为了解决寒冷地区低温导致混凝土性能劣化的问题。基于纳米材料改善混凝土性能的理论，从宏观和微观两个尺度研究了纳米二氧化硅对混凝土性能的影响。抗压强度试验结果发现，低温养护下普通混凝土的抗压强度衰减10%左右；掺入纳米二氧化硅后混凝土的抗压强度提升20%左右，最佳掺量是2%。通过压汞、X射线衍射和扫描电镜等微观试验数据探讨了纳米二氧化硅对混凝土性能的改良机理。结果表明，常温和低温养护下纳米二氧化硅都能促进水泥水化，消耗水化生成的氢氧化钙，产生更多的水化硅酸钙和水化硅铝酸钙凝胶，从而降低混凝土的孔隙率，优化混凝土的微观结构，提升混凝土的性能。相比常温环境，低温下纳米二氧化硅对混凝土性能的提升效果略有下降，但其完全可以弥补低温对混凝土性能造成的不利影响。

To solve the problem of deterioration of concrete performance caused by low temperature in cold regions. Based on the theory of nanomaterials to improve the properties of concrete, the effect of nano-silica on the properties of concrete was studied from the macro and micro scales. The results of the compressive strength test show that the compressive strength of ordinary concrete is attenuated by about 10% under low temperature curing. After being mixed with nano silica, the compressive strength of concrete is increased by about 20%, and the optimal dosage is 2%. The improvement mechanism of nano-silica on concrete properties was explored through microscopic test data such as mercury intrusion, X-ray diffraction and scanning electron microscopy. The results show that nano-silica can promote cement hydration at room temperature and low temperature curing, consume calcium hydroxide generated by hydration, and produce more hydrated calcium silicate and hydrated calcium aluminate gel, thereby reducing the porosity of concrete, optimizing the microstructure of concrete, and improving the performance of concrete. Compared with the room temperature environment, the improvement effect of nano-silica on concrete at low temperature is slightly reduced, but it completely overcomes the adverse effects of low temperatures on the performance of ordinary concrete.