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Rheological properties of coal gangue slurry

coal gangue particles under shear temporarily reduced
internal friction, thereby improving fluidity. However,
this effect is often limited due to the inherent high water
absorption and fine particle characteristics of fly ash.
Figure 10 shows the variation curves of the water
bleeding rate of slurries with a 70% solid volume
concentration under different pressure conditions. The
results demonstrated that higher pressure accelerated
water bleeding and shortened the time required to
complete the process, exhibiting an approximately
linear relationship between bleeding rate and pressure.
Finer coal gangue particle sizes reduced the water
bleeding rate and prolonged the precipitation process of
the slurry.
As the fly ash-to-coal gangue mass ratio decreased,
the time required to complete bleeding increased,
Figure 8. Effect of sulfamic acid and polycarboxylate suggesting that a higher coal gangue content in
superplasticizer on the zeta potential of mixed the mixture lowers the bleeding rate. This effect is
slurries attributed to the larger interparticle voids in coarse
coal gangue particles, which must be filled by fly
carbon-storing polymeric compound—exhibits superior ash or water. Variations in mass ratios resulted in
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environmental compatibility and minimal ecological differences in void filling by water and fly ash, thereby
impact. Its molecular structure promotes efficient influencing the bleeding rate. Finer coal gangue
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particle dispersion and robust fluidity retention, making particle sizes further suppressed bleeding by reducing
it a more viable option for reducing viscosity in backfill interparticle voids. For slurries containing 50-mesh
grouts while ensuring long-term stability. coal gangue, the water bleeding rate ranged from 50%
to 70%. At 100 mesh, the bleeding rate increased to
3.3. Effect of injection pressure on rheological 55–75%, while at 150 mesh, it stabilized around
properties 55–65%. Overall, no distinct correlation was observed
Figure 9 illustrates the viscosity of the fly ash–coal between coal gangue particle size and bleeding rate
gangue mixing slurry at different fly ash-to-coal gangue under pressure conditions, suggesting that particle size
mass ratios under various injection pressures. An increase does not directly determine the bleeding behavior of
in both injection pressure and fly ash proportion in the slurry under such conditions.
slurry resulted in higher viscosity. Since the particle size
of fly ash is smaller than that of coal gangue, a decrease 3.4. Prediction of slurry diffusion distance using the
in coal gangue particle size resulted in a significant power‑law fluid fracture grouting diffusion model
increase in slurry viscosity. Increasing the fly ash The power-law fluid fracture grouting diffusion model
content not only raised the viscosity but also reduced was used to analyze the behavior of slurry diffusion in
injectability, thereby negatively impacting grouting and inclined fractures under various influencing factors,
filling operations in coal mine goaf foundations. This aiming to determine the optimal injection pressure,
effect is attributed to the fine particle size and high spacing, and strata layout for horizontal branch
water absorption capacity of fly ash. holes. This model provides valuable insights into the
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When 150-mesh coal gangue was incorporated, a fundamental relationships between injection parameters
large amount of water in the slurry was absorbed by the (e.g., pressure, fracture geometry), slurry rheology, and
coal gangue particles, substantially reducing the free diffusion distance.
water content. This reduction in free water severely The model highlights the sensitivity of diffusion to
weakened the lubricating effect between particles, key controllable parameters and serves as a guide for
ultimately increasing the viscosity and deteriorating initial parameter selection. However, its predictions
injectability. At elevated injection pressures, slurry represent an upper bound. The findings of this study
viscosity increased as shear stress rose. This occurred provide crucial complementary insights into slurry
because the aligned arrangement of finer fly ash and behavior relevant to mitigating clogging risks.

Volume 22 Issue 5 (2025) 223 doi: 10.36922/AJWEP025210162