Basic ingredients of concrete

The basic ingredients of concrete are:

1. Cement: the binding material (OPC 33/43/53 grade, PPC). It reacts with water (hydration) to produce the paste that glues the aggregates; typically 10-15 per cent of the concrete volume.
2. Fine aggregate: natural sand or crushed stone sand passing the 4.75 mm sieve (IS 383 Zones I-IV). It fills the voids in the coarse aggregate and improves cohesion.
3. Coarse aggregate: crushed stone or gravel retained on the 4.75 mm sieve, with a nominal size of 10, 20 or 40 mm. It gives bulk, strength and volume stability. Fine and coarse aggregates together make up 60-75 per cent of the volume.
4. Water: clean potable water (IS 456 cl. 5.4) for hydration and workability; the water-cement ratio is normally 0.4-0.6.
5. Admixtures (optional): chemical or mineral admixtures to modify the properties of fresh or hardened concrete.

Cement + water forms the paste; paste + fine aggregate is mortar; mortar + coarse aggregate is concrete. Steel bars are added in reinforced concrete.