Preparation of coal gangue-slag-fly ash geopolymer grouting materials

•LCGGM with a large content of CG was prepared by composite activation.•The comprehensive advantages of CG, BFS and FA can be utilized.•The RSM was utilized to obtain the quantitative trend of each response and each factor.•The main reaction products of LCGGM are C-(N)-A-S-H and C-S-H gels. To prepare a low-cost geopolymer grouting material (LCGGM), the industrial solid wastes coal gangue (CG), blast furnace slag (BFS) and fly ash (FA) were used as silica-alumina materials; desulfurized gypsum and an alkaline activator were used as ligands; and small amounts of additives were supplemented. The response surface methodology (RSM) was used to design macroscopic tests of the fluidity, setting time, compressive strength and impermeability of LCGGM, and XRD, FTIR, TG-DSC and SEM-EDS were used to analyse the mechanism of action. The results showed the following: (1) Optimized formulation could be achieved at coal gangue powder: slag: fly ash ratio of 5:4:1, 1.64 M sodium silicate modulus, 6.7% sodium silicate and 5% Na2O. The LCGGM possesses clean production, high fluidity, fast setting, low bleeding rate, high compressive strength and seepage pressure, providing appealing properties as grouting materials for reinforcement. The establish regression model and response surface well reflect the impacts of various factors on the properties of the LCGGM. (2) Microscopic analysis showed that the three materials with different fineness improved the density of the stone body and participated in the hydrolytic polymerization reactions of the multiple systems at different times, which ensured the strength of the stone body in the early and late stages.