Desulfurization-modified red mud for supersulfated cement production: Insights into hydration kinetics, microstructure, and mechanical properties

Investigating the production of supersulfated cement (SSC) using desulfurization-modified red mud is essential for enhancing the high-value utilization of calcium-based solid waste and advancing the development of low-carbon cementitious materials. In this study, red mud (RM) underwent desulfurization modification via a simulated flue gas desulfurization process, yielding red mud desulfurization residue (RMD). This RMD was subsequently employed as a resource component for the production of SSC samples. The effect of RMD addition on compressive strength was examined. The hydration kinetics and microstructural characteristics of the SSC based on RMD (SSCR) system were analyzed using various techniques, including ICC, XRD, TGA, FT-IR, MAS NMR, MIP and SEM-EDS. The results indicated that gypsum generated from the desulfurization reaction constituted the primary component of the resulting RMD. The gypsum particles exhibited a regular columnar morphology, while the unreacted residual particles displayed a coarser and more porous microstructure. Compared to a single alkali-activated system utilizing Ca(OH)₂, the appropriate incorporation of RMD significantly accelerated the hydration process of the SSCR system. The increase in products such as AFt and C-(A)-S-H gels, along with an increased proportion of gel pores (<10 nm), collectively contributed to the enhancement of mechanical properties. However, the presence of larger residual particles within the RMD might lead to the formation of larger voids and microcracks in the hardened paste, potentially limiting strength development, particularly when RMD was incorporated in excessive amounts.