This study investigates the performance and mechanism of bauxite residue (red mud) and multiple solid wastes as active cement replacements in precast concrete. The effects of mixing ratio, water-to-binder ratio, and steam-curing temperature on mechanical properties and microstructural evolution were systematically evaluated. Results showed that incorporating 10–20% red mud significantly accelerates early hydration under 45–60 °C steam curing, enabling demoulding strength above 15 MPa within 8 h. Microstructural characterization reveals that the enhancement originates from the alkali–thermal synergistic mechanism: alkali released from red mud promote dissolution of fly ash glass phases and formation of C–(A)–S–H gels, which interweave with AFt to generate a dense microstructure. A suitable steam curing temperature will further enhance this synergistic effect. This synergistic hydration not only improves early mechanical performance but also supports stable long-term strength development. Sustainability assessment further indicated that the optimized mix design reduces carbon emissions by 46.1% and lowers material cost by 40.8% compared with the pure cement system. Overall, this study clarifies the alkali-thermal synergistic hydration mechanism in solid-waste-based precast concrete and demonstrates an effective pathway for large-scale synergistic utilization of industrial solid wastes such as red mud. • Reveals alkali–thermal synergistic hydration enabling efficient solid wastes utilization. • Synergistic effect accelerates hydration achieving 8 h demoulding strength exceeding 15 MPa. • Adding 10–20% red mud can balance early strength gain and long-term strength development. • Cuts carbon emissions by 46.1% and reduces material cost by 40.8% versus pure cement.
Ma et al. (Sun,) studied this question.