Defect detection of concrete in infrastructure based on Rayleigh wave propagation generated by laser-induced plasma shock waves

Defects in large concrete structures, including critical infrastructure such as bridges and tunnels, are traditionally detected by hammering tests by inspectors. However, the results depend on the inspectors’ skills. Additionally, hammering tests are impractical to thoroughly inspect massive structures in a short time. Herein defect detection in concrete structures is realized by telemetry using shock waves generated by laser-induced plasma (LIP). LIP is generated by irradiating a Nd:YAG pulsed laser near the concrete surface. As LIP spreads to the surrounding area at an ultrafast speed, a spherical shock wave is generated. This shock wave realizes a non-contact, non-destructive impulse excitation force on a concrete structure. The response of the concrete structure is measured with a laser Doppler vibrometer (LDV). Applying this method to detect defects in an artificial concrete specimen can identify the natural frequencies and modes of the defects. By measuring the propagation of the Rayleigh waves generated by the LIP shock waves, defects and the approximate location of the boundary between the defective part and the defect-free part are detected.