my first post ( just sharing my knowledge )
Aggregates occupy ¾ space in the concrete mass and have following functions ( a ) provide a filler for concreting material ( b) provides mass to the concrete and reduce volume changes while setting and hardening of concrete. ( c ) the rest ¼ is occupied by the paste ( water + cement ) binder which is an active component of concrete and having following functions: ( a) it fills the voids between aggregates ( b ) it gives strength to hardened concrete The Reinforced Concrete ( R.C.C.) , the steel and concrete forms a very good combination because the co-eff of expansion of concrete and steel are nearly equal. Concrete has low tensile strength & hence cracks easily .Therefore concrete is to be reinforced with mild steel bars, high tensile steel bars or mesh . Concrete expands and contracts with change in temp. Constituents of cement Lime ( Ca O ) calcium oxide 60 – 67 % Silica ( Si O 2 ) Silicon Oxide