The current research on the application of nanomaterials in concrete is mainly carried out under positive-temperature curing conditions, while research under negative-temperature curing conditions is very scarce. This paper investigated the effect of nano-SiO₂ on long-term strength and chloride diffusivity of cement pastes cured at negative temperature (−5 °C). Thermogravimetric analysis (TGA) confirms that the low-dosage nano-SiO₂ can still exert the pozzolanic effect within negative-temperature cement paste even after 120 days. The macro results show that low-dosage nano-SiO₂ effectively shortens the curing age required for strength and durability development. It is further proved that compared to the promotion effect of nano-SiO₂ on hydration, the optimization of internal pore structure by nano-SiO₂ plays the dominant role in shortening the curing age required. Furthermore, it is found that the low sensitivity of strength to the microstructure results in the insignificant effect of nano-SiO₂ on the long-term strength. In contrast, nano-SiO₂ can effectively improve the long-term chloride permeability resistance through increasing the tortuosity of pore structure and decreasing the critical pore diameter and threshold pore diameter.

中文翻译：

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纳米 SiO2 对负温水泥浆体长期性能影响的实验研究


目前纳米材料在混凝土中的应用研究主要在正温养护条件下进行，而负温养护条件下的研究非常稀缺。本文研究了纳米 SiO₂ 对负温 （-5 °C） 固化水泥浆体的长期强度和氯化物扩散率的影响。热重分析 （TGA） 证实，即使在 120 天后，低剂量纳米 SiO₂ 仍可在负温水泥浆中发挥火山灰效应。宏观结果表明，低剂量纳米 SiO₂ 有效缩短了强度和耐久性发展所需的固化年龄。进一步证明，与纳米 SiO₂ 对水合的促进作用相比，纳米 SiO₂ 对内部孔隙结构的优化在缩短所需的固化年龄方面起主导作用。此外，研究发现强度对微观结构的低敏感性导致纳米 SiO₂ 对长期强度的影响不显著。相比之下，nano-SiO₂ 可以通过增加孔结构的曲折度和减小临界孔径和阈值孔径来有效提高长期抗氯化物渗透性。