Design And Fabrication Of Highly Efficient Cement-based Piezoelectric Sensor And Its Properites Research

0-3cement-based piezoelectric composites were novel smart materials preparedwith cement as the matrix and piezoelectric ceramic as the functional phase. Theyhave many advantages including good compatibility with concrete, simple preparationtechnology and low cost, indicating wide application prospects in the area ofweigh-in-motion (WIM) and structural health monitoring. In this paper, highlyefficient piezoelectric element was independently manufactured. Then through theoptimization of preparation technology and structure, novel0-3cement-basedpiezoelectric sensor was successfully prepared with the composite as the sensingelement, and basic properties and durability were studied systematically.Based on the design theory of close packing,0-3cement-based piezoelectriccomposites with high performance was manufactured with cement as the matrix,piezoelectric ceramic as the functional phase and cementitious materials with highfineness and high dielectric constant as the enhanced phase. Results indicated that theintroduce of enhanced phase could improve the piezoelectric properties, mechanicalproperties and microstructure significantly. When the content of PZT and enhancedphase was60vol.%and20wt.%, respectively, the piezoelectric strain factor reached90.6pC, splitting tensile strength reached6.6MPa and water absoption reached1.67%.Meanwhile, PZT particles were uniformly distributed in cement matrix, andinterfacial transition zone (ITZ) between PZT particles and cement matrix was prettydense.With cement and epoxy resin as main raw materials, the encapsulation materialswere successfully prepared based on various technical ideas about reducing viscosityand eliminating bubbles. Results indicated that the optimum mechanical properties,low water absorption and stable mechanical properties were obtained when the massratio of cement and epoxy resin reached3:1. Besides, Thermal analysis results alsoshowed that the introduce of rigid filler restricted the thermal expansion ofencapsulation materials effectively and the thermal expansion rate increased linearlywith the increasing of temperature, presenting relatively stable temperature sensibility.With the method of bonding before welding and reasonable structuraloptimization design, working reliability of sensors can be improved effectively.Results indicated that the layout of sensing element had a great influence on themechanic-electric response. The sensor showed good linearity characterized by linear correlation coefficient in the range of0.31~1.09MPa when the sensing element waslocated in the upper part of sensor. However, when the sensing element was located inthe bottom part of sensor, the sensor presented good linearity (0.994) in a wider rangeof0.31~2.34MPa and the sensitivity reached1187mV·MPa-1. With the increasing ofthe ratio of cement and epoxy resin, the linear correlation coefficient firstly increasedand then decreased in a way, the optimum linearity was obtained when the ratio was3:1and load can be passed on to the sensing element effectively. The phase shiftbetween input and output was nearly zero independent of loading system, indicatingthat the sensor prepared had a rapid response to sine load and pulse load withouthysteresis phenomenon. In the range of0.1~20Hz, basically containing the vibrationfrequency in civil engineering structure, the frequency firstly increased with theincreasing of output voltage amplitude and then tended to be constant after thefrequency surpassed10Hz; In the range of0.05~1s, the mechanic-electric responsealmostly kept stable when loading time was less than0.2s, which contained the timerange when vehicles passed the sensor at normal speed.The mechanic-electric response of cement-based piezoelectric sensor preparedwas evaluated under complex environment conditions stimulating the real road traffic,including temperature fatigue, drying-wetting cycle and fatigue load. Resultsindicated that in the range of0~40℃, when the temperature gradually increased, theoutput voltage increased, sensitivity firstly decreased and then increased, the linearitypresented an trend contrary to the sensitivity (more than0.99); Phase shift betweenoutput and input was nearly zero independent of temperature. After saturated water,drying-wetting cycling and fatigue load, respectively, the mechanic-electric responseof sensor almost showed no change, indicating that the operating environment had anegligible influence on the output, the sensors showed good temperature stability anddurability.