Corrosion of reinforcing steel within concrete slabs can be identified by spalling or splitting of the concrete surface and rust staining. As the steel corrodes it expands which causes the concrete to split apart and spall off the surface.
Corrosion of reinforcing steel in concrete slabs can be caused by several things. The most common causes include exposure to harsh environments like water and road salt, the reinforcing steel not having enough concrete cover to protect it, or excessive chlorides being present in the concrete mix at the time it was placed. Common sources of chloride in concrete include admixtures which are used to accelerate curing at the time the concrete is placed and contaminated aggregates. Chlorides may also be added to the concrete in an attempt to lower the freezing point, although this not very effective as it may lower the freezing point by only a couple of degrees. The level of chloride required to start the corrosion process of embedded reinforcing steel is extremely low at approximately .026%.
Repairing deteriorated reinforced concrete slabs is labor intensive and time consuming:
- First the slab may require shoring to prevent collapse during construction.
- The slab must be broken up and the concrete removed to the point where undamaged reinforcing steel is exposed.
- New reinforcing steel is spliced to the exposed undamaged reinforcing steel.
- Galvanic corrosion protection in the form of sacrificial galvanic anodes is provided at the perimeter due to differences in electrical potential between the original concrete and the new concrete patch which can cause localized corrosion.
- All exposed reinforcing steel is coated with a corrosion inhibitor.
- The removed concrete is replaced.
- Shoring is removed.