Concrete Structure Health Monitoring Based On Piezoelectric Composite Acoustic Emission Sensor

Concrete is the basis of the large civil engineering construction materials, the dosage of every years up to 5 billion cubic. Large concrete structures(such as dam, foundation, high buildings, Bridges, etc.) of large investment and long-term service, are often under the action of external coupling factors, which will inevitably be damaged and lead to the occurrence of catastrophic events extremely. The damage of concrete will bring serious hidden dangers. It is the recognized techniques to solve the problem of monitoring of concrete structure in service. This paper studies the types of receiving acoustic emission sensors, working frequency and acoustic performance, which is the incompatible problems, and studied the concrete structure damage characteristic parameters of acoustic emission, that realized the online monitoring of concrete structure. The research and experimental results are obtained as follows:In this article, through the cutting processing we make the thickness of the sensing element electromechanical coupling coefficient increases, the bandwidth increased, fitting the relationship between the resonance frequency and the thickness of the sensing element. It provides for the preparation of resonant acoustic emission sensor provides a theoretical basisThe acoustic emission sensor matching layer was prepared by forming method, which was made up of cement and silicon nitride material. The acoustic impedance of matching layer is 11.3 MRayl, fully meet the requirement of acoustic impedance of monitoring sensors used in concrete structure.The sensing element and matching layer were bonded together, which improve the effect of the coupling. By matching the charge amplifier effective improve the sensitivity of the sensor, the sensor's working frequency was widened from 20 to 400 KHz to 20-1000 KHz, which expanded the bandwidth of the sensor. The sensor of preparation is of high accuracy, through the broken lead experiment simulated defect source, measured sensor linear positioning accuracy is above 95%, the source of defects can be accurately positioningThe acoustic emission techniques monitoring concrete parameter setting Determined, which determine the acoustic emission monitoring of concrete when the peak identification to 150 us, waveform identification to 300 us, waveform blocking time determined for 450 us, sound velocity for 4250 m/s, and determine the acoustic attenuation curve in C30 concrete materials.The damage of concrete and implantable sensor is stuck outside source of positioning was studied, found that the acoustic emission technique to the source to the damage of linear positioning and three dimensional positioning, positioning results is quite coincident with the actual situation.It was found that the AE amplitude, the impact number and energy change, early material stress, the amplitude, the impact number and the rate of change of energy is larger, after a sharp change show a plateau, eventually produce damage, suggests a process of accumulating damage of concrete material.Concrete structure damage, the parameters of acoustic emission is a clear inner link, acoustic emission energy increases, the impact number increased. Reinforced concrete structure in the process of damage, the advantage of acoustic emission signal frequency is changing, and as the force loaded on the signal frequency, concrete material fracture, there are two obvious frequency were 9.4 kHz and 32.9 kHz...