Experimental study on the early compressive strength, fluidity, and microstructure of multisource coal-based solid waste cemented backfill

The production of coal-based solid waste (CBSW) from coal mining operations poses a significant threat to the ecological environment in mining regions. This research addresses the proper management of CBSW accumulation by utilizing coal gangue, fly ash, and gasification slag as primary materials for backfill preparation. This study focused on evaluating the early uniaxial compressive strength and fluidity of the backfill while investigating the changing characteristics of early compressive strength, fluidity, and microstructure during the early age of backfill development. Findings showed that the slurry fluidity significantly decreased as the mass concentration increased, whereas factors such as the aggregate–cement mass ratio, fine aggregate content, and fiber content demonstrated no noticeable impact on slurry fluidity. Notably, the early compressive strength of the backfill decreased significantly with an increase in the aggregate–cement mass ratio; however, increases in the mass concentration and fine aggregate content effectively enhanced the early compressive strength of the backfill, serving as key influencing factors. The inclusion of fiber significantly enhanced the early compressive strength of the backfill, with the optimal fiber concentration determined to be ~0.2 wt%. Furthermore, increasing the mass concentration or fine aggregate content alleviated the negative impacts of higher aggregate–cement mass ratios on early compressive strength. However, it must be noted that an elevated fine aggregate content may reduce the reinforcing effects of mass concentration on early compressive strength. This leads to enlarged void structures in the samples, whereas increasing the fine aggregate content reduces the void size and range, thereby improving the early compressive strength of the backfill.