Rayleigh wave-based monitoring of mortar coating and concrete core cracking on prestressed concrete cylinder pipe under external pressure using piezoelectric lead zirconate titanate

Prestressed concrete cylinder pipe (PCCP) is a critical type of pressure pipe widely used in major water conveyance projects worldwide. As essential components of a PCCP, the mortar coating and concrete core are directly linked to its operational safety. This study employed piezoelectric lead zirconate titanate (PZT) devices as transducers to generate excitation vibrations and measure the resulting Rayleigh waves, thereby providing a means to detect cracking in and monitor the health of the mortar coating and concrete core of a prototype 1400 mm inner-diameter PCCP under external pressure. First, a theoretical analysis was conducted to define the propagation laws of Rayleigh waves. Next, a finite element analysis was undertaken to identify the tensile regions of the PCCP mortar coating and concrete core when under external pressure applied along the length of the PCCP and thereby establish the locations for the PZT devices. Experiments were subsequently conducted by incrementally increasing the external pressure load from 0 to 700 kN while monitoring the cracking in the mortar coating and concrete core using sinusoidal excitation signals with frequencies of 5, 10, and 20 kHz. The voltage amplitudes measured at each external pressure load were analysed, confirming the Rayleigh wave propagation laws and revealing that the change in the measured voltage amplitude curve aligned with the experimental observations, thereby validating the proposed measurement method. Finally, the relative percentage deviation of amplitude (RPDA) and relative percentage deviation of energy (RPDE) damage indices were established based on the voltage measurements to further evaluate the damage state of the mortar coating and concrete core. The RPDA measured at an excitation frequency of 20 kHz was best for detecting cracks in the PCCP mortar coating, whereas the RPDA and RPDE measured at excitation frequencies of 20 and 10 kHz, respectively, were best for monitoring concrete core cracking.