CEMENT AND CEMENT CONCRETE

Guided by Prof. Manish Jain

Prepared by Rohit Galani

CEMENT Cement is the costliest and most

important ingredient of concrete. Cement has cohesive and adhesive

properties which make him capable of bonding the materials.

The cements of interest in the making of concrete have the property of setting and hardening under water by virtue of chemical reaction with it are, therefore called Hydraulic Cement.

Hydraulic cements consist of mainly of silicate, sand aluminates of lime and can be classified broadly as natural cements. For e.g. Portland cement, high alumina cement, etc.

CHEMICAL COMPOSITION OF CEMENT Cement mainly consists of lime, sand, alumina, and iron oxide.

The major compounds of cement are classified as follows: Tricalcium Silicate (C₃S) : 50±5%

Dicalcium Silicate (C₂S) : 30±5%Tricalcium Aluminate (C₃A) : 9±4%Tetracalcium Aluminoferrite (C₄AF) : 12±3%Free Lime : 1±.5%

Different Types Of CEMENT Ordinary Portland cement (i) Ordinary Portland cement 33 Grade- IS 269:1989 (ii) Ordinary Portland Cement 43 Grade- IS 8112:1989 (iii) Ordinary Portland Cement 53 Grade- IS 12269:1987 Rapid Hardening Cement - IS 8041:1990 Sulphate Resisting Cement –IS 12330:1998 Quick setting Cement Low Heat Cement –IS 12600:1989 Portland Pozzolana Cement – IS 1489 (Part-1) 1991 (Fly ash based) Air Entraining Cement Colored Cement - (White Cement IS 8042:1989) Expansive Cement High Alumina Cement- IS 6452:1989

CONCRETE Concrete is a composite material

composed of gravels or crushed stones (coarse aggregate), sand (fine aggregate) and hydrated cement (binder),and imparts considerable hardness to the mixture.

The cement reacts chemically with the water and other ingredients to form a hard matrix which binds all the materials together into a durable stone-like material that has many uses.

Sometimes, additives such as pozzolans or super plasticizers are included in the mixture

Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.

Properties Of Concrete Compressive strength Tensile strength Elastic Deformation Shrinkage

Compressive Strength Compressive strength is defined as the measured maximum

resistance of a concrete or mortar specimen to an axial load, usually expressed in PSI(pound per square inch) at an age of 28days.

Concrete compressive strength depends upon many factors:- -Quality & Proportions of the ingredients -The curing environment The grades are designated by one letter M (for mix) and a

number from 10 to 80 indicating the characteristic compressive strength (fck) in N/mm2.

As per IS 456 (Table 2), concrete has three groups as (i) ordinary concrete (M 10 to M 20), (ii) standard concrete (M 25 to M 55) and (iii) high strength concrete (M 60 to M 80).

Note: The following grade of concrete are generally used in highway pavements and are M30 M35 M40 M45.

Tensile Strength Concrete is not normally resist to direct tension, the knowledge of

tensile strength is use to estimate to load under which cracking will develop.

This is due to its influence on the formation of cracks and its propagation to the tension side of reinforced concrete flexural member.

The tensile strength of concrete is relatively low. The flexural and splitting tensile strengths are obtained as described

in IS 516 and IS 5816, respectively. However, the following expression gives an estimation of flexural

strength (fcr) of concrete from its characteristic compressive strength. fcr = 0.7ck in N/mm2

Elastic Deformation

It is seen that the initial tangent modulus is much higher than Et (tangent modulus inelastic respectively) components of strain. The initial tangent modulus Ec in N/mm2 is estimated from

Ec = 5000ck

The initial tangent modulus Ec is also known as short term static modulus of elasticity of concrete in N/mm2 and is used to calculate the elastic deflections.

Shrinkage Shrinkage is the time dependent deformation,

generally compressive in nature. The constituents of concrete, size of the member

and environmental conditions are the factors on which the total shrinkage of concrete depends. However, the total shrinkage is most influenced by the total amount of water present in the concrete at the time of mixing for a given humidity and temperature.

The approximate value of the total shrinkage strain for design is taken as 0.0003

Additives & Admixture Admixtures are chemicals which are added to concrete at the mixing

stage to modify some properties of the mix. The reason of using admixtures in concrete are as follows: To Improve Durability. Water Reduction in the Mix without changing workability. To produce High Strength Concrete. Accelerate the rate of strength development at early stages. Strength Enhancement. Crack Control (shrinkage reduction) To improve pump ability. Finish Enhancement. Early Strength and Reduced Permeability. Produce a fluid backfill, which flows easily and is self-leveling. To reduce the total cost of the materials used in concrete.

Type of Admixture Plasticizers (water-reducing agent):When concrete of

high workability without using excess of water is required then, Plasticizers are used. The main types of plasticizers are: LignoSulphates based, Melamine Sulphate based, and Naphthalene Sulphate based.

Super plasticizers (high range water reducers):The use of plasticizer is practiced for production of flowing, self levelling, self-compacting and for the production of high strength concrete and high performance concrete. Super-plasticizer are chemical compounds such as modified lingo Sulphates (MLS), sulphonated melamine formaldehyde (SMF), sulphonated naphthalene formaldehyde (SNF) and other polycarboxylate based materials.

Type of Admixture (contd) Retarders: They are used when delay in setting time

is required to ensure sufficient placement, vibration or compaction. Commonly known retarders calcium Sulphate, hydroxylated carboxylic acids, sugars, acids or salts of acids.

Accelerators: Accelerators work by accelerating cement hydration, which results in shortened setting times and increased early age strengths, particularly in cooler temperatures. For e.g.. Calcium chloride

Types of concrete used in pavement construction:

High strength concrete High performance concrete Stamped concrete Fibre reinforced concrete Self Compacting concrete

High strength concrete High strength concrete has a compressive strength greater

than 40 MPa (6800 psi). Recently, this strength has rose to 50 to 60 MPa and its use has increase in construction of high-rise bldg. and long span bridges. High strength concrete is made by lowering the w/c ratio to 0.35 or lower.

Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which reduce the strength at the cement-aggregate bond.

Low w/c ratios and use of silica fume make concrete less workable, which is particularly likely to be perform in high-strength concrete applications where dense rebar cages are likely to be used.

To compensate for reduced workability, super-plasticizers are commonly added to high-strength mixtures.

High Performance concrete HPC is being vastly used for highway pavement due to

potential economic benefits that can be derived from early strength gain of HPC, it reduced permeability, increased water or abrasion resistance to steel studded tires and improved freeze-thaw durability.

Different types of HPC are being considered for pavement repairs for early opening of traffic, bridge deck overlays, etc.

A durable concrete called fast track concrete designed to give high strength at very early stage without using special materials or techniques has been developed.

Fast track concrete paving (FTCP) technology can be used for complete pavement reconstruction, partial replacement by an inlay of atleast one lane, strengthening of existing bituminous or concrete pavements by a concrete overlay, rapid maintainence and reconstruction processes, and air-field pavement.

Benefits of applying FTCP is to reduce construction period, early opening of pavement to traffic, and minimizing the use of expansive concrete paving plant.

Stamped concrete Stamped concrete is an architectural concrete which has

superior surface finish. After a concrete floor has been laid, floor hardeners (can be

pigmented) are impregnated on the surface and a mold which may be textured to replicate a stone/brick or even wood is stamped on to give an attractive textured surface finish.

After sufficient hardening, the surface is cleaned and generally sealed to give protection.

The wear resistance of stamped concrete is generally excellent and hence found in applications like parking lots, pavements, walkways, etc.

Fibre reinforced concrete

Fibre-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity.

Fibres include steel fibres, glass-fibres, synthetic-fibres and natural fibres – each of which lend varying properties to the concrete.

The amount of fibres added to a concrete mix is ranging from 0.1 to 3%.

Fibre reinforced concrete is increasingly used on account of the advantages of increased static and dynamic tensile strength, energy absorbing characteristic and better fatigue strength.

Self Compacting Concrete

Self-consolidating concrete or self-compacting concrete(SCC) is characterized by a low yield stress, 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.

Such concrete can be used for casting heavily reinforced sections, places where there can be no access to vibrators for compaction and in complex shapes of formwork which may otherwise be impossible to cast, giving a far superior surface than conventional concrete.

It has been demonstrated that a total sand content of about 50% of total aggregate is favorable in designing for SCC.

Dry Lean Concrete (For Sub-Base) Dry lean cement concrete

(DLC) is used as a sub- base for concrete construction.

It is a plain concrete with a large ratio of aggregate to cement than conventional concrete.(i.e. 15:1)

The work should not proceed if the temperature rises above 30c and in that case ice water may be applied.

The curing of DLC can be done by spraying liquid curing compound or by covering the surface with wetted jute bags.

Conclusion Concrete is the material which can stand for longer span

without any structural deterioration or wear and tear of surfaces.

There are many types of concrete and further more development in the mix of concrete will improve the quality of pavements surface at very low cost rather than asphaltic paved roads.

It provides economical benefits such as low cost, less maintainence, last long, stand up the seasonal stresses, etc.

It also provides environmental benefits such as use less energy to build and maintain, reusable and recyclable, requires less aggregate for road base, make use of industrial by-products thereby reducing waste, etc.

Thank You

Reference :• Concrete Technology by M.S.Shetty• FRC-pdf• The concrete institute, ―Admixture for Concrete‖,

www.theconcreteinstitute.org.za• Cement Concrete Pavements, Oxford & IBH Publishing Co.

Pvt. Ltd., 1996.