Synergistic effects of red mud, calcium carbide residue and phosphogypsum for eco-friendly road materials

Red mud (RM), calcium carbide residue (CCR), and phosphogypsum (PG) are industrial solid wastes with low utilization rates, posing significant environmental challenges. This study explores their synergistic use in developing eco-friendly road materials without external activators, addressing both waste disposal and resource scarcity. Using response surface methodology, we optimized the mix design for mechanical strength, water resistance, and freeze-thaw durability. The results reveal a strong synergistic effect within the RM-CCR-PG system, with an optimal PG content significantly enhancing performance. Specifically, the optimal mixture (85 % RM, 10 % CCR, 5 % PG) achieved a 7-day unconfined compressive strength (UCS) of 6.83 MPa-a 412 % increase over pure RM (1.33 MPa). CCR provided calcium ions and alkalinity, facilitating RM dissolution, while sulfates from PG further activated the reaction. Key hydration products, including ettringite, C-(A)-S-H, and N-A-S-H, contributed to the improved microstructure and strength. Leaching tests confirmed effective stabilization of Na and heavy metals, meeting environmental standards. This work demonstrates a sustainable approach to repurposing industrial wastes into high-performance road materials, supporting waste management and green construction.