Why must the reinforcing steel be covered with adequate conc

Why must the reinforcing steel be covered with adequate concrete cover? Why must there be a sufficient concrete dimension between adjacent rebar to provide separation? What is the minimum concrete cover for steel reinforcing in an interior slab? The drawing details of a concrete beam indicate that 2 #6 bars are to be located at the bottom of the member. What is the diameter of a #6 bar? What is the distance from the bottom of the beam to the center of this bar assuming #4 stirrups and appropriate cover?

Solution

The concrete cover must have a minimum thickness for three main reasons:

to give reinforcing bars sufficient embedding to enable them to be stressed without slipping.

The concrete cover between the rebar and the outside surface is for corrosion protection. Too little cover means insufficient protection; too much cover can lead to cracking because of shrinkage, temperature or stress.

The bond created by utilizing rebar and concrete can also be attributed to the ridged rebar surface. This allows stresses to transfer from the concrete to the steel, and from the steel to concrete.

The minimum cover for slab is follows:

For tensile, compressive shear or other reinforcements in a slab or wall not less than 15 mm, not less that the diameter of such bar.