Effects of temperature on the performance of the piezoelectric-based smart aggregates active monitoring method for concrete structures

The smart aggregate (SA)-based active monitoring method has been widely used in detecting micro-cracks, early age strength, and water seepage of concrete structures. Using this method, a pair of SAs is usually adopted, in which one SA is used as an actuator to emit signals, and the other is used to receive the propagated signals. SAs embedded in concrete may experience significant temperature variation during field monitoring. Until now, research on the temperature-dependent performance of the SAs-based monitoring method has rarely been reported. In this study, the temperature-dependent performance of this active monitoring method was investigated. Specifically, the effects of temperature on the amplitude and wave velocity of the transmitted signals were studied. A temperature chamber was used to change the temperature of bare SA pairs and SA pairs embedded in concrete from -20 degrees C to 80 degrees C. The results showed that the amplitude of low frequency signals increases significantly with an increase in temperature, while the wave velocity decreases monotonously with an increase in temperature. Furthermore, the effect of temperature on the signal amplitude is greater than that on the wave velocity. This result indicates that the change in signal amplitude or velocity-based monitoring indices should be carefully considered, and velocity-based monitoring indices are preferred for in situ monitoring of concrete structures experiencing significant temperature variation. This study provides a comprehensive examination in regards to the temperature effects on SAs-based active monitoring method for concrete structures.