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Hou, et al.

optimal balance between mechanical performance and 3.4. Influence of particle size pairing on the
flowability. Its 28-day compressive strength reaches rheological properties of the slurry
5.25 MPa, meeting the basic strength requirements 3.4.1. Influence of particle size matching on the fluidity
for typical backfill applications (≥5 MPa), while its and stability of the slurry
7- and 14-day strengths are 2.52 MPa and 3.69 MPa, To investigate the effect of particle grading on the
respectively – indicative of stable early-age strength performance of coal gangue slurry, a comparative
development. Compared with higher concentrations analysis was conducted on the slurry’s flowability,
(74% and 76%), the 72% concentration not only water separation, and structural stability under
ensures structural stability but also mitigates the different grading coefficients (i = 0.88 – 0.92). Figure 9
k
risk of pipeline blockage and enhances construction illustrates the influence of particle size distribution on
efficiency. Therefore, considering the compressive the slurry flowability. A clear inverse relationship was
strength, flowability, and process adaptability, 72% is observed between the particle gradation index and the
identified as the optimal solid concentration for coal slurry’s flowability. As the gradation index increased
gangue slurry backfill. The reuse of coal gangue and fly from 0.88 to 0.92, the flow diameter decreased
ash in backfilling not only improves mining efficiency from 29.53 cm to 26.53 cm, indicating that a higher
but also provides an effective route for large-scale solid proportion of coarse particles adversely affect slurry
waste utilization, aligning with sustainable mining and mobility. Further analysis, in conjunction with the
ecological restoration goals. particle composition data presented in Table 2,
Environmental safety is equally important. Coal reveals that the proportion of fine particles (<1 mm)
gangue and fly ash may contain trace heavy metals increased from 74.33% to 82.41% as the gradation
(e.g., Pb, As, Cr). Although present at low levels, their index rose, while the fractions of coarser particles
leachability under alkaline curing conditions must be (1 – 3 mm and 3 – 5 mm) declined significantly. The
verified. Hydration products, such as C(A)SH gel and increased content of fine particles leads to a higher
ettringite can immobilize heavy-metal ions through specific surface area and greater water demand,
encapsulation and chemical bonding, while the slurry’s thereby enhancing the cohesiveness of the slurry and
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high pH further reduces metal mobility by promoting reducing its flowability. Consequently, appropriately
precipitation and adsorption. Even so, a comprehensive
toxicity-characteristic leaching procedure test is controlling the proportion of fine particles is essential
recommended for future work to quantify environmental for optimizing slurry flow performance, improving
risk and ensure safe large-scale application in backfilling pumpability, and enhancing operational efficiency
and mine reclamation. during the backfilling process.
Figure 10 shows the results indicating the influence of
different particle sizes on the overall slurry performance.

Figure 8. Compressive strength of different mass
concentrations of slurry after 7, 14, and 28 days of Figure 9. The influence of particle size on slurry
curing flowability

Volume 22 Issue 5 (2025) 188 doi: 10.36922/AJWEP025200154