What should be done in the absence of lean concrete (PCC- Plain cement concrete ) below the footing
It is well known that the cover is provided below footing to protect Re-bar from direct contact with atmosphere. So we shall know about the cover provided to footing.
The minimum thickness of cover to
main reinforcement shall not be less than 50 mm for surfaces in contact with earth face and not less than 40 mm for external exposed face.
However, where the concrete is in direct contact with the soil, for example, when a levelling course of lean concrete is not used at the bottom of footing,
it is usual to specify a cover of 75 mm. This allows for the uneven surface of the excavation.
In case of raft foundation, whether resting directly on soil or on lean concrete, the cover for the reinforcement shall not be less than 75 mm.
Gyan of engineering (Mukesh Kumar)