Estimation of Defecs in Concrete in Early Age by Using Acoustic Emission Method

本研究采用声发射方法对混凝土早期因干燥收缩、浇注不良和热应力引起的缺陷进行了研究和估计。模型试样在浇筑后28天内进行了不同材料、配合比和钢筋约束率的试验。在试验期间连续测量AE计数率、收缩应变。并与强度、杨氏模量等参数进行了比较。从结果来看，声发射计数率随着混凝土试件拉应力的增大而增大。结果表明，声发射计数率与混凝土早期缺陷的发展有明显的相关性。同时，对流动混凝土进行了相同的试验。流动混凝土的声发射计数率明显小于普通混凝土。这说明流动混凝土具有很好的相容性，很少出现混凝土早期发育的缺陷，如大空隙。用线性遍历法从空腔观测试验中证实了这一点。

In this study, defects in concrete causing in early age due to drying shrinkage, and poor casying and thermal stress were investigated and estimated by acoustic emission metod.Model specimens varying materials, mix proportions and the rate of restriction by reinforced bar were tested during 28days after casting. AE count rate shrinkage strain, were measured continuously during the test period. And the results were compared with parameters such as strengths and Young's modulus. From the results, AE count rate became large acording to that the tensile stress causing in concrete specimens became large. And the correlation between AE count rate and the development of defects in concrete in early stage was clearly obseved.At the same time, Same tests for flowing concrete were carried out. AE count rate of flowing concrete was evidently small compared to that of normal concrete. This shows that flowing concrete have very good compativility and the defects in concrete developing in early stage such as large air void are rare. Tllis was confirmed from the air voids obsevation test by linear traverse method.