Properties of Coal Gangue-Based Alkali-Activated Cementitious Materials: Effects of Combined Chemical, Thermal, and Mechanical Activation

The disposal of industrial solid waste poses significant challenges in the context of sustainable global development. This issue is particularly critical for low-calcium solid waste, which is generated in large quantities and accumulates in extensive stockpiles. Owing to its low reactivity, the high-value utilisation of such waste remains challenging. In this study, three representative and readily available industrial solid wastes—coal gangue (CG), fly ash, and blast furnace slag—were selected for investigation. CG was activated using a combination of chemical, thermal, and mechanical treatments. Experiments were conducted to improve the working performance of CG-based alkali-activated cementitious materials. The microstructural characteristics of the materials were characterised using isothermal calorimetry, nuclear magnetic resonance spectroscopy, and X-ray diffraction. The results indicated that the biomass ash-composite-modified sodium silicate solution provided the best working performance among the activators evaluated, outperforming conventional NaOH and sodium silicate solutions. The thermal activation parameters had a greater influence on the cementitious system than the grinding time. Under the investigated conditions, CG exhibited the highest cementitious reactivity after 2 h of grinding followed by calcination at 800 °C for 4 h. These findings provide a reference for the efficient activation of large quantities of low-reactivity solid waste and support its large-scale, high-value utilisation.