ACI 364.3T-10 TREATMENT OF EXPOSED EPOXY-COATED REINFORCEMENT IN REPAIR.
Discussion 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 diffculty 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 contamination. 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 fow 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 frst. Corrosion will occur in locations where there is both a defect in the coating and a suffcient 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.
In addition to coatings, other options exist to address these issues. They include the use of noncorrosive reinforcement, metallic coatings for steel reinforcement (both sacrifcial or noble and nonsacrifcial types), chemical inhibitors, and cathodic protection systems (both impressed current and galvanic types), which are discussed elsewhere (ACI Committee 222 2001; ICRI 1995). It is recommended that supplemental corrosion protection be provided for existing steel reinforcement by coating the reinforcing bar using either a high-electrical-resistance repair concrete that may contain an appropriate inhibitor, embedded galvanic anodes, or both, as illustrated in Table 1. A combination of corrosion protection methods from Table 1 will usually provide better corrosion protection than any individual method.ACI 364.3T pdf download.