Preparation and characterization of coal gangue geopolymers

•Coal gangue is silicon-aluminium materials, which can be used to prepare geopolymer after high-temperature calcination.•Coal gangue geopolymer has a high early strength, higher than that of OPC.45 cement paste specimens.•The generation of the zeolite facies crystallization plays an obvious role on the compressive strength of coal geopolymer.•This paper provides experimental and theoretical basis for the development and wide application of coal gangue cementitious materials.