Treatment of Exposed Epoxy-Coated Reinforcement in Repair (ACI 364.3T-10)

Description

When epoxy-coated steel reinforcement is exposed in a repair area, the exposed reinforcement requires treatment prior to repair material placement During concrete removal and preparation of the repair area, the epoxy coating on the bars within the repair will be damaged, may already have defects or, as part of the repair procedure, be completely removed. Measures should be considered to avoid or minimize the risk of accelerated corrosion. It is common practice to clean, prepare, and re-coat any exposed epoxy-coated steel reinforcement during the repair process, usually with an epoxy coating compatible with the existing fused coating on the steel.

Additional protection should be considered because of the difficulty to re-coat the steel completely. Areas left uncoated (defects) may result in corrosion problems after the repairs are completed. When a concrete repair is undertaken, chloride-contaminated or carbonated concrete is typically removed and replaced with repair material. In many cases, not all of the contaminated concrete is removed. After the repair, the reinforcing steel may be in contact with concrete outside the repair area having varying levels of contami-nation. The differences in pH levels and in chloride ion concentrations between the new repair materials and the remaining contaminated concrete will result in differing corrosion potentials or voltages through the length of the reinforcing bar. A current will flow as a result of these voltage differences, leading to corrosion.

Reinforcement locations surrounded by concrete with the highest moisture and chloride contamination are likely to corrode first. Corrosion will occur in locations where there is both a defect in the coating and a sufficient level of contamination present. In general, the corrosion rate is proportional to the ratio of the cathodic area to the anodic area. Because the amount of coated steel is often far greater than the exposed steel, the rate of corrosion of the exposed steel can be extremely high. Additionally, the repaired area increases the cathodic (protected) area.

As a result, corrosion of the steel immediately adjacent to the repair area at locations with defects or where the epoxy has delaminated will continue, and the rate may even accelerate. The uncoated area of steel inside the repair area will contribute toward the overall corrosion cell, which could result in corrosion of steel in the existing concrete in the locations where sufficient contamination, oxygen, and moisture are present. It is also possible that corrosion will occur within the patch by current flow between any re-coated epoxy coating defects.