Resource Utilization of Red Mud in Low-Carbon Binders: A Review of Reaction Mechanisms, Performance, and Microstructure

The cement industry plays a critical role in infrastructure development, but is a major contributor to CO2 emissions, driving the search for low-carbon binders that can also valorize industrial wastes. This review examines the engineering performance of red mud (RM)-based binder systems, highlighting the relationships between mixture design, processing, fresh-state behavior, mechanical properties, durability, and microstructural evolution. Special attention is given to how RM’s particle characteristics and mineralogical/chemical composition influence reactivity during geopolymerization, thereby affecting strength development and pore structure. Across the literature, moderate RM incorporation (commonly ≤15–20%) generally preserves workable fresh properties and adequate compressive strength, whereas higher RM contents (≥30%) often increase total porosity and pore connectivity, resulting in reductions in strength and durability. To mitigate these drawbacks, effective strategies such as thermal activation of RM and synergistic blending with supplementary cementitious materials like ground granulated blast-furnace slag and phosphogypsum are consistently reported to enhance reaction extent, densify the gel matrix, refine pore structure, and improve long-term durability. Overall, RM-based cementitious binders demonstrate considerable potential for both structural and non-structural applications; however, further research is needed on long-term performance under realistic exposure conditions, scale-up and quality control to address RM variability, and performance-based mix design guidelines to support reliable field implementation.