A low-carbon supplementary cementitious material via synergistic utilization of coal gangue and calcium carbide slag for sulphoaluminate cement

Coal gangue generates high strength, accumulates in large quantities, and has low reactivity, causing significant environmental impacts and severely constraining the sustainable development of the coal industry. This study investigates the effects of utilizing self-heating coal gangue (SCG) as a modified supplementary cementitious material (SCM), in combination with calcium carbide slag (CCS) and blast furnace slag powder (BFS), in sulphoaluminate cement (SAC). The effects of these components on the physical properties, mechanical performance, hydration characteristics, and microstructure of the composite cementitious system were systematically evaluated. The results indicated that SCG incorporation reduced paste fluidity and prolonged the setting time of SAC. An optimal SCG content of 10 % enhanced the 28-day compressive strength by 4.5 %, whereas a 50 % SCG content led to a significant strength reduction. SCG demonstrated higher reactivity than raw coal gangue, as reflected by the 35.4 % lower 28-day compressive strength of the RCG-blended sample. compared to its SCG counterpart. The incorporation of CCS effectively optimized the pore structure, enhanced matrix density, and improved mechanical of the cementitious system. Furthermore, introducing 15 % BFS reduced the total porosity to 21.71 % and increased the 28-day compressive strength to 76.8 MPa. Microstructural and hydration analyses revealed that CCS elevated the system alkalinity, thereby accelerating the pozzolanic reaction of SCG and promoting the formation of additional hydration products, including ettringite, C-(A)-S-H gel, and aluminum gel phases. This process contributed to pore structure refinement and a denser matrix. Finally, economic and environmental assessments confirmed that the developed SAC mixture incorporating SCG as an SCM exhibited lower cost, energy consumption, and CO₂ emissions compared to portland fly-ash cement. This study provides a viable strategy for overcoming the incompatibility between large-scale disposal and high-value utilization of SCG, offering a theoretical foundation for producing green, low-carbon building materials from coal gangue. • A novel SCM based on coal gangue, carbide slag and blast furnace slag is developed for sulphoaluminate cement. • The ternary SCM system improves strength and porosity of sulphoaluminate cement. • Microstructure analysis reveals enhanced hydration and denser matrix formation. • The blended cement shows lower cost, energy use and CO 2 emissions than conventional cement.