Monitoring and evaluation of concrete damage based on acoustic emission technique

Due to existing few mature techniques to estimate the mechanical damage of concrete, and could not judge structural state real-time, acoustic emission technology is presented to monitor its damage evolution under three point bending testing. The mechanical properties of cement mortar and acoustic emission characteristics are obtained. Based on the monitoring data, firstly, the relationship between the acoustic emission counts and load is studied, through comparing with acoustic emission counts embraceable curve and load curve, it is found they have good corresponding connection. Secondly, the cement mortar damage evolution law is studied applying the AE characteristic parameter time series fractal theory. The acoustic emission fractal features of all stress levels in the whole cement mortar failure and the changing rules of fractal value are studied. The results show that, in the initial and middle stage of loading, the fractal value of cement mortar is unsteady. When the cement mortar crack begins its fast propagation, the fractal dimension appears the 'increase-decrease' pattern, which could be used to identify the cement mortar critical failure. At last, by analyzing acoustic emission mechanics, damage factors are (defined as variation of acoustic emission energy, the equation of damage evolution and the constitutive equations presented by acoustic emission parameters are derived. The evolution equation has been verified through experiments.