Introduction to Concrete Technology

NED UNIVERSITY OF ENGINEERING &TECHNOLOGY, KARACHI-75270

ENGINEERING MATERIALS By

Dr. Amanullah Marri Associate Professor

SYLLABUS 1.

2. 3. 4.

5. 6.

7.

Classification and general aspects of construction materials Concrete materials Metals and alloys Natural stones, bricks and tiles Timber Rubber, plastic and bituminous materials Insulating materials 2

BOOKS 1) 2)

3)

Engineering Materials by R. K. Rajput Advance concrete technology by John Newman and Ban Seng Choo Concrete technology Theory and practice by M. S. Shetty

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CEMENT

WHAT IS CEMENT Material with adhesive and cohesive properties Any material that binds or unites-essentially like glue.

FUNCTION OF CEMENT to bind the sand and coarse aggregate together to fill voids in between sand and coarse aggregate particle

to form a compact mass

PROPERTIES OF CEMENT Good quality cement posses the following properties (which depend upon its chemical composition, thoroughness of burning and fineness of grinding). 1. Provide strength to masonry. 2. Stiffens or hardens easily. 3. Possesses good plasticity. 4. Easily workable. 5. Good to moisture resistant. 7

TYPES OF CEMENT There are mainly two types of cement, normally used in building industry are as follows: a) Hydraulic Cement b) Non hydraulic Cement

HYDRAULIC CEMENT Hydraulic Cement sets and hardens by action of water, such as Portland Cement  In other words it means that hydraulic cement are:  Any cements that turns into a solid product in the presence of water as well as air, resulting in a material that does not disintegrate in water. 

HYDRAULIC CEMENT

Most common Hydraulic Cement is Portland Cement

NONHYDRAULIC CEMENT Any cement that does not require water to transform it into a solid product.  Two common Non hydraulic Cement are a) Lime - derived from limestone / chalk b) Gypsum 

CHEMICAL CONSTITUENTS OF CEMENT 1) 2) 3) 4) 5) 6)

Lime (CaO) Silica (SiO2) Alumina (Al2O3) Iron oxide ((Fe2O3) Magnesium oxide (MgO) Sulphur trioxide (SO3)

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PRINCIPAL MINERALS IN CEMENT

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PORTLAND CEMENT Chemical composition of Portland Cement: a) Tricalcium Silicate C3S (50%) b) Dicalcium Silicate C2S (25%) c) Tricalcium Aluminate C3A (10%) d) Tetracalcium Aluminoferrite C4AF (10%) e) Gypsum (CaSO4 ·2H2 O) (5%)

FUNCTION :TRICALCIUM SILICATE Hardens rapidly and largely responsible for initial set & early strength  The increase in percentage of this compound will cause the early strength of Portland Cement to be higher.  A bigger percentage of this compound will produces higher heat of hydration and accounts for faster gain in strength. 

FUNCTION :DICALCIUM SILICATE Hardens slowly It effects on strength increases occurs at ages beyond one week Responsible for long term strength

FUNCTION :TRICALCIUM ALUMINATE Contributes to strength development in the first few days because it is the first compound to hydrate. It turns out higher heat of hydration and contributes to faster gain in strength. But it results in poor sulfate resistance and increases the volumetric shrinkage upon drying.

FUNCTION :TRICALCIUM ALUMINATE Cements with low Tricalcium Aluminate contents usually generate less heat, develop higher strengths and show greater resistance to sulfate attacks. It has high heat generation and reactive with soils and water containing moderate to high sulfate concentrations so it’s least desirable.

FUNCTION : TETRACALCIUM ALUMINOFERRITE Assist in the manufacture of Portland Cement By allowing lower clinkering temperature also act as a filler Contributes very little strength of concrete even though it hydrates very rapidly. Also responsible for grey colour of Ordinary Portland Cement

WET PROCESS 

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Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No. 200 sieve. The mix will be turned into form of slurry by adding 30 - 40% of water. It is then heated to about 2750º F (1510º C) in horizontal revolving kilns (76-153 m length and 3.6-4.8 m in diameter.

WET PROCESS 

Natural gas, petroleum or coal are used for burning. High fuel requirement may make it uneconomical compared to dry process.

DRY PROCESS Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No. 200 sieve. Mixture is fed into kiln & burned in a dry state This process provides considerable savings in fuel consumption and water usage but the process is dustier compared to wet process that is more efficient than grinding.

DRY PROCESS & WET PROCESS In the kiln, water from the raw material is driven off and limestone is decomposed into lime and Carbon Dioxide. limestone lime + Carbon Dioxide  In the burning zone, portion of the kiln, silica and alumina from the clay undergo a solid state chemical reaction with lime to produce calcium Aluminate. silica & alumina + lime calcium Aluminate 

DRY PROCESS & WET PROCESS The rotation and shape of kiln allow the blend to flow down the kiln, submitting it to gradually increasing temperature. As the material moves through hotter regions in the kiln, calcium silicates are formed These products, that are black or greenish black in color are in the form of small pellets, called cement clinkers Cement clinkers are hard, irregular and ball shaped particles about 18 mm in diameter.

DRY PROCESS & WET PROCESS The cement clinkers are cooled to about 150ºF (150ºF) and stored in clinker silos.

When needed, clinker are mixed with 2-5% gypsum to retard the setting time of cement when it is mixed with water. Then, it is grounded to a fine powder and then the cement is stored in storage bins or cement silos or bagged.

Cement bags should be stored on pallets in a dry place.

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TYPES OF CEMENT ASTM classification and general classification According to ASTM classification, cement is designated as Type I, Type II, Type III, Type IV, Type V and other minor types like Type IS, Type IP and Type IA IIA and IIIA.

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ASTM CLASSIFICATION Type I-For use in general concrete construction where the special properties specified for types II, III, IV, and V are not required. Type I is also called ordinary Portland cement (OPC). Type II-For use in general concrete construction exposed to moderate sulphate action, or where moderate heat of hydration is required. Type III For use when high early strength is required (Rapid hardening cement).

Type IV-For use when low heat of hydration is required (Low Heat Cement)

Type V-For use when high sulphate resistance is required (Sulphate resisting cement).

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TYPES OF CEMENT 1. 2. 3.

4. 5. 6. 7. 8. 9.

Ordinary Portland Cement Rapid Hardening Cement Extra Rapid Hardening Cement Sulphate Resisting Cement Quick Setting Cement Super Sulphated Cement Low Heat Cement Portland Pozzolana Cement Air-Entraining Cement

10. 11. 12. 13. 14.

15. 16. 17. 18.

Coloured Cement Hydrophobic cement Masonry Cement Expansive Cement IRS-T 40 Special Grade Cement Oil-Well Cement Rediset Cement High Alumina Cement High Early Strength Cement 29

ORDINARY PORTLAND CEMENT 

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Ordinary Portland cement (OPC) is the most important type of cement. The OPC was classified into three grades, namely 33 grade, 43 grade and 53 grade depending upon the strength of the cement at 28 days when tested as per IS 4031-1988. If the 28 days strength is not less than 33 N/mm2, it is called 33 grade cement, if the strength is not less than 43 N/mm2, it is called 43 grade cement, and If the strength is not less than 53 N/mm2, it is called 53 grade cement.

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MANUFACTURING OF PORTLAND CEMENT The three primary constituents of the raw materials used in the manufacture of Portland Cement are: • Lime • Silica • Alumina

Lime is derived from limestone or chalk, Silica & Alumina from clay, shale or bauxite

MANUFACTURING OF PORTLAND CEMENT There are two chief aspects of the manufacturing process:  First to produce a finely divided mixture of raw materials – chalk / limestone and clay / shale  Second to heat this mixture to produce chemical composition

RAPID HARDENING CEMENT  

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This is similar to ordinary Portland cement. The rapid rate of developing strength is attributed to the higher fineness of grinding, higher C3S and lower C2S content. Should not be used in mass concrete construction

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EXTRA RAPID HARDENING CEMENT

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EXTRA RAPID HARDENING CEMENT

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SULPHATE RESISTING CEMENT

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SULPHATE RESISTING CEMENT

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QUICK SETTING CEMENT

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LOW HEAT CEMENT

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SIEVES

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SIEVES

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CEMENT MANUFACTURING

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EXTRACTION OF RAW MATERIALS

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GRINDING AND STORAGE OF RAW MATERIALS

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THE FIRING OF RAW MATERIALS

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CEMENT CLINKERS

STORAGE AND GRINDING OF CEMENT

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CEMENT

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PACKING

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PACKING AND SHIPMENT

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SETTING AND HARDENING OF CEMENT When cement is mixed with water a stiff and sticky paste is formed, which remains plastic for a short period. With the passage of time the plasticity gradually disappears and the cement paste become stiff due to initial hydration of cement. This phenomenon by virtue of which the plastic cement changes into a soil mass is known as setting of cement.

Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood. The different constituents slowly crystallise and the interlocking of their crystals gives cement its strength. Carbon dioxide is slowly absorbed to convert the portlandite (Ca(OH)2) into insoluble calcium carbonate. After the initial setting, immersion in warm water will speed up setting. In Portland cement, gypsum is added as a compound preventing cement flash setting.

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SETTING AND HARDENING OF CEMENT

On setting the cement binds the aggregates into a solid mass which gain strength as the time lapses, till the hydration of cement is complete. Thus, the phenomenon by virtue of which the cement paste, which is finally set, develops strength is known as hardening of cement. 52

STANDARD CONSISTENCY TEST The standard consistency of a cement paste is defined as that consistency which will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top of the mould. The apparatus is called Vicat Apparatus. This apparatus is used to find out the percentage of water required to produce a cement paste of standard consistency. The standard consistency of the cement paste is some time called normal consistency (CPNC). 53

SETTING TIME TEST An arbitrary division has been made for the setting time of cement as initial setting time and final setting time. It is difficult to draw a rigid line between these two arbitrary divisions. For convenience, initial setting time is regarded as the time elapsed between the moment that the water is added to the cement, to the time that the paste starts losing its plasticity. The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure. 54

SETTING TIME TEST Prepare a cement paste by gauging the cement with 0.85 times the water required to give a paste of standard consistency.

Start a stop-watch, the moment water is added to the cement.

Fill the Vicat mould completely with the cement paste gauged as above, the mould resting on a non-porous plate and smooth off the surface of the paste making it level with the top of the mould. The cement block thus prepared in the mould is the test block. 55

VICAT APPARATUS

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VICAT APPARATUS

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SETTING TIME TEST INITIAL SETTING TIME:-Place the test block under the rod bearing the needle. Lower the needle gently in order to make contact with the surface of the cement paste and release quickly, allowing it to penetrate the test block. Repeat the procedure till the needle fails to pierce the test block to a point 5.0 ± 0.5 mm measured from the bottom of the mould. The time period elapsing between the time, water is added to the cement and the time, the needle fails to pierce the test block by 5.0 ± 0.5 mm measured from the bottom of the mould, is the initial setting time. 58

SETTING TIME TEST FINAL SETTING TIME:-Replace the above needle by the one with an annular attachment. The cement should be considered as finally set when, upon applying the needle gently to the surface of the test block, the needle makes an impression therein, while the attachment fails to do so. The period elapsing between the time, water is added to the cement and the time, the needle makes an impression on the surface of the test block, while the attachment fails to do so, is the final setting time. 59

AGGREGATES

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AGGREGATES

Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. Typically include both sand and gravel.

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AGGREGATES Essentially aggregates can refer to any granular material formed from a natural rock substance. It is usually further defined either:

By its source: primary, secondary, recycled By its geology: limestone, granite, sand and gravel, etc, By its grading: coarse, fine, By its end use: concrete aggregates, etc. Mostly confined to sand, gravel and rock chippings. 62

CONCRETE Concrete is a composite construction material, composed of cement (commonly Portland cement) and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravel or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water and chemical admixtures.

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TERMINOLOGIES Workability Flowability

Compactability Stability Pumpability 64

WORKABILITY Workability-that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished is called the workability of concrete (ACI). Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like super plasticizer.

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WORKABILITY Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. 66

WORKABILITY The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot be readily made more workable by addition of reasonable amounts of water. Workability can be measured by the concrete slump test, a simplistic measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. 67

FLOWABILITY Flowability-The flowability of self consolidating concrete (SCC) is measured in terms of spread when using a modified version of the slump test (ASTM C 143). The spread (slump flow) of SCC typically ranges from 18 to 32 inches (455 to 810 mm).

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FLOWABILITY Compactability- The ease by which a concrete can be compacted is called Compactability. Pumpability- the ease by which concrete slurry can be pumped to the point to the placement is called the Pumpability.

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COMPOSITION OF CONCRETE the main ingredients of concrete are  Cement  Water  Aggregates (i.e., coarse aggregate and fine aggregate)  Reinforcement  Chemical admixtures

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MIXING CONCRETE Mixing concrete correctly is vital for durable and long lasting foundations. Thorough mixing is essential for the production of uniform, high quality concrete. For this reason equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work.

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MIXING CONCRETE Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, superplasticizers, pigments, or silica fume. 72

MIXING CONCRETE The premixed paste is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment.

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CONCRETE MIXING

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CONCRETE MIXING

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PLACING AND COMPACTION The methods chosen for placing and compacting the concrete will depend on the type of construction, the total volume to be placed, the required rate of placing and the preferences and expertise of the construction companies involved. There are, however, several basic rules which should be followed to ensure that the concrete is properly placed and compacted into a uniform, void free mass once it has been delivered to the formwork in a satisfactory state: 76

PLACING AND COMPACTION The concrete should be discharged as close as possible to its final position, preferably straight into the formwork;

A substantial free-fall distance will encourage segregation and should therefore be avoided; With deep pours, the rate of placing should be such that the layer of concrete below that being placed should not have set; this will ensure full continuity between layers, and avoid cold joints and planes of weakness in the hardened concrete;

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PLACING AND COMPACTION Once the concrete is in place, vibration, either internal or external, should be used to mould the concrete around embedment e.g. reinforcement, and to eliminate pockets of entrapped air, but the vibration should not be used to move the concrete into place;

High-workability mixes should not be over vibrated – this may cause segregation.

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PLACING AND COMPACTION

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TYPES OF CONCRETE 1) 2) 3)

4) 5)

6) 7) 8)

Regular concrete High-strength concrete high-performance concrete Self-consolidating concretes Vacuum concretes Shotcrete Pervious concrete Stamped concrete 80

REGULAR CONCRETE Regular concrete- is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa (1450 psi) to about 40 MPa (5800 psi), depending on the purpose, ranging from blinding to structural concrete respectively. 81

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REGULAR CONCRETE

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HIGH STRENGTH CONCRETE It is a type of high performance concrete generally with a specified compressive strength of 6000 psi (40 MPa) or greater. High strength concrete is required to:  Put concrete into service at much earlier age, for example opening the pavement at 3-days  To build high-rise buildings by reducing columns sizes and increasing available space. etc. 84

High-Strength Concrete

High-Value Concrete

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90% of ready-mix concrete 20 MPa - 40 MPa (3000 – 6000 psi) @ 28-d (most 30 MPa – 35 MPa)

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High-strength concrete by definition — 28 day – compr. strength 70 MPa (10,000 psi)

High-Strength Concrete Materials Aggregates —

High-Value Concrete

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9.5 - 12.5 mm (3/8 - 1/2 in.) nominal maximum size gives optimum strength

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Combining single sizes for required grading allows for closer control and reduced variability in concrete

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For 70 MPa and greater, the FM of the sand should be 2.8 – 3.2. (lower may give lower strengths and sticky mixes)

High-Strength Concrete Materials Supplementary Cementing Materials —

High-Value Concrete

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Fly ash, silica fume, or slag often mandatory

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Dosage rate 5% to 20% or higher by mass of cementing material.

High-Strength Concrete Materials Admixtures — 

Use of water reducers, retarders, HRWRs, or superplasticizers — mandatory in high-strength concrete

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Air-entraining admixtures not necessary or desirable in protected high-strength concrete. 

Air is mandatory, where durability in a freeze-thaw environment is required (i.e.. bridges, piers, parking structures)

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Recent studies: 

High-Value Concrete

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w/cm ≥ 0.30—air required w/cm < 0.25—no air needed

High-Strength Concrete Placing, Consolidation, and Curing 

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High-Value Concrete

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Delays in delivery and placing must be eliminated Consolidation very important to achieve strength Slump generally 180 to 220 mm (7 to 9 in.) Little if any bleeding—fog or evaporation retarders have to be applied immediately after strike off to minimize plastic shrinkage and crusting 7 days moist curing

HIGH STRENGTH CONCRETE

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HIGH-PERFORMANCE CONCRETE High performance concrete (HPC) has been defined as concrete that possesses high workability, high strength and high durability. High Performance Concrete (HPC) is a concrete made with appropriate materials combined according to a selected mix design; properly mixed, transported, placed, consolidated and cured so that the resulting concrete will give excellent performance in the structure in which it is placed, in the environment to which it is exposed and with the loads to which it will be subject for its design life. The primary application for HPC have been structures requiring long service lives such as oil drilling platform, long span bridges and parking structures. HPC still requires good construction practice and good curing to deliver high performance. 91

HIGH-PERFORMANCE CONCRETE

Lightweight high performance concrete was used for the cast-in-place superstructure segments.

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Characteristics of HighPerformance Concretes

High-Value Concrete

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High early strength

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High strength

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High modulus of elasticity

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High abrasion resistance

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High durability and long life in severe environments

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Low permeability and diffusion

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Resistance to chemical attack

Characteristics of HighPerformance Concretes

High-Value Concrete

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High resistance to frost and deicer scaling damage

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Toughness and impact resistance

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Volume stability

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Ease of placement

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Compaction without segregation

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Inhibition of bacterial and mold growth

Materials Used in HighPerformance Concrete Material Portland cement

Primary Contribution/Desired Property Cementing material / Durability

Blended cement Fly ash / Slag / Silica fume

Calcined clay/ Metakaolin Calcined shale Superplasticizers High-range water reducers Hydration control admix. High-Value Concrete

Cementing material / Durability / High strength Flowability Reduce water-cement ratio Control setting

Materials Used in HighPerformance Concrete Material Retarders Accelerators Corrosion inhibitors

Primary contribution/Desired property Control setting Accelerate setting Control steel corrosion

Water reducers Shrinkage reducers

Reduce cement and water content Reduce shrinkage

ASR inhibitors Optimally graded aggr.

Control alkali-silica activity Improve workability/reduce paste

Polymer/latex modifiers

Durability

High-Value Concrete

Selected Properties of HighPerformance Concrete Property

Test Method

Criteria that may be specified

High Strength

ASTM C 39

70-140 MPa @ 28 to 91 days

H-E Comp. Strength

ASTM C 39

20-30 MPa @ 3-12 hrs or 1-3 days

H-E Flex. Strength

ASTM C 78

2-4 MPa @ 3-12 hrs or 1-3 days

Abrasion Resistance

ASTM C 944

0-1 mm depth of wear

Low Permeability

ASTM C 1202

500 to 2000 coulombs

Chloride Penetration

AASHTO T 259/260

Less than 0.07% Cl at 6 months

Low Absorption

ASTM C 642

2% to 5%

High Mod.of Elast.

ASTM C 469

More than 40 GPa

High-Value Concrete

Self-consolidating concrete 

High-Value Concrete

Self-consolidating concrete (SCC) is characterized by a low yield, high deformability, and moderate viscosity necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets.

Self-Consolidating Concrete

High-Value Concrete

Self-consolidating concrete

Self-consolidating Concrete

Vacuum concrete

High-Value Concrete

It is a well known fact that excessive w/c ratio is detrimental for concrete. We always try to restrict the w/c ratio in order to achieve higher strength. The chemical reaction of cement with water requires a w/c ratio of less than 0.38, whereas the adopted w/c ratio is generally much more than that mainly because of the requirement of workability. Workability is also important for concrete, so that it can be placed in the formwork easily without honeycombing.

Vacuum concrete 

High-Value Concrete

After the requirement of workability is over, this excess water will eventually evaporate leaving capillary pores in the concrete. These pores result into high permeability and less strength in the concrete. Therefore, workability and high strength don't go together as their requirements are contradictory to each other.

Vacuum concrete

High-Value Concrete

Vacuum concreting is the effective technique used to overcome this contradiction of opposite requirements of workability and high strength. With this technique both these are possible at the same time. In this technique, the excess water after placement and compaction of concrete is sucked out with the help of vacuum pumps. This technique is effectively used in industrial floors, parking lots and deck slabs of bridges etc.

Vacuum concrete The magnitude of applied vacuum is usually about 0.08 MPa and the water content is reduced by up to 20-25%. The reduction is effective up to a depth of about 100 to 150 mm only.

High-Value Concrete

Shotcrete Shotcrete refers to a process in which compressed air forces mortar or concrete through a hose and nozzle onto a surface at a high velocity and forms structural or nonstructural components of buildings. The relatively dry mixture is consolidated by the force of impact and develops a compressive strength similar to normal- and highstrength concrete. High-Value Concrete

Shotcrete Shotcrete may be applied to surfaces using a dry- or wet-mix method. The wet-mix concrete method consists of Portland cement and aggregate premixed with water before the pump pushes the mixture though the hose. Additional compressed air is added at the nozzle to increase the velocity of the mixture. High-Value Concrete

Shotcrete In the dry-mix process, compressed air propels a premixed blend of Portland cement and damp aggregate through the hose to the nozzle. In the nozzle, water is added from a separate hose and completely mixed with the dry mixture just as both streams are being projected onto the prepared surface. High-Value Concrete

Shotcrete

Shotcrete

Shaft Shotcrete

Shotcrete

Shotcrete Tunnel

Pervious concrete Pervious concrete is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass directly through, thereby reducing the runoff from a site and allowing groundwater recharge. Pervious Concrete

Pervious concrete The high porosity is attained by a highly interconnected void content. Typically pervious concrete has little or no fine aggregate and has just enough cementitious paste to coat the coarse aggregate particles while preserving the interconnectivity of the voids. Pervious concrete is traditionally used in parking areas, areas with light traffic, residential streets, pedestrian walkways, and greenhouses. It is an important application for sustainable construction and is one of many low impact development techniques used by builders to protect water quality.

Pervious concrete

Pervious Concrete

Architecture

Stamped concrete

High-Value Concrete

Stamped concrete is concrete that is patterned and/or textured or embossed to resemble brick, slate, flagstone, stone, tile, wood, and various other patterns and textures. Stamped concrete is commonly used for patios, sidewalks, driveways, pool decks, and interior flooring. The ability of stamped concrete to resemble other building materials makes stamped concrete a less expensive alternative to using those other authentic materials such as stone, slate or brick.

Stamped concrete

High-Value Concrete

There are three procedures used in stamped concrete which separate it from other concrete procedures; the addition of a base colour, the addition of an accent colour, and stamping a pattern into the concrete. These three procedures provide stamped concrete with a colour and shape similar to the natural building material. It also is longer lasting than paved stone, and still resembles the look.

Stamped concrete

Stamped Concrete

Slump Test

Slump test of Concrete

The concrete slump test is used for the measurement of a property of fresh concrete. The test is an empirical test that measures the workability of fresh concrete. More specifically, it measures consistency between batches. The slump test is a means of assessing the consistency of fresh concrete. It is used, indirectly, as a means of checking that the correct amount of water has been added to the mix. The slump test is used to ensure uniformity for different batches of similar concrete under field conditions, and to ascertain the effects of plasticizers on their introduction.

Slump test procedure The steel slump cone is placed on a solid, impermeable, level base and filled with the fresh concrete in three equal layers. Each layer is rodded 25 times to ensure compaction. The third layer is finished off level with the top of the cone. The cone is carefully lifted up, leaving a heap of concrete that settles or ‘slumps’ slightly. The upturned slump cone is placed on the base to act as a reference, and the difference in level between its top and the top of the concrete is measured and recorded to the nearest 5 mm to give the slump of the concrete.

Slump test procedure When the cone is removed, the slump may take one of three forms. In a true slump the concrete simply subsides, keeping more or less to shape. In a shear slump the top portion of the concrete shears off and slips sideways. In a collapse slump the concrete collapses completely. Only a true slump is of any use in the test. If a shear or collapse slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which the flow test is more appropriate.

SLUMP MOULD (ABRAMS CONE )

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SLUMP TYPES

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SLUMP MEASUREMENT

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SLUMP TESTING

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SLUMP CLASS Class

Slump range

Target slump

S1

10 ~ 40

20

S2

50 ~ 90

70

S3

100 ~ 150

130

S4

160 ~ 210

180

S5

210 ~ n/a

220

Slump class from BS 8500 125

CURING OF CONCRETE Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration. It may be either after it has been placed in position (or during the manufacture of concrete products), thereby providing time for the hydration of the cement to occur. Since the hydration of cement does take time – days, and even weeks rather than hours – curing must be undertaken for a reasonable period of time if the concrete is to achieve its potential strength and durability. Curing may also encompass the control of temperature since this affects the rate at which cement hydrates. 126

CURING METHODS Plastic sheeting- Plastic sheets, or other similar material, form an effective barrier against water loss. Ponding- Flat or near-flat surfaces such as floors, pavements, flat roofs and the like may be cured by ponding. Wet coverings- Fabrics such as hessian, or materials such as sand, can be used like a ‘mulch’ to maintain water on the surface of the concrete 127

CURING OF CONCRETE Sprinkling or fog curing -Using a fine spray or fog of water can be an efficient method of supplying additional moisture for curing and, during hot weather, helps to reduce the temperature of the concrete.

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CURING OF CONCRETE

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CONCRETE MIX DESIGN Concrete mix designs is best defined as a process in selecting suitable ingredients, which is cement, aggregate, sand and water, and determining their relative proportions to give the required strength, workability and durability. To find a combination of constituents that would give concrete of properties complying with certain specifications, economically. Mix design properties are selected depending on the application and expected performance. 130

OBJECTIVE OF CONCRETE MIX DESIGN To determine the proportions of concrete mix constituents of; Cement, Fine aggregate (or normally Sand), Coarse aggregate, and Water.  To produce concrete of the specified properties.  To produce a satisfactory of end product, such as beam, column or slab as economically as possible. 

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METHODS OF MIX PROPORTIONING 1) 2) 3) 4) 5) 6) 7) 8) 9)

Arbitrary proportion Fineness modulus method Surface area method High strength concrete mix design Mix design based on flexural strength Road note No. 4 (grading curve method) ACI Committee 211 method DOE Method Mix design for pumpable concrete 132

VARIABLES IN MIX PROPORTIONING With the given materials, the four variable factors to be considered in connection with specifying a concrete mix are: 1) Water cement ratio 2) Cement content or cement aggregate ratio 3) Gradation of the aggregates 4) Consistency

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METHODS OF MIX PROPORTIONING 1) 2) 3) 4) 5) 6) 7) 8) 9)

Arbitrary proportion Fineness modulus method Surface area method High strength concrete mix design Mix design based on flexural strength Road note No. 4 (grading curve method) ACI Committee 211 method DOE Method Mix design for pumpable concrete 134

SELECTION OF TARGET PARAMETERS Selection of target parameters by the contractor for any mix design must consider the influence of the following: 1) material availability and economics 2) variability of each material throughout period of usage 3) Control capability of production plant 4) Ambient conditions expected at the time(s) of concrete placement 135

SELECTION OF TARGET PARAMETERS 5)

6) 7)

logistics of concrete production, delivery, and placement variability in testing concrete properties generation of heat in large structural elements and differential in thermal gradient (i.e. 2 - 3 ft thick and cement content above 600 lb/yd3)

136

COMMON TERMINOLOGIES OF MIX DESIGN

137

AGGREGATES Coarse aggregate: Aggregates predominately retained on the No. 4 (4.75 mm) sieve. For mass concrete, the maximum size can be as large as 150 mm. Fine aggregate (sand): Aggregates passing No. 4 (4.75 mm) sieve and predominately retained on the No. 200 (75 μm) sieve.

138

DRY RODDED UNIT WEIGHT

139

BULK SPECIFIC GRAVITY

140

FINENESS MODULUS(FM) 

141

FINENESS MODULUS(FM) % Sieve sieve opening mass retaine cummulative % No. (mm) retained (g) d retained

Cummulative % Passing

4

4.750

66

13.21

13.21

86.79

10

2.000

78

15.61

28.81

71.19

20

0.850

102

20.41

49.22

50.78

50

0.300

160

32.02

81.24

18.76

100

0.150

78

15.61

96.85

3.15

200

0.075

14

2.80

99.65

0.35

Pan

0.000

1.75

0.35

100.00

0.00

142

ABSORPTION ABSORPTION Absorption is the process by which a liquid is drawn into and tends to fill permeable pores in a porous solid body. It is expressed as a percentage of the dry weight of the body. For example, the oven dry weight of a sample of sand is 60-pounds and its absorption is 5%. The weight of the sample after it has absorbed all of the moisture it can absorb is: 143

ABSORPTION 60 lb x 1.05 = 63 lbs The amount of water absorbed by the 60-pound sample is: 63 lb - 60 lb = 3 lbs

144

AIR ENTRAINMENT Air entrainment is the intentional creation of tiny air bubbles in concrete. The bubbles are introduced into the concrete by the addition to the mix of an air entraining agent, a surfactant (surface-active substance, a type of chemical that includes detergents). The air bubbles are created during mixing of the plastic (flowable, not hardened) concrete, and most of them survive to be part of the hardened concrete. The primary purpose of air entrainment is to increase the durability of the hardened concrete, especially in climates subject to freeze-thaw; the secondary purpose is to increase workability of the concrete while in a plastic state. 145

AIR ENTRAINMENT

146

BULK VOLUME The volume of a granular material including the volume of the solid particles and the volume of the voids between the solid particles.

147

ABSOLUTE VOLUME 

148

EXAMPLE 1 The specific gravity of a dry coarse aggregate (Gs) is 2.65. The unit weight of water is 62.4-lb/cu ft. The absolute volume of a 90-lb sample of the aggregate is how much? Absolute Volume = 90 lb / (2.65 x 62.4 lb/cu ft) = 0.544 cu ft.

149

EXAMPLE 2 For a concrete mix with 90-lbs of coarse aggregate with Gs = 2.65, 60-lbs of fine aggregate with Gs = 2.63, 25-lbs of cement, and 12-lbs of water. Calculate the absolute volume:

150

EXAMPLE 2 CA = 90 lb / (2.65 x 62.4 lb/cu ft) = 0.544 cu ft FA = 60 lb / (2.63 x 62.4 lb/cu ft) = 0.366 cu ft Cement = 25 lb / (3.15 x 62.4 lb/cu ft) = 0.127 cu ft Water = 12 lb / (1 x 62.4 lb/cu ft) = 0.192 cu ft Total Volume = 1.229 cu ft. For the same mix containing 4% air the total volume would be: Total Volume = 1.229 cu ft x 1.04 = 1.278 cu ft.

The volume of air in the mix is: Air = 1.278 cu ft - 1.229 cu ft = 0.049 cu ft. 151

POZZOLANA (P) A Pozzolana is a substance that, in-itself, has little or no cementitious properties but when combined with Portland cement forms compounds possessing cementitious properties. Fly ash is the most widely used Pozzolana.

152

COMMON TERMINOLOGIES OF MIX DESIGN 

153

VARIANCE Variance- this is the measure of variability of difference between any single observed data from the mean strength.

154

STANDARD DEVIATION 

155

COEFFICIENT OF VARIATION 

156

157

Number N Strength Average strength

N

x

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

43 48 40 38 36 39 42 45 37 35 39 41 49 46 36 38 32 39 41 40

40.2

Deviation

Deviation

2.8 7.8 -0.2 -2.2 -4.2 -1.2 1.8 4.8 -3.2 -5.2 -1.2 0.8 8.8 5.8 -4.2 -2.2 -8.2 -1.2 0.8 -0.2

7.84 60.84 0.04 4.84 17.64 1.44 3.24 23.04 10.24 27.04 1.44 0.64 77.44 33.64 17.64 4.84 67.24 1.44 0.64 0.04

standard deviation

4.36

158

EXAMPLE 

159



160

TYPICAL VALUES OF STANDARD DEVIATION FOR DIFFERENT CONDITIONS OF PLACING AND MIXING OF CONCRETE

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TYPICAL VALUES OF STANDARD DEVIATION FOR DIFFERENT CONDITIONS OF PLACING AND MIXING OF CONCRETE

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SPECIMEN PREPARATION

SAND CEMENT PROPORTION The following is the procedure for the determination of the void ratio of a cemented specimen, Determine • The specific gravity of sand G sand • The specific gravity of cement G cement • The dry mass of specimen M dry i.e., the mass of solid M solid • Specimen dimensions i.e., height H and diameter D

AVERAGE SPECIFIC GRAVITY • The average specific gravity of the specimen G (taking cement content = C %)

G

100 C Gsoil 100

C Gcement 100

INITIAL VOID RATIO The volume of solid (i.e., sand + cement) V solid

Vsolid

M solid G w

The total volume of the specimen V total

VTotal

4

D

2

The volume of voids V voids Vvoids Vtotal Vsolid

INITIAL VOID RATIO • The initial void ratio of the specimen e

e

Vvoids Vsolid

CONSTANT DRY DENSITY WITH INCREASING CEMENT CONTENT • The mass of sand M sand and mass of cement M cement can be calculated as follow:

M sand M cement

100 M total 100 C C M total 100 C

SAND CEMENT MIXING BUCKET Once dry sand and cement mixed thoroughly, water of required percent must be added and mixed to get a uniform and consistent sandcement paste.

SAND CEMENT MIXING The targeted dry unit weight of the material for a standard size specimen can be maintained by varying the weight of the moist sample using the following equation. The required weight of mixture should be taken for specimen preparation

d

1

ACI MIX DESIGN 1)

2) 3)

Determine the job parameters - aggregate properties, maximum aggregate size, slump, w/c ratio, admixtures, calculation of batch weight, and adjustments to batch weights based on trial mix.

171

MIX DESIGN PROCEDURES Required material information -- sieve analyses of both fine and coarse aggregates, unit weight, specific gravities, and absorption capacities of aggregates. Choice of slump -- Generally specified for a particular job. However, if not given, an appropriate value may be chosen from Table 1. As a general rule, the lowest slump that will permit adequate placement should be selected. 172

MIX DESIGN PROCEDURES

173

MIX DESIGN PROCEDURES Maximum aggregate size -- The largest maximum aggregate size that will conform to the following limitations: Maximum size should not be larger than 1/5 the minimum dimension of structural members, 1/3 the thickness of a slab, or 3/4 the clearance between reinforcing rods and forms. These restrictions limit maximum aggregate size to 1.5 inches, except in mass applications. 174

MIX DESIGN PROCEDURES Current thought suggests that a reduced maximum aggregate size for a given w/c ratio can achieve higher strengths. Also, in many areas, the largest available sizes are 3/4 in. to 1 in. Estimation of mixing water and air content -- An estimation of the amount of water required for air entrained and non-air-entrained concretes can be obtained from Table. 175

MIX DESIGN PROCEDURES One major disadvantage of concrete is its susceptibility to damage by single or multiple freeze-thaw cycles. However, concrete can be made frost-resistant by using air entraining admixtures. Approximate mixing water (lb/yd3) and air content for different slumps and nominal maximum sizes of aggregates 176

177

WATER/CEMENT RATIO Water/cement ratio - This component is governed by strength and durability requirements. Relationship between water/cement ratio and compressive strength of concrete:

178

Calculation of cement content -- Once the water content and the w/c ratio is determined, the amount of cement per unit volume of the concrete is found by dividing the estimated water content by the w/c ratio.

179

Estimation of coarse aggregate content - The percept of coarse aggregate to concrete for a given maximum size and fineness modulus is given by Table

180

Volume of dry-rodded coarse aggregate per unit volume of concrete for different coarse aggregates and fineness moduli of fine aggregates.

181

Estimation of fine aggregate content -- There are two standard methods to establish the fine aggregate content, the mass method and the volume method. We will use the "volume" method. "Volume" Method -- This method is the preferred method, as it is a somewhat more exact procedure. The volume of fine aggregates is found by subtracting the volume of cement, water, air, and coarse aggregate from the total concrete volume. 182

ACI MIX DESIGN EXAMPLE Concrete is required for an exterior column located above ground where substantial freezing and thawing may occur. The 28-day compressive strength should be 5,000 lb/in2. The slump should be between 1 and 2 in. and the maximum aggregate size should not exceed ¾ in. The properties of the materials are as follows:

183

ACI MIX DESIGN EXAMPLE Cement : Type I, specific gravity = 3.15 Coarse Aggregate: Bulk specific gravity (SSD) = 2.70; absorption capacity = 1%; dry-rodded unit weight = 100 lb/ft3; surface moisture = 0% Fine Aggregate: Bulk specific gravity (SSD) = 2.65; absorption capacity = 1.3%; fineness modulus = 2.70; surface moisture = 3%

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MIX DESIGN CALCULATION

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