Effect of Processing Techniques on the Suitability of Red Mud as a Supplementary Cementitious Material

Abstract Red mud (RM) is an industrial waste generated during the production of alumina. The red mud poses serious threat to the environment due to its hazardous nature, especially high alkalinity (pH of ∼ 11 to 13), iron content, and heavy metals. In this study, an Indian red mud which was rich in iron content ( > 40 % Fe 2 O 3 , by wt.) and deficient in calcium content ( < 3 % CaO, by wt.) was processed for its use in cementitious system. The processing involved calcination (600°C) and CO 2 mineralization. Calcined and mineralized red muds were substituted in ordinary portland cement (OPC) at various levels ranging from 5% to 20% (by wt.). OPC-RM blends were prepared to explore the reaction kinetics, phase assemblage, microstructure, and mechanical performance. Accelerated carbonation influenced the early hydration kinetics; however, no notable difference was observed in mechanical and microstructural properties. In comparison to carbonated red mud, calcined red mud reduced the dormant period and improved the compressive strength of OPC-RM blends. The calcination of red mud at 600°C increased compressive strength of OPC-RM blends by enhancing its reactivity. The pozzolanic property of calcined red mud improved due to the formation of desilicate products (cancrinite/sodalite). At 15% substitution level, OPC-RM blend achieved the maximum 28-day compressive strength. The findings of this study provide a pathway to utilize an iron-rich red mud in cement-based composites, addressing the problems associated with its management.