Constituents, Ingredients of Cement Concrete

UNIT - II

Chapter - 4 (F)

CEMENT CONCRETE

Lime concrete made of limė, surkhi and water was used in earlier days of construction. Later, cement concrete and reinforced cement concrete came in this field. Cement Concrete (or simply Concrete) is defined as a building material prepared by mixing 1. Cement, 2. Fine Aggregate, 3. Coarse Aggregate and 4. Water, in suitable proportions. It is allowed to cure to become hard like stone.

CONSTITUENTS / INGREDIENTS OF CEMENT CONCRETE

1. Binding Material

Cement binds the fine aggregate and coarse aggregate into a solid mass. It helps to fill the voids and gives density to the concrete. [Lime is the binding material in Lime Concrete.]

2. Fine Aggregate

Fine Aggregate is river sand or surkhi. Fine aggregate serves to fill the voids in coarse aggregate and reduce the quantity of cement. Fine aggregate should be in the size range of 0.15 mm (150 microns) to 4.75 mm. What is Surkhi? Surkhi is brick dust. It is made from slightly under-burnt bricks. If used wholly in place of sand, surkhi causes disintegration of concrete.

3. Coarse Aggregate

Coarse aggregate is crushed or broken stone, gravel or broken brick. Around the surfaces of the course aggregate, the binding material adheres in the form of a film. Coarse aggregate is graded in the size range of 4.75 mm to 20 mm.

4. Water

Water used for concreting should not contain chemicals. Chemicals cause harmful effects. Water fit for drinking is fit for concreting too. Water serves two purposes in concrete mixing. The purposes are:

(i) Paste: Water acts chemically with cement to form a paste. The paste which upon hardening, binds the fine and coarse aggregates to form a permanent mass.

(ii) Workability: Water gives workability to the mixture by enabling the concrete-mix to flow into moulds. Workability of concrete is the ease with which it is mixed, transported and placed in position so that the concrete remains homogeneous.

Water Cement Ratio: It is the ratio of weight of water used to that of cement. It depends upon workability and strength desired. Wet concrete is more workable than dry concrete. If concrete is too wet, it will have a non-uniform composition. If the concrete is too dry, it will be difficult to handle and place it in position.

Volumetric Proportions of Ingredients of Concrete: Proportions of cement : sand : coarse aggregate for various types of constructions range from 1:1:2, 1:2:3, 1: 2:4 and 1:3 : 6.