Study on the effect of multi-source solid waste on the performance of its backfill slurry

The preparation of slurry from multi-source solid waste for underground backfill adds a way out for solid waste disposal, which is beneficial to reduce environmental impact. In this paper, the effects of gangue, fly ash, gasification coarse slag and desulfurization gypsum on the fluidity, early strength, thermal stability and other properties of the backfill slurry were studied by fluidity test, strength test, Thermo-Gravimetric Analysis (TGA), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD). The results show that: (1) When G/SW (mass ratio of gangue to solid waste) < 23%, gangue is beneficial to improve the fluidity and early strength of backfill slurry; with the increase of fly ash content, the fluidity of backfill slurry decreases, but its early strength increases; gasification coarse slag has a negative effect on the fluidity of backfill slurry, but it is beneficial to its early strength when GCS/SW (mass ratio of gasification coarse slag to solid waste) < 33%; desulfurization gypsum can improve the fluidity of the backfill slurry, but it is not conducive to the increase of early strength. (2) The compression failure mode of the backfill is mainly divided into the crack-intensive failure, the single main crack penetration splitting failure, and the double main crack conjugate splitting failure. (3) Endothermic dehydration reactions of adsorbed water and crystallization water generally occur at 55–65 °C and 110–130 °C for backfill with different solid waste contents; As the temperature continues to increase, the backfill material undergoes a slow exothermic decomposition reaction; Increasing the content of gangue, fly ash and gasification coarse slag and reducing the content of desulfurized gypsum can make the backfill less weight loss at high temperature and better thermal stability. (4) The main mineral phases in the backfill material are gypsum and quartz, and there are also a small amount of acicular and hexagonal hydration products thaumasite. After high temperature, the thaumasite is dehydrated and decomposed. The research results are helpful to deeply understand the performance of multi-source solid waste for underground backfilling.