Restrained autogenous shrinkage behavior of high strength concrete at early ages

荧光显微镜检查，以确定损伤引起的自干燥和抑制自收缩。讨论了高强混凝土早期荧光区特征与闭环单轴约束收缩试验装置评价的粘弹性行为的关系。还讨论了水、硅灰和饱和轻骨料对收缩行为的影响，重点讨论了荧光显微镜、显微硬度测量和SEM-BSE图像分析所观察到的微观结构变化。本研究得到的主要结果如下：(1)密封混凝土比水固化混凝土多孔性更强。(2)早期蓄水对高强混凝土自收缩具有抑制作用。水浸混凝土形成致密的微观结构。(3)密封混凝土在骨料颗粒周围形成弱区。刚性骨料克对自收缩的约束在骨料颗粒附近造成了看不见的微裂纹。(4)硅灰混凝土早期存在大量被细小缝隙包围的残余芯水泥颗粒。(5)以缝隙为夹杂物的水泥颗粒作用较弱，可能是硅灰混凝土早期蠕变潜力较大的原因。(6)轻骨料部分替代正常重量骨料对降低高强混凝土的自收缩是有效的。然而，置换效果取决于轻骨料的初始水分状况。

The fluorescence microscopic examinations were conducted to identify damages induced by self-desiccation and restraining autogenous shrinkage. Characteristics of fluorescent areas detected in high strength concrete at early ages were discussed in relation to the viscoelastic behavior evaluated by the closed loop uniaxial restrained shrinkage testing apparatus. Effects of water ponding, silica fume and saturated lightweight aggregate on the shrinkage behavior were also discussed with emphasis on changes in microstructure observed by the fluorescence microscopy, microhardness measurements and the SEM-BSE image analysis. The major results obtained in this study are as follows ;(1) Sealed concretes were more porous than the concretes cured in water.(2) Water ponding at early ages was effective to prohibit autogenous shrinkage of high strength concretes. Dense microstructure was formed in the water ponded concrete.(3) Weak regions were formed around aggregate grains in sealed concretes. The restraint provided by, rigid aggregate grams against autogenous shrinkage caused invisible microcracks in the vicinity of aggregate grains.(4) There were many remnant core cement particles surrounded by fine gaps in silica fume concrete at early ages.(5) Less effective function of the cement particles with the gaps as an inclusion may account for the greater creep potential of silica fume concrete at early ages.(6) A partial replacement of normal weight aggregate by lightweight aggregate was effective in reducing autogenous shrinkage in high strength concrete. However, effectiveness of replacement was dependent on the initial moisture condition of lightweight aggregate.