Practical issues related to the application of piezoelectric based wave propagation technique in monitoring of concrete curing

Smart piezoelectric material, namely, the Lead Zirconate Titanate (PZT) has recently found its application in concrete curing and strength development monitoring using the wave propagation (WP) technique. Real-life application of this technique is sometimes questioned as various practical issues have not been attended. In this paper, a series of experimental studies are performed to investigate a range of practical issues related to the application of this technique, in an attempt to reduce the gap between laboratory studies and real-life applications. Issues such as the consistency of wave velocities and repeatability of the sensor's electrical signatures, the optimum frequency of actuation, the effect of PZT transducer's spacing and sizes, the waveform of actuation signatures, the effect of input voltage amplification, the effect of different surface roughness, the environmental effect and the effect of different types of coarse aggregates are experimentally studied. Results showed that 5-peaks sinusoidal tone burst actuated at 30 kHz or 120 kHz are preferred input voltage. Spacing of transducers should be approximately 90 mm. Smooth and even surface of the host structure is preferred for bonding. The WP technique is found to be reliable and its performance is consistent across different specimens up to a period of 365 days. It is also capable of differentiating the strength concrete with different types of coarse aggregate. Studies conducted in this paper provide basic understanding into various practical issues, which is expected to serve as guidelines to future development, design, optimization and commercialization of a more effective PZT based WP technique in monitoring of concrete curing.