Red mud-based multicomponent industrial by-product cementitious materials: Hydration mechanisms and synergistic activation

The global accumulation of red mud (RM), a highly alkaline and polluting industrial waste, poses immense environmental challenges. To address this, a novel cementitious material with a high RM dosage was developed. It was blended with RM, ground granulated blast-furnace slag (GGBS), steel slag (SS), and a small amount of ordinary Portland cement. This study systematically investigated the synergistic activation and cementitious mechanisms of the system. Research results show that when the content of red mud is fixed at 50%, the ratio of the content of GGBS to that of SS is 3:2, and the content of cement is 7%，the 28-day unconfined compressive strength reached 16.1 MPa. The hardened matrix exhibits a dense microstructure, a pore volume of 0.253 mLg-1, and 78% harmless/low-hazard pores, when the mixing ratio of GGBS to SS is 4:1 and 3:2 respectively. The underlying mechanisms were also clarified. RM acted as the principal alkali and supplementary providing Si 4+ and Al 3+ source. GGBS formed an early C-S-H gel skeleton. SS initially accelerated hydration and provided nucleation sites. Later, it promoted the formation of flocculent C-A-S-H gel. The C-A-S-H gel can densify the C-S-H skeleton and enhanced the overall strength. A successful synchronous shield grouting trial on Beijing Subway Line 13 confirmed the material's engineering feasibility. This work highlights its potential for the large-scale utilization of RM. • Excellent cementitious performance was exhibited by the high dosage RM solid waste system. • The synergistic activation mechanism among RM, GGBS, and SS was revealed. • Up to 50% reduction in economic cost and 85% reduction in carbon emissions were achieved. • The engineering applicability of high dosage RM binders was validated through field trials.