Preparation of the geopolymer grouting material by coal-based solid wastes for the aquiclude key strata and its application

The application of grouting to repair cracks in the key strata of the aquiclude is an effective measure to safeguard the overlying aquifer during underground coal mining. However, conventional grouting materials are expensive and can induce serious environmental pollution. In this study, a cost-effective geopolymer grouting repair ma-terial was prepared by using coal gangue, fly ash, bentonite, and other additives. The response surface meth-odology was employed to design the compressive strength and seepage strength tests on the cemented body, and the microstructure of the cemented body was also explored. The results show that when the ratio of coal gangue to fly ash to bentonite is 23:22:5 and the NaOH content is 4 %, the optimal performance of the grouting material is achieved, with a compressive strength of 10.11 MPa and a seepage strength of 2.38 MPa at the curing age of 28 d. The compressive strength and seepage strength of the grouting material are significantly improved by the network structure formed by the cross-linking of ettringite generated from the hydration of the material and the gel of sodium silicate hydrate.