Study on the performance of cement composites using composite-activated coal gangue

This study investigated the feasibility of utilizing thermally activated coal gangue as a partial replacement for Portland cement through a composite activation strategy involving red mud and sodium silicate. Orthogonal experimental design, together with isothermal calorimetry, low-field nuclear magnetic resonance (LF-NMR), X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS), was employed to systematically evaluate the hydration behavior, microstructural evolution, and compressive strength development of the cementitious system. he results showed that sodium silicate significantly influenced hydration kinetics by delaying the main hydration stage and broadening the exothermic peak. LF-NMR analysis further indicated that systems containing sodium silicate maintained continuous water consumption during the later stages of hydration, suggesting a sustained hydration process. Red mud contributed to the regulation of hydration and partially compensated for the strength reduction associated with the incorporation of thermally activated coal gangue. Compared with sodium silicate activation alone, the combined incorporation of red mud and sodium silicate resulted in lower compressive strength at all curing ages. RD and SEM–EDS analyses indicated that the co-activated system exhibited a relatively heterogeneous distribution of hydration products and a less compact microstructure. These microstructural characteristics were consistent with its comparatively lower mechanical performance. Overall, this study provides insight into the interaction between red mud and sodium silicate in coal gangue-based cementitious materials and offers theoretical support for optimizing composite activation strategies and promoting the efficient utilization of industrial solid wastes.