Factors affecting cathodic disbondment of epoxy coatings for steel reinforcing bars

Fusion-bonded-epoxy coatings have been used successfully for more than 20 years to prevent corrosion of concrete reinforcing steel. Recent attention in the epoxy-coated rebar (ECR) industry has focused on service in hot/wet environments. New specifications mandate quality control programs that include cathodic-disbondment testing. A number of systems are available to meet the new industry requirements; including chromate and non-chromate surface treatments, coatings for prefabricated rebar and developmental coatings that combine bendability and good adhesion retention. Beyond the choice of a coating system, various other factors play a role in the cathodic-disbondment resistance of ECR. The application temperature and thickness of the coating, and steel surface preparation and contamination are significant contributors. If a surface treatment is used, the weight of treatment applied is important. Finally, the test conditions of time, temperature, and pH have a dramatic impact on the cathodic-disbondment test results for a given system and even on the relative test performance of different systems.