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Hou, et al.

is achieved when the slump spread is about 50 cm network that strengthens the interparticle interactions
and plastic viscosity remains below 0.25 Pa·s. In and minimizes the availability of free water. Notably,
this study, coal gangue slurry satisfied these criteria once the mass concentration exceeds 72%, the yield
only between 68% and 72% solids. Above 72%, stress exhibits a more pronounced growth rate, while
the increasing viscosity could pose challenges in the water bleeding rate drops to a minimal level. This
practical construction applications, such as difficulty phenomenon can be explained by the formation of a
in pipeline transportation, higher energy consumption more compact particle skeleton, which increases the
during pumping, and potential clogging. Therefore, slurry’s cohesive forces and reduces the number of
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from both theoretical and practical standpoints, water migration pathways. The higher solid fraction
optimizing the mass concentration of coal gangue effectively binds the free water within the slurry matrix,
slurry becomes essential to balance flowability and mitigating the risk of excessive bleeding. However,
structural stability. while a higher mass concentration improves stability,
it also introduces potential challenges. Excessive yield
3.3.2. Influence of solid concentration on slurry stress may hinder the workability and pumpability of
stability the slurry, leading to increased energy consumption
The study by Liu et al., suggests that the yield stress during transportation and difficulties in achieving
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of 30 – 45 Pa and a water bleeding rate of 1.5 – 5% uniform filling. Therefore, maintaining a balance
are ideal. As illustrated in Figure 6, an increase in mass between stability and flowability by optimizing the
concentration leads to a progressive rise in yield stress mass concentration is imperative. According to the
while simultaneously reducing the water bleeding rate. above research, when the mass concentration of the
At lower mass concentrations (68 – 70%), the yield coal gangue filling slurry was 72 – 74%, the fluidity and
stress remains relatively low, and the water bleeding stability reached the best balance. Within this range,
rate is noticeably higher, indicating insufficient the yield stress remains sufficiently high to prevent
structural integrity and a higher likelihood of phase segregation, while the water bleeding rate is controlled
separation. These findings suggest that the slurry at within an acceptable limit, ensuring smooth placement
these concentrations lacks the necessary cohesion to and effective filling performance. Future studies should
retain water effectively, making it prone to instability further investigate the impact of additional factors, such
during transportation and placement. as particle size distribution, admixtures, and hydration
With the gradual increase in mass concentration, the reactions, on the long-term stability and mechanical
slurry’s yield stress rises steadily and the water bleeding strength of the filled structures. Excessive yield stress,
rate declines significantly, reflecting a denser particle however, can hamper workability and pumpability,
raising energy demand and complicating uniform
placement. An optimal balance was achieved at 72 –
74 % solids: Yield stress was high enough to prevent
segregation, yet the bleeding rate remained within the
recommended range, ensuring smooth pumping and
effective filling. Future work should explore the effects
of particle size distribution, chemical admixtures, and
hydration reactions on the long-term stability and
mechanical performance of filled structures.
The yield stress and segregation rate can also be
used to characterize slurry stability. As shown in
Figure 7, with the increase in the mass concentration
of coal gangue slurry from 68% to 76%, the yield stress
significantly rises from 34.89 Pa to 60.12 Pa, while the
segregation rate decreases from 28% to 5%. At mass
concentrations between 68% and 70%, the yield stress is
Figure 6. Influence of coal gangue‑fly ash slurry with relatively low (<41 Pa), and the segregation rate remains
varying mass concentrations on yield stress (blue high (20 – 28%), indicating weak particle interactions,
line, left axis) and bleeding rate (orange line, right a loose structure, and a high tendency for free water
axis) migration, leading to significant segregation and poor

Volume 22 Issue 5 (2025) 186 doi: 10.36922/AJWEP025200154