Ternary cementless composite based on red mud, ultra-fine fly ash, and GGBS: Synergistic utilization and geopolymerization mechanism

Industrial solid wastes, such as ultra-fine fly ash (RUFA) and ground granulated blast-furnace slag (GGBS), hold tremendous potential for recycling due to their abundance and excellent pozzolanic properties. However, red mud (RM), a highly alkaline waste, has not received comprehensive attention in the construction industry. Thus, this study investigates the synergistic effect and geopolymerization mechanism of industrial solid wastes in ternary cementless composites based on RM, RUFA, and GGBS. The experimental program includes macroscopic comparative analyses of water consumption, fluidity, setting time, permeability, and compressive strength of the ternary cementless composite. Additionally, SEM and EDS analyses examine the microscopic morphology and elemental distribution of the composite. The results indicate that RM prolongs the setting time while reducing fluidity and compressive strength. A 30% increase in RM content led to a substantial rise in the initial and final setting time by approximately 191.6% and 164.7%, respectively. In contrast, GGBS enhances the compressive characteristics of the composite systems but shortens the setting time and reduces fluidity. Notably, Group D4 demonstrates the highest compressive strength, reaching an impressive 47.3 MPa. Moreover, the content of GGBS influences the hydration products in the ternary cementless composite. At low GGBS content, the material contains a significant amount of N-A-S-H gels, whereas at high GGBS content, partial N-A-S-H gels are replaced by C-A-S-H gels. These findings significantly enhance our understanding of the synergistic effect and geopolymerization mechanism of RM, RUFA, and GGBS, thereby facilitating the reuse of these three industrial solid wastes.