Mechanical properties and hydration mechanisms of coal gangue–slag cementitious materials activated with alkali under different activation methods

Aiming at the problem of insufficient hydration activity of coal gangue in cementitious materials, this study systematically compared the effects of two activation methods, calcination and ultrasonic treatment, on the hydration mechanism and mechanical properties of alkali-activated coal gangue slag cementitious materials. Using uncalcined and calcined coal gangue, by changing ultrasonic parameters, combined with quantitative analysis of particle dispersion, fractal theory, compressive strength testing and various microscopic characterization methods, the mechanism of two activation methods and their effect on the microstructure and properties of the materials were revealed. The results show that ultrasonic treatment can significantly improve the distribution of slurry particles, the best dispersion effect of the slurry was achieved when the ultrasonic power was 600 W for 1 min, and the compressive strength of the material reached 88.9 MPa, This value is higher than the 82.7 MPa observed in the Y-000–0 group, indicating that there is an optimal threshold for ultrasonic treatment and that it can effectively enhance the mechanical properties of the material. Microscopic analysis indicates that ultrasonic treatment promotes uniform spatial distribution and effective connectivity of the gel, resulting in a lower proportion of harmful pores and more rational pore distribution, leading to a denser structure in the formed cementitious material. Ultrasonic treatment can address the high carbon emissions caused by coal gangue calcination, and the results can provide new insights for the application research of coal gangue-based building materials.