Effects of chloride ion in cement pore solution on the corrosion of embedded iron.

摘要

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.