The particularity of construction and environment lead to the emergence and development of cracks of shaft lining concrete. In order to study the cracking condition of concrete structure, in this paper, during three point bending notched tests of concrete, according to the concrete crack critical state identification characteristics of acoustic emission, acoustic emission technology is used to predict the time of the crack of concrete specimen, to analysis the relationships between the time distribution of acoustic emission events and critical state of crack, so as to create the accurate judgment of specimen cracking.
When materials and components are deformed and fractured under stress, or when the inner stress exceeds the yield limit thus enter the irreversible stage of plastic deformation, the strain energy would released in the form of the transient elastic wave (Xu & Chen 1997). This phenomenon is called acoustic emission or stress-wave emission. Acoustic emission, as a technical method, usually used to detect the internal cracks development in concrete material. The test results can reflect the development process of internal defects of concrete.
The defects in concrete pouring phase, such as the in homogeneity on the microstructure and initial cracks, could result in severe concrete crack and even fracture accident. Therefore the emergence and development of the concrete cracks have huge effects on the whole life process (Xu & Wang 2006), so it is very important to the research on fracture properties of concrete.
Concrete fracture development is a continuous process essentially, that is, from initial fissure to micro-crack growing and finally becoming a macroscopic fracture (Ji & Cai 1999). This article elaborates at three point bending fracture test on concrete material. During the loading process, as loading increase, additional stress made the concrete to form the buckling fracture. Because acoustic emission signals are along with the whole process of the damage and show different characteristics at different stages (Ji 2004), acoustic emission technology was used to test the process from the appearance of cracks in the concrete sample to buckling fracture.