Research on the hydration process of cemented coal gangue backfill based on radon monitoring

Backfill mining is a method in which coal gangue, fly ash, solid waste, and cement are used to make slurry backfilling materials while coal mining, and the cemented coal gangue backfill (CCGB) is transported to the underground to fill up the mining area. At present, the hydration mechanism is not clear and uniform. This study introduces a physical method that can be used to monitor the hydration of CCGB using the radon monitoring method. The influence mechanisms of the hydration process of raw materials, cement-fly ash ratio, mass concentration of CCGB, and microscopic characteristics on radon exhalation were experimentally investigated. The kinetics of hydration heat development and microscopic characteristics are discussed. The results show that for pure cement, the cumulative radon concentration of the cement slurry is much larger than that of the cement particles and cement-fly ash mixture slurry. The radon concentration was higher in the cement-fly ash mixed slurries with a higher cement content. The higher the mass concentration in the backfill material, the higher the radon concentration. A strong correlation was observed between the radon exhalation rate and the heat released from hydration. This was also due to the early hydration reaction of the cement. In addition, the hindering effect of the water film is discussed. The higher the ratio of hydration products, the higher the radon concentration. The radon concentration can effectively monitor the hydration process of cement slurry and backfill material slurry.