Research Of Concrete Damage Detection Based On PZT Sensor Under Controlled Temperature Conditions

To solve the problem that the material parameters of piezoelectric ceramics(PZT)are susceptible to temperature,a temperature controller suitable for surface-bonded PZT sensor was made in this paper and it can control the working temperature of PZT sensor indirectly by keeping its internal temperature stable.Then,the damage identification of concrete block and full-size tunnel segment based on PZT sensor under controlled temperature conditions was studied.Besides,the electromechanical impedance(EMI)method based on surface-bonded PZT sensor to identify and locate the damages of tunnel segments which can be regarded as large concrete structures was also explored.The main research and results are follows:(1)The changing rules of conductance curve with temperature for surface-bonded PZT sensor are obtained.In this study,the working temperature of surface-bonded PZT sensor was changed by the temperature controller and the structure temperature was kept stable.It shows that,both for concrete block and tunnel piece,the conductance curve under various damages will be shifted upward with the temperature rises and it is more sensitive to the temperature change in the high frequency region.In addition,the resonance frequency will shift slightly to the left and the basic shape of curve remains unchanged.Furthermore,there is a good linear relationship between RMSD and working temperature of PZT sensor.(2)The feasibility of identifying damage by temperature-control PZT under changing ambient temperature is verified.In order to change the temperature of concrete block,the thermostat was used.Then,the RMSDs of temperature-control PZT sensor and surface-bonded PZT sensor were calculated under different conditions.It is found that temperature-control PZT sensor is less sensitive to ambient temperature change and the RMSD caused by damage is twice that caused by temperature.Thus,the influence of temperature on the conductance curve can be eliminated by setting a proper threshold.Besides,the change rules of admittance data caused by structural damage will change with different working temperature of PZT sensor,so the temperature of controller should be set to the highest temperature of the environment to keep the working temperature stable.(3)The effectiveness of surface-bonded PZT sensor for large tunnel segment structural bolt looseness detection is investigated.In the test,the PZT sensors were installed on different locations and three bolts were loosened successively.The results show that the conductance curves measured by surface-bonded PZT sensors will change regularly with the damage degree,which can effectively identify the bolt looseness damage.And the RMSDk of PZT sensor which is near the damage is twice that of PZT sensors at other locations,so the approximate location of damage can be intuitively determined.