Study on the Strength Formation Mechanism of Coal Gangue-Based Composite Cementitious Materials

Conventional cement production relies heavily on the consumption of natural resources, posing significant challenges to sustainable development. Incorporating activated coal gangue (CG) into cementitious materials not only reduces cement usage but also promotes the resource utilization of solid waste. In this study, the compressive strength (CS) and microstructural evolution of CG-based composite cementitious materials were systematically investigated under activated CG replacement levels of 0–50% and water-to-binder ratios (w/b) of 0.40–0.50. The results showed that the optimal performance was achieved at a CG replacement level of 30% and a w/b of 0.40, where the 28-day CS reached 59.1 MPa, representing an 18.9% improvement compared with the control group. The pozzolanic reaction of CG reduced the Ca(OH)2 (CH)content within the cementitious matrix and promoted the formation of ettringite (AFt) and C-(A)-S-H, thereby enhancing matrix compactness. These findings provide theoretical support for the application of CG in sustainable cementitious materials.