Promoting the early hydration of cement and enhancing its strength at low-temperatures can reduce the occurrence of freeze-thaw damage in concrete structures. Amorphous nano-SiO2 particles (NS) have been proven to effectively facilitate cement hydration at low temperatures. However, crystalline nano-SiO2 particles (CS), which share the same chemical composition as NS, have received little attention from researchers. The aim of this study is to investigate the effectiveness of CS in prompting the properties of cement mortar cured at low temperature. Both CS and NS were utilized as modifiers to enhance the properties of cement mortar. Their effects on cement’ setting time, hydration heat, micro-pore structure, and mechanical property were compared and analyzed at low temperature (7 °C) and room temperature (23 °C). Additionally, the mechanism of their influence was discussed based on experimental data. The results indicate that CS can significantly accelerate the hydration of cement at 7 °C, whereas this ability is virtually negligible at 23 °C. At 7 °C, CS was able to increase the degree of cement hydration by 8.7 % at 3d and enhanced the 28d strength of the cement mortar by 11.1 %. NS showed an increase in these two indices by 11.3 % and 13.4 %, respectively. Moreover, CS and NS can result in a 23.8 % reduction in the total porosity of cement samples hydrated for 3d, and refine the overall pore structure of the specimens. Both CS and NS particles can react with CH and generate C-S-H seeds on their surfaces, thereby promoting cement hydration. The findings are of significant importance for enhancing the quality of concrete engineering in cold regions and broadening the channels for the utilization of solid waste.

中文翻译：

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结晶纳米 SiO₂ 波特兰水泥复合材料在低温下的水化行为和微孔结构


促进水泥的早期水化，增强其在低温下的强度，可以减少混凝土结构冻融损伤的发生。无定形纳米 SiO2 颗粒 （NS） 已被证明在低温下能有效促进水泥水化。然而，与 NS 具有相同化学成分的结晶纳米 SiO2 颗粒 （CS） 很少受到研究人员的关注。本研究的目的是探讨 CS 在促进低温固化水泥砂浆性能方面的有效性。CS 和 NS 均被用作改性剂以增强水泥砂浆的性能。比较分析了它们在低温 （7 °C） 和室温 （23 °C） 下对水泥凝结时间、水化热、微孔结构和力学性能的影响。此外，根据实验数据讨论了它们的影响机制。结果表明，CS 在 7 °C 时可以显著加速水泥的水化，而在 23 °C 时这种能力几乎可以忽略不计。 在 7 °C 时，CS 能够在 3 天将水泥水化程度提高 8.7%，并将水泥砂浆的 28 天强度提高 11.1 %。NS 显示这两个指数分别增长了 11.3 % 和 13.4 %。此外，CS 和 NS 可以使 3d 水化水泥样品的总孔隙率降低 23.8%，并细化样品的整体孔隙结构。CS 和 NS 颗粒都可以与 CH 反应并在其表面生成 C-S-H 种子，从而促进水泥水化。研究结果对于提高寒冷地区混凝土工程质量、拓宽固体废弃物利用渠道具有重要意义。