Passivation behavior of steel in novel low-carbon binders with belitic calcium sulfoaluminate cement

Belitic calcium sulfoaluminate cement (BCSA) is a promising low-carbon binder, but it may negatively affect the steel passivity owing to its low alkalinity. This study aims to evaluate the steel passivation behavior in BCSA blended with ordinary Portland cement (OPC), which is further modified by adding red mud (RM) to increase its alkalinity and further reduce carbon footprint. It reveals that, compared with the OPC pore solution, the BCSAOPC blend pore solution leads to the formation of a more protective and less defective passive film, and a passive film with comparable passivation ability could be gained for steel in the BCSA-OPC-RM blend pore solution. It is worth emphasizing that, the oxygen availability at the steel-mortar interface, as determined by the pore structure and hydration products of mortar matrix, is crucial to the formation of stable steel passive films in reinforced mortars. Consequently, the findings of this study shed light on the promising applications of the novel low-carbon binders with BCSA and RM in reinforced concrete structures.