The cement concrete is mixture of cement, sand, pebbles or crushed rock and water, which, when placed in a skeleton of forms and allowed to cure, becomes hard like stone. The cement concrete has attained the status of a major building material in all branches of modern construction because of the following reasons:
- It can be readily moulded into durable structural items of various sizes and shapes at practically no considerable labour expenditure.
- It is possible to control the properties of concrete within a wide range by using appropriate ingredients and by applying special processing techniques – mechanical, chemical, and physical.
- It is possible to mechanise completely its preparation and placing process.
- It possesses adequate plasticity for the mechanical working.
Properties of cement concrete:
The cement concrete possesses the following important properties:
- It has a high compressive strength.
- It is free from corrosion and there is no appreciable effect of atmospheric agents on it.
- It hardens with age and the process of hardening continues for a long time after the concrete has attained sufficient strength. It is this property of cement concrete which gives it a distinct place among the building material.
- It is proved to be more economical than steel. This is due to the fact that sand and pebbles or crushed rock, forming the bulk of concrete, to the extent of about 80 to 90%, are usually available at moderate cost. The formwork, which is of steel or timber, can be used over and over again or for other purposes after it is removed.
- It binds rapidly with steel and as it is weak in tension, the steel reinforcement is placed in cement concrete at suitable places to take up tensile stresses. This is termed as reinforcement cement concrete or simply R.C.C.
- Under the following two conditions, it has a tendency to shrink:
- There is initial shrinkage of cement concrete which is mainly due to the loss of water through forms, absorption by surfaces of forms.
- The shrinkage of cement concrete occurs as it hardens. This tendency of cement concrete can be minimized by proper curing of concrete.
- It has a tendency to be porous. This is due to the presence of voids which are formed during and after its placing. The two precautions necessary to avoid this tendency are as follows:
- There should be proper grading and consolidating of aggregates.
- The minimum water cement ratio should be adopted.
- It forms a hard surface. Capable of resisting abrasion.
- It should be remembered that apart from other materials, the concrete comes to the site in the form of raw material only. Its final strength and quality entirely depends on local conditions and persons handling it. however the materials of which concrete is composed may be subjected to rigid specifications.