Synthesis and hydration of calcium sulfoaluminate cement produced using red mud

Calcium sulfoaluminate–belite (CSAB) cements are produced using limestone, bauxite and gypsum at clinkering temperatures below 1350°C, offering a low carbon dioxide alternative to Portland cement for various applications. In this study, red mud (bauxite residue) is used as a partial substitute for bauxite, addressing both the high cost and environmental burden attributed to conventional alumina sources. CSAB clinkers were synthesised with 15% and 20% (by weight) red mud in the raw mix and cements were prepared by clinker grinding and gypsum addition. These compositions were systematically compared with a reference clinker produced without red mud and a commercially available CSAB cement of similar composition. The increased iron content in red mud, acting as flux during clinkering, resulted in reduced clinker porosity. Iron also stabilised more of the cubic form of ye’elimite at the expense of the orthorhombic form. In addition, the free alkalis from red mud increased the apparent pH of cements, from 11.3 to 12.4, which also influenced the early-age hydration reactions. The synthesised CSAB cements produced similar hydration heat in 3 days compared to the commercial CSAB cement. The findings from this study demonstrate the technical feasibility of using red mud as an alternative alumina source for producing ye’elimite-rich CSAB cement.