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.

Bayer red mud (RM)-based geopolymers are economical and ecofriendly alternatives to cement because of their superior performance. This study investigated alkali-activated cementitious materials by combining RM, fly ash (FA) and slag, and the mixtures were used to produce ecofriendly composites. The influence of the Si/Al molar ratio (3.30–3.79) on the initial properties (setting time and flowability) and hardened properties (compressive strength, drying shrinkage and water permeability) of the composite materials was studied. The Na₂O content was fixed at 4 wt%, and the thermal activation temperature was 800 °C. The phase evolution and geopolymerization mechanism of the effect of the initial Si/Al molar ratio on the material properties was investigated by FTIR, XRD, TG–DTG and SEM–EDS. The results of M1.2Si333 indicated that the compressive strength of the blends can reach 33.5 MPa at 28 days, with a drying shrinkage rate of 1.20%. Compressive strength decreases, while drying shrinkage increases with a higher initial Si/Al ratio. Microstructural analyses revealed that a low Si/Al ratio and alkali activator modulus enhance the dissolution of precursors to form C–(A)–S–H gels, which increase the compressive strength. The results promoted the application of RM-based geopolymer-engineered cementitious composite and enhanced the resource efficiency of the bauxite residue.

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 revealed that increasing the SiO₂/Al₂O₃ molar ratios and replacing RM with GGBS reduced the fresh properties of RM-based geopolymers. The increase of the SiO₂/Al₂O₃ molar ratio was beneficial to the compressive strength development of RM-based geopolymers, which was likely related to the high concentration of soluble silicates. The RM-based geopolymers also exhibited higher compressive strength than those with lower GGBS addition. Moreover, the drying shrinkage and water permeability of RM-based geopolymers increased with an increase in the SiO₂/Al₂O₃ ratio and the amount of GGBS addition. Sustainability analysis showed that the CO₂ emissions of RM-based geopolymers were related to 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.