Fabrication Of Cement Based Piezoelectric Sensor And Its Application Research

The structural health monitoring based on piezoelectric sensors has gained concernsfrom the academic and engineering. But there are compatibility issues between thetraditional piezoelectric sensors and civil engineering structures. According to thecharacteristics of civil engineering structures, a kind of cement-based piezoelectric sensor wasprepared, and its application research was investigated based on both active and passivefluctuation method in this paper. The research and experimental results are obtained asfollows:In order to get the sensor suitable for structural health monitoring of civil engineering,the1-3cement based piezoelectric composites with different resonance frequencies wereprepared by the cutting-pouring. The results show that the cement-based piezoelectriccomposite has the smaller the internal resistance between50kHz and150kHz, the impedancevalue with small amplitude variations has remained at a very low level.To study the influence of the matching layer, the backing layer and a shield on thesensors, the sensors were prepared by the1-3cement-piezoelectric and piezoelectric ceramic,respectively.The result show that the electrical impedance spectrum of the sensor is more flat whenthe matching layer is added, the impedance value of the cement-based piezoelectric sensor issignificantly larger than that of piezoelectric ceramic sensor. Meanwhile, the matching layerincreased the bandwidth and receiver sensitivity of the sensors. The sensitivity of thecement-based piezoelectric sensor and piezoelectric sensor have an increase of0.954dB and2.728dB, respectively. The backing layer reduces the sensitivity of the sensors at a certainextent, but improves the acoustic attenuation properties of the sensors, so that the sensorshave good interference ability. At the same time, the threshold value of the sensors are lessthan30dB after shielding-processing.Used the cement-based piezoelectric sensors and piezoelectric ceramic sensors as thereceiving unit, to monitor the cement and the cement mortar hydration reaction process basedon the of ultrasonic. The results give that the primary frequency and the frequency peak in the frequency domain spectra showed an increasing trend as the hydration reaction process, andclose stable in late ages. The time-domain waveform with the cement hydration reaction givesthat the cement hydration reaction can be basically divided into five stages, the inductionperiod, accelerated phase, wave period, attenuation and stable period within24hours ofhydration. When the ultrasonic propagates from the cement mortar, it has lower amplitude andpropagation velocity decreases relative to the cement slurry. Meanwhile, the compressivestrength and ultrasonic velocity had a positive linear relationship, with a correlationcoefficient greater than0.9.Acoustic emission properties of cement-based piezoelectric sensor were studied based onacoustic emission technique. Firstly, use the pencil core fracture simulation as the acousticemission signals on the different surfaces of the sensor, respectively. And broken lead in thesensor at different distances. It is found that the sensor receives maximum signal amplitude,when the electrode surface of the sensor was vertical with the concrete block. Meanwhile, theamplitude of the reception signal decreases with the increase of sound emission distance. Thefrequency domain has different main frequency spectral peak, but its frequency is the same.The responses of the sensor to the cement mortar under different stress conditions wereinvestigated. It also shows that the embedded AE sensor can accurately reflect the continuoussignal when the cement mortar was loaded, and the number of the AE signals increaseslinearly. And, the energy of AE signals increases suddenly as the loading reach to70%of thefailure load. In the three-point bending test，loading curve and the distribution curve ofacoustic emission events have good consistency. AE process can be divided into three stages,initial stage, stable stage and unstable stage. So the sensor is sensitive to the variation of theAE signals, and can reflect the characteristic of the AE process well in both the uniaxialcompression test and the three-point bending test.