| The effects of pore solution factors on iron corrosion in hardened cement paste were studied using miniature cement electrodes and cyclic voltammetry. Topics investigated included chloride threshold concentrations for corrosion; externally added chloride vs. admixed chloride; effects of sulfate additions; ordinary Portland cement (OPC) vs. sulfate resistant Portland cement (SRPC); chloride binding; cation effects and electrochemical chloride removal (ECR). Overall, cyclic voltammetry was found to be a fast, convenient, economical way to study iron corrosion in cement. The results showed that: corrosion begins at cement chloride contents of about 0.25% by weight; externally added chlorides are much more corrosive than admixed chlorides; calcium sulfate (but not sodium sulfate) increases corrosiveness; OPC and SRPC exhibit similar corrosion resistance; and the rate-limiting step in ECR may be chloride ion desorption from cement hydration products. Also, a simple extrapolation technique is suggested to determine chloride diffusion coefficients in hardened OPC. |
