Concrete is a porous material, which means it absorbs the acid created during the chipping process, accelerating corrosion and exposing the internal steel structure to air and water. This is what causes concrete cancer, a term used to describe when steel reinforcement within a concrete slab begins to rust. As the steel oxidizes, it expands and displaces the surrounding concrete, making it brittle and causing it to crack. Concrete cancer is caused by concrete absorbing water and salt air, which oxidizes the steel it contains.
This causes the steel to expand, cracking the concrete. The first sign of concrete cancer is usually ferrous stains on the concrete surface. Plastering the concrete won't help, as the oxidation process will continue underneath, leading to further displacement of the concrete and possibly requiring replacement of the reinforcing steel. Sometimes there is not enough room left between the reinforcement and the edge or surface of a slab. To detect if your building has concrete cancer, look for ferrous stains on the concrete surface.
If you find any, you should contact a professional to assess the damage and determine if any repairs are necessary. To prevent concrete cancer, make sure that there is enough cover on all reinforcement when pouring concrete, and that all surfaces are sealed properly.