Smart Concrete with Embedded Piezoelectric Devices: Implementation and Characterization

Abstract

A scheme for monitoring concrete structures, by embedding PZT ceramics into concrete modules has been proposed previously. These modules can be used as building blocks in the infrastructure engineering. Owing to the piezoelectric device embedment, the blocks are sensitive to ambient condition changes including stress, temperature, and humidity. It is suggested that by measuring the equivalent circuit parameters of embedded piezoelectric ceramics, the structural-static or quasi-static state may be interrogated. The equivalent circuit parameters of a piezoelectric device represent the characteristics of the piezoelectric, dielectric, and mechanical performances. By analyzing the parameters, the signal related to the structural-mechanical state can be acquired. Theoretically, a piezoelectric device can be modeled as a multiple-input-multiple-output transducer. In practice, the problem remains that the equivalent parameters, the sensing outputs, are also dependent on the ambient settings such as temperature which may cause either expansion or shrinkage. However, through dozens of experiments with smart concrete specimens embedded with piezoelectric elements and piezoelectric elements free of embedment, it is observed that the characteristic frequencies (anti-resonance and resonance) are quite sensitive to temperature but have little dependence on stress. This way, by sensing data fusion, the characteristic frequencies are used as temperature indicators to remove the variation in equivalent circuit parameters resulting from temperature, exclusive of using additional sensors for compensation. In turn, the structural stress-monitoring (static or quasi-static) through the detection of the equivalent circuit parameters is achieved.