Synergistic preparation of one-part geopolymers from fly ash and calcined coal gangue: Performance, reaction mechanisms, and sustainability assessment

To promote the low-cost and large-scale utilization of coal-based solid wastes, this study aims to develop a one-part geopolymer using fly ash (FA) and calcined coal gangue (CCG) and to elucidate the effects of raw material proportions and auxiliary activators on its mechanical performance, fresh properties, and reaction behavior. The results indicate that with increasing CCG content, the compressive strength gradually increases, while the fluidity decreases. The incorporation of an appropriate amount of NaOH as an auxiliary activator significantly enhances early-age strength and promotes later strength development. Microstructural analyses indicate that CCG incorporation promotes geopolymerization, facilitating the formation of zeolite-like phases and contributing to strength development. Under the preferred conditions (40% CCG and NH/NS = 0.02), the geopolymer achieves compressive strengths of 5.17 MPa at 1 day and 17.58 MPa at 28 days, showing increases of 3.82 MPa and 10.23 MPa compared with the geopolymer without CCG at 1 and 28 days, respectively. Meanwhile, carbon emissions increase by 33.49% and the cost rises by only 6.39%. Further increasing the CCG content provides limited strength improvement while substantially reducing fluidity and increasing carbon emissions and cost. Overall, the results demonstrate the feasibility of producing low-cost one-part geopolymers through the synergistic utilization of FA and CCG.