Corrosion behaviour of steel in CAC-mixed concrete containing different concentrations of chloride

Abstract

High aluminate in cement arising from Al2O3 in oxides is presumed to form the higher level of CA-type of hydration, which can subsequently bind chlorides then to reduce the corrosion risk. To maximise the chloride binding in the cement matrix, in this study, a mixture of calcium aluminate cement (CAC) with ordinary Portland cement (OPC) was used as binder. The ratio of CAC to total binder was 5%, 10% and 15%. The resistance of CAC mixture to chloride-induced corrosion was assessed by a monitoring of the corrosion rate, and its binding of chlorides and buffering against a pH fall of the cement matrix were simultaneously measured. As a result, the CAC mixture was very resistive to corrosion; there was no corrosion observed in CAC mixture at exceeding 3.0% of chlorides by weight of binder, whilst OPC produced about 0.5–1.0% of the critical chloride threshold for the onset of corrosion. The inhibitive measure of CAC mixture may arise from increased binding capacity of chlorides and buffering to acidification. In particular, the buffering zone for CAC mixture occurred at 10.5–11.5 and 11.8–12.6 in the pH, at which bound chlorides in the matrix would be kept immobile, unreactive in the corrosion process.