Development of geopolymer with red mud, fly ash, calcium carbide slag, and phosphogypsum as a step toward low-carbon...

Developing geopolymer materials as sustainable alternatives to traditional cement-based products has become a major research focus in the field of green construction materials. However, conventional geopolymers typically depend on commercial alkali activators, which increase both cost and carbon emissions and hinder large-scale application. To address this limitation, this study developed a low-carbon, clinker-free quaternary geopolymer using fly ash, red mud, phosphogypsum, and calcium carbide slag-without the need for commercial alkali activators. The mechanical performance of quaternary geopolymer mortars was investigated under various mix proportions and curing conditions, and the fluidity, microstructural characteristics, and leaching behavior of selected samples were further examined. When the dosage of phosphogypsum and calcium carbide slag was both 15%, the mortar fluidity reached 175 mm. Under water curing, the 28-day compressive strength reached 14.09 MPa. Sealed curing enhanced the matrix densification by promoting the formation of C-(A)-S-H gel and AFt, resulting in a 33% increase in the 28-day compressive strength. High-temperature sealed curing was found unsuitable for this system. Microstructural analyses confirmed the synergistic effects of hydration products, which filled pores and reduced overall porosity. Leaching tests showed heavy metal concentrations well below Chinese regulatory limits, ensuring environmental safety. This study establishes a novel quaternary geopolymer system prepared without commercial alkali activators, enabling synergistic utilization of multiple industrial wastes and offering a scalable, low-carbon alternative to conventional cement materials.