Performance of epoxy-coated reinforcing steel in highway bridges

Laboratory, test yard and field research studies were performed to evaluate the performance of epoxy-coated reinforcing steel (ECR) with regard to corrosion protection. The effort consisted of a critical interpretative literature review, consideration of ECR production plant and job site practices and quality control methodologies. The testing program included bars acquired from ten sources and involved coating characterization, 80 deg C aqueous exposure testing, chemical immersion testing (ambient temperature) in various electrolytes and test yard exposure of ECRs in chloride contaminated concrete slabs. Performance was assessed by electrochemical impedance spectroscopy and coating adhesion testing. Where appropriate, the testing was also performed upon in place ECRs at bridge construction sites. ECR performance in the different tests varied according to bar source, and it was concluded that impedance and solvent extraction weight loss were the coating properties with which long-term corrosion protectiveness best correlated. Coating failure mechanisms were identified as underfilm corrosion in association with either conductive pathways through the coating, wet adhesion loss, cathodic disbondment and corrosion at coating defects (or combinations of these). It was concluded that an unacceptably high percentage of the coatings evaluated would not provide long-term corrosion protection in chloride contaminated concrete transportation service.