Cover to Reinforcing Steel

According to AS3600, cover is the distance between the outside of the reinforcing
steel or tendons and the nearest permanent surface of the member, excluding any
surface finish.

The two primary purposes of cover are durability and fire resistance. As a general
rule, cover is selected from an appropriate table but there are several cases where
additional cross checks are required.

A secondary reason for adequate cover is to ensure that the stresses in steel and
concrete can be transferred, one to another, by bond. These actions are called
stress development and anchorage. The cover required for these purposes is
measured not to the nearest bar, but to the bar whose stress is being developed.