Restrained autogenous shrinkage behavior of high strength concrete at early ages

高强混凝土早期自收缩行为的抑制

基本信息

批准号：
12650459
负责人：
IGARASHI Shin-ichi
金额：
$ 2.37万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

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.

进行荧光显微镜检查以识别由自干燥和抑制自收缩引起的损伤。讨论了早期高强混凝土中检测到的荧光区域的特征与闭环单轴约束收缩测试仪评估的粘弹性行为的关系。还讨论了积水、硅粉和饱和轻骨料对收缩行为的影响，重点讨论了通过荧光显微镜、显微硬度测量和 SEM-BSE 图像分析观察到的微观结构的变化。本研究取得的主要结果如下：（1）密封混凝土比水养护混凝土孔隙率更高。（2）早期积水可有效抑制高强混凝土的自收缩。积水混凝土中形成致密的微观结构。(3)密封混凝土骨料颗粒周围形成薄弱区。刚性骨料克数对自收缩的抑制，导致骨料颗粒附近出现肉眼看不见的微裂纹。(4)早期硅粉混凝土中存在许多被细小间隙包围的残余核心水泥颗粒。(5)骨料有效作用较差。具有间隙的水泥颗粒作为夹杂物可能是硅粉混凝土在早期具有较大蠕变潜力的原因。(6)用轻骨料部分替代普通骨料可有效减少高强混凝土的自收缩。然而，更换的有效性取决于轻骨料的初始水分状况。