Development of Novel Red Mud and Steel Slag-Based Low-Carbon Quaternary Geopolymers for Sustainable Civil Engineering Materials

The increasing accumulation of industrial solid waste and the urgent demand for low-carbon construction materials necessitate innovative solutions. This study develops a novel quaternary geopolymer system using red mud, steel slag, calcium carbide slag, and phosphogypsum as raw materials, effectively eliminating the need for commercial alkali activators. Specifically, the mechanical properties and hydration mechanisms were systematically investigated by varying the ratios of calcium carbide slag to phosphogypsum and testing different curing methods. Results indicate that optimal mix proportions (30% red mud, 40% steel slag, 15% calcium carbide slag, and 15% phosphogypsum) under sealed curing achieved a 28-day compressive strength of 15.42 MPa. Microstructural observations confirmed that the synergistic formation of ettringite and calcium (aluminum) silicate hydrate gel enhances matrix densification; however, excessive phosphogypsum was found to cause expansion cracking, thereby leading to a significant reduction in compressive strength. Furthermore, leaching tests confirmed low heavy metal concentrations, ensuring environmental safety. Overall, this geopolymer offers a sustainable and cost-effective solution for industrial waste utilization in civil engineering.