Valorization of Alkali–Thermal Activated Red Mud for High-Performance Geopolymer: Performance Evaluation and Environmental Effects

This study investigates the influence of SiO₂/Al₂O₃ molar ratios (2.25–3.00) and the replacement of red mud (RM) with GGBS (50–63%) on the performance of RM-based geopolymers to address the environmental issues posed by RM, including its high alkalinity and heavy metal content. The results indicated that increasing the SiO₂/Al₂O₃ ratio and incorporating GGBS reduced the fresh properties of the geopolymers. A higher SiO₂/Al₂O₃ ratio promoted the development of compressive strength, likely due to the elevated concentration of soluble silicates. The RM-based geopolymers with higher GGBS content also exhibited greater compressive strength. Moreover, the drying shrinkage and water permeability of RM-based geopolymers increased as the SiO₂/Al₂O₃ ratio and the GGBS content increased. The sustainability assessment revealed that CO₂ emissions were influenced by the SiO₂/Al₂O₃ ratio. In comparison to other RM-based geopolymers, the CO₂ emissions and costs in this study were reduced by 13.13–44.33% and 3.64–39.68%, respectively. This study discusses the effects of the SiO₂/Al₂O₃ molar ratios on the reaction process and strength formation mechanism of RM-based geopolymers, which provides an effective strategy for the resource utilization of RM.