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<p>Ensuring the long-term durability of shotcrete in aggressive environments remains a critical engineering challenge. One promising strategy lies in exploiting the hydration-enhancing effects of nanomaterials to refine microstructure and improve resistance to chemical degradation. This study investigates the enhancing effects of nano-silica and synthesized nano-crystalline C-S-H seeds to enhance sulfate resistance and mitigate calcium leaching in accelerated shotcrete. Specimens were prepared using both alkali-free and low-alkaline accelerators and subjected to semi-immersion sulfate attack and short-term leaching tests. Durability performance was evaluated through residual strength measurements, and degradation mechanisms were elucidated using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Results demonstrated that alkali-free nano-enhanced shotcrete significantly outperformed its low-alkaline counterparts, exhibiting 15.7%, 7%, and 17.9% lower residual strength loss following sulfate exposure. Microstructural analyses revealed severe ettringite and gypsum formation in low-alkaline systems, whereas alkali-free nano-enhanced mixtures showed only moderate ettringite corrosion. In terms of leaching resistance, the alkali-free nano-enhanced shotcrete achieved superior leachability indices, measuring values as low as 0.05 in groundwater and 0.15 in 5% sulfate solution for optimal mixtures, indicating notable reduced calcium loss. These enhancements are attributed to nanomaterial-induced microstructural refinement, driven by enhanced nucleation and pozzolanic reactions that densify the hydrate matrix. The major contribution of this study is the quantitative demonstration that combining alkali-free acceleration with specific nanomaterials effectively mitigates both sulfate attack and calcium leaching. Consequently, alkali-free nano-enhanced shotcrete can be recommended for critical applications such as permanent tunnel linings and other infrastructures exposed to sulfate-rich or chemically aggressive groundwater.</p>

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Potential exploit of the hydration-enhancing effect of nanomaterials on sulfate durability and calcium leaching mitigation of accelerated shotcrete

  • 期刊论文

  • 发表日期：

    2026年3月18日

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  • Chenglong Yu,
  • Yi Tian,
  • Xiaofeng Zhou,
  • Yanqun Xu,
  • Yousry Shalaby,
  • Hussaini Abdullahi Umar,
  • Mustapha Jamaa Garba,
  • Qiang Yuan

摘要

Ensuring the long-term durability of shotcrete in aggressive environments remains a critical engineering challenge. One promising strategy lies in exploiting the hydration-enhancing effects of nanomaterials to refine microstructure and improve resistance to chemical degradation. This study investigates the enhancing effects of nano-silica and synthesized nano-crystalline C-S-H seeds to enhance sulfate resistance and mitigate calcium leaching in accelerated shotcrete. Specimens were prepared using both alkali-free and low-alkaline accelerators and subjected to semi-immersion sulfate attack and short-term leaching tests. Durability performance was evaluated through residual strength measurements, and degradation mechanisms were elucidated using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Results demonstrated that alkali-free nano-enhanced shotcrete significantly outperformed its low-alkaline counterparts, exhibiting 15.7%, 7%, and 17.9% lower residual strength loss following sulfate exposure. Microstructural analyses revealed severe ettringite and gypsum formation in low-alkaline systems, whereas alkali-free nano-enhanced mixtures showed only moderate ettringite corrosion. In terms of leaching resistance, the alkali-free nano-enhanced shotcrete achieved superior leachability indices, measuring values as low as 0.05 in groundwater and 0.15 in 5% sulfate solution for optimal mixtures, indicating notable reduced calcium loss. These enhancements are attributed to nanomaterial-induced microstructural refinement, driven by enhanced nucleation and pozzolanic reactions that densify the hydrate matrix. The major contribution of this study is the quantitative demonstration that combining alkali-free acceleration with specific nanomaterials effectively mitigates both sulfate attack and calcium leaching. Consequently, alkali-free nano-enhanced shotcrete can be recommended for critical applications such as permanent tunnel linings and other infrastructures exposed to sulfate-rich or chemically aggressive groundwater.