Page 220 - AJWEP-22-5

Asian Journal of Water, Environment and Pollution. Vol. 22, No. 5 (2025), pp. 214-230.
doi: 10.36922/AJWEP025210162

ORIGINAL RESEARCH ARTICLE

Rheological optimization and diffusion modeling of fly
ash–coal gangue composite slurries

Zhu Liu , Shupeng Wen , Jian Wang , Xiao Wang , Yang Yang ,
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3
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1
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Zhongquan Liu ,and Linqiang Mao *
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1 Department of Mineral Engineering, 113 Team, Guizhou Coalfield Geology Bureau, Guiyang, Guizhou, China
2 Department of Mineral Engineering, Guizhou Coalfield Geology Bureau, Guiyang, Guizhou, China
3 Guizhou Qiandi Jingkai Technology Co., Ltd, Guiyang, Guizhou, China
4 Department of Environmental Engineering, School of Environmental Science and Technology, Changzhou University,
Changzhou, Jiangsu, China
*Corresponding author: Linqiang Mao (maolq@cczu.edu.cn)
Received: May 20, 2025; Revised: July 10, 2025; Accepted: July 17, 2025; Published online: August 6, 2025

Abstract: The separation of overburden strata in coal mining directly affects surface subsidence, the ecological
environment, and mining safety. Backfilling technology is currently the primary solution to address these issues.
This study examines the rheological performance of a coal gangue and fly ash mixed slurry as a filling material under
different raw material proportions and injection pressures, and predicts its diffusion distance using a theoretical
model. Orthogonal experiments were conducted to evaluate the influences of solid volume concentration, coal
gangue particle size, and fly ash-to-coal gangue mass ratio on the density, viscosity, and water bleeding rate of
the slurry. Results demonstrated that solid volume concentration had the most significant influence on density and
viscosity, followed by coal gangue proportion and particle size. Increasing coal gangue content elevated density and
viscosity due to higher interparticle friction, while finer particles reduced viscosity by 30–40%. The introduction
of a polycarboxylate superplasticizer achieved a 45% viscosity reduction with an optimal dosage of 0.3 wt%, by
dispersing particles and enhancing the availability of free water compared to sulfamic acid. Injection pressure
accelerated water bleeding rates by 20–35%, while finer coal gangue particles prolonged bleeding time. A power-
law fluid fracture grouting diffusion model predicted that higher injection pressures (0.1–0.4 MPa) and fracture
widths (0.4–1.0 mm) linearly increased diffusion distance, whereas steeper fracture angles (5–20°) enhanced the
spread range. This study provides a broad perspective for designing cost-effective, environmentally stable grouting
systems using coal-based waste, balancing injectability and long-term performance in mining applications.

Keywords: Overburden separation; Injection in separated-bed technology; Coal gangue; Fly ash

1. Introduction strata, and inhibit stratum closure (Figure 1). This
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technique aims to reduce ground subsidence and mitigate
The overburden separation space injection technique hazards caused by water accumulation in the separated
refers to a method that involves sealing the separated strata. By effectively addressing mining-induced ground
strata space above the water-conducting fracture zone subsidence, reducing the surface accumulation of
and subsequently injecting grouting materials under industrial waste, and preventing water-related stratum
high pressure to minimize the subsidence of overlying hazards, this technique is beneficial for coal mine
rock layers, prevent water infiltration into the separated structural safety and environmental conservation. It has
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Volume 22 Issue 5 (2025) 214 doi: 10.36922/AJWEP025210162