Abstract: Improving the early strength of cement concrete can effectively shorten the demolding and tension waiting time of prestressed precast members，so as to shorten the construction period. However, using traditional early strength accelerator to improve the early strength of the cement concrete often affects its durability or workability. In order to solve this problem, the effect of compound regulating agent made of nanometer silica and calcium silicate hydrate on the early performance, volume stability and durability of concrete was studied, and the effect of compound regulating agent on the microstructure of cement concrete was observed by SEM test. The research shows that the use of compound regulating agent can improve the workability, early compressive strength and durability as well as reduce drying shrinkage rate of cement concrete. When the content of the compound regulating agent content is 1.0%, compared with the reference group, the slump and expansion of concrete increases by 11.9% and 17.6%, the emptying time of the inverted slump cylinder decreases by 26.5%，the 3d compressive strength increases by 14.4%, the 56d electric flux decreases by 32.7% and the 56d drying shrinkage rate decreases by 39.7%. Through SEM test, it is found that the compound regulating agent can make cement more compact, reduce the defects of concrete interface transition zone and furtherly refine fly ash particles.

Key words: bridge engineering; nano-silica; Nano-SiO2-CSH; prefabricating box-girder; early performance; microscopic mechanism

摘要： 提高水泥混凝土的早期强度可有效减少预应力预制构件的脱模与张拉等待时间，从而缩短工期，但采用传统早强剂提高水泥混凝土早期强度往往会影响其耐久性或工作性能。针对这一问题，笔者研究了采用纳米二氧化硅与纳米水化硅酸钙制备的复合调节剂对混凝土早期性能、体积稳定性、耐久性的影响，并通过SEM观测了复合调节剂对水泥混凝土微观形貌的影响。研究表明：采用复合调节剂可提高水泥混凝土的工作性能、早期抗压强度与耐久性，降低干燥收缩率。当复合调节剂的掺量为1.0%时，较基准组混凝土坍落度与扩展度提升了11.9%与17.6%，倒置坍落度筒排空时间减少了26.5%，3 d抗压强度提高了14.4%，56 d电通量降低了32.7%，56 d干燥收缩率降低了39.7%；通过SEM试验发现，采用复合调节剂能够使得水泥石界面更加密实，减少混凝土的界面过渡区的缺陷，并能进一步细化粉煤灰颗粒。

关键词: 桥梁工程；纳米二氧化硅；纳米水化硅酸钙；预制箱梁；早期性能；微观机理