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

•A low-cost geopolymer grouting material was prepared by coal-based solid wastes for the aquiclude key strata.•The interaction mechanism of various factors on the compressive strength and seepage strength of grouting materials were revealed.•The hydration reaction products are AFt and N-A-S-H gels.•The filling effect of cementitious substances refines the pore structure of grouting materials.