Corrosion of Epoxy- and Polymer/Zinc-Coated Rebar in Simulated Concrete Pore Solution

This work is an initial examination of mechanistic issues on the comparative corrosion performance of regular epoxy-coated rebar (ECR) and dual polymer-zinc-coated reinforcement (DCR) in simulated concrete pore solution with and without chloride ions, at polarizations from 100 mV to −1,000 mV in the saturated calomel electrode (SCE) scale and exposure periods of 1 month or longer. Both materials had intentional coating breaks exposing the base steel. Polymer adhesion degradation of DCR relative to the as-received condition was comparable to, or less than, that experienced by ECR under both anodic and cathodic polarization and with and without chloride ions. Both DCR and ECR experienced severe corrosion at breaks under strong anodic polarization with chloride ions, but distress for DCR was significantly less than for ECR. Under open-circuit conditions DCR experienced an initial high-activity period both in the presence and absence of chloride ions after which the open-circuit potential (OCP) stabilized to ∼−400 mV_SCE, and the exposed steel remained free of corrosion in either environment. In contrast, ECR in the presence of chlorides developed more negative OCP and visible corrosion. After the initial period of high activity, OCP consumption of the zinc exposed at the defect rim proceeded at a very low rate, both in the presence or absence of chloride ions. In the absence of chloride ions and under medium to strong cathodic polarization, DCR showed cathodic current (and hence an ability to support corrosion macrocells with through-the-steel defects) no greater than that for ECR.