Preparation method of composite cemented filling paste

The invention discloses a preparation method of composite cemented filling paste, which comprises the following steps: taking the following raw materials in parts by weight: 12.5-15 parts of waste concrete, 20-25 parts of carbide slag, 25-30 parts of fly ash, 12.5-15 parts of coal gangue, 20-25 parts of geopolymer, pretreated coal gangue and waste concrete, mixing the solid raw materials for 1-3 minutes, adding water according to the mass ratio of solid to water of 7: 3, stirring, standing for 1-3 minutes, and cooling to room temperature to obtain the composite cemented filling paste. The stirring rotation speed is 80-100 r/min, and the stirring time is 2-5 minutes. The paste with good flowing property, curing property and mechanical property is prepared, and the goaf of the mine field is filled with the paste, so that the goaf supporting strength is improved, the goaf is supported, ground surface settlement is prevented, the ecological environment is protected, solid waste is reasonably utilized, heavy metal