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<p>Deep coal seams are characterized by low permeability and complex fracture-pore networks, which make borehole sealing for gas drainage difficult and limit extraction efficiency. Grouting-based borehole sealing can effectively enhance gas drainage performance; therefore, developing high-performance sealing grouts is essential. Previous studies have shown that rapid-setting materials are favorable for fast and efficient borehole sealing, but they undergo a solid–liquid phase transition within a short workable window, during which viscosity and yield-related resistance evolve sharply with time. As a result, the diffusion process cannot be reliably predicted or designed using time-invariant rheological parameters, as is commonly done for conventional cement slurries. To address this issue, this study combines macroscopic rheological tests, scanning electron microscopy (SEM) observations, and finite-element simulations to systematically investigate the effects of water-to-cement ratio (W/C) on the rheological evolution, microstructural development, and diffusion performance of a rapid-setting cement-based grouting material (RSGM). The results demonstrate a pronounced W/C-dependent rheological regime transition: mixtures with W/C = 0.7–1.0 conform to the Herschel–Bulkley model, whereas those with W/C = 1.2–1.4 and 1.6–2.0 are better approximated by the Bingham and Newtonian models, respectively. During the solid–liquid phase transition, viscosity exhibits strong time dependence and can be characterized by an exponential-type relationship with reaction time, highlighting the necessity of incorporating time-dependent rheology into diffusion assessment. SEM observations qualitatively indicate that a lower W/C favors the formation of more connected hydration product frameworks, whereas excess free water in higher-W/C systems leads to more dispersed hydration products and reduced apparent compactness. Numerical simulations further show that rheological properties significantly regulate diffusion capacity: under the same grouting pressure, Newtonian fluids achieve the largest diffusion radius, followed by Bingham and Herschel–Bulkley fluids. Moreover, diffusion gains exhibit a diminishing-return trend as grouting time and pressure increase, and this effect is more pronounced for yield stress fluids. These results support an improved understanding of the coupled time-dependent rheology–diffusion behavior in rapid-setting grouts and provide reference for mix design and pressure–time parameter optimization for underground borehole sealing in coal mines.</p>

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Rheological behavior and diffusion of rapid-setting cement-based grouting materials: experimental and theoretical study

  • 期刊论文

  • 发表日期：

    2026年4月24日

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  • Bo Li,
  • Peng Lu,
  • Junqi Cui,
  • Junxiang Zhang,
  • Aitao Zhou,
  • Chao Xu,
  • Qinghai Li

摘要

Deep coal seams are characterized by low permeability and complex fracture-pore networks, which make borehole sealing for gas drainage difficult and limit extraction efficiency. Grouting-based borehole sealing can effectively enhance gas drainage performance; therefore, developing high-performance sealing grouts is essential. Previous studies have shown that rapid-setting materials are favorable for fast and efficient borehole sealing, but they undergo a solid–liquid phase transition within a short workable window, during which viscosity and yield-related resistance evolve sharply with time. As a result, the diffusion process cannot be reliably predicted or designed using time-invariant rheological parameters, as is commonly done for conventional cement slurries. To address this issue, this study combines macroscopic rheological tests, scanning electron microscopy (SEM) observations, and finite-element simulations to systematically investigate the effects of water-to-cement ratio (W/C) on the rheological evolution, microstructural development, and diffusion performance of a rapid-setting cement-based grouting material (RSGM). The results demonstrate a pronounced W/C-dependent rheological regime transition: mixtures with W/C = 0.7–1.0 conform to the Herschel–Bulkley model, whereas those with W/C = 1.2–1.4 and 1.6–2.0 are better approximated by the Bingham and Newtonian models, respectively. During the solid–liquid phase transition, viscosity exhibits strong time dependence and can be characterized by an exponential-type relationship with reaction time, highlighting the necessity of incorporating time-dependent rheology into diffusion assessment. SEM observations qualitatively indicate that a lower W/C favors the formation of more connected hydration product frameworks, whereas excess free water in higher-W/C systems leads to more dispersed hydration products and reduced apparent compactness. Numerical simulations further show that rheological properties significantly regulate diffusion capacity: under the same grouting pressure, Newtonian fluids achieve the largest diffusion radius, followed by Bingham and Herschel–Bulkley fluids. Moreover, diffusion gains exhibit a diminishing-return trend as grouting time and pressure increase, and this effect is more pronounced for yield stress fluids. These results support an improved understanding of the coupled time-dependent rheology–diffusion behavior in rapid-setting grouts and provide reference for mix design and pressure–time parameter optimization for underground borehole sealing in coal mines.