Page 186 - AJWEP-22-5

Hou, et al.

The large-scale exploitation of mineral resources thereby improving delivery performance. Consequently,
results in extensive underground voids, leading to surface an in-depth investigation of the rheological behavior of
subsidence, groundwater loss, and severe ecological coal gangue-fly ash slurry is essential for optimizing
degradation. To mitigate these adverse effects, the slurry formulations and improving its applicability in
8,9
mining industry widely employs slurry backfilling practical engineering applications.
technology, wherein suitable solid materials are mixed This study aims to systematically examine the
with water to form a slurry that is subsequently used to rheological properties of coal gangue-fly ash slurry
fill mine voids, thereby enhancing the stratum stability at varying solid concentrations. The effects of solid
and reducing environmental impact. 10,11 Traditional content, particle size distribution, and microstructure on
backfill materials, 12,13 such as cement-based binders, are viscosity, shear stress, and other rheological parameters
costly and associated with high carbon emissions. For will be analyzed to optimize slurry compositions. The
instance, the production of one ton of Portland cement findings will provide a theoretical foundation for the
emits approximately 0.9 tons of carbon dioxide (CO ), efficient utilization of coal gangue and fly ash and offer
2
and cement mixtures often require chemical admixtures technical guidance for slurry preparation and application
and additives that further increase environmental and in mine backfilling projects, thereby advancing waste
economic burdens. In contrast, coal gangue and fly ash valorization and promoting environmentally sustainable
are cost-effective and sustainable alternatives due to mining practices.
their abundant availability and favorable mineralogical
characteristics. 14,15 Coal gangue, primarily composed 2. Materials and methods
of aluminosilicate minerals (e.g., kaolinite and quartz),
provides structural support due to its high density 2.1. Materials
and strength. Fly ash, rich in reactive SiO and Al O , The coal gangue was sourced from a mine in Guizhou,
3
2
2
exhibits pozzolanic activity that enhances the bonding China. It was ball‐milled at 400 r/min for 1 h, followed
properties of the filling material. 16-18 Utilizing these by sieving through a 5 mm mesh. The resulting material
materials as backfill not only reduces reliance on was classified into three particle size fractions: <1 mm
cement but also promotes the recycling of industrial (density = 2.65 × 10³ kg m⁻ ), 1 – 3 mm (density = 2.58 ×
3
solid wastes, contributing to carbon emission reduction, 10 kg m⁻ ), and 3 – 5 mm (density = 2.52 × 10 kg m⁻ ).
3
3
3
3
energy conservation, and environmental protection. The These fractions were designated as fine, medium, and
synergistic interaction between these two components coarse aggregates, respectively, for subsequent mix design
forms a composite system integrating physical support experiments. Fly ash was sourced from a power plant
and cementitious properties. By optimizing mixture in Changzhou, China. The X-ray fluorescence (XRF)
proportions and activation techniques, coal gangue- compositions of both materials are listed in Table 1.
fly ash slurry can significantly reduce backfilling costs Figure 1 presents the results of the laser particle
while facilitating large-scale waste disposal, offering size analysis of the fly ash. Particles are primarily
both environmental and economic benefits. distributed in the range of 10 – 200 μm, with an average
In recent years, the application of coal gangue-fly of 76.4 μm. The D50 and D90 values are approximately
ash slurry in mine backfilling has attracted increasing 72.5 μm and 264.1 μm, respectively, indicating a
attention, with research primarily focused on proportion moderately wide particle size distribution. The presence
optimization, bonding strength, and durability. Studies of unburned carbon or nanoscale glass microspheres in
have demonstrated that an appropriate fly ash content the fly ash may reduce slurry yield stress and plastic
improves slurry fluidity and the long-term strength of viscosity, enhancing flowability.
the backfill. However, the rheological properties of the
18
slurry play decisive roles in its transportability and filling 2.2. Experimental procedure
performance, ultimately affecting the uniformity and 2.2.1. Effect of mass concentration on slurry
stability of the backfilled stratum. The effective control performance
of rheological parameters is essential for ensuring Total solid mass concentrations of 68, 70, 72, 74, and
pumpability and reducing pipeline resistance. 19-21 Rawat 76 wt% were evaluated, with solids comprising 85 wt%
et al., reported that slurries composed of gangue and fly coal gangue and 15 wt% fly ash, 23-25 while the balance
22
ash behave as a non-Newtonian Bingham plastic fluid, was deionized water. This experimental design isolated
and the addition of fine-grained materials, such as fly ash the effect of gangue-dominated solid concentration
reduces resistance loss during pipeline transportation, while maintaining a constant fly ash contribution.

Volume 22 Issue 5 (2025) 180 doi: 10.36922/AJWEP025200154