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Use of coal gangue for mine backfill

sharply, suggesting a transition to a more cohesive and
less flowable system. Although this improves stability
and reduces segregation, it may cause increased pressure
losses and clogging risks during pumping.
Overall, the Bingham model provides a robust
framework for characterizing the rheological behavior
of the coal gangue-fly ash slurry. Both plastic viscosity
and yield stress increase with solid concentration,
reflecting a shift toward reduced flowability but
enhanced structural integrity. These findings offer
critical insights into optimizing slurry formulations for
practical applications. Careful control of concentration,
therefore, allows engineers to balance flowability and
stability, ensuring efficient pipeline transport, improved
workability, and reliable performance in backfilling and
grouting applications. Figure 4. The influence of solid concentrations on

3.3. Effect of mass concentration on slurry rheology coal gangue slurry fluidity
and flow
3.3.1. Influence of solid concentration on slurry fluidity
Figure 4 illustrates the influence of solid concentration
on slurry flowability. A clear negative correlation exists
between the mass concentration of coal gangue slurry
and flow diameter. As the concentration increased from
68% to 76%, the flow diameter steadily decreased from
33.64 cm to 25.19 cm. Notably, the rate of decline in
flowability diminished progressively with increasing
concentration: 3.18 cm (68 – 70%), 2.01 cm (70 – 72%),
1.82 cm (72 – 74%), and 1.44 cm (74 – 76%). This non-
linear trend suggests that, at higher concentrations,
intensified particle-particle interactions (increased
friction and reduced free water) dominate rheology and
approach a structurally balanced state. Optimizing solid Figure 5. Influence of coal gangue‑fly ash slurry with
concentration is therefore critical in mine backfilling: varying mass concentrations on slump flow (red line,
Higher concentrations improve mechanical strength but left axis) and plastic viscosity (green line, right axis)
impair flowability. The behavior is consistent with non-
Newtonian fluids, where yield stress and viscosity rise slurry particles and reducing their ability to flow. The
non-linearly with solids loading. observed trend aligns with the rheological behavior
Figure 5 compares slump spread and plastic of high-concentration slurry, where increasing solid
viscosity across concentrations. As shown in the concentration results in a more compact particle
figure, an increase in mass concentration leads to network, thus reducing the available free water and
a reduction in slump spread while simultaneously leading to greater resistance to deformation. The
increasing the plastic viscosity. Specifically, when sharp increase in plastic viscosity suggests that
the mass concentration increases from 68% to 76%, beyond a certain concentration threshold, the slurry
the slump spread decreases from 65 cm to 52 cm, undergoes a transition from a relatively fluid state to
representing a 20% reduction. In contrast, the plastic a more viscous and less workable mixture. This effect
viscosity rises by 92.3%, indicating a substantial is particularly critical for practical applications, as
decline in flowability. This phenomenon can be excessive viscosity may cause difficulties in pumping
attributed to the higher solid content, which intensifies and placement, leading to potential segregation and
particle interactions and enhances interparticle uneven filling in underground mining operations.
friction, ultimately restricting the movement of Experience indicates that optimum pumpability

Volume 22 Issue 5 (2025) 185 doi: 10.36922/AJWEP025200154