Study on the properties and hydration mechanism of coal gangue-power plant ash filling bodies activated by alkali

In order to utilize solid waste materials such as coal gangue and fly ash and address issues like land occupation and environmental pollution caused by waste accumulation, a coal gangue-fly ash alkali-activated cementitious material was prepared using coal gangue, fly ash, and cement as the primary raw materials. Calcium hydroxide was incorporated as an alkaline activator. A three-factor, three-level orthogonal experiment was conducted to investigate the effects of cement content, calcium hydroxide dosage, and water-binder ratio on the 28-day compressive strength of the cementitious material. The results were analyzed using range analysis and analysis of variance. The microstructural changes of the samples were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The study further explored the activation role of calcium hydroxide in the filling material. The results indicated that the introduction of calcium hydroxide significantly improved the compressive strength of the filling material. The optimal mix ratio was found to be 30% cement, 8% calcium hydroxide, and a water-to-binder ratio of 0.35. Microstructural analysis revealed that the addition of calcium hydroxide facilitated the depolymerization of the silica-alumina network and directly participated in the formation of C-A-S-H gel, which accelerated the hydration process and densified the paste structure. This process is critical for the resource utilization of coal gangue and fly ash and the enhancement of the mechanical properties of composite cementitious materials.