Effect of rusting on steel reinforcement

Corrosion of steel reinforcement inside a concrete structure is undesirable in the subsequent ways: 

(i)  Presence of rust impairs the bond strength of deformed reinforcement since corrosion takes place at the raised ribs and fills the gap between ribs so evening out the original deformed shape. Basically the bond between concrete and deformed bars originates from the mechanical lock between raised ribs and concrete. Reduction of mechanical locks by corrosion results in the decline in bond strength with concrete.

(ii) Presence of corrosion decreases the effective cross sectional area of steel reinforcement. Therefore the available tensile capacity of steel reinforcement is reduced by a considerable reduction in the cross sectional area.

(iii) Corrosion products occupy about 3 times the original volume of steel from that it is formed. Such radical increase in volume generates significant bursting forces in vicinity of steel reinforcement. Subsequently cracks are formed along steel reinforcement when tensile strength of concrete is exceeded.