Electrochemical investigation of chloride-induced depassivation of black steel rebar under simulated service conditions

Electrochemical measurements of chloride thresholds are reported in simulated concrete pore solution for as-received and surface-modified rebar in an experimental apparatus designed to simulate service conditions. Surface modification led to higher chloride thresholds and reduced variability. The variability in thresholds for as-received rebar was represented by a log-normal distribution; therefore, simple averages of chloride thresholds, without reference to underlying distribution, might not provide reliable indicators of depassivation. The relative constancy of electrochemical measurements below thresholds, and the dependence of the thresholds on surface conditions, suggests that rebar depassivation is likely caused by local critical chemical conditions at the steel surface.