Insights into improved chloride resistance of carbon steel in Portland cement blended with belitic calcium sulfoaluminate cement

While extensive evidence demonstrates that blending belitic calcium sulfoaluminate (BCSA) cement with ordinary Portland cement (OPC) can effectively passivate carbon steel, its corrosion resistance under chloride exposure remains insufficiently investigated. In this study, chloride-induced corrosion behavior of carbon steel embedded in mortars was systematically investigated, taking into account several critical factors such as pore solution chemistry, pore structure, hydration products and the steel-mortar interface. Additionally, red mud (RM) was incorporated into the OPC-BCSA blend to evaluate the corrosion resistance of steel in the modified cementitious system under chloride exposure. The results indicate that the alkalinity of pore solutions plays a decisive role in pitting corrosion resistance, despite the varying passivation properties of passive films formed in simulated pore solutions. However, although OPC mortar exhibits high alkalinity and strong chemical chloride binding capacity, the more compact steel-mortar interface in the OPC-BCSA and OPC-BCSA-RM blended mortars serves as effective physical barriers against chloride ingress and significantly suppresses the propagation of corrosion pits. The results of this study are beneficial for the application of low-carbon binders in concrete structures subjected to marine environments.