In building construction there are many constituents such as brick work, cement concrete, wood work, steel work and painting etc. Cement concrete is the main constituents in the building construction mainly used in Columns, beams, slab and floor etc. The strength of the building is mainly related with the strength of cement concrete used in the building.
Concrete has relatively high compressive strength but weak in tensile strength. To make concrete strong in tension the concrete is reinforced with steel bars. There are four ingredients used in the cement concrete mix i.e. cement, fine aggregate, coarse aggregate and water. The quality of materials, process of mixing and lying has very much effect on the strength of cement concrete and thus on the life of building. There are some points if we follow during cement concrete mixing and lying can get more strength with the use of same quantity of cement.
1. Quality of materials:-
Quality of cement, sand and aggregate should be according to the specifications and the value of various tests in fields should be according to the prescribed norms of the specifications. The specified materials if used give more strength than ordinary materials.
2. Less surface area of aggregate:-
- Cement is the binding material in the concrete mix. A better coating of cement to the particles can provide more strength and this can be achieved when coarse aggregate is used.
- When proper graded materials are used, lesser the voids in concrete and tightness of the mix provide more strength.
3. Water Cement Ratio:-
- It is generally seen that some one consider to add more cement for getting more strength. The factor that mainly influences concrete strength is the ratio of water to cement in the cement paste that binds the aggregates together and this is called water cement ratio. The higher this ratio is, the weaker the concrete and reduce the strength of concrete. To make concrete more workable by adding more water that will be adversely affected the strength of cement concrete.
- In the graded material the surface area of the aggregate being low, water requirements for lubrication of particle will be less. Hence less shrinkage and more strength may be obtained using the same amount of cement, because of low water cement ratio.
- To control the quantity of water in the mix, slump test is conducted in the field. But for common man, he should watch that minimum water is mixed in concrete up to the extent that concrete may lay easily.
Mixing should be done in a mixer operated by diesel so that all constituents are thoroughly mixed and become homogeneous mass without showing segregation which increases the strength of the cement concrete.
6. Pouring or Placing:-
Placing of cement concrete mix at the time of casting either column or beam or slab has great effect on the strength of cement concrete. Never place cement concrete above one meter height if so done than concrete mix will be segregated which leads to reduce the strength of cement concrete.
Better compaction is achieved leading to less number of voids. When cement concrete is vibrated, it reduces the voids and mix become homogeneous leads to more strength.
- Cement needs water for its hydration. If water is inadequate or it is not properly cured than it will not hydrate completely, which leads to inadequate strength. So all cares should be taken for curing cement concrete properly.
- Horizontal surface of cement concrete member such as raft, slab etc shall be cured by pounding the water where as vertical surface should be kept wet by wetting the gunny bags.