Synergic effect of steel slag-coal gangue powder on the properties of cementitious grouting materials with SAC modification

To enhance the comprehensive performance of cementitious grouting materials as well as the utilization of solid waste, this study developed eco-friendly cement grouting materials by using high volume of steel slag and coal gangue powder to replace a portion of Ordinary Portland cement (OPC), while sulphate aluminate cement (SAC) was subsequently used to further replace part of the remaining OPC as modification. The construction performance, rheological behavior, and hardened strength characteristics of the grouts were systematically investigated under different solid waste replacement ratios, steel slag-coal gangue powder ratios, and SAC contents. Correlation analysis was conducted to explore the relationship between raw material dosages and key performance indicators. The results indicate that the rapid hydration of SAC shortens the setting of slurry and reduces the bleeding rate. The hydration of steel slag micro powder forms a gel network that intertwines with SAC hydration products, improving compressive strength, but excessive replacement prolongs the setting time. Coal gangue powder accelerates setting but impairs strength development due to its inert phases and weak interfaces. In addition, its irregular particle morphology increases yield stress and plastic viscosity, leading to reduced flowability. The optimal performance is achieved when the solid waste replacement ratio is 0.5, and the ratio of steel slag-coal gangue powder is 0.75:0.25, balancing shorter setting time, lower bleeding rate, and higher 28-day compressive strength. This study achieved a high solid waste incorporation and revealed the relationship between raw material dosages and slurry performance. It provides a novel technical pathway for developing sustainable grouting materials, and offers practical guidance for the mix design in concealed engineering applications.