Properties of Concrete.

Concrete:-  Concrete is obtained by mixing cement, aggregate (sand +stone) and waterin required proportion, with or without admixture.

Properties of Concrete:-

When it is in freshly mixed . In this stage it have the following properties :-

1)    Workability:-  It simply mean the ability to work with concrete. The ease of placing, compacting and finishing of concrete in the desired manner is called its workability. It depends on following factors: -

Ø  Water – cement ratio.

Ø  Fine aggregate to Coarse aggregate ratio (FA/CA)

Ø  Cement to aggregate ratio

Ø  Admixtures

2)    Segregation:- It is the separation of constituent material of concrete . Like separating of coarse aggregate , separating of cement pest or separating of water from concrete.

·       Causing factor of Segregation :-

Ø  Transporting concrete mixes for long distance.

Ø  Poorly proportioned mix, where sufficient matrix is not there to bind the aggregate.

Ø  Dropping concrete from more than 1 m.

Ø  Vibrating concrete for a long time.

·       Control of segregation:-

Ø  It controlled by maintaining proper proportioning the mix.

Ø  By peculiar handling, placing, transporting, compaction and finishing of concrete.

Ø  Adding air entraining agents, admixtures and pozzolanic materials in the mix.

                                   

It result in honey combing, decrease in density and ultimately loss of strength of hardened of concrete.

3)    Bleeding :-  It is defined as the separation of water and water – cement  mixture from the freshly mixed concrete . It  causes the concrete porous and weeak.    

4)    Harsh:-  Harsh of concrete is the mix which doesn't give proper smoothness to the surface even after certain amount of trowelling. It's because of poor grading of course aggregate, cement mortar not sufficient to fill the voids.

When it is in hardened stage, should have the following properties :-

1)    Strength :- The hardened concrete should have high compressive strength so that it can resist the heavy load of the structures.

2)    Durability :- Durability is defined as the capability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. It is mainly affected by water- cement ratio.

3)    Impermeability :- Impermeability of concrete is an ability of concrete to resist pressurized water penetration. Penetration of aggressive liquids into the concrete has considerable effect on its durability. Concrete permeability determines the intensity of such penetration, as well as its frost resistance.

4)    Shrinkage:-  The volumetric changes of concrete structures due to the loss of moisture by evaporation is known as concrete shrinkage or shrinkage of concrete. It is a time-dependent deformation which reduces the volume of concrete without the impact of external forces.

Type of shrinkage :-

Ø  Plastic shrinkage

Ø  Drying shrinkage

Ø  Autogeneous shrinkage

Ø  Carbonation shrinkage

5)    Creep :- Concrete creep is defined as: deformation of structure under sustained load. Basically, long term pressure or stress on concrete can make it change shape. This deformation usually occurs in the direction the force is being applied. Like a concrete column getting more compressed, or a beam bending.

6)    Thermal expansion :- Materials expand or contract when subjected to changes in temperature. Most materials expand when they are heated, and contract when they are cooled. When free to deform, concrete will expand or contract due to fluctuations in temperature.