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<p>This study investigates the rheological behaviour of clay–cement sealing suspensions modified with dry size-fractionated coal fly ashes of contrasting chemical composition. High-calcium S1 ashes and siliceous S2 ashes were separated into ultrafine (&lt; 10&#xa0;μm), fine (5–20&#xa0;μm), and middle (20–100&#xa0;μm) fractions to isolate size-dependent reactivity. Rotational and oscillatory rheometry demonstrate that Ca-rich fractions induce rapid structuration: at 20wt% ash addition, the Bingham yield stress rises from ~ 20–30&#xa0;Pa in reference suspensions to &gt; 150&#xa0;Pa, and exceeds 400&#xa0;Pa at 30wt% S1 loading, accompanied by steep increases in storage modulus (G′ up to 10⁷–10⁸Pa for ultrafine fractions). In contrast, S2 ashes disperse the clay–cement network, lowering yield stress to ~ 15–60&#xa0;Pa even at 40 wt% replacement and maintaining moderate viscoelastic stiffness (G′~10⁴–10⁵Pa). Particle fineness amplifies these trends: S1.UF promotes early hydration products precipitation and slip-layer formation, whereas S2.UF preserves fluidity. Sodium-silicate activation introduces a distinct threshold—at 1.0–1.5wt% Na₂SiO₃ the S1 systems undergo a sol–gel transition, with τ₀ surging above 200&#xa0;Pa, while S2 systems respond gradually. These results quantitatively shows how ash chemistry and granulometry govern early yield stress, viscosity, and G′/G″ ratios, and identify composition windows for either rapid sealing (Ca-rich, fine fractions) or long-distance pumpability (Si-rich, fine fractions). The work demonstrates that fractionated fly ash provides an effective design tool for tailoring rheology of low-cement, sustainable sealing slurries for hydraulic and geotechnical applications.</p>

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Rheological characterisation of clay-cement sealing suspensions with fractionated coal fly ashes

  • 期刊论文

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  • 发表日期：

    2026年1月22日

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  • Jurij Delihowski,
  • Piotr Izak

摘要

This study investigates the rheological behaviour of clay–cement sealing suspensions modified with dry size-fractionated coal fly ashes of contrasting chemical composition. High-calcium S1 ashes and siliceous S2 ashes were separated into ultrafine (< 10 μm), fine (5–20 μm), and middle (20–100 μm) fractions to isolate size-dependent reactivity. Rotational and oscillatory rheometry demonstrate that Ca-rich fractions induce rapid structuration: at 20wt% ash addition, the Bingham yield stress rises from ~ 20–30 Pa in reference suspensions to > 150 Pa, and exceeds 400 Pa at 30wt% S1 loading, accompanied by steep increases in storage modulus (G′ up to 10⁷–10⁸Pa for ultrafine fractions). In contrast, S2 ashes disperse the clay–cement network, lowering yield stress to ~ 15–60 Pa even at 40 wt% replacement and maintaining moderate viscoelastic stiffness (G′~10⁴–10⁵Pa). Particle fineness amplifies these trends: S1.UF promotes early hydration products precipitation and slip-layer formation, whereas S2.UF preserves fluidity. Sodium-silicate activation introduces a distinct threshold—at 1.0–1.5wt% Na₂SiO₃ the S1 systems undergo a sol–gel transition, with τ₀ surging above 200 Pa, while S2 systems respond gradually. These results quantitatively shows how ash chemistry and granulometry govern early yield stress, viscosity, and G′/G″ ratios, and identify composition windows for either rapid sealing (Ca-rich, fine fractions) or long-distance pumpability (Si-rich, fine fractions). The work demonstrates that fractionated fly ash provides an effective design tool for tailoring rheology of low-cement, sustainable sealing slurries for hydraulic and geotechnical applications.