Synergistic Effects of Multi-Source Solid Waste in Low-Carbon Cementitious Materials: Mechanical Properties, Physical Properties and Microstructures

The global challenge of effectively using and treating solid wastes in an environmentally sustainable way is significant. This study explores the creation of ternary low-carbon gelling materials made from red mud (RM), mineral powder (MP), and soda residue (SR). Using techniques such as SEM-ED, XRD, and FTIR, the microstructure of the red mud–mineral powder–alkaline slag (RM-MP-SR) mixture was analyzed, and the mechanical and physical properties of the material, as well as the leaching behavior of heavy metals, were investigated. The MRS16 sample, containing a 16% SR replacement, exhibited the best properties: compared with the control sample MRS0 (without replacement), its 28-day compressive strength increased by 43.7% to 51.3 MPa, the drying shrinkage rate decreased by 43.2%, and the mass loss rate reduced by 73.9%. After 100 freeze–thaw cycles, the mass loss was only 3.7%. The addition of SR can decrease the porosity in ternary materials, enhancing their mechanical properties; this is mainly due to SR promoting the increase in C-S-H, C-A-S-H gel, and ettringite. Meanwhile, MRS16 showed excellent freeze–thaw resistance, and the leaching levels of Cu, As, Pb, Cr, and Ni were within China’s non-hazardous limits. This study emphasizes the potential of combining RM, MP, and SR, providing useful scientific and theoretical insights for the joint use of alkaline, silica–aluminum, and calcium-based solid wastes.