CEMENT CONCRETE
Cement concrete is an intimate mixture of cement, sand, coarse aggregates and water. Occasionally
some admixtures are added to introduce special properties. Water lubricates aggregates, activates
chemical reactions and give workability to mix. However, the quantity of water to be used should be
determined carefully since workability of concrete increases with quantity of water but the strength
deereases.
Various admixtures used with concrete are:
(1) Accelerators; (2) Retarders; (3) Air entraining agents and (4) Colouring agents.
Important properties of concrete in plastic stage (green concrete) are workability, segregation and
bleeding.
The important properties of hardened concrete are:
(1) Strength; (2) Resistance to wear; (3) Impermeability and (4) Durability.
IS code classifies concrete mix as M 20, M 25, etc. which means mix of strength 20 N/mm*, mix of
strength 25 N/mm', etc. at the age of 28 days.
IS: 10262-1982 and SP 23-1982 give detailed procedure to design concrete mix of required
strength.
For small works nominal mixes as shown is Table 1 may 
be used.
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