Durability and Corrosion of Reinforced Concrete Due to Sulfates

Abstract Corrosion of reinforced concrete for various civil infrastructure has been a challenge in certain aggressive environments. The effect of sulfates on the corrosion of steel in alkaline cementitious materials has not been widely addressed and discrepant findings have been presented in the literature and there remains interest to elucidate the role of sulfates in the corrosion of reinforced concrete. Testing is described with 0.4, 0.5 or 0.6 water-to-cement (w/c) ratio concrete exposed to either sulfate-or sulfate free- calcium hydroxide solution at earlier times during its curing and hydration. The OCP, Rp, and Rs were measured from the time of initial ponding to termination of the test after ~18 mo. Rebar exposed to sulfate free solutions remained in passive condition. Rebar with sulfate solution exposures showed a shift to more electronegative potentials and small Rp values, giving indication of the corrosion activity associated with the negative impact of the sulfates on steel passivation and concrete degradation. Rs values for the concrete specimens exposed to sulfate solutions gave indication that the sulfate solution ponding allowed for a decrease in the concrete electrical resistance whether it be due to increase in pore water conductivity or degradation of the cement paste. In addition to the effects of the concrete degradation, the sulfates created conditions where anodic electrochemical noise events, that can be indicative of metastable pitting, developed.