reaction product (mainly Ca(OH),, CaCI, and spent active carbon) is trapped using a fabric filter.

Finally it should be noted that the limits for the quality of waste water to be drained off varies considerably in the Netherlands. Some new MWI (not listed in Table 7) are not allowed to drain of waste water containing substantial amounts of SO[ and CI'. These new installation will be equipped with wet scrubbers in conjunction with a spray dry adsorber. In the Netherlands APC-residues are disposed of by means of landfilling. The criteria for landfilling are equal to those for MWI fly ash. As with fly ash the leachability is to be validated using the column test (NEN 7343) at US = 1. In Table 8 the leaching limits (U, and U,) are listed, together with the measured leaching behaviour of Dutch MSW APC residues. Based on Table 8 most APC residues should be disposed of at C,-conditions.

644 Table 8

10,OO 25,OO

Leaching behaviour of Dutch APC residues.

40,OO 280,OO

4,325 77,455 C2

5-13

0,072 11,373 2,473 C3

33,072 C3 8,607

N.M. 2,088

1,055 C2 5,005 C2

0,005 0,731

3-13 3140

203746

13490

FUTURE DEVELOPMENTS The data presented in this paper have been gathered as part of an inventory study on the state of the art for upgrading techniques for the quality improvement of MWIresidues. The results of this inventory are presented elsewhere in this book of abstracts of WASCON '94. Briefly, the following options seem viable: Bottom ash: 1) tighter acceptance criteria for the waste feed 2) separation of grate-siftings and/or boiler ash from bottom ash 3)washing of bottom ash, possibly in conjunction with 4) induced aging of the bottom ash Fly ash: 5) immobilization using an inorganic binder 6) melting aiming at a produce with an added value (La:energy, economy) 7) artificial gravel production APC-residue 8) immobilization using an inorganic binder Currently research programmes in order to evaluate all these options have been launched by (members of) the Waste Processing Association.

6.

ACKNOWLEDGEMENT This paper is based on the results of an inventory study of existing data on MWI residues supported by the National Research Programme for the Recycling of Waste substances (NOH), project number 353320/1910. NOH is administered by the Netherlands Agency for Energy and the Environment (Novem) and the National Institute of Public Health and Environmental Protection (RIVM). The data on the chemical composition of MSW fly ash were a kind gift of dr. J.B.M. Hudales (Vulstof Combinatie Nederland B.V.).

7.

Environmentol Aspects of Construction with Woste Motenoh J.J.J.M. Goumons, H A . von der Sloot and Th.G.Aolbers (Editors) a1994 Elsevier Science B.V. All rights reserved.

645

UPGRADING TECHNIQUES FOR THE QUALITY IMPROVEMENT OF MUNICIPAL WASTE INCINERATION RESIDUES

F.J.M. Lamersa and J.G.P. Bornb aKEMA Netherlands BV, P.O. Box 9035, 6800 ET Arnhem, The Netherlands %VAV (Waste Processing Association), P.O. Box 19300, 3501 DH Utrecht, The Netherlands Abstract An inventory was made on the state of the art for upgrading of Municipal Waste Incineration (MWI) residues by primary methods and post treatment systems. The main goal for upgrading of MWI residues is the reduction of the leaching rate of the particular residue and a secondary goal is the improvement of the utilization quality. Based on leaching rate changes, technical and economical criteria, the most viable systems seem to be: primary measures and washing / aging for MWI bottom ashes; vitrification and immobilization for MWI fly ashes and immobilization for MWI flue gas cleaning (fgc) residues. 1. INTRODUCTION

Nowadays in the Netherlands, about 750,000 tons of residues from the incineration of municipal waste (MWI residues) are generated yearly. It is expected that this number will be doubled in the next ten years. The MWI residues consist of bottom ash, fly ash, flue gas cleaning (fgc) residues and spent carbon. Because of new legislation in the Netherlands, restrains on the utilization and disposal of MWI residues are upcoming; these restrains are related to the leaching rate of the MWI residues. In the near future, quality improvements of MWI residues will therefore become necessary, considering the growing supply of MWI residues and the tightening of environmental demands. In anticipation of the necessary quality improvements, a literature study has been performed on the state of the art for the effective upgrading of MWI residues [I]. The upgrading methods were evaluated on the following criteria: stage of development, technical feasibility, environmental improvements, utilization potential of the upgraded product and costs. The results of the study are presented in this paper.

646 2. MWI BOlTOM ASH 2.1. General remarks At the moment, the main part of the MWI bottom ashes is utilized as embankment materials for roadbuilding. As a consequence of the enforcement of the Building Materials Decree (BMD), environmental restrictions will arise. The leaching rates of molybdenum and copper will likely exceed the limits of the future BMD. Figure 1 and 2 show that for a large part of the MWI bottom ashes, the N2 leaching requirements for utilization will probably not be met [2,3]. The goal for upgrading of MWI bottom ashes is to meet the N2 requirements of the BMD consistently. Both primary and post treatment techniques are available for the upgrading of the A survey of upgrading methods is shown in environmental quality of MWI slags [4,5]. table 1. In the following sections, several primary measures and post treatment techniques are shortly discussed. frequency

frequency

1 2 1 - 7 -

~-

Boundary N2

I 2

3

4

5

6

r

8

g i o i i

leached amount, mglkg

Fig. l a Frequency distribution of the copper leaching rate of MWI bottom ashes

"

0.30.6 I 2

3 4

5

6

7

8

9 10 11

leached amount, mglkg

Fig. l b Ibid., molybdenum leaching rate

2.2. Upgrading of MWI bottom ashes by primary measures

Acceptance criteria It is significant, that the molybdenum leaching rate of MWI bottom ashes is dependant of the MWI where the bottom ash is generated. It is assumed that in the MWl's with high molybdenum leaching rates, a certain amount of molybdenum containing waste is accepted. If this turns out to be true, the molybdenumleaching rate can be significantly reduced through tightening of the acceptance criteria for municipal waste. Research into this aspect is being performed.

647

Table 1 Upgrading measures for MWI bottom ashes Primary methods

- Tightening of acceptance criteria for municipal

Acceptance

waste ~~

Post treatment methods

~

~

~~~

0, - NO, measures lay out of the incinerator residence time in the burning zone windsift at the end of the burning zone

Measures during the burning process

-

Separation in plant

- separation of bottom ash and boiler ash - separation of bottom ash and grate siftings

Separation measures

- conventional upgrading (separation at 40 mm, ferro separation)

- non ferro separation - separation of the fine fraction ( c 2 mm) Washing

/ aging

Immobilization Thermal treatment

- sintering - vitrification

Measures during the burning process A combination of oxygen dosage under the grate and nitrogen dosage above the burning zone, appears to influence the copper leaching potential significantly.Through the oxygen dosage, the temperature in the grate bed is increased, leading to an optimal burn out, better sintering and reduction of leaching (up to 10 times for Cu) [6]. The nitrogen is necessary, to prevent too high temperatures rises. For new MWl's, this measure could be considered. Optimum burn out and sintering can also be reached through an optimal incinerator design and through a maximum residence time of the slag in the burning zone [5]. A so called "burn out beam" [7], that can be easily constructed, operates like a sort of windsifter at the end of the burn out zone; because fine organic particles are blown back into the burning zone, the loss on ignition of the bottom ash can be reduced significantly. It is expected that this measure will work optimal for an MWI with low contents of grate sifting. Separation measures In the literature, the positive effect of the separation of boiler ashes from bottom ashes on the leaching behaviour is stated [El. Strange enough, in the Dutch practice, the bottom ashes of the MWl's where this measure was performed, did not show significantly better leaching behaviour than others. In any case, the N2 limits were not met. The separation of grate siftings from the bottom ashes can lead to lower copper leaching [8],probably because the content of digestible carbon, that can act as a complexing agent, is diminished significantly.

648 2.3. Upgrading of MWI bottom ashes by secundary measures

Separation measures The intensive conventional upgrading of MWI bottom ashes (separation and crushing of grains > 40 mm, intensive iron separation), will lead to a technically good bottom ash with a low iron content and a low content of unburnt organic parts. This kind of post treatment does not lead to a bottom ash that meets with the leaching limits of the Building Materials Decree. Non ferro separation from bottom ashes leads to an optimized slag quality for cement stabilized slag foundations (expansion reactions are prevented). The leaching behaviour is not improved, since only coarse non ferro’s are removed [9]. About the hypothesis, that the separation of fine particles diminishes the leaching from the bottom ash [lo] the literature is controversial. We feel that on the following grounds this measure should be rejected: 1) technically it is difficult to operate sieves with an opening < 4mm, if the material is not dried; 2) the bottom ashes contain 30 50% of fine fraction, that should be dumped as a waste material after the separation. Washing / aging Washing of the bottom ashes can lead to a substantial reduction in the leaching of both copper and molybdenum [l 11. The suitable washing of bottom ashes directly after their generation appears to lead to a product that meets with the N2 limits of the Building Materials Decree. An aging period prior to washing of the bottom ashes even seems to improve the leaching characteristics.A drawback of washing is the amount of fine sludge that will be generated. The aging of slags leads to a reduction of copper leaching. The influence on molybdenum is unclear [ 121. Immobilization Immobilizationof bottom ashes is not practized, except in situations where the slag is dumped together with MWI fly ashes and / or fgc neutralization sludges. Thermal treatment Sintering and vitrification of bottom ashes lead to a product with a strongly improved leaching behaviour. Those techniques are so energy intensive and so expensive, that it is generally recommended not to use them. 2.4. Conclusions

To realize sufficient quality improvement in MWI bottom ashes to meet with the N2 limits of the Building Materials Decree, in an economically interestingway, the following techniques can probably be used, sometimes in combination. primary measures - acceptance criteria (Mo) - measures during the burning process (02/N2) - separation of grate sifting and boiler ash from bottom ash post treatment - washing - aging

649 3. MWI FLY ASH

3.1. General remarks Utilization of (part of) the MWI fly ash At the moment, about 25,000 tons of Dutch MWI fly ash are utilized as a raw material for asphalt fillers. Although this utilization is sound according to the building materials decree, (the leaching of asphalt with this filler, meets with the V1 limits), there is discussion about the continuation of the use of MWI fly ash as an asphalt filler. The rest of the MWI fly ash is disposed. Environmental quality of M WI fly ash Based on its very high leaching rate of inorganic hazardous components, MWI fly ash is classified as a chemical waste material, that has to be disposed in the strictest disposal regime (C2), at high costs. Aside from the leaching rate of MWI fly ash, its content of dioxins is regarded as a problem by some parts of the society. Disposal The disposal regimes in the Netherlands are called C2, C3 and C4. C2 is the strictest and C4 the mildest regime. The leaching of inorganic hazardous components from waste materials is decisive for their classification. Starting from 1996, it is forbidden to dispose MWI fly ash in an untreated form. Upgrading measures Taking into account the growing quantities of MWI fly ash that will be generated yearly in the future, upgrading measures are sought that offer an environmentally and economically feasible alternative for disposal at C2 level. The goal for these upgrading measures is at least disposal at a milder regime and if possible, utilization as a building material. In table 2, the known upgrading measures are listed [4, I]. They are shortly discussed. 3.2. Wet cleaning

Washing + disposal By washing the MWI fly ash with neutral water, the leachable chloride content is removed. By washing with slightly acid water, some heavy metals are removed [4]. Judging from the literature, washing of MWI fly ash does not lead to sufficient upgrading to reach the C4 level. Washing is promoted exclusively, to upgrade the disposal regime of MWI flyashes. Washing results in mass increase of the MWI fly ash (by the water that is taken up) and in an increased quantity of FGC neutralizing sludges. Washing, pelletizing, refeed in the MWI In one specific washing process [13], the wet MWI fly ash is dried through filterpressing, after that the moist ash is mixed with cement and pelletized; the pellets are fed back into the MWI. The results of the leaching tests of the MWI bottom ash with

650

Table 2 Upgrading measures for MWI fly ashes Wet cleaning

-

Removal of dioxins

- reducing conditions, 400 - 500C - oxidizing conditions, 600 - 700C

immobilization

-

washing t disposal washing, peiietizing, refeed in the MWi microbioloaicai cieanina

immobiiization with inorganic binders

- combination with fgc neutralizing sludge - low T artificial gravel production (through pozzolanic reaction)

- chemical fixation

-

immobilization with organic binders

Sintering techniques

- sintering techniques - aiinite cement

Vitrification techniques

-

melting

- melting under reducing conditions - plasma techniques

pellets, are comparable with the leaching results of normal MWI bottom ash. It is still unclear wether these "combined" bottom ashes meet with the limits of the Building Materials Decree. Microbiological cleaning In the past years a study has been performed into the possibilities to use microbiologicalcleaning for MWI fly ashes. The results of the study indicated that there was only minimum upgrading of the leaching behaviour of the fly ash; furthermore a large quantity of sludge was generated, that has to be dumped at a C2 disposal. 3.3. Removal of dioxines

By heating the MWI fly ash at 300 - 400C (under reducing conditions) or 600 - 700C (oxidizing), dioxins can be destroyed. During the oxidizing process, also mercury is removed. The processes for removal of dioxins cannot lower the leaching rate of MWI fly ash. They can possibly be used as a pretreatment technique for cold immobilization. 3.4. Immobilization

Immobilization with an inorganic binder In foreign countries, immobilization of MWI fly ash with inorganic binders (such as The portlandcement, blastfurnace slag and waterglass) is practiced commercially [14]. purpose of the immobilization is the environmentally safe disposal of MWI fly ashes. The immobilized MWI fly ash is physically encapsulated and chemically stabilized. The immobilized and stabilized MWI fly ash is allways disposed. For the Dutch situation, the MWI fly ash can probably be upgraded to a C4 level disposal, if the correct recepture

65 1

is used. There is no certainty that products can be made that meet with the limits of the Building Materials Decree and with the technical demands for utilization. The actual level of upgrading is dependant on the dose and the type of the immobilization binder. Possibly, high dosages of binder have to be utilized, which will also realize in large volume increases, which can be considered as a drawback. An advantage of immobilization is the low price level. With very limited information on the actual leaching behaviour of immobilized products, we still assume that in the majority of cases, diposal costs have to be added to the immobilizing costs. Immobilization of MWI fly ash combined with FGC neutralizing sludges FGC neutralizingsludges from MWl’s have a surplus in sulfide; this can be used for the stabilization of MWI fly ash. Often an inorganic binder has to be added. In Germany, Switzerland and Austria, this combined immobilization is practiced at some disposal sites, for the purpose of environmentally safe dumping [15]. From the literature, we conclude that is difficult to reach the C4 level, if not sufficient quantities of binder are used. Low T artificial gravel Low T artificial gravel production has been tested for gravel that contains about 35% of MWI fly ash. Concrete that contains this type of gravel, meets with the strictest limit of the Building Materials Decree. Economically it is more interesting to produce a gravel that contains more than 75% of MWI fly ash. Regretfully that option has not been tested. Immobilization with organic binders The immobilization with organic binders (the utilization in asphalt fillers is not meant here) is based on an optimal physical encapsulation of the MWI fly ash. No chemical stabilization occurs. The costs are so much higher than for immobilization with an inorganic binder that this is no real option for MWI fly ash. 3.5. Sintering

Sintering techniques Sintering of MWI fly ash probably will not lead to a product that can meet the N2 or the V2 limits of the Building Materials Decree. In the past, some efforts have been done to utilize MWI fly ash in sintered gravel; they were not continued, as the gravel with MWI fly ash (25%) showed an unacceptable leaching rate. Alinite cement Alinite cement is a special cement that is produced from MWI fly ash and dry flue gas cleaning residues. Although laboratory tests showed a favorable leaching behaviour, there are still doubts about the leaching rate of the product at an industrial scale. Additionally it is felt that the marketing possibilities for alinite cement in the Netherlands are very small. The cost price is high compared to immobilization.

652 3.6. Vitrification techniques

Melting techniques The final product that results from the treatment of MWI fly ash in a melting furnace, is a granulate that has a very low leaching rate (it meets the N1 limits of the Building Materials Decree). The hazardous inorganic components are partly removed and partly immobilized in the granulate. The dioxins are completely destroyed [16]. Melting techniques + reduction The difference with "oxidizing" melting techniques is the possibility to separate all hazardous inorganic components. The reduced metal phase can possibly be sold [16, 171. Plasma techniques The granulates from plasma techniques and melting techniques are comparable. A general remark about all electric vitrificationtechniques is that they have a very high energy consumption (ca 1MWh/ton for melting techniques and 2MWhlton for plasma

techniques). The costs are uncertain because in the available literature, investment costs are often unclear; the reported costs of melting vary between NLG 250 and 1,000.=. Because of the high energy consumption and the high costs, these techniques should only be considered when a high grade market for the granulate is available and certain. 3.7. Conclusions

In the study, the following was concluded: To realize sufficient quality improvement in MWI fly ashes to meet with the C4 limits for disposal or with the limits of the Building Materials Decree, in an economically interesting way, the following techniques can be used, in order of decreasing priority: - immobilizationwith an inorganic binder (probably C4) - melting techniques and melting techniques t reduction, if the market for the granulate is available (N1 utilization, destruction of dioxins) - low temperature artificial gravel production - joint immobilizationwith neutralizing sludges 4. MWI FLUE GAS CLEANING NEUTRALIZING SLUDGES

4.1. General remarks

In the past few years, wet flue gas cleaning has been installated at several Dutch MWl's. There is only limited information about the quality of FGC neutralizing sludges in the Netherlands; because of that only tentative remarks can be made. It appears that the FGC sludges have a varying quality. Based on the the leaching rate, FGC neutralizing sludges are C2 waste materials and sometimes C3 waste materials. FGC neutralizing sludges are disposed at high costs. Upgrading must lead to a milder disposal regime. Upgrading measures are summarized in table 3 [17].

653 Table 3 Upgrading measures for MWI FGC residues

-

Immobilization

immobilization with inorganic binders - combination with MWI fly ash - low T artificial gravel production (through pouolanic reaction)

Vitrification techniques

- melting - melting under reducing conditions

4.2. Immobilization

Immobilization with inorganic binders Immobilization can possibly result in a product that meets the limits of the C4 disposal class. Immobilization with sulfur is also considered. Because of the high contents of chlorides, sulfates and alkalies in the FGC neutralizing sludge, immobilizationwill be even more difficult than for MWI fly ashes. The costs will therefore be higher. Combined immobilization with MWI fly ash In Germany, Switzerland and Austria, this combined immobilization is practiced at some disposal sites, for the purpose of environmentally safe dumping, often with addition of cement. As stated earlier, we conclude that it is difficult to reach the C4 level, if not sufficient quantities of binder are used. Low T artificial gravel production Theoretically, possibilities exist for the preparation of artificial gravel. 4.3. Vitrification MWI FGC neutralizing sludges could possibly be treated in a vitrification plant, together with MWI fly ash. Because of high chloride and alkalies emissions, this option is not recommended. 4.4. Conclusions

For MWI FGC neutralizing sludges, the main option for upgrading is immobilization. Immobilization with an inorganic binder is preferred, but combined immobilization is also possible. 5. EVALUATION

In this article, an overview was given of the present state of the art on upgrading measures for MWI residues. No reference was made to new municipal waste processing methods such as pyrolysis. A selection was made of techniques that could possibly be used in the future. The evaluation was based on literature data. Further

654

practical R&D is necessary to be able make a founded choice for the future upgrading approach. 6. ACKNOWLEDGEMENT

The financial support (contract number 35332011910) of the National Research Program for the Recycling of Waste Substances, which is jointly managed by the Netherlands Agency for Energy and the Environment and by the National Institute of Public Health and Environmental Protection, is gratefully acknowledged. 7. REFERENCES

1 KEMA, (in Dutch) Upgrading methods for MWI residues, NOH publ. 93028, 1993. 2 W A V , Internal data technical/environmental quality of MWI residues, 1993. 3 W A V , (in Dutch) Residual materials from municipal waste incineration, NOH publ. 93029, 1993. 4 M. Faulstich and D.Zachaus. Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 1. 5 D.O. Reimann, Mull und Abfall 9/92, (1992) 609. 6 F. Rampp et al., VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 13, 1993. 7 D.O. Reimann, VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 9, 1993. 8 J. Vehlow, Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 161. 9 Feniks recycling Maatschappij, (in Dutch), Expansion of MWI slags, reports 91.009/n/5 and T&A N/092/me/wdw/5 10 J.A. Stegemann and J. Schneider, Proc. WASCON conf, Maastricht, nov 1991, Elseviers studies in environmental science 48, (1991) 135. 11 TAUW, Research into the possibilities of upgrading of MWI bottom ashes by washing processes, TAUW report 51161.50, 1989. 12 U. Lahl, Ruckstande aus der Mullverbrennung, EF Verlag Berlin (1992) 609. 13 J. Vehlow et al., Mullverbrennung und Umwelt 3, EF Verlag Berlin (1989) 687. 14 CSO, (in Dutch) The "state of the art" of immobilisation, report nr 090.90, 1990. 15 H . 4 . Ponto and J. Demmich, Ruckstande aus der Mullverbrennung, EF Verlag 16 M. Faulstich and P. Kocher, VDI Seminar "Schlacke, Aufbereitung, Verwertung und Entsorgung", Presentation nr 17, 1993. 17 F.J.M. Lamers et al., Proc. WASCON conf, Maastricht, nov 1991, Elseviers studies in environmental science 48, (1991) 513. 18 J. Demmich, Report VGB Congress 09.02.1993, Essen, nr VGB - TB 703.

Environmental Aspecfs of Conshuction wilh WmfeMaterials JJJ.M. Goumans, H A van der SIoot and lI1.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN rights resewed.

655

Re-use of colliery spoils in construction materials using Fluidized Bed Combustion J . J.M Heynen", H.N.J . A. Bolkb, G.J. Senden' and P.J. Tummers"

YWACO B.V., Consultants for Water and Environment, P.O. Box 525, 5201 AM 's-Hertogenbosch, The Netherlands 'Heijmans Milieutechniek B.V., P.O.Box 377, 5240 AJ Rosmalen, The Netherlands "NOVEM, Netherlands Agency for Energy and the Environment, P.O. Box 17, 6130 AA Sittard, The Netherlands "COMAN B.V. Consulting Engineers, P.O. Box 198, 6400 AD Heerlen Abstract This article describes a plan to upgrade colliery spoils to construction materials. The plan is based on the idea that the mineral composition of which colliery spoils are made of are similar to the composition of construction materials. However, colliery spoils also contain carbon and sulfides whilst construction materials mostly do not. By thermal treatment, i.e. burning out the carbon and oxidation of sulfides, the mineral part can be upgraded into a form, suitable for production of construction materials. An optimized Fluidized Bed Combustion (FBC) technology in combination with treatment of coarser particles in a shaft-furnace, is regarded the most suitable method for this purpose. An integrated processing facility based on proven technologies will be able to upgrade colliery spoils into (1) basic minerals to be used for the production of construction materials (a high valued re-use), simultaneously recovering the remaining energy-content, i.e. (2) electricity and (3) heat. The facility itself can very likely be a basis or crystallization point for innovative building material industry, thus causing an economic stimulus for the region. Furthermore, the removal of colliery spoil deposits will prevent groundwater contamination caused by percolate which may contain sulphuric acid resulting from the oxidation of sulfides. A feasibility check for this project has been carried out for FBC capacities up to 200 MW-fuel, aimed at the removal of an uncovered colliery spoil deposit of about 30 million tonnes in Liinburg, the southernmost province of The Netherlands. Production of ceramic limestone as an end-product was found to be a very interesting option.

656

1. INTRODUCTION In Limburg, the most southern province of the Netherlands, large scale coal mining activities were carried out until 1975, leaving considerable amounts of colliery spoils in the direct environments of the former collieries. Most of these colliery spoil heaps have been covered and integrated in the landscape, but some 36 million tonnes are still uncovered and not integrated, thus forming an obstacle in the landscape. More important, the groundwater quality is threatened by these uncovered heaps. Colliery spoils and minestone contain a considerable amount of pyrite (ironsulfides) which can be oxidized to sulphuric acid. Moreover, the oxidation can be accelerated by thiobacilli bacteria, especially at lower pH values. As a result of this biological catalyzation, the oxidation process can be speeded up, at pH-values below 2.5, by lo5 lo6 times [I]. As long as the colliery spoils contain enough lime, the sulphuric acid will be buffered. However, when the lime buffer is exhausted, pH values in the percolate will drop (and boost accelerated biological oxidation) and form a threat for the groundwater quality as a result of acidification of the percolate[2-3]. In order to prevent groundwater pollution in the future, the best solution is to remove the colliery spoil heaps. An appropriate approach to accomplish this aim is to upgrade the colliery spoils by thermal treatment towards basic materials for production of construction materials, thus accomplishing a total, high valued re-use of colliery spoils and recovery of the remaining energy content. The basic ideas of this approach can, in principle, be used in any region where colliery spoil and/or low-grade coal deposits are available. In this perspective Novem, the Netherlands Agency for Energy and the Environment, and Mauran B.V. investigated a plan for a relatively small upgrading unit (50 MW-fuel) in the municipality of Kerkrade, Limburg. This moment this approach, based on upgrading by thermal treatment, is being further developed and implemented by Heijinans Milieutechniek B.V., aimed at a location in the municipality of Brunssum, The Netherlands, at a scale of about 150 MW-fuel. A feasibility check is being finalized and more detailed cost calculations and engineering are planned for 1994. 2. PRINCIPLES OF THE COLLIERY SPOIL UPGRADING FACILITY (CSUF). 2.1. General It is known that by using the proper upgrading technologies, colliery spoils can be used as a basic material for the production of high-valued construction materials [4]. As colliery spoils can still contain a relatively large amount of coal (especially older, lowefficient washed minestone can contain up to 40 % coal), energy recovery is also an interesting feature. In the Netherlands, the development of a Colliery Spoil Upgrading Facility (CSUF) was initiated[5]. This facility will be an integrated colliery spoil processing plant producing: construction materials; electricity; heat (which can be used in greenhouses and/or municipal heating systems).

The CSUF is based on a combined Fluidized BedlShaft Combustion reactor in which the

657 colliery spoils are burnt-out to a sufficient high extent. As a result of the carefully chosen burning conditions the combustion products are suitable for producing high-valued construction materials, whereas the produced electricity and heat are useful by-products. 2.2 Fluidized Bed Combustion Fluidized Bed Combustion (FBC) is a proven technology especially suitable for the combustion of smaller particles containing a relative low caloric value. Coarser particles > 20 mm can be burnt in a shaft furnace [6]. For completeness the FBC technology will be briefly explained. Simplified, a FBC-furnace can be described as a cylindrical vessel with a porous bottom plate. The combustion air is blown through this bottom plate with a such velocity that the particles in the furnace will be lifted and be whirled: they get in a so-called "fluidized" condition. When fluidized the solids behave almost like a liquid. Because of this, process conditions like temperature, heat exchange, residential time etc. can be well controlled. Furthermore additives (such as limestone for SOz emission reduction) can be added easily. In figure 1 a principle scheme for a FBC furnace is drawn. This is a so-called "slow" or "bubbling" fluidized bed. There are several other types (e.g. the "fast" or recirculating fluidized bed) which will not be further discussed here. Further details on FBC-technology are available in literature [6].

A

I

Dust

Air distributor plate

Figure 1. Principle scheme of a Fluidized bed system.

2.3. The Colliery Spoil Upgrading Facility (CSUFJ The CSUF in the Netherlands is planned to be situated in the municipality of Brunssum on the site of a colliery spoil deposit of about 30 million tomes. These colliery spoils will be fed into a pre-treatment unit (drying, breaking, sieving, grinding) from which the fines (0-6 mm) will be fed into the FBC-unit. The coarser particles (20-45 mm) will be fed into the shaft-furnace. This will result in two types of mineral product: calcinated clay, applicable as a raw material for production of construction materials and broken burnt-out minestone, for direct use as gravel and tillers. Simultaneously, a minestone washery plant has just been taken into operation on this colliery spoil deposit as well. By use of gravitational separation techniques, this washery

658

.

plant separates the colliery spoils into: washed minestone (usable as filling material); low-grade coal; washery sludge. The low-grade coal and the washery sludge can very well be used as an additional feed for the FBC, thus acting as a replacement for a caloric equivalent of unwashed colliery spoils. If done so, the CSUF can be operated complementary to the washery-plant, thus increasing the possibilities for re-use of the colliery spoils. A flow-sheet the CSUF has been drawn in figure 2.

Colliery Spoils 0-300 mm

I I1

CSUF

I Pretreatment

I

I

I I

I I

I

i

I

: I

I

I

I I

I

I

--

I I

Washery-plant

washery sludge

I shaft-furnace

I

I

V

Fluidized Bed Combustion (FBC)

- -- - - - - -

I

I 1

lowgrade coal

Dossible FBC-feed

I gravel I

washed minestone

cerainic limestone production

Figure 2. Flow-sheet of the Colliery Spoil Upgrading Facility (CSUF). At the time of writing, a feasibility check was carried out by Heijmans Milieutechniek B.V., COMAN B.V. and IWACO B.V. under supervision of LIOF (Limburg regional economic development institute) and NOVEM. In the next chapters a brief overview of this feasibility check will be given.

659

3. FEED OF THE COLLIERY SPOIL UPGRADING FACILITY In table 1 properties of the feed of the CSUF are given: Table 1 Approximate composition of feed of the CSUF Ash content (%-weight) Untreated colliery spoils Low-grade coal Washery sludge

Combustion value (MJ/kg)

90

4.25 18 12

40

60

These values have been used for the feasibility check, however, they need to be further investigated for verification. 4. PRODUCTS AND APPLICATIONS The feasibility of the CSUF depends largely on possibilities to actually sell the products that are made. In table 2 some potential products are given. Table 2 Potential Droducts of the CSUF ~

Product

Application

broken burnt-out minestone

- bulk-fill material

- aggregate material

Market potential in The Netherlands (tonneslyear) 40,000,000 8,000,000

Estimated revenue (Dfl. per tonne) 5 to 6 7 to 8

1,200,000 (gravel) 1,700,000 (split)

13 17 to 26

9,000,000

13 to 26

25,000 to

15 to 30

for road-bases - supplementary

calcinated clay

materials for asphaltic concrete (warm production) - supplementary materials for cementous concrete brick industry

50,000 500,000*

ceramic limestone construction industry 80 to 100 (via end-production using dcinated clay) *: based on 20% of the market volume of ordinary limestone and 75% replacement of primary raw materials by calcinated clay; ceramic limestone is a new product with improved properties.

660

Remarks on table 2 the mentioned market volume of 8 million tonnes for aggregate materials for roadbases is a very competitive market, where also many demolition debris products are used; in the estimate for the market potential for supplementary materials for cementous concrete (9 million tonneslyear) a maximum use of demolition debris granulates is already assumed. in the estimate for the market potential for supplementary materials for asphaltic concrete (3 million tonnedyear) maximum recycling of secondary asphaltic concrete is already taken into account. Regarding the applications of broken burnt-out minestone, applications like supplementary materials for cementous and/or asphaltic concrete seems to be most interesting because of the higher revenues to be obtained. With regard to applications for calcinated clay, ceramic limestone is an especially interesting material because it can be directly produced from calcinated clay (as estimated by TNO [7]). For ordinary production, natural clay has to be calcinated whereafter ceramic limestone bricks can be produced by pressing, by use of an autoclave. The FBC, however, produces calcinated clay as a ready-to-use product, not needing further pretreatment. This overall process of FBC-combustion (in which calcination is integrated) followed by autoclave production of limestone bricks seems to be a very attractive option which is planned for further detailed investigation in 1994. 5. ENVIRONMENTAL ASPECTS OF THE CSUF

The operation of the CSUF will lead to positive effects on the environment: a likely long term groundwater pollution source can be eliminated; by using upgraded colliery spoils as a basis for the production of construction materials, primary raw material resources (sand, clay, gravel etc.) can be preserved and the amount andlor size of landscape destroying sandlclaylgravel exploitations can be reduced; burnt-out minestone can be produced without uncontrolled emissions (e.g. SOz) to the air; large obstacles in the landscape (the colliery spoil heaps) will be removed. -

With respect to the environmental effects of the upgrading process itself, the following precautions will be taken: reduction of emissions to the air by process-integrated measures; lime supplied in the reactor-feed will cause a significant SO,-emission reduction (85 to 90%); NO,emission reduction can be reached by staged combustion at low temperatures (down to 200 mg/m3) and dust emissions can be reduced by a dust filter (to 20 mg/m3). These measures together will assure low emission concentrations. minimization of the needed amounts for process and cooling water, since the Dutch governinent’s policy is to restrict further use of groundwater; at the planned location, no surface water is available.

66 1

The potential leachability of the CSUF-products has been looked at. Based on available information on the composition and a few cascade leaching tests of locally available colliery spoils, it is deducted that the composition and leachability of the (at low temperatures, 850 "C) burnt-out CSUF-products will be similar to natural clay soils and thus will fully comply with the Dutch Construction Materials Act. This however should be confirmed by tests at the actual CSUF-products. In the Netherlands an Environmental Impact Assessment (EIA) is compulsory and will be dealt with by the authorities together with the demand for legally required permits. By carefully balancing the complementary environmental effects and costs of extra emission reducing measures, the authorities will have to impose well-considered requirements (described in the permits to be given). Eventually, the EIA should balance the positive and negative environmental effects and compare several variants with each other and with the so-called zero variant: when nothing at all will be done. At this moment (January 1994) the actual Environmental Impact Assessment has not yet been carried out. The preliminary inventory has been made and discussions with governmental authorities confirmed that no major constrains are to be expected.

6. ECONOMIC ASPECTS OF THE CSUF 6.1 Financial calculations Based on literature [8-91, expertise and experience with similar projects, preliminary economic calculations for a CSUF have been made based on the location in Brunssum. Financial data were calculated over FBC capacities in the range of 50 to 200 MW fuel. Because most of these figures are regarded as confidential, at present, they will not entirely be described in this paper. However, a brief overview of the assumptions will be given below as well as the resulting Costs of Mineral Product (COMP).

Assumptions have been made on investment costs regarding:

- fuel preparation: excavating, transport, breaking, sieving, drying and grinding; - FBC-unit; - shaft-furnace; - civil works, infrastructure.

Annual costs comprises: - capital costs: calculated from annuities of investment costs at an interest rate of 8 % and

a life-time of 20 years. Also governmental investment premiums were taken into -

account, ranging from 0 to 50% energy costs of fuel-preparation; maintenance: 2 to 8% of respective investment costs personnel (a total of approx. 80 persons); miscellaneous; risk and profits. Further, electricity revenues are calculated assuming:

- 54 MW electric power at 200 MW (FBC) fuel capacity;

662

- 13.5 MW electric power at 50 MW (FBC) fuel capacity; - 8000 production hours per year; - electricity prices (supply to local electricity distributing company) ranging from Dfl 0.06 to 0.12 per kWh; Dfl O.O84/kWh is considered as a basic minimum price to be obtained. - potential revenues from produced heat are until now not taken into account. After calculating the annual costs and subtracting the electricity-revenues the Costs of Mineral Product (COMP) remain. Several variants in the above mentioned ranges including variants where colliery spoil is partly replaced by washery sludge and/or washed low grade coal (at zero prices) have been calculated. In table 3 a brief overview of some variants for a CSUF with a capacity of 150 MW-fuel (40.5 MW electric) is given. In the 150 MW,,, -variant the total amount of CSUF-product will be about 1,4 million tonnes of product/year. In the case of replacement of colliery spoils with washery sludge and washed-out low grade coal (both approx. 80,000 tonnedyear) from the on site present washing facility, the total product amount will be about 700,000 tonnedyear. Table 3 Overview of Costs of Mineral Product in some selected variants at 150 MW-fuel Costs of mineral ~roduct(Dflhonne. total average) Input: Colliery spoil only (1,564,000 t/a)

Electricity price (Dfl/kWh)

0.06 to 0.12

Output: calcinated clay (915,000 tla) and burnt-out minestone (493,000 t/a)

Input: Colliery spoils (695,000 t/a) plus washery sludge and lowgrade coal (80,000 t/a each) Output: calcinated clay (487,000 tla) and burnt-out minestone (219,000 t/a)

No investment premi u i n

40 % investment premium

No investment premium

40 % investment premium

30 to 17

22 to 8

45 to 17

30 to 3

Remarks on table 3 Replacement of a caloric equivalent of colliery spoils with washery sludge and low grade coal results in higher COMP at lower electricity prices. Because of the higher caloric content of the washery product less total feed is needed. This results in a lower amount of product over which the total remaining costs are divided. At lower electricity prices this is not sufficiently coinpensated by lower investment costs in handling equipment.

6.2 Econoniic feasibility The facility is feasible if the revenues obtained from products to be sold equal the COMP. If broken burnt-out minestone and calcinated clay are the only products (described

663 in chapter 4) from the CSUF, the revenues of the products can be estimated at about Dfl. 13 to 26/tonne. In this perspective, the option for producing ceramic limestone is very interesting from a financial point of view. The revenues for ceramic limestone can be estimated at Dfl. 80 to 100/tonne. However, costs of the autoclave end-production process still have to be added to the COMP. Because the produced calcinated clay does not need further pre-treatment and the CSUF produces heat, which can be used for the autoclave-process, it is estimated this option could be economic feasible. This should, however, be further investigated. In particular, the market potential of this new product and technical details should be further analyzed. However, by granting an investment premium and/or higher electricity prices, the regional government can encourage an elegant way to remove the remaining colliery spoil deposits. In that way a future threat for groundwater quality will be removed and the economic development of the region will be stimulated. 7. CONCLUSIONS A Colliery Spoil Upgrading Facility (CSUF) offers a realistic opportunity for a highvalued 100% re-use of colliery spoils and/or low grade coal. Furthermore, in this way an obstacle in the landscape can be removed and future groundwater quality deterioration can now be prevented at probably lower costs than curing will require after acidification of the deposit’s percolate. A CSUF is especially interesting for regions with large colliery spoil and/or low grade coal deposits and where a need for building materials is present. Once realized it will probably form a regional stimulus for economic development and innovative construction material industry. Economic feasibility mostly depends on: revenues: dependent of the size and accessibility of the market and kinds of construction materials; revenues are also dependable on possibilities to sell or use the surplus of electricity and heat. investment and exploitation costs; environmental requirements. These parameters will undoubtedly differ for each considered region, and should be investigated in an at the target region aimed feasibility study.

In the investigated case of the Brunssum location of the CSUF, the option for production of ceramic limestone appears very interesting: the CSUF-product will be a ready-to-use basic material for this purpose and the in the CSUF recovered energy can find a direct application in this end-production. This idea should be further investigated. Local government supports (investment premiums and/or higher electricity prices) could tip the feasibility balance into a clearly positive scale. Such support will stimulate economic development and employment (directly approximately 80 men, excl. ceramic limestone end-production) and can very well stimulate further development of innovative ceramic industry.

664 8. REFERENCES 1 B.B. Jrargensen, The microbial sulphur cycle, Microbial Geochemistry (Ed. W.E.

Krumbein), pp. 91-124, Blackwell Sc. Publ., Oxford, 1983. 2 I. Twardowska and J. Szczepariska, Transformations of pore solutions in coal mining wastes, Proc. 3rd. int. Symposium on the Reclamation, Treatment and Utilization of Coal Mining Wastes, Glasgow UK (Ed. A.K.M. Rainbow), pp. 177-185, Balkema publ., Rotterdam, 1990. 3 M. Kerth, Untersuchungen zur Pyritverwitterung in einer Steinkohlenbergehalde des Ruhrgebietes, N. Jb. Geol. Palaont., 1988 (lo), pp. 592-604, Stuttgart. 4 J. Leonhard and Th. Schieder, Utilization of Washery Waste as Secondary Raw Materials in Civil Engineering and other Industries/Verwendung und Verwertung von Aufbereitungsabgangen als Sekundarrohstoff in der Bauindustrie und anderen Industriezweigen (in English and German), Aufbereitungstechnik, No. 3 1, pp. 89-97, 1990.

5 J.J.M. Heynen, G.J. Senden and P.J. Tummers, Re-use of Mining Wastes in Construction Materials via Fluid Bed Combustion and combined Energy-Utilization, Proc. 4th. int. Symposium on the Reclamation, Treatment and Utilization of Coal Mining Wastes, Krak6w Poland, (Ed. K.M. Skariyriska), pp. 681-688, Dept. Soil Mech. and Earth Str.,Un. Agr. Krak6w, 1993. 6 R.H. Perry and D. Green (Eds), Perry’s Chemical Engineers’ Handbook, 50th int. ed., pp. 20-47 to 20-48 and 20-58 to 20-75, McGraw-Hill Book Co, Singapore, 1984. 7 R. van der Stel and A.H. de Vries, Verkennend onderzoek naar de mogelijkheden om gecalcineerde kleiachtige inassa’s te verharden in een autoclaaf, TPD-KK-RPT-93-124, TNO-report, Eindhoven, 1993.

8 Northeastern Power Company, Resource Recovery Facility Kline Township Pennsylvania, Reading Energy Company, Philadelphia USA (information sheet). 9 J. Bailey, Colliery Spoil as a feedstock in Fluidized-Bed Combustion, Minerals and the Environment, London, V01.2. P. 49.

Environmental Aspects of Construction with Waste Materials JJJM Goumans, H A . van der Slmt and Th.G. Aalbers (Editors) el994 Elsevier Science B.V. All rights resewed.

665

Recovery of raw materials from reclaimed asphalt pavement E. Mulder'), C. de Groot'), C. Joke$) and J. van der Zwan4) *)

TNO Environmental and Energy Research, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands

')

Rasenberg Wegenbouw B.V., Breda, The Netherlands

3,

Wegenbouwmaatschappij J. Heijmans B. V., Rosmalen, The Netherlands

4,

Dutch Ministry of Transport and Public Works, Road and Hydraulic Engineering Division, Delft, The Netherlands

Abstract A research programme is being carried out to find a way to re-use all the constituents of bituminous asphaltic concrete, as well as the mineral fractions of tar-containing asphaltic concrete. From the results of a feasibility study it may be concluded that this is technically feasible. The most critical process step is the extraction of the asphalt. A twostage counter-current extraction with toluene as a solvent seems to be convenient to obtain mineral fractions (gravel and sand) containing only 0.1 % asphalt and a filler containing ! asphalt. Recovery of the solvent from the mineral fractions can best be done about 1.5% by means of drying.

1.

Introduction

In The Netherlands a large part of reclaimed asphalt pavement is re-used. Mostly the crushed asphalt granulate is added to a mixture of primary raw materials during the preparation of new asphaltic concrete [l]. However, the supply of reclaimed asphalt is higher than the capacity of this high grade "re-use'' option. For this reason, more and more reclaimed asphalt is being used as a low grade foundation material in road construction, or is being dumped. A special category of asphaltic concrete is formed by the tar containing asphaltic concretes. Reclaimed pavement of this category cannot be re-used by means of "in-plant" mixing because of the emission of polycyclic aromatic hydrocarbons (PAH's) at the prevailing temperature. From an environmental point of view, PAHcontaining reclaimed asphalt should be removed from the chain. To overcome the above mentioned problems, two road construction firms, i.e. Rasenberg Wegenbouw B.V. and Wegenbouwmaatschappij J. Heijmans B.V., started a research programme to fmd a way to re-use all the constituents of bituminous asphaltic

666 concrete, as well as the mineral constituents of tar containing asphaltic concrete. This research is being carried out by TNO Environmental and Energy Research and is being guided by the Road and Hydraulic Engineering Division of the Dutch Ministry of Transport and Public Works. The research consists of three phases, the first of which, a feasibility study, has already been completed [2]. Based on this work, the road construction firms have applied for a patent for the process. The second phase, aiming a further technical development of some major unit-operations, is now in progress. The third phase will be an optimisation of the defined process on a pilot-plant scale. In this paper in chapter 2 a description will be given of preliminary investigations that have been done, according to some important parameters. Then the results of this parameter study are evaluated in chapter 3. In chapter 4 the results are translated in a design of the different process steps. The paper will end with some conclusions.

2.

Parameter study

The intention of the research programme was to develop a process to recover all raw materials from reclaimed asphalt pavement. These raw materials are gravel (the coarse aggregate > 2 mm, 55%), sand (mineral aggregate between 63 pm and 2 mm, 35%), filler (fine mineral filler material < 63 pm, 5%) and asphalt 5 % . In the first instance, a raw process design was made, consisting of the following steps: - extraction of the bituminous (or tar containing) asphalt by means of an organic solvent; - separation of the coarse mineral fractions (gravel and sand) and recovery of the adhering solvent; - separation of the filler from the loaded solvent and recovery of the filler as a dry powder; - separation of the asphalt from the solvent. In order to be able to make a more detailed process design, a number of parameters had to be investigated. These parameters were the type of solvent (for the extraction of the asphalt), the extraction conditions and the way of recovering solvent from the mineral fractions. The study of these parameters is described in the following sections.

Type of solvent This study was started with a literature search. A number of solvents were found to be able to dissolve bituminous (or tar containing) asphalt. The solvents were divided into three categories: halogenated solvents, aromatic solvents and aliphatic solvents. From each category one solvent was chosen (based on characteristics such as toxicity, inflammability, boiling point, cost etc.). The following three solvents were chosen: dichloromethane, toluene and heptane. Knowing that part of the bitumen and tar components do not dissolve very easily in the a-polar solvent heptane, 10%methanol was added to the heptane.

667 After this pre-selection, a laboratory research was carried out, in which two types of asphalt granulates (bituminous and tar-containing, respectively) were mixed up with the three types of solvent in a liquid to solid ratio (L/S ratio) of 1 I/kg. The mixture was rolled in a flask on a roller table for 30 minutes. The following conclusions were made: - From the 3 solvents the heptane/methanol mixture showed the poorest ability to dissolve both bituminous and tar containing asphalt from the granulates. - As far as bituminous asphalt was concerned, dichloromethane and toluene were equally good, but toluene happened to be better than dichloromethane for tar containing asphalt. - So, from a technical point of view, the best choice was toluene. However, also other selection criteria have been taken into account. For that reason in the experiments as described in the following sections both dichloromethane and toluene were used as solvents. The final choice between dichloromethane and toluene was made after that also these experiments had been carried out.

Extraction conditions The extraction of asphalt from reclaimed asphalt concrete granulates is affected by several parameters. The effect of the following parameters was investigated: the way of agitation, the agitation time, the number of extraction steps, and the L/S ratio. It was clear from the beginning that the mixture of asphalt granulates and solvent had to be agitated. Investigations with a so called Soxhlet extraction apparatus had shown that, if the granulates were not agitated, the extraction time would be up to about 5 hours. The next step was to put the flask with the mixture on a roller table (as described before). This decreased the extraction time to about 2 times halve an hour (in two subsequent steps). It seemed that a more intensive agitation would further decrease the extraction rime. Stirring was not thought to be a real option because of erosion, caused by the heavy coarse mineral fraction. Then a small cask was supplied with obstructions to make the granulates tumble over each other, when the cask was rolled on the roller table. This decreased the extraction time to 2 times 20 minutes. A counter-current extraction always has a higher efficiency than a co-current extraction. To simulate a counter-current extraction the mixture of asphalt granulates and solvent was decanted after an agitation time of 20 minutes and a settlement time of 15 minutes. New solvent was then added to the half-extracted asphalt granulates and the mixture was agitated for another 20 minutes. After these two extraction steps, the coarse mineral fractions (gravel and sand) appeared to be clean enough (appr. 0.1 % asphalt). As far as the L/S ratio is concerned, a ratio as low as possible is, of course, the most profitable. However, the ratio has to be high enough to guarantee a good liquid to solid contact and to have enough capacity to dissolve the asphalt. Investigations were done with L/S ratio’s of 0.5 and 1 I/kg. The L/S ratio of 1 llkg yielded much cleaner products than 0.5, so for following investigations an L/S ratio of 1 l/kg was chosen. The extraction conditions that were found suitable for the extraction of asphalt (both bituminous and tar containing asphalt) from reclaimed asphalt concrete granulate are summarised in table 1.

668

Table 1: Optimum extraction conditions Condition / parameter

Optimum / quantity obstructions

Way of solvent recovery Two different ways of recovering the solvent from the coarse mineral fraction have been investigated. One way is a kind of washing (or suppression) of the solvent by means of adding subsequently another solvent and water. A second way is drying (evaporation of the solvent). To obtain a good starting-material for the solvent recovery experiments, the following activities were carried out: - a mixture of 2 kg of reclaimed asphalt concrete granulates and 2 1 solvent were agitated for 20 minutes in the cask with obstructions as described before; - after settlement and decantation of the loaded solvent new solvent was added and the mixture was agitated for a further 20 minutes; - now the mixture was sieved over a 90 pm sieve to separate the solvent, asphalt and filler inclusive, leaving the clean but wet mineral fractions (gravel and sand). In the wash route, the last step has to be a washing with water. It is not a problem to have wet mineral aggregate fractions as a product. Nevertheless, washing at once with water is not possible because of the insolubility of the used solvents (toluene and dichloromethane) in water. For this reason, a second solvent was chosen that had to be able to dissolve toluene and dichloromethane on the one hand and to dissolve itself in water. Methanol was found to be such a solvent. The wet mineral fractions from the preliminary experiment, carried out with dichloromethane, was mixed with methanol (in an L/S ratio of 1 Vkg) and was agitated for 20 minutes. The agitation time may have been too long, but it had to be ensured that all dichloromethane was suppressed by methanol, also in the pores. After agitation and settlement the methanol was decanted and the mineral fraction was mixed up with water. After the mixture had been rolled for 20 minutes, the coarse aggregate (gravel) was separated by means of sieving over a 2 mm sieve. Then the fine aggregate (sand) was de-watered by means of filtration. In this way it appeared to be possible to obtain wet, but clean and solvent-free mineral fractions (remaining asphalt content < 0.1%). The results of these investigations are summarised in the next chapter. In the dry route, the most important assessment criterium was the solvent content in the product. To prevent asphalt molecules remaining in the aggregate fractions after evaporation of the solvent, the aggregate fractions were washed with new solvent once more. After agitation, settlement and decantation of the solvent, the solids were dried at the boiling point of the solvent. The evaporated solvent was condensated again to be

669

recycled. The dry mineral fractions could simply be sieved into a coarse and fine fraction. Also, in this case, the remaining asphalt content was approximately 0.1 %. In both cases the filler was separated from the loaded solvent by means of filtration. It was then mixed with new solvent and intensively agitated by means of stirring. (Here, erosion was not expected to be a problem.) After filtration, the filler was dried also, like the other mineral fractions in the drying route. The remaining asphalt content appeared to be still rather high, about 1.5%.

3.

Evaluation

From a technical point of view, toluene seemed to be the most appropriate solvent, but dichloromethane has better characteristics as to inflammability and boiling point. After a severe discussion, politics turned the scales. In future, the production of halogenated solvents will be decreased because of EC legislation, so the choice was made for toluene as a solvent. Starting from an extraction under optimum conditions as summarised in table 1, two different ways were investigated to recover the solvent from the mineral fractions (as was described in the previous chapter), the wash route and the dry route. Four experiments were carried out to compare the results: 1 Subsequent washing with methanol and water of the mineral fractions from bituminous asphalt concrete, extracted with dichloromethane. 2 Drying at a temperature of 40 "C of the mineral fractions from bituminous asphalt concrete, extracted with dichloromethane. 3 Drying at a temperature of 110 "C of the mineral fractions from bituminous asphalt concrete again, extracted with toluene. 4 Drying at a temperature of 110 "C of the mineral fractions from tar containing asphalt concrete, extracted with toluene. The results of these four experiments, expressed in terms of remaining asphalt content, are given in table 2.

extraction step

1

7

After second extraction step

After solvent recovery (coarse)

After solvent recovery (filler)

1.0 %

0.1 %

< 0.1 %

1.4 %

1.0 %

0.1 %

0.1 %

1.4 %

0.5 %

0.1 %

< 0.1 %

1.7 %

0.7 %

0.1 %

0.2 %

1.1 %

The choice between the two recovery routes was made on the basis of the results of experiments 1 and 2. Table 2 shows that the wash route probably gives a slightly better

670

result. However, from an economic point of view, the dry route is preferred. The wash route leads to much higher investment costs because of washing and distillation columns. The dry route "only" needs a drying apparatus. If the 0.1 % asphalt content in the mineral fractions is acceptable, an additional washing step of the coarse mineral fractions is not necessary. The second extraction step already yields a product with an asphalt content of only 0.1%. The results of experiments 2 and 3 show that the difference between dichloromethane and toluene can be assessed. Table 2 shows that in the first extraction step toluene is able to extract slightly more asphalt than dichloromethane. This also holds for the final coarse mineral product. The filler, however, still contains more asphalt in the experiment with toluene. Overall, the two solvents do not differ very much, so the choice was made on other bases than technical ones (as has been described before). The results of experiments 3 and 4 show that both bituminous and tar containing asphalt concrete can be extracted with toluene as a solvent. In the mineral fraction (more specifically the sand fraction) of the tar-containing asphalt concrete some more asphalt remained. It is not quite clear what the reason is for this. The recovered mineral fractions gravel and sand contained only 0.1% of asphalt, whilst the filler still contained approximately 1.5%. The PAH-contents of the three mineral fractions, recovered from the tar containing asphalt concrete were measured. The total PAH-content was found to be 3.9, 0.8 and 0.2 mglkg for filler, sand and gravel respectively. When assessed visually all three mineral fractions seemed to be re-usable. The filler was a loose, dry powder. Nevertheless, the quality of the products (technically as well as environmentally) has to be proved in the next phase of the research. From the results of the feasibility study it may be concluded that the process for the recovery of the original raw materials from reclaimed asphalt pavement is technically feasible.

4.

Process Design

Based on the results of the investigations, carried out during the first phase of the research programme, and the choices that had been made, the next step was to obtain an insight into the equipment that will have to be used in the next phase. The aim is to work in phase 2 on a pilot-plant scale with a capacity of about 100 kg/h. The design of the pilot-plant equipment should, preferably, also be usable for the equipment in practice. First of all, the implications of working with toluene as a solvent were mapped out. Especially the flammability of toluene makes that safety measures will have to be taken. Some of the implications and measures are listed below: - To prevent the origin of explosive gas mixtures in the process equipment, the whole installation has to be operated under nitrogen atmosphere.

67 1 The whole system therefore has to be leak proof and possible leakage has to be detected. All in- and output of solid materials (asphalt concrete granulate, gravel, sand and filler) has to be operated by means of locks. Because of the poor conductivity of toluene, the liquid will charge when transport velocities become higher than 7 d s e c because of static electricity. This has to be avoided and, if this is not possible, buffer tanks will have to be implemented to enable the toluene to relax. All process parts have to be coupled and the whole installation has to be earthened. In designing the process and the different process steps, the most difficult step is the extraction of the asphalt from the asphalt concrete granulates. No commercial apparatus seems to be convenient for this, especially because of the stickiness of the asphalt, coming into contact with toluene. The tentative conclusion was that the extraction apparatus had to be specifically designed and verified by means of experiments. The other process steps consist mainly of unit operations that do exist, namely separation and washing of the mineral fractions (gravel, sand and filler), distillation (asphalt from solvent) and drying (of the mineral fractions again). The overall, but simplified process scheme is shown in figure 1. Tentatively the choice has been made to firstly separate the gravel from the sand fraction and then dry it (instead of drying the gravel and sand fractions together and then separating them) because of the expectation that drying the gravel will be much easier than drying the sand. So, the chosen sequence might lead to a more profitable overall process.

*

Sand

igure 1: Simplified process scheme

612

5.

Conclusions

The following, tentative conclusions can be drawn from the research that has been carried out:

*

From the results of the feasibility study it may be concluded that the process for the recovery of the original raw materials (gravel, sand and filler) from reclaimed asphalt pavement is technically feasible.

*

The extraction conditions that were found suitable for this extraction of asphalt (both bituminous and tar containing asphalt) are: - a liquid to solid ratio of 1 Ilkg; - a two-stage counter-current extraction (with agitation); - with an extraction time of two times 20 minutes.

*

After extraction, the mineral fractions, gravel, sand and filler respectively, contained < 0.1, 0.1 and 1.5%asphalt.

*

For the recovery of the solvent from the mineral fractions drying is a better option than washing (subsequently with another solvent and water).

*

From a technical and political point of view, toluene has been chosen as the most appropriate solvent, notwithstanding its flammability. This choice implicates operation under nitrogen atmosphere.

*

The most critical process step is the extraction of the asphalt. For this a new technology is needed. For the remaining process steps use can be made of existing unit operations.

6.

References

[l]

H. Helfrich, Re-use of reclaimed asphalt in-plant (in German), Strassen- und Tiefbau (1990), vol. 44, no. 9, pp. 41-44.

[2]

E. Mulder, Recovery of raw materials from reclaimed asphalt pavement, phase 1 : feasibility study (in Dutch), TNO-report ref.no. 93-032, Apeldoorn, February 1993.

Environmental Aspects of Constmction with Waste Materials JJJM Goumans, H A . van &r Sloot and Th.G. Aalbers (Edton) 019p4 Ekevier Science B. V. AN rights reserved.

613

Applications for coal-use residues: an international overview L. B. Clarke IEA Coal Research, Gemini House, 10-18 Putney Hill, London, SW15 6AA, England Abstract The utilisation of coal produces large quantities of residues. Worldwide production of coal-ash is estimated to exceed 550 Mt/y. In addition to fly ash and bottom ash from pulverised coal combustion, that comprise the bulk of these residues, there are now a whole range of by-products produced by the many technologies developed for flue gas desulphurisation (FGD). Alternative methods of utilising coal, for example in fluidised bed combustion (FBC) and integrated gasification combined cycle (IGCC) systems, produce residues with other, distinctive, properties. Many utilisation options have been demonstrated for coal-use residues, including applications in building materials, for civil engineering uses, in industrial materials and in agriculture. Various commercial applications are well documented and have been carried out for many years. Research into new applications for residues is in progress at many countries around the world. Applications range from high-volume uses that require minimal processing, to low-volume, but highly specialised applications. 1. INTRODUCTION

Coal utilisation produces large quantities of residues. In addition to fly ash and bottom ash from pulverised coal combustion, which comprise the bulk of coal-use residues, there are many different by-products produced by technologies developed to control air pollution. Coal utilisation technologies such as fluidised bed combustion and gasification systems also produce a range of distinctive by-products. The general heading coal-use residues includes the following materials: fly ash, collected in particulate control devices bottom ash and slags, discharged from the boiler residues from atmospheric or pressurised fluidised bed combustion (FBC), which may contain spent sorbents from in-bed desulphurisation residues from wet-lime FGD processes, discharged either as mixture of calcium sulphite and sulphate or, after additional processing, as gypsum

674 residues from dry and semi-dry FGD processes, which consist either of a mixture of fly ash and spent sorbents or a separate by-product stream containing mainly calcium sulphite/sulphate gasification residues, including those from integrated gasification combined cycle (IGCC) systems, discharged as glassy slags or fluidised bed residues (similar to FBC residues) Most residues produced from the utilisation of coal may be described as nonhazardous. In many countries landfill provides a simple way of disposing of a large proportion of the coal-use residues produced. However, dumping is likely to become more strictly controlled and more expensive. In many countries there is now a greater emphasis on the utilisation of by-product materials, with disposal only permitted if utilisation is not possible (Clarke, 1994). 2. ASH PRODUCTION AND USE

Many uses have been developed for coal ash and other residues (Figure 1).In some countries applications have been found for a large proportion of the residues produced. Table 1 lists recent coal ash production and utilisation figures for some major coal using countries.

fly ash

absorbent, plant propagation media, fertiliser, soil amendment

agriculture

building

I I I

residues FBc

residues gasifier

FGD residues

t-

I

'

I

cement, concrete, concrete filler, foamed concrete, mortar

t H 1

artificial aggregate, artificial reef, asphalt filler, backfill, foundations, land reclamation, mine fill, paving, soil stabilisation

civil engineering

artificial sand and aggregates, ceramics, decorative material, filter media, gas cleaning, industrialfiller, liming agent alumina, silica, ceramics, trace elements, integrated materials recovery

materials recovery I

I coalprep. ........

i

residues

Figure 1

j

artificial aggregate, bricks, building blocks, tiles, wallboards and panels

.

4

waste treatment

Utilisation of coal-use residues

I

grout, waste disposal, waste stabilisation, waste solidification

675 Table 1 Coal ash production and use, kt/y a. OECD countries ~~

Country Australia Austria Belgium Canada Denmark Finland France Germany Italy Japan Netherlands Spain Sweden UK USA

Fly ash

7050 375 930 3280 840 640 2290 20460 1250 3480 815 7865 300 9950 51300

Coarse ash Total ash

850 25 160 1100 140 70 420 10910 130 445 85 1530 190 2590 19350

7900 400 1090 4380 980 710 2710 31370 1380 3925 900 9395 490 12540 70650

Utilisation %Used

800 100 795 1290 880 180 1550 17870 1270 1920 940 1570 100 6120 21800

10 25 73 29 90 25 57 57 92 49 >lo0 17 20 49 31

Year

1990 1989 1990 1989 1990 1988 1989 1989 1989 1989 1991 1991 1988 1989 1991

Data includes ash from hard and brown coals. Data for Finland and Sweden also includes peat ash.

b. Other countries

Country China Czech & Slovak Reps Hungary India Poland Romania South Africa Former USSR

Fly ash

Coarse ash Total ash

55000 13800 3880 36000 26300 7000

7500 4300 940 4000 3200 20000

90000

35000

62500 18100 4820 40000 29500 27000 13000 125000

Utilisation O/oUsed

16200 1400 600 6750 4500 700 580 11500

26 8 12 17 1s 3 4 9

Year

1989 1989 1989 1991 1989 1989 1987 1989

676

- Other uses 1% -Asphalt filler, 9% Artificial aggregates, 18%

Netherlands

grlculture and fisheries, 3% adbase and asphalt filler, 7% Artificlal aggregates 3% Concrete, 6%

1

L Building materials. 9%

Japan Blocks, 64%

-Other uses, 2% -Grouting. 4% Structural fills 18%

United Kingdom ement and concrete products. 39% Structural fills. 15%

Other uses, 21%

Blasting grit and roofing granules, 10% Roadbase and sub-base. 8 Snow and ice control, 4%

A L Grouting. 1%

USA

Figure 2

Source: Vliegasunie, Japan Coal Ash Ass.. NatPowerlPowerGen. ACAAI

Utilisation of coal ash (fly ash, bottom ash, boiler slags) by sector

677

In several European countries and Japan, the cement and concrete industries use a high proportion of the residues produced. Figure 2 shows coal ash utilisation by industrial sector for the Netherlands, Japan, the United Kingdom, and the USA. The UK is unusual in the large proportion of ash utilised in the building block industry, and also the relatively poorly developed use of fly ash in the cement industry compared with other European countries. It is also noticeable that those countries with stringent environmental legislation utilise larger quantities of residues compared with countries where disposal is either cheap or poorly regulated. The USA produces a much larger amount of ash compared with other O E C D countries (about 70 Mt/y). Whilst the total per cent utilisation is lower than many other countries (about 31%), the actual quantity of ash and other residues used is enormous (about 22 Mt/y). In the USA applications which involve little or no processing are important, and structural fill and road construction applications account for almost 25% of the total ash used. Countries where power stations are situated far from the centres of population (for example Australia, Canada, and the USA) generally utilise less of the residues produced because it is currently uneconomic to transport the ash to market. Table 1 also lists production and utilisation figures for some other countries. Many eastern European countries, the states of the former USSR, and those countries which are undergoing rapid industrialisation, such as China and India, are producing huge quantities of ash. Widespread industrial restructuring in many central and eastern European nations and the states within the former USSR has resulted in a reduction in demand for coal in these countries. As a consequence the quantity of fly ash produced is currently static or falling. In countries such as China and India the rate of ash production will probably continue to increase over the course of the decade. 3. APPLICATIONS FOR RESIDUES

The following sections provide a n overview of the most important applications for residues. Most applications centre on fly ash, the most voluminous by-product from coal utilisation. A more comprehensive review of applications for coal-use residues is provided in a report by IEA Coal Research (Clarke, 1992). 3.1. Concrete Fly ash has been used widely in concrete and in pre-cast concrete products for many years. In addition to acting as an inexpensive filler or extender, the use of fly ash yields certain benefits as a result of its pozzolanic activity, rounded particle shape, and reduced demand for water. The following technical advantages have been noted when using fly ash as part of the design mix for concretes:

greater cementitious activity, reducing permeability reduced heat of hydration superior surface finish and workability improved chemical resistance, especially against sulphates and chlorides

678

Fly ash may be added to a concrete mix either as a separate material, or as a blended component with Portland cement. If fly ash is incorporated as a separate material, then the optimum proportions may be predetermined for the design mix in order to meet the specific requirements of concrete (for example, improved chemical resistance). Pre-blended mixtures of Portland cement and fly ash eliminates the need for additional handling and mixing, resulting in improved batch consistency. However, pre-blending also removes the ability to select the optimum mix for a given situation. Many fly ash-concrete mixes have been described in the literature and it is clear that the best mixes are designed for specific applications based on inherent conditions and trial mixes. International specifications for fly ash used in concrete vary considerably from country to country (Clarke, 1992). 3.2. Cement Fly ash may be used in cement in a variety of ways. Up to about 8% of the cement clinker can consist of fly ash if it is used as a raw material during the production stage. The ash can be of a relatively low quality, and if it contains a high carbon content, may be used as part of the fuel in the manufacturing process. It has also been suggested that glassy IGCC slags could be suitable, after sizing and grading, as a substitute for natural ahminosilicates in the manufacture of Portland cement clinker (Clarke, 1991). Fly ash can also be used as a replacement for cement in the production of Portland fly ash cement; a mixture of Portland clinker, gypsum anhydrite, and up to 30% fly ash. Bijen and others (1991) note that in principle the effects of this fly ash addition on concrete properties should be similar to those of fly ash added as a partial Portland cement replacement. However, treatment of the fly ash during the manufacturing processes (such as screening and grinding) and adjustment of the quantity of gypsum anhydrite allows production of cement with strength and other characteristics similar to Portland cement. Figure 3 illustrates various methods for the production of Portland fly ash cement. In many European countries (notably Belgium, Denmark, Germany, the Netherlands, Norway, and Sweden) the production of ordinary Portland cement is now being wholly or gradually replaced by the production of Portland fly ash cement (Bijen and others, 1091). The cement industry is a large consumer of gypsum. Portland cement contains gypsum, used as a retarding agent. The quantity of gypsum incorporated varies depending on the application, but may be up to 5 wt%. Gypsum granules are ground together with cement clinker. Gypsum usually needs to be agglomerated prior to use in cement (Clarke, 1993).

3.3. Aerated and foamed concretes Fly ash may be used as a raw material for the production of autoclaved aerated concrete, a lightweight material used to manufacture building blocks for residential, commercial, and industrial use. Fly ash is used to replace ground quartz sand or ground quartz sand and binders. Given an appropriate fly ash it is possible to replace up to 30% of the lime/cement binder without greatly altering the properties of the concrete. Fly ash is being used in autoclaved aerated concrete blocks produced by Celcon, Durox, Thermalite, YTONG, and other European manufacturers. In the UK,

619

Open circuit grindinglmixing processes

A

p*

@+ .-

a

5=

..............................

'

mill

finemill

...........................

:

+-

;

Closed circuit grinding processes

B

sifter

I

b .c Y

f

c m v)

I:

2.

+ <

...........................

t

sifter

or to kiln

Figure 3

Methods for the production of Portland fly ash cement (after Bijen and others, 1991))

680

this application provides an important market for fly ash; Celcon and Thermalite together consumed over 1 Mt of fly ash in 1990. Several attempts have been made to introduce this technology into the USA, especially for the manufacture of blocks for use in masonry construction in underground mines (F'ytlik and Saxena, 1991), but these attempts have failed. More recently, in a renewed bid to enter the US market, a mobile plant has been touring several US power stations demonstrating the production of the autoclaved blocks (EPRI, 1992). Foamed concrete has similar constituents to autoclaved aerated concrete: cement, a filler (mostly a-quartz sand), water, and air. Foamed concrete has different properties compared with autoclaved concrete products, it hardens at ambient temperatures, and can be placed in situ. Foamed concrete has found a number of uses, including the following applications: a material for floors, roofs, and walls because of its insulating properties foundations on soils with a poor load bearing capacity because of its lightness a material to fill disused pipes, tanks, and other voids Complete or partial replacement of cement is possible. The final properties of concrete with substitutions of up to 20-30% are similar to that with no added fly ash (Bijen and others, 1991). 3.4. Other binders

Coal residues have been successfully used with a variety of binders other than as a constituent of concrete and cement, including the following applications:

.

masonry mortars for brick walls plastering specialist cements and grouts manufacture of bricks, blocks, and aggregates asphaltic concrete

In many of these binders fly ash is mixed with other materials such as lime, lime and gypsum, small amounts of Portland cement, and slag and alkaline activators. Aggregates, fillers, or extenders may also be added. The source of lime and gypsum in these binders depends on the lime content of the fly ash and the presence of desulphurisation sorbents. Spray dryer desulphurisation residues may be a suitable source in some cases. Calcium sulphate hemihydrates, produced from FGD gypsum, are suitable for the manufacture of a variety of gypsum plasterboards and fibre reinforced gypsum boards. The wallboard industry is currently the biggest market for FGD gypsum. Gypsum plasterboards are typically manufactured by casting a slurry containing calcium sulphate P-hemihydrate, fibres, starch, and other additives between two sheets of paper. During setting the hemihydrate rehydrates to gypsum. The boards are used for interior wall panelling, for ceilings, and to produce lightweight partition walls, temporary walls, and prefabricated components for modular construction. FGD gypsum can also be used for plaster (stucco), which requires similar physical and

68 1

chemical properties to the plaster used in wallboards. Processes have been developed which dry and briquette the gypsum from FGD plants, such that it can be used as a direct substitute for natural gypsum in most existing manufacturing facilities (Hamm, 1991). However, additional processing consumes energy and it is generally preferable to use FGD gypsum directly in dedicated plants. A full scale demonstration plant has been construction in the Netherlands, partly funded by the European Community, which will produce anhydrite from FGD gypsum (Kappe and others, 1991). The main market for this anhydrite will be for use in selflevelling floor screeds. A fluid mortar is pumped on to the construction floor to produce a smooth floor screed. The mortar consists of sand, water, and a binding agent (in this case anhydrite). If the demonstration plant operates as intended, it should produce 80,000-90,000 t of anhydrite annually, utilising about 110,000-130,000 t of FGD gypsum. 3.5. Bricks and other ceramics In many countries building products, such as bricks, tiles, and pipes, are usually manufactured from clay. Fly ash has a similar chemical composition to that of clay, and it has been suggested that it may be used as a replacement or partial substitute for the clay fraction in bricks and other ceramic products. Because the chemical compositions are similar the firing properties of the green (raw) products are also alike. However, the molecular structure and particle shapes are quite different and this can lead to dissimilar requirements during the shaping or moulding part of the manufacturing process, unless mixtures are used in which only a small proportion of fly ash substitutes for clay. In Europe, building bricks are often manufactured from clay containing a large proportion of water (30-40%). The wet clays may be easily shaped without applying high compaction pressures. Up to about 40% of the raw material can be replaced by fly ash (Bijen and others, 1991). Fly ash can also be used as a filler for clays which are too plastic to reduce the drying shrinkage of the products. An alternative method of manufacturing, suitable for mixtures with high percentages of fly ash, is the semidry process. The mixed raw materials are compacted under pressure (typically 1040 MPa) to produce the green products, which are subsequently dried and fired. Some form of binder, such as clay, is added to the fly ash to produce a green product strong enough to survive handling during the manufacturing process. A third type of brick manufacturing process utilises any unburned carbon in the fly ash as a fuel. Porous bricks are produced by extrusion, dried, and then fired in a kiln. The process heat is maintained by fuel in the brick. An alternative type of brick, popular for house building and other purposes in some European countries, is the sand-lime brick. These bricks are usually manufactured using a quartz sand and lime mix, which is autoclaved after moulding or shaping. The sand component of the mix can be replaced partially or totally by fly ash, together with a proportion of the lime content. 3.6. Artificial aggregates The demand for natural sand and aggregates is growing, particularly in populated areas. Alternative materials developed from coal-use residues could in future provide

682

important substitutes for diminishing or restricted natural resources. Most synthetic aggregates are lighter than natural aggregates and are suitable for the manufacture of lightweight concrete blocks and for use in structural concrete. Low grade aggregates and pellets have been utilised in road base and as a filler in asphaltic concrete. Many processes have been described for the production of artificial aggregates from fly ash or other coal-use residues. They can be distinguished by the method employed for hardening the manufactured pellets or agglomerates: sintering, pellets hardened at r900"C hydrothermal processes, pellets treated at 100-250°C cold bonding, operating at < 100°C Figure 4 shows a simplified process chart for the manufacture of artificial aggregates (Agglite, Granulite, Aardelite, and Lytag are examples of commercially available aggregates). The residues are usually mixed with binders and in the case of hydrothermal and cold bonded processes with lime or cement. Sintering processes may require the addition of some pulverised fuel if the carbon content of the fly ash is insufficient. Sintering processes have been operated successfully for a number of decades, but those working at lower temperatures have attracted attention recently because of their lower operating and production costs.

Fly ash/ residue

CernenV lime

Additives

Water

I Pelletising

I I I I I I I

I

Agglife

Granulite

Aardelite

Was

Cold bonding

Controlled curing in insulated silo

Steam curing

Sintering

I I

I

CIOO'C

I I

I

I

100'-250'C

>900'C

I 1

I I I I I

--

Figure 4

Manufacture of artificial aggregates using coal-use residues

683

The production of synthetic aggregates using FBC residues has been demonstrated in several countries. Production methods tend to use mixes of fly ash and FBC residue, either pelletised or briquetted. The manufacture of aggregates from FBC residues produces a more consistent by-product. Synthetic aggregates can be manufactured from IGCC residues, either by fusing or bonding ash into pellets, or by ballooning slag particles (Clarke, 1991, 1992). 3.7. Fill, foundations, and soil stabilisation Coal residues have been used as fill material in road construction, bridge repair, mining, void filling and as a general landfill. Fly ash has three main advantages over conventional fill materials:

it is lightweight, suitable for applications on ground of poor load-bearing capacity it has self-hardening properties, reducing settlement within the fill, and decreasing horizontal pressures on infilled structures liquid fly ash-based grouts can be hydraulically placed enabling complete infilling of voids, tunnels, and disused tanks Fly ash has been used for a number of years as a road construction material. It has been used as fill, sub-base, and as a road base material. Both cement and lime have been employed to stabilise the fly ash. Several types of slag have also been used in road construction. Bottom ash from pulverised coal-fired power stations has been used widely as a sub-base material, and has a number of beneficial properties:

9

it can be handled and compacted easily sub-base construction may take place in most weather conditions it provides protection for the subgrade against cold or wet weather and damage during construction works it is not susceptible to frost heave bottom ash is a granular, free-draining material

Fly ash, mixed with lime or cement, can be used to stabilise soils. Pozzolanic reactions between fly ash, lime, and water yield products which bind soil particles together. Residues possessing self-hardening properties can be used to stabilise soils without additional additives. FBC residues with a high lime content may be especially suited to acid waste neutralisation or mine soil rehabilitation. Fixated sludges from wet scrubber systems have been successfully used as a subbase for road construction. The material is cementitious and forms a monolithic layer which may be suitable for a variety of other civil engineering applications, such as structural fill. F G D gypsum could also be used for similar applications, but its solubility and thixotropic properties require stabilisation with other materials (such as fly ash) and therefore discourage its use as this adds to the cost. In Germany, FGD gypsum from lignite-fired power stations is mixed with lignite fly ash which contains a high concentration of lime. The fixated product, known as stabilisate, is used to backfill lignite surface mines (Demmich and others, 1991). This application provides a method of utilising gypsum which does not meet the required specifications of the

684

wallboard industry and is also useful for disposing of surplus gypsum in times of overproduction. 3.8. Waste stabilisation Immobilisation of toxic wastes has been carried out successfully using stabilisation and solidification. Fly ash has been used in these processes, together with water and bonding and activating agents such as lime, lime and gypsum, or Portland cement. Tests have also been carried out using FBC residues, which do not require the addition of lime or Portland cement because of their high lime content. Most processes aim to produce a hardened mass with a low leachability. The majority of applications have been used to stabilise inorganic wastes. Physico-chemical bonding occurs and additives may be used to make specific ions insoluble. Organic wastes, such as oil sludges, have also been successfully stabilised. 3.9. Miscellaneous uses Some coal-use residues may be used in agricultural applications as fertilisers or soil amendments, However, application of residues containing ash to agricultural land is not permitted in some countries, such as the Netherlands. Gypsum is a useful conditioning agent on saline and sodic soils and is typically applied at rates of 57 t/ha (CRE, 1992). It is also reported that gypsum addition enhances the production of root nodules, which promote the conversion of nitrogen to nitrogenous compounds (Steffan and Golden, 1991). FGD gypsum could potentially supply this market, providing the moisture content of the residue is reduced to prevent problems during use. The calcium content of the gypsum may be especially useful as a plant food for peanut farming and a utility in Florida, USA, is supplying FGD gypsum for this purpose (McIntyre, 1991). Residues from FBC systems and some F G D residues (for example furnace injection residues) could be added to soils to control acidity. The neutralising capacity of these residues is usually much lower than that of pure limestone. Other miscellaneous applications include substitute abrasives, mineral wool, specialist ceramics, and materials recovery. These uses are reviewed elsewhere, together with more esoteric applications (Clarke, 1992). A variety of processes have been developed for the recovery of materials from coal residues, including alumina, titanium, trace elements, and ceramic materials. Most recovery processes, although feasible, are currently uneconomic compared with processing natural ores. Research has recently centred on integrated materials recovery, in which streams such as alumina and/or magnetite are extracted together with silica or aluminosilicates which can be used as fillers or raw materials in various industries. 4. CONSTRAINTS ON UTILISATION

The potential for use of coal-use residue depends on their physical and chemical properties, and the extent to which they might vary. In addition to technical requirements the following factors also influence utilisation potential:

685

competition with other natural or traditional materials attitudes of potential users subsidies and incentives equating supply with demand transport and storage of resources The success of each application will depend on local requirements, and must be based on detailed market assessments. Natural prejudices against a new product must be overcome, even if the new material is technically superior or more cost effective. Problems also exist in certifying new products which do not use conventional raw materials. It is important that such barriers are removed to allow the effective re-use of materials rather than disposal. High-volume, low-technology applications such as road and embankment fill have in the past dominated the market for coal-combustion by-products. The commercial potential of such applications depends largely on local demand, which allows transport and storage costs to be kept to a minimum. Governmental action and incentives have served to promote the market for coaluse residues Japan, Germany, and the Netherlands. The following measures have been identified: restrictions on disposal of materials, thus promoting production and availability of a usable by-product research and development initiatives to find new applications for residues funding of studies to assess and ensure by-product quality financial support for demonstration projects More unusual applications may be needed in future if the viability of current applications decreases, or the market becomes over-supplied. Discontinuous applications (such as road construction) usefully dispose of large quantities of waste, but need to be balanced with continuous applications (for example building materials) in order to optimise supply and demand, and thus minimise environmental impact by reducing disposal. 5. CONCLUSIONS

Legislation concerning disposal of coal-use residues varies from country to country. Nevertheless most residues may be described as non-hazardous under current legislation. In the past disposal has been the main option for dealing with residues. There is now a greater emphasis on recycling and reuse. In some countries dumping of residues is now only permitted if utilisation is not possible. As the cost of landfill escalates, greater utilisation of residues becomes a more feasible alternative to disposal, provided environmental criteria are satisfied. The most promising applications for most residues are in the building and construction industries. Fly ash and bottom ash have been used in these industries for many years. FGD gypsum is now widely used in the wallboard industries and in

686

cement manufacture. Favourable uses have been developed for other residues, but at present few of these applications have reached commercial status. More unusual uses for coal-use residues may be needed in future if the viability of current applications decreases, or the market becomes over-supplied. 6. REFERENCES Bijen J, Skalny J P, Vazquez E (1991) Other uses of fly ash. In: Fly Ash in Concrete, Properties and Performance, RILEM report 7, Technical committee 67-FAB (Use of fly ash in building), K Wesche (ed). London, UK, E & FN Spon/Chapman and Hall, p160-178 (1991) Clarke L B (1992) Applications for coal-use residues: Handbook. IEACR/SO, IEA Coal Research, London, UK, 406p (May 1992) Clarke L B (1993) Management of FGD residues. IEACR/62, IEA Coal Research, London, UK, 82p (Oct 1993) Clarke L B (1994) Legislation for the management of coal-use residues. Report for IEA Coal Research, London, UK (Apr 1994) CRE Coal Research Establishment (1992) Disposal and utilisation of flue gas desulphurisation (FGD) residues. EUR report EUR-14071-EN, Commission of the European Communities, Luxembourg, vp (1991) Demmich J, Weinflog E, Roeser G, Ghoreishi F (1991) German experience of FGD by-product disposal and utilisation. Paper presented at: The 1991 SO, control symposium, 3-6 Dec 1991, Washington, DC, USA, p397-419 (Dec 1991) EPRI (1992) Mobile demonstration plant produces fly ash-based cellular concrete. ECS Update, 27 (Fall/Winter), Electric Power Research Institute, Palo Alto, CA, USA, p6-8 (1992) Hamm H (1991) Overcoming the desulphurisation gypsum problem in Germany from the technical, economic and marketing points of view. Paper presented at: XIX EUROGYPSUM congress, Interlaken, Switzerland, 16-20 Sep 1991 Kappe J, Moonen L, Ellison W (1991) Growth in by-product gypsum yield, use for floor screeds. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p30.1-30.10 (1991) McIntyre W W (1991) The St Johns River Power Park experience with by-product gypsum production and sales. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p12.1-12.11 (1991) Pytlik E C, Saxena J (1991) Autoclaved cellular concrete: A unique fly ash based building material. In: Eighth annual international Pittsburgh coal conference, Pittsburgh, PA, USA, 14-18 Oct 1991. Greensburg, PA, USA, Pittsburgh coal conference, pS75-581 (1991) Steffan P, Golden D (1991) FGD gypsum utilisation: survey of current practices and assessment of market potential. In: Proceedings of the second international conference on FGD and chemical gypsum, Toronto, Canada, 12-15 May 1991. Mississauga, Ontario, Canada, Ortech, p4.1-4.18 (1991)

-

Environmental Aspects of Conshuction with Waste Materials JJJM Goumans, H A . van der SIoot and Th.G.AaIbers (Editors) 01994 EIsevier Science B.V. All rights reserved.

687

Specifications and the use of wastes in construction in the United Kingdom R J Collins and C J Atkinson Building Research Establishment, Watford WD2 7JR, United Kingdom British Crown copyright 1994. Published by permission of the Controller of HMSO

Abstract Recycling and the reuse of wastes is expected to play an increasing part in the UK construction industry but this must be achieved within acceptable standards of performance, including health and safety. This paper reviews the present position in the UK with regard to current Standards, specifications and other guidelines, and introduces some current initiatives in Government policy, research and the development of European standards, with particular reference to the supply of aggregates and the reuse and recycling of demolition materials. 1. INTRODUCTION

A comprehensive statement of UK environmental strategy is given in the Government White Paper ""his Common Inheritance" [l] in which commitments are made to encourage the best use of valuable raw materials, minimisation of waste, and recycling of waste, as part of a duty of care for the world in which we live. "he largest producers of waste are the minerals and construction industries and thus in terms of tonnage have the greatest potential to make an impact on the construction industry. Such wastes are thus given greatest coverage in this paper, however consideration is also given to concerns on wider issues of waste utilisation and waste minimisation. 2. MINERALS PLANNING RESEARCH

Aggregate requirements are expected to increase and long term projections indicate that over the next 20 years the construction industry in the UK may need as much as 7,000 million tonnes (Mt). Already by-products and waste materials account for 10% of aggregates and bulk construction materials in the UK [21, however it is Government policy to increase this level of usage where this furthers aims of materials conservation and environmental protection.

688

The UK Department of the Environment (DOE)in its Geological and Minerals Planning Research Programme has recently commissioned several research studies to follow up these issues and make recommendations for consideration by Government. Some of the findings are now being used in the revision of Government minerals planning guidance to the local authorities and aggregates industry on what needs to be done to ensure an adequate and steady supply of minerals at the best balance of social, environmental and economic costs, compatible with the objectives of sustainable development. The initial project in this series was a new survey of the current situation in the UK with regard to the occurrence and utilisation of secondary aggregates and recycled construction materials. The report, by Arup Economics and Planning, which was published in mid-1991 [21, makes a number of recommendations on how an increased utilisation of wastes could be promoted. There is also a concern that the most efficient use of all aggregates materials, including waste and recycled ones is inhibited by standards and specifications and this is the subject of a second project carried out and published by the Building Research Establishment [3]. This has found that wastage through overspecification occurs quite frequently, major causes being the avoidance of any risk, however small, and the economic pressure of fiercely competitive fee bidding. Waste materials in particular tend to be marginalised by these factors. A follow-up report explores in more detail the accommodation of waste materials within British Standards and other UK specifications [41. The present paper discusses the recommendations of these reports in relation to the latest developments including current progress in the development of specifications, particularly within the context of European harmonisation. 3. ENVIRONMENTALIMPACT

Historically the UK has had an excellent supply of high quality aggregates but increasingly, traditional sources have been unable to keep up with demand. The reasons for this are many and varied but include resource depletion, loss of land through development and tighter planning controls due to growing awareness of the environmental impacts of raw materials extraction. New consents to develop quarries now normally require an environmental impact assessment (EIA) to be carried out. The EIA should consider all aspects of the environment likely to be significantly affected by the development including population, fauna, flora, soil, water, air, climate, resources, architecture, archaeological heritage, landscape and transport infra-structure [5]. Alternatives to the development also have to be considered together with ways of alleviating the worst environmental impacts. Tighter planning controls are not the only manifestation of environmental concerns and architects and designers are increasingly demanding information about the environmental impacts of the products they specify. There is now an EC

689

ecolabelling scheme [6] which although developed for consumer goods is also applicable to building products. The EC regulation on ecolabelling is designed to promote the use, design and production of products which have a reduced environmental impact a t all stages in their life cycle. The application of the EC regulation on ecolabelling to building products is discussed in BRE papers by Atkinson et al. [7-81. BRE’s work has shown that for many building materials the environmental impacts associated with raw materials extraction are very significant. BRE has also developed a number of environmental assessment methods for buildings which are known collectively as BREEAM (Building Research Establishment Environmental Assessment Method) [91. Some companies require eco-audits of their suppliers in order to promote a “green“ image or in some cases to ensure compliance with legislation. Eco-audits are management tools used to evaluate how well organisations, management and equipment are performing against defined environmental objectives. A recent EC regulation [lo] has established an eco-management and audit scheme which has been designed to promote continuous improvement in the environmental performance of industrial activities. The regulation gives guidance on a range of issues which should be addressed including assessment, control and reduction of the impact of the activity on the environment, energy management, raw materials management, waste avoidance, noise control, product planning, environmental performance and practices of contractors, sub-contractors and suppliers, prevention of environmental accidents and provision of information for internal and external use. Clearly it is very important that the best use is made of all the nation’s resources and that primary aggregate resewes are conserved. One way of doing this is to encourage greater use of waste and recycled materials. Whilst some of the environmental concerns associated with extraction of primary aggregate also apply to the utilisation of secondary materials (notably production of noise, dust, visual intrusion and transportation problems) [23 extraction of primary aggregate gives additional environmental concerns. These include permanent loss of land related amenities, loss of habitats and possibly damage to aquifers. Other arguments in favour of greater use of waste materials where possible are loss of land related amenities or landfill space as a consequence of tipping as well as the loss of potentially useful materials. 4. SPECIFICATIONS AND THE USE OF MINERAL WASTES 4.1. Aggregate for concrete Aggregates for concrete are covered by BS882 for natural aggregates, BS3797 for lightweight aggregate and BS1047 for air-cooled blastfurnace slag [ll-131. The use of waste materials is covered by BS6543 [141 but a survey of specifiers [31 found that this standard is little known. Specifications for building contracts refer to BS882 and frequently to BS1047 and BS3797, but never to BS6543. This

690

essentially precludes use of crushed concrete and demolition waste even though theoretically it is not excluded by British Standards. The Department of Transport, however, in the recent revision of their Specification for Highway Works [15] have recently extended the use of crushed concrete (conforming to the grading and quality requirements of BS882) to use in pavement concrete. Full details of the current position of demolition waste with regard to British Standards and specificationsis in a paper presented at Odense in 1993 [161. Much of the mineral waste available in large quantity in the UK could without dfliculty be classified as natural materials as they have not been subject to processing other than crushing, washing and sieving. This would apply to china clay sand, slate waste, unburnt colliery spoil, dredged silt and various other quarrying wastes. This would not apply to pulverised fuel ash (pfa), burnt colliery spoil, spent oil shale, and various metalliferous slags, as well as to demolition wastes. Wastes classified as natural materials could be assessed for use in concrete according to the British Standard for natural aggregates (BS882 [ll])without reference to the guide for wastes (BS6543 [141). The use of an aggregate need not necessarily rely on aggregate Standards. The British Standard for concrete, BS5328 [17] refers to BS882, BS1047 and BS3797 but the use of aggregates to these Standard specifications is not mandatory in all circumstances. For "designed' and "prescribed' mixes it is possible to select aggregates outside British Standards as long as the properties of the concrete are satisfactory. This is rather too open-ended for producing job specifications because it places a responsibility on the specifier to guarantee long term durability. 4.2. Aggregates in unbound applications The main use of unbound aggregates is in road construction and this is covered in detail by the Department of Transport's Specification for Highway Works [151, in which specific reference is made to a wide range of situations where waste materials can be used. Roads are constructed in layers, so that an economical use can be made of materials, with the lowest quality materials at the bottom and the highest quality materials at the surface. Only a few waste materials are capable of use in all layers of road construction, but most are suitable for use in lower layers subject to certain minimum requirements (ie they do not contain appreciable quantities of compressible material, do not cause chemical attack or corrosion of other materials, do not pollute aquifers, and conform to minimum stability requirements). The main limiting factor for waste materials is availability and the cost of transport. A detailed analysis of the position of the major waste materials has been prepared for DOEMinerals Planning Division by BRE [4].

In building construction unbound aggregates are used as fill and hardcore; this is not covered by British Standards and the main source of advice is BRE Digests, and in particular BRE Digest 276 "Hardcore" 1181. This recommends the use of wastes such as colliery spoil, clean demolition waste, modern blastfurnace slags, pfa and oil shale residue (subject in all cases to limits on water-soluble sulphate content to

69 1

prevent attack on concrete floor slabs etc), but warns against the use of steel slags, old blastfurnace slags, refractory bricks and gypsum mine waste which could cause heave. 4.3. Bituminous bound aggregates. The Department of Transport’s Specification for Highway Works [151 currently permits the use of in-situ recycling for bituminous road materials, but for the production of bituminous materials in plant off site the maximum content of reclaimed bituminous material is limited to 10%. There is opportunity to use rubber in bituminous mixes, however this makes eventual recycling of such mixes more difficult due to burning of the rubber and consequent air pollution.

4.4. Cement replacement materials. The pozzolanic and hydraulic properties of pfa and ground granulated blastfurnace slag (ggbfs) are well recognised in the UK and partial replacement of Portland cement is commonplace and well covered by British Standards [19-221. Particular impetus to the use of these materials has been given by a desire to exploit their low heat and chemical resistance properties [23-261. Blending such materials with cement is the most effective way of saving energy in cement use and also in reducing C02 emissions. In addition to the opportunities for substitution of primary materials by wastes, cement kilns may use secondary fuels such as tyres, domestic refuse and methane gas from landfill sites [27]. 5. DETAILS OF MINERAL WASTES

5.1. Demolition waste Demolition materials are extensively recycled in the UK and it has been estimated that l l M t or nearly half of present arisings of old concrete and masonry are recycled [2]. The major use is as fill and hardcore. Demolition waste is frequently crushed on the demolition site by portable plant and used on the same site as a base for new construction. There is also a long history of recycling concrete from road and airfield pavements for use as road sub-base. This is also conveniently prepared by portable plant. There are fewer “fixed site” ie stationary plants in the U K although these sites should be capable of producing a higher quality product there is little information to corroborate this. The input to such centralised facilities is potentially more variable as there are no statutory requirements to separate waste before arrival at the recycling facility; the plant operator must rely heavily on visual inspection of the waste and on his charging policy for acceptance of materials. Economies achieved by larger scale operations on fixed sites are offset by costs of transport and the need to register material removed from demolition sites as waste.

It is UK policy to increase the recycling of demolition waste, and central to this is the need for universally acceptable standards [2,3] This would also have the effect of improving the viability of fixed site plants with regard to portable operations, where it is suspected that more of the crushed product is used on site than is

692

strictly necessary just to avoid the need to classify it as a waste if it is removed from the site. Improvements in the efficiency of aggregate utilisation would thus be achieved by: (1)Setting up the conditions where some demolition materials could be used in higher grade applications (2) Increasing demand for demolition materials through [2] and an overall greater acceptance of these materials (3)Discouraging the use of more demolition materials on site than is strictly necessary for the construction process. Standards for aggregates are being developed by CEN under Technical Committee TC154, and specification standards for mortar, concrete and lightweight aggregate are mandated so that standstill applies to the production of national standards for these categories. It is hoped that the specification for aggregates for concrete will be ready for national comment in 1994; provision has been made for the specification of recycled materials as directed by a resolution of the CEN Technical Board. Recommendations with regard to recycled material are being made by an ad hoc group of TC154 specially for this purpose. This ad hoc Group on recycled aggregate is considering current national requirements where they exist, including a RILEM specification presented a t the Odense conference (24-27 October 19931, so that recycled materials can be specified with no less assurance of performance and quality as could be expected for natural aggregates. A variability trial on recycled aggregate is currently being carried out for BRE using the statistical methods being employed for the estimation of the precision of aggregate test methods for TC154. 5.2. China clay sand China clay sand, a residue of the winning of kaolin deposits in Cornwall (SW England), with a suitably adjusted grading, will pass BS882 and has frequently been used as an aggregate for concrete, although it reduces the workability. Some specifiers are worried about the mica content and some contractors have also experienced problems working with an unusual material so it needs to be offered for sale at prices considerably below the usual price for natural sands. A further problem arises as china clay sand deposits are located in Cornwall which is some distance from areas of high demand and transport costs are prohibitive [2]. 5.3. Slate waste

Slate waste fails the flakiness requirement in BS882 [ll],but with carefkl mix design can sometimes be used in concrete. Alternatively many sources of slate can be expanded to produce lightweight aggregates with excellent properties and covered by BS3797 [121. The British Standard Guide to the use of wastes for building (BS6543, [14]) in section 18.4 cites the case of a dam in SW England in which crushed slate waste was used in conjunction with a china clay sand. To obtain some workability the aggregate:cement ratio was reduced from 8:l to 7:l and a plasticiser was used. Even so, the concrete had no slump. Cubes cast with this concrete had a 28 day

693

strength of 27 N/mm2 and a density of 2500kg/m3. This dam was visited by BRE staff in 1990 and the concrete was found to be in excellent condition 17 years after construction. There is one further twist in the specifications which has particular relevance to Delabole slate which was used in the Crowdy Dam referred to above. Delabole slate contains some pyrite and matches almost exactly a type of rock described as deleterious in an Advice Note 1281which is referenced by the latest (1992) version of BS882 [ll].The Advice note was issued to combat the "Mundic" problem in Devon and Cornwall where serious deterioration has occurred in some houses about 40-70 years old; these were built with concrete blocks in which there was indiscriminate use of metalliferous mining wastes for aggregate. This has been a set-back to the use of wastes and other lower grade materials in that area and probably to some extent in the country as a whole. A number of different degradation mechanisms are involved in "Mundic" deterioration, but their relative importance has not yet been hlly elucidated. Such factors reinforce a deep underlying mistrust of waste materials by many specifiers. The recent DOE Advice Note [28] has attempted to encompass the "Mundic" problem but in the process has excluded from use certain materials that would be acceptable. Further advice to be published early in 1994 will more closely define those aggregates which are likely to be suspect. Slate waste, like china clay sand, is remote from areas of high construction activity, but Arup [2] in their report to the DOEconsider long distance transport (by sea) to have greater potential. Crushed slate has been established in North Wales as an excellent "Type 1" sub-base material specified according to the DOT specification [151 and its use for such purposes could release supplies of crushed rock for use in concrete. 6.4. Unburnt colliery spoil Unburnt colliery spoil is widely available in the UK but in general terms cannot be used in concrete without high temperature processing either as a part of the raw feed for cement manufacture or to form synthetic aggregates. A few unburnt spoils will in fact pass BS882 for concrete but the high content of clay and the susceptibility to water mean that the quality of the concrete is poor [4,29]. The main usefulness of unburnt spoil is in the availability of large quantities of filling material eg in road embankments which releases other sources of aggregate for higher grade use and reduces the need for "borrow" pits. Although high quality synthetic aggregates can be made from colliery spoil [30], the cost of processing plant currently makes this economically unviable [311. 6.6. Burnt colliery spoil and spent oil shale Burnt colliery spoil (from old tips which have caught fire) and spent oil shale (the residue after heating oil shale to remove oil - a now defunct Scottish industry) have some similarities in properties and potential. They are less susceptible to water than unburnt colliery spoil because clays have been converted to harder mineral phases, but sulphides are oxidised to sulphates so that there is a greater risk of

694

sulphate attack on concrete. Apart from BS6543 [14] these materials are not covered by British Standard, but there has been extensive use in the lower layers of road construction [41. 5.6. Dredged silt Dredged silt collected by port and harbour authorities is normally too fine to comply with the grading requirements of BS882, however it has been demonstrated that silts with low clay contents could be used successfully in concrete [32]. Some clay containing silts can be used to produce sintered lightweight aggregates [33]. 5.7. Quarry wastes Fine material excess to normal requirements is also available in large quantity at some crushed rock quarries. Natural sand is usually preferrred for making concrete and if a crushed rock sand is used the quanity of fine material is strictly controlled. Much of this sand however could be successfully be used in concrete. In a detailed study of concrete made with crushed rock aggregates at BRE it was found that although the overall tendency for fine material was to increase water demand, in a significant number of cases the addition of fines actually reduced water demand 1341. Opportunity also exists for some fine material to be added as part of a composite cement to BS12 [201 as well as part of the aggregate. 5.8. Pulverised fuel ash Pfa, as well as being well established as a cement replacement material (see 4.4 above) can be used to replace part of the fine aggregate. This is also suitable for fly ashes with little or no cementitious properties and is covered by BS3892 Part 2 [35]. Pulverised fuel ash can be used as a lightweight fill material which as well as saving on other aggregates on a volume-for-volume basis, saves on ground preparation where this has low bearing capacity. 5.9. Slags All blastfurnace slag currently produced in the UK is used, either for aggregate [12,13] or for cement (see 4.4 above) although some tips still exist which contain material produced before British Standard BS1047 was first introduced in 1942. Steel slag produced in the UK contains free lime and magnesia which will hydrate and expand when in contact with water. Surface degradation has made some steel slags particularly suited to use as skid-resistant roadstone. Some use of steel slag is possible in the lower layers of road construction but use as fill and hardcore in building construction has resulted in serious cracking [41. 6. OTHER USE OF WASTES IN CONSTRUCTION As an alternative to recycling, some of the construction and demoliton waste produced in the United Kingdom could be reused. This might necessitate some dismantling rather than demolition which would be labour intensive and hence costly. Expensive sorting, distribution, cleaning and testing operations might also

695

be required. In general, for these reasons the costs of reclaiming low price products such as bricks, stone, tiles etc are usually much greater than the price of new products. Other higher priced products such as timber and metals are already recovered and used to some extent. Much of the material which could not be reused directly such as concrete and mortars could be recycled as aggregate. In order to comply with the Building Regulations a reused product or material must be shown by experience to be capable of performing the hnction for which it is intended. Clearly, unless accurate records are kept of how and where specific products were used then some form of performance testing is needed in order to demonstrate fitness for purpose. This is clearly costly for small batches of products. For bricks a particular problem arises in that some bricks have only been fired at low temperatures making them unsuitable for external use. Their appearance is often similar to that of bricks used externally making them difficult to distinguish through visual means. In parts of Denmark where high disposal taxes are levied on each tonne of demolition waste, bricks from demolition may sometimes be economically reclaimed by refiring. This process makes it easier and cheaper to separate the bricks from the mortar (by brushing) and the firing is reported to eliminate the need to separate facing bricks from commons [36]. However, the process is costly in terms of energy consumption and is unlikely to be applied in the United Kingdom. Construction practice strongly influences the ease with which building materials can be recovered. The use of cement based mortars rather than traditional lime based mortars makes it more difficult to recover bricks without damaging them although the Danish process of refiring is reported to reduce the damage [36]. A related problem is that some old stock bricks can themselves be damaged through the use of cement based mortars which are stronger than lime mortars. At present work is in progress at BRE to design mortars with better bonding to brickwork in order to reduce rain penetration. Use of these mortars will make reusing bricks more difficult. Most of the metal content of demolition and construction waste is already recovered as it commands a high price [37]. Metal components are rarely reused but are usually recycled. The main exceptions to this are rebar, aluminium window frames with thermal breaks, wiring and other small items for which recycling costs are usually too great. Clearly, greater reuse could be promoted by a modular approach to design of components. This is being explored by some manufacturers. Whole timbers (floorboards, rafters, doors etc) are often recovered and may be reused for renovation or new construction purposes [37]. One of the major problems associated with reuse or recycling of construction timber is that it is has a wide range of contaminants such as nails, screws, heavy metal preservatives, paints and diseases. Timber fragments can be recycled in chipboard or low grade pulp applications even if they contain nails and screws, by using a hammer mill and separator. Chipboard manufacturers require a large continuing input of material

696

which is difficult to ensure from demolition. In Denmark [38] timber components are commonly recovered and reused or recycled. Treatment plants are available for stripping paint from window frames, doors etc and these can then be reused providing there is no evidence of decomposition. In the United Kingdom old timber is rarely used in new construction but there is a strong market for old timber for conservation and heritage applications. Plastic building products are diverse and in general have been designed to have very long lifetimes so only small quantities of plastic components are available for recovery. Some construction site scrap is recovered and reused or recycled and work is currently going on to modify technical standards to allow the use of recycled plastic construction components. 7. CONCLUDING REMARKS

Growing environmental concerns have produced demands for greater use of waste materials in construction. Whilst sufficient minerals exist for long term needs in the UK changes are needed to improve the efficiency of utilisation including an increased use of lower grade and waste materials where appropriate. Legislation, minerals planning, specifications, construction designs and site practice all need to be directed towards the efficient use of materials. Risk is often quoted as the reason why innovation is neglected, but unless the building industry is seen in a wider context, the overall cost both in real terms and in damage to the environment will be higher. Risk sharing, incentives, demonstration projects, ecolabelling and environmental audits all provide a way forward. 8. REFERENCES

HM Government White Paper, This Common Inheritance - Britain’s Environmental Strategy, HMSO, London, 1990. Arup Economics and Planning, Occurrence and utilisation of mineral and construction wastes, Report for the Department of the Environment, HMSO, London, 1991. Building Research Establishment, Efficient use of aggregates and bulk construction materials - the role of specifications. Volume 1: An overview; volume 2: Technical data and results of surveys, BRE Reports BR243 & 244, BRE, Watford, 1993. R.J. Collins and P. Sherwood, Use of waste and recycled materials as aggregates: standards and specifications, To be published 1994. Department of the Environment, Environmental Assessment - A guide to the procedures, HMSO 1989. European Economic Community Council Regulation No 880/92 (EEC), 23 March 1992 on a Community eco-label award scheme, Official Journal of the European Communities 11.4.92,No L 99/1.

697

7 8

9

10 11

12 13

14 15

16

17 18

19 20 21 22

C. Atkinson, J. West and S. Hobbs, Life cycle assessment and ecolabelling of building products, CIB Conference on Buildings and the Environment, Building Research Establishment, Watford, May 1994. C.J. Atkinson and R.N. Butlin, Eco-labelling of Building Materials and Building Products, BRE Information Paper IP 11/93, Building Research Establishment, Watford, 1993. Building Research Establishment, BRE Environmental Assessment Method: Version 1/93 B R E E M e w Offices (1993); Version 2/91 An environmental assessment for new superstores and supermarkets (1991); Version 3/91 An environmental assessment for new homes; Version 4/93 BREEAMlExisting Offices (1993); Version 5/93 BREEAM/New Industrial Units (1993), BRE, Watford. European Economic Community Council Regulation No 1836/93 (EEC) of 29 June 1993 allowing voluntary participation by companies in the industrial sector in a Community eco-management and audit scheme, No L 168/1. British Standards Institution, Aggregates from natural sources for concrete, British Standard BS882: 1992, BSI, London, 1992. British Standards Institution, Specification for lightweight aggregates for masonry units and structural concrete, British Standard BS3797: 1990, BSI, London, 1990. British Standards Institution, Air-cooled blastfurnace slag aggregate for use in construction, British Standard BS1047: 1983, BSI, London, 1983. British Standards Institution, Guide to the use of industrial by-products and waste materials in building and civil engineering, British Standard BS6543: 1985, BSI, London, 1985. Department of Transport, Scottish Office Industry Department, Welsh Office and Department of the Environment for Northern Ireland, Specification for Highway Works, HMSO, London, 1991. R.J. Collins, Reuse of demolition materials in relation to specifications in the UK, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994, p.49-56. British Standards Institution, Concrete: Part 1. Guide to specifying concrete; Part 2. Methods for specifylng concrete mixes, British Standard BS5328: 1991, BSI, London, 1991. Building Research Establishment, Hardcore, BRE Digest 276 (minor revisions 1992), BRE, Watford, 1992. British Standards Institution, Pulverised fuel ash: Part 1 Specification for pulverised fuel ash for use as a cementitious component in structural concrete, British Standard BS3892: Part 1: 1982, BSI, London, 1982. British Standards Institution, Specification for Portland cement, British Standard BS12: 1991, BSI, London, 1991. British Standards Institution, Specification for Portland blastfurnace cement, BS 146: 1991, BSI, London, 1991. British Standards Institution, Specification for high slag blastfurnace cement, BS 4246: 1991, BSI, London, 1991.

698

23 J.D. Matthews, Pulverised-fuel ash - its use in concrete parts 1 and 2, Building Research Establishment Information Papers IP 11/87 and IP 12/87, BRE, Watford, 1987. 24 G.J. Osborne, Durability of blastfurnace slag cement concretes, Building Research Establishment Information Paper IP 6/92,BRE, Watford, 1992. 25 Building Research Establishment, Sulphate and acid resistance of concrete in the ground, BRE Digest 363,BRE, Watford, 1991. 26 Building Research Establishment, Alkali aggregate reactions in concrete, BRE Digest 330,BRE, Watford, 1988. 27 P.J. Hoddincott, R.A.F. Macrory and N.Roberts, UK Cement Manufacture and the Environment, Institute of Concrete Technology Annual Conference, April 1993. 28 Department of the Environment, Advice on certain unsound rock aggregates in concrete in Cornwall and Devon, DOE(Buildings Regulations Division), London, February 1991. 29 Commission of the European Communities, Coal research reports - utilisation of colliery spoil in civil engineering applications, National Coal Board (London) contract no. 6220-73/8/805, CEC Directorate General Scientific and Technical Information and Information Management, Luxembourg, 1977. 30 W.Gutt, P.J. Nixon, R.J. Collins, and R. Bollinghaus, The manufacture from colliery spoil of synthetic aggregates for use in structural concrete, Precast Concrete (MarcWApril1980) 120-124and 183-185. 31 P.J. Nixon, and E.M. Gartner, An assessment of processes for the manufacture of synthetic aggregates from colliery spoil, International Journal of Lightweight Concrete 2(3) (1980)141-164. 32 P.F.G. Badill, Alternative materials for concrete - Mersey silt as fine aggregate, Building and Environment 15 (1980)181-190. 33 R.J. Collins, Dredged silt as a raw material for the construction industry, Resource Recovery and Conservation 4 (1980)337-362. 34 D.C. TeychennB, The use of crushed rock aggregates in concrete, Building Research Establishment Report BR18, BRE, Watford 1978. 35 British Standards Institution, Pulverised fuel ash: Part 2 Specification for pulverised fuel ash for use in grouts and for miscellaneous uses in concrete, British Standard BS3892:Part 2: 1984,BSI, London, 1984. 36 P. Kristensen, Recycling of Clay Bricks, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994,p.411-414. 37 P. Lindsell and M. Mulheron, Recycling of Demolition Debris, The Institute of Demolition Engineers, Virginia Water, Surrey, 1985. 38 B. Olsen, The "Recycled House" in Odense, in Demolition and reuse of concrete and masonry ed. E.K. Lauritzen, Proceedings of the Third International RILEM Symposium, held in Odense, Denmark, 24-27 October 1993. E & FN Spon, London, 1994,p.521-527.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van &r S l w t and Th.G. Aalbers (Editors) @I994 Elsevier Science B.V. AN n g h ~ sreserved.

699

OVERVIEW OF COAL ASH USE IN THE USA

Samuel S. Tyson American Coal Ash Association 1913 I Street N.W. - Suite 600 Washington, DC, 20006 USA SUMMARY

This paper describes coal ash produced by electric utilities in the USA. An overview is presented of the various applications in which this coal ash is used. 1. INTRODUCTION

The American Coal Ash Association, Inc. (ACAA) is an organization of producers, marketers and other organizations involved with utilization of coal ash, or coal combustion byproducts (CCBs). ACAA’s goal since its founding in 1968 has been to gain recognition and acceptance of coal ash as an engineering material on par with competing virgin, processed and manufactured materials by advancing coal ash uses that are technically sound, commercially effective, and environmentally safe. The use of CCBs is affected by local and regional factors including production rates; processing, transportation and handling costs; availability of competing materials; and experience of materials specifiers, design engineers, purchasing agents, contractors, legislators, regulators and other professionals. 2. ANNUAL CCB SURVEY A n annual survey of electric utilities is conducted by ACAA to determine the quantities of CCBs produced and used in the United States (1). In 1992 approximately 82 million short tons (for metric tons multiply short tons by 0.9078) of CCBs were produced in the USA in the form of fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) material. Approximately twenty-five percent of the combined production of these byproducts was used, while the remainder went to disposal areas. The approximate use quantities for these by-products are summarized in Table 1.

Table 1. Use of Coal Combustion By-products [1992 data; million short tons] Tons Used ( % Use)

Fly Ash 13.1 (27%)

Bottom Ash 3.9 (28%)

Boiler Slag 3.1 (75%)

FGD By-product 0.3 (2%)

700 It is clear from survey data gathered by ACAA over the years that the annual use of CCBs represents a major continuing effort by a number of parties, including the electric utility producers of ash and their marketers. It is equally clear, however, that significant tonnages of coal ash are not used each year. Therefore it is essential for ACAA to promote the use of coal combustion byproducts in numerous applications that are technically sound, commercially effective and environmentally safe. 3. CCB USES

CCBs are engineering materials with uses similar to the uses for competing virgin, processed and manufactured materials. It is instructive to consider the total tonnages of CCBs (fly ash, bottom ash, boiler slag and FGD material) that are used in the four leading markets for coal ash based on ACAA's 1992 survey results. This information is presented in Table 2. Table 2.

Use of CCBs in the Four Leading Markets [1992 data; million short tons)

Markets

Amount

Cement and Concrete Products Structural Fills Road Base and Subbase Blasting Grit/Roofing Granule Other Markets Total CCB usage

*

7.9 2.7 2.4 2.1 5.2 20.3

% of Usaqe*

38.9% 13.2% 11.7% 10.2% 26.0% 100.0%

Total CCB usage was 20.3 million tons which was 24.8 percent of the 82.0 million tons produced.

This paper describes each of these four leading markets for CCBs which together account for 74 percent of total CCB use in the USA. Additionally, the several categories of CCB uses that make up the other markets are summarized. 3.1

Cement and Concrete Products 3.1.1

Tmical Concrete

In 1992 approximately 7.1 million short tons of coal fly ash was used in the USA in cement and concrete products (1). The amount of fly ash in typical structural concrete applications ranges from 15 to 35 percent by weight of the total cementitious material (cement plus fly ash), with amounts up to 70 percent for massive walls and girders, road bases and dams.

70 1

Various concrete mixtures are produced with coal fly ash including normal weight and lightweight concretes, high strength concrete, early strength concrete for form removal requirements, low-slumppaving concrete, controlled low strength material (CLSM), and architectural concrete. With the principal exception of high strength concrete, all of these fly ash concrete mixtures are routinely air-entrained for added workability and for resistance to freezing and thawing. A state-of-the-artreport on the use of coal fly ash in concrete has been prepared by the American Concrete Institute (ACI) (2). Fly ash for use in concrete is covered in an ASTM specification (3). 3.1.2 Mixture Proportioninq The selection of mixture proportions for fly ash concrete is accomplished through the use of the same standard practices that are applied to any portland cement concrete. A document detailing a standard practice for normal, heavyweight and mass concretes is available from ACI (4). The ACI document shows computations for fly ash content specified either as a weight percentage or as a volume percentage of the total cementitious material content. The first approach, using weight equivalency, is probably the most common method in use. If the trial batches with and without fly ash are made to have the same ratio of water to cementitious material, then, as demonstrated in the ACI example: w/cl

=

w/(c2 + f ) ; where w

=

weight of water,

cl= weight of cement only, c2= weight of cement when used with fly ash, and f

=

weight of fly ash.

Because many fly ashes will bring about a significant decrease in water demand for the mixture, an absolute volume calculation is used to determine the small increase in sand to accommodate this slight volume decrease. Similarly, because of the assumption in the above example that cl = (c2 + f), and because fly ash has a lower specific gravity than portland cement, the mixture with fly ash will have a slightly greater volume. Again, absolute volume calculations are used to determine the small reduction in sand to accommodate this slight volume increase.

702 3.1.3

Roller ComDacted Concrete and Concrete Road Bases

The amount of fly ash in roller compacted concrete and concrete road bases, and in dams and massive walls and girders may be 70 percent or more of the total cementitious material. In such mixtures, where the fly ash content exceeds the portland cement content by a weight ratio of two or more, substantially increased curing times may be needed before placing the structure in service. For typical paving applications the percentage of fly ash will frequently be from 20 to 35 percent by weight of total cementitious material content, and normal curing times can be applied. For roller compacted concrete in paving applications reference documents are available from the ACI (51, the American Society of Civil Engineers (6) and the U.S. Army Corps of Engineers ( 7 )( 8 ) . 3.1.4 Concrete Block and Pilse

Fly ash and bottom ash are used in the manufacture of concrete masonry units, i.e., concrete block. Fly ash, because of its contribution to workability, strength and durability, is an important ingredient in the stiff mixtures used for concrete block. Similar attributes are cited for the selection of fly ash as a component of the stiff concrete mixtures used for concrete pipe. The several ASTM specifications for concrete pipe allow the use of fly ash by reference to either ASTM C 618, as discussed above for typical concrete mixtures, and ASTM C 595 (9). The concrete pipe specifications from ASTM are available through the American Concrete Pipe Association in a three-ring binder for convenient updating (10). 3.1.5

Lishtweisht Assresate

An ACAA symposium publication contains a number of papers describing traditional as well as developing uses of coal combustion by-products (11). One developing market is the manufacture of pelletized lightweight aggregate from coal fly ash by incorporating chemical admixtures and either lime (12) or portland cement (13) as activators, and from a third process using fly ash and coal cleaning mixtures (14). These lightweight aggregates are produced without the use of heat energy for sintering, however there is another process that produces a The lightweight aggregates sintered fly ash aggregate (15). produced without sintering are used primarily in concrete block, however some may be used in non-structural and structural concretes. A sub-committee of ACI Committee 213, on lightweight aggregate and lightweight aggregate concrete, is collecting information for publication on lightweight byproduct aggregates.

703 3.1.6

Flowable Mixtures

ACI Committee 229 deals with certain flowable grout-like materials under a general designation, "Controlled Low Strength Materials" (CLSM) (16). Such materials have compressive strengths equivalent to well compacted soils and may represent a wide range of fly ash contents. Applications include but are not limited to: backfills, structural fills, insulating fills, road and slab base, trench bedding and so on. While flowable mixtures can be produced without fly ash, it is very easy demonstrate that economical mixtures with the most desirable characteristics, including flowability, cohesiveness, minimal bleeding, and controlled density, can be produced only with fly ash in combination with relatively small amounts of portland cement. The percentage of fly ash used in grout mixtures may be in a wide range from 20 to 95 percent by weight. To produce a flowable mixture having a flowable consistency without segregation of the constituents, coal fly ash is typically proportioned with portland cement and water, with or without aggregate or other fillers. Some fly ashes with hihg lime contents can be used to produce a flowable mixture without cement. The use of CLSM flowable mixtures is open to numerous innovative engineering solutions for everyday problems that would otherwise be viewed as traditional soils backfilling and foundations problems. Such mixtures help to achieve economies through reduced labor and inspection costs, and allow contractors to reduce or eliminate certain labor and equipment costs. 3.2 Structural Fill Numerous structural fill applications of CCBs have been designed, constructed and evaluated over the last several decades. A number of such projects are described in re-publishedpapers from the proceedings of ACAA's international symposia (17). Coal fly ash is readily available in many locations to be used as a borrow material in lieu of soils for the construction of fills. When fly ash is compacted in lifts, the resulting structural fill is capable of supporting parking lots, buildings and roadways. Moistened fly ash can be used alone for structural fill applications. As with ordinary soils, optimum and target moisture contents can be established, along with procedures for achieving required levels of compaction. Open trenches can be cut in the compacted, non-cemented, fly ash for the placement of building footings and for the installation of pipes and cables.

704

When used in structural fills and embankments, fly ash offers several advantages over soil and rock: Low Unit Weight--Thecompacted maximum dry density of fly ash is typically about 10 to 20 percent less than that of ordinary soils. Placing fly ash over weak, compressible foundation soils results in lower total settlement. High Shear Strength--One of the most significant characteristics of fly ash used as a fill material is its strength. Compacted fly ash is as strong or stronger than many compacted soils. Moisture Control--Althoughthe optimum moisture content of fly ash is greater than that of silty soils, the compaction behavior of fly ash is relatively insensitive to variations in moisture content when it is placed with a moisture content that is less than its optimum moisture content. 3.3

Road Base and Subbase

ACAA has published a manual on the design and construction of pavement systems incorporating fly ash stabilized bases. The project to produce the manual was reported at a 1988 meeting of the American Society of Civil Engineers (18) where advice and comments were solicited. The ACAA pavement manual (19) offers pavement design engineers, materials engineers, and construction managers guidance in the design and construction of low- to high-strength Ilpozzolanic stabilized mixturer1( IIPSM1l) base and subbase layers having coal fly ash in combination with activators, aggregates and water. Users can choose from three pavement thickness design methods included in this manual: o

Method A - Flexible pavement structural layer coefficients;

o

Method B - Mechanistic pavement design procedures, using resilient modulus values for the pavement layers;

o

Method C - A combination of Method A and Method B, using mechanistic concepts to determine pavement layer coefficients.

design

procedures

using

To capture the long-term service and cost-saving features of PSM design, the document details a mixture proportioning system, a thickness design procedure, and established mixing and construction techniques. The user can apply the contents of this manual with professional advice to produce satisfactory pavement structures of acceptable uniformity in accordance with typical specifications and quality requirements of individual departments of transportation.

705 3.4

Blastinq Grit and Roofins Granules

Blasting grit and roofing granule applications, with an annual usage of 2.1 million short tons in 1992 represents 10.2% of the total coal ash used in that year. This market is extremely important to the coal ash industry as high-quality blasting grit and roofing granules are in fairly constant demand. The largest users of blasting grit are the large shipyards that perform contract maintenance for the U.S. Navy and for commercial shipping lines. The other users of blasting grit are supplied by a small number of companies which collect, size and bag the boiler slag and distribute it in small lots to numerous locations for use. Because the boiler slag that can be used for blasting grit is typically limited to slag produced in wet-bottom cyclone boilers, the long-term supply of this material will be related to the life of those boilers. The use of boiler slag as a roofing granule is subject to some of the same limitations as found for blasting grit. The large investment in facilities and equipment are factors which make use of boiler slag for roofing granules a regional manufacturing application with shipments of a finished product in small lots to numerous locations for use by a multitude of individual users. Miscellaneous uses of boiler slag are found in several decorative aggregate applications. For example, boiler slag has been used as a sand-substitute in sandtraps on golf courses; as an aggregate in precast and cast-in-placeconcrete to which a surface treatment is applied to expose this visually attractive material; and in less glamorous uses such as a sand-substitute in ashtrays for public buildings. 3.5

Other Markets

The several market categogies which together consume annually about 5.2 million short tons of CCBs in the USA are: filler in asphalt; anti-skid material for snow and ice on roadways; grouting; coal mine applications; wallboard manufacture; waste stabilization and solidification; and other low-volume applications such as fillers in plastics and paints. 4. CONCLUSION

ACAA is committed to increasing the use of CCBs in technically sound, commercially effective and environmentally safe applications and will work to ultimately achieve full use of these materials.

706 5. REFERENCES 1.

1992 Coal Combustion Bv-product Production and Consumption, American Coal Ash Association, Inc., Washington, D.C., 1993, 1 page.

2.

Use of Flv Ash in Concrete, American Concrete Institute, Committee 226 Report, ACI Materials Journal, Detroit, September-October 1987, pages 381-409.

3.

Standard Specification for Flv Ash and Raw or Calcined Natural Pozzolan for Use As a Mineral Admixture in Portland Cement Concrete, ASTM C 618, American Society for Testing and Materials, Philadelphia, 1993, 3 pages.

4.

Standard Practice for Selectins Proportions for Normal. Heavweisht and Mass Concrete, Committee 211 Report, ACI Manual of Concrete Practice, Part 1, Detroit, 1989.

5.

Roller ComDacted Concrete Pavement, Publication C - 8 , American Concrete Institute, Detroit, 1987, 55 pages.

6.

Roller Compacted Concrete 11, Conference Proceedings, American Society of Civil Engineers, San Diego, February 29-March 2, 1988.

7.

Encrineerins and Desisn - Roller ComDacted Concrete, U.S. Army Corps of Engineers, Engineer Manual 1110-2-2006, 1985.

8.

Roller ComDacted Concrete (RCC) Pavement for Airfields, Roads, Streets and Parkins Lots, U.S. Army Corps of Engineers, Guide Specification 02520, 1988.

9.

Standard Specification for Blended Hydraulic Cements, ASTM C 595, American Society for Testing and Materials, Philadelphia, 1986, 5 pages.

10.

ASTM Standards for Concrete PiDe, Authorized reprints of the American Society for Testing and Materials, American Concrete Pipe Association, Vienna, VA, 1988.

11.

Proceedinss: Eishth International Coal Ash Utilization Svmposium, Volumes 1 and 2, CS-5362, Washington, D.C., Prepared by American Coal Ash Association, Published by Electric Power Research Institute, October 1987, 870 pages.

12.

Ibid., Hay, Peter, "Aardelite - An Economical Lightweight Aggregate from Fly Ash," Paper No. 57, 7 pages.

13.

Ibid., Styron, Robert W., "Fly Ash Lightweight Aggregate: The Agglite Process,Il Paper No. 58, 12 pages.

707

14.

Ibid., Burnet, George, "Experimental Studies of the Production of Lightweight Aggregate from Fly Ash/Coal Cleaning Refuse Mixtures," Paper No. 61, 17 pages.

15.

Pulverized Fuel Ash Utilization, Central Generating Board, England, 1972, 104 pages.

16.

Committee Rosters, Missions, Goals, and Activities, American Concrete Institute, Detroit, June 30, 1988, 142 pages.

17.

Structural Fill ADDlications of Coal Ash, American Coal Ash Association, Washington, DC, 1993, 100 pages.

18.

"Guidelines for Design and Construction of Pozzolanic Stabilized Base Course Mixtures", DisDosal and Utilization of Electric Utility Wastes, Session Proceedings, American Society of Civil Engineers, Nashville, May 1988, page 35-49.

19.

"ACAA Pavement Manua1,I' Recommended Practice: Coal Fly Ash in Pozzolanic Stabilized Mixtures for Flexible Pavement Systems, American Coal Ash Association, December 1991, 64 pages plus Appendix.

Electricity

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A van der Sloot and 7'h.G. Aalbers (Editors) 61994 Elsevier Science B.V. All rights resewed.

709

Environmental life cycle analysis of construction products with and without recycling M. Sc.A. M. Schuurmans-Stehmanna 'Intron, institute for materials and environmental research B.V., P.O. Box 5187, 6130 PD Sittard, The Netherlands

summary To evaluate the effects of (construction) products on the environment a standardized methodology called Environmental Life Cycle Analysis of Products (LCA), has been developed in the Netherlands. This methodology evaluates products in their specific function and during their entire life cycle. "Environment measures" are obtained, which are used for a large number of objectives, varying from product comparison, environmental management within industries, product improvement and certification of construction products. Various LCAstudies of construction products have already been performed. Effects of recycling can be assessed fairly well. 1. INTRODUCTION The production and use of products have an influence on the environment. This influence, or environmental impact extends itself to all phases of the product life, from the winning of raw materials to the processing of waste. In this account the life cycle analysis (LCA) methodology for evaluation of the environmental impact as developed in the Netherlands will be examined as well as the possibilities this methodology offers. Examples of the application of this "cradle to grave" approach on construction products and the influence of recycling on the LCA-results will be discussed. 2.

METHODOLOGY

In the Netherlands the first National Environmental Policy Plan (NEPP) has been published in 1989 in which the objectives are set to come to a sustainable development of the environment. The NEPP introduces the so-called product policy aimed at promoting the use of products with the lowest possible environmental impact. To enable an evaluation of the environmental impact a standardized methodology has been developed by the Centre for Environmentology of the (state) University of Leiden (CML). This project was ordered by the Dutch Ministry for Housing, Physical Planning and Environment (VROM). The methodology is named "Environmental Life Cycle Analysis (or:

710

Assessment) of Products", in short LCA [l]. The concept of this LCA-methodology was also initiated by international discussions on LCA's within the Society for Environmental Toxicology and Chemistry (SETAC) in which environmental scientists, policymakers, industrialists and interest groups from various countries are involved. In a LCA, as the word indicates, the entire life cycle of a product is evaluated. In this life cycle about 3 phases are to be considered: the production, usage and the waste phase. Subject to the product these phases can be subdivided. The life cycle of construction products for example ranges from the winning of raw material, through producing materials and products, construction, use, maintenance and demolition to the treatment of waste. In the LCA-method all environmental effects of the product during its life cycle are quantified. To do so the processes of all life cycle phases which together form a so-called "process tree", are evaluated. If this is done in all details the amount of data required is enormous and the method is not feasible. As a consequence choices have to be made. That is why for example capital goods (machines, buildings) are not taken into account. In the analysis a large number of environmental aspects can be taken into account. In Table 1 a summary is given of the aspects the Ministry of VROM has chosen in 1992 [2]. For each product a relevant number of these aspects is selected. When all data are collected the environment-related data are aggregated per environmental aspect into one identification number. Aggregation is only possible when the data for one environmental aspect are expressed in the same unit; such units are called identification numbers. These numbers are calculated by means of standards and indices, called classification factors. The contribution of a product to the greenhouse effect for example is calculated by dividing the emissions per greenhouse gas by the global warming potential (GWP) of the gas. If for example a 100 mg CO, emits of which the GWP is 100, the contribution to the greenhouse effect following the C 0 2 emission is 1 unit greenhouse effect contribution. The methodology provides such classification factors for a large number of environmental aspects. By reproducing these factors in identification numbers the so-called environment measures are created. Each environmental aspect corresponds with an environment measure. This environment measure gives information in quantitative form about the environmental impact of one specific environmental aspect. The set of environment measures is called the environmental profile, signifying a sort of "environmental characteristic" of a product. Quantification presents several advantages, in particular for the evaluation. In the evaluation similar environmental aspects are compared. As a result of the fact that the aspects are quantified, the comparison is objective. However, because of this quantitative approach, there is a risk that qualitative aspects, such as the affects upon the landscape, are left aside. Therefore qualitative aspects are mentioned separately. As a basis for product comparison a functional unit is applied. The functional unit defines the function of the product, its size, its required service life in the context of the structure, its actual service life, the maintenance required and the possibilities for reuse. A LCA is thus performed on a product in its function. Consequently one cannot

Table 1. General framework for environment measures in the building industry II

aggregatmn environment measures..

raw matenals

pollution

1 2 3 4 5 6 7 8 9 10 11 12

depktmn of searcety renewable raw matenals (e g tropral wood ivory) depletlon of non-renewable raw matenals (a o minerals) total amount used raw materlals acldfcatlon nubmcatmn greenhouse effect depklwn ofozone layer toxical substances for people toxical substances for flora en fauna waste heat radlalwn waste bef6re treamnt

*-

not possible m many cases environment measures rehted to Other measures

.*.

waste

13 14 15

IS 17 18 19 20 21 22

23 24

25

nuisance

energy

re-usability

waste after treatment (final waste) chemical waste stench and d o u r noise pollution for userlenvironrnenl calamles damage lo eco systerrmandscape/environmental quallty depletlon of non renewable energy caners total amount used energy re usabihly of total product re-usability ofproduct components recyclabiltf of matenals extent of repairabiltf of the product servw llfe of Droduct

repairability

lfe

712 determine environment measures of a material as such, but very well of the product manufactured out of that material. Herewith justice is done to the specific application of the material in a product and the specific function of the product itself. For the building industry this has to be considered a prior condition for the evaluation of environmental aspects [lo].

3. APPLICATION Obviously it is meaningful to deal with the question for what purpose evaluations made by means of a LCA will be used. Several applications are possible, each of them intended for and corresponding with a specific target group in the building industry. An LCA is first of all an instrument to obtain environment-related information about a product. In the Netherlands this information is used as: - a marketing instrument for producers and suppliers on behalf of their customers (”instruction leaflet” for sales argument); - a means for product comparison (only acceptable with standardized method), on behalf of designers, clients, customers and users; - a comparison of products with standards, or the development of standards, useful for government institutions; - a basis for product or process improvement or innovation having producers as a target group; - a starting point to set up and study policy strategies, on behalf of the authorities; - a management tool as part of the environmental managment systems within a company; - a basis for the eco-labelling of products (EEC council regulation NP 880/92 of March 1992); - a basis for the certification of environmental aspects. The initiative to have life cycle assessments made, was initially taken by the government. At present environment-related information obtained by means of LCAs is used more and more in the promotion and communication policy of companies. 4. LCA OF WINDOW FRAMES

One of the first construction products on which a life cycle assessment (LCA) was performed, was the window frame [3]. Compared are frames of hard wood, pine wood, PVC and aluminium. Next to the frames as such, all other materials/products used for the assembly of window frames have been included in this study. They are packaging foils, finishing materials, sealants, paints etc. The most important results are summarized in Table 2. When we arrange the various environment identification numbers in another way by assigning the value 10 to the highest number and then linearly extrapolate the lower numbers, Table 3 is created. From this table we can deduce that none of the window frames scores better than the other ones on all points. However it is clear that the aluminium frame has the most negative points in general and stands somewhat out from

713 Table 2. Environment identification numbers of the various types of window frames for the living room of a public housing unit; state on July 1. 1990 [3] environment ldenbflcalron number

aluminium

pine wood

PAW MATERIALS

-

.

total use energy carner (MJ) affected kopical forest (m‘)

23 195 3.1

10 774 0,625

EMISSION INTO AIR

I

I merantl

1 1 lroko

12 088

222

”’%

2 583 1.1

251 7.1

514 ~_______

DISCHARGE INTO WATER . toxical substances (I) - others (kgll) * 2-chloroelhanol * lnchloroethanol * vinyhc chlonde =

soflener

6 020

74 500

6 770

8.49404 3.4040’ 1.61 405 3.65 . l o 3

1.10.10‘ 4.41 .lo‘ 2.094 Oa 0

16.1 162

Table 3. Relative environment identification numbers of the various types of window frames for the living room of a public housing unit [3] environment ldentfcdtton number RAW MATERIALS . total use energy carriers affected trooical forest

.

EMISSION INTO AIR toxtcal substances aciddying substances others * CFK 1 1 * carbon dmxide

-

DISCHARGE INTO WATER toxtca~substances others * 2-chloro-elhanol * trichbro-elhanol

-

*

vinyl chbnde

* soflsner

WASTE - chemtcal waste - other waste

aluminium

el ol

pine wood

I I 1:

iroko

1;

meranti

I

wc

Table 4. Environmental impact concrete first span of bridge (period of 75 years) [6]

4 e

P deplemn raw

drying up

acdmicamn

greenhouse

air pollwn

water pollubon

malenals 1Oe-12

1oe-12

1oe +5

effect 1De*5

1&+6

(kg)

chemical

nonchemlcal

energy

waste

waste (ton)

(GJ) 1&+3

103 36 16 13

(ton)

Pmducban Semmanuf

46000Oe+3

1200e+5

435

76

86725

56

79712

23254

PmducMn

1342e+3

108 31

48

113

21460

0.5

765

44 15

13 6

38065 212438 26540 21967

31 0.2

30728 382

1547 312 5862

634

149

385735

200 7

133047

mpl-

5e+3

Maintenance Renmval

3768e+3 4e+3

286ei5 0 168e+5 0

Total

46511-3

1654e+5

6

Table 5. Sensitivity analysis use of concrete rubble to replace gravel (concrete first span of bridge) [6] 20% broken cnnwete. 80% gravel

acidifation ChemlCal waste (kg) energy (GJ)

40% broken concrete. 60% grave4

4.65119.104

- 2.5%

634 .lo5

+ 2.7%

133.047 ton 176.10’

+ 2.9%

+ 1.8%

1

8

30976

176

715

the others. But if we state that the aluminium frame is less environment-friendly than the other window frames we enter into the field of the weighing factors. However a weighing can only be made between similar environmental aspects. Dissimilar aspects cannot be compared; this would be like comparing "apples and oranges": how can m2 of affected tropical forest be compared with units of polluted water or solid waste? In order to reduce environmental impact to a minimum, the university of Amsterdam has developed software to determine the effects of alternatives on the environment. Besides some design and material alternatives, the effects of recycling on the environmental profile are determined. Recycling of the window frame (material) as well as the use of secondary raw materials are considered. The environmental yield due to recycling varies from appr. 20% when recycling PVC frames to a 50% for pine wood frames. When measures are to be taken one should always consider that a measure which has a positive effect upon one of the environment identification numbers, might adversely affect other identification numbers. The study of the environmental data proves that other initial hypotheses do not give cause for other conclusions, at least for the principal aspects. The Life Cycle Assessment of the window frames shows that none of the frames scores better than the others in all aspects. The information provided and considered to be objective, offers the customer only an objective starting point from which he is to make a subjective choice. 5. LCA OF A BRIDGE

For a bridge crossing the river Waal an LCA-study is made on the impact of one of the spans of the bridge [ 6 ] .Two alternatives have been compared: one of concrete (reinforced concrete), the second of steel with concrete for the bridge deck. In both alternatives asphalt is the road topping. The LCA covers the total span including coatings, pipes (HDPE), PVC tubes to protect electrical cables, etc. For the alternative in concrete 20% concrete granulate produced from demolished concrete structures is used. For the alternative with steel, it was assumed that 17% of the steel was produced from scrap iron. In Table 4 the environmental profile of the span made of concrete is given. The study shows that on a number of environmental aspects the alternative in concrete scores better than the steel structure. But in this case as well, it is difficult to decide upon which alternative is the most environment-friendly. The purpose of the study was a(mong) o(thers) to gain a clear insight in the way both alternatives affect the environment. An effect analysis should help to reduce the impact as effectively as possible. Therefore it has been analysed which factors contributed most to the environmental impact and also a sensitivity analysis has been made. For the concrete for example the analysis has revealed that an increased use of concrete granulate (40% instead of the 20% assumed in the study), even though reducing the use of gravel, did not have much influence on the final figures. The depletion of raw materials is somewhat diminished, because of a decreased need for gravel, but the other units slightly augment as a result of the production of concrete granulate, see Table 5 . The steel alternative

716 profits substantially from a higher use of scrap iron (a 100% instead of 17%). 6. LCA OF ROADS

Intron has in cooperation with TNO-Bouw performed an LCA-study of a concrete and an asphalt road [9]. One of the objects of the project was to assess the feasability of the LCA-method adopted by the Ministery VROM for the building industry and to discover areas which have to be improved. As the functional unit has been chosen a road section with a service life of 60 years. It was concluded that transport of road construction materials and energy for production of the materials were main sources of the environmental impact. Recycling of road construction materials at the road construction site when asphalt etc has to be renewed is identified as an important possibility for reducing the environmental impact. In the concrete road for example on-site crushing of concrete is possible for use as unstabilized roadbase or for preparing new concrete with this concrete ”waste”. On-siteheuse of asphalt is already common practice. Crushed asphalt is mixed with sand and cement for use as roadbase (cold reuse). However, off-site recycling, is still preferred. Techniques to obtain the same quality of secondary material on-site is still in development. In a follow-up of the project environmental profiles of alternative road constructing, the effects of recycling options, the use of industrial secondary materials such as replacement of gravel by secondary material or concrete aggregate, secondary asphalt, will be studied.

7. DEVELOPMENTS The Dutch ministry of VROM has commissioned LCAs of other building products such as roofing sheets and building paints [7, 81. LCAs are not only made on the initiative of the government, but also and frequently on the initiative of the industry. Intron has recently made an LCA of the building cladding material TRESPA G2. TRESPA G2 is a product of Hoechst Holland. Hoechst intends to use the environmental profile of Trespa for environmental management within the company and for certification. In the past year it is studied in which way LCAs can be used in the certification of building products and processes. A so called ”environmental paragraph” will be added to the already existing certificates. It is likely that products of which environmental data based on the adopted LCA-method are available and which meet environmental requirements will be granted such an additional environmental certificate. The first environment paragraphs are in development at the moment. The Dutch ministry of VROM plans to make operational the environment measures system in the building industry beyond 1994.

717

8. CONCLUSION The methodology for an environment-oriented life cycle assessment of products offers a potential basis for a standard method to measure the potential effects of a (construction) product on the environment. The LCA provides a set of environment measures, the environment profile, which represents the environment characteristic of the product. Only similar environmental aspects can be compared. Attempts to arrive at one figure for each product are deemed to be based on biased criteria. The examples show that a final judgement of the environment-friendliness of a product in relation to another product based on unbiased criteria cannot always be made. However analyses will offer well-founded and qualified information as an objective starting point for a subjective choice to be made by the purchaser of the product. Besides product comparison numerous other applications of LCAs are possible, from which environmental management within industries, product improvement, marketing and environment certification are already applied in the Dutch building branch. The effect of alternatives such as recycling can be measured fairly well.

9. LITERATURE 1. Guinee, J.B., Heijungs, R., Huppes, G., Lankreijer, R.M. (Centrum voor Milieu-

2. 3. 4.

5.

6.

kunde Rijksuniversiteit Leiden CML/Centre for Environmentology R. U.Leiden), Ansems, A.M.M., Eggels, P.G. (TNO),De Goede, H., Van Duin, R. (Bureau Brand- en grondstoffen B&G/Bureau for Fuels and Raw Materials), "Milieugerichte levenscyciusanalyses van produkted "Environment-oriented life cycle assessments. Deel I: handleiding/ Part I: Introduction. Deel 11: achtergrondedpart 11: Backgrounds", oktober 1992. DGM ministerie VROM, "Milieumaten in het milieubeleid-Stand van zaken per I September 1991/ Environment measures-State of affairs per September 1. 1992", 3 September 1991. Lindeyer, E., Mekel, O., Huppes, G., Hacke, R., "Milieu-effekten van kozijneniEnvironmenta1 effects of window frames", Centrum voor Milieukunde R. U. LeidedCentre for Environmentology U./Leiden, 1990. Hoefnagels, F.E.T., Kortman, J.G.M., Lindeyer, E.W., "Minimaliseren van de milieubelasting van buitenkozijnedTo minimize the environmental impact of outside window frames", Interfacultaire Vakgroep Milieukunde U. A./Interfaculty department U./Amsterdam, 1991. VNCI. "Integrated substance chain management", uitgevoerd door McKinsey & Company, december 1991. Fraanje, P., Jannink, H., De Lange, V., Lim, R., "Milieu-vergelijking van twee aanbruggedEnvironmenta1 comparison of two first spans of bridges", Interfacultaire Vakgroep Milieukunde Universiteit van Amsterdam (IVAM)/Interfaculty department Environmentology U./Amsterdam, in opdracht van /commissioned by VROM-DCB, IVAM-onderzoeksreeks N.57. oktober 1992.

718 7 . Tromp, W.F.T., Korenromp, R.H.J., Nieuwenhuis, J.W. ( T A W Infra Consult BV), "Milieumaten van dakplaten, een casestudie (concept)/Environment measures of roofing sheets, a case study (concept)", ministerie van VROM-DGMlIBPC, nog niet gepubliceerdlnot published yet. 8. Manders-Maanders, E.H.C., Technische Universiteit Eindhoven (Faculteit Bouwkunde, Vakgroep Fysische Aspecten van de Gebouwde Omgeving, Groep Materiaalkunde/Faculty of Civil engineering, department Physical Aspects of the built environment, Group Materials science), "Milieumatenstudie van vier bouwverven. Een oefenprojekt/Study of environment measures of four building paints. A work project", performed within the National Research program 'Re-use of Waste materials/ uitgevoerd in het kader van het Nationaal Onderzoekprogramma Hergebruik van Afvalstoffen (NOH), NOVEM, RIVM, mei 1992. 9. Schuurmans-Stehmann, A.M. (Intron), Siemes, A.J.M. (TNO-bouw), "Uitwerking milieumatenconcept voor de bouw aan de hand van een voorbeeld. Proefprojekt weg/Elaboration of environment measures concept for the building industry based upon an example. Road test project", CUR Gouda, november 1992. 10. Schuurmans-Stehmann, A.M., Hendriks, Ch.F. (Intron), "Naar een milieumaat voor bouwproduktedTowards an environment measure for building products", Cement nr. 718, 1992 p. 56-59.

Environmental Aspects of Conshcction with Waste Materials J.J.J.M. Goumans, H A . van &r SIoot and Th.G.Aalbem (Editom) el994 Elsevier Science B. K All tights reserved.

719

ASSESSMENT OF THE ENVIRONMENTAL COMPATIBILITY BY-PRODUCTS AND RECYCLED MATERIALS

OF INDUSTRIAL

R. Bialucha *, J. Geiseler and K. Krass **

Forschungsinstitut der Duisburg (Germany) **

Forschungsgemeinschaft

Eisenhuttenschlacken,

lnstitut fur Strassenwesen und Eisenbahnbau, Ruhr-Universitat Bochum, Bochum (Germany)

SUMMARY

Substantial quantities of industrial by-products and recycled materials can be used in road construction. This means a saving in the consumption of natural resources. The precondition for the utilization of industrial by-products and recycled materials is their technology and ecological suitability. Attempts have repeatedly been made to assess the environmental compatibility - in particular the impact on surface water and groundwater - of industrial by-products and recycled materials in the same way as for waste materials. However, a clear distinction must be made between waste materials which are to be disposed of by dumping and the industrial by-products and recycled materials which can be used as aggregates for road construction. The test methods which are used for waste materials therefore cannot be applied to industrial by-products and recycled materials that are employed in the building and construction industry.

1.

INTRODUCTION

The theme of this conference is "Waste materials in construction".The term "waste materials" can have a very broad meaning in English: it covers both waste materials which are disposed of by dumping and residual and by-products of a series of industries which are suitable for use in many different sectors, including road construction. A clear distinction must therefore be drawn between these two groups of materials. Materials which are to be used, for example, as aggregates for road construction must have a carefully defined and uniform composition. Their origin must be known, their production characteristics must remain constant over a lengthy period of time and they must satisfy the requirements laid down in the relevant specifications. On the other hand, waste materials which have to be disposed of by dumping are often of unknown composition and origin and certainly do not satisfy the

720 requirements of road construction specifications. These waste materials must therefore undergo a completely different process of investigation and assessment than materials whose origin and composition are known. To enable a clear distinction to be drawn between these two different groups of materials, we do not describe materials which are suitable for use in road construction as "waste materials" in this article but use instead the terms "industrial by-products" and "recycled materials" or, more generally, "aggregates".

2.

ASSESSMENT OF THE ENVIRONMENTAL COMPATIBILITY OF AGGREGATES

Various methods are available to assess the environmental compatibility of an aggregate. Firstly, the total content of all the individual components may be determined and secondly the leaching characteristics of a particular aggregate may be investigated. Information on the chemical composition enables the risks of the relevant material to be determined, but it remains unknown whether the individual components will ever be released. In Germany, it is therefore widely accepted that while the chemical composition can be used for general characterization of an aggregate, this information is not appropriate for an assessment of the acceptability of the material as far as effect on water resources is concerned. The potentially harmful substances which may be released under practical conditions tend therefore to be decisive in assessing the influence of an aggregate on the soil and water. The compatibility of an aggregate with water resources is therefore determined by reference to the concentrations of environmentally relevant components which may be leached out. It is only in the case of certain organic compounds for which the eluate values are insufficiently, if at all, relevant that the solid composition is partly also taken into account in addition to the eluate values. Based on the eluate contents there are two fundamentally different systems for determination of the compatibility of industrial by-products and recycled materials with the water resources. The first possibility consists of determining uniform limit values for the aggregates which may, for example, be guided by the leaching characteristics of natural soil and rocks. These limit values are considered to be environmentallycompatible and must then be respected by all the different industrial by-products and recycled materials. The second possibility is to determine the normal range of contents of environmentally-relevant components on the basis of extensive investigations and long years of experiences. It will then be possible to arrive at limit values for the specific substance which must be respected by a regular quality control. In practice, the uniform assessment of all industrial by-products and recycled materials on the basis of universal limit values is very unfavourable. The acquisition of extensive data on the leaching characteristics of all the industrial by-products and recycled materials which currently undergo quality control in North Rhine Westfalia has shown just how different these materials in fact are and how their potential uses

72 1 also vary as a result. A great many aggregates will not be able to satisfy universal limit values on every point. In consequence, the use of an aggregate may be ruled out because a single limit value is exceeded. The result of this approach is that a great many aggregates which would be particularly suitable for use in road construction, provided that certain background conditions are satisfied, cannot be used. The only remaining solution is to dispose of these materials by dumping. On the other hand, the definition of specific limit values for a particular material offers a much better possibility of finding suitable application areas for industrial byproducts and recycled materials. As a function of the leaching characteristics of an aggregate which are determined by the limit values specific to the particular material, the potential uses can be determined having regard to the engineering application areas and the hydrogeological circumstances. That is the concept underlying working document No. 28/1 entitled "Environmental compatibility of aggregates, Section: compatibility with water resources" [ l ] which was published at the end of 1992 by the Forschungsgesellschaft fur Strassen- und Verkehrswesen (FGSV)). That document deals with the compatibility with water resources of eight different industrial by-products and recycled materials which currently undergo quality control. The particular materials are as follows:

- Air cooled blast furnace slag - Granulated blast furnace slag

-

BOS slag Electric arc furnace slag (from bulk steel production) Slag tap (from coal fired power plants) Coal fly ash Municipal waste incineration ash (1,Il) Colliery spoil (I, II) Recycled material (I, II)

The three following types of aggregate: municipal waste incineration ash, colliery spoil and recycled material are further subdivided into two sub-groups whose leaching characteristics differ as a result of various possible ways of quality improvement. Specific limit values are determined for these aggregates and potential uses indicated as a function of the construction technique and hydrogeological background conditions. Fiaure 1shows, by way of example, the limit values determined for air cooled blast furnace slag, municipal waste incineration ash and recycled material. In general, a distinction will be drawn between the construction techniques shown in Fiaure 2 as far as the use of industrial by-products and recycled materials is concerned. Decisive factors for the potential uses of aggregates with reference to their influence on the water and soil include, in particular, the use of an aggregate in a bound or unbound layer and the accessibility of seepage water which will depend in part on the permeability of the layers above the aggregate.

722

1) not limit values but typical values 2) value corresponds t o Thiosulphate sulphur 3) sum of the single compounds named in the drinking water supply regulation 4) for record only 5) eluate value is decisive BFS = air cooled blast furnace slag MWI = municipal waste incineration ash RCL = recycled material

m: Limit values for some aggregates Fiaure 9 shows the hydrogeological background conditions for the use of industrial by-products and recycled materials. The location of the site must be assessed so as to ascertain whether it is situated within or outside areas which are either particularly relevant from the aspect of water resources or hydrogeologically sensitive. In addition, the distance between the aggregate layer and the highest ground water level must be taken into account. A matrix is plotted for each individual aggregate with the construction technique (see Figure 2) and the location of the site (see Figure 3) as its coordinates.

123

T

. .

Y P E

0 F

road pavement

inbound layers

C 0 N

.

S T R U C

Iound layers

.

T

ioise barrier

. . .

I 0 N

earthworks

Lubgrade ;tabilization

as wearing course under waterproof wearing course (concrete, asphalt, sett paving with waterproof joints) under semi-pervious wearing course ( sett paving, plates, wearing course without binders) under water pervious wearing course (open porous sett pavina) as course with hydraulical binder as course with bitumen with surface water proofing with water pervious course

m: 3.

Possible applications for industrial by-products and recycled materials

LEACHING PROCEDURE

Working document No. 28/1 prescribes a modified DEV-S4 technique as the leaching procedure. The DEV-S4 procedure (DIN 38414, Part 4 [2])is currently the only leaching technique to be covered by a standard in Germany and is therefore the most widely used. It was originally developed for the investigation of sludges and sediments, i.e. for materials with a very fine particle size. This technique therefore only has limited suitability for the investigation of road construction materials which generally consist of larger lumps. The working document accordingly sets out a number of modifications in relation to the standardized DEV-S4 procedure; these modifications relate essentially to the grain size and quantity of the material to be investigated. The aggregates which are to be studied should be leached in quantities of up to 2,500 g in their original grain size. The tank leaching test (see Fiaure 4, 131) is more suitable for use in practice. 2 kg of the material under investigation in the original grain size up to a maximum grain size of 32 mm are leached with ten times their volume of demineralized water

124 for 24 hours in a tank made of polypropylene or glass with a capacity of about 30 litres. The material sample is placed on a mesh to permit the best possible flow rate.

LOCATION OF CONSTRUCTION PROJECT outside of areas important to water supplies and hydrogeologically sensitive 0,l < G W < l I GW > 1

I

I

restricted parts of catchment areas/ ,mineralspring 1 reserves GWe1 GW>1 GW>O,l

Fia. 3 :

aquifer with natural cover

fissure- and karst- aquifer

near to catchment area of surface waters

near to margins of sensitive waters

GW<1 GW>1 GW<1 GW>1 GW<1 GW>l GW>O,l GW>O,l GW>O,l

Hydrological conditions for the employment of industrial by-products and recycled materials

The advantage of the tank method, as compared with the modified DEWS4 procedure, lies in the fact that it is unnecessary to agitate the entire container; only the leaching medium is constantly circulated round the aggregate to permit intensive leaching within a short period of investigation. The leaching medium is circulated by means of a magnetic stirrer positioned on the base of the tank. This avoids severe mechanical stress on the material undergoing investigation in the tank method. Another advantage of the tank method is that both unbound and bound substances can be investigated. Figure 4 shows, by way of example, a test cube resting on the mesh. This permits direct comparison of the leaching characteristics of a material in both unbound and bound form. The procedural specification for this tank method is currently being incorporated into the FGSV working document. The intention is to use the tank method in future as a substitute for the modified DEV-S4 procedure for routine examinations. However, for that to be possible it remains necessary to define limit values. Previous comparative tests have shown that the results obtained by the tank method are of the same order of magnitude as the results of the modified DEV-S4 procedure.

725

tank

40 cm

test cube

I

I /lE

mesh /aperture:

2 mm

stopcock magnetic stirrer

not to scale

Fig.4 :

Tank leaching test

To permit the investigation of unknown, or inadequately known, substances, a comprehensive suitability test must first be carried out. For this purpose, routine methods such as the DEV-S4 procedure and the tank method are not sufficient on their own. Other techniques must also be used which will, for example, enable conclusions to be drawn in respect of the long-term behaviour of an aggregate. A percolation method and a pH-4-stat method are currently being considered. However, both these techniques are still in the development phase and cannot therefore be described in more detail.

4.

CONCLUSION

1.

A clear distinction must be drawn between waste materials that have to be disposed of by dumping and materials which can be used for road construction.

726 2.

Because of the imposition of uniform limit values and the assessment of all industrial by-products and recycled materials on the basis of those limit values, many of these materials are excluded from further processing, although they might be used under certain circumstances.

3.

The optimum use of industrial by-products and recycled materials is made possible by taking account of the special features of each aggregate by determining specific limit values for each material. If these limit values are respected in the framework of regular quality control, the aggregates can be used having regard to the prevailing construction engineering and hydrogeological conditions.

4.

In order to ascertain whether an aggregate satisfies the limit values for a specific material, a routine leaching method is required which can be used rapidly and easily and provides readily reproducible results. A modified DEV-S4 procedure is used as the routine technique and might later be replaced by the tank leaching test

5.

Unknown aggregates must first undergo more extensive investigation. Techniques such as the percolation and pH-4-stat method can be used for this purpose. Both these methods are currently undergoing further development.

REFERENCES

FGSV- working document no. 28/1 "Environmental compatibility of aggregates, Section: compatibility with water resources" Forschungsgesellschaft fur Strassen- und Verkehrswesen, 1992 DIN 38414, part 4: German standard methods for water, wastewater and sludge investigation; sludge and sediments (group S); Determination of the leachability with water, 1984

[31

R. Bialucha and G. Spanka: "Tank leaching test for aggregates" Report of the working group no. 6.4.1 "Leaching tests for aggregates" of the FGSV Strasse + Autobahn 5/1993, pp. 297 - 300

Environmental Aspects of Constmction with Wasre Materials JJJM. Goumans, H A van der Sloot and Th.G. Aalbem (Editom) @I994 Elsevier Science B. V: All rights reserved.

727

Environmental management in large construction projects. Erik K. Lauritzen DEMEX Consulting Engineers AIS, Hejrevej 26, 3rd floor, DK-2400 Copenhagen NV, Denmark

Abstract Based on experiences gained from the Great Belt Link and 0resund Link projects together with the work in the RILEM Technical Committees 34 and 121 on Demolition and Recycling of Concrete and Masonry, it is stated that much of the demolition and construction waste material generated in large construction projects can be reused. Construction and demolition waste management and handling is an important part of environmental management according to BS 7750. Recycled building rubble could substitute natural resources.

1. Introduction In December 1992 the construction of the 0resund Link between Denmark and Sweden started with the demolition of houses and site clearing before the proper construction work. Due to the high requirements of environmental protection and quality assurance, the management of the Oresund Link Company dealing with the Danish land structures decided to implement the Environmental Management System as described in British Standard BS: 7750: 1992 [l]. According to this standard, an environmental management policy was stated and certain goals for the environmental protection were specified for the construction work as well as the operation of the link-structures, Among the issues of the environmental policy, it has been stated that all generated demoliton and construction waste (C&D waste) should be reused as much as possible and handled in such a way that the load of the enviornment should be limited. In May 1993 another great project in Denmark, the Great Belt Link between Zealand and Fyn, reached an important milestone. The Great Belt Link consists of three major projects: the 6,800 m long bridge and the 8,000 m long railway tunnel under the eastern channel between Zealand and Sproge, and the combined road and railway bridge across the western channel between Sproge and Fyn. The construction of the 6.6 km long West Bridge was completed, whereafter, the demolition of prefabrication yard could be started. The two great projects clearly demonstrate what is typical for most modem construction projects: They start with demolition work and they end with demolition work. Furthermore, during the construction process a lot of waste is generated.

728

Fig. 1. The two giants of civil engineering in Denmark - The Great Belt Link between the Danish islands Zealand and Fyn, and The Bresund Link between Denmark and Sweden. A third project, m e Fehmam Belt Link to Germany, is also discussed.

2. Generation of C&D-waste During the life cycle of any building and construction, waste will be generated, and the disposal of the waste will require some considerations and money. Referring to the two mentioned construction projects the generation of the different types of waste can be classified as follows: a.

Preparatory works Demolition of buildings and structures Clearing of old or superfluous infrastructures (roads, sewers etc.)

b.

Construction works Spill of resources and materials Surplus of resources and materials Rejected resources and materials Demolition of provisional structures Demolition of structures due to failures, hazards and changes of the project Packing, containers, etc.

729 c.

Site clearing Demolition of provisional structures Different kinds of remains

-

d.

Operation of the structure Maintenance Repair work

e.

Reconstruction or demolition

Fig. 2. Demolition of one of houses before the construction works of the 0resund Link 1993 in Copenhagen. The timber is recovered for reuse, und the insulution material is removedfrom the walls and disposed of ar controlled 1und.fill. 2.1. Preparatory works The need for demolition during preparatory works depends on the the actual construction site. The connection roads and railways on the Danish side of the Oeresund Belt Link go through city areas which requires the demolition of more than 400 family houses, shops and other structures, comprising some hundred thousand tonnes of demolition waste. The demolition of the houses has been performed as selective demolition with a very high demand for the reuse of waste materials. Most of the windows, doors, boards and timber have been reused, and the concrete and masonry rubble has been recycled and used as construction materials. The recycling of materials has been very successful, 90-95 % of all building waste has been reused [2]. The construction of the Great Belt Link did not require the demolition of so many houses. However, a 5 year old motorway bridge with 11.OOO tonnes heavily reinforced

730

concrete has been demolished, and all the concrete has been recycled. Some of the concrete rubble has been crushed and used as aggregates in new concrete in "The Recycled House" in Odense [3]. See fig. 3. 2.2. Construction works Due to the strict requirements of concrete quality and to other difficulties, a considerable number of tunnel elements and some bridge elements were rejected in the initial stages of the tunnelling contract and the West Bridge contract. Many of the rejected tunnel elements were reused for other purposes, and the rejected bridge elements were demolished by use of explosives on site. According to Loosemore [4], the construction of the West Bridge involved the production and placing of some 480,000 m3 of concrete. Approximately 1% of the concrete produced, ie. some 12,000 t, had to be disposed of due to over-ordering of concrete and the rejection of mixed concrete. During the peak construction period, 7,000 m3 of concrete were produced per week. The concrete was distributed from two site batches using a fleet of concrete wagons each with a capacity of 6 m3 Certain plans for the management and disposal of the waste ready mixed concrete were necessary, and in the peak periods approximately 70 m3 waste concrete was produced! Initially, investigations took place to see if the concrete could be used to prefabricate small temporary works items as used by most contractors. This solution was not progressed because the supply of waste concrete was generally intermittent and, when available, usually in large loads (6 m3 per wagon). Estimates indicated that the cheapest solution would be to crush the concrete and sell it to other contractors for either haul roads on their sites or to upgrade temporary roads on farmland. The concrete was ideal for crushing as it contained no reinforcement or incast items. An area of approximately 50 m x 40 m was designated as the official tipping area for waste concrete. Once the storage area started to become full, a mobile crushing plant was hired to crush the concrete in two sizes, 0 to 32 mm and 32 mm to 60 mm, which was sold at 30-40 DKK per m3. Generally, from the construction work a lot of paper, plastic, insulation, coating etc. is produced which not is reusable and must be disposed of at controlled land fills.

2.3. Site Clearing After completion of the West Bridge project, the temporary Lindholm Concrete Prefabrication Yard was demolished. This demolition project, involving 35,000 m3 reinforced concrete, 7,000 t of steel and 5,000 t of asphalt, started in June 1993 and was finished by the end of 1993. Some of the demolition works were planned and prepared for blasting. For instance, parts of the structures have been supplied with pipes during the construction with the purpose that the pipes should be used as boreholes for the blasting work. Unfortunately, many of the pipes were wrongly placed and unfit for the blasting job. By the end of the entire Great Belt Link construction work, the temporary tunnel prefabrication yard in Korsm and the construction site in Kalundborg for the East Bridge will also have to be cleared. In considering the total amount of construction and demoli tion waste, spill, refuse, packaging etc. we are dealing with very large figures - several hundred thousand tonnes - which clearly indicates the need for planning, management and recycling.

73 1

Fig. 3. Photos showing reinforced concrete bridge which has been demolished because it was not applicable to the Great Belt Link. After demolition some of the crushed concrete was used as aggregates in new concrete in "The Recycled House" in Odense.

732

As a concluding remark concerning the Great Belt Link project we should also mention that the link will close the present ferry line across the Belt. This will make all f e q berths superfluous, and result in several hundred thousand tonnes more concrete waste!

2.4. Operation of the structure Maintenance and repair of the structure require a certain amount of structural work and will cause some waste product. However, we are not dealing with greater amounts of waste, but we should not forget to take the waste management into consideration. 2.5. Reconstruction and demolition Normaly nobody will think of reconstruction and demolition during the construction process of major structures. Unfortunately, it happens that bridges and other structures get damaged from hazards and disasters, which requires reconstruction work. Dealing with Environmental Managment according BS7750:92 it should be noticed that risk analyses of different hazard scenarios are recommended.

3. Selective demolition of houses In accordance to Law no. 590 of 19th August 1991 concerning the establishment of the land infrastructure for the Oresund Link, expropriation and demolition of a large number of buildings in Copenhagen has begun. This consists of approximately 200 family houses in T h b y borough and 150 detached houses in the Municipality of Copenhagen. The demolition is being carried out in a number of different contracts, each of 15 - 30 houses. The management and planning body concerned with the land infrastructure in Copenhagen, A/S Oresundsforbindelsen, has sub-contracted the project planning and supervision of the demolition work to DEMEX Consulting Engineers AIS. The separate contracts are carried out as the houses are expropriated and cleared for demolition. As a result, buildings to be demolished under any one contract are spread throughout the area, some of these being adjacent to still inhabited houses. This places considerable demands on the demolition techniques. Consequently, A/S 0resundsforbindelsen has decided that the demolition should be carried out in three steps: 1. Initially buildings are demolished to the foundation, and the cleaned demolition waste is temporarily deposited within the foundation area. This avoids the use of large machinery and thus reduces the environmental impact on the surrounding neighbourhood. The sites are cleared of trees and bushes, concrete and masonry rubble removed, 2. and buried oil tanks dug up. Roads and remaining structures which are not needed for temporary use are 3. removed. The initial demolition of the buildings is carried out as selective demolition, according to experience gained during demonstration projects performed with the Danish National Agency of Environment. Since A/S Oresundsforbindelsen emphasises the importance of the demolition not disturbing the surrounding environment, the demolition work is executed as follows:

733 -

-

All demolition products are dismantled and sorted on site with the intention of maximum recycling. All environmental nuisance is kept to a minimum. Movement of machinery and vehicles is carried out with great care and the least possible disturbance to neighbours. Disturbance to gardens surrounding the houses is kept to a minimum. Demolition and temporary dumping sites are kept in a clean and orderly manner.

Before the start of the separate contracts, the previous owners are asked to remove all possessions of personal interest, such as doors and fixed effects. Thereafter, the nearby youth clubs are given the opportunity to remove remaining effects for sale, the profits of which go directly to the operation of the clubs. It is the contractor’s duty to demolish the houses in the following order: Removal of remaining furniture and other efects. 1. Removal of all wastes for special treatment: e.g. asbestos, oil tanks, chemical 2. wastes etc. Removal of all indoor installations and building materials, doors, windows, floors 3. for reuse. All plaster, insulation and other dust-producing material must be removed by vacuum in closed containers. Dismantling of roof structure for reuse as rooting materials and timber 4. Demolishing of walls, leaving the rubble in proper heaps. 5. Sorting of the rubble for all impurities such as paper, wood, plastics etc. 6. All materials except foundation and the rubble must be removed without any noise or inconvenience to neighbours. Most of the materials are kept for reuse, and only very little has been deposited in controlled landfills. Fig. 4 shows a cross section of a typical Danish family house with some 100 - 150 mz floorage. It produces approximately 1.0 - 1.5 t building waste per square meter. Because situation concerning the acquisition of property under compulsory powers is politically sensitive, special consideration must be paid to the remaining inhabitants in the area. Demolition must be carried out with wheeled machinery under 12 tonnes net weight. Noisy tools are not permitted, and emission of dust is not accepted. The provision supply of electricity, heat, water, and sewage etc. must not be interrupted, and the roads must be kept clean and free of any obstructions. In fig. 4 the different classes of wastes are shown. Class A contains recyclable materials of which concrete and masonry rubble should be left on site, whereas Class B and C should be removed for special treatment, incineration or tipping. The figure shows the distribution of the different fractions of waste materials, also. The philosophy of leaving the concrete and masonry rubble was that it would be easier, and hence cheaper, to remove of all the rubble when the greater part of the houses has been demolished and no special considerations were needed any longer. Initially, it was planned to crush the concrete and masonry rubble into aggregate for temporary roads used in the project. Later, however, it was discovered that Copenhagen Harbour needed material for construction of new dams for a planned land reclamation project. Therefore, it was necessary to calculate the most feasible economic solution.

134

Sla-

Fig. 4 Cross section of a typical Danish.family house with indication of the dwerent kinds of building materials and classes of waste.

I74doond2u)-MU5W& =TCWONVi a i - - p l F a u m i a d ~ * * ~ ~

*

735

4. Recycling and cleaner technology In June 1992, the Danish Minister of Environment presented two action plans, "Waste and Recycling 1993-97" and "Cleaner Technology 1993-97", to the Danish Parliament's Environmental Planning Committee. The plans included initiatives to be taken in the next five year period in order to reduce the amount of waste and to ensure the development and implementation of cleaner technology. Attention was especially drawn to the increased goal for reuse of building and construction waste. The previous target of 50 % of all construction and demolition waste to be reused by the year 2000 was increased to 60 %. Furthermore, the disposal fees for waste were increased from 1 January 1993, the new values being 195 DKK/ton (32 US$/ton) for dumping and 160 DKK/ton (27 US$/ton) for incineration. The two action plans have been combined to form one action plan for the construction industry. This is due to the difficulty of separating the concepts recycling and cleaner technology in the field of building and construction. The long term aim of the plan is to promote the initiatives for reducing both the use of resources and also the environmental impact in all stages of the life-cycles of buildings and constructions. The basic strategic element of the plan is the consideration of the life-cycle of total resource utilisation and the resulting impact on the environment. Thus, we are able to show the possibility of introducing cleaner technology, thereby aiding the decisionmaking process by fixing an order of priority, classification and implementation of the necessary initiatives. The plan strongly emphasises the following areas: Investigation of materials and building components Investigation and development of minimal forms of construction Minimisation of excess and waste, combined with an increase in recycling Analysis of industry and construction Development of models for life-cycle evaluation Environmentally, friendly planning Economic and administrative control systems.

As examples of actual projects where considerations for cleaner technology are required, we have used the two above mentioned construction projects in Denmark. Due to the size and importance of these projects, the decision-making processes involved have been heavily influenced by the evaluation of the resources required and the resulting impact on the environment. During the project planning of building and construction projects, it is important that a very accurate evaluation is carried out of all the relationships concerning the extraction of raw materials, production of components, actual construction and operation. The immediate requirement for demolition concerns structures which either lie in the way of the project or ones which were specifically built for the purpose of the project. During the construction of The Great Belt Link, considerable resources were used for the construction of concrete mixing plants, foundations, roads and such; these will be removed when the project is completed. The same kind of temporary works are to be built for the Oresund Link.

736

5. Conclusions From the work performed in the the two RILEM Technical Committees 34 and 121 on Demolition and Reuse of Concrete and Masonory, which has been presented at three symposia on demolition and recycling (Rotterdam 1985, Tokyo 1988 and Odense 1993) [5,6 and 71, it has clearly been demonstrated, that there is no technical limit for the reuse of concrete and masonry rubble - in principle. However, at lot of questions and barriers will always exist, and the economical and legal aspects are not clearly described, yet. Thus, with the beginning of the Oresund Link project, much care has been taken in the conservation of natural resources and the impact on the environment. At the same time it has become clear that the terms Recycling and Cleaner technology are gaining more and more recognition and importance in the building and construction industry. Recycling and cleaner technology are no longer idealistic concepts which never reach the reality of the construction site. In this project 90 % of all C&D Waste has been reused. Cleaner technology concerns the rational principles and attitudes which aim to continuously reduce the use of resources and the load on the environment for the benefit of society as a whole.

References: 1

Environmental management systems, British Standard BS 7750:1992

2

Lauritzen. Erik K. and Jannerup, Morten: Guidelines and experiences from demolition of houses in connection with the 0esund Link between Denmark and Sweden, 3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

3

Olsen, E.B.: The "Recucled House" in Odense,3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

4

Loosemore, C.E.: The Great Belt Link Project, 3rd International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24 - 27 October 1993

5

Kasai, Y. (editor): Demoltion and Reuse of Concrete and Masonry, Vol. I and 11. Proceedings of the second International RILEM Symposium on Demolition and Reuse of Concrete, Tokyo, 7-11 November 1998, Chapmann & Hall, London

6

Hansen, Torben C. (editor): Recycling of Demolished Concrete and Masonry, Third State-of-the-art report 1945-1989, RILEM report No. 6, E & F.N.Son, London

7

Lauritzen, Erik K. (editor): Demolition and Reuse of Concrete and Masonry. Proceedings of the Third International RILEM Symposium on Demolition and Reuse of Concrete and Masonry, Odense, Denmark, 24-27 October 1993, E. & F.N. Spon, London

Environmental Aspects of Construction with Waste Materials JJJM Goumans, H A . van &r Slmt and n . G . Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

131

A CONCEPT FOR THE ENVIRONMENTAL EVALUATION OF WASTE MANAGEMENT BENEFITS A. Tukker and D.J.Gielena.b a Study Centre for Environmental Research TNO, P.O. Box 6013,2600 JA Delft, The Netherlands

Present address D.J. Gielen: Netherlands Energy Research Foundation (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands Abstract

For the removal of a certain waste stream in general several options are available. According to the common applied 'stair concept' prevention of waste should be the first option. If this is not possible the waste should be re-used and otherwise it should be incinerated or landfilled. Though a valuable rule of a thumb, scientific and public discussions show that this approach can be in quite a few cases too rough to make common accepted decisions. This paper presents a more sophisticated approach, called the Waste management benefit concept. It has been developed on the basis of methodologies used in Environmental Impact Assessment, (health) risk analysis and product Life Cycle Analysis. A system-approach is presented, in which all relevant environmental effects related to whole life-cycle of the waste removal process are analyzed and aggregated to an integrated judgement. The methodology has been tested in a case on the removal of polluted sediments. Four options have been compared: (1) no removal, (2) covering the polluted sediment with an isolating clay layer, (3)dredging and landfill of the sediment and (4) dredging the sediment and sintering it with sewage sludge to so-called 'eco-gravel'. Apart from the theme 'acidification' the re-use alternative (4) shows to be the most environmental friendly option. The case-study has shown that the approach in principle is suitable to perform a quantitative, integral and transparent comparison of the environmental benefits of waste management options. 1

INTRODUCTION

Achieving a sustainable development is in general considered as the central goal in environmental policy. The means to reach this goal are the closing of substance cycles in society and the minimization energy use [I, 21. With regard to waste management, central goals are to ensure 1) treatment with a high level of protection for the environment; 2) minimization of the danger of illegal treatment and 3) promotion of prevention and re-use [Z,31.

738 In general several options are available for the removal of a waste. As a rule of a thumb the so-called 'stair-concept' is widely used to choose between removal options [4]. According to this concept prevention of waste should be the first option. If this is not possible the waste should be re-used and otherwise the waste should be incinerated or landfilled. This concept implicitly assumes that in the sequence reuse, incineration and landfill the effects on the environment will enlarge. There is no scientific evidence for this implicit assumption. Scientific and public discussions show that in quite a few cases an environmental assessment of waste management options on the basis of the 'stair concept' is not sufficient. The preference for incineration above landfill is subject to an intensive discussion [5,6, 71. Common sense approaches have proven to result in conflicting conclusions. According to [7]in Switzerland incineration of domestic waste would be preferred, in order to solve the problem in one generation, where Swedish researchers argue that incineration leads to ashes that leach out, and for this reason direct landfill could be preferred. Also for some types of waste, e.g. plastic waste, the environmental benefit of re-use above incineration is thoroughly questioned [8, 91. These examples show that the charm of a simple concept, like the stair concept, is also its weakness. Counting the amount of kilo's of a certain waste that is removed according to a certain level on the stair is just a too simple yardstick to avoid discussions. If capital- and/or energy-intensive processes are necessary for pre-treatment of a waste before it can be re-used the problem arises that the pretreatment process might have more negative environmental consequences than there are positive consequences related to the re-use itself. In waste management strategic choices have to be made by authorities and waste management firms and big interests are involved. Decisionmaking by authorities can be totally frustrated when no common accepted criteria exist to make preferences between waste management options. Denied permit extensions can be easily attacked in court. An objectivated methodology for environmental assessment of alternatives can make discussions more transparant and enhance the quality of decisionmaking [lo]. The paper will present a methodology called the Waste management benefit concept. It has been developed on the basis of methodologies used in Environmental Impact Assessment, (health) risk analysis and product Life Cycle Analysis (LCA) [ l l , 12, 13, 141. The basic idea is that the evaluation of waste management options needs an approach in which a whole waste management system and all the relevant environmental impacts are analyzed and aggregated to an integrated judgement. Paragraph 2 gives an outline of this approach. 2

METHODOLOGY

2.1 Introduction

In Environmental Impact Assessment (EIA) the following steps in the evaluation of alternatives can be distinguished 1131:

139 A: 1) inventory of potential effects; 2) choice of relevant effects and target variables; 3) choice of criteria; B: 4) analysis of the process system; 5) inventory of relevant effects; C: 6) selection of relevant alternatives; 7) sensitivity analysis; 8) integrated judgement of remaining alternatives; 9) final choice of the alternative. This general evaluation scheme can be divided in three parts. Part A) defines how and on which criteria alternatives are judged. Actually in this phase the 'yardsticks' are chosen to score alternatives. Part B) analyzes the process chains that have to be included in the system and makes an inventory of the (according to part A) relevant effects. In part C) the aggregation and final evaluation takes place. In fact this introduction gives a general framework for environmental evaluations. Depending on choices made in the 9 steps given above concrete, quantitative evaluation frameworks like Health Risk Assessment and Life Cycle Analysis can be derived [ l l , 12, 15, 161. The following paragraphs will give a discussion on choices that can be made within this general framework.

2.2 Part A: selection of yardsticks and criteria The first part in the evaluation scheme involves the selection of yardsticks and criteria that will be used to analyze the waste management system. Basically these choices involve [ 13, 151:

-

the effects that are considered; the position in the emission-effect chain chosen as the basis for evaluation; the criteria used to evaluate effects.

For example, in health risk assessment only one effect of an activity is evaluated: the effect on human health. The whole emission-effect chain is taken into account and the actual or potential daily intake is calculated, taking into account the local situation. The criterium used to evaluate the risk is the exceedance of an intake related to the Maximum Tolerable Risk (MTR); this equals the Accepted Daily Intake (ADI) for non-carcinogenics and the chance on death for carcinogenics [14, 161. In LCA methodologies, whole series of potential effects are distinguished [l1, 121. Effects include the greenhouse effect, acidification, land use, ozonlayer depletion, ecotoxicity, use of biotic and abiotic resourses, etc. In LCA, effects in general are described on the level of emissions. Local situations and subsequent calculation of emission-effect chains are not taken into account [I 11. In the case to test this methodology we have chosen to evaluate a waste

740 management system on the basis of a limited set of classification factors, mainly based on those given in the first draft CML methodology for LCA [ l l ] . For Human Toxicity we used as classification factor the sum of the emission of toxic substances, weighted on the basis of the Tolerable Daily Intake. Table 1 gives a review of effects and criteria used. This part of the evaluation is location independent. We added a location-specific evaluation of risks for natural functions and human health [14, 161. Table 1 :Classification factors chosen II

I

Affected varlable Man Environment

Resources

E, TDI, k,

GWP,

I

I

I

Effect

I

I1

I

Target variable

I

Unit

Human toxicity

Emission of toxic substances

Potential Human Toxicity [kg.day] PHT=2 EJTOI,

Acidification

Emission of SO,. NO, and NH,

Acidification Unit [ha.jr] AU =Z

Greenhouse effect

Emission C,H, CO,

CO,-equivalent F g COJ CO,-equiv.= Z E,'GWP,

Squandering of energy msources

Energy use

MegaJoule [MJ]

Squandering of resources of sand and grid

Use of sand and/or grid

Ton

Use of scarce space

Land use

Hectare [ha]

= Emission substance x [kg] = Tolerable daily intake substance x [kg/kg.day] = Correction for effechviiy [ l l ] . in Fg/ha.yr] = Global Waning Potential substance x [-]

2.3 Part B: System analysis and inventory The waste management system consists of several operations, that together form the process chain for the alternative. Time and place of the operations can be of importance if these aspects play a role in judgement of the alternatives. The waste management system is analyzed according to a system approach. This means that all relevant process chains are inventoried and taken into account as a part of the system. This approach is similar to that followed in LCAs for products; the difference in this situation is that not a product but an amount of waste has the central position in the analysis. The input of the system consists of the waste, capital goods, energy and other materials. The output consists of emissions to the environment. Landfill is a part of the system. Only emissions from the landfill are taken into account as output of the system. Incineration processes are, like re-use, seen as operations that take part in the system [17, 181. In every operation capital goods, energy and other materials are needed. Each of these elements is a part of its own process chain. Figure 4 gives an example of the process chain related to the re-use of polluted sediments as eco-grid, one of

74 1 the alternatives in the case discussed in paragraph 3. In theory an infinite amount of process chains could be included in the system analyzed. In practice system boundaries have to be chosen. The boundaries should be such that the system includes all processes or operations that have significant effects. It is common practice to neglect the production of capital goods [19]. Quite a few LCA's follow a first-order approach; this means only the main process chains and main material inputs are followed (201. However, the best approach is to neglect input of materials only if there is good evidence from similar studies that they do not have significant effects. Problems can arise when processes have multiple-input or multiple-output flows. In that case the emissions out of the system have to be allocated to each of the waste inputs or material outputs. Allocation could take place on the basis of mass, the contents of toxic substances in the waste, or the costs related to removal of the waste. Every choice has its own advantages and drawbacks. Since in the presented case study the contamination in the waste streams that are treated in a combined process didn't differ too much we have chosen to allocate on mass basis In recycling situations primary material is replaced by a secondary material. This means that processes and effects related to the winning of the primary material do not occur if waste is recycled; we allocated these environmental benefits to the waste management option if recycling takes place. Actually we defined a combined system consisting of the waste removal process and the winning of primary materials. In product LCA's these process chains are separated [11,12]. In a product LCA effects related to waste treatment are allocated to the product that is responsible for the waste. When this waste can be re-used in a second product no effects for waste treatment have to be taken into account for the first product. Effects related to upgrading processes necessary for making the waste suitable for re-use are allocated to the second product. We avoided these allocation discussions but payed the price that we had to analyze a more extended system. 2.4 Part C: Comparison of alternatives

For each waste management option the analysis in paragraph 2.3 results in scores on the yardsticks defined according to paragraph 2.2. Options that score worse on every yardstick than other alternatives can be eliminated directly. Options that do not meet legal limit values for the score on one or more yardsticks can be eliminated as well. E.g., in the Netherlands limit values have been set for soil and water quality; if an option causes exceedance of these limit values it can not be taken into account. For the remaining alternatives the different scores somehow have to be weighted. In EIA and LCA this has proven to be a very problematic item. One of the problems involves the differences in time scale and location of effects. Some authors use a positive interest calculation, that means that effects in the future are seen as less severe than the same effects in present [22]. Other authors regard

742 this as creating a negative environmental heritage for future generations and see this more negative than effects in present [23].At this moment no consensus seems achievable on the weighting problems related to time, place and kind of effect. Therefore a political assessed judgement on weighting factors seems to be the 'cleanest' option. This approach has been followed in the project on priority setting of waste materials (PRIAF) [24]. In the VNCVMcKinsey study on the evaluation of alternative processes in the chlorine industry weighting factors on the basis of expert judgement were used [25].A sensitivity analysis can indicate the importance of uncertainities in data inventoried and calculations made.

3

CASE: THE REMOVAL OF POLLUTED SEDIMENTS

3.1 Introduction

The methodology has been tested in a case on the removal of polluted sediments [21]. Polluted sediments is one of the most voluminous waste streams in the Netherlands. Annually about 70 million tons of sediments are dredged from rivers, estuaries and lakes. The sediments in general are polluted with heavy metals, PCB's, PAH's and organic micropollutants. Four options have been compared: (1) no removal, (2) covering the polluted sediment with an isolating clay layer, (3) dredging and landfill of the sediment and (4) dredging the sediment and sintering it with sewage sludge to so-called 'eco-gravel', a material that can be used as an alternative for primary building materials. The next paragraphs will briefly discuss the alternatives. It has to be stressed that the case was mainly meant to evaluate the idea behind the method, and not to give precise calculations. For simplicity reasons we sometimes made assumptions in the data inventory and simplifications in the system analysis or related calculations. Results of calculations therefore have to be regarded as tentative. For the calculations reference is made to literature [21]. Final results are given in table 2 in paragraph 3.6. 3.2 No removal

Figure 1 gives the situation of the polluted location. At the bottom of a river about 880 ha is covered with polluted sediment. It is assumed that as a result of source-oriented measures no further deposition of polluted sediments will take place. Without any remediation measures, due to resuspension processes about 30 % of the toxicity equivalent of the hazardous substances in the sediment will be released to the water in a time frame of about 100 year. The rest, 70 YO,will be released to the ground water in a period of several thousands of years. A locationspecific risk analysis shows exceedance of the permitted level for ecotoxicity.

743

T

water 880 ha polluted sediment

~

30% in 100 year

A ,//// ,’,/’/,,’,//

I \L 70% in > IO.OOO year

Figure 1: Situation to be remediated

3.3 Covering with a clay layer The first possible remediation option is covering the polluted location with an isolating clay layer. Only during the period the cover is constructed (about 2 years) emission of substances to the surface water takes place. This counts for about 0,5 % of toxicity equivalent of the amount of toxic substances. The rest, 99,5Yo,will be released to the ground water in a period of several thousands of years. The remediation process involves several activities with effects that have to be taken into account. Clay has to be dredged and transported to the location to be isolated. The process chain is given in figure 2. In the calculation of effects the construction of capital goods and processes related to oil well operations and refining are neglecied. It is assumed that after clay winning a multifunctional surface remains; this means no land use arises from clay winning.

Input

Capital goods

outpul

(

Input

n day

)

Energy (luel) Capilal goods

Emissions

0

,T (

output

Emissions

sediment

clay winning

transport

sox c02

isolation

processes

Figure 2: Process chain option 2: covering with clay layer

.

Figure 3: Process chain option 3: disposal

toxic subst

144 3.4 Disposal

Another remediation option is dredging the polluted sediment and disposal of the sediment. It is assumed that disposal takes place in an old sand excavation location, below water surface. It is assumed the disposal site is filled in about 10 years. In this period, emission of substances to the surface water takes place. This counts for about 3 % of toxicity equivalent of the amount of toxic substances. The rest, 97 %, will be released to the ground water in a period of several thousands of years. The surface of the disposal site is about 88 ha.

The disposal process involves several activities with effects that have to be taken into account. The sediments have to be dredged, transported and disposed. The process chain is given in figure 3. In the calculation of effects the construction of capital goods and processes related to oil well operations and refining are neglected. The creation of this disposal site is allocated to sand winning. 3.5 Re-use as ecogrid

A re-use option that might be operational in the near future has been evaluated as the last waste management alternative. The polluted sediment is dredged, transported and separated in a sand and organic fraction. The sand can be re-used directly as a material in road construction or for other purposes. The organic fraction is mixed with sewage sludge and is converted in a thermic process to an artificial grid, the so-called eco-grid. During this process the organic components in the sludges are burned; the heavy metals are partially immobilized in the matrix of the eco-grid and partially emitted with the flue gases. Due to flue gas cleaning most of the metals in the flue gas are trapped with the fly ash.

Figure 4 gives the process beam of the eco-grid process. The ecogrid process results in production of 4,8 10' tons of sand and 3,2 lo6 tons of ecogrid. Processes related to the winning of primary building materials and treatment of sewage sludge are avoided. The related environmental effects are taken into account as benefits of this particular waste management option. Since in some cases the effects of winning of primary materials are bigger than those related to the ecogrid process, the overall result is a positive environmental effect of this ecogrid process (minussigns in table 2). E.g., in the Netherlands the winning of primaly grid and sand takes place near rivers, creating big lakes and thus uses scarce space. The emissions and effects after the moment of co-processing of sewage sludge and the organic fraction of the sediment are allocated on mass basis. It is assumed that only 1 % of the metals in the ecogrid leach out in a time frame of several million years.

145

atput:

sediment

)

separation

j

j

Enissions

use in ccncrete

Figure 4: Process chain option 4: the Eco-grid process

3.6 Comparison of options Table 2 shows the results of the calculations of effects. Apart from the theme 'Acidification', the re-use alternative scores better than all the other options. Note that the emission of toxic substances is the same in option 1 , 2 and 3. However, the time scale and location of emissions differ quite a lot. We made locationspecific calculations, that show that only in alternative 1 the risk limit values for ecosystems are exceeded [21]. Also methodological choices can have important influences on the comparison. We compared the land use on the basis of affected surface area. In that case, differences arise between alternative 1 or 2 and 3. If we would have compared on volume no difference could have been made. We allocated the co-processing of sewage sludge and sediment on mass basis. Allocation on another basis could have lead to different results.

746 Table 2: Comparison of options

a = original location b = elsewere

4

OVERALL CONCLUSIONS

Methodological problems still remain. We only partially made location- and timespecific calculations. By choosing the (time and location independent) total emissions for comparison, we avoided weighting discussions for time and location differences. The case doesn't give an alternative that scores best on all the yardsticks. This means that in fact a discussion on weighting factors should have been made. Similar, still unsolved problems are present in other sectors of environmental policy, specifically in product policy [ l l , 261. The case shows that in some situations a LCA-alike approach is not enough to make a final choice between options, but that local dispersion calculations are needed to choose between option 1 and 2 or 3. Further the description of the case shows that consensus on other methodological choices still is needed. Specifically the enormous time frame related to landfill emissions still needs methodological attention [17, 181. However, the case-study shows that the Waste management benefit concept is suitable to give a quantitative, integral and transparent comparison of waste management alternatives. The methodological approach forces to take into account all relevant effects, to take into account a whole system and to make transparent choices when simplifications are made. The method also gives the possibility to take country-specific preferences into account. E.g., the effect land use is regarded as very important in a densely populated country like the Netherlands. Since the Netherlands do not have much natural resources of building materials, this is another drive for re-use. In countries like Spain or France, with lots of space and natural resources of building materials these factors will not be seen as big advantages. By choosing country specific weighting factors these differences can be made transparant.

141 In the Netherlands, the method has been accepted by the Dutch committee on EIA for EIA's on waste management plans. Several waste management plans have or are being evaluated according to the approach presented here [27,281.We think the method can offer a framework for structuring consensus processes when a choice has to be made on waste removal options. This can specifically be useful for choices on tense subjects like incineration in rotary kilns versus incineration in cement kilns and immobilization of waste followed by landfill under light regime versus direct landfill under strict regime [I 0, 291. References 1

National Environmental Policy Plan (NEPP). Dutch Parliament, Lower house, year 1988-1989, 21137 nrs. 1-2

2

National Environmental Policy Plan Plus (NfPP+), Dutch Parliament, Lower house, year 19891990,21137 nr. 20

3

Paper on prevention and re-use of waste, Dutch Parliament, Lower house, year 1988-1989, 20877, nr. 2

4

Dutch Parliament. Lower House, year 1979-1980, 15800, nr. 21, chapter XVII.

5

Samson H.D. Tjeenk Willink, Alphen aan RIVM: National environmental forecast 2 (1990-2000), den Rijn. 1991, pp. 357-358

6

Duvoort, G.L.: Solid waste In : Koernan. N.; Winkel, P.: Code of practice environment, Kluwer. Deventer, 1977-....

7

Bresser, A.H.M.: Nagelhout. D.: Risk assessment as a basis lor integrated waste management , Paper presented a1 the Joint International Symposium on Environmental consequences of hazardous waste disposal, Stockholm, Sweden, 27-31 Mei 1991

8

ECOBiLAN, Ecobilans compares des sacs d dechets en polyethylene vierge et regenare. Paris, augustus 1991.

9

Cayla, A , , Association Francaise de Normalisation, personal communication

10 Mulfy-year Programme on Hazardous Waste, Ministry of Housing, Physical Planning and Environment and IPO, The Hague, July 1993. 11

Heijungs, R. el. al: Methodology for LCA's on products. Parf 1 to 3. CML, Leiden, concept 1991, (Final draft 1992).

12 Fava, J.; Denison, R.; Jones, B.; Curran, M.A.; Vigon. 8.; Selke, S . ; Barnum, J.: A technical framework for life-cycle assessmenf. SETAC workshop report. Smugglers Notch, Vermont, 1990. 13 EIA-series nr. 13, Assssment mefhods, theory and practice. Ministry of housing, Physical Planning and Environment and Ministry of Agriculture and Fishery, the Hague 1982 14

Paper on risk policy (Omgaan mef risico's). Dutch Parliament, Lower House, year 1988-1989, 21 137, nr.5.

15 W.T. de Groot. H.A. Udo de Haes. Estimations in the first phase of €/A, Milieu 1987/5 16 Berg, R. v.d.. Roels, J.M.: Risk assessment for man and environment in cases of contaminated soil. lntegration of aspects Report no. 725201007, RIVM Bilthoven. 1991.

748 17 A. Tukker: Waste management and LCA, Lecture on the SETAC-Europe symposium on case studies, Brussels, 7 December 1993 18

Finnveden, G : Landfilling . a forgotten parf of the life cycle assessment. 1992, as clled in Finnveden el al., Classification (impact analysis) in connection with Life Cyde Assessments - A preliminary study. Manuscript prepared for the Nordic Council of Ministers, IVL, Gothenburg, Sweden, 1992

19 APMEIPWMI, A methodology for ecoprofiles on commodofy plastics. Brussels 1993 20

Korenromp, R.J.H., de Zeeuw, J.H., de Zoeten, G . : Development of ecolabels, TAUW lnfra Consult, Deventer, 1991

21

Gielen, D.J., A new method for environmental assessment of alternatives in waste managemant, Report 92/103, SCMO-TNO, January 1992

22

Phung, D.L.; v . Gool. W . : Analyzing lndustrial Energy Conservation Folicies: The Method of CostEnergy Dynamics. Energy systems and Policy 6 nr. 1, 1982

23

Reijnders, L.: Limit values for environmental pollution with regard to sustainable development. Milieu 5 , 1990, pp. 138-140.

24

Kaltenbrunner, D. e.a.: Priory setting for waste materials, RPC, Delft, 1988

25

VNCCMcKinsey. integrated substance chain management, Leidschendam, 1991

26

Raad voor het Milieu- en Natuuronderzoek: Assessment of risks of new technologies. RMNOpubl. no. 60, the Hague 1991.

27

Waste management council (AOO), Environmental Impact Assessment on the Multi-year waste management plan 1990-2000, Utrecht, the Netherlands, January 1992.

28

Commission for the EIA, Terms of reference for the € / A on the third waste management plan of the province of South-Holland, Utrecht, the Netherlands, June 1993.

29

A. Tukker, R. Klein Entink: Standard setting for immobilization - an analysis on the basis of the concept of integrated substance chain management, Report 9311 60, TNO-SCMO, June 1993 (concept)

Environmental Aspects of Consbuction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G.Aalbers (Editors) 01994 Elsevier Science B. V. All rights resewed.

749

TECHNOLOGICAL AND ENVIRONMENTAL PROPERTIES OF CONCRETES WITH HIGH PFA CONTENT

H.A.W. Cornelissen and R.E. Hellewaard KEMA Environmental Technology, KEMA Nederland B.V., P.O. Box 9035, 6800 ET Arnhem, The Netherlands

Abstract Concretes were made in which up to 60% of the amount of cement was replaced by PFA. In order to compensate the slow increase of strength several measures were taken. The water to cement ratio was reduced, rapid hardening cements were applied and the effect of curing at elevated temperature was studied. In all cases the addition of superplasticizers proved to be necessary. The compressive strength values were recorded over a period of two years. Also the efficiency factor (k-value) was determined as well as the development of permeability. Durability data were also gained from carbonation tests and chloride penetration. Leaching was determined by standard diffusion and availability tests on high volume PFA concretes in comparison with reference concretes. The results showed good quality concretes with properties which are highly sensitive to proper mix design. Furthermore it was found that mixtures containing up to 60% PFA as replacement of cement, did not exceed the limits for leaching.

1.

INTRODUCTION

The utilization in concrete of pulverized fuel ash (PFA) from coal fired electric power plants, is widely accepted. Normally about 20%-30% (m/m) of the amount of cement is replaced by PFA. However, in Canada and in the United Kingdom This is beneficial for reasons these replacement levels may reach 50% to 60% [l]. of reuse of byproducts, for economical reasons and for the realization of specific concretes where for instance heat generation must be limited. In the Netherlands PFA concretes have to meet the strict technical and environmental requirements as defined in the standards, CUR recommendations, certification documents and regulations with respect to among others leaching. In order to verify the results from the literature for these boundary conditions, an extended research project was carried out by KEMA [I-21.

750

2.

MATERIALS AND COMPOSITIONS

In this research project a typical Dutch PFA was used having a mean grain size of 22 micrometer. With respect to the chemical composition, the carbon content was 4.2% , the amounts of the other main components were 57% Si02, 26.4% A1203, 4.4% Fe203 and 1.8% CaO. The standard concrete composition (denoted as REF) contained 320 kg/m3 cement and the maximum quartz aggregate size was 31.5 mm. The water content was related to the total cement plus PFA content (water to binder ratio). For the tests 150 mm cubes were cast and stored in a fog room at 20 "C and over 95% relative humidity. In general compressive tests were performed in triplicate. The various PFA mixes are indicated like H40, in which 40 stands for the weight percentage cement replacement.

3.

CONCRETE HARDENING CONTROL

Preliminary tests learned that at increasing PFA contents, the development of concrete strength slowed down. Therefore various methods were applied to enhance the evolution of early strength. In the literature especially a low water to binder ratio is recommended for this purpose [ l ] . In those cases, however, a suitable superplasticizer is necessary. At KEMA also methods were investigated based on rapid hardening cements, curing at elevated temperature and the addition of chemicals which increase the alkalinity of the pore water. The addition of these chemicals being NaOH (2.5-30 grams per litre mixing water) and Na20.Si02 (2-92 grams per litre) proved not to accelerate strength development and will therefore not be further discussed in this paper. Curing at elevated temperature Standard concrete was made with 320 kg/m3 normal hardening Portland cement (PC-A). From this mixtures were derived in which 20%, 40% and 60% of the amount of cement was replaced by PFA. The water to binder ratio was about 0.50, resulting in fresh concrete slumps of 75-100 mm. A temperature treatment was chosen according the RMC method [4]. For that the moulded concrete cubes were stored for 16 hours at 82°C in a water storage tank, immediately followed by demoulding. After that three cubes were tested and the remaining three cubes were stored in the fog room and tested after 28 days. The results as presented in Table 1 are compared with the results of cubes cured at 20 "C. As durability parameter, the water penetration (DIN 1048/5 1991) at 28 days is given as well. As can be seen the temperature treatment results in practical strength levels for all mixes tested. For the H60 mix, however, the 28 days permeability proved to be relatively high. 3.1.

75 1

Table 1 Effect of temperature treatment (82°C for 16 hours) on concrete strength (f'c) T = 20 "C

T-treatment

REF H20 H40 H60

*

35.3 31.5 30.7 24.8

49.4 42.8 35.6 25.6

32.1 26.2 17.3 8.9*

16 20 13 92

41.8 37.2 28.4 15.5*

water to binder ratio = 0.54

3.2.

Effect of rapid hardening cement

It is obvious that by the use of rapid hardening cements early strength development can be accelerated. Therefore the results of concretes based on this type of cement (PC-C) were compared to PC-A based concretes. In the mixes 320 kg/m3 cement was replaced by 20%, 40% and 60% PFA. The slump was 70-90 mm at water to binder ratios of about 0.50. The results are presented in Table 2. The 7 and 28 days compressive strengths are higher for PC-C cements, as expected. After one year hardening, the PC-A concretes show higher strength values. It can be seen that for PC-C concretes with up to 40% PFA, compressive strength values are in the normal practical range. This is also true for H60 concretes after one year hardening caused by the pozzolanic effect of PFA. Table 2 Effect of type of cement on the development of strength (f'c) PC-A cement MIX

PC-C cement

f'c(7d) f'c(28d) f'c(l8fd) (N/mm 1

REF 32.1 H20 26.2 H40 17.3 H60 8.9

41.8 37.2 28.4 15.5

54.8 61.0 50.7 34.5

f'c(365d)

f'c(7d) f'c(28d) f'c(i82d) f'c(365d) "/mm 1

55.8 63.7 59.1 49.0

44.6 38.5 27.2 13.9

53.1 47.5 40.9 20.5

55.9 59.4 52.0 35.7

54.3 58.9 55.4 49.0

752

3.3. Effect of low water content In concrete technology the water to binder ratio is an important parameter for the strength (and also the durability) of concrete. A low water to binder ratio will generally result in high strength. However, a certain surplus of water is needed to reach sufficient workability of the fresh concrete. In order to fulfil these two conflicting requirements, additives such as superplasticizers are added. In this research project a naphthalene formaldehyde condensate was selected. In the mixes 320 kg/m3 PC-A cement was used; the water to binder ratios varied between 0.35 and 0.52 in order to realize slumps between 100 and 190 mm. Details of the mix composition are given in Table 3,in which results are given as well. In Figure 1 the development of strength for high volume PFA concretes with 0% and 2.5% superplasticizer (m/m binder) is illustrated. The results indicate the strong effect of the low water to binder ratio, as made possible by the superplasticizer. Because of the continuation of the pouolanic activity, the strength increases over time and the differences in strength diminish between the mixes with various PFA contents. Table 3 Effects of low water to binder ratio in combination with the addition of superplasticizer MIX

SP

WBR

SLUMP f'c(7d) f ' ~ ( 2 8 d ) ~f'c(365dJ f'c(730dJ (mm) (N/mm2) (N/mm 1 (N/mm 1 "/mm 1

REF

0

0.52

100

32.1

41.8

55.8

59.0

H20 H40 H60

0 0 0

0.51 0.51 0.54

125 130 150

26.2 17.3 8.9

37.2 28.4 15.5

63.7 59.1 49.0

66.5 63.7 56.3

H20 H40 H60

1.5 1.5 1.5

0.40 0.40 0.40

140 120 140

42.2 29.0 15.3

56.0 46.6 28.0

79.1 78.5 68.8

87.9 86.6 79.6

H20 H40 H60

2.5 2.5 2.5

0.35 0.36 0.37

120 190 190

53.1 39.3 18.1

71.6 56.0 32.3

95.5 93.9 81.5

104.6 100.6 92.6

("w

753 f’c (N/mrnz)

110, 100 90 80

-

70

-

60

-

50 40 -

30 20 -

0’

1

I

I

I

3

7

28

I

I

I

182 365 730 age (days)

Figure 1. Compressive strength development (f‘c) of high volume PFA concretes. For mixes with 20%, 40% and 60% cement replacement efficiency factors (k-values) were calculated. These factors represent the binder effect of PFA. Starting point for the calculation of the k-values was the compressive strength. The calculated k-values are shown in Table 4. The 7 days and 28 days k-values are affected by the PFA content. Even at 60% replacement levels the value exceeds the generally accepted value of 0.20. Table 4 k-values of hiah volume PFA concretes MIX

H20 H40 H60

SP

2.5 2.5 2.5

WBR

0.35 0.36 0.37

K-VALUE

7d

28d

0.73 0.48 0.23

1.17 0.67 0.31

The effects of methods to accelerate strength development are summarized in Figure 2 and compared to standard curing, no-treatment (NO). In the figure the methods are denoted as TEMP for temperature treatment, RHC for the application of rapid hardening cement and SP for the addition of superplasticizers (1.5% and 2.5%).

754 For concretes with 60% PFA, especially the temperature treatment proved to be effective for the enhancement of the 7 days strength. Reduction of the water to binder ratio proved to be most successful in all cases. The optimal method is of course dependent on the requirements under actual conditions. f'c (N/rnrn2)

182 days

0

23

60

1 2 3

-

40 -

20 0

8o 60

-

--

1

--

-

1

t

1 : 20% PFA 2 : 40% PFA 3 : 60% PFA

7 days

NO

TEMP

RHC

1.5SP

2.5SP

Figure 2. Effect of early strength control methods for high volume PFA concretes. 4.

CONFORMITY TESTS

For the assessment of high volume PFA mixes, conformity with the appropriate national documents for technical approval (BRL 1802/01 1992) was applied [5]. Concrete mixes were designed based on 340 kg/m3 PC-A and HOC-A (blastfurnace) cements. Replacement levels of l8%, 26% and 32% were chosen. The slump was held between 190 and 240 mm. The water to cement plus 0.2 PFA content was 0.45 for all mixes. For the reference mix (REF') no additives were necessary; for the mixes with PFA a combination of 0.5% plasticizer and 1.5% superplasticizer (for HI8 1.0%) was used. The plasticizer was a ligno sulphonate whereas the superplasticizer consisted of naphthalene formaldehyde condensate. Some typical results of compressive strength development are shown in Figure 3. At increasing age the strengths of the PFA concretes exceed the strengths of the reference concretes because of the pozzolanic reactivity of the PFA.

755

The results of durability tests like water penetration, carbonation depth and chloride penetration, as far as available up to now, are summarized in Table 5. In this Table chloride penetration is taken as the average of four readings from 0-5, 5-10, 10-15 and 15-20 mm depth.

f'c (N/mm2)

60

-

50 40

-

20 -

10 -

REF x

32% PFA

Figure 3. Compressive strength development (f'c) of high volume PC-A and HOC-A concretes The test results were compared to the requirements in BRL 1802/01. The assessment is based on comparison of the properties with reference mixes (REF'), taking into account the statistical variation in the results. In this research it was found that these variations were about equal for both the reference and PFA mixes. So mean values of the properties could be compared. According to the BRL strength and durability have to be checked. For strength the 28 days compressive strength must be taken, whereas for the durability the 7 days and 90 days strength values have to be taken into account, as well as carbonation and, depending on the environmental conditions, deicing salt resistance. For the 7 and 28 days strengths, the criteria are 95% of the reference mix strengths; the 90 days strength must be at least the 28 days strength of the corresponding reference mix. Further, the maximum accepted carbonation depth is the carbonation depth of the reference concrete exposed to similar conditions. In Table 6 an overview is presented of the comparisons. The criteria were calculated from the properties of reference mixes with the same type of cement (i.e. PC-A or HOC-A). As can be seen all HOC-A mixes fulfil the requirements. For the PC-A mixes, the H32 concrete does not reach the 7 and 28 days strength limits, also the carbonation depth is too much as was found for the H26 concrete as well.

156

According to the BRL, concretes must be compared to an accepted reference concrete. So strictly spoken the PFA concretes with PC-A may be compared to HOC-A reference concrete. In that case it can be seen that also the PFA mixes with PC-A cement meet the BRL requirements. Table 5 Results of tests to check the durabilitv of PFA concretes MIX

waterpenetration 28d 91d (mm) (mm)

CI--penetration carbonation 35 d depth (91d) (mm) (mm)

PC-A REF' HI8 H26 H32

30 29 32 36

22 10 10 27

2.4 1.8 1.7 1.7

2.0 1.5 2.5 3.0

HOC-A REF' H18 H26 H32

20 9 7 5

5 8 2 6

1.o 1.o 0.9

4.5 4.0 4.0 3.0

Table 6 Properties of high volume PFA concretes compared with the requirements MIX

PC-A criterion H18 H26 H32

compressive strength

carbonation

f'c(7d) (N/mm2)

f'~(28d)~

35.4 39.1 35.5 32.4*

43.1 54.1 46.1 42.9"

(Wmm

1

f'c(91d)2

"/mm 45.4 63.9 57.6 60.2

HOC-A criterion 27.4 42.4 44.6 H18 31.6 49.8 59.0 H26 28.1 45.5 60.1 H32 27.7 42.9 54.3 * exceed PC-A criterion, but comply with HOC-A criterion.

1

depth (90d)

(mm) 3.0 3.0 4.0* 4.5" 5.5 5.5 5.5 4.5

757 5.

ENVIRONMENTAL PROPERTIES

For the application of building materials, environmental properties have to be considered. With respect to leaching the corresponding Dutch regulations (abbreviated as BSB) have to be taken into account. In general the leacheability of numerous components must be checked. However, in previous research it was found that for PFA, mainly seven components proved to be decisive (see Table 7). Diffusion tests were performed according the Dutch Standard NVN 7345 (1992). The results have to meet the limits in the BSB. Another type of test is the availability tests based on the Dutch Standard NVN 7341 (1992). This type of test gives an indication of maximum possible leaching. Concrete specimens were subjected to both diffusion and availability tests at an age of 2 years. The results of high volume PFA concretes (20%, 40% and 60% PFA and 2.5% superplasticizer) were compared to the results of reference concrete. The test specimens originated from the batches as indicated in Table 3. The two sets of results are given in Tables 7 and 8. Table 7 shows that all PFA mixes investigated fulfil the BSB requirements. In the well accepted reference mix, however, the leaching of selenium slightly exceeds the limit. Also in the availability test a higher selenium content was found for the reference mix. This finding may be explained by the higher alkalinity of the reference mix compared to the PFA mixes. Table 7 Results of diffusion tests according NVN 7345 and corresponding limits (6%) Component BSB (mg/m2)

REF (mg/m2)

H20 (mg/m2)

H40 (mg/m2)

H60 (mg/m2)

As

25

< 0.8

< 0.8

< 0.8

< 0.8

Cr

90

<3

<3

<3

< 3

< 1.0

< 1.0

Se

1.8

2.5

< 1.0 ~

V Mo

Zn

so,-

60

3

<3

<3

3

4

< 2

< 2

< 2

< 2

125

7

20

9

11

15000

485

4450

150

350

758

Table 8 Results of availability tests according to NVN 7341 Element REF H20 H40

Cr Se V Mo Zn

6.

1.2 4.1 < 0.4 < 0.4 13.7

1.o 3.4 < 0.4 < 0.4 15.8

1.5 2.7 < 0.4 < 0.4 9.8

H60

1.3 2.8 0.4 0.6 12.2

CONCLUSIONS

According to the findings in the literature, good quality concretes can be produced based on 320-340 kg/m3 binder that contains cement and up to 60% PFA. After prolonged curing periods, high volume PFA concretes reach or exceed the strength values of reference concretes (with 100% cement), because of the pozzolanic reactivity of PFA. The slow development of strength can be accelerated by means of several methods like the use of rapid hardening cements, enhanced curing temperature and especially a low water to binder ratio in combination with a suitable superplasticizer. The addition of NaOH and NaO.Si02 proved to be not effective for this purpose. High volume PFA concretes (up to 60% PFA) proved to meet the environmental requirements for leaching (BSB). Ongoing conformity tests show that it is likely that high volume PFA concretes (up to 32% PFA), will be in accordance with the BRL criteria for technical approval. 7.

REFERENCES

1

V.M. Malhotra, ACI SP-132, Detroit (1993). KEMA Report 20155-KET/R&B 93-4062 (1993). KEMA Report 53145-KET/R&B 94-4038 (1994). M.H. Wills, Jnl. Testing and Evaluation 4 (1975). BRL SBK/Vecibin num 1802/01 NL/SfB code: Eq4 (1992).

2

3 4 5

ACKNOWLEDGEMENT This research project was financially supported by the Dutch electricity production sector.

Environmental Aspects of Constmction with Waste Materials JJJ.M. Goumans, H A . van der Sloot and Th.G.Aalbers (Editors) el994 Elsevier Science B. V. AN rights resewed.

759

TOWARDS SUSTAINABILITY WITH CONSTRUCTION AND DEMOLITION WASTE IN BELGIUM ? J. Desmytera, B. Laethemb, B. Simonsc, J. Van DesselC and J. Vynckea

aBelgian Building Research Institute, Lozenberg I, 7 B-I932 Sint-Stevens-Woluwe bFlemish Institute for Technological Research (VITO), Boeretang 200, B-2400 Mol CRecymat, Excelsiorlaan 57, B-1930 Zaventem

Abstract An overview is given of the actual situation in Belgium, related to construction and demolition waste. The implementation of EC policy and Directives by the different regional authorities resulted in waste management plans, in which C&D waste is considered as a priority waste stream. The different strategies followed concerning disposal and recycling of C&D waste are covered. Information related to quantities of C&D waste, dumping tariffs and prices and costs of primary and secondary aggregates is provided. The disposal, treatment, recovery and recycling practices differ among the regions. Particular attention is given to the present efforts of the authorities. The use of other secondary materials forces the authorities to focus on environmental and health aspects. In order to avoid higher treatment costs and possible contaminations the installation of a demolition permit and an environmental legislation could be appropriate.

1. INTRODUCTION

Already in march 1991 the EC Directive 91/I 56EEC on waste promoted a 'Sustainable Development'. In the Brundtland Report 'Our Common Future' this was defined as a development which meets the needs of the present without compromising the ability of future generations to meet their own needs. The directive actually forced the member states to stimulate : the prevention and reduction of waste through the development of clean technologies as well as products that can be re-used or recycled; the recycling and recovery of waste as secondary raw material; the recovery and disposal of waste without endangering human health or the environment; the drawing up of waste management plans by national authorities; the self-sufficiency in waste disposal by the member states

760 the establishment of an integrated and adequate network of disposal installations, taking into account the best available technology and enabling the Community as a whole to become self-sufficient; the use of waste as an energy source. In December 1992 the community made a significant change in policy by the adoption of an action program entitled "Towards Sustainability" [ 11. This program embodies the central theme of the 1992 'Earth summit', the United Nations Conference on the Environment and Development (UNCED) as set out in the Agenda 21 document. Both set aims for achieving sustainable patterns of economic and social growth. The Community strategy is based on partnership - between government, industry and consumers - and on shared responsibilities among the main actors. The Community will set minimum requirements. Individual EC countries are free to fix national standards which are higher than those set at the Community level. As far as concerns construction and demolition waste (C&D waste) the yearly production in Western Europe amounts to approximately 0.7 to 1 ton per inhabitant, this is twice the amount of municipal solid waste generated. It is expected that total C&D waste generation will reach 215 million tonnes in the year 2000, with about 175 million tonnes coming from demolition work and some 40 million tonnes from construction [2]. The composition of the C&D debris varies from region to region, but for most of the countries concrete and masonry take by far the largest part. All this explains why the Directorate General XI of the Commission, Environment, Nuclear Safety and Civil Protection, identified C&D waste as one of the Priority Waste Streams. In this respect the Directorate General XI started at the end of 1992 with a project group "Construction and Demolition Waste". The main goal of this project group is the development of a strategic plan in order to stimulate reuse and recycling. Hot topics are at the moment the technical specifications for the use of recycled aggregates, the environmental legislation for granular and moulded materials and the development of a demolition permit system. In this article an overview is given of the actual situation and the future evolutions in Belgium, compared with the implementation of these European programs, in relation to C&D waste.

2. LEGISLATION AND POLICY IN THE THREE REGIONS National policy in Belgium is administered by a number of government bodies which outline general environmental policy and implement EC Directives. Three regions exist within Belgium - Flanders, Walloon and Brussels - which, since 1981, have been responsible for formulation of waste disposal policy. Broadly, waste is categorized into inert (Class III), municipal (Class 11) and industrial (Class I) waste. Other wastes such as pesticides, toxic

76 1

waste and radioactive waste are subject to national regulations and are generally not acceptable for landfilling. In particular the responsibility to draw up waste management plans has fallen under the authority of the regional administrations "Openbare Vlaamse Afvalstoffen Maatschappij (OVAM)" for Flanders, "Institut Bruxellois pour la Gestion de l'EnvironnemenUJ3russels Instituut voor Milieubeheer (IBGE/BIM)" for Brussels and "Office Regional Wallon des DCchets (ORWD)" for Wallonia. All regions were able to work out Waste Management Plans for the period 1991- 1995, in which one part specifically considers C&D waste. 0

The Flemish public institute OVAM was founded in 1981 and is responsible for the stimulation of prevention and recycling of waste. In relation to the Flemish Strategic Waste Management Plan 1991-1995 a new environmental legislation "VLAREM 11" has been introduced in 1992. By this legislation dumping of recyclable waste coming from construction and demolition is being prohibited. The institute is currently also dealing with legislation in the field of environmental hygiene and quality standards. Related to the reuse of C&D waste this institute strives for a recycling percentage of 75 % by the end of the century. At the moment OVAM is working on the final form of the "Implementation Strategy of Construction and Demolition Waste" [3], [4]. It has the intention to give the necessary pulses to make recycling rule rather than exception. The plan formulates a double goal : quantitative and qualitative prevention 0 75 % recycling of the construction and demolition waste This plan is a reflection of the goal set by the government and the will of the construction sector to collaborate actively. The basics for this global strategy were the authorities environmental policy, consultation of the sector, and an extensive inquiry carried out in 1992 by Recymat in order to evaluate potential bottle necks and to focus on the most effective incentives. The main topics in this global plan are :

0

prevention waste management demolition specifications

0 0

technology research market research and strategy certification and environmental standardisation

The efforts that are necessary to reach these objectives are summed up in a global implementation plan. The period of time involves 5 years. In order to anticipate on changing circumstances and unforeseen evolution's a yearly evaluation is proposed. In this respect this document is a charter for future legislation and incentives and clarifies the governments policy. The adaptation of official tender specifications is also a necessity. A working group dealing with the reuse of waste was established in 1990 on the initiative of the Ministry of

762 the Environment and Infrastructure (LIN). This group studied the necessary amendments to tender specifications in order to allow and to promote recycled aggregates to be used in public works. Some amendments have already been published in the form of circulars, more specifically about : the use of concrete and masonry aggregates in roads the use of broken asphalt aggregates in lower road layers the use of secondary materials in water works the use of "hot recycled" asphalt in upper layers A draft proposal in relation to the use of concrete and masonry rubble in buildings and civil engineering works (foundations, inner walls, ...) is still under discussion [5]. It is believed that a more general application will start to grow in the coming years both in the public as in the private sector. A well organised follow up should be worked out in order to be able to set up sensitisation actions. In the Brussels region, environmental issues are the competence of the IBGEBIM, which was created in 1989. For the evacuation of its waste Brussels has to rely totally on the recycling and dumping possibilities offered in Flanders and Wallonia. This uncomfortable situation explains the manifest interest in recycling and in prevention of waste. The aim of the Brussels Waste Plan, which was approved in 1992, is therefore to realise 70 YOrecycling of C&D waste by 1996. In order to achieve this goal, major attention is currently directed towards the evaluation of the possibilities offered by selective demolition, this in collaboration with the Confederation of Brussels Contractors (CCBC). A practical guideline with recycling opportunities in Brussels will be made available in the near future. Besides this the obligation to use recycled aggregates in public works by adoption of modified tender specifications is studied. This is one of the responsibilities of the Public Works department and IBGEBIM. a

The Walloon Waste Management plan was realised by the ORWD, which was founded in 1991. In this plan particular attention is given to the prevention of waste and to the limiting of the burden caused by the treatment or disposal of waste. In this way the plan considers all existing technologies such as recycling, waste minimization, incineration, pre-treatment and landfilling. The need for a global implementation plan concerning C&D waste resulted in the creation of the co-operation Tradecowall by the Confederation of the Walloon Construction Companies (CCW). The objective of Tradecowall is to work out, in collaboration with the regional authority, a global solution in relation to dumping of C&D waste [6]. The main aim is the establishment of an adequate network of dumpsites for inert waste and the exploitation of stock sites for non-contaminated excavated soil (soil banks). Further the relandscaping of existing unauthorised dump sites and closed quarries and last but not

763 least the promotion of recycling are the top-priorities. In this respect projects are being considcred to set up 2 recycling and waste separation centres. Lately initiatives have been taken by the Ministry of Infrastructure and Transport (MET) to make amendments to their tender documents so as to allow the use of recycled materials (not only C'&D waste. but also other inaterials such as blast furnace slag, ...) in road construction.

In most of these initiati\.es a strong appeal was made to the Belgian Building Research Institute (BBRI). which started already 17 years ago with studies on the reuse of C&D waste 171. 181. 191. Recently an interregional project group was founded in order to tune in the policies of the three regions and to define comparable technical specifications for the use of recyclcd materials.

3. REGIONAL STATISTICS ON C&D WASTE 3.1. Natural Resources [lo] l'he annual production of the Belgian quarries is approximately 64 million tons, of which about 60 %, is iised i n construction. More than 15 million tons are exported to neighbouring countries. 'l'he use in Belgium of natural resources in construction of buildings, civil engineering works and road construction is estimated at some 6 tons per inhabitant. The localisation of the quarries throughout the country can be appreciated from the figures in table 1.

Annual production of app. 64 million tons Flanders 13r u s e 1s Wallonia

Number of quarries

Number of employees

169

1097

301

5514

'l'able 1 : Number of quarries [ 101

llanders (1 3.5 17- kin*) \vhich is situated in the North of Belgium has a very high population density of422 inhabitants per square kilometre. Except for some winning of sand and sea (2 million tons) and river gravel (8.1 million tons) no natural resources are available. Existing quarries are mostly small production entities. as can be scen in table 1 looking at the ratio of the number of quarries and the number of employees. Moreover the decision of the Flemish government to stop the production ol'rivcr gravel before January 2006 may not be neglected.

164 Brussels (161 km*) is the smallest of the three regions and counts 6025 habitants per square kilometre. Its territory is limited to the urban region of the city of Brussels. No quarries whatsoever are available. Wallonia (16,844kmz) is situated in the South of Belgium and has a population density of 190 habitants per square kilometre. A large number of quarries, which produce approximately 75 % of the total annual production of Belgium, is dispersed over the territory. 3.2. C&D Rubble In Flanders the production of construction and demolition waste has been calculated to amount to circa 4.6 million tons per year, i.e. 807 kg per year and per habitant [3]. In a recent study [3] of which some results are presented in the figures 2 and 3, it was found that approximately 40 % of the waste consists of concrete and about 40 % of masonry. The remaining 20 % is a mix of bituminous materials (12 %), ceramics (3,4 %) and various other wastes. The sources of the waste are residential and non-residential buildings, roads and building material manufacturing companies.

Flanders, constr.& demol. waste Bituminous

Flanders, 8ources of the waste

Other roads

3%

Figure 2

Industry

Non m i d build

Ceramics

Figure 3

Due to the lack of natural resources it is quite logic that in Flanders already a wellestablished recycling industry is operating. For the moment approximately 50 recycling installations are in use. It is estimated that actually about 2 million tons demolition waste are being recycled each year. For non-recyclable, inert C&D waste about 50 Class 111 dumpsites exist in Flanders.

765 In Brussels the production of construction and demolition waste has been calculated to be 850.000 tons per year, i.e. 876 kg per year and per habitant [l 11. No dump sites or recycling plants are available. However, opportunities to start in the near future with a recycling plant in the Brussels region are being evaluated. In Wallonia no official studies have yet been undertaken regarding the production of construction and demolition waste. Estimates indicate a production of about 2.6 million tons per year, i.e. 625 kg per year and per habitant [12]. Although the number of authorised dump sites is very limited (in total only 14 of them exist) at the moment only one recycling plant is operating. As already mentioned, the construction of two more plants is brought into discussion by Tradecowall. Table 2 compares the composition of C&D waste in the three regions :

Comuosition (in %) concrete masonry bituminous material ceramics

Flanders 41 40 12 3

Brussels 38

Wallonia

45 10 3

nther

4

4

Total production (in mill. t/a)

4.6

0.85

2.6-2.8

Table 2 : Quantities and composition of C&D waste

4. TREATMENT, RECOVERY AND RECYCLING PRACTICES IN BELGIUM The capacities for C&D waste disposal/treatment and of the recycling plants are quite different among the regions. According to an inventory, made in 1989 on the basis of the granted permits, some 40 plants were in operation [3]. They can be classified into actual fixed plants, mobile installations with a fixed location and actual mobile installations. About 75% of all installations belong to the first two categorieh. Essentially most plants were set-up by demolition contractors who in this way resolved the problems they faced in dumping their demolition waste. The most important plants are grouped in the Association of Demolition Waste Recycling Corporations (VVS). The installations are generally composed of the following elements : a weighing bridge, equipment for pre-processing, a preliminary sieve to eliminate earth, sand and gypsum, a primary crusher, electrical magnet systems, a sieve installation to separate the materials, an air sieve or washing installation and a secondary crusher and sieve installation.

766

On a yearly basis the total recycling capacity can be estimated at 4.4 million tons, which means that more or less the total quantity of construction and demolition waste could be covered by the plants. The real production does however not approach the capacity, because there is still a lack of sale potential mainly with regard to masonry rubble. So the latter, which accounts for approximately 40% of all the rubble, is at the moment only recycled to a small extent. Changes in this situation are expected to result from recent taken measures in relation to technical specifications and further expected measures which will be introduced in relation to selective demolition. In Brussels selective demolition is of prime interest, as there is neither landfill capacity nor are there any recycling plants. Actually about 30% of C&D waste is recycled in Flemish plants in the neighbourhood of Brussels. The remaining 70 % is land-filled, generally in Wallonia, where the landfill capacities are considerably higher than in Flanders. As already said, only 14 landfilling capacities exist in Wallonia. The construction of two recycling plants is brought into discussion by Tradecowall. Another possibility that is being considered is the establishment of a network of local stock sites for construction and demolition waste. At regular intervals a mobile crusher could be installed on this sites to recycle the waste stocks. In this context however it is felt that the marketing of the recycled products will be a problem as primary raw materials are cheap and in large quantities available. However, another evolution may be an interest of the raw material producers to take initiatives and to set-up recycling plants at their quarries.

5. PRICES AND COSTS OF PRIMARY AND SECONDARY AGGREGATES

The average cost for a demolition contractor for waste disposal vary from about 450 to 750 BEF/t (excluding transportation costs) [6] : In Flanders tipping costs for construction and demolition waste are typically in the range of 150 to 400 Belgian francs per ton. An environmental tax of 350 Belgian francs per ton ads up to this. For the evacuation of its waste Brussels has for the moment to rely totally on the recycling and dumping possibilities offered in Flanders and in Wallonia. No need to stress that this is a rather difficult situation for the Brussels region. The interest in recycling is then also manifest as well as the interest in prevention of waste. Actually about 30% of the waste find its way to recycling plants in Flanders that are situated close to Brussels. The remaining 70% is evacuated to the nearest dump site, i.e. a dump site in Wallonia. In Wallonia tipping costs are typically in the range of 80 to 300 Belgian francs per ton. An environmental tax of 150 Belgian francs per ton ads up to this.

767

The recycling plants try to promote selective demolition by using different dumping tariffs for mixed and clean material. In comparison average prices for delivery at recycling plants are : concrete reinforced concrete masonry rubble, containing plastics, wood

free of charge 50 - 200 BEFlt 0 - 50 BEFH 100 - 300 BEF/t

Recycled products have to compete with traditional building materials. The recycling plants use on average the following average market prices [6] : Concrete aggregates 80/200 : This kind of aggregates finds their application exclusively in hydraulic works as filling material for river embankment protections. The market demand is anyhow rather limited. Concrete aggregates 0180, 0156 or 0/40 (4/32) : The market price of this kind of aggregates is about 220 to 240 Belgian francs per ton and as such about 100 Belgian francs per ton below the price of natural aggregates. These aggregates with a continuous particle size distribution are the bulk of the production and are mainly used in road construction applications, i.e. as road-sub base material, M h e r they are also used in the private sector for soil filling and the creation of unhardened parking areas. At few occasions the material is split in a 0120 and 20/40 fraction for example and recycled as aggregate in lean concrete. The limited number of recycling plants which have their own concrete mixing installation uses typically a 4/32 fraction for their concrete production. A full 100% substitution of the coarse aggregates by recycled aggregates is in this cases most generally used. Sieve and crusher sand : This material has a very low market price of about 80 Belgian francs per ton. Mainly the product is sold as sand for pavement subbases or for the construction of embankments. Crushed masonry 0/56 : Masonry aggregates have a market price in the range of 150 to 170 Belgian francs per ton. If recycled the product is up to now only used in the private sector for soil filling and the creation of unhardened parking areas. Asphalt : Recycled asphalt aggregates have a market price in the range of 200 to 220 Belgian francs per ton. These products are recycled as base materials for roads and parking areas and reused in new asphalt. Asphalt aggregates are mainly produced in the winter period considering that problems otherwise arise in relation to their processing. In comparison the considerably higher cost for traditional materials is given in the following table [ 131 :

Category and type of material Porphiry 32/56 Porphiry20/32 Porphiry 7/20 Porphiry 217 Sandstone 32/56 Sandstone 20132

Material cost (exc. transport) in BEFlt 336 332 360 41 5 289 272

768 Category and type of material Sandstone 7/20 Sandstone 217 Limestone 20132 Limestone 14/20 Limestone 7/14 Limestone 217 Limestone 0/2 Belgiansand River gravel 4/28 River sand 015 Rhine sand (Netherlands-Germany) Rhine gravel (Netherlands-Germany)

Material cost (exc. transport) in BEFlt 275 277 25 1 266 283 299 215 113 300 160 260 450

Table 3 : Primary raw material cost

6. ENVIRONMENTAL AND HEALTH ASPECTS 6.1. Approach for secondary materials in general Related to environmental and health aspects the C&D waste problem is only part of a far more important issue : the reuse of any kind of secondary materials (f.i. produced from industrial or household waste). Waste in general may contain a more or less low percentage of hazardous substances. These contaminations can impede in some cases disposal or recovery. However, it is a fact that most of the building and construction waste is in nature not harmful at all. Anyhow, actually there is no clear definition as what has to be considered as contaminated waste. Questions about which materials should be refused, which limits of heavy metals, poly aromatic hydrocarbons and such are acceptable in waste, and which applications depending on certain pollutant concentrations are possible, still have to be clarified. In order to attain a consistent standardisation with realistic values and measures, additional research is necessary. A frame of reference should be realised by extensive research on the quality of the common used building materials and of the waste. In Flanders the methodology of approach, developed in co-operation with the Flemish Institute for Technological Research (VITO), is inspired on the one developed in the Netherlands [ 141. A policy is in preparation in order to prevent any pollution caused by the reuse of secondary materials as building materials. According to this policy the producer of a secondary material will have to prove the technical suitability of his product. In a second step an "application certificate" could be granted in which the possibilities and conditions of use are specified. Materials would be evaluated in terms of chemical composition and leaching characteristics.

769

Building materials are defined as either moulded or granular. Moulded materials should remain durable and intact for at least the lifetime of the application. Granular building materials are those used for embankments, road foundations, and similar applications. This distinction is made because moulded and granular materials have different leaching characteristics.

6.2. Granular secondary building materials In the present proposal granular building materials are divided in two categories, G I and G2 (see Figure 4), according to leaching behaviour. Each category represents a certain risk of causing soil pollution, requiring different precautions. Leaching from GI materials must remain below a lower limit, L1, and results only in a small (marginal) additional burden to the soil (or marginal burdening of the ground water in case of chloride and sulphate). As in the Dutch "Bouwstoffenbesluit" marginal burdening is defined as a 1 % increase, with respect to reference values, in concentrations in the top 1 m of soil over a period of 100 years. Building materials for which leaching exceeds the L1 limit are classified in group G2. These materials must remain isolated from ground water and rainwater to reduce the risk of leaching. An upper limit for leaching, L2, is calculated in the same way as the L1-limit but considering lower infiltration in the soil (isolated applications). Use is prohibited if leaching exceeds this limit. A composition limit, C 1, is actually defined as 25 times the reference value for soil quality. These limits are nevertheless still under discussion. It is likely that those limits will be changed according to the "practice of use". This means that the C1 limit could be derived from the result of an extensive research on the quality of the common used building materials.

The proposals introduce certain restrictions before utilisation is allowed. GI materials can be used without provisions to avoid leaching, but must be removed after their hnction has finished. G2 materials must be used in amounts exceeding 10 000 ton for a single application ( I 000 ton when used in road foundations). They must remain above ground water level and must be isolated from rain water. After the lifetime of an application, G2 materials must be removed. No special measures are required for GI materials following removal from a site and they may be recycled under the same (GI) conditions. Recycled G2 materials are subject to the same measures for isolation from ground water and rain water as applied to the primary cycle. Probably, a third category of granular materials, G3, will be defined. Building materials for which leaching remain below the L1 limit but for which the composition exceeds the C1 limit will be classified in this new category. G3 materials can be used without

770 provisions to avoid leaching, but must be used in a single application of 10 000 ton (1 000 ton when used in road foundations). They can not be used in certain areas where water resources are protected. Recycled G3 materials are subject to the same measures.

Granular Materials Leaching

L2

L1

c1

Composition

Figure 3 : Proposal for classification of granular secondary building materials

6.3. Moulded secondary building materials For moulded building materials (see Figure 5 ) only one leaching limit has been proposed (LI). Use is only allowed for moulded materials from which leaching does not result in pollution exceeding the marginal burdening of the soil. The proposal categorise moulded materials according to their composition. MI materials can be used freely. Their composition does not exceed C1, the same composition limit defined for granular materials. Special regulations are applied to moulded materials that exceed the C l limit (M2 materials). The provisional maximum concentration allowed for heavy metals, C2, is set at 100 times the reference value for soil quality for heavy metals. This limit is still under discussion. Materials with concentrations exceeding C2 may not be used. Although the same allowable maximum leaching value applies to MI and M2 materials, there are some extra requirements to isolated M2 materials from ground water or rainwater (as leaching should be similar). However, to avoid future environmental risks it will be specified that M2 materials should have a minimum volume of 50 cm3, should be used in a single application in a minimum amount of 10 000 ton, and should not be used in certain areas where water resources are protected. Because the C1 limit is the same for granular and moulded building materials, the MI materials may be recycled as granular building materials (subject to classification by leaching). M2 materials may only be recycled into new moulded products.

77 1

Moulded Materials Leaching

c1

c2 Composition

Figure 4 : Proposal for classification of moulded secondary building materials

7. DEMOLITION PERMITS

A complementary approach that is under discussion on a regional as well as on a European level is a kind of regulation of demolition activities. The regulation of demolition activities via a demolition permit would allow a development of recycling which is environmentally well-considered.

In theory a large amount of C&D waste can be recycled, especially when the content of concrete and masonry rubble is high. In the process of recycling care should be taken to avoid that contaminated material enters the circuit. Knowledge about the origin and therefore, about the composition of the C&D waste is important for the recovery process and future acceptability of the recycled material. In this respect the acceptance policy at the plants is of major importance. Re-use and recovery of C&D waste depend very much on the demolition technique applied. Waste generated by demolition activities often is neither separated nor treated in a way that permits recovery. Because of contractual obligations the demolition procedure may result in unrecoverable waste. The rubble coming from roads (concrete rubble, asphalt concrete) is indeed relatively homogeneous or can be held homogeneously with rather simple means. Buildings consist in general in a mixture of all kind of materials (such as concrete, bricks, ceramic materials, wood, glass, isolation material, plastic, ...). Another approach to demolition is evident [ 151. This is also advisable concerning the price fixing for the demolition. The demolisher needs objective details (kind of materials, quantities, ...) to fix his price. The clients should be obliged to make a demolition scheme containing the quantities of materials and their historical use (concerning possible pollutions) of the construction. A

772 demolition permit should only be awarded when such a scheme is presented. A specific removal policy can furthermore be imposed when awarding the permit. This demolition scheme should be presented to the demolition contractor. This way he will be able to take the necessary precautions (asbestos, chemical pollution, ...). When unmentioned suspicious materials are found during demolition, the self-control of the contractor will be activated. Recycling plants can by means of such a demolition scheme also be informed with regard to the origin of the material. The place where the rubble is transported to, can, after the demolition, be verified by a comparison of transportation forms and dumping forms. This range of thoughts concerning the regulation of demolition activities is at the moment, as already mentioned, as well on a regional as on a European level under discussion. [6].

8. CONCLUSION In all three regions initiatives have been taken in order to come to an appropriate C&D waste management and to tune in with the EC policy. The recycling of C&D waste has made progress since several years. The numerous recycling plants and the adaptation of a convenient regional legislation proves the latter. The adaptation of amendments to tender specifications, in which the use of secondary aggregates is allowed, is believed to be a stimulating factor for recycling. An important aspect in current discussions, besides the technical issues, is the environmental legislation. In some specific cases, waste may contain contaminating materials. To avoid that recycled materials (based on any kind of waste) constitute a risk for the environment, they should be evaluated in terms of composition and leaching characteristics. As far as concerns C&D waste, it's clear that most of it is not harmful at all. However, with a kind of demolition permit problems with non-separated or contaminated materials could be avoided.

9. REFERENCES [11 Commission of the European Communities, "Protecting our environment", ECSC-EEC-

EAEC, Brussels-Luxembourg, July 1993 [2] European Demolition Association, "Demolition and Construction Debris : Questionnaire about an CE priority Waste Stream", The Hague, 1992. [3]

"Problematiek van bouw- en sloopafvalstoffen. Voorbereidend rapport i.0. van de OVAM", WTCB-Recyma, January 1990 (In Dutch).

[4]

"Uitvoeringsplan Bouw-en sloopafval", OVAM, In preparation (In Dutch)

773 [5]

J. Vyncke, "Hergebruik van Bouw-en Slooppuin als Granulaat in Beton voor Gebouwen en Kunstwerken : Omzendbrief van het Departement Leefmilieu en Infrastruktuur (LIN) van de Vlaamse Gemeenschap", B.B.R.I., still to be published (In Dutch and French).

[6] J. Vyncke and E. Rousseau, "Recycling of Construction and Demolition Waste in Belgium, Actual Situation and Future Evolution", Proceedings of the Third International RILEM Symposium, London, UK, 1994. [7]

C. De Pauw, "Beton recycle", CSTC-revue no 2, June 1980 (In French and Dutch).

[8]

C. De Pauw, "Recyclage des decombres d'une ville sinistree", CSTC-revue, no 4, December 1992, (In French and Dutch)

[9]

"Hoe 80.000 m3 gewapend beton veilig laten springen en recycleren", KVIV-WTCB studiedag. Antwerpen, 1987, (In Dutch).

[ 101 "De Groeve, Onbekend en Onbegrepen", FEDIEX - Verbond van Ontginnings- en

Veredelingsbedrijven van Onbrandbare Gesteenten C.V., Brussel. [ 1 I] "Problematiek van bouw- en sloopafval in het Brussels Gewest", Rapport i.0. van het

BIM, WTCB-Recymat, March 1991, (In Dutch). [I21 H. Motteu and E. Rousseau, "Recycleren van Afvalstoffen in de Bouw", W.T.C.B.Tijdschrift, B.B.R.I., Brussels, summer 1992, (in French and Dutch). [13] "Referternaterialen en prijzen", Bouwbedrijf no 36, NCB, Brussel, July 1993.

[14] B. Laethem, H. Elslander, P. Geuzens, D. Wilczeck, "Onderzoek naar de implicaties voor het milieu van het hergebruik van bouw-en sloopafval", VITO, 1992. [15] B. Simons & F. Henderieckx, "Selective demolition. Guidelines and experiences in Belgium", RILEM 3rd International Conference, Odense, 1993.

This Page Intentionally Left Blank

Environmental Aspects of Conshuction with Waste Materials JJJ.M. Gounians, H A . van der Sloor and 7h.G.Aalbers (Editors) Q1994 Elsevier Science B.V. AN rights resewed.

715

Disintegration of fly ashes in the rotary-vibration mill J. Sidora and M.A. W6jcikb

aFaculty of Mechanical Engineering and Robotics, Department of Technological Equipment and Environment Protection, Av.Mickiewicz 30, A-3, 30-059 Cracow, Poland bFaculty of Materials Science and Ceramics, Department of Building Materials, University of Mining and Metallurgy, Av.Mickiewicz 30, A-3, 30-059 Cracow, Poland ABSTRACT

The investigation of the disintegration of the wasted fly ashes from EPS IILFGf* is presented. The effect of a composed motion of a mill chamber and a way of the transmition of the energy during grinding process on the granulation, dimension and shape of the grains of fly ashes is shown. The granulation parameters of tested fly ashes was selected according to its application in the production of a calcium-silicate brick in Cracow Building Ceramic Company. Disintegrated fly ashes can be used as the activated filler in other building materials. 1.INTRODUCTION.

The technology of building materials uses such fillers as a natural sand, aggregate or wastes blast furnace slags and fly ashes. The wasted fly ashes originated during a combustion of a various kinds of a hard and brown coals belong to the well popular fillers. The utilization of a fly ash is based on their physical or physicochemical properties as thermal, adsorption, hydraulic. In particular, the hydraulic properties of fly ashes depend, in great part, on the chemical and mineral composition. Usually, fly ashes contain an increase quantity of calcium compounds, also free CaO, and a glassy phase responsible on their pozzolanic properties [l]. It is also known, that the hydraulic properties of fly ashes is improved together with higher disintegration. In most cases, the industrial wasted fly ashes exhibit the collection of a porous particles having various dimensions and shapes undefined geometrically. They consist in coarse particles (>500 pm) , middle (1-50 pm) as well as a very fine ( < 1 pm) . Most of industrial fly ashes show all of the geometric shapes. The quantity and mass portion of a given shape demonstrate the randomize character [2]. Considering the particle porosity of a

116 fly ash it is often impossible to determine univocal of a given physical value, first of all, dimension, density, volume, surface. The diversity of meaning of values being the function above parameter is that consequence. In respect of above, fly ashes are activated during disintegration where: - the dimension of particle are lowered, - agglomeration are crushed, - particles are homogenized, - interior pores are opened, - particles shape are changed. Usually, the industrial disintegration of fly ashes is carried out in the ball mill in a defined time (from a few up to several dozen hours) and to a required specific surface (30005000 cm2!g according to Blaine) Disintegrated product characterized with a normal distribution of particle dimensions. Moreover, disintegration of a such fine and hard (more than 6 in Mohse's scale) as a fly ash is very expensive, especially, when process endure many hours. It is more efficient to use other type of a mill characterized with faster disintegration, lower energy consumption and production of a very fine mono fraction (<5 pm) The vibration mill belong to this category where is a need to grind the materials of hardness from 3 to 9.5 in Mohse's scale. They are used in an industry and laboratory from a several dozen years [ 3 , 4 , 5, 61. They have good points in: - the technological aspects as a chance in disintegration of a material below 2-10 pm, - the technical ones as a compacted and simple construction, lower (2 times) energy consumption in contrary to gravitic, stream and mixer mills and high yield up to 60 Mg/h. From the second hand, they possess the limitations as follows : - destructiveness onto environment, - noise emission, - propagation of a vibration into the ground, - quick fatigue of elements of a mill construction due to high frequency (about 2 5 Hz). The new type of vibration mill was constructed in University of Mining and Metallurgy in Cracow in order to moderate above faults. This is the rotary-vibration mill (RVM) and the characteristic parameter are as follows: - frequency of 10-16 Hz, - vibration acceleration about 2-3 times less than in the case of a classic vibration mill, - introduction of a rotary motion of a mill chamber keeping similar velocity of grinding process as in the case of a typical vibration mill [ 7 , 81. The RVM can be used in period as well as continuous grinding. The material can be disintegrated in a gas or liquid environment. Basing on results of model investigations the series of RVM was constructed in the laboratory and industrial scale. The greatest polish industrial RVM were: - MOW-E-125 with a chamber volume of 125 dcm3 and power of 8 kW, constructed in 1985 for the grinding of a dolomite [8],

.

.

777

Table I

Physicochemical properties of the tested fly ashes

+o 500 05013-0250 0250-0 $ 2 5

$ 0 125-004) o, 0090-0063

Y

0063-0040

am

00~0-0032

-0032 20

LO

60

% 8 n band

Figure 1 Particle size distribution of fly ashes

BC

- MOW-E-200 with a chamber volume of 200 dcm3 and power of 13 kW, constructed in 1989-90 for the fine grinding of alumina [9]. Is it also known, that in Technical University in Berlin, the other RVM was constructed with circular trajectory of vibration. The acceleration of vibration motion was 250 m/s2, and power was 132 kW. The final product was more uniformed than of one ground in a vibration mill [lo]. In this paper, LAMOWB-512, constructed for the fine and colloidal grinding of a hard material (Sic) was used for grinding of fly ashes [ll, 121.

2.EXPERIMENTAL. 2.1.Material. By-product, the fly ash from the electric power station llLFG" (EPS) was used in the disintegration process. Samples of fly ashes numbered I, I1 and 111 respond the number of zones of

778

Figure 2 Slightly porous grains from I zone, ( 2 0 0 ~ )

Figure 4 Very porous grains from I1 zone, (400x)

Figure 3 Very porous grains from I zone, (400x)

Figure 5 Very porous grains from I11 zone, (400x)

779

a

b

Figure 6 Principle operation of RVM, a-LAMOW-B-5j2 with quasi linear trajectory of vibration, b-RVM with circular trajectory of vibration:l-chamber,f-frequency,A-amplitude andtrajectory,oangle velocity of a chamber,S-intensive grinding

EPS dust collector system, respectively. Sample IV was a sample I initially grinded in a roller mill. Sample V was collected from the mixture of samples I, I1 and 111. The average chemical composition shows that the fly ash (sample V) is consisted as follows: 53% of SiO,, 26% of A1,0,, 9% of Fe203, 5% of CaO, 3 % of MgO, 4% of alkalies. Other physical properties are given in Table 1. The observations of grains of fly ashes coming from all of the zones of the dust collector was made under the TESLA electron microscope (Figure 1-4). Results revealed that there is no compacted particles among the ones above 5-10 wm coming from all zones. only porous particles was found. The porosity of particles was different. Some of them exhibited pores which are expanded to whole interior of grain but other show small pores having dimensions below 1-2% of a maximum size of a grain. The shape of particles

Figure 7 M O W - B - 5 1 2 (description in text)

780

was irregular with a domination of the oval grains. However, the spherical grains was dominated among the particle below 10 pm. In respect of above, the impact crushing of porous particle of a fly ash should be used as a chief mechanism of the grinding process. That mechanism is found in RVM. Thus, the disintegration of fly ash particles should be more faster than in the case of ball mill. The attrition process predominates in this cascade grinding. 2.2.The

goal of the tests.

The technological tests show that I*LEGl1 fly ash exhibited the best properties after disintegration in the laboratory ball mill during 8-10 hours. The grain size distribution checked by MALVERN 3600E laser granulometer was ranged as follows: d,,=7-8 pm, d,,=22-25 pm. The goal of presented investigation was to obtain the similar parameter of disintegrated fly ashes in RVM during the shortest time with a maximum yield of mill. 2.3.Procedure.

The technological parameters of RVM was as follows: steel balls, chamber of 2 dcm3 with steel lining, mass of balls, 4100g, mass of dried fly ash feed, 3009. The kinetic parameter of RVM was as follows: frequency, 12Hz, vibration amplitude, 4-10 mm. The disintegration time of an individual sample was calculated basing on testing results of sample I. The granulometric analysis of grain size distribution was carried out using two following methods: - diffractometric (MALVERN 3600E laser granulometer), - sedimentation (Andreasen's pipette). The final product was observed under the TESLA electron microscope.

-

2.4.RVM

-

construction, operation and parameters.

The grinding in RVM consists in set of the composed motion of the mill chamber filled with balls and feed. The motion is collected with the rotary and vibration movement. The amplitude of the vibration motion is perpendicular to the axis of a chamber rotation. It gives quasi linear amplitude of a vibration. The schema of a basic work of RVM i.e. chamber and charge motion as well as the work of RVM with circular trajectory of vibration is shown in figure 5. LAMOW-B-512 is shown in figure 6. RVM are constructed from modules. The basic setting work is vibration module (l), consisting of sub-assembly of chamber (2), inert vibrator (3), driving gear of chamber (4), chamber ( 5 ) , engine(6), cover (7), electrical circuit ( 8 ) .

78 1

Figure 8 Histogram of the f l y ash I, Sample PI after 20 min of a grinding process

Figure 11 EMS of the fly ash I Sample P2, 2000x

Figure 9 Histogram of the f l y ash I, Sample P2 after 40 min of a grinding process

Figure 10 Histogram of the f l y ash I, Sample p3 after 6 0 min

Figure l2 EMS

of a grinding process

Sample P3, 2000x

the

ash I

782 A

0 d50

d90

0

d10

I

0

20

10

30

50

40

60

m n d ~ n g tlme h n )

Figure 13 The effect of the grinding time on dPold50,d,0 of fly ash I

A

0

-96um

0

-4.6um

-2.2um

70

56

gr

Figure 16 EMS of the fly ash TI, Sample P5, 2000x

42

E

8,, 28 14

/:--------'-. , , A -

C lo

PO

30

40

50

60

GrlndlnQ time (mi")

Figure 14 The effect of the grinding time on under external band of grains of fly ash I

ash IV

ash I1

Figure 15 Effect of a kind of the fly ash on the grain size distribution

Figure l7 EMS

Of

Sample P7, 2000x

the

ash

783

One (5 dm3) or two (2 dm3 each) chambers can only be inserted in the chamber set. Dimensions of RVM are as fol1ows:length-920 mm, width-650 mm, height-830, weight-155, power-0.75kW. 3.RESULTS AND DISCUSSION.

The experiments includedVI1 series of disintegration of fly ashes. The llall ball set and three levels of time (20,413and 60 min) were used in series I. Results show that required particle size distribution of the most coarse fraction of the fly ash (I zone) was obtained already after 40 minute of disintegration process and is shown in Table 2 and on figure 7,8 and 9 . In respect of above, the maximum time of 40 minute of a disintegration of the finer granulation of fly ash (I1 and I11 zones) was accepted. The flv ash from I1 zone was ground in series I1 ("aff ball set). I P i .a" PB 'b' fly ash v f l y am v The fly ash from I11 zone was ground in series 111 (Ifall i ball set). The fly ash, numbered IV, (fly ash from I zone initially disintegrated) was ground in series IV (llall ball set). The mixture of fly ashes (I, I1 and I11 zones) was ground 0 0 zu in V series (l1aflball set). nard The mixture of fly ashes (I, I1 and I11 zones) was ground Figure 18 Effect of the ball in VI series (IlblI ball set). set on the grain size The samples of distribution of the fly ash V disintegrated fly ashes presented in this paper was marked as follows: after 20 minutes of grinding - series I. P1 - fly ash I after 40 minutes of grinding - series 11. P2 - fly ash I after 60 minutes of grinding - series 111. P3 - fly ash I P4 - fly ash IV after 40 minutes of grinding - series IV. P5 - fly ash I1 after 40 minutes of grinding - series 11. P6 - fly ash I11 after 40 minutes of grinding - series 111. P7 - fly ash V after 40 minutes of grinding - series V. after 40 minutes of grinding - series V. P8 - fly ash V The results of grinding of fly ashes in RVM (Table 2, figure 8-14) show that in the time interval of 40 minute it is possible to obtain a product characterizing with a high degree of dispersion. The disintegrated fly ash coming from I zone of a dust collector (coarse) possessed dmax=56. 6 pm, d,,=17.2 pm and d5,=7.8 pm, where dmax of a feed was 500, 420 and 110 pm, respectively (Figure 13). The increase of a grinding time up to 60 minutes caused the further lower of the dimensions of fly ash particles. The d d,, and d,, was 36.3, 14.3 and 6.5 pm, respectivelly. TF;' disintegrated fly ash become the mono -0

I"

784

Table I1

Grain size distribution of fly ash from series I

dispersion material when progressing of the grinding time. If d,,, was lowered 300% during 4 0 minutes (from 20 to 60 minutes of grinding) , that d,, was lowered 200%, while d,, was lowered only 50%. Figures 0 , 9 and 10 show above tendencies of the particle conversion after 20, 4 0 and 60 minutes of grinding. It is clearly seen that final product is going to be more mono dispersion material. The band of 3-15 pm of grains was amounted of 75%. The technologically required the size of the ground fly ash, equal to d,,=7-0 pm, was obtained after 4 0 minutes of the grinding of

785

Table I11

Grain size distribution of fly ashes ground during 4 0 minute, Samples P4-P8

-9.6

pm

60.4

66.5

67.5

65.6

61.2

-4.6

pm

26.8

29.8

32.5

31.3

27.8

-2.2

pm

5.9

6.1

7.9

6.8

5.8

4900

5200

5600

5400

4900

Specific surface according to MALVERN'S method, cm2/9

the most coarse fly ash I. The contents of the under external grain class of a product increase during the grinding time, but at the same time, the highest progress (30%) concerns the class 9.6 pm (Figure 1 4 ) . In respects of the differences of the structure of fly ashes in the nature form (Figures 1 - 4 ) : the sedimentary method (Andreasen) was used for characterization the particle size distribution beside the diffractometric one (Malvern). Results show (Table 2 ) that sedimentary method demonstrates higher contents of the under external grain class of a product then in the case of the coarser. Generally, presented results from both methods show the similar tendencies in the kinetic of the change of the individual grain classes. The observations under the electron microscope (Figure 11, 1 2 ) confirmed results of the particle size distribution verified by the aim of mentioned two methods. Particles of the disintegrated fly ashes exhibited, in most cases, the irregular and sharp-edged forms. It is also seen the many spherical grain, however, it was not found the plate and

786

pillar-shaped grains in the bulk of the final product. Observations also proved the increase of the mono dispersion of the ground fly ash after 60 minutes of the mill operation. Considering the effect of the kind OP fly ashes on the grain size distribution, it should be ascertained that results show small differences between tested materials (Table 3, Figure 1518). It is seen that the granulation of the fly ash I, initially grinding in the roller mill (sample P4), does not vary from the granulation of sample P2 without that operation. Also, the grain size distribution of the fly ashes I1 and I11 are very comparable as well as sample P7 (mixture of fly ashes I+II+III) which shows a similar granulation (Figure 16 and 17). Above results univocaly indicates, that independently on the particle size distribution of the starting fly ashes, the final product after grinding in RVM demonstrates to be mono dispersion material containing about 75% of grains fitting class 3-15 pm. Deliberating the effect of the ball set (llall = 8 mm and I1bl1 = 12 mm) on the grain size distribution it should be certified that, as results show, using the first one, the final product exhibits more available granulation (Table 3, Figure 18). The specific surface of the disintegrated final product of an individual samples shows the analogous dependencies as the results of their granulation (Table I and 11). 4.CONCLUSIONS.

Results of presented investigations of the disintegration of fly ashes from IILEGtl allows to draw the following conclusions: 1. The grian size distribution of the all tested fraction of fly ashes executed the technological need equal dS0=7-8 pm and d9,=22-25 pm after 40 minutes of the grinding time. 2.

Due to the mechanism of the grinding process in RVM it is possible to disintegrate the fly ashes about 10-12 times faster than in the ball mill, producing the mono dispersion final material.

3.

The shape, form and granulation parameters as dmax,dgO,dS0, d,% and highly developed the specific surface (4900-5800 cm)/g make that product as the chemically active material.

4.

Results certified the possibility of the producing the mono dispersion material as fly ashes in the vibrating mill with rotary chamber [lo].

REFERENCES

[l] [2]

[3]

J.D.Wett, D.J.Thorne, J.Appl.Chem.,15,585 (1965; 15,595, (1965);16,33 (1966) B.Courtault, 7th ICCC Paris,t.II.p.III-117,Paris (1980) E.Beasley, G.Slin, Vibrating grinding, Ceramics Nr 226, (1975)

787

H.G.Papacharalambous, Convertional versus vibrating milling, Ceramic Age Nr 2 (1972) H.E. R.Sullivan, Vibrating mills and vibrating milling, Constable London (1972) K.Hoff1, Zerkleinerungs und Klassiermaschinen VEB Deutscher Verlag fur Grunstoffindustrie, Lepzig (1985) J.Sidor, The optimization of the work of rotary-vibration mill, Doctor's Thesis, University of Mining and Metallurgy, Krak6w (1978) J.Sidor, The approximation method for construction of the industrial rotary-vibration mills, Scientific Bulletin Nr 1159, p.49-61, University of Mining and Metallurgy, Krak6w (1988) J.Sidor, Preliminary tests of a prototype of the industrial rotary-vibration mill for fine milling of aluminum oxide, Physicochemical Problems of Mineral Processing, 26, p.5764, Wroclaw (1992) [lo] E.K.Kurer, E.Gock, S.Michaelis, The rotary chamber vibration mill, a further development of the customary tube vibration mill, XVI International Processing Congress, edited by E.Forssberg Elsevioer Science Publishers B.V. Amsterdam (1988) [ll] J.Sidor, Examination of kinetic of the process of grinding of copper ore and high silica sand in the prototype of post vibration mill of LAMOW-B-512 type, Miner Review,4, p.1620, (1988) [12] J.Sidor, E.Ermer-Kowalczewska, Preliminary investigation of the colloidal grinding of Sic in the laboratory rotaryvibration mill, Material Science Bulletin, Nr4, (1989)

This Page Intentionally Left Blank

Environmental Aspects of Conshrction with Waste Materials J.J.J.M. Goumans, H A . van der S l w t and Th.G. Aalbers (Editors) 91994 Elsevier Science B.V. All rights reserved.

789

Release of heavy metals from a municipal solid waste incineration residue stabilized in non-traditional matrices V.Albinoa, R. Cioffia, B. de Vitoa, M. Marroccolib and L. SantoroC Wniversith degli Studi di Napoli "Federico 11", Dipartimento di Ingegneria dei Materiali e della Produzione, Piazzale Tecchio, 80125 Napoli, ITALY. buniversith degli Studi della Basilicata, Dipartimento di Ingegneria e Fisica dell'Ambiente, Via della Tecnica 3, 85100 Potenza, ITALY. CUniversith degli Studi di Napoli "Federico 11", Dipartimento di Chimica, Via Mezzocannone 4,80134 Napoli, ITALY.

Abstract Two binding matrices based on blast furnace slag and fly ash-lime mixture have been used for solidification/stabilization of a residue from municipal solid waste incinerator containing heavy metals. The same matrices have also been used in model systems, each containing the soluble nitrate of one of the metals of the waste. The scope was to get useful information for understanding the interactions between each metal and the two matrices. When the metals are initially present as soluble salts, can respeciate and are leached in variable amounts depending on the nature of metal itself and matrix, as well as on the initial content of soluble metal salt. When the metals are present as stable oxides produced in the incineration process, no respeciation takes place and leachability results to be strongly dependent on the physical properties of the hardened product. 1. INTRODUCTION

The stabilization of inorganic solid wastes, especially when they contain heavy metals, largely relies on cement-based processes. In this type of processes stabilization is mainly due to the formation of a calcium silicate hydrate (C-S-H) matrix, not only when Portland cement is used alone, but also in mixture with clay, fly ash, soluble silicate, etc.. This type of processes comprises also those based on lime/fly ash, lime/clay and lime kiln dust [l]. In all the above cases, the chemical immobilization potential of heavy metals is given by a number of interactions which include: (a) sorption of ions by forming C-S-H; (b) precipitation of insoluble hydroxides, owing to high alkalinity;

790

(c) lattice incorporation into crystalline components of set cement and (d) development of hydrous silicate and basic calcium-containing salts [2]. Matrices containing calcium sulphate and reactive oxides or hydroxides of calcium and aluminium are of high potential in the field of waste stabilization, due to the formation of calcium trisulphoaluminate hydrate (ettringite), a product having good binding properties [3-61. In these systems, the source of sulphate can well be a chemical gypsum (phosphogypsum, desulphogypsum, etc.) while that of reactive oxides or hydroxides of calcium and aluminium can equally well be blast furnace slag or a fly ash-lime mixture [7-lo]. This sources of reactive alumina can also act as sources of reactive silica and generate C-S-H. Hence in these systems the binding-stabilizing properties are due to the formation of both ettringite and C-S-H. In this paper two binding matrices based on blast furnace slag (BFS) or fly ashlime mixture (FA) have been studied with a twofold purpose. On one side, the two matrices have been used in model systems containing soluble nitrates of six heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in order to get an understanding of the mechanisms which control the release of heavy metals toward the environment. On the other side, the two matrices have been used for the stabilization/solidification of a residue from a municipal solid waste (MSW) incinerator in order to evaluate their effectiveness in an actual application. This study has been carried out by means of three leaching tests. They are: (a) the dynamic test based on the Am. Nucl. Soc. 16.1 protocol [ll], (b) a batch test which makes use of a pH 4.74buffered acetic acid/sodium acetate solution and (c) a batch test making use of a controlled pH 4 f 0.2 nitric acid solution. The first two of these tests have been carried out with monolithic samples and have the purpose of well characterising the long term leaching behaviour of stabilized systems in terms of metal release. The third leaching test makes use of powdered samples and has the purpose of discerning whether physical or chemical retention occurs. 2. EXPERIMENTAL

Table 1 reports the composition of the binders utilized. Table 2 shows the chemical compositions of blast furnace slag and fly ash. Model systems were obtained by adding 5 to 10 wt% of a metal nitrate to both the binders in Table 1. The nitrates used were of Cd, Cr, Cu, Ni, Pb and Zn.These model systems were paste hydrated and cured at 2 5 T, 100% R.H. for 28 days in cylindrical polyethylene moulds 5 cm high and 3 cm in diameter. The water/solid ratio was 0.5. The chemical composition of the waste to be stabilized is reported in Table 3. For any of the two matrices used, four mixtures were prepared containing 20, 40, 60 and 80% of waste. All the mixtures were paste hydrated as the model systems, but with a water/solid ratio of 0.65, due to their higher water demand.

79 1

Table 1 Binders compositions (wt%) Material

BFS

FA

Blast furnace slag Coal fly ash CaS04.1/2 H 2 0 Portland cement Ca(OH)2

61.5

--

--

43.3 26.0 17.4 13.3

18.5 20.0

--

Table 2 Principal chemical components of by-products used (wt0%) Component

Blast furnace slag

Fly ash

33.2 41.1 14.1 0.5 1.6

Mgo Na20 K20

7.0 0.4

56.8 4.8 25.5 2.2 4.2 1.5 3.0 0.2

so3

2.6

0.4

Si02 CaO A1203 Ti02 Fe203

--

Three different leaching tests were carried out with the model systems. The dynamic ANS 16.1 test was carried out up to 6 months time with 14 water renewals. The monolithic samples, as obtained at the end of the above test, were then used in a batch leaching test in which the leachant was a buffered acetic acid/sodium acetate solution at pH=4.74. The solid surface/leachant solution volume ratio was the same as for ANS test. The leaching time was 6 days. In addition to these tests, which made use of monolithic samples, 3 grams of each sample, ground to pass a 180 pm sieve, were leached by means of 300 ml stirred nitric acid solution hold at constant pH=4+0.2. In this case the leaching time was 24 hours.

792

Component Si02 A1203 ZnO Fe203 MgO Pbo CUO MnO

14.30 7.40 0.52 3.29 2.74

0203

0.12 0.03 0.01 31.20 5.60 12.40 5.72 1.02

NiO CdO CaO so3

c1

co, p205

0.18 0.08 0.09

The monolithic hardened binder-incinerator waste mixtures were only tested by means of the dynamic ANS 16.1 leaching test. Chemical analysis of leached metals was carried out by means of the Atomic Absorption Spectrophotometer VARIAN SpectrAA.1OPlus. 3. RESULTS AND DISCUSSION

Table 4 shows the results of dynamic leaching test carried out on all the model systems investigated. These results are expressed as cumulative amount released after 6 months in terms of percentages of the initial quantities added as soluble nitrate. It is seen that the results are widely variable and depend on: (a) nature of stabilising matrix; (b) nature of metal and (c) initial metal concentration. However it should be outlined that these three variables not always act all together. For example, in the case of lead the effect of metal initial concentration is not detected, while in the case of chromium it is that of nature of matrix which is not detected.

793

Table 4 Results of A N S 16.1 leaching test System FA

System BFS ~~

Nitrate Added

5 yo

10%

5 yo

10%

4.10 2.26 0.13 0.03 <0.01 0.72

4.06 1.35 0.08 0.03 <0.01 0.36

0.16 0.81 0.11 0.03 <0.01

0.10 0.42 0.07 0.02 <0.01

n.d.

n.d.

Element

I% cu Cr Ni

cd

Zn n.d.=not determined

In the case of cadmium the concentration in the leachate was always below the detectability limit of the analytical equipment used. This is not surprising because cadmium is completely precipitated as insoluble CaCd(OH)4 in strongly alkaline stabilizing matrices [12-141. Water renewal in the dynamic leaching test did not alter significantly the alkalinity of leachate, and pH in this case was never less than 10. The behaviour of nickel is very similar to that of cadmium, as almost constant, very low concentration was detected. Evidently, this behaviour can be ascribed to respeciation of nickel in strongly alkaline media with formation of insoluble phases. Their nature is difficult to establish, as confirmed by the lack of information in the pertinent literature. Figure 1 shows the results of the dynamic test as cumulative quantities released after each water renewal in the case of lead stabilized with both matrices. In this case the two matrices are able to entrap quantities of metal that, although very different from one another, are proportional to the initial amount added. In other words it can be said that lead leachability in the matrices used is not limited by thermodynamic factors such as solubility.

194

X

FA-10% nitrate

0 BE-5%nitrate

A BE-10% nitrate 0

2

0

0

5

Figure 1 - Results of ANS 16.1 test on model systems containing lead Figure 2 shows the some results as Fig.1, but for copper. It is clearly seen that in this case leachability is limited by the solubility of respeciated product, as the absolute (not fractional) quantities are constant, although different for the two matrices. The systems containing chromium showed similar behaviour. In the case of zinc, the blast furnace slag-based matrix did not harden after 28 day curing and then it was not possible to carry out any leaching test. The data available for this metal stabilized by fly ash-based matrix indicate that its behaviour is similar to that of copper and chromium. The results shown in Figs. 1 and 2 are typical of any system tested in the sense that the maximum quantities are released after 672 hours leaching (10 water renewals). Further increasing the number of water renewals does not give any information useful for assessing the long-term behaviour and environmental impact in actual disposal scenarios. To this scope the leaching test at pH=4.74 was conceived in order to better simulate actual conditions. Furthermore, the leaching test at p H 4 M . 2 was carried out in order to get a better understanding of the actual nature of the mechanisms responsible for entrapment in any of the systems tested.

795

0 FA-5%nitrate X

FA-10%nitrate

0 BFS-5%nitrate

A BFS-10%nitrate Q,

d

0

1000

3000 Time, h

2000

4000

5000

Figure 2 - Results of ANS 16.1 test on model systems containing copper

Figures 3 and 4 show the results of the acidic batch tests for FA and BFS matrices, respectively. The amount of initial nitrate added was 10% in both cases. The results for 5% initial amount are very similar and are not shown. For the sake of comparison, the results of Table 1 are also reported in the above figures. Cadmium, which proved to be insoluble in the dynamic leaching test, shows an almost constant solubility in the acidic media used in the other two batch tests. This solubility does not exceed about 10% of initial quantity and it should be pointed out that the physical state of the sample (monolithic or powered) did not affect the leachability which, in this case, is ruled by the chemical properties of the products formed. Nickel and copper show similar behaviour. They are respeciated as soluble products in acidic media. When the samples are monolithic, the amount released in the acetic buffer is of the order of a few units per cent in any case. This proves that the nature of the formed products is very similar for the two matrices. When the samples are powered, much larger quantities are released and the two stabilizing matrices behave differently, the one based on blast furnace slag being by far the best. Obviously, different pH values can strongly influence leachability, but the difference observed when the two matrices are compared in relation to powered samples (nitric acid test) makes clear that the blast furnace slag-based systems exhibit a much better stabilizing efficiency. This is in agreement with the previous finding that the blast furnace

196 slag based-system has better mechanical and physico-chemical properties in respect to that based on fly ash-lime mixture [15].

100

8

$ $ B

5m

rz

80

60 40 20

0

Cd

Cr

Cu

Ni

Fb

Zn

Figure 3. Results of ANS 16.1,acetic buffer (pH=4.74) and nitric acid (pH= 4 f 0.2) leaching tests. FA system; 10% nitrate added

The results for chromium are in agreement with literature data [16,17] and show that this metal is always released in small amount. Systems based on blast furnace slag are again more effective than those based on fly ash. To this regard, the results of the buffered acetic test are particularly significant. As far as lead is concerned, it is reported in the literature [18,19] that cement based systems convert this metal in such a form that leachability increases very rapidly as pH decreases below 8. The results obtained in water (dynamic test) with blast furnace slag-based systems confirm those obtained by Cote [20] who stabilized lead in a number of cement based systems. Furthermore, the results of the acidic tests clearly show the high efficiency of the blast furnace slag-based systems tested here. Finally, it should be pointed out that the results for lead in the case of blast furnace slag-based systems were the lowest in any of the acidic tests. The results obtained for lead stabilized by means of the fly ash-based matrix are quite anomalous in relation to the fact that this matrix, so as all those cementbased, respeciate the metals as alkaline precipitates. Their solubility should then increase with the acidity of leachant. Our results show that lead is released to a lesser extent as pH decreases and this behaviour cannot be explained neither with our data, nor with the results reported in the literature.

191

pH4.74

80

60

pH4k0.2

F

40 20 0

cd

Cr

Cu

Ni

Pb

Figure 4.Result of ANS 16.1, acetic buffer(pH= 4.74) and nitric acid(pH = 4 f 0.2) leaching test. BFS system; 10% nitrate added.

The two matrices used in the above model systems have been tested with regard to the residue from MSW incineration referred to in the introduction. Fig. 5 and 6 show the cumulative absolute (not percentages) quantities released in water after 6 months leaching. The figures are relative to the two stabilizing matrices and report the data for any of the four matrix-residue mixtures tested. Again, the nature of the metal strongly influences the leachability (cadmium is not released at all), while the nature of the stabilizing matrix has very little effect. The ratio waste/matrix has a strong effect on the leachability in the sense that a sharp positive change occurs when the waste content increases from 40 to 60%. These observations lead to the conclusion that the metals retain their chemical nature and are not respeciated by the matrix itself. This is not surprising inasmuch as the high-temperature incinerator process converts the metals into stable oxides. The observed net increase of leachability is then due to the reduced solidification potential as a consequence of increased waste content in the wastematrix mixtures. This is in agreement with previous results which showed a sharp decrease of compressive strength observed on the same systems when the of waste increases from 40 to 60% [15]. amount

798 Waste content

0 0

Cr

cu

Ni

rb

20% 40% 60%

Zn

Figure 5. Result of ANS 16.1 leaching test for samples of MSW incinerator waste. FA system mixtures.

0 20% [I 40%

Cr

cu

Ni

rb

Zn

Figure 6. Result of ANS 16.1 leaching test for samples of MSW incinerator waste. BFS system mixtures.

799 4. CONCLUSIONS

The two non-traditional matrices based on blast furnace slag and fly ash-lime mixtures tested in this work have great potential for use in stabilization/solidification processes. These matrices are particularly attractive among those on which cement processes are based, because they contain up to 61.5% waste materials such as blast furnace slag and coal fly ash. Moreover, also the source of calcium sulphate, pure gypsum in this work, could be replaced with chemical gypsum such as phosphogypsum, desulphogypsum and so on. Model systems solidified with both matrices have shown that metals are retained to an extent depending on the nature of metal itself, the nature of matrix and initial metal concentration. As in all alkaline cement-based matrices, cadmium was not released at all in water during the dynamic leaching ANS 16.1 test. The other metals were released in quantities never greater than approximately 1%when solidified with the blast furnace slag-based matrix. The fly ash-based matrix proved to be less efficacious and the quantities of metal released were at most slightly higher than 4%. Much larger quantities were generally released in acidic leaching media. To this regard, it has been proved that the chemical properties of the products of metal respeciation, as well as the physical and structural properties of the hardened products, play a fundamental role. When these matrices are used in mixtures with a residue from MSW incineration, leachability is ruled almost exclusively by physical factors, as the waste contains the metals in stable oxide form. 4. REFERENCES

1 J.R. Comer, Chemical Fixation and Solidification of Hazardous Wastes,Van Nostrand Reinhold, New York, (1990). 2 F.P. Glasser in Chemistry and Microstructure of solidified Waste Forms, R.D. Spence Ed.,Lewis Publishers, Boca Raton, Florida, 1 (1992). 3 J.Beretka, LSantoro and G.L.Valenti, Proc. 4th Int. Conf. on Durability of Building Materials and Components, Singapore, (1987) 64,Vol. I. 4 G.L. Valenti, L.Santoro and J. Beretka, Proc. 2nd Int. Symp. on Phosphogypsum, Miami, 2 (1988) 167. 5 J.Beretka, R.Cioffi, L.Santoro and G.L.Valenti, Proc. 3rd Int. Symp. on Phosphogypsum, Orlando, (1990) 417. 6 J.Beretka, R.Cioffi, L.Santoro and G.L.Valenti, Proc. 3rd NCB Int. Seminar on Cement and Building Materials, New Delhi, 3 (1991) 110. 7 LSantoro, G.L.Valenti and G.Volpicelli, Thermochimica Acta, 74 (1984) 35. 8 G.L.Valenti, L.Santoro and G.Volpicelli, Thermochimica Acta, 78 (1984) 101.

800

9 L.Santoro, LAletta and G.L.Valenti, Thermochimica Acta, 98 (1986) 71. 10 G.L.Valenti, R.Cioffi, LSantoro and S.Ranchetti, Cement and Concrete Research, 18 (1988) 91. 11 American Nuclear Society, Measurement of the leachability of solidified lowlevel radioactive wastes by a short-term procedure. Working group ANS-16.1, (1986). 12 J.D. Ortego, S. Jackson, G.S. Yu, H.G. Mcwhinney and D.L. Cocke, J. Environ. Sci. Health, 24 (1989) 589. 13 D. Cocke, J. Haz. Mat., 24 (1990) 231. 14 F.K.Cartledge, L.G. Butler, D. Chalasani,H.C. Eaton, F.P. Fray, E. Herrera, M.E. Tittlebaum and S. Yang, Environ. Sci. Technol., 24 (1990) 867. 15 V. Albino, R. Cioffi, L. Santoro and G.L. Valenti, Waste Management & Research, in press, (1994). 16 D.L. Cocke, H.G. McWhinney, D.C. Dufner, B. Horrell and J.D. Ortego, Haz. Wastes Haz. Materials, 6 (1989) 251. 17 R.C. Davis and D.L. Cocke, Proc. 5th Tnt. Symp. on Ceram. in Nucl. and Haz. Waste Manag.,Cincinnati, (1991) 1. 18 P.H. BruMer and P. Baccini, U.S.EPA, Cincinnati, (1988) 343. 19 J.A.Mundell and K.R. Hill, Proc. Haz. Wastes. and Env. Emerg. Conf., Houston, (1984), 177. 20 P.L. Cot6 and D.P. Hamilton, Proc. Haz. Wastes and Env. Emerg. Conf., Houston, (1984) 302.

Environmental Aspects of Construction with Waste Materials JJ.J.M. Goumans, H A . van der Sloot and Th.G. Aalbers (Editors) a1994 Elsevier Science B.V. AN rights reserved.

801

APPLICATIONS OF BY-PRODUCTS FROM COAL GASIFICATION POWER PLANTS: QUALITY- AND ENVlRONMENT-RELATED ASPECTS M.L. Beekes', J.W. van den Bergb, and A.J.A. Konings' 'KEMA Nederland B.V., P.O. Box 9035, 6800 ET Arnhem, The Netherlands bVliegasunie B.V., P.O. Box 3254, 5203 DG 's-Hertogenbosch, The Netherlands

Abstract A 250 MW, Integrated Coal Gasification Combined Cycle power plant has been

build and started up recently in Buggenum, the Netherlands. The utilization of byproducts originating from this plant, more especially the slag from the Shell Coal Gasification Process, in concrete elements and road construction is described, with the emphasis on quality- and environment related aspects.

1. INTRODUCTION

The more stringent requirements with respect to emissions and by-products from industrial processes evoke additional facilities in power plants. Increasing costs of these facilities force the efficiency downwards. Oil and gas reserves are decreasing and nuclear power has its waste problem and is politically complicated. Therefore there is a need for other clean and safe ways of power production. Coal accounts for over 70% of all fossil fuels. This fact implies that coal will be important for the generation of electricity in the world. In the Netherlands 37% of the electricity production is fuelled by coal. The usage is coal demands proper technologies to minimize environmental impact. Ongoing technological developments enable us to cope with more stringent emission requirements. Coal-based IGCC (Integrated Gasification Combined Cycle) is such a new technology. Gasification of coal is a process in which coal is partially oxidated by air, oxygen, steam or carbon dioxide under controlled conditions to produce a fuel gas. The hot fuel gas is cooled in heat exchangers (with the production of steam), and cleaned before combustion in a gas turbine. The offgases from the turbine are

802

used in a boiler to produce additional steam for a steam turbine. The electrical efficiency can be around 45% with minimal impact on the environment. A demonstration-unit of 250 MW, has been constructed in Buggenum, the Netherlands, based on the Shell Coal Gasification Process, which is build around an entrained flow slagging gasifier.

2. BY-PRODUCT FORMATION

The by-products coal gasification slag and fly ash are formed in the gasifier reaction vessel and differ clearly from bottom ash and fly ash from (powder)coalfired boilers. This is due to the reducing conditions and the higher operating temperatures in the gasifier. The slag which runs from the reactor wall is quenched in a water-bath at the bottom of the reactor and subsequently lock out off the system (Figure 1). It is a coarse granular, glassy material. The heavy metals are fixated in a matrix consisting of SiO,, AI,O,, Fe,O, and CaO

Figure 1.

Slagging coal gasifier

The fly ash is separated with a cyclone. Part of the fly ash is recirculated to the gasifier to obtain higher carbon conversion levels. The composition and properties of the fly ash will depend on the degree of recycling.

803 There will also be a significant difference with respect to the partition of ash over the by-products. In a powder coal-fired boiler about 90% of the ash reports to the fly ash and about 10% in the bottom ash, whereas in the Buggenum gasifier approximately 90% of the ash will end up in the slag and 10% in the fly ash. Characteristic for the Buggenum unit will be that the sulfur present in the coal is converted to elemental sulfur instead of gypsum as is normal practice in Dutch powder coal-fired units. The raw coal-gas is cooled, dedusted, dehalogenated and subsequently desulfurized by absorption of hydrogen sulfide in sulfinol-D. Finally the hydrogen sulfide is stripped and converted to elemental sulfur by the Claus process with an efficiency of over 98%. This pure form of sulfur is a basic raw material for the chemical industry. A research program has been started in order to identify timely industrial applications for coal gasification slag and other coal gasification by-products. A steering committee consisting of representatives of Demkolec, KEMA, Novem and the Vliegasunie (Fly ash Corporation) supervises the research- and development work in accordance with the Industrial Development Program Coal Gasification (IOKV).

The research is primarily concerned with the by-products originating from the SCGP gasification technology that has been the choice for the demonstration unit in Buggenum. The by-products from other gasification processes that may be applied by the end of the century (for instance the Texaco and the British Gas/ Lurgi process) are investigated to a lesser extend. The research program has been started in 1990 and was focused initially on the characterization of coal gasification slag and fly ash. In 1991 several projects directed towards applications have been set up. The research has been conducted and reported by several laboratories and institutions and was mostly bench-scale type of work. In accordance to the planning this work has been continued on a (semi)pilot plant scale, whereafter in 1994 demonstrations are foreseen.

3. CHARACTERIZATION OF BY-PRODUCTS

Coal gasification slag and to a lesser extend fly ash from a number of coal gasification processes (SCGP, Texaco and BGL) have been characterized chemically and physically. The macro- and trace-elementalcomposition (Figure 2), particle size distribution, morphology, specific surface area, melting behaviour, radio-activity level and the leaching properties have been determined together with a variety of CI' I-technical properties that are important for specific applications such as bulk density, proctor density, moisture tension, water porosity, raise due to frost and the angle of inner friction. It appeared that coal gasification slag originating from the SCGP process is a substance, which seems to be more benign from an environmental and sanity point of view than fly ash originating from powder coal-fired boilers.

804 The particle size distribution of most gasification slag is in general similar. About 7580% lies in the range of 0,5-4 mm, as represented in Figure 3. The bulk density is in the range of 1300-1450 kg/m3, the cohesion in the range of 10-20 kN/m2 and the moisture content is with < 5% relatively low. The melting points (fluid point under reducing conditions) are in the 1200-1400 "C range. Leaching tests carried out in accordance with Dutch Standard procedures (NEN 6465) show that the gasification slag of all processes show a leaching behaviour similar to that of bottom ash from conventional dry bottom boilers, which is utilized in the Netherlands as road base material.

50 40

30 20 10

0 Si02

A1203

13

Figure 2.

Fe203 CaO MgO Macro composition s1 1 52

-

Na20

K20

Ti02

C

s3

Macro composition of SCGP slag samples

The fly ash of the gasifiers is very fine (90% < lopm), with round and irregular shaped particles. Compared to the slag the Ca-content is low, the C-content about 10% and some trace element are enriched.

805

Figure 3.

Typical particle size distribution ranges for BGL, SCGP and Texaco slag

4. APPLICATIONS

OF BY-PRODUCTS

The suitability of coal gasification slag for civil-technical applications has been investigated firstly on a small scale by means of specimens in the laboratory. Subsequently larger quantities have been produced industrially on pilot plant scale and in batchwise production. The properties of these applications have been investigated by laboratory testing (leaching behaviour, pressure strength a.0.) and via the preparation of road sections and buildings in which the materials are exposed to weather conditions and actual usage. This kind of testing, which often runs for a longer period and requires larger quantities of raw materials, will be continued and elaborated during the demonstration period of the Buggenum plant. The partial substitution of sand in concrete elements by IGCC slag has been investigated. Several parameters important for concrete technology such as volumetric mass, gradation and water absorption have been determined. It was also concluded that the chemical composition of the slag did not have an adverse effect on the cement hardening. The compression strength of concrete with 50% substitution seems to be acceptable. The application of slag as raw material in the cement clinker production has been investigated. Incorporation of slag in the raw materials up till 20% slag per ton clinker appeared to be feasible, in practice 510% kg will be realistic. The cement industry located near Maastricht and Liege will be able to utilize 150.000-300.000 ton slag per year in this way. Another option in the cement manufacturing is the production of composite cement: part of the portland clinker is replaced by slag before milling. Based on bench scale tests (see Figure 4) a feasibility study has been performed in the replacement range of 20-35% slag. Composite cement with 25% slag is comparable with widely used Portland-fly ash-cement. With representative slag from Buggenum full scale demonstration tests are scheduled.

806

50 r compressive strength (N.mm.2,

40 30 20

72% slag 55% slag a 40% slag +

//.-,,-------

_i

10

*!,

/

tY

&

0

I

5

10

time (d)

Figure 4.

15

20

, 25

25% slag HC "PVLC

30

Compressive strength development of composite cements compared with Blast furnace cement (HC) and Portland-fly ash-cement (PVLC)

Special attention has been paid to slag application in gravelconcrete pavement. Those tiles contain gravel, sand, cement and a small amount of fly ash. The top layer is enriched in gravel. Sand and part of the gravel has been replaced by coal gasification slag. The handling in the production plant, the tile properties and environmental aspects (leaching) appear not to deviate from the reference tiles (Figures 5a, b and c). The substitution of sand in asphalt seems be to beneficial, despite of the fact that the slag that were investigated are not conform the present requirements for sand in bituminous mixtures. Additional bench scale research seems advisable.

807

Figure 5a.

Gravel-concrete pavement, experimental production. BIT1 = gravel/ -/cement/fly ash (reference)

Figure 5b.

Gravel-concrete pavement, experimental production. 63T1 =gravel/ &/cement/fly ash. In 63 the gravel volume is reduced with 18%

Figure 5c.

Gravel-concrete pavement, experimental production. 64T1 = gravel/ &g/cement/fly ash. In 64 the gravel volume is reduced with 25%

808 Finally the option for slag utilization as road subbase and embankment material is under investigation. To get insight in the specific handling problems of slag, a demonstration road section with 1000 ton slag from the SAR in Holten Germany, a commercial coal gasification plant operated by Hoechst A.G., was constructed in 1989 at the KEMA site and is in good shape up till now. The cross section of this demonstration road is represented in Figure 6. An extensive demonstration program for the utilization of slag in road subbases and embankments is scheduled for the period 1994-1999 to take place at the Buggenum site. A well-instrumented embankment (30x30 m2 base, 10x10 m2 top,5OOO ton slag) will then be monitored.

earth

/

3 layers asphalt, 140 rnm

/

, Gc-slag, a m m

\

Figure 6.

sand

Cross section of the demonstration road at the KEMA site (1000 ton Texaco slag, 250 m length, 1989)

5. MARKET POTENTIAL

The by-products originating from coal-fired power plants produced today in the Netherlands are marketed by the Vliegasunie. The Vliegasunie is a 100% subsidiary of the Dutch electricity producing companies and has the goal to take care of an optimal processing and marketing of the by-products. The utilization has to be done in an environmentally sound way and at as low as possible cost. The Vliegasunie can be regarded is the final link in the electric power production chain. Nowadays the by-products originating from coal-fired power plants in the Netherlands are marketed by the Vliegasunie for 100%. These by-products are:

- pulverized coal fly ash - bottom-ash - FGD gypsum

approximately approximately approximately

850.000 ton/year 80.000 ton/year 250.000 ton/year

809

In order to guarantee the utilization of coal gasification by-products in the future the production of these by-products during the demonstration period will be used for large scale demonstration projects. Major attention will be paid to verification of the results obtained thus far, certification of the by-products for specific applications and commercial negotiations with potential customers. It is expected that the marketing of coal gasification by-products will pose no problems, based on the available results.

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, H A . van &r SImt and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. AN rights resewed.

81 I

Quality improvement of MSW-fly ash and APC-residue from MSWIncinerator Amsterdam-West using different immobilisation processes H.T.M. van de Laar, J. Slagter, R.F. Duzijn and J.H. de Zeeuw Tauw Milieu bv, Department of Environmental Hygiene, P.O. Box 133, 7400 AC Deventer, The Netherlands

Abstract Tauw Milieu bv has carried out a project on immobilisation of fly ashes and air pollution control (APC) residues for the Municipal Waste Incinerator Amsterdam. Both residues have to be classified as "C2-waste" in the Netherlands. Purpose of the project was to determine if the leachability of these residues could be reduced by means of immobilisation in such a way that they could be classified in a lenient category. Five selected companies, using their own licensed process, have immobilised either the fly ash, a mixture of fly ash and APC residues, or both. It appeared that by means of immobilisation the leachability of fly ash can be reduced well enough in order to classify it as "C3-waste". For the mixture of fly ash and APC residues, the leachability of chloride and strontium was still too high after immobilisation. 1.

INTRODUCTION

In the Municipal Waste Incinerator in Amsterdam Municipal Solid Waste (MSW) is incinerated and several residues are being produced. Among these residues are fly ash and APC residues, which arise from the flue gas treatment. Both residues have to be considered as hazardous waste. The leachability of both residues causes classification as "C2waste", which is considered as hazardous waste having a high leachability. These kinds of waste have to be disposed of at a specially equipped landfill site. The costs for landfill could be reduced considerably by reducing the leachability. Hazardous wastes having a medium or low leachability can be classified as respectively "C3-waste" and "CCwaste". A landfill site for disposal of these wastes will do with less equipment and the costs for disposing the residues can be reduced. It is expected that the leachability of the fly ash can be reduced far enough in order to enable classification as "C3-waste". Immobilisation of the APC residues is expected to be more difficult, since this residue has a very high content of soluble salts. Therefore examining immobilisation of a mixture of fly ash and APC residues is preferred. Since the residues arise in equal amounts, the preferable proportion of the residues in the mixture could be 50/50 (w/w).

812 Aim of the project is to determine the possibilities for reducing the leachability by means of immobilisation of both fly ashes and a 50/50 mixture of fly ashes and APC residues. This article gives an overview of the project results, a more extensive report has been written by Tauw for the Municipal Waste Incinerator Amsterdam (Mr W.M. Sierhuis). In order to examine the possibilities for immobilisation, first the composition (total analysis) and leachability of the untreated residues were determined. In this way the starting point is set and a frame of reference is created. The samples were then used for immobilisation experiments by five selected companies, after which the immobilised products were analyzed. The leachabilities of the immobilised products were compared with the limit values for classification. Furthermore they were mutually compared and related to the leachability of untreated residues. Next conclusions were drawn regarding the possibilities for reducing the leachability of both fly ash and a 50150 mixture of fly ash and APC residues. 2.

IMMOBILISATION PROCESSES

2.1. Introduction

In the scope of this project, six companies were preselected for participation by carrying out immobilisation experiments. These companies have been interviewed and visited. The purpose of this interview was to estimate the chances for successful immobilisation by these companies and to gain a general idea about the costs for immobilisation on full scale. The companies which have been preselected were Pelt & Hooykaas (Rotterdam, the Netherlands), Aardelite (Umuiden, the Netherlands), Kansai Engineering (Zwijndrecht, the Netherlands), Tauw Milieu bv (Research and Development Department, Deventer, the Netherlands), Esdex (Maarssen, the Netherlands) and Heitkamp Umwelttechnik (Bochum, Germany). The interviews resulted in a final selection of five companies for further participation. Two companies were selected for carrying out experiments on immobilisation of both fly ash and a 50150 mixture of fly ash and APC residues, one company was selected for immobilising a 50/50 mixture of fly ash and APC residues only, and two companies were selected for immobilising fly ash only. The sixth company could not meet the prescribed time schedule. The five selected companies i.e. Pelt & Hooykaas, Aardelite, Tauw (R&D), Esdex and Heitkamp received residue samples for immobilisation. In this chapter the processes of these companies are described shortly. 2.2. Pelt & Hooykaas Pelt & Hooykaas uses the "Multifix process" (IWT) for immobilisation of residues. This process contains three steps: firstly the residues are pretreated (i.e. by means of neutralizing or breaking), secondly additives are added in order to obtain a chemical fixation, thirdly water and anorganic binders are added in order to physically stabilize the residues. After mixing, the product needs hardening.

813 The amount of additives used depends on the residues to be treated. A typical dilution rate for the considered residues is 20 to 25% (dry matter), a typical volume reduction is 10%. The immobilisation process is carried out in batches. The immobilised product is a monolith. Pelt & Hooykaas does not have significant experience in a full scale use of this process. Before building a full scale plant, a pilot plant will be developed.

2.3. Aardelite The immobilisation process of Aardelite contains two steps. In the first step siliciumcontaining additives are mixed with the residue. After addition of water and mixing, the mixture is pelletized and the pellets are embedded in a matrix. In the second step of the process, the embedded pellets are heated in a reactor at a temperature of 90°C,a pressure of 1 atm and a relative humidity of 100%. Under these conditions the metalcompounds are bound and enclosed at microscale. After 16 to 20 hours the pellets can be removed from the matrix, no hardening is necessary. A typical dilution rate for the incineration residues is 5 to 10% (dry matter), a typical volume reduction amounts to 25%. Because the immobilised product consists of pellets, the volume for landfilling will be about 10% higher than the volume of the untreated residues. Aardelite is able to build a full scale plant for immobilisation, without first building a pilot plant. 2.4. Tauw Milieu (R&D)

The immobilisation process of the R&D department of Tauw Milieu is a single step process. The additive which is added to the residues, causes a chemical fixation of the (hazardous) compounds. The reaction takes a few days, the product does not need hardening. A typical dilution rate is about 10% (dry matter). If the fly ash or APC residues is moistened, the volume can be reduced by 50%. The process can be carried out either in batches or continual. At the moment, the process is only available at labscale. 2.5. Esdex Esdex uses the Soliroc process, which is based on a chemical conversion of metal compounds into metal silicates. Grinded blast furnace slags are used as a silicium source for the chemical fixation. Lime is added for pH control. Cement and water are added for physical stabilisation. After mixing the product (monolith) needs hardening. The Soliroc process can be carried out in batches or continual. A typical dilution rate is 80% (dry matter), the high amount being caused by the amount of blast furnace slags which is necessary for a sufficient fixation. The volume of the residues will not change significantly due to immobilisation. Esdex has gained full scale experience abroad using the Soliroc process.

814

2.6. Heitkamp The Heitkamp immobilisation process uses both organic and hydraulic binders. The organic binders enclose the particles at microscale. The hydraulic binders cause physical binding of the particles. All ingredients need to be mixed intensively (in batches or continual). After hardening a monolithic product is obtained. In order to sufficiently immobilize the compounds, a typical dilution rate is 15%, a typical volume reduction is 20%. Heitkamp operates various mobile full scale installations available, which may be used.

3.

MATERIALS AND METHODS

3.1. Sampling

Tauw Milieu bv has taken samples of both the fly ash and the APC residues at the Municipal Waste Incinerator Amsterdam. The samples were taken from big bags (1 m3) and transferred into small containers (0,l m3). Each residue was sampled in 6 small containers in such a way that the samples in all containers were equal. These 6 samples were used for the analysis of the untreated residues and for immobilisation experiments. 3.2. Research into chemical composition The chemical composition of the residues is not significant for the determination of the hazardousness, since the waste incineration residues are designated as hazardous waste in the Hazardous Waste Designation Decree (Dutch BAGA). Nevertheless for purposes of identification of the residues it is useful to know the composition at both macro as well es micro level. The residue compositions have been analyzed in the environmental laboratory of Tauw Milieu bv. The untreated residues have been pretreated for analysis by digestion using aqua regia (NEN 6465). Total analyses of fly ash and APC residues were carried out on both macro as well as microcompounds. The hazardousness of the residues is caused by microcompounds and two macrocompounds (chloride and sulphate). For the aim of this project only the leachability of these compounds needs to be examined. For immobilisationpurposes the macrocomposition of the residues needs to be known, in order to determine the kind and the amount of additives to be added. Therefore the untreated residues are examined on a broad range of compounds. For analysis, the immobilised products have undergone a more extensive pretreatment than untreated residues. The cylinders were broken and grinded, after which they were digested using aqua regia (NEN 6465). Only two microcompounds were analyzed in order to determine the dilution rate which was caused by immobilisation. In table 1 the compounds which have been analyzed for composition are specified; they are indicated by "C" (for composition).

3.3. Research into leachability The leachability of the residues has been determined by using a shortened column test (NVN 2508). In the column test the pretreated residue is packed in a column and water is percolated in upflow. A shortened column test finishes at a liquidholid rate (w/w) of 1.

815

Analysis of the leachates is mainly carried out on microcompounds. The compounds which were analyzed for leachability are specified in table 1 and indicated by "L" (for leachability). The concentrations of compounds in the leachate (in mg/l) were recalculated as leached quantities (in mg/kg). For the leached quantity of compounds in the leachate of a shortened column test, limit values have been set in order to classify the hazardous residues as either C2, or C3 or C4 waste [2]. Two limit values have been set, UO and U1. The classification of hazardous waste is as following (symbols for comparison are given between brackets): - leached load < UO limit value - classification as C4-waste (--); - leached load is between UO and U1 - classification as C3-waste (-); - leached load > U1 limit value - classification as C2-waste (+). The leachability of the residues was compared with these limit values in order to determine the classification of it. Table 1 Compounds for analysis of composition and leachability Untreated fly ash

Immobilised mixture

fly ash

mixture

L

L

L

L

Macrocompounds: aluminum ammonia calcium carbonate chloride fluoride iron magnesium organic carbon potassium silicium sodium sulphate sulphite

Microcompounds: antimony barium cadmium lead mercury molybdenum strontium zinc

C C C C,L C C C C C C C,L

C C C C,L C

816

4.

RESULTS

4.1. Introduction The five companies have carried out experiments using either fly ash or a 50/50 mixture of fly ash and APC residues. Since a tight time schedule had to be met, only a preliminary optimisation of the recipes by the companies could take place. The results which were obtained by the companies therefore only can be regarded as an indication. In this chapter the results of immobilisation are presented. The results of each single company are to be kept confidentially, therefore the results are presented anonymously. The results of the five companies will be presented in random order and they will be indicated as A to E. 4.2. Untreated residues The untreated fly ashes and the 50/50 mixture of fly ash and APC residues have been analyzed on both their composition and their leachability. The leached quantity (1.q.) has been compared with the limit values for classification. The 5060 mixture of fly ash and APC residues could not be analyzed by means of a shortened column test, because the flow through the column was blocked after a short period of time. The symbols which have been used for comparing the leachability of fly ash with the limit values are described in paragraph 2.3. Table 2 presents the results for the untreated fly ashes and untreated 50/50 mixture of fly ash and APC residues. Table 2 Results for untreated fly ash and 50150 mixture of fly ash and APC residues (in mglkg dry matter) limit values u1 value

uo value

fly ash composition

50150 mixture 1.q.

composition

Macrocornpounds: aluminum ammonia calcium carbonate chloride fluoride iron magnesium organic carbon potassium silicium sodium sulphate sulphite

> 17,000

34,000

50,000 280

50,000 25

110,000 3.2 >56,000

36,600(--)

11,000 9,500 16,000 25,000 5.800

> 750 115,000 2.2 213,100 > 13 >5,500 >4,750 > 8,000 > 12,500 >2,900

> 110,Ooo 80,000

80,000

>54,000

3,450(--)

>63,000

>275

817 limit values

Microcompounds: antimony barium cadmium lead

mercury molybdenum strontium zinc

fly ash

uo

50/50mixture

u1 value

composition

1.q.

composition

value

0.8 60 0.2 25 0.1 3 5 40

0.1 20 0.05 4 0.1 0.04 I 10

850 540 135 3,500 0.5 9 215 11,000

0.015(--)

595 350 103 2,800 1.9

2.05(--) 1.15(+) 12 (3 0.00005(--) 1.6(-) 9.9(+) 5. I(--)

<8 >115 8,150

From table 2 it can be seen that for fly ash the loads of both cadmium and strontium exceed the U1 limit value. Because of this the untreated fly ash has to be considered as C2-waste.

4.3. Treated residues 4.3.1. h o b i l k a t i o n of fly ash Four companies have carried out experiments on immobilisation of fly ash. The results of the leachability tests on the immobilised products are presented in table 3. Table 3 Results of leachability test for immobilised fly ash (in mg/kg dry matter)

antimony barium cadmium chloride*’ lead mercury” molybdenum strontium sulphate*’ zinc classification

untreated fly ash

immobilised fly ash

composition

1.q.

1.q.

A

850 0.015(--) 540 2.05(--) 1.15( +) 135 > 56 37(--) 3,500 W-) 500 0.05(--) 9 1.6(-) 215 9.9( +) > 85 3.5(--) 11,000 5 . I(--) c2

O.Ol(--) 0.215(--)

1.q. B

1.q.

1.q.

D

E

0.0005(--) 0.04(--) 0.4(+) 43(--) < O.l(--)

0.1(-) 0.275(--) 0.0002(--) 15(--) 2.9(--) 0.05(--) 1.75(-) l.O(-) 1.2(--) I.%(--) c3

47(--) 2.2(--) 0.03(--) 2.75(-) 2.4(-) 6.8(--) 0.78(--)

1.9(-) 2.4(-) 2.2(--) 0.4(--)

0.2 1(-) 0.54(--) < 0.0 1(--) 78(+) 16(-) <0.03(--) 0.66(-) 23.6( +) 2.4(--) 0.54(--)

c3

c2

c2

0.013(--)

0.05(--)

1): leached quantities higher than U1 cause designation as C2-waste 2): amounts are in glkg dry matter 3): amounts are in pglkg dry matter

u 1/UO” value O.WO.1

60/20 0.2/0.05 50/50

25/4 1001100 3/0.04 511 80/80

40/10

818 Table 3 shows that fly ashes which have been immobilised by the companies B and D still need to be classified as "C2-waste". The product of company B still has a leached quantity of cadmium which is twice the U1 limit value. Company D could not sufficiently reduce the leaching of strontium, also the leaching of chloride is close to the U1 limit value. Both companies B and D expect that after optimization of their recipes, the limit values for "C3-waste" can be met. The immobilised products of the companies A and E meet the U1 limit values. For some compounds the leached load approaches the limit value, but after optimization of the recipes, classification as "C3-waste" can be expected. Table 4 presents the volume and weight reduction due to immobilisation. The volume of the products to be disposed of at a landfill site is directly related to the costs for disposal. Table 4 Volume and weight reduction of 1 ton fly ash

weight (tons) volume (m3) costs (in Dfl) of immohilisation

untreated fly ash

immobilised fly ash

incinerator Amsterdam

A

B

D

E

1.o

1.2

1.0

1.6

1.2

1.6

90

20

1.5 0.9 250

1.7 -2.1 0.9 - 1 . 1 70 - 95

Table 4 shows that the costs for immobilisation at a full scale are moderate for company B, while company D is rather expensive. Immobilisation by either company A or E has medium costs. It can also be seen that the largest volume reduction will be achieved by company D, companies A and E have lower volume reduction. This is caused by the shape of the immobilised products or by the amount of additives used. Company B produces no volume reduction.

4.3.2. Immobilisation of a 50150 mixture of fly ash and APC residues Three companies have carried out experiments on immobilisation of a 50150 mixture of fly ash and APC residues. The immobilised products have been analyzed (see. also chapter 3). The results of the leachability tests are presented in table 5.

819 Table 5 Results of leachability test for immobilised 50/50mixture (in mgkg dry matter)

antimony barium cadmium chloride" lead mercury2' molybdenum strontium sulphate" zinc

untreated mixture

immobilised mixture

composition

1.q. A

1.q. C

1.q.

595

0.3(--) 0.32(--) 0.027(--) 166(+) 0.14(--) 0.03(--) 0.67(-) 21.4(+) 6.9(--) 0.07(--)

0.002(--) 0.68(--)

<0.03(--) 0.17(-) 66(+) 2.2(--) 0.04(--)

0.005(-) 0.88(--) 0.023(--) 103(+) 32(+) < 0.03(--) 0.07(-) 24.2(+)

c2

c2

350 103 >213 2,800 1,850 <8 > 115 > 63 8.150

classification

<0.005(--)

148(+) 0.04(--)

D

Ul/UOvalue 0.810.1 60/20 0.2/0.05 50/50 2514 100/100 310.04 5/1

1.9(--)

80180

0.56(--)

40/10

c2

1): amounts are in glkg dry matter 2): amounts are in pglkg dry matter

Table 5 shows that all 50/50 mixtures of fly ash and APC residues still need to be classified as "C2-waste" after immobilisation. No company could sufficiently reduce the leaching of strontium and chloride. In the product of compony D, the leached quantity of lead exceeds the U1 limit value as well. Since the high amount of chloride in the mixture, a sufficient fixation of this compound can not be expected. Chloride salts are soluble and appear to be very hard to immobilise. Besides, the immobilisation processes mainly focuses on immobilisation of the metals in the residues. Table 6 presents the volume and weight reduction due to immobilisation. The volumina of the products to be disposed of at a landfill site have a major influence on disposal-costs. Table 6 Volume and weight reduction of 1 ton mixture

weight (tons) volume (m3) costs (in Dfl)of immobilisation

untreated mixture

immobilised mixture

incinerator Amsterdam

A

C

D

1.0 1.5

1.2 1.1 70

1.6 0.9 > 275

1.4 0.9 220

-

820

Table 6 shows that the costs for immobilisation at full scale are moderate for company A, while both companies C and D are expensive. It can also be seen that the largest volume reduction will be achieved by both companies C and D, whereas company A has a lower volume reduction. 6.

CONCLUSIONS AND RECOMMENDATIONS

From indicative experiments on immobilisation of fly ash and of a 50/50 mixture of fly ash and APC residues, the following preliminary conclusions can be drawn: - In general, the leaching behaviour of fly ashes can be sufficiently reduced by means of immobilisation in order to classify the product as "C3-waste". Two companies meet these limit values, and two companies expect they can meet these limits after optimization. - The leaching behaviour of a 50/50 mixture of fly ash and APC residues could not be reduced sufficiently by means of the considered immobilisation processes. None of the companies could meet the U1 limit values for the compounds chloride and strontium. It is likely that the amount of chloride which has to be fixed in order to meet the limit values, can not be realised by means of immobilisation. Besides, the considered immobilisation processes mainly focus on immobilisation of metals. - The processes carried out by the companies appear to differ significantly in prices and the volume-reduction that may be achieved. On the basis of this research it can be stated that only immobilisation of the fly ash gives promising results which make further elaboration and optimisation useful. The two companies having produced the best results for these residues, may be invited for taking further steps. The next steps should be 1). optimization of the recipe, 2). a specification of the costs for immobilisation at a full scale and 3). the handling of the immobilised products.

[ 11

[2]

Tauw Milieu bv, Immobilisatie vliegas en rookgasreinigingsresidu AVI-Amsterdam, report number R3285790.T04/T05 (1994). Dutch Ministry of Housing, Physical Planning and Environment, Grenswaardennotitie Storten gevaarlijk afval (1993).

Environmental Aspects of Construction with Waste Materials 3.JJ.M. Goumans, H A van der Sloot and 7'h.G.Aalbers (Editors) a1994 Elsevier Science B.V. All rights reserved.

82 1

Certification system for aggregates produced from building waste and demolished buildings Ch.F. Hendriks Director of Intron, Institute for Materials and Environmental Research, P.O. Box 226, 3990 GA Houten, The Netherlands

')

Professor of Materials Science, Delft University of Technology, P.O. Box 5048, 2600 GA Delft, The Netherlands

b,

Abstract In the Netherlands per annum about 14 million tons of building and demolishing waste are produced. Nowadays about 8 million tons are recycled, mainly for unbound road base courses. This market is almost saturated and a further increase in re-use must be realized within other sections of the building industry. One of these is the use as an aggregate in concrete. However, quality requirements for concrete are more difficult to meet for various reasons. The concrete industry is rather reluctant to accept the material, in the first place because of a lack of confidence in the quality. Another aspect is that the government on the one hand stimulates the re-use for building and demolishing waste as much as possible but on the other hand also fears pollution of the soil if incidentally contaminated building and demolishing waste is applied. This has stimulated the implementation of quality assurance systems by the recycling industry. Initially this industry established its own foundation which camed out attestation of conformity with the requirements of a quality assurance guideline. In 1993 this system has been converted into a certification system which will be approved officially in 1994 by the Dutch Council for Certification. Within the tight quality control scheme of this third-party certification the customers can confidently rely on the quality of this recycling aggregate.

1. INTRODUCTION The extraction of natural (primary) building materials increasingly meets with environmental objections. Moreover, the amount of waste and industrial residues increases alarmingly, which also involves environmental and economic objections. However, a large part of these waste materials and residues can (after processing) be used to partly compensate for the shortage of primary building materials. As a result of efforts of the government these so-called secondary materials are also becoming economically attractive.

822 2.

THE BUILDING CYCLE

Maintenance, renovation and demolition of constructions produce a considerable amount of waste. Recent estimations for building and demolition waste indicate an annual amount of 14-16 tons, mainly consisting of asphalt (2.5 million tons), concrete (5.3 million tons) and masonry (3.8 million tons). These numbers might still increase in the near future. A similar development can be seen throughout Europe. Presently the EC countries produce 200 million tons of building and demolition waste, an amount that may well double in ten years time. Dumping these materials causes more and more problems because of the space it takes up and the costs of sufficient care. Moreover, the establishment of this type of dump sites causes the NIMBY syndrome. Reuse would be the ideal solution. The building cycle, which indicates how each phase is influenced by the input and output of resources and energy, would then be closed. Building waste mainly consists of miscarried productions, superfluous materials and packing materials. Research in combination with the inventiveness of some entrepreneurs, has shown that when building waste is collected separately a large number of sub flows could be re-used in a cost effective way. In fact separate collection should become part of the quality system or the environmental care system of the construction company. With demolition waste things are more complicated. Especially the demolition waste of houses and other buildings contains, apart from the stony main components, a number of side components of which wood, metals, rubber, glass, paper, cardboard, textile, synthetic materials, soil and paint, are the most important ones. Materials that cause problems in re-use are: gypsum aerated concrete fibre concrete some applications of synthetic materials asbestos tarry materials some coatings and paints The problems mainly arise when these materials are offered in combination with other materials or are even attached to them. -

A re-use friendly design should take this into account. Pollution in demolition waste is mainly brought in during the period a construction is used, this is even valid for houses. Although the situation is somewhat more favourable with demolition waste from road and hydraulic constructions, re-use of demolition waste is only possible after upgrading, usually in combination with selective demolition.

823 A modern and well equipped demolisher draws up his plan of action on the basis of information about the construction, inspection and if required additional research. Moreover, he has various mechanical, chemical and physical methods at his disposal to go about selectively and therefore environmentally sound. ’Peeling’ old concrete with radio waves is an example of this. Because of this the demands with regard to the demolisher’s competence have risen to a high level. Further treatment of demolition waste is done in processing installations. Since the end of the seventies this has become a growing branch of industry in the Netherlands, which makes 7-8 million tons of demolition waste suitable for re-use and puts it on the market.

3. ENVIRONMENTAL ASPECTS In the Netherlands the acceptable burden of building materials to the environment is subject of an in-depth discussion. Most attention is focused on: * $radon emission in the indoor environment * leaching to soil and (ground) water. The authorities are working on the establishment of limit values to acceptable ionising radiation from building materials on the basis of a general (health) risk policy. A final point of view has not yet been established, since both the calculation of the risks and the measuring methods are still subjects of intense discussions. Compared to the primary materials extracted in the Netherlands the radiation load of secondary materials is equal or somewhat higher. The significance of this small increase is being investigated. Eventually the result of this investigation will have to be balanced against the importance of the application. With regard to soil and ground water the preliminary assumption is that the average natural content may not increase with more than 1% over a period of 100 years. From this assumption, limit values have been derived with regard to leaching of building materials, dependent on the application conditions. Since the leaching of organic pollution cannot be measured very well, limit values have been formulated for the composition. By far most bound applications of building materials meet with the requirements. This means that the use of aggregates made of building and construction waste has no environmental limitations concerning soil and (ground) water.

824 4. REUSE OF BUILDING AND DEMOLITION WASTE Most of the material is sold as 0/40 fraction concrete granulates or mixed granulates (which is a mixture of concrete and masonry granulates) in road foundations. The material can be sufficiently compacted, has a good crushing resistance and both the plastic and the elastic stiffness make the material suitable for heavy duty roads. Research into this material, among others executed by the Delft University of Technology, has had a positive influence on the constructive knowledge of stone foundations in general. Although the Netherlands are the leader in Europe with the present amount of this type of re-use, further growth in this sector is improbable. The market is saturated and is even becoming smaller in view of the shift in road construction from new construction to maintenance. A recently published implementation plan for building and demolition waste, written by order of the ministry for the environment, aims at a re-use percentage of 90% in the year 2000. This can only be achieved if the granulates will also be used as an aggregate in concrete. That market, however, renders far more problems. Technically the application has been extensively studied. 5.

STANDARDS

In 1984 - 1985 preliminary standards were made based on several years of thorough research for the use of building and construction waste in roads and in concrete. Last year, under the responsibility of a Rilem group, a proposal for the European standard was made for the use in concrete. This document is at present discussed by CEN TC 154 "Aggregates" in order to see if a European specification can appear based on this document.

6. SCOPE OF THE RILEM DOCUMENT This document gives the framework for a Rilem guideline dealing with recycled coarse aggregates 2 4 mm for concrete. These guidelines are based on the assumption that the fine ( < 4 mm) fraction of the concrete is composed of materials where traditional specifications for this material are applicable. Consequently, recycled materials may be used as substitute for the natural sand or parts hereof as long as above mentioned material specifications are complied with for the total sand fraction. In addition hereto the same requirements concerning content of sulphate and PAC as for coarse aggregate according to table 1 apply if the sand fraction contains recycled materials. This specification classifies different categories for the recycled coarse aggregates and indicates the field of application for concrete containing these recycled aggregate classes in terms of acceptable environmental exposure classes and strength classes for concrete in accordance with Eurocode 2; Design of concrete structures.

825

Eventually, the design values to be adopted for the different concretes are defined in relation to the applied aggregate class. The document gives the framework for use of recycled coarse aggregates in concrete. The use of recycled fine aggregates is limited for the following reasons: - The recycled fine materials do often contain large amounts of contaminants. It has been assessed that operational testing procedures and acceptance criteria are not readily available. Further research in this field is recommended. - The impact of the recycled fine materials on durability and strength of concrete is not sufficiently documented. Further research in this field is recommended. - A relevant test method for determination of the strength of the fine recycled aggregates is not available. - A reliable test method for determination of residual alkali reactivity of the fine recycled aggregates is not available. - Use of recycled fine aggregates has been reported to lead to production problems, e.g. in the control of free water and in the flow of materials during production. It is recommended to consider the use of recycled fine aggregates in the fraction 2 - 4 mm by change of definition of coarse aggregates.

7. CLASSIFICATION Recycled coarse aggregates are classified into three categories, i.e.: - Type I aggregates which are implicitly understood to originate primarily from masonry

rubble. - Type I1 aggregates which are implicitly understood to originate primarily from concrete

rubble.

III aggregates which are implicitly understood to consist of a blend of recycled aggregates and natural aggregates. This classification of the materials is based on the mandatory requirements stated in table - Type

1.

For the production of these 3 types of aggregates the following additional rules apply: The composition of type 111 aggregates shall meet the following requirements; Min. content of natural aggregates ( m h ) : 80% Max.content of aggregates type I ( m h ) : 10%.

In table 2 is given a list of material properties for which requirements may be specified. Such requirements are not mandatory unless specified in national documents or CEN standards.

826

7.1 Classification of aggregates The reason for introduction of a class of aggregates as defined in type I11 is that the application of traditional construction rules and design values can be accepted as indicated in table 3. Table 1 Classification of recycled coarse aggregates for concrete (RCAC) RCAC Type I

RCAC Type 11

RCAC Type 111

Test Method

1800

2200

2500

ASTM C123

20

10

3

IS0 6783

10

10

ASTM C123

10

1

1

ASTM C123

1

0.5

0.5

ASTM C123

5

1

1

Visual

Max. Content of Metals (46 d m l

1

1

1

Visual

Max. Content of Organic Materials (9% d m )

1

0.5

0.5

NEN 5933

Max. Content of Filler (< 0.063 nun) ('% d m )

3

2

2

prEN 933-1

5**

5**

5**

prEN 933-1

M~datofy Requirements Min. SSD Density* (kglm3) ~

Max. Water Absomtion

(46 d m ) Max. Content of Material with SSD < 2200kglm3

(46 d r n ) Max. Content of Material with

SSD < 1800kg/m3 f % m/m) ~~~

~

~

Max. Content of Material with SSD < 1OOOkgld (% d m )

Max. Content of Foreign Materials (metals, glass, bitumen, soft material, ...) (96 d m )

Max. Content of Sand ( < 4 mm) (96 d m ) Max. Content of Sulphate

1

(96 din)*** ~

Max. Content of PAC @pm)

50

1

1

BS 812, Part 118

______~

~

50

50

Dutch Building Materials Order

*) **)

***)

Water Saturated Surface Dry condition If the maximal allowable content of sand is exceeded this part of the aggregates shall be considered together with the total sand fraction Water soluble sulphate content calculated as SO,.

827 Table 2 Properties of recycled materials which have to comply with the requirements of national or implemented CEN documents Static Strength Grading Form Index Abrasion Value ~~

Chloride Content

Iron and Vanadium Content for Clean Concrete Applications Pop out Potential (Ca, Fe content) Content of swelling Clav ~

~~

Frost Resistance (if different from requirements in table 3) Leaching and Radiation The recycled aggregates must not contain any material or any other substances which retard the setting of the concrete by more than 15% compared to the setting time of the identical composition with traditional aggregates or which are detrimental or harmful to the concrete. The indicated test methods are introduced to exemplify the type of testing which is suggested. These methods may be applied until relevant CEN standards are implemented. However, the use of the specific standards is not considered to be mandatory. Existing national standards may be used if applicable.

828

8. FIELD OF APPLICATION Recycled coarse aggregates, complying with the specifications mentioned in paragraph 1, can be used in plain and reinforced concrete under the provision that the restrictions mentioned in table 3 are satisfied. If additional testing is required in accordance with table 3 the specifications given in table 4 shall comply. Table 3 Provisions for the use of recvcled concrete Recycled aggregates

RCAC Type I

Max. Allowable Strength Classes Required additional testing when used in the exposure class 1”

RCAC

RCAC

IJ

Type m

C 16/20”

C50l60

No limit

None

None

None

Type

Mortar bar expansion test. Use in class 4a not allowed

*

Mortar bar expansion test

*

Mortar bar expansion test

Required additional testing when used in the exposure class 2b and 4b

Usein class 2b and 4b not allowed

*

Mortarbar expansion test Bulk frost thaw test

*

Mortar bar expansion test Bulk frost thaw test

Required additional testing when used in the exposure class 3

Use in class 3 not allowed

*

Mortar bar expansion test Bulk frost thaw test Deicing salt test

*

Required additional testing when used in the exposure class 2a and 4a

*

*

* *

*

*

*

Mortar bar expansion test Bulk frost thaw test Deicing salt test

1) However, the strength class may be increased to C30J37 conditioned the density of the recycled aggregates exceeds 2,000 kg/m3. 2) Conforming with ENV 206.

829

Table 4 Specifications and compliance criteria for the additional testing

Test procedure

Criteria

Mortar Bar Expansion Test

50°C Sodium hydroxide, 20 weeks ....

Max. expansion < lOlW

Bulk Freeze Thaw Test

ASTM C666

Durability factor > 80%

Deicing Salts Test

SS 137244

Max. Weight Loss < 500 g/m2

For concrete with recycled aggregates used in the exposure classes 2, 3 and 4 attention should be paid to the durability aspects of reinforced concrete as the speed of carbonation and chloride ingression may be larger than in conventional concretes. If these properties are relevant, more accurate values for the concrete to be used should be determined.

9. DESIGN VALUES For concrete with recycled aggregates the same design and application rule principles apply as those stated in prENV 1992-1-1 for conventional concrete. Due account must, however, be taken of the possible influence of density of the aggregates on the strength and deformation characteristics of the concrete. In the absence of more accurate experimental data, a worst case estimate of these material characteristics, can be obtained by multiplying the values stated in prENV 19921-1 by the coefficient given in the following table 5. Table 5 Factors for the evaluation of the material properties of recycled concrete.

RCAC Type 1

RCAC TYPen

RCAC TYPm

Tensile strength (f,d

0.85

1

1

Modulus of Elasticity (E,,,,)

0.65

0.8

1

Creep coefficient (0(m ,to))

1

1

1

Shrinkage ( E J

2

1.5

1

Where accurate data are needed, e.g. where deflections are of great importance, tests should be carried out.

830

For design of a structure more parameters may be of importance than the ones given in table 5. It is recommended to use procedures for light weight aggregates in such cases (Eurocode 2). 10. EVALUATION OF THE PRESENT SITUATION

Technically the prospects are good and yet there are a lot of bottle necks in the market. * Users hold the opinion that the quality demands with regard to pollution are not met. * There are extra costs, such as extra quality controls, extra storage, adaptation of the production process or the concrete composition. * The costs of transport are unfavourable because crushing plants are usually not situated on the waterfront. * On balance the material is sometimes more expensive than gravel. * People are prejudiced: it is waste material and it may not be environmentally sound. * The producers of granulates are careful with investments required to improve sale on the concrete market. There are also opportunities:

* The government policy is increasingly aimed at sending building and demolition waste

*

* * * *

to processing installations. Dump sites and agricultural application in the ballasting of private grounds fade into the background. The production costs of granulates for road construction and for concrete are getting closer together; in both cases the material has to be clean, which can for example be achieved by washing. The authorities stimulate contacts between suppliers and users of granulates and in some cases even impose the use of granulates. The establishment of regional consultants may help to remove all sorts of reservations. The issuing of quality declarations will also support this development. The authorities try to make things clear by drawing up environmental demands. When these are univocal they may stimulate the acceptance of re-use of waste. These demands are based on specifications for leaching and radon exhalation and will be available in a final draft within one year.

For reasons mentioned above a certification system is developed which is yet in an operational phase.

83 1 11. THE ORGANIZATION OF CERTIFICATION IN THE NETHERLANDS

The total process can be divided into separate constituent processes. There is a quality control and assurance (quality system) for each constituent process. By definition, any party carrying out a constituent process has a quality system. The delegation of constituent processes can only be controlled after three questions have been answered. 1. If the secondary process consists of supplying a product, is it clear which characteristics the product has to possess and which requirements have to be satisfied with regard to supplies?

2. If the constituent process consists of performing work, is it clear which quality requirements the work has to satisfy? 3.

If the party who is delegated to carry out the constituent process capable of maintaining proper control over it.

Therefore, the essential points in quality management are: Product specifications 2. Process specifications 3. Quality-system specifications 1.

Certification affects these essential points. In quality control, which is an important part of quality management, it is important to check products against product specifications and processes against process specifications. The certification of products and processes takes care of this. What is certification? Certification involves having an independent third party in addition to the first party (the supplier) and the second party (the customer). The third party declares that the product or service supplied may be considered to meet the specifications. One of the advantages of certification is that there is no need for a new second party to carry out a check on the first party every time. The control can be carried out much more efficiently by one party, provided that party can be relied on to do the job properly. Quality systems can also be certificated, as well as products and processes. In certification, there is symbiosis between the first party (the supplier) and the third party (the certifier). The symbiosis is laid down in the certification system: this is a sort of quality system for which the third party is responsible. So, certification adds another essential point to the three essential points of quality management already mentioned.

832 12. CERTIFICATION SYSTEM SPECIFICATIONS

In the Dutch situation, the certification bodies are accredited by the Council for Certification (Raad voor de Certificatie) and the certification scheme for which they are accredited is laid down. This covers the product certification, the attestation, the process certification and, of course, the quality-system certification. The basis for certification issuing certificates for each product or group of products is laid down in a document which is usually referred to as the assessment guidelines. This states that the manufacturer’s method of production and the control of the production process must be arranged so that the products produced by that process meet the requirements. It also states how and how often the certification body has to inspect the production-process controls carried out by the manufacturer and the products produced by that process. It is important that these principles for product certification but also those for qualitysystem certification are aligned, that is to say, that the bodies that work in the same field also employ the same assessment principles. It is also important that the intrinsic technical aspects as well as the quality-assurance aspects are properly named at the right level. This applies to statutory requirements and also the requirements agreed on according to private law. A lot has been done over the past few years to incorporate paragraphs on the environment and working conditions into these assessment guidelines.

The assessment guidelines clearly state the difference between statutory requirements and the requirements agreed on privately in society in general. This action will make it possible for the conversion in Europe to take place imperceptibly in the future. 13. CERTIFICATION OF GRANULATES, MADE OF CONSTRUCTION AND BUILDING WASTE

The basis for the certification of granulates is an assessment guideline. This document is developed as a follow up of some years of experience with internal requirements for quality systems for the producers of granulates. In the assessment guideline all relevant specifications are given with regard to: - acceptance of rough building and demolition waste; -

upgrading of this material;

- properties of the granulates produced after upgrading; - the quality system of the producer.

For an integral quality system guidelines will be made for selective and environmental friendly demolition being the step before the acceptance of the waste which is of great importance for the final quality of the granulates.

833 The assessment guideline deals with the application of granulates: for subbases as unbound material in road constructions as aggregates for asphalt as aggregates in lean concrete or cement of bitumen stabilized subbase layers. b. in concrete as aggregates c. in hydraulic works as unbound material. a.

Furthermore, the assessment guideline deals with different qualities of aggregates: - masonry granulates; - concrete granulates; - mixed granulates consisting of a mix of masonry and concrete granulates; - hydraulic granulates consisting of mixed granulates and hydraulic slags; - asphalt granulates. The following scheme supplies a summary of the standards used as a base for the assessment guideline. description

standard

acceptance criteria type and origin of waste control and assurance of upgrading proces of the waste (sieving, handpicking, crushing, magnetic separation, other separation techniques such as washing, windsifting etc.

remarks including how to handle if criteria are not met

EN 29002

granulates for road constructions

National RAW Standard 1990

granulates for concrete

NEN 5905

granulates for hydraulic constructions

no specifications available

specifications are agreed upon between producer and client

A testing scheme is made in which the frequencies are laid down of sampling during production.

834 For road constructions this scheme deals with: size distribution composition content of plain particles crushing value durability for frost and moisture density CBR (only unbound application) - organic components.

-

-

For concrete constructions this scheme deals with: size distribution particle density content of concrete particles content of non stony materials dust content crushing value content of plan particles chloride content sulphate content alkali-silica reactive components content of organic substances content of weak components

14. CONCLUSIONS Certification of granulates made of building and construction waste is a very important step forwards for the reuse of these materials. The assessment guideline in the Netherlands consists all relevant technical properties and will be completed with environmental properties within one year.

Environmental Aspects of Constnrction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and l71.G.Aalbers (Editors) 01994 Elsevier Science B.V. AN rights resewed.

835

Sampling and sub sampling of primary and secondary building materials: a statistical treatise A.M.H van der Veen, D.A.G. Nater Materialenbank Nederland MBN, P.O.Box 15 1 , 6470 ED Eygelshoven, the Netherlands Abstract The statistics of sampling and sub sampling of primary and secondary building materials are reviewed. A Monte Carlo model is described, which is capable of describing the sub sampling process of granular materials at a particle level. The model is demonstrated for the socalled cross-riffling process and for distribution heterogeneity. It is concluded from the computational results as well from experiments, that the model is capable of describing the statistics of a sub sampling process. However, the model should be extended in order to study the influence of the distribution of the critical parameter(s) over the sub samples. 1. Introduction

In order to do experiments, reliable starting materials are required. The processes of sample taking and sample preparation from primary and secondary building materials are far from simple. Many steps are involved, and each of them steps may be of influence on the properties of the material. The property of interest, usually called the critical property, should be maintained during the process as good as feasible. When preparing a sample, the only objective is to reduce the amount and the particle size of material in such a way, that a portion suitable for the experiment remains. Under strict controlled conditions, it is possible to do both maintain the property of interest and to make the material suitable for the experiment. In a previous paper [I], an outline over standardised sample preparation and use of reference materials has been given. In this paper, emphasis will be put on the statistical aspects of sample taking and sample preparation. Special attention is being paid to the heterogeneity concept, which is of great importance when sampling construction materials.

2. Sub sampling

When sampling a material, it should be considered that any practical sampling process is to be treated as sampling from a finite population. This observation is very important, since it has great practical implications. After a sample is taken from the population, the properties of the population may have changed. If sampling takes place under strictly controlled conditions, it is possible to minimise this effect, but it may never be excluded that the sampling process itself changes the properties of the population. The effects become stronger as the ratio between the sample mass and the population mass increases. Thus, for sub sampling, the observation of a finite population becomes even more important. If a sub

836 sampling fails, than both the sub sample and the remainder of the original sample become useless. In a sub sampling process, the orders of magnitude of the sub samples and the population (the sample before subdividing) are comparable. Usually ratios between 1:2 and 1:20 are observed. For the preparation of reference materials, it is even more important that the properties of the sub samples are as equal as possible. Although the material being subdivided may be very heterogeneous with respect to its constitution, the objective of a subdividing process is always to distribute the properties of the material equally over the sub samples. If this attempt succeeds, then it is said that the sub samples are homogeneous The distribution heterogeneity (DH), which only exists if there is also constitution heterogeneity (CH) [ 2 ] should be minimised in the sub sampling process. If a bulk material is to be sampled, it is usually desirable to have a sample that amounts a few 100 kg, depending on the sampling conditions. If, for instance, a depot is sampled that contains about 100 tonnes of fly-ash, it is no use to take only a few kilograms of material. A sample of 100 kg for instance allows to design a sampling process that is suitable to the purpose. In practice, a severe problem is how to prepare samples of good quality from such an amount. Any treatment by hand will not meet the quality requirements stated in the introduction. For this type of operations, specially designed large-scale equipment can be used [I]. However, the accuracy of this type of equipment is lower than that of a laboratory riffler. Experiments have shown, that weight differences in the 10 sub samples from the large scale riffler of about 10% may be observed. The differences in particle size distribution, as well as the properties of the sub samples are far less fortunately. The sample size and the particle size distribution may indicate whether a sub sampling step may be successfbl or not. These indicators are not sufficient however when preparing materials for a special purpose. Then the critical parameter should be investigated. In order to guarantee that the samples are homogeneous after sub dividing the 10 sub samples (of 10 kg on average in the example), a special procedure has been developed. Since the process originates from using spinning rifflers, it has been called cross-rij’jing (X-riffling), and it is carried out as follows. The 10 sub samples (labelled #01..#10 in the scheme on the next page) are riffled each into 10 sub samples. After riffling each of the 10 sub samples, a matrix of 100 samples is constructed. The samples are arranged in such a way, that 1. in each column the samples from one sub sample appears 2. in each row from each of the 10 tubes just one sample appears (indicated by the second pair of digits in the scheme) Finally, 10 new sub samples are created by recombination of each of the rows. The recombined samples are labelled #A..#J. The X-riffling process is very efficient with respect to reducing the random error. The Monte Carlo model, to be introduced shortly, has been used to investigate the statistics of this process. The reason for recombining samples from different tubes from the riffler is quite obvious: if samples were taken from one tube (the samples #01.05, #02.05, ,,,,#10.05 for instance), propagation of a systematic error in the riffler is possible.

837

u

u

u

u

u

u

u

u

u

u

3. Segregation

Segregation is the greatest potential risk in the sub sampling process. Segregation is favoured by two factors: 1. a particle size distribution 2 differences in density Segregation due to the particle size distribution is only possible as long as the particles move. The process favoured by density differences is a slow process, but it can proceed even if the material is in rest. There are two ways to circumvent the problem of segregation while sub sampling, in fact mixing or sub sampling with a technique that is not sensitive to differences in constitution or particle size. Mixing will solve only a part of the problems, since any method of sub dividing will allow the particles to move, and thus favouring segregation of the first type. It can be proved that using a vibrating feeder will certainly cause this type of segregation to occur. The Monte Carlo model is also used to investigate the influence of gradually changing properties when subdividing.

4. Monte Carlo model

In order to enable a thorough study on various aspects of the sampling and sub sampling of granular materials, a Monte Carlo model is developed [ 3 ] . The model was intended to be a tool for validation of the cross-riffling procedure, as implemented at MBN for several years. The model was tested first on coals [4], and after that the applicability was tested for other materials. The results of the first computational experiments are that promising, that a fbrther development of the Monte Carlo model is planned. The model developed so far is based on the riffler mechanism. A riffler consists of a head, which turns around an axis. This head allows the material being fed by a continuous feeder to pass one tube at a time. If the rotational velocity of the riffler head and the feeding rate are constant, then it may be expected that all sub samples have about the same properties

838

Inpul

1

N. a v e r a g e . slaridard devlitllon L,Se Po,sso,,,B,no Cpne,.n,o,.s

,,,,",

.~~ -

DrLrrrnine # c1ustcrs

~ i i u s s r a n ene erst or

{_-# _par11cies i z z J &J& ;: D e te 1.111 I" e # "red"

8"' """s'

Omeralor

I

Oulpul

~ i ~ , 1, ,..Algorithm ~ of the Monte

Model

carlo

If the particles stick together, it still must be expected that the average volume of the through-put is constant. The distribution of the average number of particles differs however. Depending on the strength of the clusters, these clusters can be treated as if they were single particles, just of a larger radius. The cluster size will not be distributed normally. Especially at low average cluster sizes, it must be expected that the distribution function of this size will not be symmetrical. The Poisson distribution seems to be suitable for modelling this feature.

Heterogeneity is probably the most complex property to describe. A true quantitative approach would require the knowledge how the various components are distributed over the particles. The theory of Gy [2] provides us with a general treatment on heterogeneity, but this theory is not readily applicable in calculations. In the Monte Carlo model, a method has been sought for, which allows the simulate heterogeneity, without demanding for a true quantitative description. So far, only distribution heterogeneity has been taken into account. The implementation of the distribution heterogeneity (DH) is quite straight forward. DH can simply be regarded as having particles of two types (e.g. red and white particles). In statistics, normally experiments with two possible outcomes are described by means of the binomial distribution. In the MC model the binomial distribution is used in the final step to fix the number of particles of one kind (the number of particles of the other type is fixed then automatically). Figure 1 summarises the algorithm. 5. X-riflling

The first task for the Monte Carlo model was to evaluate the statistics of the X-riffling procedure. From round robin tests, it was known that the process yielded sufficiently homogeneous sub samples. However, one of the questions still remaining was how many times the

839 scheme should be applied before a sufficiently homogeneous batch of samples was prepared. The results of the simulations are shown in figure 2. The figure clearly shows that the standard deviation of the samples is effectively reduced to a level specific for the equipment. The variations after the first cycle are due to the fact, that a stochastic process is being investigated. The various values of n in the figure (where n is the average number of particles falling through a tube per cycle) can be translated to different angular velocities

X-riffling performance at various feeder speeds

10,000 1,000

The larger the value Of n, the greater is the angular velocity. A simulation where the initial standard deviation was lower than that of the riffler yielded exactly the same result as in figure 2. The standard deviation of the samples after the first cycle was equal within the precision of the simulations 6. Blending and heterogeneity

Both blending and distribution heterogeneity can be described accurately by using the binomial distribution. The greater the similarities between the particles in the blend, the better the description will be. I f a material is sampled which can be regarded as a blend (like metal particles in soil, or a mixture of sand and clay in a soil sample), the Monte Carlo simulation f d l y applies. DH increases when the probability to obtain a particle from one part of the sample decreases. Figure 2 shows the results of the MC calculation, where the total number of particles is 100000, the average is 100, the riffler standard

840

deviation is 10, and the number of sub samples is also 10. At the y-axis, the standard deviation divided by the 'binomial' probability is plotted. This correction is made to correct for the number of particles involved for which the probability applies. Two important observations have been made when testing the modelling of DH. First of all, the riffler mechanism allows to treat materials with gradually changing properties. This observation is very important, since it implicates that segregation will not be of influence on the riffling process. Secondly, when the total number of particles is increased, the relative standard deviation decreases. Depending on the requirements of the samples, the minimum sample size can be determined. It is a clear demonstration of a well-known fact, that an insufficient amount of material will not result in sensible analytical data.

7. Discussion and conclusions

The Monte Carlo model under development provides a flexible basis for sampling and sub sampling modelling. Depending on the assumptions made when sub sampling, the algorithm can be modified to be applicable for other equipment. One of the main issues is how to translate the results from the Monte Carlo model to the real world. One of the features to be implemented is to study how the value of the critical parameter is affected by (1) the distribution of this parameter in the material, (2) the distribution heterogeneity, and (3) blending. The approach of the model becomes somewhat different when implementing these features, since the 'analysis' of the sub samples has to take place also by the Monte Carlo principle. On the other hand however, the model comes closer to the real world, and thus the quality of the predictions will become better. Parallel to the development of the model, the knowledge of how certain sources of errors are translated into the final results on analysis will help to improve the quality of environmental measurements. The model is at this stage already a valuable tool in design, development and validation of sampling and sub sampling strategies. Additional refinements of the model in this direction will certainly be beneficial to our knowledge on how to sample in environmental studies.

8. Literature

1 . F.J.M. Lamers, G.J de Groot, "Standard sample preparation and reference samples as a

tool for determination of the environmental quality of building materials", Waste Materials in Construction, Proceedings of the WASCON Conference 1991, Elsevier, Amsterdam 1991, pp 375-378. 2. P.M. Gy, "Sampling of particulate materials", Elsevier, Amsterdam 1982. 3 . A.M.H. van der Veen, "Computer simulations of subsampling with use of spinning rifflers", final report, SBN/MBN Eygelshoven, the Netherlands 4. A.M.H. van der Veen, D.A.G. Nater, "Sample preparation from bulk materials: an overview", Proc. Third Rolduc Smyposium on Coal Science, Elsevier, Amsterdam pp 1-7

Environmental Aspects of Construction with Waste Materials J.J.J.M. Goumans, H A . van der Sloot and Th.G.AaIbers (Editors) Q1994 Elsevier Science B.E All rights resewed.

84 1

Industrial scale application of the alkali activated slag cementitious materials in the injection sealing works Brylicki Witold, Malolepszy Jan and Stryczek Stanislaw University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, POLAND

Abstract As it results from many years observations and studies, the alkali activated vitreous calcium and magnesium aluminosilicates give cementitious materials of very good properties. These materials can be produced for special purposes, e.g. for the cementing and sealing works by injection method. Their parameters, such as setting time, shrinkage and rheology can be controlled in a wide range depending on the activators and mineral admixtures used. The alkali activated slag pastes show many advantageous properties: they interact well with the rocks surrounding a bore hole, they are resistant to chemical corrosion and filtration. They can immobilize heavy metals and other detrimental substances. The low cost of the slag cementitious materials should be also of importance. The properties of the alkali activated slag pastes will be presented together with the examples of their application on a large scale in hydrotechnics drilling, sulphur mining and as a stabilizer of subsoil under the industrial and hydraulic structures. 1. INTRODUCTION

The effluent of drilling fluid in the zone of absorptive rocks is one of the serious technical difficulties in drilling. The effective methods of the absorptive area separation consist in the utilization of proper sealing agents. The sealing of the rock mass is of significate importance not only in drilling but also in geotechnology and hydraulic engineering. The pastes can be classified into 3 groups [ 1-31: - mineral suspensions, - organic and inorganic gelation agents, - organic emulsions and dispersing media. The following parameters must be taken into account when the sealing substance, particularly the cementing component, is selected: - the mineral and petrographic composition of the rock mass,

842

- the tectonic of walls, - the strength parameters of rocks,

- the absorbing capacity of surrounding rocks, - the occurrence of deposit wastes and chemical composition of wastes. The traditional sealing (walling) of injects are produced from the ordinary or metallurgical portland cements. The clay-cements pastes can be also used. The most important features of these pastes are: - possibility to control their fluidity, - setting and strength. The good adhesion to the surrounding rocks, compactness, low shrinkage and high corrosion resistance are required also. In many cases the portland and metallurgical cement pastes can meet the above requirements. As it results from our studies the better effect can be archived when the alkali activated slag materials are used as injection pastes [4, 51. The properties of the alkali activated slag pastes can be controlled in a very wide range [5, 61. First of all they exhibit very high corrosion resistance and low porosity [7]. The prevailing pores are the gel ones of diameters less than 2 nm. The alkali activated slag pastes show also a very good adhesion to the rock mass. Therefore these materials can be successfully used in the formation of the cut off walls. The effect of the alkali activated slag pastes on the industrial scale application, in different conditions, will be presented in the next part. 2. THE INDUSTRIAL MATERIALS USED IN THE ALKALI ACTIVATED SLAG PRODUCTION The granulated blast furnace slag of the specific surface 3500 cm2/g(Blaine) has been used on the industrial scale. The chemical composition of slag is given in table 1, Table 1 Chemical composition of slag Component

Percentage wt [ %]

CaO SOz

41.1 38.1 9.6 8.4 0.4 1.1 1.2 0.1

A1203

MgO Fez03

so3

+

Na,O K,O residuum

843

The OPC has been used as a mineral admixture; the sodium carbonate and water glass or their mixture - as activators. The Na,O content calculated in relation to the slag binder was 5%.

2.1. Some applications of the alkali activated slag pastes on the industrial scale The antifiltration cut off wall at the Wisla river dam is an example of the alkali activated slag paste utilization in geotechnology [9]. This cut off wall has been formed on the depth 60 m, in the rock mass consisting of the metamorphized shales, sandstones sand and gravel. The conditions in the rock mass were difficult: the proportions between the components varied and in some places the underground water invasion appeared. Therefore the high and variable absorbing capacity towards the injection media, in which the different proportions of activators and water to Solid ratio from 2.5 to 0.45 have been assumed. The properties of the alkali activated slag paste injections are given in table 2.

Table 2 The properties of the slag injection Parameter Sample No

WIS

Density [kglm']

Fluidity test [mml

Viscosity, test Ford [s]

1

2.5

1279

260

10.8

2

1.85

1356

260

10.8

3

1.47

1413

270

11.9 ~~

~~~~

4

1.14

1492

260

12.3

5

0.75

1646

260

12.5

6

0.48

1838

190

28

7

0.58

1753

240

18.5

8

0.57

1761

220

25.5

9

0.45

1872

200

33.7

The sealing works under the reinforced concrete pillars supporting the overbridge are the other example of the alkali activated slag paste injections. The pillars were embedded into the ground on the bottom of the river, consisting of the gravel, sand and clayey sludge. After a time, the dangerous falling down of the construction could be noticed. The sealing of the rock mass to the depth 12 m using the OPC paste failed because of the high absorptivity of the surrounding rock towards this medium and, in some places, the paste out flow on the surface ("volcanos"). The alkali activated slag paste applied subsequently produced a concrete plate under the pillar, as a result of quick setting and hardening of the paste with gravel and

844

sand filler. The paste thus used revealated high fluidity and rapid hardening. The exploition of sulphur in Poland is carried out by a hole method [Fig. 13.

10 /---

1. Water filter, 2. Technological column, 3. Superheated water (115.5"C),4. Melted sulphur from raw, 5. Floor, 6. Main filter, 7. Column of pipes, 8. "Air" lift, 9. Column of facing pipes, 1O.Top of layer (sand, clay, gravel).

Figure 1. Scheme of hole exploition conditions. Because of difficult geological conditions, the cementing works are strongly disturbed [ 101. The OPC pastes used earlier in the lining pipes columns cementing did not form any stable joint with the clayey rocks covering the walls of the holes. The cement seals between the lining pipes columns and the walls of holes undergo a deformation under the influence of the past-exploition settlement of the rock mass. This process results in the shearing and break of exploition pipes. Subsequently, the outflow of deposit water can take place. The consequences are very serious: the pollution of natural environment by sulphur compounds and hydrogen sulfide on one side and economical losses on the other side. The hydrothermal conditions in the rock mass and in the holes favorite the alkali activated slag setting and hardening [7]. These slag pastes have been successfully used in the cementing works during the petroleum and gas deep exploratory drilling. The particular compositions of pastes are worked out every time depending on the depth of cementation, technical and geological conditions of the bore hole and underground water mineralization. The alkali activated slag pastes are used in the cementing works on the depth up to 2000 m

845

in extremely difficult conditions, to prevent the outflow of drilling fluid and in preliminary cementation of fissured rocks as a drilling fluid [ 111. The alkali activated slag paste has been used at the outflow of drilling fluid on the depth 1716-1796 m during the exploratory drilling on the hole Wysoka 3. The rock mass was so full of cavities, as the drilling could not be continued without preventing the drilling fluid outflow. The earlier attempts with OPC-clay, OPC-gypsum, bentonite, oil-bentonite pastes failed. Only when the alkali activated slag paste was used, the absorptive zone became sealed.

2.2 The characteristics of cares from control bore holes The cores from the control bore holes were examinated. The macroscopic evaluation and microstructure observations were carried out. One can notice the good adhesion between the paste and rock mass (Fig. 2,3). The SEM-EDAX studies and porosity measurements prove that the paste meets the requirements for the injection sealing medium. A substantial amount of the compact gellike material, consisting mainly of C-S-H phase (Fig.3,4,5). In the presence of clayey minerals in the rock mass, the sodium and calcium zeolites are formed (Fig.6,7). The microporosity measurements show the occurrence of gel pores of diameters less than 2 nm, without capillary pores ( > 100 nm) practically.

Figure 2. Sandstone cemented with slag - alkaline binder (bore hole W-6,depth 41.5 m -left; bore hole W-7, depth 39 m - right).

846

Figure 3. Sandstone cemented with slag - alkaline binder (bore hole W-9, depth 48 m)

Figure 4. EDAX diffractogram of paste.

847

Figure 5. SEM. The microstructure of pastes. Visible C-S-H phase.

Figure 6. SEM. The microstructure of pastes after 2 months curing in bore hole. Visible sodium zeolites. ~5000.

848

Figure 7. SEM. The microstructure of pastes after 2 months curing in bore hole. Visible calcium and sodium zeolites.

3. CONCLUSIONS Some years lasting industrial practice and experience indicate that the alkali activated slag pastes can be successfully used in sealing works and cut-off walls formation (Fig.9,12). The properties of pastes particularly the setting and fluidity can be controlled in a wide range. Their hydration products are highly corrosion resistant. For this reason they can be applied in the cementing works to stop the eruption of hydrogen sulfide. The OPC pastes cannot be used for this purpose. One should underline the good adhesion between the paste and different rocks. The slag pastes react with the clayey substance forming the zeolites mentioned above and hydrogarnets. The zeolites give the possibility to immobilize the heavy metals by the hydrated slag matrix [ 131. The alkali activated slag pastes can be applied, with good results, to stop the overflow of drilling liquid, as it was been confirmed in industrial practice [ll]. This fact is important from the environmental point of view. Because the works described above are the human interference to the environment, they must be effective. It means that the best material should be used for cementing works. Alkali activated slag pastes guarantee the high effectiveness of cementation.

849

4. REFERENCES 1 2

3 4 5 6 7 8

9

10

11 12

13

J. Bernsted, World Cement, 2 (1987). W.G. bielikov, A.T. Bulatov, R.F. Uhanov, Promyvka priburienii i kreplenii i cemientirowaniju, Moskva 1974. S. Stryczek, Criteria of selection technical parameters of the monoportland cement pastes for the sealing of absorptive zones in the rock mass through bore-holes, Wiertmictwo, Nafta, Gaz, Krakbw, 12 1993 (in polish). W. Brylicki, J. Malolepszy, S. Stryczek, 9th I.C.C.C., New Dehli, VoI.111, (1992) 312. Polish patent NO285 071, Paste for bore holes sealing and cut off walls construction. W.D. Gluchovski, Gruntosilikatni virobi i konstrukcji, Budivitnik, Kiev, 1967. J. Malolepszy , Hydration and properties of alkali activated slag cementitious materials, Zeszyty Naukowe AGH, Ceramika, 53, 1989 (in polish). J. Deja, J. Malolepszy, 3rd Int. Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Trondheim, Vol.11, (1989) 1547. J. Dziewahski, W. Brylicki, A. Gonet, S. Stryczek, Z. Olszamowski, Utilization of alkali Activated Slag Cement For Antifiltration Screens in Hydrotechnics, Proc. 4th Int. Symp. On the Reclamation Treatment And Utilization Of Coal Mining Wastes, Krakbw, Vol.11 1993, 41 (in polish). A. Gonet, S. Stryczek, W. Brylicki, J. Malolepszy, Liquidation blow out deposit water for example the Mine of Sulphur "Jeziorko", Proc. Int. Conf., Krakow, 1992, 41 (in polish). S. Stryczek, W. Brylicki , J. Balasz, J. Sztorc, Practical aspects of the utilization of new, alkali activated slag materials assailing agent in drilling operations, Oil Industry Prospect - Year 2000, Tripoli, Libya, 1992, 590. W. Brylicki, S. Stryczek, J. Malolepszy, Properties And Use of alkali activated Slag Paste, Proc. 4th Int. Symp. On the Reclamation Treatment And Utilization Of Cool Mining Wastes, Krakbw, Vol.11, 1993, 925. D. Breck, Zeolites Molecular Sieves, New York (1974)

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SIoot and Th.G. Aalbers (Editors) 91W4 Elsevier Science B. V. All rights reserved.

85 1

THE USE OF MSWl BOlTOM ASH IN ASPHALT CONCRETE. M.M.Th. Eymael', W. de Wijs', D. Mahaded

' Feniks Recyclingmaatschappij B.V., P.O.Box 9265, 1800 GG Alkmaar, The Netherlands * Hoogovens Technical Services E&E, P.O. Box 10.000, 1970 CA idmuiden, The Netherlands ABSTRACT Municipal Solid Waste Incinerator (MSWI) bottom ash has been used by Feniks Recyclingmaatschappij (Feniks) as a mineral aggregate in asphalt concrete for more than five years. Several projects with asphalt concrete containing MSWl bottom ash have been carried out. In the year 1991 Feniks started a research program which included laborato tests and two pilot projects. This research program was guided by a CUR/CROW research committee. The objective was to find out whether it is possible to produce and apply asphalt concrete with MSWl bottom ash that meets the normal requirements for stability and durability. Problems were expected due to the moisture and filler content in the MSWl bottom ash. The pilot projects with asphalt concrete containing MSWl bottom ash provided the opportunity to learn more about the behaviour of this asphalt concrete during production and paving.

Y

1. INTRODUCTION

The annual amount of MSWl bottom ash produced in The Netherlands is about 700,000 tonnes. It is expected that this amount will strongly increase in the next

tonnes. The major part of the MSWl bottom ash will be used in decade to 1,500,000 large scale land fill projects and in road and railway embankments. However, an increasing amount might be used in cement treated base courses and in asphalt concrete if the products containing MSWl bottom ash can meet the requirements for leachate and mechanical properties. In this paper the results of a research program towards the use of MSWl bottom ash in asphalt concrete will be discussed. The research was carried out as a part of a more comprehensive research program "Application of MSWl bottom ash in cement treated base course and in asphalt concrete" which was initiated by Feniks Recyclingmaatschappij (Feniks) in 1990 and was guided by the 657 CUR/CROW committee. history In the early seventies in the USA some reports were published dealing with the application of MSWl bottom ash in bituminous base courses (asphalt concrete). The

'

CUR: Centre for Civil Engineering Research and Codes CROW: Centre for Research and Contract Standardisation in Civil and Traffic Engineering

852

experiences with the asphalt concrete containing MSWl bottom ash were quite good but it never became a standard application due to the availability of cheap new aggregates all over the country. There was also no reason for searching new applications for MSWl bottom ash as it was easy and cheap to bring the MSWl bottom ash to waste disposals. In The Netherlands there was not so much space and the costs of waste disposal were already rising in the early eighties, so it became interesting to search for new applications. Some projects with asphalt containing MSWl bottom ash were carried out in the late eighties [2]. Feniks has been studying the possibilities of using MSWl bottom ash in asphalt concrete extensively since 1988 and carried out laboratory tests and pilot projects. The annual production of asphalt concrete in The Netherlands is about

6,000,000tonnes. To produce these 6,000,000 tonnes about 1,500,000 tonnes of old asphalt is used. So, in The Netherlands new asphalt concrete contains on the average about 25 % of recycled material and this percentage will increase in the next decade to a practical maximum of about 35 %. It is not dutch policy to exchange the old asphalt in new asphalt concrete by MSWl bottom ash, but Feniks believes that there might be a role for MSWl bottom ash. 2. RESEARCH PROGRAM

obiectives The main objective of the research program was to find out whether it is possible to use MSWl bottom ash as a mineral aggregate in asphalt concrete for base and binder courses. The aim is to add as much MSWl bottom ash to the asphalt concrete as is theoretically and practically possible. The research program consisted of: - literature research; - environmental research to determine the chemical composition and the leachate of MSWl bottom ash and asphalt concrete containing MSWl bottom ash; - laboratory tests to determine the mechanical properties of MSWl bottom ash and asphalt concrete containing MSWl bottom ash; - pilot projects with asphalt containing MSWl bottom ash. This paper deals with the results of the research program and the experience with the pilot projects. Presented is also a technology to improve the environmental properties of the MSWl bottom ash by processing it. With this technology the MSWl bottom ash can be treated and will become a kind of mineral aggregate that can be used in asphalt concrete. pilot DrOf all Pilot projects with asphalt concrete containing MSWl bottom ash, two will be discussed as the results were used in the research program. The first pilot project was carried out in Enkhuizen (1991) and the second in Rotterdam (1993).

853

In Enkhuizen a parking area of 3500 m2 for trucks has been paved by order of a private company. In the asphalt concrete for the base course 50 % (by weight) of the mineral aggregate has been substituted by MSWl bottom ash. On this base course a surface course of normal dense asphalt concrete was applied. In Rotterdam an area of 5000 rn2 for handling contaminated soil was constructed using a pavement consisting of two layers of asphalt concrete containing 25 % (by weight) of MSWl bottom ash: 70 mm asphalt concrete base course and 50 mm asphalt concrete wearing course. In both pilot projects the asphalt layers were put on a base course of cement treated MSWI bottom ash.

3. PROPERTIES OF MSWl BOlTOM ASH general MSWI bottom ash is the solid residual result of the incineration of domestic waste and similar light industrial waste, without fly ash. MSWI bottom ash should meet standard requirements in The Netherlands. When the MSWI residue leaves the incinerator and has been cooled down, it is sieved on a 40 mm sieve and deironed. After this treatment the MSWl bottom ash is stored for a period of at least 6 weeks before it may be used in landfill or other applications. During this storage period several chemical and microbiological processes take place resulting in an increase of the environmental properties of the MSWl bottom ash. MSWl bottom ash is a continuously graded mixture containing filler, sand and gravel. The biggest particles are about 20 mm and about 8 % is smaller than 0.063 mm (filler). The filler can absorb a relatively high amount of asphalt binder and the sand-fraction is relatively coarse.

The unit weight of MSWl bottom ash is lower than the unit weight of conventional mineral aggregate, due to the properties of the particles and the porosity of the coarse aggregate. This has to be taken into account on designing a recipe for asphalt concrete containing MSWl bottom ash. Theoretically, an asphalt mix design is based on a volumetric composition using the particle size distribution of the mineral components. However, usually asphalt mixes are designed by weight composition of the mineral components. This does not give problems when homogeneous aggregates with a constant and known unit weight are applied. So, on using MSWl bottom ash the specific mass of all components to be used in the asphalt mix must be determined. The standard method to determine the specific mass of mineral aggregate 'Pycnometer test' could not be used for MSWl bottom ash because the porosity of the MSWl bottom ash is very high. Asphalt binder can not penetrate the small voids in the mineral aggregate so the water in the pycnometer is exchanged for oil. The

854 viscosRy of the utilized oil at 25 "C is the same as the viscosity of asphalt binder at 150 "C. Having determined the specific mass by using this method, it is possible to calculate the amount of voids in the aggregate and the amount of voids in the asphalt mix to be designed. In table 1 the specific mass of the components in MSWl bottom ash is listed. Table 1. Specific mass of MSWl bottom ash. Size of aggregate

Density In water [ks/m31

in oil

[ks/m31

Difference in Air Void

[%I

8-40

2321

2334

4-8

2349

2264

3.6

2-4

2302

2167

5.9

63 pm 2 mm

2483

2377

4.3

0-63m

2449

2246

8.3

-

The pycnometer is filled with water or with oil. The viscosity of the utilized oil (at 25 as the Viscosity of bitumen sO/lOO at 150 "C.

"C)is the same

chemical comDosition The average chemical composition of the MSWl bottom ash is given in table 2. Most of the elements are present as an oxide or as a hydroxide. On the other hand, also metal salts, chlorides, sulphates and carbonates are available within the MSWl bottom ash. Iron, aluminium and zinc, but also some other non-ferrous metals may be present as a metallic. The MSWl bottom ash is being formed at a relatively high temperature and thereafter quenched in water. Consequently, the MSWl bottom ash is not stable and during storage several reactions will take place. Due to these reactions the chemical composition of the MSWl bottom ash will change, pH will decrease to 9 -10 and the temperature can rise to 60 - 70 "C. The chemical composition and leachate of six weeks old MSWl bottom ash have to meet requirements to get a certificate. However, also MSWl bottom ash with a certificate may only be applied under certain conditions in landfills or in road and railway embankments. The MSWl bottom as must remain at least 0.50 m above the highest groundwater level and must be covered with an impermeable layer, which must be inspected regularly. Also the environmental quality of the groundwater must be monitored.

855

4. ASPHALT CONCRETE MIX-DESIGN

general The requirements for dutch asphalt concrete are specified in the standard requirements “De Standaard 1990”[3].All standard asphalt concrete mixes contain asphalt binder (bitumen), ground particles of limestone and mineral aggregate. The mineral aggregate consists of fine (sand) and coarse (gravel or stone) aggregate. The standard requirements specify the composition and the mechanical properties such as Marshall stability, Marshall flow and durability. MSWl bottom ash can replace a portion of the filler and the mineral aggregate (sand and stone). The particle size distribution, the density and the void content of the MSWl bottom ash were determined. It appeared by calculating that the amount of MSWI bottom ash in asphalt concrete mixtures can reach a maximum of 65 % by weight. Practically the amount of MSWl bottom ash will be lower than 65 %. The maximum amount has to be estimated during production. Table 2. Marshall properties of asphalt concrete containing MSWl bottom ash.

I

As~haltconcrete for base course 125% MSWl bottom ash)

I

856

laboratoy tests In the laboratory a number of samples asphalt concrete containing up to 65 % MSWl bottom ash was made and the mechanical properties (Marshall) of the samples were determined. Also samples with 50 and 25 % MSWl bottom ash were investigated. The use of MSWl bottom ash in asphalt concrete has a good impact on the Marshall stability while the Marshall flow decreases. So asphalt concrete containing MSWl bottom ash has a high Marshall quotient, which is a parameter for the material's resistance to permanent deformation. The durability of asphalt concrete with MSWl bottom ash is determined with the retained Marshall test. The decrease of the Marshall stability after immersing in water of 60 "C during 48 hours is comparable to conventional asphalt (table 2). The amount of filler in the MSWl bottom ash is about 8 % and exceeds the specific maximum for filler in mineral aggregate. The amount of natural filler from the aggregate in the asphalt concrete is also too high. However, asphalt concrete mixtures with MSWl bottom ash meet most of the dutch requirements for asphalt concrete. The mechanical properties of asphalt concrete containing MSWl bottom ash are as good as the properties of new asphalt concrete. Table 3. Retained Marshall stability of asphalt concrete with 25 % MSWl bottom ash. Asphalt base course Immersing time

Stability

Asphalt wearing course

Retained

Stability

Retained

10,962

N

t=O

9,565

N

t = 24 hours

8,636

N

90 %

10,910

N

99%

t = 48 hours

8,278

N

86%

10,440

N

95%

The Marshall Stability of the asphalt concrete with 25 % MSWl bottom ash is measured at 60°C.

environmental research The leaching behaviour of asphalt containing MSWl bottom ash was investigated by an environmental laboratory. Marshall tablets were tested by the diffusiontest (Standtest NVN 5432). Two mixtures of asphalt concrete containing MSWl bottom ash with different asphalt binder content were tested (asphalt binder content 6.0 % and 6.5 %) and the results were compared with the results of tests on a reference asphalt concrete without MSWl bottom ash. The composition of the tested asphalt concrete mixtures are presented in table 4.

857

Table 4. Composition of the asphalt concrete mixes for environmental tests.

After analyzing the chemical composition of all components the concentrations of elements in asphalt concrete containing MSWl bottom ash were calculated and are summarized in table 5. The contribution of asphalt binder (bitumen), limestone filler, sand and gravel to the metal content in the asphalt concrete is, except for the metal Chromium (Cr), of no significance in relation to the contribution of MSWl bottom ash. Table 5. Environmental properties of asphalt concrete with and without MSWl bottom ash. Element

Na

Concentration Asphalt with bottom ash in m g / h

I

I

284

Bottom ash

Reference 5.5% bit.

I

0.66*103

Bottom ash 6.5% bit.

6.0% bit.

I

4.0*103

I

3.5*103

<1.2

<1.2

<1.2

<0.1

0.1

<0.1

<0.3

<0.3

<0.3

<0.6

1.3

<1.2

4.8

<5.9

<5.9

<1.2

<1.2

<1.2

<1.7

I

<1.2

I

<1.2

The leaching of the asphalt concrete is investigated with the diffusion test. The results of this test can be compared with the existing standards. The leachate is

858

analyzed for nine elements and the results are written in table 5. The leaching of the asphalt concrete with MSWl bottom ash is very good as the concentration of all elements in the leachate is less than the detection limit. The cumulative diffusion of asphalt concrete containing MSWl bottom ash is similar with the diffusion of asphalt concrete without MSWl bottom ash. So, asphalt concrete containing MSWl bottom ash meets the requirements for building materials in The Netherlands [8].

Since 1988 several thousands of tonnes of asphalt concrete containing MSWl bottom ash have been produced and applied in about ten pilot projects. In all pilot projects the asphalt concrete was produced with a batch mixing plant. In the batch mixing plants, that had a normal capacity of 100 to 125 ton per hour, the mineral aggregate is heated and dried in a main drum, stored in hot bins, weighed and mixed with filler and asphalt binder in a mixer. The drum is fed through cold feeders; for each type of mineral aggregate and for the MSWl bottom ash a separate feeder is used. The MSWl bottom ash has to be put in cold feeders with a vibrating device to ensure a continuous input in the drum. All minerals are sieved after drying and heating and then they are stored temporarily in hot bins before they are weighed and put in the mixer. The fine particles, that were collected by the dust collectors, are also stored and have to be added in the mixer. gxoeriences In this paper only the experiences with the pilot projects in Enkhuizen and Rotterdam is discussed. The asphalt concrete for the pilot project in Enkhuizen was produced in The Asphalt Mixing Plant Akersloot and the asphalt concrete for the pilot project in Rotterdam was produced in The Asphalt Mixing Plant Schiedam. Although the MSWl bottom ash content in asphalt concrete can reach theoretically 65% by weight, in practice the amount is limited due to variations in the particle size distribution, the high moisture content and the large filler content in the MSWI bottom ash. For the first production trial the amount of MSWl bottom ash in the asphalt concrete was estimated at 50 % by weight. In the pilot project in Enkhuizen all mineral aggregates including the MSWl bottom ash were heated and dried in the main drum. During production it appeared that the amount of MSWl bottom ash had to be reduced from 50 % to about 25 % due to the high moisture and filler content in the MSWl bottom ash. Due to the moisture content in the MSWl bottom ash the fuel consumption during asphalt production increased with 1 to 2 litres of oil per ton asphalt concrete. The amount of MSWl bottom ash had to be reduced because the dust collector could not handle the filler that was sucked from the main drum. Most of the dust was added

859

to the mixture again, but the capacity of the dust transporters was to small. By reducing the amount of MSWl bottom ash it also became easier to control the temperature of the aggregates in the drum. When the amount of MSWl bottom ash in the mix is less than 25 % the capacity of the asphalt plant is hardly influenced. In the pilot project in Rotterdam the amount of MSWl bottom ash in the asphalt concrete was directly estimated at 25 % by weight. No problems did occur. Extraction tests for asphalt binder content and particle size distribution of the asphalt concrete proved that the composition of the produced asphalt did meet the job mix formula.

6.LAYING OF ASPHALT CONCRETE During the paving of the asphalt concrete on the different pilot projects it appeared that there were practically no differences between the behaviour of asphalt concrete with and without MSWl bottom ash. The asphalt concrete containing MSWl bottom ash behaved very well in the asphalt paver. The spreading and laying of the asphalt mix happened in the same way as for conventional asphalt concrete using a vibrating tamping bar screed. The final compaction was carried out with dynamic and static rollers. The required compaction rate could easily be achieved in all pilot projects. Results are shown in table 6. Table 6. Compaction rates of paved asphalt concrete. COMPACTION I

I

density cores

density after re-compaction

compaction rate

average kg/m3

deviation kg/m3

average kg/m3

deviation kg/m3

average

deviation

%

%

DOP-NOAP, base course

2,326

19.28

2,319

5.36

100.4

0.91

DOP NOAP, surface course

2,341

19.46

2,357

5.98

99.3

0.93

Amsterdam, base course

2,232

30.49

2,274

19.58

98.2

0.73

Amsterdam, surface course

2,332

28.03

2,352

7.8

99.1

0.94

860

ton will be larger. From an economical point of view the application of MSWl bottom ash as a mineral aggregate in asphalt concrete can be profitable. In spite of a greater asphalt binder demand and the extra fuel needed, the reduction of filler, fine aggregate and coarse aggregate in combination with the low unit weight the use of bottom ash reduces the total costs. 7. PERFORMANCE OF ASPHALT CONCRETE

In november 1993 the pavements with the asphalt concrete containing MSWl bottom ash on the pilot projects in Enkhuizen and Rotterdam were visually inspected. There was no damage found that could be related to the use of MSWl bottom ash in the asphalt concrete. To date no minor or major repair works have been carried out. 8. DEVELOPMENTS FOR IMPROVEMENTS

The experiences so far make clear that the use of MSWl bottom ash in asphalt concrete is feasible but copes with moisture content, dust content and a higher asphalt binder demand. The Aardelite technology comprise a cold-bonded process, based on the activation and control of puuolane reactions in residues. Herewith stone-like gravel can be obtained in which elements like heavy metals are encapsulated in the cementitious matrix to be formed. This gravel can be used in a number of applications, for example as a substitute for natural gravel in asphalt concrete [7]. The fine particles in the bottom ash are the main problem as they contain the heavy metals. Therefor Feniks and Hoogovens Technical Services E&E, who is owner of the Aardelite technology, are performing a study for upgrading the MSWl bottom ash. The idea is to separate the fines from the coarse particles and to use the fine particles, together with MSWl fly ash, for the production of artificial gravel with improved leaching behaviour. Subsequently this artificial gravel together with the coarse particles from the MSWl bottom ash can be used in relatively higher amounts for the same applications as mentioned above. Herewith an effective utilisation of incinerator residues as secondary raw material will be possible. 9. CONCLUSIONS AND RECOMMENDATIONS

conclusions MSWl bottom ash can be used as a mineral aggregate in asphalt concrete. Amounts up to 25 % are possible without problems.

86 1

Asphalt concrete mixtures containing MSWl bottom ash behave in the same way as asphalt concrete with only normal aggregates. The asphalt concrete can be laid easily with a normal asphalt paver and corrections can be carried out in handwork. The asphalt concrete can be compacted with static and vibrating rollers, just as normal asphalt concrete. Using MSWI bottom ash to produce asphalt concrete can be economical. Savings will be made on the decrease of the demands of filler, fine aggregate and coarse aggregate. These savings will be only partially lost by a higher demand of asphalt binder. Results of laboratory tests and field evaluations show that asphalt concrete containing MSWI bottom ash meets the current dutch specifications for bituminous mixtures for pavements. The environmental properties of asphalt concrete containing MSWI bottom ash, as investigated with the diffusion test, are comparable with the properties of asphalt concrete without MSWl bottom ash. recommendation Feniks has planned to carry out a research program into the mechanical properties of the asphalt mixtures, the health aspects during asphalt production and milling and the possibilities for recycling asphalt concrete containing MSWl bottom ash. Further cooperation between the government, the union of incinerators and companies that apply the MSWl residues like Feniks is necessary to achieve a high level of successful use of MSWl residues. LITERATURE [l] FHWA-RD-Reports-75-81, -76-12, -77-150, -78-114, -78-144. Federal Highway Administration, Offices of Research & Washington, D.C. 20590.

Development,

[2] The use of incinerator slag in Asphalt for road constructions.

D.J. Nonneman, F.A. Hansen and M.H.M. Coppens. Waste Materials in Construction, Wascon '91. [3] Standaard RAW Bepalingen 1990.

Stichting CROW, Ede. [4] Aanleg proefvak met AVI-slakken in asfaltbeton.

Feniks Recycling Maatschappij B.V., Amstelveen, november 1993. [5] Rapportage over het proefvak op DOP-NOAP.

Feniks Recycling Maatschappij B.V., Amstelveen, november 1993. [6] Produktie en verwerking AVI-asfalt bedrijfsterrein Amsterdam West. Feniks Recycling Maatschappij BV. Amstelveen, november 1993.

862 [7] Haalbaarheidsstudie naar de toepassing van industriele assen, fase 1.

Novem, RIVM, Stichting Indas, Nijkerk. aa n ong ebo nd e n , cementg est ab iIis ee r d e bitumengebonden AVI-slakken, rapportnummer 91354. lntron B.V., Siard, november 1991.

[8]Uit Ioo go nd er zo e k

en

Figure 1. Laying of asphalt base course containing MSWl bottom ash on a cement treated base course containing MSWl bottom ash.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der Sloot and Th.G. Aalbers (Editors) el994 Elsevier Science B.V. AN rights reserved.

863

HOW TO PREVENT EXPANSION OF MSWI BOTTOM ASH IN ROAD CONSTRUCTIONS ? M.M.C. ALkemade”, M.M.Th. Eymaelb, E. Mulder“, W. de W i j s b TNO Environmental and Energy Research, P.0.-Box3 4 2 , 7300 AH Apeldoorn, The Netherlands

a

’ Feniks

Recycling Maatschappij B.V. P.0.-Box 9 2 6 5 , 1800 GG Alkmaar, The Netherlands

Abstract Since the late seventies substantial effort has been put into searching for structural applications for bottom ash originating from the incineration of municipal solid waste (MSWI). Processing the MSWI bottom ash into cement-treated base courses (CTBC) appeared to be an attractive application to handle the large amount o f bottom ash. As a result, several hundreds of thousands of tonnes of MSWI bottom ash have been applied in CTBC. However, in asphalt pavements, with a base course containing cementtreated MSWI bottom ash, sometimes the surface shows unevenness, because of local expansions occurring in the MSWI bottom ash. Therefore, an investigation into the expansion of asphalt pavements has been carried out. The first results of the research lead to the theory that particles of aluminium in the MSWI bottom ash cause the CTBC to expand. On the basis of this theory, several parameters which might affect the occurrence of local expansions in the bottom ash have been defined

1. INTRODUCTION In the Netherlands, about 700,000 tonnes of bottom ash originating from the incineration of municipal solid waste (MSWI) has to be handled annually. Most of the MSWI bottom ash is used in embankments as a landfill material. In the next decade, a sharp increase in the amount of bottom ash is anticipated due to the growing amount of industrial and municipal waste to be incinerated. The policy of the Dutch government, however, has been aimed at increased reclamation and recycling of waste, and a growing amount o f bottom ash to de deposited i s therefore undesirable. Therefore, Feniks Recycling has been searching for more structural applications since the late seventies. It was concluded that, in view of

864 the composition of the ash, it seemed possible to use this material in cement-treated base courses (CTBC) . As a result, several hundreds of thousands of tonnes of MSWI bottom ash have been applied in this way until now. This application seems attractive to handle the large amount of bottom ash. However, in asphalt pavements, with a base course containing cement-treated MSWI bottom ash, sometimes the surface shows unevenness, because of local expansions. The amount of asphalt pavements containing this kind of unevenness is limited. However, if unevenness is found, the density of expansions is large, 2 to 3 per square metre. Although the strength o f the pavement remains, the expansions have a negative effect on the smoothness of the surface and on the maintenance costs. A better control of the expansion will lead to an improved image of the use of the bottom ash in base courses and, moreover, to a decrease of the maintenance costs. Therefore, Feniks Recycling Maatschappij B.V. and the TNO Institute of Environmental and Energy Technology (IMET-TNO) have carried out an investigation into the unevenness found in asphalt pavements. The research has been guided by the committee CROW') / CUR B57 " ) . The goal of the research is (1) to understand the formation of unevenness in asphalt pavements with a cement-treated base course containing MSWI bottom ash, and (2) to give guidelines to prevent this problem, This paper presents the results of the investigation. *) CROW: Dutch institute which co-ordinates research regarding road constructions (Stichting Centrum voor Regelgeving en Onderzoek in de Grond-Water en Wegenbouw en Verkeerstechniek) ") CUR: Dutch institute which co-ordinates research regarding civil constructions, especially concerning concrete civil constructions (Civieltechnisch Centrum Uitvoering Research en Regelgeving).

1.1 Starting point of the investigation In cement-treated MSWI bottom ash, chemical reactions can occur even after a considerable amount of time, resulting in a substantial increase in volume. Because of this increase in volume, unevenness can be found on the surface of an asphalt pavement. In several papers, the cause of this phenomenon has been discussed [Ref. 1, 2 1 . The parameters which might affect the chemical reaction resulting in increased volume are:

-

the presence of a relatively large content of metallic aluminium and zinc in the MSWI bottom ash; usage of ash that has been kept in storage before utilization for a relatively short period of time; addition of an excess of cement; too much humidity within the base course layer; short period between the construction of the base course and the asphalt pavement.

A combination of these parameters possibly gives rise to the abovementioned problems. To prevent unevenness in the asphalt pavements, several proposals were made [Ref. 3 1 . These resulted in three measures which have been taken in several projects:

865

-

the bottom ash has to be kept in storage for a minimum period of time before utilization; a certain time period has to be taken into account between the construction of the base course layer and the asphalt layer, and the amount of humidity in the base course layer has to be controlled.

These proposals were based on practical experiences and non-scientific insight. However, this set of measures appeared to have been not always sufficient enough to prevent unevenness. A s a result, it seemed worthwhile to investigate the occurrence of expansion into more detail. Therefore, this research was focused on the understanding of the formation of expansions in order to give more accurate guidelines to prevent unevenness in asphalt pavements with cement-treated base courses containing MSWI bottom ash. On the basis of analyses and literature search, two mechanisms which may probably cause the volume increase in the cement-base course construction have been formulated [Ref. 4 1 :

1.

2.

Chemical reactions on non-ferrous metallics, particularly on aluminium and zinc, can cause an increase in volume. Under alkaline conditions, which occur during cement hydratation, metallic aluminium can form hydroxides. The conversion of metallic aluminium into aluminum hydroxide gives an increase in volume o f about 3.2. Ettringite formation is another well-known reaction which may occur. Reactions in which calcium sulphates, calcium oxides, aluminium oxides and water are involved can give rise to complex molecules, ettringite, resulting in an increase in volume.

Results of various microscopic analyses clearly showed that the first mechanism probably causes the unevenness found in the asphalt pavements. Therefore, the research was focused on the reaction of non-ferrous metallics under alkaline conditions.

2 . MATERIALS

AND METHODS

2.1. Cement treated base course containing MSWI bottom ash MSWI bottom ash is the solid residual result of the incineration of domestic waste and similar light industrial waste, without fly ash. MSWI bottom ash is generally screened at about 40 mm and parts of iron are eliminated. This bottom ash is a highly alkaline alumino-silicate based material which is similar in many ways to cement-based solidified wastes; the major difference is its physical structure which is more granular than monolithic. Therefore, this material seems more suitable for use in cement based constructions. Cement-treated MSWI bottom ash is an in-plant produced mixture of MSWI bottom ash, mineral aggregate (sand) and cement. The cement-treated MSWI bottom ash consists of 60 - 80 wt. % MSWI bottom ash, 40 - 20 wt. % sand (together 100 % ) and, based on 100 % aggregate, 2 - 6 wt. % cement. This material is used as base courses under asphalt pavements.

866 2.2. Chemical composition of the MSWI bottom ash The average chemical composition of the main elements of the MSWI bottom ash is given in Table 1: Table 1 The average composition of the main elements of MSWI bottom ash [wt. % dry solid] Element silicium (Si) calcium (Ca) sodium (Na) iron (Fe) aluminium ( A l ) potassium (K) chloride (Cl) sulphur ( S )

Amount [wt. %] 25 7 4 4 3

1
Most of the elements are present as an oxide or as a hydroxide. Of course, also metal salts, chlorides, sulphates and carbonates are available within MSWI bottom ash. Iron, aluminium, zinc, but also some other non-ferrous metals may occur as a metallic. The ash is formed at a relatively high temperature and thereafter quenched in water. Consequently, the ash is not chemically stable and during storage of the ash, several reactions will take place. These reactions will change the physical composition of the ash. In the s o called 'aged' ash, precipitation of metals will be found due to sulphide and carbonate formation. Furthermore, oxides can be converted into hydroxides and metals can be oxidised or reduced. The temperature can rise to 60 - 70 OC as a result of these reactions [5]. After incineration, the ash is highly alkaline (pH about 11). The pH will gradually go down to 9 - 10 during storage (normally at least six weeks), since oxidation of organic material will form CO,, which will give a decrease of the pH as a result of carbonation. The pH change will depend on several parameters:

-

the starting pH of the ash; the content of digestible material. More digestible material will result in less (hydr)oxides and therefore a lower pH will be found; the place of the ash in the depot (at the edge o f a depot more carbonation is possible and resulting in a lower pH).

If oxygen is not available, the pH change will cease. The ageing process will continue only if oxide is available again.

867 2.3. Aluminium In domestic waste and comparable industrial waste, aluminium can be found. The melting point of aluminium is 660 O C . Aluminium oxidises resulting in a thin aluminium oxide layer which prevents further oxidation. The reaction can take place as follows: 2 A1

+

3 0,

-> 2 A1203

Aluminium oxide is only soluble at high (pH > 10) or low (pH < 3 ) pH. If the pH is low, the aluminium oxide will dissolve as Al” and OH-. At high pH, aluminate (A10;) will be formed. MSWI bottom ash is highly alkaline and, if oxidation occurs, this will result in the reaction of aluminium into aluminate. The reduction of water can be the counter reaction: 1 2 H,O

+ +

1 2 e-

4 A1

+

4 OH-

4 A1

16 OH-

+

4 H,O

-> 4 A10; -> 6 H,

+ 8 H,O + + 12 OH

-> 4 A10;

+

12 e

6H,

The above reactions can only take place if water and OH- ions are present near aluminium particles. Another reaction, which is also likely to take place instead of the reduction of water, is the reduction of iron. Investigations in this field have proved that expansions are often found near iron particles. The aluminate ions can diffuse through the MSWI bottom ash. The amount of diffusion will depend on the moisture content in the bottom ash and on the period of time in which diffusion can take place. The aluminate ions will convert to aluminium hydroxide if the alkalinity of the ash decreases to a pH lower than 9 - 10. Aluminium hydroxide is not mobile in the bottom ash. This reaction can be described as follows: A10;

+

2H,O

-> Al(OH),

+

OH

The conversion of aluminium into aluminium hydroxide gives rise to an increases of volume of about 3 . 2 .

2.4. Testing programme The investigation has been focused on the reaction of non-ferrous metallics under alkaline conditions. The effect of the following parameters on the expansion were investigated in this research programme: the incineration plant from which the MSWI bottom ash originated; the composition of the cement mixture; the kind of cement used; the conditions during storage of the ash. Several kinds of proctor testing cylinders were produced to determine the effect of these parameters on the development of expansions. Eight series of 9 cylinders were made and kept under different circumstances. The 72 cylinders were produced as follows: 4 different MSWI

868

*

bottom ash >t 2 kinds of cement * 3 storage conditions 3 cylinders per series. In Table 2 more details are given on the various parameters. Furthermore, 20 cylinders were made with Portland cement B and Spanish cement. Table 2. Different parameters which were investigated Parameter

Levels

origin of MSWI bottom ash

incineration incineration incineration incineration

kind of cement

Portland cement A Blast furnace cement A

storage conditions

under water, 25 O C wet/dry cycles, 25 O C in air, relative humidity 70 % , 25 O C

-

plant plant plant plant

Alkmaar Amsterdam-Noord Roteb Rotterdam Rijnmond

The samples of the MSWI bottom ash were taken in accordance with quality control systems. The composition of the cylinders (as to the amount of cement, MSWI bottom ash and sand) was kept constant: 80 X MSWI bottom ash, 20 % sand and - on the basis of 100 % aggregate - 3 X cement. The proctor cylinders were prepared by compacting the mixture in a PVC cylinder with a serrated edge. The formation o f expansion followed by measuring the circumference.

3 . RESULTS 92 testing cylinders were produced to investigate the effect of three parameters on the expansions in cement-treated base courses. The development of expansion was followed by measuring the circumference of the cylinders. After 72 days, the circumference and the compression strength of the cylinders was measured and the materials were visually evaluated. After 259 days, the circumference was measured a second time. The results of this test programme are given in Appendix 1. An expansion is shown in Figure 1.

869

Figure 1. Testing samples with expansion To understand the effect of the parameters on the expansion of the cylinders, a statistical analysis was carried out on the results. The analysis clearly showed that o n l y the conditions under which the cylinders had been kept during the testing period had a significant effect on the expansion. The largest expansion was found for cylinders which have been kept in air with a relative humidity of about 70 % . After the test programme (259 days), some additional tests were carried out :

-

-

some of the cylinders that were given wet/dry cycles during 259 days, were brought in air; some of the cylinders that were kept in air for 259 days, were given wet/dry cycles; several of the other cylinders were kept under the same conditions as during the first 259 days.

It appeared that the proctor cylinders reacted on the changing testing conditions:

-

-

more expansion increase than found in the first 259 days, could be found for cylinders which were given a wet/dry cycles for 259 days and then, afterwards, kept in air; less expansion increase than before, was measured for cylinders kept in air for 259 days and, thereafter, were given wet/dry cycles; the cylinders having the same conditions after 259 days as before this time, showed an continuous increase in the amount of expansion,

870 The proctor testing specimen, in which no expansion could be measured, contained a lot of humidity and seemed to consist of relatively small particles of MSWI bottom ash.

4.

DISCUSSION

On the basis of the data gained in this research programme, a theory has been formulated. This theory tries to explain the formation of expansions in cement-treated base courses. As well as on the data, the theory is based on literature and on experiences from asphalt pavements which are already used at the moment. The theory has to be verified in an additional research programme. Background information has been given in Chapter 2.

4.1. Theory bottom ash

regarding

the

formation of

expansion

in MSWI

Aluminium will be oxidised in (cement-bound) MSWI bottom ash resulting in the formation of soluble aluminate ions. The aluminate will diffuse only a little if the moisture content in the base course is low. Therefore, the concentration of aluminate could be high near aluminium particles. After some time, the pH of the (cement-bound) ash will decrease, if carbonation is taking place. Aluminate will be converted into aluminium hydroxide under the changing conditions. This will result in an increase in volume. The increase in volume causes unevenness in the asphalt pavements if the aluminate ions are concentrated around an aluminium particle. If enough diffusion of the aluminate has taken place (because of a high moisture content), the increase of volume can be absorbed by the CTBC. Expansions can be seen in MSWI bottom ash in depot as well as in cementtreated MSWI bottom ash:

MSWI bottom ash in depot From experience it is known that expansions in depots are found mainly in the ash on the outside of the depot. At this place, more carbonation will occur and therefore, the pH of the ash decreases. This will result in the conversion of aluminate into aluminium hydroxide causing an increase in volume. It is expected that the dispersion of the aluminate is low as the moisture content in the ash will be relatively low: the high temperature in the ash (see above) will cause the evaporation of water (only near the surface). Cement treated MSWI bottom ash Also cement-treated MSWI bottom ash may have a low water content, The water is used during the hydratation of the cement. Furthermore, the base course layer is generally covered quickly to prevent leaching of elements. Consequently, the dispersion of aluminate ions will be small and expansion of the ash will be significant. The expansion will take place at the time the pH has reached the

87 1 critical value, because aluminate is then converted into aluminium hydroxide. The critical pH value will be reached if the free lime from the cement has been carbonated or has been bound in another way. This theory gives an explanation for the results of the experiments described in Section 3 . Test samples which were kept under a relative humidity of 70 % , show significantly more expansion than cylinders which were kept under water. In the cylinders which were kept under water, the diffusion of the aluminate ions will be high as a lot of water is present. In that case, the expansion of the ions can be absorbed by the cement matrix and expansion cannot be seen on the surface. The other cylinders (at r.h. of 70 %) will have a smaller amount of dispersion and therefore expansion is found. In addition to this, it is expected that carbonation within cylinders (and so the decrease of pH) is faster under a relative humidity of 70 % than when kept under water, as more air is present. If this theory is correct, the content of metallic aluminium in the MSWI bottom ash, the pH and the humidity are the most important parameters that determine the occurrence of expansions.

5.

GUIDELINES TO PREVENT EXPANSION

Based on the theory discussed in Chapter 4 , one may conclude that expansion will mainly occur near aluminium particles and if iron particles are available as well, the expansion will be more likely to happen. Furthermore, the development of expansions is dependent on the circumstances in which the ash is stored. Therefore, guidelines to prevent expansions can be divided into guidelines which are aimed at the removal of the causes of expansion and guidelines which are aimed at the realisation of conditions under which expansion can not occur. Both kind of guidelines are given hereafter.

5.1. Quality of the MSWI bottom ash MSWI ash from which the non-ferrous metals have been removed, will not expand, because the expansion is mainly caused by aluminium particles. At the moment, separation o f non-ferrous metals in MSWI bottom ash is practically possible for particles larger than about 10 nun. With this, the possibility of expansions resulting in unevenness will be reduced. However, non-ferrous particles smaller than 10 nun can still give rise to significant expansions. The amount of digestible material in the ash is another characteristic of the ash which can affect the formation of expansions, for a low pH o f the ash (as an effect of a large amount of digestible materials), increases the probability of the formation of unevenness in the asphalt. To sum up, if ash is used containing only a small amount of digestibles (1 - 2 %) and in which non-ferrous particles are removed as much as possible, the chance of the development of expansions is reduced. The aluminium particles should be removed before the bottom ash is stored to mature.

872 5.2. Conditions during storage of the MSWI bottom ash In the previous section it is concluded that small particles (< 10 mm) of non-ferrous metals have to be expected in the ash which can cause expansion. Perhaps, it will be possible to control the circumstances in the depot of the ash in such a way that the chance of expansion is reduced. This could be effected if the aluminium is converted into aluminate during storage: the aluminate will be distributed with the cement during the construction of the base course layer and consequently small expansions can be absorbed by the matrix. The conversion from aluminium into aluminate will be most successful under the following conditions:

-

the initial pH of the bottom ash in high; the pH of the bottom ash in the depot is kept high; a relatively long storage time will enlarge the dispersion of the aluminate in the ash (more time available for diffusion); the relative humidity must be high, as this will give a more rapid diffusion (and therefore a greater dispersion); remove aluminium particles as much as possible before storage. The best way to keep the pH of the ash high (pH > 11) is to start with ash containing a small amount of digestible material. If this is not sufficient, lime can be added to the ash. Furthermore, the contact with air must be avoided as much as possible, as carbonation gives a decrease in the pH. A s a result, the depot has to be large. A s has been explained before, the humidity is another parameter which might influence the formation of expansions. The humidity in the depot can be kept high by sprinkling the bottom ash. However, it must be kept in mind that the percolation water may contain some hazardous materials.

5.3. Conditions in the base course layer The conditions in the base course layer can be focused on prevention of the formation of aluminium hydroxide. The best conditions to prevent the formation of aluminium hydroxide are: low initial pH in the base course layer containing the ash; a rapid decrease of the pH in the base course layer. A low initial pH in the base course layer results in a slower conversion of aluminium into aluminate ions. The concentration of OH- ions is too low for a fast conversion. To reach a low initial pH, the amount of cement has to be as low as possible. Furthermore, the use o f Blast Furnace cement is preferable compared with Portland cement, as the initial pH o f Blast Furnace cement is lower. A quick reduction of the pH will give a rapid formation of aluminium hydroxide. This will result in less conversion of aluminium into other structures as the aluminium hydroxide may give a layer around an aluminium particle that can prevent further oxidation. However, it is not sure that the conversion of aluminium will indeed stop after a reduction in the pH. Therefore, another option, to prevent the unevenness in asphalt is t o create conditions in the base course layer in which all the aluminium is converted and dispersed through the base course before the pH has been reduced below the critical value. This will

873 give less local expansions. The best conditions in this situation are probably: a high initial pH in the base course layer containing bottom ash; a high humidity in the MSWI bottom ash; the pH of the base course must be reduced after all the aluminium has been converted into aluminate. A high initial pH in the base course results in a fast conversion of the aluminium in aluminate as a high proportion of OH^ ions is available. A high pH can be reached by the addition of a relatively large amount of Portland cement (see above). If the pH reduces slowly, the dispersion of the aluminate will be high if sufficient moisture is available. A high amount of cement will give a long period of time before the critical pH is reached. If the base course layer is covered directly with bitumen after construction, the humidity in the base course will remain relatively high. However, this can give less bond between the base course and the covering asphalt layers. Furthermore, fast construction of the base course layer is also desirable, because the contact with carbondioxide (resulting in carbonation) will be small.

6. CONCLUSIONS The results of the research programme clearly demonstrate that the conditions of the cement-treated base courses containing MSWI bottom ash, have a significant effect on the formation of expansions in this kind of base course layer. Furthermore, it was found that the o r i g i n of MSWI bottom ash and the k i n d of cement used seem to have a less significant role in the development of the expansions. On the basis of this information as well as literature data and experiences from asphalt pavements with MSWI bottom ash which are already used nowadays, a theory on the formation of unevenness has been formulated. If this theory is correct, a few guidelines to prevent the formation of expansions can be given.

*

*

The amount of aluminium in the bottom ash; The local expansions are caused by metallic aluminium and therefore the number and size of the particles of metallic aluminium in the MSWI bottom ash will have a large effect on the possibility of expansion in the base course. The moisture content of the CTBC material; The research has made clear that expansion will occur when the base course is relatively dry. This can be explained as follows. Water can give rise to a faster diffusion of the ions in the material. If the ions are dispersed in the bottom ash, the expansion can be absorbed by the CTBC.

874 >k

*

*

The period of storage of the MSWI bottom ash in the depot; During the period of storage in the depot, the aluminium-ions can be dispersed through the bottom ash. Again, this will lead to a better dispersion o f the ions and therefore will give less local expansions. Consequently, this will lead to less expansion in the CTBC . The cement content; In base course material with a high amount of cement, the pH will decrease more slowly than in a material with a relatively low cement content. A slow decrease o f pH in the cement-treated material is desirable because more time is available for the ions to diffuse through the bottom ash. A s explained above, this will reduce the chance of expansion of the base course. The digestible material content. If the digestible material content in the MSWI bottom ash is low, a slow decrease o f pH of the material is found, resulting in a slower conversion of aluminium into aluminate and consequently in less local expansion of the CTBC.

In a future research programme attention will be given to the validation the described theory and to the development of a quick testing procedure to determine whether bottom ash will expand. of

8.

REFERENCES

1

Notice of Ing. P. Leenders, Veabrin, The Netherlands

2

J . Hartlen, Incineration ash utilization in some countries Europe, Proc. Ash I - Conference, Philadelphia (1988)

3

Zwellen van AVI-slakken. Tussenrapportage van CUR-studiecommissie B57, Feniks Recycling Maatschappij B.V., Alkmaar, report T&A 91/009/n/5, (1991)

4

Dip1.-Ing. G . Kluge, Prof. Dr. H. Saalfeld, Dr. W. Dannecker, Untersuchungen des Langzeitverhaltens von Mullverbrennungsschlacken beim Einzatz im Strassenbau, Texte Umwelt Bundes Amt.

5

NOH-report, Veabrin kwaliteitscontole van AVI slakken 1987-1988, T A W rapport RAP-305/JJS/avd, Deventer, (1988)

in

7.

APPENDIX

Rijnmond

Table 1 Increase of circumference

BF-A

w/d/ cycles = wet/dry cycle r.h. = relative humidity

BF-A = Blast Furnace cement A PL-A = Portland cement A

PL-B = Portland cement B Sp.A = Spanisch cement A

Compression strength

Characterisation of sample

Compression strength after 12 weeks Investigated on 1 sample per section Disposal condition

Cement

yield strenth

yield stress [N/mn’l

“1 under water

BF-A F

I w/d PL-A

BF-A

PL-A

BF-A

PL-A

16.500

Sp.A

I

Expansions near iron particle

1.75

No expansion, strong nucleus

under water

11.200

1.49

No expansion, Strong nucleus

w/d

13.200

1.75

cvcle

I

70 X

9.800

I

1.30

Cristallisation near iron Darticle

I Large

expansions

near iron particle

1.59

Small expansions

14.000

1.86

A1 particle with small expansions

18.900

2.51

Small expansions near iron particle

under water

21.600

2.87

Small expansions

w/d cycle

23.100

3.06

No expansions

r . h . 70 X

22,200

2.94

No expansions

under water

12,800

1.70

Small expansions near iron particle

w/d cycle

16.800

2.23

No expansions

r . h . 70 I

14.100

1.87

No expansions

under water

7.000

0.93

No expansions or compression strength

w/d cycle

8,100

1.07

Small expansions, no Compression strength

r . h . 70 1

7.000

0.93

No expansions, a lot of iron, no compression strength

under Water

12,000

w/d cycle r.h. 70 X

under water

17.100

15.600

2.27

I

2.07

No exDansions

I Smalle

expansions

near iron particle

r . h . 70 I

18.600

2.47

No expansions, a lot of iron

under water

23.400

3.10

Small expansions

w/d c v c l e

26.000

3.45

No exDansions

2.92

I No exDansinns

3.34

No expansions

I r.h. PL-A

2.19

13.200

I w/d c v c l e I BF-A

No expansions

1.51

I

r.h. 70 Z

I r.h. PL-B

11.400

I

cycle

Visual aspects

1

70 X

22.000

under water

25.200

I

w/d cycle

13.500

1.79

Very small expansions

r.h. 70 I

20,000

2.65

No exmnsions

under water

29.200

3.87

No expansions

8.900

2.51

Small expansions

21.300

2.83

Small exoansians near iron oarticle

w/d cycle r.h. 70 w/d/ cycles = wet/dry cycle r.h. = relative humidity

%

BF-A

=

PL-A

=

Blast Furnace cement A Portland cement A

PL-8 = Portland cement B Sp.A = Spanisch cement A

Environmental Aspects of Constnrction with Waste Materials J1J.M. Goumans, H A . van der SIwt and Th.G.Aalbers (Editors) 61994 Elsevier Science B.V AN rights resewed.

811

Microstructure of concretes containing artificial and recycled aggregates J.A. Larbi and P.D. Steijaert

TNO Building and Construction Research, Department of Building Technology, P.O. Box 49, 2600 AA Delft, The Netherlands

Abstract The microstructure of concrete specimens containing various artificial aggregates have been characterized by means of polarizing and fluorescent microscopy (PFM) and scanning electron microscopy (SEM). The artificial aggregates in question were Lytag, Aardelite, Liapor, incinerator-source slag, recycled masonry and recycled concrete. The concrete specimens examined had prior to this study been subjected to carbonation tests for various periods of time ranging from 2 to 5 years. Of specific importance to the study were the pattern of carbonation in the concrete specimens, the capillary porosity and homogeneity of the cement paste, the intensity and distribution of microcracks, and the characteristics of the cement pasteaggregate interfacial zone. Results of the fluorescent thin section analyses revealed that the use of specific sizes of certain types of these artificial aggregates tend to influence the pattern of carbonation of the concrete. With the exception of a few distinct features associated with the concretes studied, their microstructural characteristics are in general comparable with concretes containing conventional natural aggregates. These distinct features and characteristics have been presented in this article with photomicrographic illustrations. 1 INTRODUCTION

The use of artificial aggregates, mostly specially processed lightweight aggregates and secondary (recycled) aggregates is gradually increasing not only for economic reasons but also for practical purposes. In the Netherlands, for instance, environmental constraints on exploitation of good quality river aggregates and the high costs of importation of alternative natural aggregates outside the country have necessitated the use of artificial or recycled aggregates for preparing concrete. Although there is a growing interest and need for use of these materials in concrete, not very much is known about the internal structure of these materials and the microstructural characteristics of concretes prepared with these aggregates. It is generally known that the microstructure of concrete plays an important role with regard to the performance of concrete [ 11. The characteristics of the paste-aggregate interfacial zone which determines the type of bonding between the cement paste and the aggregate particles and the structure of the external layer, a few centimetres from the surface are known to influence the strength and the durability concrete [2,3]. With regard to concrete prepared with artificial aggregates, information about the microstructure is not only useful for predicting the performance of such concretes but is also important for optimising the use of such materials in concrete in order to enhance the quality and performance of the concrete. Concrete microscopy, which is based on the study of thin sections of concrete specimens by

878 means of polarizing and fluorescent microscopy (sometimes supported with scanning electron microscopy) has been found to be one of the most useful techniques for acquiring such information. It enables on the one hand information regarding the mineralogical omposition of the materials used to be determined and on the other hand the porosity and microstructure of the concrete to be characterized without disturbing the integrity of the concrete. The aim of this study was to characterize the microstructure of some concretes prepared with artificial or recycled aggregates (used as coarse aggregate) as a way of providing more insight into the behaviour of these alternative aggregates in concrete. Three microscopic techniques, including stereo-microscopy, polarizing and fluorescent microscopy (PFM) and scanning electron microscopy (SEM) were used for this investigation. 2 MATERIALS AND METHOD OF INVESTIGATION 2.1 Materials

In all, six concrete specimens each containing one artificial or recycled aggregate material were examined in this investigation. The artificial aggregate materials included a Liapor (expanded shale), Lytag (a sintered fly ash), Aardelite (an artificially-processed fly ash-lime composite), incinerator-source slag (AVI-slag), recycled masonry and recycled concrete. In all cases the fine aggregate used was river sand. All the concrete specimens used had, prior to this investigation been subjected to carbonation in two climate conditioned rooms of either 20"C, 50% relative humidity (RH) or 20"C, 65% RH. Each of the specimens had before the carbonation test been cured in a fog room for 28 days. The composition and some properties of the concrete specimens used have been presented in Table 1 .

2.2 Methods of investigation A preliminary investigation involving examination of fractured surfaces of the specimens with the aid of a stereo-microscope was performed. The cement paste was found to be well bonded to the aggregate particles. There were no cases of detachment of the cement paste from the these particles. Further, a zone measuring approximately 50-200 pm wide, with a distinct brown colour was found bordering some of Lytag, Aardelite and in the case of Liapor, all the particles as an outermost layer or 'skin'. The microstructure and composition of this layer have been given in Section 3. The stereo-micrographs of Figures 1 and 2 for the Liapor and Lytag specimens reveal some of these features. For the PFM analysis, small blocks of the concrete specimens, each measuring approximately 50x30~15mm3 were sawn from each of the samples listed in Table 1 . After sawing, the blocks were glued to an object glass and vacuum-impregnated at approximately 40°C with an epoxy resin containing a fluorescent dye. The impregnated specimens were then left at room temperature overnight which allowed the resin to harden. Following this, one thin section was prepared from each of the blocks for the PFM analysis. Each thin section had an approximate thickness of 30 pm. Preparation of thin sections in this manner enables the specimens to be examined by means of both polarizing and fluorescent microscopy. The latter technique is especially useful in studying the microstructure (capillary porosity and microcracks) of the specimens. For the SEM-EDAX analysis, small samples of the specimens concerned were first dried under vacuum at a temperature of about 35°C overnight. They were then coated with a very thin layer of gold, mounted onto metal stubs and examined with a Philips 515 Scanning Electron Microscope (SEM). The SEM used was equipped with an Energy Dispersive X-ray Analyzer (EDAX). The investigation was performed on fractured surfaces of the specimens.

879

Figure 1. Stereo-micrograph showing an overview of the Liapor specimen - a Liapor particle

Figure 2 . Stereo-micrograph showing an overview of the Liapor specimen - a Liapor particle

880 Table 1 Composition of mix and some properties of the concrete specimens used in the investigation. Composition and properties

Aardelite

1 1 1 Liapor

i l l -

1

Crushed masonry

Crushed concrete

Artificial aggregate

50

Cement type

BFSC

~~

Cement (kg/m3)

pr

Silica fume (% m/m) Superplasticizer Melment (% m/m of cement)

320

375

I0.7

Water absorption after 30 minutes

9.1

Water absorption after 24 hours

11.5

Water-cement ratio (total) Water-cement ratio (effective)

0.48

10.8

-

14.3

0.66

0.57

0.58

0.59

0.3 1

0.5 1

0.50

Bulk density (kg/m3)

1975

2050

1780

2247

2155

Air content (%)

3.5

1.1

3.0

2.1

3.7

28-day compressive strength

58

Room condition for the carbonation test (“C, %R.H.)

20; 50

0.55

0.40

> 20; 65

20; 50

20; 50

20; 50

3.2

20; 50

This cement is the similar to OPC except that the particles are finer in size than those of OPC. (2) Blast furnace slag cement containing about 70 % by mass of cement as slag. (1)

3 RESULTS AND DISCUSSION 3.1 Internal structure of the aggregate particles Figures 3 and 4 are SEM micrographs showing the internal structure of particles of Liapor and Lytag respectively in the concrete specimens examined. It is clear from these micrographs that both the Liapor and Lytag particles have a porous internal structure. This applies also to

88 1 the Aardelite and most of the AVI-slag particles as shown in the PFM micrographs of Figures 5 and 6 but does not apply to the specimens containing the recycled aggregates. For the latter aggregates, the internal structure was found to be very much dependent on the type of masonry or concrete used. Remarkable features found about the recycled concrete particles were that they contained many microcracks and very often completely carbonated. These features apply especially to the concrete aggregate particles obtained from blast furnace slag cement concrete. Most of the pores have an irregular structure with only a few being interconnected with each other (see also Figures 1 and 2).

Figure 3. SEM micrograph of a fractured surface of the Liapor specimen showing the internal structure of the Liapor particle.

Figure 4.SEM micrograph of a fractured surface of the Lytag specimen showing the internal structure of a Lytag particle.

882

3.2 Microstructure of the cement paste The cement paste of all the concrete specimens was found to have a heterogeneous structure (variation in capillary porosity). This heterogeneity is believed to be related to the size and microstructure of the surface layer of the various porous aggregate particles. The structure of the pores of the outermost surface of the aggregate particles (whether open or closed and if open, to what depth) will control the rate and degree of sorption of fluid from the concrete when the latter is in the plastic stage. The hypothesis is that larger particles with open pores at the surface which are interconnected deeper into the aggregate particle are likely to absorb a lot more materials from the fluid phase of the concrete and at a faster rate (if not saturated prior to mixing) than similar particles but with closed pores [4-61. This process will tend to draw very fine particles of the cement together with the pore fluid into the aggregate particle. Larger grains will accumulate at the surface of the particle and hydrate which in the long run will cause a gradient in capillary porosity from the aggragte surface into the bulk of the cement paste.

Figure 5. Thin section (PFM) micrograph showing the internal structure of an Aardelite aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2). One remarkable feature about the specimens examined was that the density (microcracks/mm2) and distribution of microcracks in concretes containing these artificial aggregates were found to be different from similar concretes prepared with river aggregates. A semi-quantitative analysis of the microcracks present in the thin sections specimens by means of fluorescent microscopy revealed that the density of microcracks is, in general, higher in the concretes prepared with river aggregates than those prepared with any of the artificial aggregates for the similar water-cement ratios and cement contents. An average of 14 (microcrackslmm’) was obtained for the specimen containing Liapor, 7 for the rest as opposed to values between 28 and 36 for similar specimens containing river gravel and sand [7,8]. The discrepancy is likely to be due to the fact that microcracks in normal weight concretes prepared with river aggregates occur as paste cracks and adhesion cracks, which are cracks

883

that occur in the cement paste and along the cement paste-aggregate particles (sand and gravel) interface [2]. In the present study only paste cracks and cracks along the cement pastesand particles interface were observed. Cracks separating the cement paste and the coarse aggregate particles as well as those traversing through the coarse aggregate particles were not observed.

Figure 6. Thin section (PFM) micrograph showing the internal structure of an AVI-slag aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2). 3.3 Characteristics of the paste-aggregate interfacial zone A distinct zone of about 0.5-2 mm extending into the coarser aggregate particles was found in the specimens containing Lytag, Aardelite and some of the AVI-slag particles. The fluorescent thin section analysis showed clearly that the capillary porosity of this zone was lower than deeper in the aggregate. Differences in the capillary porosity (effective watercement ratio) of the cement paste bordering these aggregate particles and the bulk of the cement paste was not clear. Clear differences were found in the case where the concrete specimens were prepared with blast furnace slag cement. In such cases, the carbonated areas bordering the coarse aggregate particles were found to have higher capillary porosity than the uncarbonated areas. In general, the bond between the cement paste and the coarse aggregate particles was found to be very good. In the case of Lytag, Ardelite and especially Liapor, the bond was so good that the boundary separating the aggregate particles and the cement paste could hardly be traced. These observations were made from both the fluorescent microscopy and the SEM analysis. Figure 7 is a SEM micrograph of the paste-aggregate interfacial zone for the specimen containing Liapor. With the exception of this specimen, all the other specimens showed direct evidence of transport of some cement hydration products into the porous aggregate particles. Figure 8 is an SEM micrograph of the interfacial zone between a Lytag particle (left) and the cement paste (right) showing cement hydration products in the particle. Figure 9 shows

884 a representative EDAX spectra showing the bulk composition of a Lytag particle. Figure 10 shows a similar one for the outermost layer (a few hundreds of microns) of the particle in Figure 8.

Figure 7. SEM micrograph showing the microstructure of the cement paste-Liapor aggregate interfacial zone (a = aggregate; c = cement paste). The aggregate-paste boundary can hardly be distinguished.

Figure 8. SEM micrograph showing the microstructure of the cement paste-Lytag aggregate interfacial zone showing evidence of cement hydration products in the porous aggregate particle (a = part of Lytag particle; c = cement paste). The higher contents of Ca and to a less extent K support the observation made about transport of cement hydration products into the aggregate particles (see further Section 3.4). Cement grains were, however, not identified in any of these porous particles presumably because they were too coarse to penetrate the pores at the surface.

885

For the Liapor particles, there was no evidence found for penetration of cement hydration products or silica fume particles. The present investigation shows that there is a brown layer of about 50-100 pm thick bordering almost all the particles (Figure 1, 11 and 12). Analysis of this brown layer revealed that it contained closed pores within which iron oxide had crystallized (see the EDAX spectra of Figure 13). Calcium hydroxide, (Ca(OH),) crystals which are known to occur at the paste-aggregate interface were not observed at the aggregate interface for any of the specimens studied. This evidence is in agreement with observations made by Sarkar et. al. [4] and Zhang and Gjorv [ 5 ] which they attributed to pozzolanic reaction between the aggregate particles and the cement paste.

4

- L y t a g

f

2.00

0

t

O

:

B

.

6.00 0 0 K E V

4.00

O C N T

0

l

e

t o e s l a g

l

1

5

k

V

8.00 lOeV/ch

4

E 0

4 X

Figure 9. EDAX spectra showing the bulk composition of a Lytag particle.

4

- - L y t a g

f o t o : 1 6 2 2

2 00

O C N T

4.00

0

1

6 00 0 0 K E V

1

5

k

V

8.00 10eV/ch

4

E D 4 X

Figure 10. EDAX spectra showing the composition of the outermost layer of a Lytag aggregate particle of Figure 8.

886

Figure 11. Thin section (PFM) micrograph showing the internal structure of a Liapor aggregate particle (plane polarized light; micrograph = 2.7 x 1.8 mm2).

Figure 12. SEM micrograph showing the structure of the brown layer around the Liapor particles.

887

I AlKe

O C N T

0

.

0 0 K E V

lOeV/cn

A

E 0 A X

Figure 13. EDAX spectra and composition of the outermost layer of the Liapor aggregate particle in Figure 12. The crystals in this layer consist of iron oxide.

3.4 Carbonation Carbonation was found to have taken place in all the specimens examined. The depth and pattern of carbonation were, however, found to vary within a single specimen and very often among the specimens. Examination of the thin sections of these specimens in the polarizing mode and under crossed nicols revealed that the carbonation processes in these specimens proceeded mostly in the cement paste and to a lesser extent via the porous aggregate particles. Carbonation products in the form of finely-divided calcite (calcium carbonate) crystals with high interference colours were observed in almost all of the porous aggregate particles. From the PFM analysis, it became clear that the size of the aggregate particles and the microstructure of the surface layer, that is the structure of the pores of the outermost surface of the aggregate particles were the controlling factors, among others, for penetration and eventual carbonation in the particles. For smaller particles, ranging in size up to about 4 mm and occurring close to the surface of the concrete, carbonation was found to have penetrated the entire particle. For particles greater than this size, carbonation was found to be limited to a few millimetres of the outermost part of the particles. On the basis of these observations, it quite clear that for the same cement composition and effective water-cement ratio, the depth of carbonation will be greater for porous (lightweight) aggregate (with interconnected pores) concrete than for normal (dense) aggregate concrete. From durability point of view, it may be necessary to have an extra cover for the reinforcement in case porous aggregates are used to prepared concrete. From the results of this study, it may be concluded that the 5 mm extra cover specified in the Dutch Concrete Standards for concretes prepared with lightweight aggregates may not be an overestimation. 4 SUMMARY OF CONCLUSIONS From the results of the present microscopic investigations, the following conclusions ragarding the microstructure of lightweight aggregate concretes may be drawn: 1. The artificial aggregate particles of Lytag, Liapor, Aardelite and most of the AVI-slag were found to have a porous internal structure. A considerable number of these pores has an irregular structure. Most of them are not interconnected with each other.

888

2. The cement paste of all the concrete specimens was found to have a heterogeneous structure (variation in capillary porosity and water-cement ratio).

3. The density of microcracks in the artificial or recycled aggregate concretes was found to be considerably lower than the density in similar concretes but prepared with river gravel and sand. 4.A zone of about 0.5-2mm extending into the coarser aggregate particles was found in the specimens containing Lytag, Aardelite, and Liapor. In this zone the capillary porosity was found to be lower than deeper in the aggregate particle. 5. There was no difference in capillary porosity (effective water-cement ratio) of the cement paste bordering the artificial or recycled aggregate particles and the bulk of the cement paste. Clear differences were found in the case where the concrete specimens were prepared with blast furnace slag cement. In such cases, the carbonated areas bordering the coarse aggregate particles were found to have higher capillary porosity than the uncarbonated zones. 6. The bond between the cement paste and the coarse aggregate particles was found to be very good. In the case of Lytag, Aardelite and especially Liapor, the bond was so good that no boundary could be traced between the aggregate particles and the cement paste. 7. There was direct evidence of transport of cement hydration products into the porous aggregate particles. No evidence was, however, found for transport of cement grains into the aggregate particles. 8. For the Lytag, Aardelite and Liapor particles, there was direct evidence of some pozzolanic activity between the aggregate particles and the cement paste. Calcium hydroxide crystals which are known to occur at the paste-aggregate interface were not observed at the aggregate interface for any of these specimens. 9.The carbonation processes in the concrete specimens containing the porous aggregate particles was found to proceed mostly in the cement paste and to a lesser extent via the porous aggregate particles. The size of the aggregate particles and the microstructure of the surface layer, that is the structure of the pores of the outermost surface of the aggregate particles are believed to be the controlling factors for penetration and eventual carbonation in the particles. For smaller particles, ranging in size up to about 4 mm and occurring close to the surface of the concrete, carbonation was found to have penetrated the entire particle. For particles greater than this size, carbonation was found to be limited to a few millimetres of the outermost 'skin' of the particles. 5

REFERENCES

1 S. Mindess, Proceedings of the Materials Research Society Symposium, 114 (1988)3. 2 J.A. Larbi, Microstructure of the interfacial zone around aggregate particles in concrete, Heron, 1993. 3 R.I.A. Malek and D.M. Roy, Proceedings of the Materials Research Society Symposium, 114 (1988) 325. 4 S.L. Sarkar, S. Chandra and L. Berntsson, Cement and Con. Composites, 14 (1992)239. 5 M.H. Zhang and O.E. Gjorv, Cement and Concrete Research, 20 (1990)610. 6 M.H. Zhang and O.E. Gjorv, Cement and Concrete Research, 20 (1990)884. 7 R.B. Polder, R. Walker and C.L. Page, Int. Conf. on Con. and Corr. Protection of Steel in Concrete (1 994). 8 R.B.Polder, Investigation of Concrete Exposed to North Sea Water for 16 years. TNO Building and Construction Report, 93-BT-R0619-02 (1993).

Environmental Aspects of Construction with Wmte Materials J.J.J.M. Goumans, H A . van der SImi and Th.G.Aalbers (Editors) el994 Elsevier Science B.V. AN rights reserved

889

Frost Susceptibility of Recycled Aggregate M.M. OMahony Department of Civil, Structural and Environmental Engineering, Trinity College, Dublin 2, Ireland.

Abstract

An important requirement for sub-base and capping materi;il i n road construction is that it should not be susceptible to frost. Therefore if recycled aggregate is to be used in either of these cases, it also must not be susceptible to frost. Frost susceptibility is largely dependent on the flow of water to an aggregate from the soil below but tests were also conducted to determine if frost susceptibility was influenced by the moisture content of an aggregate at the time of placement. Crushed concrete was tested to represent ;Ihigh quality recycled aggregate whereas demolition debris (an unsorted demolition waste materiul) wits much lower in quality. The results, presented in the paper, show the response of these recycled ygregates to frost and highlight a strong relationship between frost susceptibility and moisture content for crushed concrete, in particular. The itim of the research was to provide additional information on the behaviour of recycled aggregates in freezing conditions and to compare this response with that of naturnl aggregates.

1. INTRODUCTION

Materials placed within 450nim of any road surfitce should not be susceptible to frost as defined by the Transport and Road Research Laboratory test described by Roe and Webster (1984). I t has been found t h a t there is an increase i n the number of road failures during and following severe winters. This deterioration can occur in three ways. a)

When water penetrates the road surface, damage can be caused by the expansion of water as ice fomis. This type of deterioration cun be avoided by better construction and maintenance techniques and p;iniculnrly if the road is adequately sealed.

b)

A more serious type of damage can be caused to rotid surfaces by the formation of ice

c)

When a pavement has been damaged by either of the ways described in a) and b), a further loss of strength may occur when the ice thaws because the material will have a higher moisture content and therefore reduced bearing capacity.

lenses i n the lower layers which cuise the road to heave.

890 Point b) is the most relevant when discussing unbound aggregates placed in the lower layers of a road pavement such as in the sub-base layer or the capping layer. It is imperative that these layers include materials which are not susceptible to frost. The pore spaces between the unbound aggregate particles itre generally large enough to accommodate the expansion of water contained in them when freezing starts. However, as the zero isotherm penetrates deeper into the pnvement, a presslire gradient is set up between the ice in the upper layers and the water table. Under this pressure gradient, water ascends towards the zero isotherm by means of ciipillnry action. The pore spaces do not have the capacity to hold this extra water when it expands on freezing nnd so ice lenses develop. Two important factors which effect this flow of water are the quantity of water present and the amount of fine particles in the material (less than 75 p i ) . The greater the ;mount of these tine particles, the easier water will be able to ascend by capill;uy nction. The object of this research was to examine the ability of recycled aggregates to match the performance of their natural counterparts with respect to the requirements of unbound aggregates for use in sub-base and cupping layers. This included a n examination of the frost heave of crushed concrete and demolition debris ;ind a coniparison of the results with those of limestone.

2. EXPERIMENTAL WORK The frost heave experiments were cnrried out in a frost heave appnratus as described by Roe and Webster (1984). The experiments involved placing compacted specimens of aggregate, of height 154mm and diameter 100mm. in a chnmber with the lower ends of the specimens in indirect contact with water by me;tns of a porous disc. The specimens were surrounded by dry pea gravel and the top of the specimens were not covered. The chamber was closed and the temperature of the water was maintained ;It 4OC but the air temperature was reduced well below freezing to -17°C. The heave was measured by the movement of brass rods placed touching the top of the samples and protruding through the top of the chmber. Although it is recommended by Roe and Webster (1984) that snmples be tested at optimum moisture content (OMC) and peak dry density (pel), testing ;it 0.5 OMC and 1.5 OMC was also attempted. Some adjustment WGS nixie to these moisture contents when stitbility of the compacted samples could not be achieved. 2.1 Test conditions of liniestone spccinieiis

Three samples at ench test condition were tested i n accordance with Roe and Webster (1984). Table 1 includes the moisture content and density values ;It which the limestone specimens were tested.

89 1 I

I

COMPACTION TARGET VALUES

TEST NO. REF.

I

pb (kdrn3)

2361 240 1 2442

Moisture Content (%)

(kg/m3)

1.75 3.5 5.25

2320 2320 2320

Pd

MEASURED VALUES Moisture Content (%) I .98 (0.56 OMC) 3.34 (0.95 OMC) 3.8 (1.08 OMC)

Pd

(kdniR) 2074 23 16 207 1

Table I . Test conditions of the limestone specimens Note: pb and pd denote bulk density and dry density respectively The target density and moisture content for L2 were peitk dry density and OMC. Although samples L1 and L3 were prepnred ;tt different moisture contents, the target density remained at 2320kg/m3 so that stable snmples could be obtained. However, it was clear during compaction that this density could not be achieved using these test conditions. compaction of these samples was continued u n t i l ;in increase i n compaction time did not change the volume of the material. When this stage w a s reached, the specimens were extruded. As they remained stable, i t was decided to use these samples i n the frost heave test. I t c;in be seen i n Table 1 that L3 had a moisture content much lower than the target v:ilue. This was due to a bleeding from the sample during mixing.

2.2 Test conditions o f the demolition debris specimens Initially, the choice of test conditions for demolition debris was siniilnr to that of limestone. The demolition debris had ;I water absorption value of 8% which was much higher than the value of 0.45% for limestone and consequently the moisture contents of the samples of demolition debris were ;tko higher. However, it w i i s difficult to obtain stable samples at a moisture content of 0.5 OMC. The OMC for demolition debris was fotind to be 13% using the BS 5835 (1980) compaction test and consequently 0.5 OMC was lower than the water absorption value. Hence, there wits not enough water present i n these samples to help compaction. It was also impossible to obtain stable samples of the material ;it it moisture content of 1.5 OMC. To rectify this situation, new target moisture contents were calculated as follows:Low moisture content = OMC - (OMC-WJ2

(1)

High moisture content = OMC+ (OMC-WJ/2

(2)

where W, is the water absorption of the aggreg;ite, It was possible to create stable snmples when these moisture contents were used. The test conditions of the demolition debris specimens are listed i n Table 2.

892

COMPACTION TARGET VALUES

pb Moisture (kg/m3) Content (Q)

TEST REF. NO.

2010 2060 2090

D1 D2 D3

10.5 13.0 15.0

MEASURED VALUES

Pd (kgjn13)

Moisture Content (5%)

I820 1820

Pd

(kgjni3)

10.94 (0.84 OMC) 1 X 15

13.0 (OMC) 14.6 (1.12 OMC)

1820

1824 1802

~~~

2.3 Test conditions of the crushed concrete sptc’.imens The crushed concrete had ;I water :ibsorption v;ilue lower thxn 0.5 OMC so the same approach was adopted a s that for limestone i t . the t:irget nioistiire content v;ilues were 0.5 OMC, OMC and 1.5 OMC. When trial specimens were prepared, ii w a s concluded, after several attempts, that the target density of 2000kg/m3 for C3 could not be achieved. Therefore the target value for C3 was changed to the m;ixiniiini density which could be oht;iined for this test condition in the trial samples. The moisttire content mid density v;ilues of the crushed concrete samples are listed i n Table 3.

COMPACTION TARGET VALUES rESTRT NO

I

ph Moisture (kg/ni3) Content (%,)

I

MEASURED VALUES Moisttire

(kg/ni?)

2000 2000

I

6.3 (0.6 OMC) X.3 (0.8OMC) 13.2 (1.2X OMC) -

Table 3. Test conditions of the crtislird concrete specimens

I838 2002 1904

893 3.

RESULTS AND DISCUSSION

The following c1assific;ition system was presented by Roe and Webster ( 1 9x4). a)

If the mean frost heave is less that 9mm, the materiiil is classed as not frost susceptible.

b)

If the mean is greater than ISmm, the materinl is classed iis frost susceptible.

c)

However, if the mean is i i i the range 9.1mm to 14.9mm. the material shall be regarded as 'not proven' and is reqtiired to be tested at other laboratories for cl;uific;ition.

The results of all frost heave tests are listed in Table 4. If L2, D2 and C2 iire examined firstly i.e. the specimens closest to Oh4C ;ind peak density, i t C;LII be seen t h a t the frost hewe measured in the L2 s;imples is quite low with :t mean of 3.Smm. However, the mean frost heave of the demolition debris (D2) samples is 12.3mm which indicated that it was in the 'not proven' range. The nioisttire content of the crushed concrete samples (C2) was 0.8 OMC which was much lower than expected. To obtain an indication of the likely frost heave at OMC, the frost heave results were plotted agiiinst moisture content i n Figure 1. By interpolation of the results, i t c m be estimsted that ;I frost heiive of IXmm might be obtained :it OMC (10%). On this basis. crushed concrete would be clxsszd ;IS frost susceptible. -

~~

TEST MOISTURE REF. ZONTENT No.

SAMPLE HEAVE (mnl)

SAMPLE 2 HEAVE (mm)

1

LI L2 L3

0.56 OMC 0.95 OMC 1.OX OMC

5.5 5.0 4.0

7.0 2.5 3.5

DI D2 D3

0.X4 OMC 1 .OO OMC 1.12 OMC

12.0 12.0 10.5

12.5 12.0 10.5

CI C2 C3

0.6 OMC 0.9 OMC 1.2X OMC

4.0 10.0

3.5 10.0 30.0

-

Table 4. Frost heave results.

30.0

~

SAMPLE 3 HEAVE (n1m)

MEAN FROST HEAVE (mm)

9.0

1.2

3.0 3.0

3.5 3.5

1.43 I .08 0.41

13.0 13.0

12.5 12.3 10.7

0.4 1 0.47 0.48

3.7

0.24 1.41 1.41

1 1 .o

3.5 13.0

33.0

1 1 .o 3 1 .o

STANDARD DEVIATION (n1111)

894 It is apparent i n Figure 1 that there is ;I strong relationship between moisture content and frost heave for the crushed concrete samples where, as the moisture content increases so does frost heave. The relationships for demolition debris and limestone ;ire much different, in that as the moisture content increases, frost heave reduces to ;I much lesser extent. Further work would need to be conducted to investigite these relntionships further. Considering the high frost heave of 30mm - 33mm recorded in the crushed concrete samples, i t can only be concluded that it would be unwise to place this material in areas where water is likely to ingress into the pavement. Increasing moisture content in the other rnvterials does not appear to incrense the probability of frost heave.

95

3025

-

CRUSHED C O N C R m

20-

15

-

DEMOLITION DEBRIS

. + 10

+

LIMESTONE

5-

o

! 0

,

, 2

,

, 4

,

, 6

,

, 8

,

, 10

,

, 12

,

, 14

, 16

MOISTURE CONTENT (%)

Figure 1. Relationship between frost heave mid moisture content. The two main factors effecting frost heave are considered to be the quantity of water below the layer of material which might ascend when freezing stiirts and the amount of fine material in the sample. Normally high frost heave is associated with large quantities of fines in the material (Jones and Hurt, 1980). The proportion of the particles possing the 7Spm sieve was close to 10% which is the m;iximum percentage allowed for sub-bnse materi:il according to the Specification for Roadworks (1981). However, the fines content of the crushed concrete samples was not significantly different to the other materials so this could not be the reason for the higher frost heave exhibited.

895 The moisture content present in the :iggreg:ite ;it pl;icernent can be considered further. It can be divided into two parts; the first being the water absorbed by the particles and the other the free water between the particles. I t is likely, upon freezing, thot the free water would be the main cause of any global damage to the layer particularly by the fonnotion of ice lenses. In the case of the crushed concrete at 1.28 OMC, it was calculated t h a t the water between the particles would induce a heave of 2mm-4mm upon freezing. A volume increase of water upon freezing of 9% was used, ;is suggested by Neville (1973, . The heave cnlculated is relatively small in comparison with the heave of 3~~l11111 - 33mm measured i n tlie smples and therefore does not serve to clarify this excessive frost heave. Additional work would be required to investigate the susceptibility of crushed concrete to frost. I t was surprising that the demolition debris, which was a lower quality aggregate with a higher water absorption, did not exhibit high frost heave values similar to those of crushed concrete. It should be noted that these results were also more consistent than those of the other materials. Croney and Jacobs (1967) found t h a t the addirion of cement to aggregates reduced frost heave. I t was found by Sweere (1989) i n ;I field triiil that crushed concrete and demolition debris, used as sub-base materinls i n m i d piveiiients, exhibited better resistance to rutting three months after construction that when the msterisl was first placed. This led Sweere (19x9) to believe that recycled aggregxes hiid it self-cenirnting effect. It may be thnt this binding effect might also reduce frost heave and so it is proposed to examine this in ;i later study. In general, crushed concrete wid demolition debris both contain relatively large quantities of cement but the self-cementing effect might not be easily identified i n tlie Roe and Webster (1984) test because the samples are rested directly after placement.

4.

CONCLUSIONS

(i)

On the basis of the results presented i n this paper. limestone would be classed as not frost susceptible but it was :ipp;irent tli;it crtished concrete would be highly susceptible to frost. The frost heave results of demolition debris indicated that i t was in the inconclusive range but its results were more consistent than those of the limestone or crushed concrete. Further testing ;it other hborntories would be required to confimi its susceptibility to frost.

(ii)

Although the frost heave of crushed concrete appeared to be directly influenced by the initial moisture content of the specimens, the increase i n volume of the material due to the expansion of this water on freezing w;is cnlculated and found to be relatively insignificant. The app:irent dependence of frost henve on the initial moisture content was not noticed for tests conducted on limestone and demolition debris and further testing therefore would be required to determine other contributing fxtors to frost heave.

(iii)

Following the conclusion of Sweere (1989) that recycled aggregates exhibit a selfcementing effect some time after placement, i t is proposed to examine whether this effect would also improve the susceptibility of these materi;ils to frost.

896 REFERENCES British Stnndnrd 5835 (1980) Compactibility test for gr;ided aggreg:ites. Pnrt I . British Standards Institution. London. Croney, D. and Jacobs, J.C. (1967) The frost susceptibility of soils and road materials. LR90. Transport and Road Resznrch Loborotory. Jones, R.H. and Hurt, K.G. (1980) The prediction of the frost susceptibility of limestone and sub-base materials. The Highway Engineer. Neville, A.M. (1973) Properties of Concrete. Pitmnn. London. Roe, P.G. and Webster, D.C. (1981) Specification for the TRRL frost henve test. SR829. Transport and Rood Research 1,;iborntory. Crowthorne, Berkshire, U.K. Specification for Roadworks ( 1981 ) Publications Office. Dublin.

Dep;irtment of the Environment.

Government

Sweere, G.T.H. (1989) Structural contribution of self-csnisnting granular bases to asphalt pavements. Proc. frd Symposium on Unbound Aggreg;itrs i n Roatls (UNBAR 3). University of Nottinghani.

Environmental Aspects of Consmction w'th Waste Materials JJJ.M. Goumans, H A , van der Slmt and Th.G.Aalbers (Editors) 01994 Elsevier Science B. K All rights reserved.

897

Use of crushed tile and concrete as filling in pipe trenches Jan Folkenberg Department of Cleaner Technology / Institute of Building Technology Danish Technological Institute, P.O.Box 141, DK-2630 Taastrup, Denmark

Abstract On the basis of detailed laboratory work and full-scale pipe work, studies have been effected to establish whether it is possible to use crushed tile and concrete in 0-4 mm fractions as filling in pipe trenches. The results of the studies prove that crushed material can be used for levelling and filling material in pipe trenches. The results have been gathered through video inspection and inclination measurements. In addition, deformation measurements were carried out on the plastic pipes in the test field. The compression of the material used in the pipe trenches does not always comply with the minimum requirements to road construction, but damage/deformation has not been demonstrated. The results only prove that the technical conditions of the piping have been observed. No studies have been carried out concerning any up-down movements in the road surface.

Objective and background On average 4.5m tonnes of building waste are generated in Denmark annually. Forecasts show that the volume will increase to reach 5.3m tonnes annually in 2015, / l / . Tiles and concrete rubble make up approximately 75% of the waste. Experience gained in practise concerning crushing of both tiles and concrete with a view to applying the material as stabilised gravel in road constructions shows that there is a large surplus of the fine 0-4 mm fraction /2/. In connection with tiles this sulplus reaches as high as 35 weight per cent of the basic material. This percentage has been confirmed by effected test crushings. To find an application field for the "surplus" material, a decision was made to study whether the material could be used as filler in pipe trenches.

898

The requirements of the existing standards of the field presuppose that the used filler predominantly consists of sand 13, 41. However, it is possible to use other materials as long as it can be documented that the alternative materials fulfil the requirements set up for the field of application. Studies were carried out to this effect, partly as laboratory studies, partly as effected pipe works. In connection with the execution of the mentioned pipe works a detailed measurement programme was executed. Execution of thorough monitoring of the compression of the materials has ensured that the materials were applied correctly in the pipe trenches. Correct application ensures that any settlement or damage/deformation of the installed pipes is attributable to the crushed material.

Applied construction machinery One of the prerequisites of the project was that the machinery used both in the laboratory tests and in the full-scale tests of the crushed materials should be the machinery which is normally used in the handling of traditional materials. This decision was spurred by the wish that the project was also to show that crushed tiles and concrete can be applied under the same circumstances as the traditional fillers, and that it will not be necessary to acquire new machinery because crushed filler is to be used.

Preliminary tests The following laboratory tests were carried out in connection with the studies of crushed tiles and concrete of the 0-4 mm fraction: Distribution of grain size at screening Determination of sand equivalent Determination of capillary absorption Standard Proctor tests. Because pipes can be made of both plastic and concrete, studies were carried out to determine whether the crushed materials fulfilled the prevailing requirements in relation to the pipe material. The results of the laboratory tests show that crushed concrete meets the requirements to base course gravel in roads 121 and that the material may thus probably also be used for this purpose. However, supplementary studies must be carried out to determine this.

899

As the results from the laboratory tests showed that crushed tiles and concrete - based on the existing requirements to fill materials - could be used as fill materials in pipe trenches, the next phase was to determine whether handling and application of the materials in practise would cause any problems. On the basis of the results a full-scale test field was then established in a gravel pit.

Full-scale test Across the entrance to a gravel pit the test field was established consisting of four parallel pipe trenches, see figure 1. The average daily traffic load was 105 trucks.

Road

Point 1

o~~~pvc

point 2

1

0 200 concrete

Point3

0-1

PdntC Point 7

0°200pvc I Point6 02ooconcrete 0-1 Point 8

Point9

00 200 PVC

Point4

Point i a

I

0 200 concrets

Pdnt 11

0-1

Pipetrench 1 wshed tiles

Pipetrench 2

mshed Concrete

Pipetrench 3

crushed tiles Point 12 :rushed Concrete

................................... Point 13

00200 Pvc

Point 14

I

0mconaete

Point 15 0 -1 Point 18 ...................................

Pipe trench 4

gravel (reference)

Road sign 0

-

inspeaionhole

Figure I Outline of the test area. The figure also contains information on the fillers used in the pipe trenches and specijies the materials and sites of the piping.

900 In principle the test fields were constructed as shown in the sectional view below.

Only the conditions in the piping trench area have been studied and documented. The four piping trenches in the field were constructed as follows:

Pipe trench no. I , construction: Construction

Thickness of layer

Stabilised gravel

0-32 mm gravel

Filling around piping

0-4 mm crushed tiles

Base course

0-4 mm crushed tiles

10 cm

Pipe trench no. 2, construction: Construction

Thickness of layer

Stabilised gravel

0-32 mm gravel

Filling around piping Base course

0-4 mm crushed concrete 0-4 mm crushed concrete

Construction Stabilised gravel Added filler/levelling course Filling around piping Base Course

Thichness of layer 0-32 mm gravel o-4 mm gravel

0-4 mm crushed tile and crushed concrete (1:l) 0-4 mm crushed tile and crushed concrete (1: 1)

30 cm 20 cm 30 cm 10 cm

90 1

Dipetrench no. 4, construction. Reference: Construction Stabilised gravel 0-32 mm gravel Filling around piping Base course

I

Thickness of layer

0-4 mm gravel

0-4 mm gravel

Execution of the work The pipe trenches were approx. 1 metre wide and approx. 0.80 metre deep. At a distance of 20 cm from the sides of the pipe trench a concrete pipe of 0200 mm was installed and in the opposite side a PVC pipe measuring 0200 mm was installed. The pipes were installed horizontally on the base course. One end of the pipes was corked up whereas inspection holes were mounted at the other end for subsequent video inspection and measurement of inclination, see figure 2.

Figure 2 The figure shows PVC and concrete pipes with mounted inspection holes.

902

When the pipes were laid, a filler course around the pipes was established measuring 30 cm, and compression was carried out with a vibration punner of the brand "Wacker", type BS65Y. After each two passings, compression was measured with an isotope probe of the brand "Troxler", type 3440. The measurements were carried out at the same points through the courses. When filler had been laid around the pipes, the levelling filler was laid, and the materials were once again compressed. This compression was carried out with a vibratory plate of the make "Wacker", type 3345. After each two passings compression was measured with the isotope probe. The measurements were repeated until twelve passings had been made of the materials with the compression machinery. When the filler had been added around the pipes, and in this case the filler and the base course of the road surface were made of the same material because of the low level of laying, 30 cm of stabilised gravel of 0-32 mm, type 2, was applied. The material was compressed and checked in accordance with the guidelines applying to the filler material. Uniform methods of laying, compression and checking were used in all four pipe trenches. In January 1993, two years after the establishment of the test field, video inspection and inclination measurement were again carried out on the pipes to determine any damage. The results of the video inspections showed that there was no visible damage to the pipes. The results showed that all pipes had settled a few centimetres. Nothing seems to indicate that there is a difference in the settlement of the pipes laid in crushed tiles and concrete and the pipes laid traditionally in gravel. After another interval the television inspection was repeated of the test field. The result showed that no visible damage to the pipes had occurred. Because it is not possible in a TV inspection to recognise deformation to plastic pipes, deformation measurements were carried out of the plastic pipes. The results of the studies at the test field show that the deformation to the PVC pipes after two years never exceeds 8%. To find a relative measure of how much the pipes "settled" in the test period, inclination measurements of the pipes were carried out simultaneously with the video inspection, see figure 3.

903 Distance from first inspection hole (metres)

I

0

-5 un

-

POim I

+5 an

2

3

4

5

6

.

7

x

POOUZ

-5 an

Paia 3

t

+5

POiDl.1

an

-5 cm

Poim 5 *5

cm

.

'

Point6

8

1

m

7

-5 cm

mm 10

mM 9 +5 on -5 cm

mint I I

+5 cm

-5 cm

mint 13

. . x

+5

M

perm 12 Y

polat 14

-5 an pdm

I5

&

mm 16

Figure 3 Thefigure shows the relative conditions of thepipes, 6 months and 2 years, respectively, afer the establishment of the test jield. The results of the studies prove that the pipes installed in crushed materials had "settled"3-5 cm in relation to the original installation, whereas the pipes in the reference field which were installed in traditional gravel had "settled"2-4 cm. The settlement had had no influence on the pipes.

904 Thus the conclusion was made that the use of the alternative tile and concrete materials entailed no increased risk of damaging the pipes in comparison to the traditional gravel materials as filler in the pipe trenches. The experience gained in the establishment of the test field also shows that the crushed concrete and tile materials can be handled in the same way as the traditional materials.

Future studies The project only proves that the technical conditions of the pipes have been complied with in connection with the use of the alternative materials. Documentation of whether the materials fulfil the technical requirements of road construction - e.g. bearing capacity, deformation resistance, permeability and application conditions -

would require further detailed studies. Furthermore, it would be necessary to study whether the pipes are tight in relation to the settlements of the materials. As a consequence an application has been submitted to the Danish Environmental Protection Agency for financial support of a continuation of the project, and it is expected that a consecutive project will start in 1994.

Literature Environmental project no. 150 (1990).Forecast of building and construction waste main report. The Danish Environmental Protection Agency (not translated). Danish Standard DS 401.Standard of sand, gravel and gravel aggregate, 2 edition 1977 (not translated). Danish Standard DS 437 (1986).Installation of rigid pipes of concrete etc. in soil (not translated). Danish Standard DS 430 (1986).Installation of flexible pipes of plastic etc. in soil (not translated).

Environmental Aspects of Consttuction with Waste Materials J.I.J.M. Goumans, H A . van der SIoot and Th.G.Aalbers (Editors) 691994 Elsevier Science B.V. All rights resewed.

905

USE OF ASHES FROM MSW INCINERATION IN CEMENTITIOUS BUILDING MATERIALS A. Gerdes and F.H. Wittmann Institute for Building Materials ETH Zurich Switzerland SUMMARY A technology has been developed which allows to separate most hazardous materials in MSW from the organic components. The so purified organic components can be incinerated. Ashes obtained from this new technology have been analysed. It was found that they contain a small and tolerable amount of heavy metals only. In addition it was shown that both the bottom and fly ashes have a puzzolanic action. Different concrete mixes in which part of the Portland cement has been replaced by these special MSW ashes have been tested. With the most promising concrete mixes concrete blocks have been produczd under industrial conditions. About 25 % of the cement content can be replaced and acceptable mechanical properties are still obtained. First leaching test have shown that these concrete blocks can be used as a usual building material. In a second test series glasses produced from traditional MSW fly ashes after vitrification have been finely ground and used in mortar prisms. Up to 20 % of the Portland cement has been replaced by these ashes. The mechanical properties are hardly influenced. 1. INTRODUCTION

A few years ago a method to separate MSW into different components has been developed Ill. Ecomat operates in Moudon, Switzerland, one factory which uses this new technology. Metals, batteries, glas and ceramics are separated consecutively from the remaining organic components. The dried organic components can be burnt in a modem heat generating power plant. It is obvious that both the bottom ash and the fly ash from this incineration contain much less hazardous elements as compared to a conventional MSW incineration station. In Tab. 1 the range of heavy metals in two different fly ashes, a Dutch and a Gennan one, are shown together with the result of the analyses of a typical bottom ash of a conventional MSW incineration station (Hagenholz, Switzerland). For comparision the corresponding values of the Ecomat ashes are also given in Tab. 1. Finally the range of the elements as observed in the earth’s crust are added. Table 1: Range of trace elements in different ashes, give in mgkg Trace Elements Cd Cr CU Ni Pb

I I

Dutch fly ashes /2/ 2.1 f 1.4 139f43 144f 37 _l h _ 7+2 _ _6 ~

143245 Zn 38Of ISO n.a. = not analysed

German fly Hagenholz ash (CHI Powerplant MSW ash Ensdorf 131 141 I 3.6-16.0 I 22 550 176-365 2300 165-380 130 91-104 1800 660-1670 n.a. 970-1990

I

I

ECOMAT Fly ash

I

I

ECOMAT Bottom ash I51 I51 ca. 10 % ca. 90% 72.8 I 0.71 406 527 27 479 263 298 < 12 16 5.86 12.7

I

I I

Minerals in the Earth’s crust 141 0.03-0.3 4-2980 4-87 2-2000 1-20 n.a.

906 In a totally different approach fly ashes of conventional MSW incineration stations are heated above 1200 "C. Under these conditions most heavy metals evaporate and can be recovered by condensation. The remaining molten mass is relatively clean and can be quenched in order to obtain a puzzolanic reactive glass 161. In this contribution it will be shown that Ecomat ashes and the vitrified fly ash can be used in concrete technology in order to replace part of the Portland cement. 2. EXPERIMENTS A N D RESULTS 2.1 Concrete blocks prepared with Ecomat ashes Many different concrete mixes have been tested in the laboratory in order to find some promising compositions. With these optimized concrete mixes concrete blocks have been produced in a specialized factory. the maximum aggregate size in these blocks is 12 mm. Strength and elastic modulus have been determined on these concrete blocks and on prisms cut from the walls of the blocks. The strength evolution is shown in Fig. 1 for different concrete mixes. It can be seen that concrete blocks in which up to 25 % of the Portland cement have been replaced by Ecomat bottom ash show a reasonable strength development. These blocks can be used in load bearing and non load bearing masonry walls. 40 35

5

n 0

50

100

150

200

250

300

350

400

timeld

Fig. 1: Development of compressive strength of concrete blocks as prepared with different amounts of Ecomat bottom ash replacing part of the Portland cement. The percentage of bottom ash in hydraulic binder is given in the box. In all mixes the binder content (cement plus bottom ash) was 280 kg/m3 and the waterhinder ratio was 0.4. Similar concrete blocks containing relatively high amouiits of Econiat ashes have been tested with respect to leaching. Results obtained on blocks with four different compositions are compiled in Tab. 2. The heavy metal ions observed in the leaching tests according to DEV-S4 /7/ as obtained on concrete blocks containing significant amounts of Ecomat ashes hardly differ from those from blocks prepared with Portland cement exclusively. Further research on the leaching behaviour is going on at present.

Specimen

A

B

C

D

Binder composition

280 kg/m3 PC

210 kg/mj PC + 140 kg/m3 BA

210 kg/mj PC + 140 kg/m3 PFA

I

Al

cu

5.6 0.008 n.d. 0.023 n.d.

Ni

0.024

5.5 n.d. n.d 0.083 n.d.I. n.d.

210 kg/mj PC + 56 kg/m! BA + 28kg/m3PFA 3.5 n.d.

I I

0.098 n.d. . . 0.14

Pb Cd Cr

I I

I

5.1 n.d. 0.18 n.d. . .-

0.02:5

I II I

I 2.2 Mortar prisms prepared with vitrified fly ash Mortar prisms in which an increasing percentage of the Portland cement has been replaced by vitrified fly ash have been prepared. The maximum aggregate size of the mortar was 4 mm. Compressive and bending strength of the obtained material has been determined on standardized prisms (40 x 40 x 160 mm). Some results are shown in Fig. 2. It can be seen that the strength evolation is hardly affected by replacing up to 20 % of the Portland cement by the finely ground vitrified fly ash. These preliminary result indicate that possibly up to 40 % of the Portland cement can be replaced without dramatic influence on the mechanical behaviour.

0

P

41

60

BD

100

1P

tinrJd Fig. 2: Development of the compressive strength of mortar prisms containing different amount of vitrified fly ash. In all mixes the binder content (cement plus finely ground vitrified fly ash) was 586 kg/m3 and the waterbinder ratio was 0.5. The percentage of the finely ground vitrified fly ash in the binder is given for each mix in the box.

908 3. CONCLUSIONS It has been shown that it is possible to separate most hazardous components of MSW with an appropriate technology. If the remaining organic components are burnt in an advanced incinerator full advantage of their heat content can be taken and the resulting bottom and fly ashes can be used profitably in cementitious materials. Further research is needed to optimize the mix composition and to further elucidate all environmental aspects. 4. LITERATURE /1/ Z. Zhang and F.H. Wittmann, Use of proccessed garbage in cement concrete, in: Proceedings of the International Conference on Environmental Implications of Construction with Waste Materials, Editor: J.J.J. Goumans, H.A. van der Sloot, Th. G. Aalbers, Elsevier Verlag, Amsterdam, pp. 643-644, (1991) /2/ CUR Report 144, Fly ash as addition to concrete, A.A. Balkema, Rotterdam, (1992) /3/ F. Kiefer, Untersuchungen zur UmweltvertrBglichkeitund Verwendung von Kraftwerksnebenprodukten, Dissertation, Saarbrlicken, (1989) /4/ Amt f i r Gewlsserschutz und Wasserbau des Kanton Zlirich, Emisionsabschiitzung f i r Kehmchtschlacke (Projekt EKESA), (1992) IS/ Laboratoire d analyses, Energie et Environment, Strtlmsund, Schweden Rapport des Tests de Combustion Eneco Laborbericht Nr. 166Y91

/6/ H. Jodeit, J. Jochum and Ch. Wieken, Das ABB-Schmelzverfahren zur Behandlung von Filtersuuben aus der thermischen Abfallverwertung, in: VGB-Kraftwerkstechnik GmbH (Hrsg.), RiickstBnde aus der Miillverbrennung (VGB-TB-221), Essen

/7/DIN 1164, (1986) Part 5 (German Standard) : Standardized German procedure for water, wastewater and sludge testing, sludge and sediments (Group S), (1986)

Environmental Aspects of Constmction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and Th.G. Aalbers (Editors) a1994 Elsevier Science B.V. AN rights resewed.

909

Effect of grain size composition of the calcium-sulphate fly ashes on the properties of autoclaved building materials Z. Pytel and J. Malolepszy

University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland

Abstract The bulk of fly ashes in ambient temperature is insufficiently chemically active in relation to water, independently on the kind of burnt coal. Nevertheless, some of them after suitable activation shows the hydraulic properties merging features of such binders as lime and cement. First, the calcium-sulphate fly ashes start as by-product in the burning of a brown coal reveal above properties. They make the chance in their application as a binder and microaggregates for the production of some kind of building materials. The pozzolanic properties of fly ashes depends on their granulation and show improvement when they are finer. The granulation effect of "Patn6w" fly ashes on the physical properties, texture and structure of autoclaved calcium-silicate brick is presented. Also, results of the investigation of the effect of the quartz sand additives on the quality of an autoclaved material get on the base of fly ashes binder is shown. 1. INTRODUCTION

The hydraulic properties of calcium-sulphate fly ashes depend on their chemical and mineral composition. Fly ashes characterized with an increase content of calcium compounds. Some amounts of free lime (CaO) is also found. Free CaO can be subjected on the slow hydration into Ca(OH), after the contact with water and then can react with active silica. The hydrated calcium silicates resulted due to such reactions and depending on the hydration conditions, mainly temperature and pressure of water vapor, can be formed into kinds ['I. Also, the glassy phase contained in fly ashes have an influence on their hydraulic properties. The pozzolanic properties of fly ashes consisting in the ability of association of Ca2+ ions from solution with the formation of hydrated compounds. According to Diamond [*I the pozzolanic reaction in 20°C starts itself tardily and shows a such slow run that the C-S-H phase is not visible before 28 days under the electron microscope. Uchikawa ['I revealed that the C-S-H phase get in such conditions shows the lower ratio of C/S equal about 1 and contain considerable amounts of Mg and Al, than in the portland cement paste where CIS is about 2 .

910

However, the distinct progress of pozzolanic reaction is seen in hydration of fly ashes in hydrothermal conditions, The glassy phase of fly ashes faster hydrolyze at an increase temperature under the pressure of the atmosphere saturated with water vapor and in highly basical environment. Resultant silicate (H,SiO;, H2SiO:-) and aluminate (H,AIO;) ions get into the solution and react with ions of Ca2' forming hydrated calcium silicates or calcium alumina silicates Also, hydrogamet can be expected among the products of hydration of fly ashes containing alumina beside silica [ 5 ] . Therefore, the free CaO and glassy phase contained in the mineral composition of fly ashes affect binding properties. It is also known, that the hydraulic activity of fly ashes increase with their degree of comminution ['I]. The pozzolanic reaction begin in the earlier stage of hydration and shows faster run. The earlier crystallization of hydrated calcium silicates and calcium alumina silicates having the chief influence on the strength properties of autoclaved material is the result that process ['I. The dry grinding of fly ashes in the ball mills is the simple and an efficient manner for their activation.

r].

2. EXPERIMENTAL 2.1. Raw materials The fly ash from the brown coal electric power station "Patn6w" (EPS) was used as a basal raw material in this investigations. The dust collection system installed in EPS "Pqtn6w" consists of three zones of electrofilters, so the fly ash exists in the three particle fractions. The degree of dust collection is highest in I zone of electrofilters and amount of 85% of a total yield, while in I1 and 111 zones is equal of 10 and 5 % , respectively. The particle size analysis of fly ash was checked by sieve test using the following set: 1.O, 0.5, 0.25, 0.12 and 0.063 mm. The sieve test was carried out for each fraction of fly ash and results is given in figure 1.

Undersize 6o material (P(d))

. . . . . . Fraction II

[%I

._ Fractlon Ill

0

0.063

0.12

0.25

0.5

1

Partlcle size (d) [mm]

Figure 1. The particle size distribution. The specific surface of the original fly ash as well as the disintegrated one was calculated according to Blaine procedure after 2h grinding in the laboratory ball mill and results are given in Table 1.

91 1

Table 1 Specific surface of "Patnbw" fly ash Specific surface S, [cm2/g]

Tested fraction Fraction I

before grinding

after grinding

600

3000

Fraction I1

1700

3400

Fraction I11

2600

4200

The chemical composition of examined fly ash (Table 2) depends on the particle size distribution. The coarse particle coming from I zone of dust collection are rich in Si02 and poor in CaO (also free CaO), MgO and SO,. The middle and fine fraction (from I1 and 111 zones) consist of highest amount of CaO, MgO, SO, and smallest amount of free SO2. The mineral composition of investigated fly ash was described by XRD method and revealed that is similar for each particle fraction, however, the participation of an individual minerals were changed. The quartz, CaO, anhydrite, periclase, hematite, magnetite and small amount of calcite belong to crystalline phases. The amorphous phase consisted mainly from glass. The unburnt coal is also seen. Table 2 The chemical composition of "Patnbw" fly ash. Chemical analysis wt (%) Component Fraction I Fraction I1 Fraction 111 L. 0.i. ( 1000 C)

2.47

2.38

2.92

SiO,

70.10

33.03

29.85

Fez03

4.59

6.02

6.08

O

A1203

2.79

4.46

4.16

CaO

15.28

37.01

37.33

MgO

2.52

6.03

6.73

so3

2.32

8.92

10.41

CaO,

2.47

8.13

7.99

residuum

2.40

4.53

5.44

2.2, Procedure The fly ash binder was used in preparation of samples designed for the testing of a new material. The binder was prepared in three different variants. The first one was made using a separate particle fraction of the natural fly ash.

912 The second one was made using the mixture of three particle fraction of the natural fly ash. Three mixtures was next collected with variable content of a given fraction. One of them had the particle size distribution similar to the structure of fly ash from the one of zone of dust collector. The moisten fly ash was matured according to I as well I1 variant at 120°C during 6h under the normal pressure. The third variant of binder was fabricated using fly ash disintegrated up to 3400 cm2/g according to Blaine. Next, it was initially hydrated in an autoclave at the temperature not higher than 150°C in the atmosphere saturated with water vapor under the pressure below 0.5 MPa during 2h. After hydration of tested fly ash, the produce binder was then mixed with a quartz sand. An addition of the quartz sand was ranged from 10 to 50%. Next, the cylinder laboratory samples was modeled using binders get according to I and I1 variant as well as using the fly ash and sand mass with a binder of the third variant under the maximum compression pressure of 20 MPa. Samples was next directly autoclaved under the conditions used in the production of the lime-sand brick.

2.3. Properties of the building material Autoclaved samples of a new building material were tested in respect of the following features: compressive strength, absorbability, density and frost-resistanceand results are given in Table 3. Table 3 Physical properties of a material with an addition of the natural and disintegrated fly ash. Properties Binder Sample variant symbol Comp.strength Absorbability Density Frost R, [MPa] Nm [%I sp [g/cm2] resistance Natural "Patnbw" fly ash I

I1

F- 1

10.7

22.3

1.65

None

F-2

18.2

29.3

1.52

None

F-3

22.1

33.2

1.51

None

M-1

14.4

23.5

1.61

None

M-2

19.3

26.7

1.54

None

M-3

25.7

29.9

1.52

None

Disintegrated "Patnbw" fly ash

111

P-10

31.8

23.3

1.64

Full

P-20

36.8

14.3

1.79

Full

P-30

34.6

12.1

1.87

Full

P-40

34.8

11.1

1.91

Full

P-50

33.5

10.9

1.92

Full

913 Results show that disintegration of fly ash is effective. In each case, material get in variant I and I1 characterized in lower compressive strength in contrary to material obtained according to variant 111. Also, samples show the higher absorbability and could be a reason of its lack of the frost-resistance.

2.4. Microstructure and material texture The texture of an autoclaved material was observed in Joel 5400 and is given on figure 2 and 3. Results show amorphous as well as crystalline hydration products. The C-S-H phase belong to the first one, and is seen under the high magnification as a submicroscopic substance similar to colloid particles resembling a gel. The tobermorite is a dominated product among the crystalline phases. The morphology of the tobermorite crystals is discriminated but usually looks in the form of slats, bands or needles. However, the tobermorite in the shape of plates is seen scarcely. It is typical, that crystals are found in the interior of the pore walls and grow up into the inside. The pore is charged with crystallization products and make the structure to be condensed. The direction of the crystals growth is different, so they make the net of the crossed and disordered themselves needles. This phenomenon is clearly demonstrated in figure 3. Also, observations under the electron microscope show the differences in the quantity of induced products during the reactions running in the hydrothermal conditions. The C-S-H gel is the dominant reaction product in samples prepared with a mass of fly ash (sample F and M). However, tobermorite is the principal product in samples get from a mass of ground fly ash and sand (sample P). Also, small quantity of C-S-H phase is observed.

Figure 2. Material produced from mass of fly ash (binder of I1 variant).

914

Figure 3. Material produced from mass of fly ash and sand (binder of 111variant).

3. SUMMARY Recapitulating, the brown fly ash prepared in a suitable procedure, instead of lime,

can be used in the production of the autoclaved building materials such as calcium-silicate brick. The fly ash plays the role as a binder and microaggregate but it should be dry disintegrated up to 3000+4000 cm2/g according to Blaine before usage. The disintegration is not only a process for an increase of the specific surface of a material but also make that That cover is a little permeable the glassy shield of fly ash particles is destroyed prohibiting the entrance of water into the inside of particles and rendering hydration of CaO and MgO. Thus, the disintegration of fly ash increase its hydration activity. Results of investigations of samples of series P, prepared with disintegrated fly ash, confirmed that fact. The samples characterize with the highest compressive strength between tested materials and the full frost resistance. Also, results of the microstructure testing of produced material proved the positive effect of a disintegration process. They show a higher quantity of the hydration products, beneficial morphology of a microcrystals of C-S-H phase and an attendance of fibrous crystals of tobermorite. It is also useful, to subject the disintegrated fly ash on a beginning hydration in hydrothermal conditions. Some of fly ash components, mainly CaO and MgO almost entirely hydrate and portlandite and brucite is formed in result. The negative soundness phenomenon being usually observed in later period of a hardening of the fly ash binder is caused by

915 retarding hydration of CaO and MgO and is eliminated by this way. As a result, the active binder is produced after started hydration of the ily ash in the atmosphere saturated with water vapor under pressure. The binder blended with a proper quantity of a quartz sand makes a raw mixture for the production of the pressed silicagel elements. The addition of a quartz sand containing an appropriate amount of a coarse and a middle size of a particle effects positively on the granulometric composition of the fly ashsand mixture improving their rheological properties. It make the direct influence on the compaction degree of molders during pressing and is related with their final porosity.

4. REFERENCES 1.

H.F.W. Taylor, Cement Chemistry, Academic Press, London 1990.

2.

S . Diamond, 7th I.C.C.C., Paris 1980 111 IV-19.

3.

H. Uchikawa, 8th I.C.C.C., Rio de Janeiro 1986 1 249.

4.

K. Takemoto, H. Uchikawa, 7th I.C.C.C., Paris 1980 I IV-2/1.

5.

J. Malolepszy, Hydration and properties of alkali activated slag cementitious materials, Ceramics, Bulletin 53, Cracow 1989 (in Polish).

6.

M. Regouord, 8th I.C.C.C., Rio de Janeiro 1986, I 199.

7.

J.B. Jambor, 6th I.C.C.C., Moscow 1974, I1 315.

8.

S. Diamond, D. Ravina, J. Lovell, Cement and Concrete Research, 10 (1980) 279.

9.

S. Diamond, Cement and Concrete Research, 16 (1986) 569.

This Page Intentionally Left Blank

Environmental Aspects of Consttuction with Waste Materials JJJ.M. Goumans, H A . van der Sloot and l3.G. Aalbers (Editors) el994 Elsevier Science B. V.All rights resewed.

917

SULPHATE AND ACID ATTACK ON CONCRETE IN GROUND AND LANDFILL C. Plowman UK Analytical Ltd, Vicarage Terrace, Kirkstall, Leeds LS5 3HL UK

ABSTRACT Disposal of industrial waste as landfill can give rise to chemicals in the groundwater which may damage concrete foundations. Possible aggressive agents include sulphate and acids. Cement replacements such as flyash or ground granulated blast furnace slag influence the mechanism and rate of attack. Mechanisms of attack by thaumasite formation, and sodium sulphate crystallisation, are briefly described. Potential for attack by low-calcium flyashes has been shown generally to be limited. Recommendations of BRE Digest 363 regarding classification of sevefity of sulphate conditions, and appropriate concrete specifications are given. Damage caused by volume expansion of industrial fill is described. 1.

INTRODUCTION

In the disposal of industrial wastes as landfill, considerable emphasis is given to the content of constituents such as heavy metals which may pollute the environment. The landfill is then considered environmentally safe to build on. It is, however, not necessarily possible to assume that concrete foundations built on such fill will be immune from chemical attack. Waste material may contain sulphate, sulphide, nitrate, chloride, or other species which, in addition to being pollutants, are capable of causing severe damage to concrete foundations. Aggressive species may occur naturally, and many clay strata contain sulphates. Industrial wastes can include materials considered suitable either in the past or at the present time as sub-base materials, such as fly ash, blast furnace slag, unburnt coal shales, or bricks and mortar used as hardcore, all of which can give rise to potentially aggressive species towards concrete, or cause very damaging volume changes. 2 CLASSIFICATION OF SOIL CONDITIONS

Table 1 of BRE Digest 363 [l] classifies soil or water conditions which may lead to sulphate attack (Table 1). The most widely found form of attack involving sulphate, is by sulphate in groundwater, which diffuses into the concrete and attacks the hydrates formed by the hydration of tricalcium aluminate to form ettringite, [ 3CaO.Al 0 .3CaSO .32H20], with consequent disruption by eqnsion. Following dishgtion 04 the cement paste by the ettringite expansion, the sulphate solution can then attack the calcium hydroxfde present in the cement paste to form gypsum, resulting in further expansion. The relationship between the tricalcium aluminate content of cement and vulnerability to sulphate attack is generally recognised and has led to the development of sulphate-resisting cements, whose predominant feature is their low tricalcium aluminate content. The mechanisms of attack where the solution is effectively sodium sulphate, were discussed by Cabrera and Plowman [ 21 , both for materials containing Ordinary Portland cement alone, and also for materials containing flyash as a partial cement replacement. Essential differences found where flyash was included were:1. Diffusion of sulphate into the matrix was at a much lower rate than for the cement alone. This was attributed to a reduction in the permeability of

918

Table 1 Classification of concentrations of sulphate and magnesium In soil or fill

In groundwater

the paste by the pozzolanic reaction. There is only limited formation of ettringite; the principal reaction products are monosulphate [4Ca0.A120 .CaSO .12H 0 ) and other members of the solid solution series of hexagonal h#dratej forded between the monosulphate and tetracalcium aluminate hydrate [ 4CaO.Al 0 ,1314 01 , which are stabilised by the incorporation of sulphate into the2s$ruct&e. Consequently, less disruption of the matrix occurs. 3. Less calcium hydroxide is present in the cement matrix due both to the presence of less cement, and the pozzolanic reaction. Subsequent studies of flyash concretes have confirmed the formation of stabilised hexagonal hydrates under a variety of site conditions, In concretes where some of the cement is replaced with ground granulated blast furnace slag, a pozzolanic reaction also takes place, resulting in a reduction in permeability, and also a reduced calcium hydroxide content. The improved performance of slag cements compared with cement alone for sulphate resistance has long been known [ 3 J , Table 2 gives the requirements in BRE Digest 363 [ I ] in terms of cement type, and content, and waterlcement ratio for the different conditions in Table 1 (for well compacted cast-in-situ unreinforced concrete 140mm to 450mm in thickness exposed on a l l vertical faces to a permeable sulphate soil or fill). The cement types are currently to the appropriate British standards, which are in the process of replacement by the corresponding European standards, Modifications to Table 2 are necessary for certain situations of exposure to sulphates. For instance, for concrete floors, a membrane is recommended between fill or hardcore and the floor for Class 1 or 2 conditions, and Classes 3, 4, and 5 are not recommended for use as a base for concrete floors. Classification is increased by one class for basement, embankment or retaining walls where there is a hydrostatic head by the groundwater greater than 5 times the thickness of the concrete (unless other precautions are taken). The conditions in Table 1 refer to permeable soils which give rise to mobile groundwater: if the water is considered essentially static, a reduction of one class may be made. 2.

919

Table 2 Cement type and content, and water/cement ratio Class

Cement type

Minimum cemegt content kg/m (Notes 1 and 2)

Maximum free water/cement ratio (Note 1)

1

A/B/C

Note 3

0.65

4A 4B

B C

360 380

0.45 0.45

5A As for Class 4 t surface protection 5B ........................................................................ Note 1. Cement content includes flyash and slag. Note 2. Cement contents relate to 20mm nominal maximum size aggregate. Minimum cement contents should be increased by 4Okg/m for lOmm aggregate, and decreased by 30kg/m for 4 0 m aggregate. Note 3. Cement type A is Portland cement, or Portland cement/blastfurnace slag or flyash. Cement type B is sulphate-resisting Portland cement. Cement type C contains Portland cement/blast furnace slag or flyash, with specified ranges for slag or ash contents. 3. MAGNESIUM SULPHATE ATTACK Magnesium sulphate attack is more aggressive, since not only is there reaction with the calcium aluminate hydrates as in sodium sulphate attack, but a direct reaction with the calcium silicate hydrates and calcium hydroxide. Ettringite, gypsum, hydrated magnesium silicate, and brucite [Mg(OH) ] are found in the reaction products. The more aggressive nature of magnes& sulphate attack is reflected in the more stringent requirements given in Table 2: however in severe conditions neither the use of sulphateresisting cement nor incorporation of cement replacements will provide lasting protection. Lawrence [ 41 has discussed magnesium sulphate attack in the overall context of sulphate attack. 4.

ACID ATTACK

Sulphuric acid and sulphates in acid solution frequently result from industrial wastes. These include colliery waste, ash from the combustion of coal from older power stations or from refuse incineration, or gasworks waste. Other acid solutions containing hydrochloric or nitric acid can result from particular industrial processes. In land previously used for the carbonisation of coal, a weak acid is formed from the solution of phenol in water. Waste creosote may also give rise to phenols, cresols, and other organic acids. Other organic acids may be produced which also cause attack. Lactic acid has caused severe attack on concrete dairy and cheese factory

920

floors, and also on mortar in tile floors; citric, malic, tartaric, and acetic acids cause similar attack to lactic acid [5]. Harrison [ 6 J reviewed recommendations for the type of concrete suitable for acid conditions and presented data on performance in field and laboratory studies. Virtually all acid conditions will attack concrete in the ground: the cement paste and calcium hydroxide which is produced as a result of the cement hydration are directly attacked. Well-cured concrete with a low water/cement ratio, and a pozzolanic replacement such as flyash or slag, with low permeability will be beneficial, although to a limited extent only. Severity of attack depends primarily on the ground conditions; in particular the pH, but also the mobility of the groundwater. For ground containing wastes, a pH above 5.5 in static ground conditions is considered to be relatively non-aggressive, but slightly aggressive if the groundwater is mobile. A pH of 4.5 to 5.5 is moderately aggressive, and less than 4.5 is highly aggressive, again, particularly with mobile groundwater. In low pff conditions, surface protection will be necessary. 5.

THAUMASITE FORMATION

Thaumasite [CaSiO .CaCO .CaSO .15H20] has been identified in a number of sites where detdriorakon 40f cementitious materials has occurred. Thaumasite is structurally similar to ettringite, and may occur together with ettringite. Crammond and Nixon [ 71 described field investigations and studies of laboratory mortars. The optimum conditions are consistently cold, wet environments, along with readily available supplies of calcium silicate, sulphate ions and carbonate ions. Where concrete contains a finely divided source of carbonate ions, the reaction can proceed very rapidly, even where the concrete is of good quality, or a sulphate-resisting cement is used. A source of magnesium ions, even in small amounts, encouraged thaumasite formation. Although it is not clear whether degradation by thaumasite formation is a widespread phenomenon, the use of concretes, mortars , etc containing limestone fines in cold, wet conditions, where sulphate is present in groundwater, should be treated with caution. 6.

SODIUM SULPHATE CRYSTALLISATION

Novak and Colville [ E l reported the formation of efflorescent salts on the surface of degrading concrete slabs in California. They attributed a possible cause of the degradation to pore pressure exerted by crystallisation of thenardite [Na SO ] , and the conversion of thenardite to mirabilite [Na SO .10H 01. A like?y dource for the sodium was weathered and poorly crystalhsdd sadium plagioclase feldspar in the soil, but found no source of sulphate. No gypsum, ettringite, or thaumasite was detected. Plowman [ 9 ] found degradation of concrete bricks in a housing scheme in the UK due to thenardite crystallisation. No mirabilite, gypsum, ettringite, or thaumasite was detected. Although the soil contained only relatively low concentrations of sulphate, the proposed mechanism was by concentration of salts in the groundwater due to capillary action in a boundary zone at ground level, with evaporation of the solution within the bricks. Matsushjta and Suga [lo] described a similar formation of thenardite and mirabilite in building foundations built on land reclaimed with unaltered coal waste in Japan. They found that deterioration was due largely to the formation of gypsum and ettringite, but considered that sodium sulphate crystallisation was also an important contributory factor.

92 1

It is significant that this mechanism can apparently occur where ground conditions would not necessarily be regarded as deleterious, i.e. a low sulphate content of the groundwater, The presence of sodium sulehates in efflorescence salts has been observed in low sulphate ground conditions; a concentration mechanism by capillary action was demonstrated in the laboratory by Matsushita and Suga. The mechanism appears to depend upon continuously wet ground conditions, with damage occurring where drying and crystallisation is within the concrete rather than on the surface. 7

FLYASH USED AS LANDFILL OR STRUCTURAL FILL

The use of flyash as landfill or structural fill involves the addition of water - typically 20-25% by weight - which causes a limited amount of hardening and development of a low strength. A comprehensive survey of the soluble alkalies in UK ashes was carried out by Sherwood and Ryley [ l l ] , in which they showed that only trace quantities of sodium, potassium, and magnesium ions were taken into solution, and that the principal soluble ions were calcium and sulphate. Gibergues and Vaquier [ 1 2 ] also found that the principal ions leaching out were calcium and sulphate: solution of calcium and sulphate was rapid and simultaneous, and gypsum precipitated on standing. Raask [ 1 3 ] reported an immediate 'acid flash' due to the faster solubility of sulphate, but calcium subsequently went into solution, and the final pH was 8-9; for a more alkaline ash, the pH rose immediately above 11. Cabrera and Plowman [ 1 4 ] studied the rate of solution of calcium and sulphate, and the rate of change of pH in detail for a typical low calcium ash. The pH and solubility study was carried out with a 5 : l water:ash ratio. Gypsum formation was studied by X-ray diffraction using a 1 : 5 water:ash ratio. The pH/time relationship is shown in Figure 1, the concentration/time relationships for calcium and sulphate are shown in Figure 2 , the increase in gypsum formation with time is shown in Figure 3 . The low initial pH is the result of very rapid solution of sulphate adsorbed on the surface of the ash particles in the electrostatic precipitators in the power station. Release of calcium into solution causes a gradual rise in pH. The solution becomes supersaturated with respect to gypsum, which then precipitates, and further sulphate and calcium dissolve. The rate at which the solution becomes saturated depends on the water/ash ratio; at the lower ratios which occur in landfill, the precipitation of gypsum is extremely fast, as can be seen in Figure 3 . The formation of gypsum is responsible for the hardening of the ash, and since calcium and sulphate are the only ions released in significant quantities, the material will give rise to only limited sulphate conditions (Class 2 in Table 1): the limit for Class 2 conditions is in fact deliberately set at the solubility of g y p s p . This mechanism is responsible for the fact that in the UK, ash used as fill in contact with concrete foundations does not cause a significant rate of sulphate attack. The same mechanism holds for almost all low calcium ashes, but care must be taken in applying the same criterion to high lime ashes, since these may have a significant level of soluble sodium or potassium, which have more soluble sulphates. It is suggested that a solubility test should be carried out if the aggressive potential of the ash is in doubt. 8

VOLUME CHANGES DUE TO PYRITES OXIDATION

Many waste materials such as colliery shale contain iron pyrites (FeS ). Where atmospheric weathering can take place, there is the possibility tiat the pyrites can be weathered to give products of greater volume, which may lead to expansion [ 1 5 ] . Grattan-Bellew and Eden found that drainage of

922

9

8

7

P" 6

5

4

3

b

I60

do

4 k TIME

Figure 1.

10.

- sbo MIMS.

TI0

Joo

Variation of pH with time for water:ash ratio of 5 : l .

0

so3

A cao 25.

Figure 2.

Solubility of CaO and SO3 with time for 5:l water:ash ratio.

923

U Y

A

.-t v) c

W t

c -

Figure 3 .

Rate of formation of gypsum for a 1:5 Water:ash ratio.

marshland led to oxidation of pyrite in shale beds, and the resulting formation of gypsum between the shale layers led to a volume increase which caused floor heave. They also proposed a series of oxidation and base exchange reactions for the oxidation of pyrite to jarosite [KFe (SO ) (OH) 1, which also results in a volume increase. The reactions can h s o 4 jiberite sulphuric acid, with the potential for both sulphate and acid attack on concrete with which it is in contact. An investigation was carried out by Nixon [16] into floor heave in houses built on shales which were both from a quarried source and waste from an ironstone mine. Deposits of both gypsum and jarosite were found in the quarried material, but only jarosite in the ironstone shale. Nixon recommends that shales likely to cause heave may be identifed by X-ray diffraction, together with total sulphur, acid-soluble sulphate, and calcium contents. The shale should be regarded as potentially troublesome if the total sulphur content (as sulphate) is greater than the acid-soluble sulphate, and a significant quantity of acid-soluble calcium is present. The author has investigated instances of pyrites oxidation of shales where both gypsum and jarosite were formed, and had caused floor heave. In most instances oxidation was virtually complete, but an X-ray diffraction examination, and analysis as recommended by Nixon is always necessary to ensure that no significant amount of pyrites remains. 9

VOLUME CHANGES DUE TO EXPANSIVE STEEL SLAG

Crawford and Burn [17] described an example of building movements due to an expansive steel slag backfill under a floor slab. Fresh slag contained substantial quantities of unslaked lime (Cao) and periclase (MgO). The

924

determine a total MgO content, since in many materials this is largely, or even entirely, present in the form of magnesium silicates, or other magnesium compounds which are not susceptible to the hydration reaction. 10 CONCLUSIONS

The disposal of industrial waste as landfill can give rise to chemicals in the groundwater which can cause damage to concrete foundations. Sulphate can arise from a number of sourcesI including pyrites oxidation. If the groundwater contains magnesium, or is acidic, more severe attack may occur. Different mechanisms of attack may be observed: in addition to the conventional form of sulphate attack by the formation of ettringite and gypsum, thaumasite formation can occur, or sodium sulphate crystallisation, The use of pozzolanic cement both of which cause severe damage. replacements such as flyash or ground granulated blast furnace slag can alter the permeability and mechanism of the severity of attack, If the landfill is a low-calcium flyash, the sulphate content of the groundwater will generally be limited to the solubility of gypsum. BRE Digest 363 classifies the severity of sulphate conditions, and recommends concrete specifications for the different classes. In addition to attack on concrete, industrial fill can cause disruption to buildings constructed on it by volume changes within the fill due to pyrites oxidation or expansive steel slag. Extracts and Tables from BRE Digest 363 are included by permission of the Director of the Building Research Establishment. REFERENCES 1 2 3

BRE Digest 363, July 1991. J, G. Cabrera and C, Plowman, Adv. Cem. Res,, 1 (3) 1988, 171. W. Gutt, W. Kinniburgh and A. J. Newman, Mag. Concr. Res., 19 (59), 1967, 71.

4 5 6

7 8 9 10 11 12 13 14

C. D, Lawrence, Mag. Concr. Res., 42 (153) 1990, 249. F. M. Lea, The Chemistry of Cement and Concrete, 3rd ed. 1970, 661. W. H. Harrison, Concrete, 21 (2) 1987. N. J. Crammond and P. J. Nixon, Conf. Durability of Building Mat. and Comp. 6, 1, Japan 1993, 295. H. Matsushita and I. Suaa. Conf. Durability of Buldina Mat. and ComD. 6. 1, Japan 1993, 647. G. A, Novak and A. A. Colville, Cem. and Concr. Res., 19, 1989, 1. C. Plowman, An investigation of the cause of degradation.of concrete bricks (unpublished), P. T. sherwood and M. D. Ryley, Road Res. Lab. Rep. no. 49, 1966. A. C. Gibergues and A. Vaquier, Mat. Const. no. 32, 1973, 141. E, Raask, Int. Symp. Use of PFA in Conc., Leeds, 1982, 5. J. G. Cabrera and C. Plowman, Int. Symp. Use of PFA in Concrete, Leeds a

1982, 15 P. E. 1975, 16 P. J. 17 C. 8.

.

I

111.

Grattan-Bellew and W. J. Eden, Canadian Geotechnical Journal, 372.

Nixon, Chemistry and Industry, March 1978, 160-164. Crawford and K. N. Burn, J. Soil Mech. and Found. Div., Am. SOC. Civ. Eng., NOV. 1969 pp. 1325-1334.

.

Environmental Aspects of Construction with Wute Materials J.J.J.M. Goumans, H A . van &r S h t and Th.G. Aalbers (Edtors) el994 Elsevier Science B.V. AN rights reserved.

925

Contaminated soil cement stabilizations for application as a construction material. P.J. Kroes' and J. van Leeuwen2 IWACO B.V., Consultants for Water & Environment, P . 0 . b ~8520, 3009 AM Rotterdam, The Netherlands

*

Gemeentewerken Rotterdam, Ingenieursbureau Geotechniek en Milieu, P.O.Box 6633, 3002 AP Rotterdam, The Netherlands

Abstract Possibilities for using non-cleanable contaminated soils as an alternative for sand in cement stabilizations, have been studied with respect to physical properties (compressive strength and durability) and leachability. Typical soil parameters like organic matter content, clay content and contaminant type and concentration that may effect the compressive strength have been investigated. It can be concluded that contaminated soil cement stabilizations conform to the construction engineering criteria and leachability standards and have potential application as an alternative for sand cement stabilizations. 1. INTRODUCTION

The excavation of primary surface minerals like sand meets more and more opposition as a result of the negative environmental aspects. The excavation policy in the Netherlands strongly advocates the application of alternative materials, including waste materials and industrial residues. The policy of the national government regarding waste materials in general offers an additional strong stimulus towards minimizing the dumping (landfilling) of waste materials and where possible, an efficient reuse. In the city of Rotterdam @art of the highly industrialized and densely populated area of the Rijnmond in the west of the Netherlands) large quantities of contaminated soil are being excavated because of remediation of sites and earth works. For the category noncleanable contaminated soil that is being landfilled the possibilities for application as an alternative for sand in cement stabilizations have been investigated [l]. These soil cement stabilizations can find there application in civil engineering constructions as can be shown in figure 1.

In the Netherlands there is little experience with respect to stabilizing contaminated soil with cement. Factors that can influence the compressive strength are the contaminants and the more heterogeneous matrix of soil (organic matter, lutum) in comparison with sand.

926

Figure 1. Application of cement stabilization in a road bed construction

2. MATERIALS AND METHODS Soil samples from 13 different sites in the Rotterdam region, from the above mentioned category, have been selected for this research. Each soil sample consisted of about 150 kg. The typical soil parameter contents and contaminant contents researched are summarized in table 1.

Soil samples 1-13

Dry matter

Organic matter

(%)

(%)

72-94

1-14

Lutum

Pb

cu

(%)

@pm)

(ppm)

0.34

7-11500

13-790

Zn (ppm) 83-900

Cd (ppm) <0.5-17

As (ppm) <5-18

@pm)

Fines (<63rm)(%)

1-340

11-36

PAH (16EPA)

Explanation: < below detection limit

The first step was to characterize the soils i.e. grading, humus, clay and moisture content and possible retarding properties on hydratation of cement from the organic matter (organic acids). After the characterization, the soil samples are mixed with different cement contents (up to 22% wlw dry matter) at the initial moisture content. The compressive strengths are investigated according to the RAW Standard Conditions [2]. The durability is tested by carrying out drylwet en freezelthaw cycles on the stabilizates. The leachability of the soil-cement stabilizations is investigated by carrying out a tank leaching test [3] on three selected mixtures. The results are compared with leachability standards [4][5]. The factors that influence the compressive strength have been investigated by carrying out correlation analysis.

927

3. RESULTS AND DISCUSSION The main construction engineering criterium for sand cement stabilizations is a minimum compressive strength of about 5 MPa after 28 days of curing. This criterium has also been chosen for the minimum compressive strength of the contaminated soil cement stabilizations. It is found that the main soil parameter that correlates with (influences) the compressive strength is the moisture content. The ideal maximum water/cement ratio is 1 (table 2). Table 2.

Mixtures at initial moisture content

Soil samples

Moisture content

Cement conlenl

46

46

Waterlcementratio

Compressive strength (MPa)

5,1 6,l-7,7 63

A (6,8 and 12)

10- 14

12

B (5. 10 and 11)

15 - 19 20 - 24

17

= I -1

22

= I

C (1,2,3 and 4)

In table 3 the contaminant contents of the investigated mixtures are summarized. Table 3.

Contaminant contents of the mixtures (mg/kgdm)

Component

A

B

C

14 92 320 300 870 560 24

6,O 0,33 19 61 420

14

~~~

As Cd cu pb

Na Zn PAH (16EPA)

150

23

0.65

330 940 520 250 5.5

The organic matter content also correlates with the compressive strength although the humific acids do not contain retarding properties on the hydration of cement. This may be due to the fact that in the investigated soils the moisture content is related to the organic matter content. The contaminants do not correlate at these concentrations with the compressive strength. With respect to the durability of the contaminated soil cement stabilizations, the dry/wet cycli did cause some mass changes but didn’t cause disintegration of the samples. The freeze/thaw cycli, however, caused volume changes for all samples and disintegration of about 20% of the researched samples. Therefore the products have to be optimized and till then it is not recommended to work under freezing conditions. The leachability research has been carried out on the mixtures of A, B and C from table 2. The results are expressed as cumulative emissions (mg/m*) and are summarized in table 4. The cumulative emissions of these contaminated soil-cement stabilizates are far below the leaching standards for A-type and B-type applications [4][5].

928

Table 4.

Cumulative emission ranges (mg/m2) at t=64 days

Component

Min. emission

Max. emission

U1A

U2A ti, U1B

40

300 7s 350

1,o

Na Zn phenanthrene

2,944.9 0-0,9 5570-6640 0.05-0,lI

4,O-34,9 7,O-7.1 5570-6640 140-142 0,05-0,1I

50 100 200

800

I500

Explanation of symbols of table 4: min. emission; concentrations below the detection limit are accounted for as zero in calculating the cumulative emission; max. emission; concentrations below the detection limit are accounted for as the detection limit in calculating the cumulative emission; U1 = leachability standard for category 1 restrictions (no blending with the underlying soil and duty to take the material back in the case that the construction has lost it's function) U2 = leachability standard for category 2 restrictions (next to category 1 restrictions also isolation and 0,7 meter above ground water level) A = A-type application (continuous wet) B = B-type application (only wet during the period of rain fall).

4. CONCLUSIONS It can be concluded that contaminated soil cement stabilizations have a potential application as an alternative for sand cement stabilizations. A critical parameter with respect to the compressive strength is the moisture content of the soils involved in relation to the amount of cement added. The leachability of the researched samples is far below the current leaching standards in the Netherlands. A demonstration project is intended to be carried out as a follow up to this feasibility study in 1994.

5. REFERENCES 1 2 3

4

5

IWACO B.V., "Immobilisatie van verontreinigde grond ten behoeve van toepassing als fundering in de wegenbouw", rapportnummer 10.2614.0, September 1993. RAW Standard Conditions of Contract for works of Civil Engineering construction 1990. Draft NEN 7345, Leaching characteristics of building and solid waste materials- Leaching tests - Determination of the leaching behaviour of inorganic components from building materials, monolithic waste and stabilized waste materials, October 1992. Tweede Kamer-stuk 22683: Brief van de Minister van VROM inzake het Bouwstoffenbesluit bodem- en opervlaktewaterenbescherming, ISSN 0921-737 1, Sdu Uitgeverij Plantijnstraat 's-Gravenhage 1992. Dr Th.G. Aalbers et al, "Milieuhygi5nische kwaliteit van primaire en secundaire bouwmaterialen in relatie tot hergebruik en bodembescherming", RIVM-rapport no. 77 1402005, 20 juni 1992.

Environmental Aspects of Construction with Waste Materials JJJ.M. Goumans, HA. van der SIoot and 711.G.Aalbers (Editors) a1994 Elsevier Science B.V. AN rights reserved.

929

THE ASSESSMENT OF POLLUTANT CHARGE OF DREDGED SEDIMENTS AS A TOOL TO MINIMIZE ADVERSE ENVIRONMENTAL EFFECTS E.Peris-Moraa; J. Monzoa; J. Payaa; J.M. Mesab aDepartamento de Ingenieria de la Construccion. Universidad Politecnica de Valencia. Espafia b

Departamento de Geologia Universidad de Sevilla. Espafia

Abstract A study of samples of materials obtained in "La Albufera" Lagoon, near Valencia, from the bottom of a eutrophic and polluted lagoon is presented. Chemical, Physical and biological analyses was done to evaluate different management possibilities in these materials. There are big amounts of clay and organic-calcareous and siliceous sand together organic matter from residual eutrophic wastes. The nature of sediments suggest different solutions for dredged materials: a) Prime material in building and construction industry (mainly cement and ceramics); b) Civil works materials in conventional civil engineering and ecological engineering (beaches and dunes restoration); c) Restoring aridized soils as material in composting. 1. INTRODUCTION A ambitious plan to transfer a big amounts of water between the different hydrologic basins is actually developing in Spain. Construction of new infrastructures: dumps, pipelines and channels will be constructed; as a part of important dispenses must be devoted to maintain the old constructions and to improve the quality of the water. Nevertheless there are not precise data about the quantity and quality of materials producing the filling up in the water reserves. Inaccurate data from several sources allows estimate in Hm3 the normal amount in most of natural and artificial water bodies in Spain. In table 1 are presented figures about rough assessment of filling up in same Spanish

930

natural and artificial ponds. These figures from different sources (1,8,Public Works Mtry.) allow take into account the panoramic knowledge of the problem. Table 1 ESTIMATION OF FILLING UP LEVEL Pond name: filling up period, years: Sichar Ma. Cristina Beniarre Forata Regajo Amadorio Guadalest Almansa Embarcadero Contreras BenagCber La Albufera

16 56 9 14 10 9 13 29 flood 1992 per year per year per year

filling up volume m3: 2 700 000 8 300 000 1500 000 1 530 000 780 000 3 461 000 2 580 000 476 175 7 800 000 933 000 600 000 between 160 000 & 285 000

The South-East Spanish region is included as a arid, pre-deserted area in the UNESCO map of world soils (7). The aridity on this area produces a big amount of fine materials carried off in the erosion phenomena. In this situation in the next future may be necessary to forward the dredging to: a) recover the capacity of artificial ponds; b) to restore the ecological values in the natural ones. Same of these ponds are eutrophic, having the bottom sediments contents big quantities of organic matter; other are highly polluted because industrial sources. The sedimentary materials in big amounts, are usually highly polluted (9) and it will be a source of troubles in his management when it will be dredged. 2. THE ALBUFERA LAGOON The Albufera Lagoon, near Valencia city, has a well known evolution since XI1 century (200.000 Has) until nowadays near 2.837 Has. His basin, with 90.000 Has, collects water over a industrial area with more than 1.000.000 inhabitants. The old waste water collectors produces a big amounts of urban and industrial pollution. The body water is a shallow reservoir 1 m deep surrounded

93 1

by an extensive protected area of 21.000 Has. It has an important value as nesting and migration birds area. The water quality has been studied during last years (4) and evaluated the hipereutrophic state moreover a various chronic and acute kinds of industrial pollution (5). In the most of the areas, the bottom materials are a black colored paste ('ltarkim'' locally named) (3) with a high level of accumulated persistent pollution, heavy metals from industrial activity and organic matter within from the urban pollution and from the self productivity in the lagoon which acts as a natural depurator system.

3. MATERIALS AND METHODS The Albufera Lagoon (Figure 1) is on the Valencia Gulf. Was produced because of filling up phenomena during the Cuaternary period over a substrate produced by subsidence during Miocene period. Eight sample points were choused in the same situation where the waters have been extensively studied before (6). Samples were collected by 2 meter length PVC corer 50 mm diameter on the surface of bottom. It corresponds with the more recent sediments. The Tube was sink in the underwater ground until the deeper position, recovered and tapped; later, in the laboratory, the samples were frozen and cut in 20 cm length portions to obtain different levels information. Nevertheless the operation produces a compression of the materials, the consecutive levels correspond to sequence in sedimentation times. A total number of 41 samples were obtained and analyzed over 8 sample points (Figure 2).

Table 2 AVERAGE CONTENTS 2 Sample points ....... 1 organic matter % carbonates % Total Cr ppm Total Cu pprn Total Zinc ppm Total Pb ppm

5,5 13 4 4 19 11

14 19 19 23 50 39

3

4

5

6

7

8

16 22 19 24 70 36

17 25 25 15 47 31

21 23 4189 66 300 89

17 25 36 25 66 35

17 22 21 48 135 41

11 23 23 20 51 36

932

TR

0

Quaternary, Holocene Albufera Muds Quaternary, Pleistocene Glacis & Piedemonte Upper Miocene Limestones, Clays, Sands Upper Cretacic Alternation Limestone & Loam Figure. 1 Geologic situation Albufera Lagoon area (from Gutierrez Herrero, 1984)

2

4Krn

933

Figure. 2 Sample points situation and irrigation network

Analytical composition was developed by triacidic treatment and AAS. Organic Matter content was determinate by calcination to 550 '. Carbonates were determinate by calcimetrich method. Free O.M. and carbonates were analyzed by XRD with powder sample, direct and oriented aggregates, using the clay traditional methods (6).

4. RESULTS AND DISCUSSION Table 2 shows the average values in 8 sample points in Organic Matter, Carbonates and four Heavy Metals. Figures 3 to 7 content information about Organic Matter and several Heavy Metals as persistent pollution

5. ORGANIC MATTER AND CLAY MINERALS Sample point number 1, the nearest to shoal zone, presents lower pollution values and consequently a cleaner material. Organic Matter appears in big amounts in all the sediments as consequence of high rates of photosynthetic productivity because his eutrophic situation in the lagoon. The amount of O.M. in the different deep levels, corresponding different time deposition, shows his stability.

934

Carbonates in the majority of sediments, between 20 and 25 %, are presents as mineral, coming from erosion mechanisms, and in organic form, preceding from aquatic organisms. Clay minerals are the majority of all the samples with the exception of number 1. This sample presents sand nature and is clay exempt. Rest of samples presents fairly homogeneous character in all the lagoon. Samples, without carbonates and O.M.,present amounts near 80 % of clay minerals. The percentage can raise until 95 % in the deeper levels. Quartz is under 10 %; a little presence of Feldspars mostly under 5 % Well crystallized Illite is the most frequent clay mineral (between 60/70 %). Chlorite are important in sample points 4 and 5 over 20 %. Smectites are present around the 10%; Caolinite is a minor component whit maxima abundance under 10 % in the three North sample points. 6. HEAVY METALS Cr, Cu, Zn and Pb have been analyzed by deep levels. All of them appear as enormous value in sample point number 5, especially in the more recent sediments consequence of modern pollution. This point is near a well identified industrial activity nowadays in several court pollution process. The layers under SO/lOO cm deep appear as more uniform concentration. Does not appears correlation between O.M. and H.M. contents, then is suggested the low importance of potentially presence of organ-metallic complexes.

935

35

30 25 20 15 10

5 0

2

3

4

5

6

7

8

sample point number/deep levels m 2 0 cm a 4 0 cm U S 0 cm 0 8 0 cm .lo0

cm H 1 2 0 cm

Figure. 3 Organic Matter contents in different deep levels ppm total Chromium

10000

1000

100

I

.. .. ........ .. .. .. .. .... ....

;;;;;i; .......

.. .. .. .. .. .. .. ....... ....... ....................

.........................

.. .. ,.. .. .. .. .. .. ....

;;;;;;: ....... .......

....

10

.. .. .-

1 2

3

4

5

6

7

8

sample point number/ deep levels m 2 0 cm m 4 0 cm

U s 0 cm

0 8 0 cm

mioo

cm W 1 2 0 cm

Figure. 4 Heavy Metals contents: Chromium

936 ppm total Copper

200

150

100

50

0

2

3

6

5

4

7

. . sample point number/aeep levels -

m 2 0 cm m40 cm =SO

8

,.

cm 0 8 0 cm m i 0 0 cm m 1 2 0 cm

Figure. 5 Heavy Metals contents: Copper

ppm total Lead

2

3

4

5

6

7

8

sample point number/deep levels m20 cm m 4 0 cm =SO

cm 0 8 0 cm ~ I O Ocm m120 cm

Figure. 6 Heavy Metals contents: Lead

937 ppm total Zinc

1000

800

600 400 200

0

2

3

4

5

6

7

8

sample point number/deep levels m 2 0 cm w 4 0 cm =SO

cm 0 8 0 cm .lo0

cm m i 2 0 cm

Figure. 7 Heavy Metals contents: Zinc

7. CONCLUSION The study of sedimentary materials in Albufera lagoon offers a double point of view consequences. One is the identification of a problem in a environmental protected area: the nature and quantity of sediments will be managed to avoid the persistent pollution in the bottom of the lagoon (Organic Matter, Heavy Metals, oxygen dissolved deficit, etc.). On the other hand, the nature of this materials offers a field of possibilities in materials recovering. The first application suggested of this big amounts of sediments, because of Organic Matter and clay minerals, is the application as sludge in aedaphic soil recovering (2, 5). However, the Heavy metals contents in same areas of this analyzed area, would must limit his application in alimentary crops (4). Is open the study of application of these materials in several building and construction-materials fields. The Organic Matter plus big proportion of clay minerals can be a useful blended mixture as cement prime material; a saving energy would be obtained because of high O.M. content in the claylcarbonated material. Civil works filling material is other way to use this big amounts of refuses. The ceramic Industry is the other big consumer of clay minerals, but the presence of mineral or organic carbonates can limit the direct application of this purpose.

938

8. REFERENCES: DUTCH DREDGING ASSOCIATION, 1990. Aquatic Pollution and Dredging in the European Community. Delwel Ed. ISBN 90-61-55430-6. The Ague. FULLER, W. et al. 1985. Soils in waste treatment 8i utilization. Vol I. Land Treatment Boca Rat. C.R.C. Press Inc.

.

KENT, A. et al. 1987. Color removal in a reservoir and the dredging and dewatering of the deposited waterworks sludge. J.Inst. Water Environ. Manag. 1 (13) 349-357 LICK, W. et al. 1987 Entrainements and dredged materials in shallow lake waters. J.Great Lakes Res. 13 (4) 619-628 OLSON, K. et al. 1988. Effect of scrubber sludge on soil and dredged sediment aggregation and porosity. Soil. Sci. 145 (1) 63-69 SCHULZT, L.G. (1964). Quantitative interpretation of mineralogical composition from X ray and chemical data for the Pierre shalle. Geolog. Survey. Prof. Paper 391-e SOTO, Q. 1990. Aproximacion a la medida de la erosion y medios para reducir 6sta en la Espafia peninsular. ICONA, Madrid, Fuera de Serie no. 1 pp169-196 UNESCO 1985. Methods of computing sedimentation in Lakes and Reservoirs. IHP Stewar Bruk. Rapp VICENTE, E.; MIRACLE, Ma.R. The coastal lagoon Albufera de Valencia: an ecosystem under stress. Limnetica, 8537-100 (1992)

Environmental Aspects of Consbuction wifh Waste Maferiafs JJJ.M. Goumans, HA.van der SImt and Th.G.Aalbers ( E d t m ) 91994 Elsevier Science B.V. All rights reserved

939

MINESTONE SUBSTRATUM BEHAVIOUR UNDER LOADING Skarlyhska, E. Zawisza Department of Soil Mechanics Agriculture, Krakdw, Poland K.M.

and

Earth

Structures, University

of

1. INTRODUCTION

The investigations of geotechnical properties of minestone were often conducted with respect to their prospective utilization river embankments. Minestone, however, can also be considered as substratum for building foundations as well as fill material in subsidence areas and excavations in regions degraded by industry or mining works. Therefore it is important in engineering practice to learn about the behaviour of the material under different conditions of utilization, during the building period as well as during the use of the structures. The poster presents the results of investigations on the deformation of minestone substratum formed in a model case. The investigations are aimed at determining the course of settlement and deformation of minestone under loading depending on its compaction and water conditions. 2. METHOD OF INVESTIGATIONS

The tests were carried out under two different water conditions: * Saturated substratum. After forming the model substratum havi.ng 8-9 % initial moisture content, water was supplied from the bottom, Two experiments were performed on: slightly compacted substratum of Is= 0.80, loaded to 193 kPa (Experiment l), highly compacted substratum of Is = 1.0, loaded to 438 kPa (Experiment 2), * Substratum not saturated in the first phase of loading. The model substratum had an initial moisture content of 7 % and a compaction index of Is = 0.91. It was gradually loaded to ca. 9 5 kPa and at that point saturated for about 3 days. Loading was than continued to the final value of 438 kPa. The substratum remained under this loading for more then 1.5 months to estimate the course of settlement under constant loading (Experiment 3). In all experiments the plate was loaded at 24.52 kPa by steps in

940

surfaces of the substratum was measured. After completing the the moisture content of the material was recorded.

tests

3. RESULTS

1. Compaction of the minestone substratum at Ie = 0.80 is inadequate for a building foundation, since the material under saturated conditions shows substantial and long-lasting settlement (Fig.1) as well as very low deformation moduli ( < 2 MPa). 2. When the compaction index of the saturated material is Is = 1.0 the settlement process is very favourable. Within the loading range 0-438 kPa the relationship between loading and settlement is almost a straight line and the deformation moduli are mainly 20 MPa. 3 . When the compaction index is I . = 0.91 and the substratum is saturated at the load of 95 kPa it is found that saturation causes extra settlement. Prior to saturation the deformation moduli reaches 30 MPa. After saturation the moduli values decreases relatively quickly from 25 MPa to 2 MPa. The final value at plate loading of 438 kPa is close to the ultimate bearing capacity of the substratum. 4. The results show distinctly a lflubricatingll action of water, ir the saturated Substratum, enabling better reciprocal packing of rock grains and particles. This increases the strength parameters of the minestone resulting from its consolidation. This signifies that more favourable conditions of substratum work under loading can be achieved when the minestone of high moisture content or even fully saturated is compacted. It should be mentioned, however, that an excess of water may be dangerous when the material has a high content of sand and silt size fractions or when it can be easily disintegrated mechanically.

4-

1

-

Fig. 9. Settlement of minestone fill vs loading. minestone saturated at the beginning: a - IS = 0.80, b - 10 = 1.0 2 minestone saturated under loading of 9 5 kPa: 10 = 0.91

-

Environmental Aspects of Consmction with Waste Materials JJJM Goumans, H A . van &r S l w t and Th.G.Aalbers (Edtom) el994 Elsevier Science B.V. AN rights reserved.

94 1

Ecological and energy-savingadvantages and benefits of building withearth Hugo Houben CRATerre-EAG, Centre Simone Signoret, BP 53, F-38090 Villefontaine, France

Abstract Unlike competing technologies, the building material unfired earth, naturally made up of gravel, sand, silt and clay, can be used a s such after extraction, without using techniques which are sometimes very polluting or which consume a great deal of energy, such as firing (most often using organic combustibles). Building with unfired earth also contributes to the preservation of the ecological balance: vegetable cover, water resources, o r even aggregate resources (such a s sands, gravel) extracted from a quarry o r a river-bed. It results in energy savings which, on the scale of the building sector, reduce the debt of developing countries. From a cultural and social point of view, this technology has a remarkable capacity to adapt t o the aspirations of local populations, and enables them to take responsibility themselves for producing their own built environment. The text which follows illustrates some of this potential using examples from the field. Indexwords Energy-consumption, deforestation, e a r t h e n architecture, cultural environment, appropriate architecture. 1. REDUCING ENERGY-CONSUMPTIONFOR PROCESSING The production of industrially manufactured building materials and semifinished products uses up an extreme amount of energy. As we can see in the following list : to produce 1 kg of cement needs 1 kWh of energy. Steel needs about 7 kWh, aluminium more than 70 kWh per kilogramme. A cubic meter of concrete uses up 400 to 800 kWh. To produce common perforated bricks one needs 590 kWh/m3 and for solid bricks even 1 140 kWh/m3. This means solid bricks need about twice as much energy a s concrete. On the other side, natural materials such as earth need only up to 5 kWh per cubic meter. Therefore concrete needs about 100 times as much as earth. The reason for this is that, in the case of cement for example, much energy is required not only to burn cement, but also to pulverize, pack, and transport it.

942

However, for the production of earth bricks or for the construction of a rammed earth wall, no energy is needed for the material itself and only very little for transportation and the handling on site. Table 1. BUILDING MATERIAL

kWh/m3

Solid bricks Perforated brick Porous light weight bricks Sand lime bricks Cement Concrete Precast concrete Earth Timber Chipboard Mineral wool Glass wool Flat glass Steel (plates) Aluminium (sheets1 PVC Polystyrene foam

1140 590

kWh/kg

400 350 1

500 800

5-10 600 1100

100 150 15000 6 100 195000 12 800 470

5

5 6 7.7

72.5 9.5 19

2. ELIMINATING ENERGY WASTED ON TRANSPORTATION The decentralization of earth product production units using local resources allows very great transportation economies to be made. On the island of Mayotte, setting up 19 earth-block production units spread throughout the territory has enabled a saving equivalent to more than 4 million USD to be made over 10 years. 3. SLOWING DOWN DEFORESTATION The fact that raw earth has no high temperature firing stage (more than 1000 "C for industrialized materials) saves the environment from atmospheric pollution and protects it from massive deforestation. Fired clay stock bricks in Malawi for example are produced exclusively by Malawian tradesmen. The bricks are hand made and fired in "kilns" of approximately 100 000 bricks each. The kilns consist of stacked sundried clay bricks constructed with firing tunnels a t the base and smeared with mud on the outside for nominal insulation.

943

The firing is a very inefficient process even though Malawi clays vitrify a t a relatively low temperature. It is estimated that 60 tonnes of timber is required to fire 100 000 bricks in this manner. The resulting bricks are soft, fragile, irregular in size, and differ in strength and durability depending on how well the kiln was fired and their position in the kiln. Approximately 25 % of the bricks are broken during transport and handling and end up as hardcore. Very severe deforestation has resulted in restricted transportation of firewood which is now often moved a t night. The price of bricks is rising by the month and the quality (degree of firing) is decreasing. In the major commercial centres the price of bricks has doubled in the last two years. Programmes for converting this industry are taking place in this country and also i n Uganda, Mali, Burundi, Rwanda, Angola, Burkina Faso and many others. 4. MAXIMIZING THE ENERGY PERFORMANCE OF BUILDINGS

It is a recognized and scientifically proved fact that earth buildings consume less energy as far as heating and cooling are concerned. In regions where winters are harsh, savings in heating can be as high as 20 to 30%. In hot countries such as the south-west United States or Saudi Arabia airconditioning costs can be reduced to nil.

Figure 1. 250 m2 exhibition pavilion built by the Royal Commission of Jubail and Yanbu in collaboration with CRATerre-EAG a t Janadriyah in Saudi Arabia. It can receive up to 150 visitors a t 40 "C without recourse to high energy-consumption air-conditioning systems. 0 Th. Joffroy.

944

5. RECYCLING AND PROCESSING INDUSTRIAL, POLLUTING WASTE MATERIAL When bauxite, the raw material for production of aluminium is bauxite, is refined, it yields alumina, which in turn is smelted into aluminium. The red or brown mud is a waste product from alumina production and constitutes a considerable environmental problem because there is so much of i t - 30-40 million tonnes per year worldwide. Unless disposed of properly, it can contaminate the ground water and spread red dust over wide areas. Even when correctly managed, the unesthetic effect and the mere space requirement of the vast mud ponds motivate the continued search for economic uses. UNIDO (United Nations Industrial Development Organization) has undertaken a number of technico-economic studies on industrial use of red mud waste. These studies have been used to develop the technology used in China and for similar projects in India and Jamaica. In Shandong in the People's Republic of China, the traditional local brickmaking factories are able to use a mixture of brown mud from the Shandong alumina plant and fly ash from the neighbouring coal-fired power station to make bricks and tiles.

6.ERADICATING POLLUTION FROM HOUSEHOLD SMOKE Many programmes for introducing improved ovens which use earth-built structural and constructional elements in urban and rural areas allow housewives to achieve energy savings (of wood o r coke) in excess of 50%. In large towns such as Addis Ababa, where hundreds of tons of heating wood are burnt every day, pollution has been spectacularly reduced and deforestation greatly slowed down.

7. REMOVING THE NEED TO USE SCARCE WOOD Earth architecture, thanks to the use of structural elements such a s arches, vaults and cupolas, enables buildings which require no wood at all t o be put up. These techniques are increasingly used in the countries of the Sahel in order t o combat deforestation and avoid transporting imported timber over long distances.

8. PROTECTINGECOSYSTEMS Using raw earth has enabled the island of Mayotte to protect its lagoon ecosystem. Thus using sand from the beaches for the manufacture of cement blocks had t o be forbidden by law. Removing sand exposed the underlying clay layer which then dissolved into the water of the lagoon, thus asphyxiating the barrier reef coral. The parrotfish which fed on the coral caught diseases which contaminated the people

945

who ate them and whole villages were exterminated. Ten years of building with earth on the island has enabled this problem to be resolved. Building with earth also preserves agricultural soils, avoids causing the environmental problems resulting from the extraction of river sand, and in certain uses uses far less water than other building materials.

Figure 2. Solar house built a t Castellet mar, France), blending traditional and modern materials, earth, glass, etc., to increase performance in terms of strength and heat retention and to improve luminosity. (0 Pierrot. 9. CULTURAL ENVIRONMENT

There has recently been recognition, throughout the world, of the value of innumerable architectural masterpieces which have been built thanks to earth, using this creative, warm, and culture-specific architectural language.

10. APPROPRIATE ARCHITECTURE I t is now right to think of earth architecture in terms of the present and the future. There are many complementary advantages in mastering building with udired earth with regard to factors as diverse as the economy, energy, ecology, policy, diplomacy, culture, science and technology.

946

As a technology, building with earth has demonstrated that it is a material with its own right through the diversity of the solutions and benefits it provides from a n ecological point of view.

Figure 3. Housing intended for the EEC delegation a t Kigali, Rwanda, has enabled the development of non-polluting production industries suited to local resources. 0 Architechna.

11. CONCLUSION During the last decades when everything was based on economical growth, any ecological approach was considered as naive and simply discarded. Today, with world economies showing down continually, sustainable development becomes of prime importance. The idea of sustainable development is directly linked to the concept of global equilibrium. Global equilibrium can not only depend on "economical growth" but includes other factors such as socio-cultural wellbeing and ecology. The use of raw earth a s a building material can greatly contribute to the global equilibrium of our world. CRATerre-EAG received the "Technologies sans frontikres" award in 1989. The award is given in recognition of work carried out for environmental technology transfer suited t o the needs of developing countries.

947

Figures 4 and 5. Kooralbyn resort hotel and leisure complex a t Beaudesert, in Australia, which was built to integrate into its natural environment. The 100room hotel is built of earth. 0EAA P L .

948

12REFERENCES B. Baier, "Energetische Bewertung luftgetragener Membranhallen im Vergleich zu Koln, Germany, (1982). ...'I,

L.S.C. Brunette and partners, Blantyre, Malawi, (1992). G. Minke, "Ecological architecture : a demand", in Plea'86, International conference on passive and low energy architecture in housing, Pe'cs, Hungary, (1986).

UNIDO, Vienna, Austria, (1992). J. Dethier, "The renaissance of Architecture in France ; Raw E a r t h Architecture", France Information no 137, Ministere des Affaires Etranghres, Direction de la Presse de 1'Information e t de la Communication, Paris, France, (1990).

Environmental Aspects of Constnrction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and TI1.G.Aalbers (Editors) el994 EIsevier Science E.V. AN rights resewed.

949

FLY ASH AND SLAG REACTIVITY IN CEMENTS

- TEM evidence and application of thermodynamic modelling H.S. Pietersen' and J.M.J.M. Bijen' Dem University of Technology, Faculty of Civil Engineering, Materials Science Section, Stevinweg 1, 2628 CN Delft, The Netherlands. ( also lntron BV, Instflute for Materials and Environmental Research, Houten, The Netherlands). ABSTRACT

An overview is provided of the microstructural development of Portland cements, blended with fly ash (PFA) or granulated blast furnace slag (BFS). The results are linked to recent advances on the thermodynamic modelling of such cements and are used to explain experimentally obtained information on reaction products of these blended cements with transmission electron microscopy. The techniques elaborated may provide a materials framework to explain leaching characteristics, and to predict very long term stability (and durability) of waste products immobilized by cements. 1. INTRODUCTION

PFA and BFS. Pulverized Fuel Ash (PFA or simply fly ash) and Granulated Blast Furnace Slag (BFS) are secondary raw materials, which can be used mixed or interground with Portland cement, other cementitious materials and/or activators for cement manufacturing or in concrete'. Both materials are primarily applied for economic reasons. PFA' is a ponolanic material, which is collected from the exhaust gases upon combustion of powder coal in power plants. PFA is only able to react with a sufficient rate upon 'activation' in a highly alkaline environment. In Portland cement, PFA reacts with lime and water and produces cementitious compounds, commonly referred to as calcium-silicate-hydrates (CS-H or CSH-gel). The CSH produced in this reaction is very similar to the CSH formed upon hydration of ordinary Portland cements (OPC), but it usually contains elements derived from the fly ash in minor amounts. Fly ash is also able to form silica-gel like cementitious materials, if activated with specific (calcium-poor) cementitious binders or -activators. BFS - a by-product from the iron and steel making - is a (latent) hydraulic material which may react slowly by itself to form cementitious compounds. However, in order to obtain a sufficient reaction rate it is usually ground finely, followed by an alkaline activation. In case PFA is used to partly (635 %) replace cement one usually speaks of Porlland fly ash cernenf. Cements containing blast furnace slag are generally called blast furnace (slag) cement.

Reaction products in blended cements. From a civil engineers point of view, the properties of blended cements are very important. Much knowledge has been collected over the last two decennia. Summaries may be found in a report from the Portland Cement association [I], in the ACI International Conferences on Fly Ash, Silica Fume, Slag and Natural Pouolans in Concrete [2], in the report of the RlLEM Technical Committee 67-FAB [3] and the many proceedings of the Materials Research Society [4]. The way PFA and BFS react with ordinary Portland cement, has however not received much attention.

'

PFA (and some BFS which do not funil the criteria which have been drawn up for applications in cements are also used as raw materia) for Portland cement production. This thesis deals primaril with low-calcium fly ashes produced in some Western-European countries .which are ap roximately similar to tKa ASTM class-F 11 ashes. these fly ashes enerally,display ouolanic behaviour. Highc a h n fly ashes, such as the ASTM class-d;ly ashes, display hydraufc behaviour. simfar to BFS. The definition "portland 11 ash cementa is roposed in the European Prestandard ENV 197 for portland cements containing between 6 and135 % siliclous) f( ash. In (international llterature the term 'Yly ash composite (portland) cement" or "fly ash blended (port\an%cemant' is common1 used In the ENV 197 the term "composite cement" is resewed for cement containing both last furnace slag an$ elher natural- or Industrial ozzolana or (sillcious) fly ashes (both the BFS and the pouolana may be applied in quantities varying between 1850 %; the clinker content should at least be 20 %).

950 Knowledge of the particular kinds of reaction products formed in Portland fly ash cement and blast furnace slag stands for the basic knowledge, without which any explanation of propeffies will be limited. One of the major problems when studying the formation of reaction products, is the fact that they may not occur abundantly, and that in cements initially (almost) amorphous compounds (or gellike compounds) are formed, complicating identification. Still, as will be shown in this thesis, it is possible to find patterns when observing and analyzing (large amounts) of empirically obtained data. When using this way of approaching the problem the theoretical background, providing an explanation or interpretation of the results, is usually developed later on. Another method, which can not be applied without knowledge of the results of the previous one, is thermodynamic modelling. Thermodynamic modelling makes it possible to construct equilibrium phase diagrams of (parts of) any cementitious system. Knowledge of equilibrium phase diagrams is important, even when the system studied is dynamic (not at equilibrium), which will be the case at the onset of hydration. In this situation, it in fact enables the kinetic path of a reaction to be traced, and to determine whether the pore solution is undersaturated or supersaturated with respect to stable (or metastable) hydrates. Aim of this paper. This paper, which summarizes some of the result of the PhD thesis of the first author [5], starts with a brief introduction on the prime reaction product of portland (fly ash) cement, CS-H gel, and the development of microstructure in Portland cement (paragraphs 2, 3 and 4). Recent advances on thermodynamic modelling of portland cement (containing PFA or slag) are briefly touched upon in paragraph 5. In paragraph 6 and 7 the results of experimental studies using analytical transmission microscopy (TEM) on blended cements are summarized. 2. C-S-H MORPHOLOGY AND MICROSTRUCTURE OF ORDINARY PORTLAND CEMENT

C-S-H morphology. Since CS-H is the most important hydration product, its morphology is of interest for cement chemists. Four morphological types of CS-H-gel were distinguished from fracture surface by Diamond [6] with SEM. At early ages a Type I CS-H was recognized, a fibrous material, with fibre lengths of about 2 pm long. Type II is another early hydration product, with a honeycomb or rectangular network structure. Type I and II are also referred to as 'outer products', since they form on the original clinker phases. In older pastes, Type 111 occurs, a more massive form, consisting of tightly packed equal sized grains and up to 0.3 pm across. The 'inner product', or Type IV, displays a still more featureless massive form, and is exclusively observed in older pastes. Jennings et al. [7] identified with the TEM an early product, consisting of foils, flakes or honeycombs, and which appeared to exfoliate from the C,S surface; this was termed Type-E(arly). It is believed to be similar to the Types I, II and 111, which all appear to be identified because of their underlying 'foil' morphology (which may be modified or disguised by compaction, drying, etc.). Type IV C-S-H appeared also in TEM almost featureless up to the 100 nm level; only fine pore structures could be identified. With =Si NMR it is apparent that two CS-H species dominate Portland cement; Q' touter product') and Q2 ('inner product'). Although it can not be ruled out that other varieties exist, it is likely that this will not be in significant quantities [B]. Development of microstructure in Portland cement. The development of microstructure can be represented schematically by dividing the hydration in early, middle and late stages of hydration. The drawing in figure 1 is modified after Scrivener [9] and is largely based on HVTEM analysis. ,Early stage. Just after mixing, a gel layer (or membrane) is formed over the surfaces of clinker grains. This gel layer is amorphous, colloidal and especially rich in silica and alumina, but it also contains calcium and sulphate. After about 10 minutes AFt rods develop (2nd drawing). They are more abundant near the surfaces of aluminate phases, and nucleated either in solution or on the outer surface of the formed gel layer. Middle stage. The middle period starts about 3 hours after mixing and ends after about 24 hours (3rd drawing; approx. 10 hours). It is marked by a strong heat evolution, and a rapid formation of 'outer-product' CS-H (type I and II) and CH. Spherical aggregates of fibres, 2 pm in diameter, are often observed and result from the rapid hydration of small alie grains. CH is formed as massive crystals in the formerly water filled space; if nucleation sites are limited, the large CH crystals may even 'swallow' smaller cement grains. In the middle period, the C-S-H forms outwards in a thickening layer around cement grains, possibly also nucleating on AFt rods. After about 12 hours,

95 1 the C-S-H layer is 0.5-1.0 pm thick, and contact will be made with layers growing on adjacent grains. A structure of interconnected shells will form, and will play a major part in determining the final (mechanical) properties (which depend on the particle size distribution of the cement). At this stage a space (0.5 pm) will develop between the shells and the anhydrous clinker phases, which is believed to be filled with a highly concentrated colloidal solution. The mere existence of these spaces is evidence that the hydration reaction proceeds by dissolution-precipitation effects. It has been reported that in this period CH will precipitate on nucleation sites, such as PFA particles, or other (un)reactive admixtures [lo]. The middle period ends with a renewed growth of AFt crystals, with lengths of 1-8 pm. Their formation is associated with the right-shoulder on cement heat evolution curves; their formation implies an increase in the reaction of aluminate (or, less likely, ferrite). CS-H 'inner products' will start to form on the inside of shells from continuing alite hydration (4th drawing, approx 18 hours). Late stage. When the interconnected shells become thicker, their permeability will decrease, and CS-H will also be deposited on the inside of the shells. This is happening with such speed that the advance of the inward growing C-S-H is often taking place more quickly than the retreat of the alite grains. The continuing formation of 'inner product reduces any remaining separation between anhydrous grains and the hydrated shell (5th drawing, approx. 1-3days); any remaining spaces seem to be filled up after about 7 days, when the shells have become approximately 8 pm thick. As the aluminate phase reacts, the concentration of SOP-drops rapidly inside the shells, and AFm may begin to form here, directly from C,$ or by conversion of AFt (see also 1.6). AFt formed outside the shells may persist for much greater lengths of time, and perhaps indefinitely. Finally, the 6th drawing (approx. 7-20 days) indicates that sufficient 'inner CS-H has formed to fill the space between the anhydrous grain and the shell. After the spaces between shells and the anhydrous cores have been filled up, any further reaction will be slow, and will proceed through a topochemical mechanism: the paste will denslfy. Figure 1. Development of microstructure during the hydration of Portland cement.

952 3. DEVELOPMENT OF MICROSTRUCTURE IN PORTLAND FLY ASH CEMENT

The reaction products in Portland fly ash cements are generally similar to those formed in pure Portland cements. Apart from C-S-H, CH, AFt, AFm, hydrogarnet and calcium (silicium) aluminate hydrate (Stratlingite) have been reported [lI]. The major pouolanic reaction products are substituted calcium silicate hydrate gels, with additional anions and cations incorporated or sorbed into their structure (121. Another feature of a// Portland fly ash cements is, that the CH content is reduced after an initial increase (e.9. [13]). The initial increase is due to the acceleration of the alite hydration; the later decrease due to the pouolanic reaction. The fly ash, when fine enough, will act as a dispersing agent for the main clinker phases, and will provide abundant nucleation sites for the precipitation of the CH and CS-H. This is not insignificant, since it effectively avoids the crystallization of large CH crystals, which are not really functional in a cement paste. Another important aspect of fine PFA is that it will effectively occupy empty space between cement phases of unequal size, thereby simply acting as a tiller material. The relatively slow 'activation' of fly ash is attributed to the gradual development of pore water pH, a phenomena studied in detail in previous studies in Delft and elsewhere (e.9. 1141, 15)). Once the pouolanic reaction is triggered off, a gradual densification of the paste will take place. This paste desification process will be discussed in later paragraphs in this paper. The pouolanic reaction of PFA in cement continues to proceed in course of time, and often less than 50 % of the fly ash particles reacts with the cement within a year ([15];[16];117]). Figure 2 summarizes available data [17]. There is sufficient evidence that the pouolanic reaction will continue for many years [l8]. Provided a good quality fly ash is used, Portland fly ash cements will consequently display higher compressive strengths after prolonged periods of time. Figure 2. Degree of reaction of low-Ca PFA in Port/and fly ash cements, hydrated between 15 and 25 "C, as a f u n c t i o n of c e m e n t replacement and age; the numbers indicate kg of PFA reacted per 100 kg of Portland cement.

13

.q

2 10

20

10

PERCENTAGE R C P L A C E t l E N l

LO OF C E M i N T

SO BY

PFA

4. DEVELOPMENT OF MICROSTRUCTURE IN BLAST FURNACE SLAG CEMENTS

The microstructure of blast furnace slag cements is generally similar to that of Portland cement, except that initially layers of in situ formed reaction products on the outer boundaries of the slag grains will be formed. Backscattered electron images displayed up to 15 pm wide reaction rims after approximately one year [19]. Studies of a 180 to 885 day old granulated blast furnace slag cement with analytical electron microscopy ( E M ) revealed that both a cement hydration product (CHP), other than CS-H, and an 'inner slag hydrate' (ISH), resembling a hydrotalcite-like phase, were formed [20];[21]. Other studies also indicated the presence of low- or non-calcium bearing magnesium-aluminium hydroxide, similar to the naturally occurring mineral hydrotalcite, but of variable composition [22];[23]. Hydrotalcite is well known to be a reaction product of blast furnace slag cements: it is related to (Mg(OH), (brucite), in which some Mg2* is replaced by A13+ or Fe3+,and where the charge balance is maintained, by anions which occupy the interlayer sites.

953 5. THERMODYNAMIC MODELLING

The system CaO-Al,O,-SiO,-SO,-~gO-H,O. In the introduction attention has been given to the usefulness of thermodynamic modelling of Portland cement hydration. Initially, many researchers have evaluated the pouolanic reaction by making use of synthetic systems, or 'fly ash like' reactive starting compounds (see summary in e.g. IS]). The drawback of these methods is that it only provides detailed information on reactions taking place in non-Portland cement systems, which may be of little relevance to actual cements. Eventually, a Portland (fly ash) cement system will try to reach its thermodynamically stable condaion. So, although in practice other meta-stablereaction products may be detected in hydrating Portland fly ash cements, a thermodynamic approach, based on solubiliity experiments (or compatibility experiments [24]), may yield ultimately stable hydration product assemblages. The elegance and potential use of this approach is that a sound systematic scientific data-base is available with respect to the understanding and predicting of (blended) cement leaching behaviour on the (very) long term. Deteriorating mechanisms, such as the action of chloride or sulphate ions, may optionally be included. Fairly extensive (classical) studies were performed on the CaO-AbO,-H,O system by D'Ans and Eick [25] and Jones and Roberts (261. The system CaO-AI,O,SiO,-H,O was later studied by Dron [27]. A much more extended research program, based on the above mentioned studies, has recently been conducted by Glasser et al. ([28];[29];[30]). It is based on simplifying cement to a six-component system: CaO-AI,O,SiO,-SO,-MgO-H~O~ approximating about 95 % of most cement formulations. The phase relations in the calcic part of this system were verified with phase compatibility experiments. The Si0,-AI,O,-Ca(OH), phase diagram in figure 3 represents the phase relations achieved in the mature cements. Addition of sulphate to this system will cause the precipitation of ettringite (AFt) (or, at very high sulphate contents, gypsum). AFt has been shown to be compatible with most of the CASH phases. Addition of Mg to the system (in the case of blast furnace slag cements) is modelled through the precipitation of a hydrotalcite phase (M4AH,,, HT). One of the useful outcomes of this extensive research program was the development of a computer code, CEMCHEM. This program converts the bulk composition of fly ash and Portland cement into a stable hydrate assemblage. The calculation is based on the conversion of mass and the geometry of the phase diagram. Its principle is based on the subsequent precipitation of specific compounds. For instance, since AFt is the only SO,'- bearing phase in the model, the number of moles of AFt is given by moles S o p . The appropriate amounts of Al and Ca are assigned to this phase, and the residual blend composition is re-normalized to 100%. If the remaining specific blend falls in field 1 (figure 3), then the Al content is assigned to C,AH, and the Ca content is reduced accordingly. The number of moles of CS-H is calculated from the Si content, and the Ca content is reduced again (with the assumption of a CdSi ratio of 1.7 for the C-S-H). The remaining Ca is finally assigned to Portlandite. Figure 3. Phase relations in the system Si02-CaO-AIz0, and the six compositional ranges, considered in the program CEMCHEM (assuming a constant MgO, SO, and H20 concentration.

I

a: C2ASH8 b: C3ASH4 c: C3AS10.76lH14.481 d: C3AS(O 43)H(5.14) 0 . C3AH6 CSH 1 7

The six ultirnatety stable hydrate phase assemblages are: 40% A1203

1)

2) 3) 4)

5) 6)

CH, C-S-H (1.7), CAH,, AFt, HT, HO , 40 C-S-H (1.5-1.7), CAH,-CJAS,,H5,,,, A R , HT, HO , C G H (1.9,CAS,,H5,,+ C$S,,#4,.+gt AFt, HT, HZO C-S-H (1.2-1.5), C$So,,BH4,,-C,ASH4, AFt, HT, HzO C-S-H (1.2), CJASH,, CfiSH,, AFt, HT, H,O C-S-H (0.85-1.2),C+SH,, AFt, HT, H,O

Ca(OH12 60

80

100

954 CEMCHEM calculations. Calculations with CEMCHEM on Portland cement (type I) and fly ash EFA (see appendix A, table AI) resulted in figure 4. From this figure, it may be seen that the addition of only 8 % of EFA fly ash is (theoretically) sufficient to consume all calciumhydroxide in the pouolanic reaction. The incompatibility of stratlingite and calciumhydroxide is also clearly indicated. The authors of the CEMCHEM program pointed out that addlion of more than 35 % of fly ash to the Portland cement resulted in reaching the boundary of the established phase relations; phase relations in this Ca-deficient area are still poorly understood. A similar calculation may be carried out using a Portland cement (type I) and a CEMlJ blast furnace slag. Compared to Portland fly ash cements, the 'excess' CH is consumed upon addition of at least 20 % of slag. At high percentages of slag (55-75 %), as is the case with most commercial blast furnace slag cements, thermodynamically stable phase assemblages appear to consist of about 50 % CS-H gel with a very low Ca/Si ratio of about 1 , a silicious hydrogarnet (approximately 20 %), stratlingite (approximately 20 %) and hydrotalcite (8-10 %). In blast-furnace slag cements, the boundary of the established phase relations is reached only at very high slag contents (15-20%). The experimental results have been used to develop solubility models for the more stable cement hydrates. Provided that a particular hydrate assemblage is indicated, the co-existing aqueous solution composition may be calculated by 'dissolving' the relevant species to equilibrium, using for instance the available geochemical speciation programs. Limitations of thermodynamic calculations. In reality meta-stable reaction-product may be formed, which may convert extremely slowly to more stable hydrates. For instance, although C,AH, is calculated to be the only stable phase, in modern Portland cements only minor quantities are formed; only some older Portland cements appear to contain larger quantities. A crucial area, requiring further study, is the interaction of alkalies with the most important cement phase, C-S-H. By quantifying the partition of alkalies between the solid and the liquid phase, a more accurate representation of C-S-H solubility in alkaline solutions may be derived at ([32];[31]. One of the effects of alkalies (Na, K) is that they suppress the solubility of calcium when compared to a simple CaO-Si0,-H,O system; Ca/Si may thus be higher then calculated. In general, element substitution in hydrate phases, may cause the actual phase development to deviate from the one calculated here. Finally, also temperature may influence phase relations [32]. Figure 4. Predicted phase proportions for Portland cement with fly ash. The left graph displays the calciumhydroxide content (CHI, the C-S-H-gei content (CSH), the hydrogarnet content ( C & f B ) ,the stratlingite content (C,ASH$, the hydrotalcite content (HT) and the ettringite content (AFt); the latter two phases are only formed in minor amounts. The rfght graph displays again the results for CH, C&W, and CdH, but also indicates the presence of the three silicious hydrogarnets, which are predicted to be stable phases under specific conditions.

T

i

i

i

I

I

i

I

955

-

6. REACTION PRODUCTS IN PORTLAND FLY ASH AND BLAST FURNACE SLAG CEMENTS

Materials and experimental techniques. Samples of Portland fly ash cement (containing the 20 % m/m EFA fly ash) and a CEMlJ blast furnace slag cement (type A, containing approximately 65 % slag) were cast, and quickly transferred to sealed bottles and cured at approximately 20 "C. In both cases the water/solids factor was 0.40. Chemical analyses of the fly ash, the blastfurnace slag and the Portland cement are summarized in appendix A, table A l . The samples studied were demoulded after approximately 290 days; any remaining (free) water was removed by freeze drying. Further sample preparation for microscopy consisted of impregnating the sample with 'Araldite D',attaching the sample to a glass plate (using a resin which melts upon heating), and carefully polishing it to a thickness between 50-100 pm. Essentially, routine geological techniques were applied, except that non-aqueous media were used as polishing aid. Upon heating the glass plate the samples were cut loose with a razor blade and mounted on a TEM grid. Addfiional sample thinning was performed by ion-beam milling using argon ions accelerated to 5 KeV, with an ion-current of 50p. Prior to the TEM operation, the samples were coated with a thin carbon layer. The TEM study of the fly ash cement paste was performed on a Phillips EM-30, which was linked to an energy dispersive spectrometer, in order to be able to provide an impression of the sample (or spot) composition. The slag cement was studied on a JEOL 200EX microscope with a LINK AN10/855 EDS analysis system, at the University of Aberdeen, Department of Chemistry. Results and discussion. Ponland fly ash cements. A typical transmission electron micrograph of a PFA particle immediately surrounded by a clearly visible reaction zone, primarily consisting of radially fibrillar CS-H, is displayed in figure 5. The calcium-silicate hydrate appears to be quite porous, as compared to the CS-H deposited further away from the fly ash sphere. More difficult to recognize on the micrograph is a second layer (see arrow in figure 5), which is significantly more dense. This points towards some kind of (rhythmic) precipitation process. A detail of the fibrillar region is presented in figure 6. In the more dense CS-H region just outside this fibrillar region in figure 6 clusters of hydrogarnet like crystals are found (circles in figure 6). Rodger and Groves [33]were able to obtain diffraction patterns and quantitative microanalysis of similar material. Their results pointed at a silicious hydrogarnet phase with an approximate composition of C,AFS,H,,. It is important to note that both in this study, as well in the studies of Rodger and Groves the hydrogarnet regions are found within the original fly ash particle boundaries. The thickness of the fibrillar region(s) seems to vary between 300-1000 nm. The thickness of the denser outer region appears to be of the same order of magnitude, although this is more difficult to assess since this region (gradually ?) borders to the equally dense C-S-H from the Portland cement hydration. Ca/Si ratios in both reacted zones appeared to be similar to those found in ordinary Portland cement pastes, with ratios varying between 1.8 and 2.The outer zone contains somewhat more Al and especially K Rodger and Groves discussed the observed 'rhythmic precipitation. of CS-H hydration products surrounding fly ash particles in cement paste. They argued that this effect is reminiscent of a 'Liesegang ring phenomenon'. Such phenomena of rhythmic precipitation are observed in gels containing two diffusing species, which react if (locally) a specific critical supersaturation is reached [MI. In the case of reacting PFA glass particles, it may be assumed that upon 'activation' of the fly ash the silicium concentration on or near the fly ash particle surface rises (the silicium originates from the fly ash). At the same time the calcium concentration in the cement paste pore solution will rise. Taken together, this will lead to a local supersaturation of Ca and Si resulting in the precipitation of (dense) CS-H; such a process will occur when the pore water alkalinity will be sufficiently high in order to dissolve the fly ash glass. The CS-H precipitation depletes the region immediately next to the precipitating C-S-H with Ca and Si. At some distance of the first precipitate a new (dense) C-S-H precipitate may be formed, provided that diffusion of Si and Ca has again provided local supersaturation (this process explains the observation of Rodger and Groves of rhythmic precipitation of dense CS-H shells). The observed 'porous' fibrillar C-S-H is believed to be growing inward from the 'dense' C-S-H in conditions of lower supersaturation, occupying the 'empty' space between either the dense C-S-H and the fly ash surface or two dense C-S-H region.

956 Blast furnace slag cement. The principal hydration products which are formed in blast furnace slag cements are essentially similar to those formed in Portland cement; C-S-H gel, CH, CJH, and AFt. Increasing slag contents will gradually result in the formation of CASH, (incompatible with CH) and silicious hydrogarnets (see discussion in [30]). It is well known that during the hydration of blast furnace slag cements, (a) layer@)of in situ formed reaction product are deposited on the boundaries of the slag grains. Thicknesses of these gel layers range from barely detectable at a few days, to 10-20 pm after about 1 year. Upon an initial rapid 'burst' of reaction, a relatively dense rim of gel develops around the margins of slag grains. In course of time, the slag hydration reaction gradually slows down (the 'dormant' period), and the rim will only gradually thicken. Zonal structures may be formed within the rim, which may eventually crystallize. Electron-microscopy indicates that this rim progresses inward, towards the original slag centre [19].In the near vicinity of the original slag grains, but outside its original contours, also reaction products may be formed. Cement hydration products, adjacent to the slag, are usually readily distinguishable by their high Mg content, derived from the slag. Feng et al. used the name cement hydration product (CHP) in order to distinguish the material from 'ordinary' CS-H ([20];(21]). The CHP appears to be relatively dense. As typical newly formed hydration product in (Mg-rich) blast furnace slag cements hydrotalcite-like minerals (MAH,,,J have been identified. The hydrotalcite found by Feng and Glasser ([20];[21]), appeared to contain some Si; they argued that the phase they found consisted of Mg,(OH),Si,O,, talc, which they supposed was interlayered with hydrotalcite. Slag reaction zones at the boundary of the original slag contours with the cement paste are indeed commonly observed with TEM or microprobe. In figure 7, a typical TEM micrograph of a (small) slag grain is displayed; the numbers in this micrograph correspond to the chemical analysis, presented as oxide ratios, in table A2, appendix A. Since it is not clear which of the two (visible) layers in figure 7 (or both ?) represents the originally formed gel-layer at the slag edge, the expression 'outside- and inside edge' of the slag grain is used intentionally in the following text. Compared to the unhydrated slag, the slag interior (spot 3) is 'enriched' with MgO with a factor three, and it also contains less SiO, and CaO. The AI,O, content is approximately similar. The analysis of the 'inner edge' of the slag (spot 1) indicates the presence of significantly less silicium and aluminium, slightly increased MgO and an approximately similar CaO, as compared with the original slag. The 'outer edge' (spot 2 and 4) indicate an increase in CaO content, an approximately similar MgO content, and a decrease in SiO, and A1203. Just outside the slag boundary (spot 5), the paste is marked by a significantly higher CaO, an approximately similar SiO, and a significant decrease in MgO and AI,O, content. Taken together, these data clearly point at a net transport of Ca, Si and Al from the slag centre; magnesium seems to act as a chemical 'goalpost', as has been suggested by Feng and Glasser [21]. In figure 8 is may be seen that the inner slag hydrate (ISH) indeed seems to have crystallied to well-formed platelets, presumably a hydrotalcite-like phase. The apparent high internal porosity is noteworthy. It has been noted by Feng, Lachowski and Glasser [20] and Feng and Glasser [21], that there is an element transport (mainly Ca and Si) from the slag outwards into the paste, which results in the precipitation of the, relatively dense, CHP. According to Feng et al. [ZO], the inner zone of the slag (inner slag hydrate, or ISH) crystallizes to a hydrotalcite-likephase. This ISH phase consists of well formed platelets, clearly visible as a result of the high intraparticle porosity within this ISH. In their view, the process of porosification and paste densification should be considered as complementary. The element transport results in relatively porous, but isolated, areas formerly occupied by the interior of the slag grains, and a densification of the slag-cement paste outside the slag grains, resulting in an overall lowered permeability; the total porosity of the blast furnace slag cement pastes changes only little in this process. The transport of silicium into the cement matrix is not so surprising, since slags contain about twice as much silica as cement. The dimusion of calcium (and aluminium) from the slag into the cement matrix, however, requires a different mechanism, since both elements are already more concentrated in the cement paste, and their diffusion then appears to run contrary to thermodynamic expectations.

957 Figure 5. Transmission electron micrograph showing a PFA particle surrounded by a reaction zone, consisting of radially fibrillar C-S-H, and a second dense rim of CS-H. Scale: 1 cm = 1 pn.

Figure 7. Reacted sleg particle. The flgures indicate the number of the spot analysis (appendixA, table A2).

Figure 6. Detail of the porous fibrillar C-S-H. Scale: 1 cm = 200 nm.

Flgure 6. Scannlng Transmlssion Electron Microscopy micrograph of a well crystallized,hydrotaicite like phase, which has been developed within the original contours of a fully hydrated slag particle (lSH).

958 Feng and Glasser [21] suggested a 'driving force' as follows. In the early stages of hydration, water and hydroxyl ions diiuse into the slag glass, break the metal-oxygen bonds (e.g. Si-0-Si) and replace them by more complex (hydrogen) bonds resulting from hydrolysis (Si-OH OHSi). As a result, a relatively dense gel layer develops around the slag grain, with a thickness of possibly only 0.1 pm. Once this layer is established, any reaction can only continue by transport of water through the gel layer; it starts to act as a 'membrane.'. Across the membrane, a water potential gradient will be created: a high potential at the cement hydrate and pore water side, and a low potential at the side of the anhydrous slag. In order to lower the free energy of the system, ions will begin to migrate through the membrane into an area were they can form stable hydrates. So, Ca, Si and Al will begin to migrate outwards, while any water migrating inwards will be consumed directly for the formation of a hydrotalcite-likephase. The presence of a 'membrane' gel-layer may be used to explain the occurrence of chemically zoned areas at the slag edges. In this case it may be assumed that the Mg and Al rich layer (outside edge) represents the remnants of the original gel-layer, formed on the original slagcement paste boundary. The Ca and Si rich layer just within this layer (inside edge) than represents an area in which some CS-H like hydration products are formed, since it is likely that the water passing the membrane will also find some Ca and Si migrating from the slag centre. Once formed, this CS-H will remain, and may function as a second barrier. The most important question is of course the nature, chemically as well as physically, of this gellayer. It is also not clear why such a layer is formed, and what conditions favour its formation. Which factors affect the diffusional characteristics; slag andlor cement composition, blend proportion, water content or curing regime ? And what microstructural changes may be expected in blast furnace slag cements with very high (or very low) slag contents ?

...

7. CONCLUSIONS

The following conclusions may be drawn:

*

*

*

In Portland fly ash cements C-S-H hydration products are being formed in concentric rims of low and high density around fly ash particles. In the dense region, tiny crystals, or crystalclusters of hydrogarnet or stratlingite may form; this is also predicted thermodynamically. The observed 'porous' fibrillar CS-H is believed to be growing inward from the 'dense" C-S-H in conditions of lower supersaturation, occupying the 'empty' space between either the dense C-S-H and the fly ash surface or two dense CS-H region. Slag grains display a distinct outward elemental migration, notably of Si, Ca, and Al. The slag 'centre' becomes enriched in magnesium and a hydrotalcite-likephase may develop as an inner slag hydrate. The driving force for this elemental migration is believed to be caused by a postulated gel-layer, which is formed during the initial slag hydration. This gel-layer will act as a membrane, which limits elemental transport, and which creates a water potential gradient between the 'wet' cement paste and the 'dry' slag interior. Si and Ca will precipitate outside (or possibty just within) this gel-layer, and form CS-H (like) reaction products. Precipitation outside of the slag will cause a densfication of the cement-paste, lowering the porosity, a common feature of blast furnace slag cements. Thermodynamic modelling of cementiiious systems provides a supporting framework, which is useful in two ways: First, a data-base is provided which may be useful in order to predict ultimately stable hydration product assemblages. Optionally, the stability of the product assemblages with respect to the ingress of potentially deteriorating ions may be modelled. Secondly, modelling provides a useful tool to provide insight in those cement hydrates of importance for sorption of specific trace elements. These ideas have been elaborated on elsewhere in this volume [35].

' {iiquid) The presence of a 'membrane* points to an osmotic process according to the normal definition. However since water is belieyed to be absent on the "dry"sla interlo; side, there will be no question of an osmotic briving orce. Only the chemical potential of all species, includng water, in the system will act as drwing force.

959 9. REFERENCES 1.

Helmuth. R.. Fly ash in cement and concrete. POmand Cement Asmciation. Skokk. Illinois. 1987.

2.

ACI International Conferences on Fly Ash, Silica Fume, Slag and Natural Pondans in Concrete. American Concrete Institute. 1983,1986,1989 and 1992.

3

Wesche, K (ed.). Fly Ash in Concrete. Propefliea and Performance. RILEM rapofl7. 1991. E b FN Spon, London.

4.

MRS-SP on Fly Ash and Coal Conversion By-products: CharacEsrmh. Ulilimtion and Disposal I-VI. Materials Research Societv. Boston. 1982-1992.

5.

Petenurn. H.S.. Resdivihl d fly ash and slag in cemsnt PhD meais. Technical University d Darn. Facuny of Civil Engineering, Materials Science ssction. s e p m b w 1993.

6.

Diamond. S.. in: Hydraulic Cement Pasles. Their Sburmre and Pmpemes. Cem. and Con. Ass. Slough, UK. 1976. p.2.

7.

Jennings. H.M.. Dalgleish. B.J. and Pran P.L. J. Am. Ceram. Soc.. 1981, vd. 64, p.567.

8.

H.S. Pielemen el al.. Pmceedings of lhe Fourth Intarnational Wercmx on Fly Ash. Silica Fume, Slag and Natural P o ~ ~ o l a nins conaete. Ed. Malhobe. V.. ACI SP-132. Ishmbul. Turkey. May 1992. Vol. 1. pp. 795812.

9

Scrivener, KL. PhD. lhesis. Universityd Lond.m. 1984.

10.

Diamond. S.. Ravina, D. and Lovell. J.. Cam. Conu. Res.. 1880, Vol. 10, p.297.

11.

Mabsana. F. Chmisby of Ponolanlc AddiSona and Mixed Cements. II Cemento. 1976. Vd. 73.

12.

Richardson, I.G. and Groves, G.W.. The incorporalionof minor and bsce elements into calcium silicate hydrate ( C S H) gel In h a r d e d cement pastes. Cem. Concr. Res.. Vd.23. No. 1. pp. 131-138. 1993.

No. 1. pp. 3-39

13.

Larbi. J.A. The Cement Paste Aggregate Interfacial Zone in Concrete. PhD Thesis, Faculty of Civil Engineering. Materials Science Section. Technical University d DeR 1992.

14.

Fraay. ALA. PhD mesis. Fly Ash as a Ponolan in Concrete. Facub of Civil Engineering. Materials Science Group, Technical University Dent 1991.

15.

Daldel, J.A. and Gulieridge. W.A.. The influence d Pulverized-FuelAsh upon the hydration Characteristicsand Certain Physical Properties of a Portland Cement Paste. Cement and Concrele Asmciation. Slough, UK. 1986. Techn. Rep. 560.28PP.

16.

Pietersen. H.S.. Unpublished preliminary date on selective dissolution d fly ash composite cements. applying the salicylic method suggested by Mohan. K and Taylor. H.F.W.. in: Effects of Fly Ash Incorporation in Cement and Concrete (Diamond. S. (ed.)).Mat. Res. Soc. Symp. Proc.. 1981. p.54..

17.

Taylor, H.F.W.. The Chemistry of Cement. Academic Press. 1990. p.295.

18.

Pran P.. The use d fly ash in concrete - A European view, Mat Res. Sa. Symp. Proc.. 1990. Vol. 178. p. 185.

19.

Harrison. AM., Winter. N.B. and Taylor. H.F.W.. Mat MS.Sac. Symp. Proc.. 1987. Vol. 85. p. 213.

20.

Feng. Q.L. Lachowpki. E.E. and Glasser. F.P.. Densiflcation and migration of ions in blast furnace slag-poflland cement pastes. Mat Res. Sa. Symp. Proc.. 1989, Vol. 136. p!?W272.

21.

Feng. Q.Land Glasser. F.P. MaL Res. Soc. Symp. Proc.. Vol. 178. 1990, 57.

22.

Richardson. I.G.. Wilding. C.R. and Dickson. M.J.. Adv. Cem.

23.

Richardson. 1.0.. Rodger. S.A and Groves. G.W.. Mat Res. Sac. Symp. Proc.. Vol. 176. 1990, 63

24.

In compatibilii expsrimenk a number of synthetic mixtures of pure cement hydrates are mixed logether in water (or a alkaline solution). and a l l d to age, wilh periodic shaking. in order to estsblish equilibrium between solid and liquid phases. M e r about 4 w o k s the slumas are fibred. and the liquid and solid phsses are analyzed. The remaining solids are a m n redispersed in waler and again allowad to equilibrate. The fiiiration/redispe&n procedure. including solid and liquid phase characlerisation. may have to be canied wt up to eight times, since a single solubility determinatlon on a freshly prepared phase can give misleading results.

25.

D'Ans. J. and Eick. H.. Das System Ca0-A120J-HZ0bei 20 "C und das Ehwlan der Tonerdentmente. Zement-KalkGip. Vol. 6. 197-210. 1953.

26.

Jones, F.E. and Roberrr. M.H.. The system CaO~03-Hz0 at 25 "C. DSIRO Building Research Slation Note 965. Watford. Heftshire. England. 1962; and references quoted in this document to earlier studies by lha authors.

27.

Dron. R.. Experimentaland Theoretical Study of lhe CaOAJ20,-SiOZ-HZO System. 6lh InL Con. Chem. Cam.. Moskow. section 111, 1974.

28.

Glasser. F.P., MacPhee, D.E. and Lachowskl. E.E.. Modelling Approach to the Prediction d Equilibrium Phase Distribution in Slag-Cement Blends and their Solubility Propetties. Mat Rss. Soc. Symp. Proc.. 1986, Vol. 112. p.3-12.

Aes. (1989). 2.

147.

29.

Atkins. M.. Glasser. F.P. and Kindness. A. Mat Rea. Soc. Symp. Proc.. 1991, Vd. 212, p.387-394.

30.

Atkins. M.. B e n a D.. Dawes. A. Gla~uw.F.P.. Kindness. A and h d . D.. A lhermcdynamic Model for Blended Cemenk. DoE Repon No: DoE/HMIP/RFW2/OLl5. dearmber 1991.

31.

Damidot 0. and Glasser. F.P.. Thermodynamic investigahn d the C%OA1203-CeS04-H,0 System at 25 "C and the Influence of N%0. Cem. Concr. Res., Vol. 23. No. 1. pp. 221.238, 1993.

32.

Damidot. D. and Glasser. F.P.. Thermodynamic investigation of lha CaO-Al,0,-CaS04-H,0 "C. Cem. Concr. k.. Vol.22, No. 6. pp. 1170.1178. 1992.

33

Rodger. S.A. and Groves. G.W.. Electron Microscopical Studies d Tricalcium silicate - Fly Ash Blended Pastes. Mat. Res. SOC. Symp. Proc.. Vd. 113, pp. 117-118 (1988).

34.

Hedges. E.S.. Liesegang rings and other periodic structures. London, Chapman and Hall. 1932.

35.

F.P. Glasser. lmmobilisation Potential of Cementious Materials. this volume.

Syslem at 50 "C and 85

10. ACKNOWLEDGEMENT

The research for the thesis summarized in this article has been partly sponsored by NOVEM BV, The Dutch Sciety for Energy and Environment, as part of the National Coal Research Program.

960 APPENDIX A.

Table A l . Analyses of Portland cement (PCA), fly ashes furnace slag (CEMIJ). n.d. = not determined.

I cao

1.63

2.24

10.70

I 64.42 I

4.32

I 38.44

0.21

2.04

0.69

4.43

LOI’

0.55

I

n.d.

1

Alk. (Eq. N 4 0 )

I

0.69

I

11

Insoluble

I

1.10

I

Specific

0.30

I

1.28

0.51

0.00

3.95

I

and granulated blast

I

n.d.

n.d.

I

n.d.

n.d.

I

n.d.

n.d.

7.1

n.d.

n.d.

1.5

n.d.

Sult. (M2/gr)

Table A2. Oxide ratios of selected spots of a reacting slag grain (ratios are rounded).

’ LO1 = Loss On Ignition (total carbon) AA = Available Alkali (ASTM ‘318) Glass = 100 -4% mullite

D,

+ % quartz + % Fe-spinel)

= 50 % of all particles is smaller than this size (pm); span = (D-D , J,D,

SECTION 4: Closing

This Page Intentionally Left Blank

Environmental Aspects of Construction with Waste Materials J.J.I.M. Goumans, H A . van der SImt and R G . Aalbers (Editors) @I994 Elsevier Science B.V. AN rights reserved.

STATE OF THE ART REPORT USE OF WASTE MATERIALS IN CONSTRUCTION DEVELOPMENT G.R.Woolley Civil Engineering Consultant.

963

-

TECHNOLOGICAL

Abstract Massive quantities of waste materials are produced annually in the major industries of mineral extraction, electricity generation and steel production. Each in turn has vast stockpiles of their waste product. Interestingly the major chemical composition of these combined wastes are similar and each are used to a minor extent in the construction of roads, pavements cement production and asphalt. There are numerous other producers of waste materials and there is the important source of demolition waste and scalpings from road surfaces under repair. There is mounting concern for the environmental effect of depositing these wastes to spoil heaps or as in-till to large excavations. especially so in the event of leaching out of certain trace elements. In this paper, the major waste materials are introduced, considered and their utilization reviewed. Where information on development of the several wastes is available this is introduced. To mount any form of assault on the continuing use of natural aggregates or other materials in construction there has to be a fundamental change of emphasis in regard to using re-cycled waste materials. Selection of a suitable and effective stabilizing agent for these materials either in isolation or when combined is important but, although they have very similar chemical compositions, they are physically different. To reduce our dependence on natural aggregates and to increase our use of waste materials in construction there may be the opportunity to create manufactured items closer to the source of waste material production. Alternatively Legislation may be required to enforce such change. 1. INTRODUCTION lncreasingly environmental and commercial pressures are causing Government Agencies, Local Authorities and Business Ventures to question the practice of dumping waste material. The rising cost of disposal, reduction in industrial activity and clamour for preservation of the natural environment, corn bined with increasing commercial pressure, are promoting a renewed interest in ' using waste products. Some waste products have been in limited use for a number of years. Of these, perhaps the most internationally known is blast furnace slag, a by-product resulting from the production of iron. Determined by the way in which molten slag is cooled it may be a coarse mixture of vitreous agglomerates or granules of a shattered vitreous structure. These granules, granulated blast-furnace slag, are available to replace primary materials or for grinding to fotm a latent hydraulic binder. A not too dissimilar situation exists for fly ash, the solid material collected by mechanical o r electrostatic means from furnace exhaust giwes following the burning of coal in electricity generation. From the late 1930's , after its use in the United States of America, fly ash has been increasingly used as a partial replacement of cement in concrete. It has also been widely used to construct lightweight

964 fill embankments. Both slag and fly ash are used in the production of a number of sophisticated product\ like paint, powder etc. but, with tly ash there is a surplus which has to be disposed of somewhere and by someone. The two examples illustrate the dilemma of dumping to waste the balance of these useful materials, a situation which is increasingly becoming an imposition on the environment. Consideration of the current State of the Art presumes that some waste products are being used for construction but, begs the question ' are we concerning ourselves properly and fully in the on-going study and research into further applications '. Do we therefore prioritise our search for new or extended uses into

projects which provide the highest premium on our outlay, or seek to find outlets which will consume the greatest quantities of waste product. Both have advantages but, the environment is unable to distinguish between any or all of the wastes, we have that facility and only our due diligence and effort will incorporate more waste materials in construction, thereby contributing to the continued well being of our varied and several environments. We must also aim to conserve our primary material resource. By using waste products in a controlled way we should be able to reduce despoiling our environment by reducing extraction of primary materials and the deposition of unwanted waste products. Letters were sent to those named persons in ISCOWA who had recorded an interest in Technological Development associated with the use of waste materials in construction. Sadly the response was very limited, indeed most disappointing, even after a reminder to selected individuals but, some information was provided and I formally thank those respondents for their contributions. An analysis is given of data provided and of material found elsewhere in earlier papers and reports. The major individual waste materials are considered in turn, their properties given and current utilisation reported. Where new processes are under development or being newly practised, known details are given. It was not possible to mount a full literature review and in deference to the authors of papers published worldwide the references given are limited.

2. METALLURGICAL SLAGS 2.1 Blast-furnace[ iron ] slags - The Material The process of refining metallic ores involves raising the temperature of the ore in a turnace until the metal separates from the associated ore components and can be collected. The remaining matter, a mixture of ore residues and reactant used to promote separation is referred to as a metallurgical slag. The manner and rate of cooling of this molten slag will produce several different types of solid slag. If allowed to solidify naturally, a dense crystalline material referred to as air-cooled slag results. Slag may be foamed by introducing water jets into the stream of molten slag, causing it to expand and form a lightweight material. When cooled very quickly with large amounts of water it forms a glassy material called granulated slag. Pelletized slag is produced by a more sophisticated process involving water jets, revolving drums and air cascades resulting in small pellets of foamed or granulated slag ( I ).

965

2.2 Composition All slags have similar composition. In crystalline blast-fumace slag the principle mineralogical phase lies in the series from akermanite [ 2CaO.Mg0.2Si0, ] to gehlenite [2CaO.A1 0 .Si 0 ] (2). When slags have a high lime content they may contain dicalcium silicate [2CaO.SiO 1. This inclusion can cause disruption of the slag through volume increase. If sulphur is present in a reactive, leachable form. mainly as calcium sulphide, problems may also occur. Typical chemical composition of a number of blast-furnace slags is reproduced in table I . Table I Typical Chemical Compositions of Blast-furnace Slag [weight%]

Australia SiO, 33-37 Al;,O> 15-18 CaO 39-44 MgO 1-3 TiO, 0.6 Fe,O, 0.7 MnO 0.3-1.5 N a O 0.2 K 0 0.5 s 0.6-0.8

USA Germany 34-38 35 11-15 12.2 45-47 41 X 1-3 1.3-4.5

0.25 0.5 1.2 incl 0.6

Norway 34-38 7- 10 40-4x 6- 13 0.7- 1. I

UK 31-36 13.5 33-45 4-15 0.x

0.5 0.8 0.1-0.4

lridia 30-35

18-26 30-36 3-9

<0.5 <1.0

0.7 0.8 0.53

2.3 Utilisation Transport costs bear heavily on the use of slags worldwide but in general the percentage used is very high and in some countries approaching 100%. Road making uses the most amount of this material ahead of cement manufacture. Use of granulated slag to replace natural aggregate is well understood. Using the specifications for natural aggregates it may be used in blinding, base, sub-base and as coated macadam for the wearing course in roads. Granulated slag properties as a latent hydraulic binder suits it to act as the binder in gravel slag and sand slag, both used as base material in roads. When combined with water and an alkali activator it will produce cementing compounds, this hydraulic activity depending on the chemical compo on of the slag, physical properties and glass content (2). When combined with portland cement and water the alkalis and lime produced in the hydration of cement acts as the catalyst in producing the cementitious reactions of granulated slag (3). There is extensive use of this property in the manufacture of several slag cements which may contain granulated blast-furnace slag in proportions as high as 90%. Useful to reduce the heat of hydration in hardening concrete, these slag cements have lower early strength but may attain equivalent strength with time. The higher slag contents of these cements provide more resistance to attack by sulphate solution (4).

966 ple process and, subject to soundness, once Production of air cooled slag in roads, as dense aggregate in concrete or as cooled it may be crushed and graded fertilizer. It does need space for cooling pits a filter material. It is also crushed to but, the newer, larger furnaces are being equipped with granulating plant in order to maximise the advantages offered by blast-furnace slag cements. Rapid cooling by compressed air producers the slag wool product, a material used for insulating purposes. Pelletized slag offers a lightweight aggregate, the pellets being of the vitrified form and, like granulated slag, have the properties of a latent hydraulic binder. This attribute lends itself to the soil stabilisation process and production of lightweight building blocks (1).

3. STEELSLAG 3.1 The Material More variable than slag produced from iron ore smelting, steel slags result from the conversion of pig iron to steel. Chemical compositions of these slags introduce this variability but, as with blast-furnace slag the reactant used in smelting and impurities present in the pig iron produce a steel slag. Amongst these compounds is lime, which will quickly hydrate and magnesia with a slower hydration period. The basic oxygen process of steel making tends to produce a more vmable slag than the open hearth process (2).

3.2 Composition Not dissimilar in appearance to an igneous rock, steel slag chemical compositions vary greatly but, generally they have a higher CaO I SiO proportion than blast-furnace slags. Typical chemical constituents are shown in table 2. Of concern are the free calcium, magnesium oxides and metallic iron phases found. These compounds will hydrate and expand in the presence of moisture. Table 2 Typical Chemical Constituents of Steel Slags ( weight % ) Basic Oxygen Steel Open Hearth Electric Arc Germany USA UK USA UK Low C High C CaO 47.2 59.9 40.3 33-5 I 36.17 3 1-50 SiO, 14.X 13.8 21.7 9-19 18.02 11-24 Fe,O, 1.53 10.5 16.3 24-45 17.46 5-30 (total iron) 5-18 x.54 3.8 0.5-3 Al,o, 0.6 2.10 9.96 2-8 1.5 0.9 4.4 0.5-4 MgO Mn 0 5.4 3.0 4 3-10 4 6-22 3.3 Utilisation Iron and iron compounds are contained in steel slag and much is recycled as a minor component in blast-furnace charges. When the metallic iron is removed the remainder is principillly used for land reclamation and unrestrained fill to allow for any expansion that may occur. Presence of dicalcium silicate restricts the material from use as concrete aggregate but it is used for road making when unbound or bound with bitumen as a bound macadam. After controlled pre-weathering, steel slags provide a good quality

967 artificial stone for road making (5).The material may also be ground to provide a high quality fertilizer and depending on slag composition will provide phosphate or lime as a soil conditioner. Granulated electric arc furnace steel slag is used for cement manufacture in some puts of the world with evidence of hydrate formation similar to portland cement. 3.4 Developments Work is reported o n the use of alkali activated slag cement to immobilize heavy metal ions in waste ( 6 ) .Inclusion of slag in the production of lime - sand bricks has shown to be promising whereby slag may replace up to 15% of the lime constituent in the process (7 )

4. FLY ASH ( referred to in the United Kingdom as Pulverised Fuel Ash ) 4.1 The Material Coal used for steam raising in modern power stations is finely ground prior to combustion. This will typically reduce it in size from an incoming average passing a 12.7 mm sieve of 94% to 80% passing a 75 micron sieve before entering the furnace. The constituents, which may be separated to some degree by grinding, consist of carbonaceous matter and various minerals in the form of shales, clays, sulphides and carbonates. This pulverized coal is injected into the furnace at high speed in a stream of hot air and it burns instantaneously in the range of 1500 +/- 2000 deg.C . This is above the melting point of most minerals present and as a result they undergo various chemical and physical changes. For example pyrite is converted into oxides of iron, including spherical particles of magnetite ; clay forms glass spheres of complex sulphates. The exact nature of changes depends on the type of coal, fineness of grinding, temperature and retention period within the hot zone of the furnace. Between 75 - X5% of the resulting ash is carried out of the furnace with the flue gases and is known as fly ash. The remainder falls to the bottom of the furnace where it sinters to form a c o m e r material known as furnace bottom ash. Fly ash is extracted from the flue gases by electrostatic precipitators and / or mechanical methods and is collected in a series of hoppers for disposal ( 8 ) .

4.2 Composition Fly ash consists principally of glass spheres together with some crystalline matter and a varying amount of carbon. Overall colour will depend to some degree on the proportions of carbon, iron and moisture. It will have a specific gravity in the range 1.98 to 2.38 and average specific surface in the range of 260 to 595 sq.m / kg (10). Collected ash will be graded. Some suggest that the finer ash is more reactive but it dws not follow that all fine ashes have high reactivities ( I I ) . The grading from any given source under steady load is normally very consistent. There are three predominant elemene in fly ash, silicon, aluminium and iron, the oxides of which together account for approximately 75% of the material. Silicon is present partly in the crystalline form of quartz (SiO,) and in association with the aluminium as mullite (3A120, ,2Si02 ), the rest in the glassy phase. The iron appears partly as the oxides magnetite (Fe203),and haematite (Fe,O,), the rest in the glassy phase. Carbon, determined as loss-on-ignition, is present in fly ash in amounts

968

which vary with the efficiency of combustion. A typical chemical analysis of fly ash collected from a modern furnace burning sub - bituminous coal is given in table 3 (12). The operating regime differs when lignite is used as fuel and this will produce an ash which differs markedly in respect of calcium oxide. It is known as a high lime fly ash (cli~ss C) and has a typical chemical composition as shown in table 3 (13). Examination of fly ash taken from the flue gases of low NOx boilers which carry a limited amount of ammonia have been shown to have no affect on the production and properties of concrete (14). Table 3 Typical Chemical Composition of Fly Ashes From sub - bituminous coal Si 0, 49 - 53 ,4203 25 -29 Fe20, x- II Ca 0 1.x - 5.3 Mg 0 1.3 - 2.2 K2 0 2.2 - 3.7 Na, 0 0.7 - 1.5 Ti 0, I .o - 2.0 0.3 - 1.7 so3 Loss on Ignition 1.5 - X.8 Blaine specific surface 220 - 5 10 (sq. m / k g ) Fineness >45 micron 6.5 - 25.0

( weight % ) From lignite coal 2 I .o - 35.0

10.0 - 14.0

4.5 - 6.5 30.0 - 45.0 (10% free) 1.5 - 3.0 0.4 - 0.9 0.5 - 1.0 --_4.0 - x.0 3.0 - 7.0 250 - 2x0

----

Utilisation Fly ash has been used quite extensively as a fill material in road construction. When placed and compacted at optimum moisture content ( generally in the range 17 - 23% ) it has a lower density than most other fill materials, an advantage when placed on highly compressive soils. Many fly ashes have self - cementing properties when compacted which reduce settlement potential within the fill mass, a distinct advantage when placed to bridge abutments (15). Mostly however, they are trost susceptible and d o require a minimal protection. Recent developments in the technique of reinforced soil embankments have shown how suitable tly ash can be for this application (16). Stabilization of tly ash with lime or cement has allowed the material to be used for sub - base construction and as a binder it may be used to improve the physical properties of soil either alone or with lime or cement. Lime - fly ash mixes have been successfully used to stabilise a range of materials but, when clay is present the lime appears to react primarily with the clay ( I 7). Numerous applications of the use of cement / tly ash grout mixes are reported for the filling of mine workings, rock fissures and the like ( 18). As a pozzolanic material fly ash will react with lime in the presence of water. This cementitious property is used in concrete where fly ash will react with the hydration products of portland cement. It may be included by intergrinding with the cement clinker to form blended cement or included in the site mixer with portland cement. The physical properties of fly aqh produce a rheological change in fly ash concrete which allows a small

4.3

969

reduction in water content when compared to an all cement concrete of similar workability ; generally thought to give a 3 8 water reduction for each 10% cement replaced with tly has a lower temperature rise and i ash (19). Hardening mes experienced in large sections. affected by high tern mass concrete in dams and there has been considerable use of the material in these structures. Recently the traditional method of including and placing concrete in dams has received competition from the new practice of roller compacted concrete, a formation whereby layers of low water / cementitious concrete are built - up and compacted insitu by roller. In this way it is claimed that construction costs are reduced through a shorter construction programme and inclusion of high volumes of tly ash often in the range 40 60% (20). In Spain similar and even larger volumes of fly ash have been used in dam structures placed and compacted conventionally (2 1). Early records of fly ash structural concrete report inclusion of the material in small proportions by volume. Introduction of weigh batching at the mixer, perhaps more sophisticated mix designs and increasing awareness of the potential engineering and commercial benefits has raised the general replacement level of cement to 30%. Inclusion by weight of 30 - 40% is not uncommon and there are now a variety and increasing number of structures built with fly ash concrete. Fly ash is widely used for the production of lightweight aggregate. Using a sintering process pellets are formed in a variety of ways (22) (23). Sinter cake may be formed at I 150 - 1200 deg.C , a product used in the manufacture of building blocks. The lightweight aggregate produced is of good regular shape of high quality with moderate water absorption, used for structural lightweight concrete. Aerated concrete blocks are made in an autoclave process using a mixture of fly ash. cement and sand with an air entraining agent. This produces a high quality thermally efficient building block.

4.4 Development The proportions of fly ash being included in concrete as cement replacement continues to increase. In real terms however, the total amount of the material used in concrete is small compared to total production. Development work is in progress to design high volume fly ash boulders (24) and other structural elements (25), the latter including FGD gypsum with fly ash, for use offshore as coastal protection. Evaluation continues on a trial section of road surfacing which included fly ash as replacement for filler in the asphalt ( 2 6 ) .This gave a significant reduction in energy demand in the production process. The residues of tluidised bed combustion have been successfully tried in the making of artificial gravel (27). There are products in research which combined with fly ash produce construction materials suitable to replace natural aggregates in use today. This is early work, shrouded in commercial secrecy but it does illustrate a willingness to use waste materials. 5.0 COLLIERY SPOIL ( Minestone Waste )

5.1 The Material Colliery spoil is produced during the extraction of coal by deep mining. It may be pure rock removed in formation of underground roadways, the coarse material separated from the coal in the washery, tine material resulting from degradation during the mining

and transportation or tailings collected in the final separation. The latter which is almost total coal is used elsewhere for combustion. Rock types associated with coal seams are mudstones, siltstones, sandstones and shale. Quartz and clay minerals, kaolinite and illite, are the principle minerals included. Naturally grey in colour this shaley material weathers rapidly. When placed in spoil heaps and compacted in layers to exclude oxygen it will remain in the excavated form but, the older heaps often suffered combustion and the resulting " burnt shale " is a reddish-coloured material with higher strength and better resistance to weathering ( 5 ) .

5.2 Composition Spoil will contain varying amounts of carbonaceous matter but, the principle minerals will comprise quartz and the clay minerals kaolinite and illite. Chemically colliery spoil will typically include Si 0, , range 38 - 60%, A1,0, ,range 14 - 30% and Fe,O,, range 3 - 1 I %. It will include a number ot other minor elements. Chemical changes occur when spontaneous combustion has taken place which include il reduction in the proportwn of combustible matter, a breakdown of clay minerals, decomposition of carbonates and the oxidisation of sulphides to soluble sulphates. The latter change producing an undesirable increase in sulphate content affecting possible use of the material. Precautions may be necessary to avoid close contact with other engineering materials if the shale has a high sulphate content (2).

5.3 Utilisation Construction of embankments using colliery spoil is perhaps the only situation where large scale quantities are used. It is used as fill beneath dwellings and roads, the burnt shale being the preferred material because of its good grading and granular nature. Tests may be necessary to ensure against frost damage and limits may be placed on sulphate content. To minimise the potential of frost heave shale has been stabilised with ;L nominal amount of cement. Precautions may be necessary to prevent sulphate and acid attack of concrete which may have direct contact with colliery burnt shale and the use ot appropriate cements and / or pozzolanas are recommended (27). Colliery spoil has been widely used for brick making where carbonaceous matter in the spoil can contribute to the energy requirements in the kiln. A number of practical points associated with the use of colliery spoil in brick making contribute to its relatively variable appearance but, it makes a brick with good durability. Colliely spoil is also used in the production of a lightweight aggregate. The two processes used, deliver a rough, angular aggregate suitable for use in the production of lightweight concrete building blocks. 5.4 Development Studies are progressing into the use of colliery spoil in combination with tly ash, cement and bentonite for liners to waste disposal areas (29). There is continuing interest in using large quantities of the material off - shore in the formation of protective islands. In this situation it will be necessary to overcome the risks of limited pollution from surface washings and the plate like structure of shales. Perhaps in cornbination with cement and another tiller new formulations can be found.

97 I 6. MINING and QUARRYING WASTE

6.1 The Material Considerable quantities and notably different wastes are produced by the mining and quarrying industries. Those wastes produced in large quantity generally have a chemical analysis in which Si 0, predominates with varying amounts of Fe203and A203 and lesser percentages of the minor elements. Quiurying wastes will include overburden. reject rock and the fine material arising from transportation and washing. Mineral mining produces waste rock removed to expose the ore and tailings obtained through the separation of minerals from the ore. Geological formations will determine the composition of wastes which will vary by site and operation. Rock type, excavation method , transportation and preparation process are the determinants in particle size distribution. The coarser fraction of wastes are usually deposited in spoil heaps local to the source 01 used to provide landscape screening. The finer material is generally transported as water slurry to settling lagoons. 6.2 Utilisation Amongst the most common uses are for road construction or the manufacture of calcium silicate products. The coarser fraction from a number of mining and quarrying wastes are used in road construction or to produce concrete aggregate. These include the wastes from the winning of copper ore, iron and gold ores in addition to the rejected rock removed in overburden to other quarrying activities (2). The p produces a coarse waste of size > 20mm to 75 micron and a fi - 10 micron. The coarser material is used in block making and the fine sand for concrete ). China clay and laterite are used in brick making or burnt to form umber of fine wastes are used as fillers in bitumen or in the manufacture of products. Manganese mud is used as a pigment to colour bricks and ground slate as a filler in paints and plastics. Slate granules provide the decoration to bitumen felts and it has also been used to produce a lightweight aggregate. Phosphate sand can be used in concrete or for ground modelling but, the colloidal clay sized particles of phosphate slime remains unstable without mixing with sand (2).

6.3 Developnient Geographical remoteness of mining ilnd quarrying activities presents a major vansport problem for the considerable quantities of waste being produced. There appears to be little work being done on the utilisation of these many wastes in the production of a manufactured item. Investigations have been noted into the suitability of using certain shales and slates for the production of lightweight aggregates however, the energy demanded to cause them to expand makes the unit production costs too expensive, 7. MUNICIPAL SOLID WASTE INCINERATOR ASH 7.1 The Material Municipal Solid Waste is the ash resulting from the incineration of municipal

912 waste. It is quite variable, the product being determined by the process conditions, furnace type and temperature and composition of the feedstock which is largely domestic and trade refuse. Typically the majority of the ash has particles of less than 3mm with mainly glass, ceramics and slag-like matenal. The more variable nature of this ash suggestc a noticeably greater environmental impact, one demanding strict control of use or placement. 7.2 Composition In primary selection the rnedlic refuse is recovered for re-cycling. Determined by the original composition of the waste, these ashes show great variations in chemical composition. They are highly siliceous with minor components of iron calcium and aluminium. There are also numerous trace elements. Typically the Dutch AVI- Slag composition produced from MSW is given in table 4.

Table 4 General Composition AVI - slag 4% organic material 18% glass rubble, ceramics I1% 13% slag - like material iron 2% nun - ferro metals 2% fraction < 3mm 50% ( not recognizable

)

7.3 Utilization In Holland, recognising the potential for environmental impact, there are strict rules for its use. These include limits on leachability, soil-ground water protection, impermeable encasement and the subsequent facility for removal. The coarse fraction > 2mm is used as a concrete aggregate where generally only 15 - 20% of natural ,coarse aggregate may be replaced in non - reinforced items. However high chloride contents may be present, zinc and aluminium can lead to expansion and the other engineering parameters of concrete, setting time, shrinkage and high cement I water contents may be affected (3 I). This aggregate has also been included in the composition of asphalt. The pulverised refuse has been used to replace a small proportion of the pulverised coal feed for cement production without affecting the cement quality. 7.4 Development It is the practice to store this ash in the open air after production. This is to allow natural stabilization of the product and reduce the potential for leaching of certain metals. Research is indicating that there is secvndary mineral formation during this storage period,as tound in the natural pozzolana. which influence the leaching of contaminant\ (32). Post - treatment systems which include washing, sintering and smelting are being considered to ctabilize the material, thereby widening the scope for inclusion in construction. These in-plant measures may provide a vehicle for improving the ash quality and assist with fixation of heavy metals (33). Exploratory work is reported of the use of

973 ash derived from refuse incineration as a partial replacement of cement (34). Each secondary treatment, including storage before use, carries a clear cost implication.

8. DEMOLITION WASTE 8.1 The Material Largely demolition waste consists of concrete and brick rubble with minor quantities of secondary materials including steel, tiles, plaster boards, wood etc. The majority of the metal will be re-cycled and individual contractors will sepwate the minor componena from the bulk concrete and brick waste. There is also waste macadam and asphalt scalpings recovered from worn road surfaces in the process of repair or resurfacing.

8.2 Composition Concrete waste may be infinitely variable in particle size at recovery but, brick or concrete building block will be of a more uniform size. Subject to controlled c r u s h n g both will be available for grading to demand. Asphalt and macadam planings from roads under replcir will provide a coated aggregate material > 40mm m size. Reinforced concrete is clearly more difficult to handle but, it may be recovered with the reinforcing steel going for re-cycling.

8.3 Utilization Re-cycled concrete and brick rubble crushed to produce graded aggregates are used in foundations to properties and as sub-base to roads. The graded aggregate has been successfully used in new concrete but, it h been shown to be more water demanding and requires an increased cement content to fu 1 strength demands (35). The greater proportion of road planings are re-used in footpaths, car parks and the like and when crushed and graded used a s road sub-base material. Using the Minesotta process up to 25% of old asphalt is added to the other constituents in the asphalt batch. This is a practice favoured in several countries. Graded re-cycled concretes and asphalt may be stabilized with cement to provide hard standings and secondary road structures. Crushed brick and tile waste has been successfully used as backfill to trenches (36).

8.4

Development Work is reported on the use of pozzolanic additions to concrete mix designs using recovered concrete waste in order to counter the effect of higher water demand and increased cementitious content (37). Quality Control schemes are offered to ensure that re-cycled aggregates comply with given specifications and a Model is proposed for the prediction ot demolition waste in the future (3X). Work is reported on the recovery of raw materials from reclaimed asphalt (39). 9. DISCUSSION There are massive quantities of waste being produced by the major industries of mineral extraction, electricity generation and steel production. There are also innumerable smaller industries which produce waste often of a more complex nature. The latter by their

914

nature and quantity are unlikely to offer the opportunity of re-cycling or integration with other materials to form a product available for use in construction. It seems therefore entirely appropriate to consider the main contributors to an increasingly large stockpile of waste. Mounting demands for natural aggregates and a reducing availability of environmentally acceptable placements for waste materials conspire to strengthen the need to bring these waste materials back into construction. There is a predominance in the major sources of waste being considered of silica, alumina and iron. These wastes have a not dissimilar chemical composition which would suggest a similarity of outlet, even though physically there is great variation in particle size and shape. Crushing and grading of individual wastes could reduce this disparity and offer a complimentary span of product with uniformity of outlet. This may not he practical but, in developing the iugument, it should be stressed that similar end uses of these major wastes are perceived. Indeed, it is interesting to note how all are currently accepted for use in road construction to a greater or lesser degree, each opportunity and location of the waste being determined by geographical location, physical capacity of the site and ground soil conditions. All these wastes include a small, aid in some cases significant, proportion of potentially harmful mineral element. Consideration must therefore be given to reducing the potential for leaching out of these elements. Stabilization of waste products with cement offers a solution which is perceived by some to be effective. G are currently investigating the role of cement minerals. MSWl ash when stored is thought to produce secondary minerals and it could be nce of an activating agent that in combination with other wastes or alone with the similar secondary agencies would suffice. It is useful to note the success of combining fly ash, cement and bentonite in cut-off walls (42). Whatever the choice or complexity of combining and I or stabilizing wastes to contain undesirable leaching there is perhaps a more fundamental problem inhibiting the increased use of waste materials in construction. Geographically it appears that the source of major wastes is remote from the main construction activities. There is therefore likely to be a significant transport problem to overcome when trying to relate a waste stockpile to a construction site. Intrinsic production costs of natural aggregate for concrete and road construction iue low. Hence geographically remote waste stockpiles are disadvantaged even though the material may be free for collection. Attention therefore must turn to the practicability of manufactuting construction items with waste materials at the source of those waste materials. It may be that waste heat from the main production process is available to supplement the unit cost of production but avenues must be sought to overcome the transport costs of removing waste materials in bulk. In the event manufactured items may command a premium as well as reducing the stockpile at source. A draconian alternative to initiatives being sought for the inclusion of more waste materials in construction may lie in Legislation. This could take the form of a levy on unit quantities of natural aggregates used, o n transportation of those aggregates, or a simple Directive that all construction above a minimum cost shall include a given proportion of re-cycled waste product. In the more densely populated countries of the developed world this may have an appeal but, it could offer significant logistical, cost and control problems elsewhere.

975

10. CONCLUSION The major sources of waste suitable for re-use in construction have been described. reviewed and considered. There is a certain chemical similarity in these major waste materials but, real difference in mineralogyand physical properties. Limited use is being made of these materials largely as a result of geographical location in regard to construction activities. All the major wastes are used in varying quantities for road construction, general fill, to construct embankments and to a limited extent in the production of cement and asphalt. However. the replacement of natural aggregates with re- cycled w u t e materials is minimal. It is an attractive thought that because of similarity of main chemical composition in these wastes it would be relatively easy to suggest that some may combine to offer a real alternative in construction to natural materials. To reduce the opportunity for leaching of certain trace elements cement is commonly used but, given the plethora of chemical agents available it may be possible to promote secondary mineral formations within these combined wastes which would stabilize the offending elements and deny leaching activity. There are real problems associated with the geographical location of wastes in regard to construction activities. It is suggested that thought be given to manufacturing construction items at the source cif waste production, perhaps utilizing waste heat to assist with production procedures and unit costs. Ultimately it may be that the problems of geography, leaching and natural reluctance to use other than natural materials in construction will not be resolved by innovations for the use of waste materials. Reluctantly it is suggested that Legislation may have to be considered to enforce the controlled use of these wastes. This would reduce the risk of environmental pollution and lessen the burden of recovering natural aggregate.

Acknowledgement The Author gratefully acknowledges contributions received from a number of respondents interested in this important subject.

11. REFERENCES I.

2. 3. 4.

5.

Reeves C M. The Production, Properties and Application of Blast-furnace Slag etc. ICT Dip. Cem & Conc Assn, Wexham, 1980 Gutt W and Nixon P J. Use of waste materials in the construction industry, Materials and Structures vol. 12 No.70,1979, 255 - 306 Neville A M. Properties of Concrete, 2nd edition, Pitman, London, 1977, 69 - 70 Lea F M. The Chemistry of Cement and Concrete. 3rd Edition, Edward Arnold 1970 Whitbread M. et al, Occurrence and Utilization of Mineral and Construction Wastes, Dept. Environment. HMSO, London, IW I , 25

976

6. 7. X. 9. 10.

I I. 12.

Malolepszy J and Deja J. Immobilization of heavy metal ions by the alkali activated slag cementitious materials, Wascon '94, Maastricht, 1994 Maloleopszy J et al., The granulated foundry slag a%a valuable raw material in the concrete and sand-lime brick production, Wascon '9 1, Maastricht, I99 I , 475 - 47X The Concrete Society. The use of GGBS and PFA in concrete. Technical Report No.40. The Concrete Society, Wexham, London, I99 I Barber E G. et al., PFA Utilization, C E G B, London, 197 I Mathews J D and Gutt W H. Studies of fly ash as a cementitious material, Proc. of Conference. Ash Technology and Marketing, London, 1978 Cabreri J G, Woolley G R et al., Proc. Ash Tech X4, London, 19x4, 303 -312 Cabrera J G and Woolley G R., Fly Ash Utilisation in Civil Engineering, Wascon '94,

13. 14. 15.

I 6. 17.

Maastricht, 1994 Papayiaini J. Use of a high - calcium fly ash in blended type cement production, Int. Conf. Blended Cements, Shetfield, 199 I Backes H P and Koch H J., The properties of concrete made with NH - bearing coal fly ash, Betonwerk, vo1.3, I9XX. 71 - 76 Fox H. Pulverised fuel ash as structural fill, Proc. Ash Tech, London, I9X4,495 500 Jones C J F P et al., Reinforced earth trial structure for Dewsbury ring road, Proc. hst. Civ Eng, vol. XX, Part I , 1990,321 -345 Manz 0 E. Lime - Fly Ash stabilization for road building, Proc, Ash Tech., London, 19x4, 505 -5 I 2

I x. 19.

20. 21. 22. 23. 24. 25. 26. 27. 2x. 29.

Hughes D C., Performance of hardened grouts, Nat. Seminar, Dundee, 1992, X9 I03 Hobbs D W.. Portland - pulverised fuel ash concretes etc.. Proc.Inst. Civ Engrs, Part 2, VOI X5, 19x5, 317 - 331 Dunstan M R H., Development of high fly ash content concrete, Proc.Inst.Civ.Engrs, Part I , vol. 74, 19X3,495 -513 Cabrera J G. et al., Concrete International 1994, to be publi Boral Lytag, Lytag structural guide-lines and properties, 19x9 Boas A and Spanjer JJ., The manufacture and the use of artificial aggregates from fly ash to Aardelite process, Proc. Ash Tech., London, 19x4, 577 - 5x2 Woolley G R and Cabrera J G., Coastal Protection Project (1994), University of Leeds ( in progress) Gera F et al., Utilization of ash and gypsum produced by coal burning power plants, Wascon '9 I , Maastricht, I99 I , 433 -440 Cabrera J G and Zoorob S., Final Report ETSU Contract No. EICS/3580/2669, 199 I University of Leeds. Mulder E and Houtepen S M., Artificial gravel as a substitute in asphaltic concrete Lnt. Coal ash Util. Symp. Orlando, 1991 BS 6543 : 19x5, Use of industrial by-products and waste materials in building and civil engineering, BSI, London 19x5 Lattey S E and Trew J C., State of the art report un the use of low cost materials

911

30. 31. 32. 33. 34.

35. 36.

37. 38.

39. 40. 41.

42.

( Colliery spoil and pfa ) as landfill liners, Internal report. Univ. of Leeds. 1990 Walters G V., Economic treatment of quarrykhina clay waste materials Schuur H M L and Broadbent C P., Slag utilization in the Netherlands Zevenbegen C., Geochemical factors controlling the mobilization of the major elements during weathering of MSW bottom ash. Wascon '94, Maastricht. 1094 Schneider J et al.. Improving the MSWI bottom ash quality by simple in-plant measures. Wascon '94. Maastricht, I994 Hwa T J and Kiat C H., User of ash derived from refuse incineration as a partial replacement of cement, lnt. Conf. Blended Cements, Sheffield. I991 Hendriks Ch F., Ecological use of construction and demolition waste. Private communication, 1994 Folkenberg J., Application of crushed tile and concrete as filling material in pipe trenches, Danish Tech. Inst., 1994 Wainwright P J and Cabrera J G., The performance of concretes made with combinations of pfa and re-cycled concrete, Wascon '94, Maastricht, 1994 Walker I and Trankler J 0 V.. Model for the prediction of demolition waste composition, Wascon '94, Maastricht, 1994 Mulder E et al.. Recovery of raw materials from reclaimed asphalt pavement, Wascon '94. Maastricht, 1994 Glasser F P., Immobilisation potential of cementitious matrices, Wascon '94. Maastricht, 1994 Sprung S et al., Environmental compatibility of cement. Wascon '94 Maastricht, 1994 National Ash, Case Study No. 5. National Power. UK, 1990.

This Page Intentionally Left Blank

Environmental Aspcts of Constmction with Waste Materials JJJ.M. Goumans, H A . van der SIoot and i71.G. Aolbers (Editors) 01994 Elsevier Science B. K AN rights resewed

979

A Unified Approach To Leaching Behavior Of Waste Materials T.T. Eighmf and H.A. van der Sootb "Environmental Research Group, A115 Kingsbury Hall, University of New Hampshire, Durham, New Hampshire, 03824, USA bNetherlandsEnergy Research Foundation (ECN), Westerduinweg 3, PO Box 1, 1755 ZG Petten (NH), The Netherlands

Abstract There is a clear need to integrate and unify approaches towards understanding the fundamental leaching behavior of waste materials that are used in construction. Working Group B of ISCOWA (Laboratory Testing and Environmental Impact Assessment) has a mandate to work on this important topic. A framework for discussion is presented here that outlines the issues and identifies some of the needs for accomplishing this effort. 1.0 INTRODUCTION

There have been a number of recent efforts that have compiled and evaluated leaching tests for waste materials (Environment Canada, 1990 & 1991; Fallman, 1990; IAWG, 1994; TNO, 1993; van der Sloot et al., 1991; van der Sloot et al., 1992a; Zachara & Streile, 1991) and documented that leaching behavior within waste categories (IAWG, 1994) as well as between waste categories (van der Sloot et al., 1991) is quite systematic and can be described by geochemical principals including precipitation/dissolution, solution phase complexation, and sorption. Additional studies have shown the systematic leaching behavior of waste products (de Groot and van der Sloot, 1991). Researchers have also been involved in the development of accelerated leaching tests (Caldwell et al., 1994; Fuhrmann et al., 1989) so as to better predict long term leaching behavior of wastes or products and in the field verification of leaching behavior (Fallman & HartlCn, 1994; Meij & Schaftenaar, 1994; Mulder, 1991; Stegemann et al., 1994). Developments worldwide towards increased utilization of construction debris, slags, ashes, waste soils, compost, recycled plastics, tires, etc. in construction or utilization applications means that unified approaches towards waste characterization, waste leaching, product leaching, accelerated testing, and leaching modeling are needed. Additionally, there are needs for simplification of this approach, integrating the leaching of organic contaminants into this scheme, and coupling this data to fate/transport issues, environmental impact assessments and risk issues.

980

One mandate for Working Group B of ISCOWA is to focus energies on the integration of these approaches and the identification of areas needing further evaluation. This paper is designed to facilitate discussions by Working Group B towards those goals. An initial survey of ISCOWA members about these topics resulted in the accumulation of methods or issues that are included here (Djuricic & Miletic, 1994; Horiuchi, 1994; Martinez, 1994; MBhu, 1994 plus many referenced papers). 2.0 FUNDAMENTAL LEACHING PROCESSES

Figure 1 schematically depicts leaching processes that occur in inorganic granular wastes. Fluid flow through the particles is relatively slow so that flow is laminar, fluid boundary layers are large and rates of mass transfer from the particle surface can limit the dissolution of soluble phases. In almost all cases, major element chemistry dictates the pH, redox and solution phase leachate composition. pH- and redoxdependent precipitation/ dissolution reactions control the leaching behavior of most elements. Solution phase complexation reactions with inorganic or organic ligands influence solution phase solute speciation as well as impact precipitation/dissolution reactions. Sorption processes (sorption to oxide surfaces, ion exchange) also control the availability of anions and cations in the leachate. All of these processes can be described using thermodynamic principals. Some caution is urged here in that some dissolution reactions are described kinetically and do not behave according to equilibrium principles. The principals described here have been applied to leaching of coal ashes (Fruchter et al., 1990; Rai & Zachara, 1989), oil sludge ashes (Dzombak et al., 1992), MSW ashes (Comans et al., 1993; Eighmy et al., 1993, 1994a, 1994b; Theis et al., 1993), waste soils (Rai & Zachara, 1988; Rai et al., 1984), MSW wastes (Eighmy et al., 1994b), construction debris (Eighmy et al., 1994b), shredder wastes (van der Sloot et al., 1994), mining wastes (Pavlik & Runnells, 1990) and blast furnace slags (Fallman & HartlCn, 1994). It is these common geochemical processes that provide for the systematic basis towards leaching. 3.0 NEW APPROACH TO WASTE CHARACTERIZATION

It is useful to be able to describe the physical properties and element speciation in waste materials. These information provide a great deal of information about speciation at the particle surface, the presence of incongruent solids, the presence of sorptive surfaces, and the quantity of specific surface area available for leaching. Such information is crucial in understanding the factors controlling undesired leaching properties and allows for the selection of better management measures with upstream process control during waste generation as well as downstream control. Figure 2 schematically depicts how this information is integrated. This information provides a framework for understanding the physical and geochemical basis for leaching. This approach have been applied to coal ashes (Ainsworth et al.,

98 I

Key

0 MetalCalion Slow Interstitial Seepage Velocily

0

y

Anionic Ligand

X

Surlaca Sorption Site

Y

Sorption lo

9

Solution Phasa Complexation

Figure 1. Schematic of Fundamental Leaching Processes.

Matrix Structure, Particle Size, Specific Surface

Total Composition

I SPECIATION I Bulk Mineralogy

Solid Phases At The Particle Surface

Figure 2. Schematic of General Approach Towards Characterizing the Speciation of Waste Materials.

982

1993; Lichtman, 1987), MSW ashes (Eighmy et al., 1993; 1994% 1994b; Gardner 1991), construction debris (Eighmy et al., 1994b), and MSW fractions (Eighmy et al., 1994b). 4.0 SYSTEMATIC LEACHING BEHAVIOR

A number of research efforts have documented that fundamental leaching behavior is systematic for a wide variety of wastes (van der Sloot et al., 1991, 1992% 1992b, 1993, 1994). Further, the interpretation of leaching behavior in response to a multitude of regulatory leaching tests is also systematic provided that (i) data are plotted as release versus pH or (ii) as cumulative release versus cumulative liquid to solid (L/S) ratio. Release is defined as mass of an element leached per dry weight of residue (mg/Kg). L/S is defined as the volume of leachant applied per dry weight of residue (L/Kg). Two important benchmarks for both approaches are true total composition (mg/Kg) and the fraction or quantity of an element that is environmentally available for leaching (mg/Kg) over geologic time (i.e. l,OOO-l0,0o0 Yd.

Using the above mentioned methods, it is possible to place systematic leaching behavior in a conceptual framework (Figure 3). The processes depicted in Figure 1 or information determined in Figure 2 provide an underlying basis for the approach shown in Figure 3. Systematic leaching behavior involves a determination of whether the leaching process is kinetic- or equilibrium-based. Such information determines the time frame under which leaching processes should be observed (hours, days, weeks, years). It also allows for the analysis of solution-phase speciation. Knowledge as to the fraction available for leaching and the pH-dependent leaching behavior of elements also provides fundamental information. The use of serial batch, column, or lysimeter tests can provide cumulative release data that describe leaching rates (release vs L/S or time). Additional leaching tests can be employed that document the role of solution phase ligands in complexing solutes (i.e. organic acids, chelators, chloride, etc.), in measuring the effects of Eh, and the role of sorption in controlling leaching. Geochemical thermodynamic models can then be used to verify the equilibrium-based leaching behavior. These approaches have been used for coal ash (van der Sloot et al., 1992; Warren and Dudas, 1986), MSW ash (Comans et al., 1993; Eighmy et al., 1993, 1994% 1994b; Theis et al., 1993), MSW fractions (Eighmy et al., 1994b), blast furnace slags (Fallman and HartlCn, 1994) and construction debris (Eighmy et al., 1994b). Further work is needed to characterize kinetic systems. 5.0 PRODUCT LEACHING

A number of research efforts have documented the systematic leaching behavior of waste materials incorporated into monolithic specimens (using various binders such as

983 Total Available

Solution-Phase

Fraction

Spec$ion

Kinetic + Modeling

f

pH-Dependent

F l BEHAVIOR

Cumulative Leaching Rate Using Serial Batch, Column or Lysimetef Methods (USor Time)

J

Leaching Geochemical +Thermodynamic Equilibrium

Influence of Redox, Solution-Phase Complexation, and Sorption Processes

Figure 3. Schematic of General Approach Towards Characterizing the Fundamental Leaching Behavior of Waste Materials.

Monolith Test

Product Integrity

Granular

LEACHING

Dlffusion Modeling

Figure 4. Schematic of General Approach Towards Characterizing Product Leaching.

984

pozzolans, Portland cement, asphalt) or as compacted granular material (de Groot & van der Sloot, 1991; IAWG, 1994). The premise to this approach is that diffusion modeling can be used to examine leaching behavior. Figure 4 depicts a framework that describes the approach. 6.0 FIELD VERIFICATION

Many efforts have documented the behavior of waste materials leached in lysimeters, or in large-scale utilization demonstrations or in full-scale utilization projects (see Fiillman & HartlCn, 1994; Meij & Schraftenaar, 1994; Mulder, 1991; Stegemann et al., 1994 as examples). Figure 5 depicts a general approach. Most of these efforts reveal that field scale results can be predicted using approaches identified in Figures 3 and 4. There has been no systematic compilation of these data and the approach has generally been applied to coal ashes (Rai & Zachara, 1989), MSW ashes (Hjelmar, 1992), and slags (Fallman & HartlCn, 1994). This information is needed for use in waste stream or treatment process modifications. 7.0 ACCELERATED TESTING AND LEACHING, SIMPLIFIED LEACHING, PREDICTIVE LEACHiNG MODELS

Much less effort has been directed at the development of accelerated testing methods, simplified leaching procedures, and predictive leaching models. In the 1970's and 1980's, rapid leaching tests like the EP-toxicity test were developed without systematic consideration of the integrated, unified approach presented here. Clearly, the development of new tests should follow this approach. Industry is particularly in need of tests for helping with quality control, upstream and downstream modifications, and cost reductions. In Europe, a three-tiered approach is being used that involves characterization, compliance testing, and on-site verification testing. Incorporating a feedback process in this approach would be useful. Figure 6 describes a framework that could be used. Some data has been presented on accelerated extraction methods or approaches (Caldwell et al., 1994; Fuhrmann et al., 1989), simplified leaching procedures (van der Sloot et al., 1992a, 1994), and predictive models (Theis et al., 1993); however, these have not been applied to all wastes. 8.0 NEEDS

From the above discussion, a preliminary list of needs is identified. It is likely that this list will be modified and expanded during discussions by Working Group B at WASCON '94:

985 Laboratory

Comparative Evaluation

Data

J Full-scale Data

Pilot or Demonstration Data

Figure 5. Schematic of General Approach Towards Field Verification of Leaching Behavior. Simulated Long Term Leaching or Extraction Tests

Accelerated Aging, Weathering, Destruction Tests

\

II

1

J

ACCELERATED TESTING AND LONGTERM PREDICTION

2 Rapid, Coicise, Reliable Tests For Characterization, Compliance, and Verification

1

K-

Predictive Geochemical, Kinetic, or Diffusive Modeling

Figure 6. Schematic of General Approach Towards accelerated Testing and Long Term Prediction of Leaching Behavior.

986

harmonize chemical speciation data for all wastes; harmonize systematic leaching data for all wastes; expand and harmonize the product leaching database; expand and harmonize the field verification database; develop additional accelerated methods; develop a simplified, inexpensive, leaching approach for use by industry; develop predictive models; expand all leaching databases for all wastes likely to be utilized; expand all leaching databases to include organics (DOC, halogenated compounds, etc.); integrate results with fate/transport models, environmental impact models, and risk models. 9.0 REFERENCES

Ainsworth, C.C., Mattigod, S.V., Rai, D. & Amonette, J.E. (1993) Detailed Physical, Chemical, and Mineralogical Analysk of Selected Coal and Oil Combustion Ashes. EPRI TR-101785. EPRI, Palo Alto, California. Caldwell, R.J., Stegemann, J.A. & Chao, C.C. (1994) Ultrasonic agitation method for accelerated batch leaching tests. In Third International Symposium on St~iluation/Solid~cation of Hazardous, Radioactive and Mixed Wastes, November I 5, 1993, Wlliamsburg, Ktginia, ASTM, Philadelphia, Penn. (in press). Comans, R.N.J., van der Sloot, H. & Bonouvrie, P.A. (1993) Geochemical reactions controlling the solubility of major and trace elements during leaching of municipal solid waste incinerator residues, p. 667-679. In: Proceedings of the Municipal Solid Waste Combustion Conference,AWMA, Pittsburgh, Penn. de Groot, G.J. & van der Sloot, H. (1991) Determination of leaching characteristics of waste materials leading to environmental product certification. In Proceedings Second International Symposium on Stabiluation/Solid@cation of Hazardous, Radioactive and Mired Wartes, May 29-June 1, 1990, Williamsburg, Virginia, ASTM, Philadelphia, Penn. Djuricic, R. & Miletic, S. (1994) personal communication. Dzombak, D., Morel, F., Mundt, J., Hirschberg, E. & Huff, G. (1992) Modeling of leaching of metals from hazardous waste incinerator ash, p. 501-506. In: Proceedings I992 Incineration Conference on Thermal Treatment of Radioactive, Hazardous, Chemical, Mired and Medical Wastes, U. California INine Press, Irvine, California. Eighmy, T.T., Domingo, D., Krzanowski, J., Stampfli, D., and Eusden, D. (1993) The speciation of elements in incineration residues, p. 457-478. In: Proceedings of the Municipal Waste Combustion Conference, A WMA, Pittsburgh, Penn. Eighmy, T.T., Krzanowski, J., Domingo, D. Stampfli, D., & Eusden, D. (1993) The speciation of elements in incineration residues, p. 457-478. In: Proceedings of the Municipal Waste Combustion Conference, A WMA, Pittsburgh, Penn.

987

Eighmy, T.T., Krzanowski, J. Domingo, D., Sthpfli, D., Eusden, J.D., Manella, K., Killeen, K, Gaurdenier, H. & Hogan, J. (1994a) The Nahue of Lea4 Cadmium and Other Elements in Incineration Residues and Their Stabilized Products. U.S. EPA Final Report (in press). Eighmy, T.T., Eusden, J.D., Holland, B., King, W., Koehler, C. & Krzanowski, J. (1994b) The Speciation of Elements in Selected Fractions of the Municipal Solid Waste Stream and Incinerutor Residues. Environment Canada Final Report (in preparation). Environment Canada (1990) Compendium of Waste Leaching Tests. Report EPS 3/HA/7, Environment Canada, Ottawa, Ontario, Canada. Environment Canada (1991) Proposed Evalwtion Protocol for Cement-Based Solidijied Wastes. Report EPS 3/HA/9, Environment Canada, Ottawa, Ontario, Canada. F&Ilman, k - M . & Hartlkn, J. (1994) Leaching of slags and ashes-controlling factors in field experiments versus in laboratory tests. In: (J.J.J.R. Goumans, H.A. van der Sloot, Th.G. Aalbers, eds.) Waste Materials in Comtruction Elsevier Science Publ. (in press). FSillman, A-M. (1990) International Seminar on Leach Tests, Statens Geotechniska Institute, Linktiping, Sweden. Fruchter, J.S., Rai, D. & Zachara, J.M. (1990) Identification of solubility-controlling solids phases in a large fly ash lysimeter. Environ. Sci. Technol. 24, 1173-1179. Fuhrmann, M., Pietrzak, R.F., Franz, EM., Heiser, J.H. 111, & Colombo, P. (1989) Optimization of Factors That Accelerate Leaching. BNL52204,Brookhaven, NY. Gardner, KH. (1991) Chamcteriratonof Leachutes From Municipal Incinerator Ash Materials, Master’s Thesis, Clarkson University. Hjelmar, 0. (1991) Field studies of leachate from landfilled combustion residues, (suppl.). In (J.J.J.R. Goumans, H.A. van der Sloot & Th.G. Albers, eds.) Waste Materials in Construction, Elsevier Science Publ., the Netherlands. Horiuchi, S. (1994) personal communication. Lichtman, D. (1987) Micro-Sutjiace-AnalyticalTechniquesfor Characterizing Fly Ash. EPRI-EA-4820, EPRI, Palo Alto, California. IAWG (1994) Treatise on Municipal Solid Waste Incineration Residues (in press). Martinez, S. (1994) personal communication. Mkhu, J. (1994) personal communication. Meij, R. & Schaftenaar, H.P.C. (1994) Hydrology and chemistry of pulverized fuel ash in a lysimeter or the translation of the results of the Dutch column leaching test into field conditions. In (J.J.J.R. Goumons, H.A. van der Sloot & Th.G. Aalbers, eds.) Waste Materials in Constmtion, Elsevier Science Publ., the Netherlands (in press). Mulder, E. (1991) The leaching behavior of some primary and secondary raw materials used in pilot-scale road bases, p. 255-264. In (J.J.J.R. Goumans, H.A. van der Sloot & Th.G. Albers, eds.) Waste Materials in Comtruction, Elsevier Science Publ.. the Netherlands.

988

Pavlik, H.F. & Runnells, D.D. (1990) Reconstruction of reaction pathways in a rockfluid system using MINTEQ. p. 140-153. In (D.C. Melchior & R.L. Bassett, eds.) Chemical Modeling of Aqueous Systems ZI, ACS, Washington, DC. Rai, D.& Zachara, J.M. (1988) Chromium Reactions in Geologic Matenah. EPRI EA-5741, EPRI, Palo Alto, California. Rai, D.& Zachara, J.M. (1989) Field Investigation of a Flue Gas Ddfurkatwn (FGD) Sludge Disposal Site. EPRI EA-5923, EPRI, Palo Alto, California. Rai, D., Zachara, J.M., Schmidt, R.A. & Schwab, A.P. (1984) Chemical Attenuation Rates, Coefficients, and Constants in Leachate Migration. EPRI EA-3336, EPRI, Palo Alto, California. Stegemann, J.A., Caldwell, RJ. & Shi, C. (1994) Field validation of test methods for solidified waste evaluation - a status report. In Proceedings of the Third Intemational Symposium on Stabilizatwn/Solkiijication of Hazardous, Radioactive and Mixed Wastes, November 1-5, 1993, Wlliamsburg,Virginia,ASTM, Philadelphia, Penn. (in press). Theis, T.L., Iyer, R. & Gardner, K.H. (1993) Dynamic evaluation of municipal waste combustion ash leachate, p. 680-689. In Proceedings of the International Specialty Conference on Munictpal W&e Combustion,AWMA, Pittsburgh, Penn. TNO (1993) State of Art Document Waste Characterization,CEN/TC 292. van der Sloot, H.A., Hoede, D. & Bonouvrie, P. (1991) Comparison of Diferent Regulatory Leaching Test Procedutes for Waste Materials and Construction Materials, ECN-C-91-082, ECN, Petten, the Netherlands. van der Sloot, H A , Hjelmar, O., Aalbers, Th.G., Wahlstrom, M.& Falman, A.-M. (1992a) Proposed Leaching Test for Granular Solid Wastes, CEN WG2. van der Sloot, H.A., van der Hoek, E.E., de Groot, G.J. & Comans, R.N.J. (1992b) Classijication of Pulverized Coal Ash: Part 1. Leaching Behavior of Coal Fly Ash. ECN-C-92-059, ECN, Petten, the Netherlands. van der Sloot, H.A., Comans, R.N.J., Eighmy, T.T. & Kosson, D.S. (1993) Interpretation of municipal solid waste incinerator residue leaching data in relation to utilization and disposal, p. 331-346. In (M. Faulstich, ed.) RilchtWe aus der Miillverbremung,EF-Verlag fiir Energie und Umwelttechnik GmbH, Berlin. van der Sloot, H.A., Kosson, D.S.,Hjelmar, O., & Eighmy, T.T. (1994) A concise characterization scheme for testing of granular waste leachability. In (JJ.J.R. Goumons, H.A. van der Sloot & Th.G. Aalbers, eds.) Waste Materiab in Constmction, Elsevier ScientificPubl., the Netherlands. Warren, C.J. & Dudas, M.J. (1986) Mobilization and Attenuation of Trace Elements in an Ari@cally Weathered Fly A h . EPRI EA-4747, EPRI, Palo Alto, California. Zachara, J.M. & Streile, G.P. (1991) Use of Batch and Column MethodolOges to Assess Utility Waste Leaching and Subsurface Chemical Attenuation. EPRI EN-7313, EPRI, Palo Alto, California.

Environmental Aspects of Construction with Waste Materials

Read more

Waste Materials in Construction: Proceedings (Studies in Environmental Science)

Read more

Use of Waste Materials in Highway Construction

Read more

The Science of Construction Materials

Read more

Waste materials in construction: putting theory into practice: proceedings of the International Conference on the Environmental and Technical Implications of Construction with Alternative Materials, WASCON'97, Houthem St. Gerlach, the Netherlands, 4-6 Jun

Read more

Environmental Design + Construction June 2011

Read more

Handbook of Thermal Analysis of Construction Materials

Read more

Handbook of Thermal Analysis of Construction Materials

Read more

Handbook of environmental degradation of materials

Read more

Handbook of Environmental Degradation of Materials

Read more

Handbook of environmental degradation of materials

Read more

Soil and rock construction materials

Read more

Test Quality for Construction, Materials and Structures: Proceedings of the International RILEM ILAC Symposium (RILEM Proceedings)

Read more

Sustainability of Construction Materials (Woodhead Publishing in Materials)

Read more

Environmental Aspects of Dredging

Read more

Environmental Design + Construction January 2011

Read more

Environmental Design + Construction December 2011

Read more

Environmental Design + Construction July 2011

Read more

Environmental Deterioration of Materials (Advances in Architecture)

Read more

Environmental Design + Construction February 2011

Read more

Environmental Design + Construction April 2011

Read more

Construction Databook: Construction Materials and Equipment, Second Edition

Read more

Environmental Design + Construction October 2011

Read more

Environmental Design + Construction August 2011

Read more

Environmental Design + Construction February 2012

Read more

Environmental Design + Construction March 2011

Read more

Environmental Design + Construction November 2011

Read more

Environmental Design + Construction May 2011

Read more

Environmental Design + Construction January 2012

Read more

Environmental Design + Construction September 2011

Read more

Recommend Documents

Environmental Aspects of Construction with Waste Materials

ENVIRONMENTAL ASPECTS OF CONSTRUCTION WITH WASTE MATERIALS PROCEEDING OF THE INTERNATIONALCONFERENCE ON ENVIRONMENTAL I...

Waste Materials in Construction: Proceedings (Studies in Environmental Science)

WASTE MATERIALS IN CONSTRUCTION PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ENVlR ONMENTAL I MPLICATI0 NS 0 F CO NST...

Use of Waste Materials in Highway Construction

USE OF WASTE MATERIALS IN HIGHWAY CONSTRUCTION lmtiaz Ahmed Purdue University Department of Civil Engineering West La...

The Science of Construction Materials

The Science of Construction Materials Per Freiesleben Hansen edited by Ole Mejlhede Jensen The Science of Constructio...

Waste materials in construction: putting theory into practice: proceedings of the International Conference on the Environmental and Technical Implications of Construction with Alternative Materials, WASCON'97, Houthem St. Gerlach, the Netherlands, 4-6 Jun

WASTE MATERIALS IN CONSTRUCTION Putting Theory into Practice WASTE MATERIALS IN CONSTRUCTION Putting Theory into Pract...

Environmental Design + Construction June 2011

The Premier Source for Integrated High-Performance Building www.EDCmag.com June 2011 environmental design + constructio...

Handbook of Thermal Analysis of Construction Materials

HANDBOOK OF THERMAL ANALYSIS OF CONSTRUCTION MATERIALS by V.S. Ramachandran, Ralph M. Paroli, James J. Beaudoin, and ...

Handbook of Thermal Analysis of Construction Materials

1 CONTENTS Thermoanalytical Techniques Introduction to Portland Cement Concrete Formation and Hydration of Cement and C...

Handbook of environmental degradation of materials

Handbook of Environmental Degradation of Materials Edited by Myer Kutz Myer Kutz Associates, Inc. Delmar, New York ...

Handbook of Environmental Degradation of Materials

Handbook of Environmental Degradation of Materials Edited by Myer Kutz Myer Kutz Associates, Inc. Delmar, New York N...