Page 193 - AJWEP-22-5

Use of coal gangue for mine backfill

effectively preventing particle settling and stratification
while maintaining suitable flowability, thus ensuring
the smooth progress of filling operations. Balancing
stability and pumpability, therefore, requires controlling
mass concentration between 72% and 74 %, where
yield stress (≈ 43 – 50 Pa) keeps segregation below
10% while maintaining workable flow. Although higher
concentrations enhance stability, excessive yield stress
hampers pumping and placement.
A comprehensive analysis of the effects of mass
concentration on the yield stress, water separation rate,
and segregation rate of coal gangue slurry indicates that
an increase in mass concentration significantly enhances
the stability of the slurry. As the mass concentration
Figure 7. Influence of coal gangue‑fly ash slurry with increases, the yield stress gradually rises, strengthening
varying mass concentrations on yield stress (blue the interactions between particles and effectively
line, left axis) and segregation rate (purple line, right inhibiting particle settling and stratification. At the same
axis) time, both the water separation rate and segregation
rate decrease, suggesting that slurries with higher
overall stability. As the concentration increases to 72 – mass concentrations can better maintain uniform water
74%, the yield stress rapidly increases to 42.63 – 49.81 distribution, reduce the settling of coarse particles, and
Pa, and the segregation rate decreases to 9 – 17.5%. minimize liquid phase separation, thereby improving
This trend can be attributed to the formation of a dense the uniformity and stability of the system.
skeletal structure due to the increased solid particle However, excessively high mass concentrations,
content, which enhances the slurry’s viscoelasticity while improving stability, lead to an overly high yield
and shear resistance, effectively suppressing particle stress, which affects the flowability and pumpability
settling and liquid phase separation. However, when the of the slurry, thereby increasing the difficulty of
mass concentration exceeds 74%, the yield stress grows transportation and construction. Therefore, considering
sharply (reaching 60.12 Pa at 76%), and the segregation the balance between the flowability and stability of
rate drops to 5%. This indicates that the slurry gradually coal gangue filling slurry, a mass concentration of
transitions toward a quasi-solid state: Stability is high, 72% provides the best compromise for engineering
but the flowability decreases and pumping resistance applications, ensuring sufficient stability with
increases. acceptable pumpability. Field conditions – such as mine
Further analysis reveals a significant negative depth, temperature, and hydrostatic pressure – may
correlation between yield stress and segregation rate, necessitate adjustment, so future work should include
in situ testing of coal gangue-fly ash slurry under real
which aligns with the “particle skeleton reinforcement mining environments.
effect” proposed by Zhang et al. : At high mass
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concentrations, coal gangue and fly ash particles 3.3.3. Properties of the slurry after curing
form a three-dimensional network structure through Figure 8 illustrates the evolution of compressive strength
physical adsorption and chemical bonding, significantly for the different solid concentrations after 7, 14, and 28 days
increasing yield stress and reducing segregation risk by of curing. In every case, an increase in solid concentration
limiting free water migration. However, when the mass led to a notable enhancement in compressive strength. For
concentration exceeds 74%, the sharp increase in yield instance, at 28 days, the compressive strength increased
stress may push the slurry’s rheological parameters from 4.34 MPa at 68% to 7.26 MPa at 76%, indicating
beyond the pumping equipment limits. Therefore, in that a higher solid content significantly improves the long-
practical applications, both the stability and pumpability term mechanical performance of the material. However,
of the slurry should be considered. Controlling the mass the increased viscosity 74 % and 76 % mixtures may
concentration within the range of 72 – 74%, where the adversely affect the filling process, particularly in terms
yield stress remains between 42.63 and 49.81 Pa and of flowability and pumping efficiency.
the segregation rate is below 10%, is recommended, Notably, the 72% slurry concentration achieves an

Volume 22 Issue 5 (2025) 187 doi: 10.36922/AJWEP025200154