Enhanced passivity of reinforcing steel in cementitious materials with thermally-activated red mud

Abstract

Red mud (RM) is a solid waste from aluminium industry that can be used as an emerging supplementary cementitious material, and it has beneficial effects on the corrosion resistance of reinforcing steel in concrete. However, the low reactivity of RM reduces the comprehensive performance of cementitious materials, thereby limiting its widespread application in concrete. In this study, RM was thermally activated and the phase transformation behavior of the thermally-activated RM (TA-RM) was studied. Additionally, the passivation behavior of steel in extract solutions and mortars containing RM with and without thermal activation was investigated using electrochemical methods, surface characterization techniques and compositional analysis. The results showed that the reactivity of RM was effectively improved by the thermal activation treatment due to the phase transformation, and the enhanced steel passivity was observed in both extract solution and mortar with TA-RM. Compared to steel exposed to extract solutions, the mortar containing TA-RM could provide an additional protection for the embedded steel by forming a compact steel-mortar interface, further improving its passivation ability.