Evaluation of composite cements using cyclic polarization techniques

Critical tolerable limit of chloride for steel in Ordinary Portland Cement (OPC), Portland Pozzolona Cement (PPC) and Portland Slag Cement (PSC) extracts in the presence and absence of nitrite inhibitor were studied by cyclic polarization technique. Studies also carried out in composite (binary and ternary) cement extracts. The re-passivation potential ( E rep ) is an important parameter to characterize the corrosion resistant property of cements and the efficiency of inhibitor. Blended cements (PPC and PSC) have higher tolerable limit of chloride than OPC. Binary cements increase the tolerable limit of chloride than individual cements. The passivity of steel maintained by ternary cement was found to be less than 45000 ppm of chloride along with 5000 ppm of nitrite (pitting occurred at 45000 ppm). This chloride level is more than that of chlorides in natural sea water (35000 ppm). Hence the use of composite cement especially in marine atmosphere increases the corrosion resistance of steel in concrete.