Extent of Cathodic Reaction on Epoxy Coated Rebar with Partially Disbonded Coating

摘要

Corrosion of epoxy coated rebar (ECR) in chloride exposed concrete can be enabled by the oxygen reduction cathodic reaction taking place on steel exposed by coating breaks. The total cathodic current would be expected to increase if the reaction locus were to extend into crevices formed at disbonded coating regions around coating breaks. To examine the possible amount of this effect, distress in the form of controlled surface breaks was created on production samples of ECR, some of which were further subject to cathodic disbondment to create surrounding disbonded regions around the breaks. The samples were cast in concrete specimens kept at ~80% RH in air and fitted with electrodes to perform cyclic polarization (CYP) in the cathodic direction and electrochemical impedance spectroscopy (EIS) measurements under open circuit conditions. Measurements performed initially and after 6 years of aging showed for the disbonded specimens a moderately greater extent of cathodic current and greater effective electrode area compared to that of the simply distressed specimens. Results will be presented for experiments in progress where concrete moisture is elevated to increase the electrolyte content in the disbondment crevice. The implications of the findings on the estimated service life of ECR structures will be quantitatively assessed.