Detection and assessment of pitting corrosion in rebars using scattering of ultrasonic guided waves

The present study aims at developing a robust non-destructive evaluation technique by using the scattering of ultrasonic guided waves for early detection and assessment of localised damage in bare rebars in the form of corrosion pits. The guided wave interaction with the pitting corrosion is numerically simulated by using finite element analysis, and the results are validated with experiments. The received signal contains several wave packets, which could be identified as various scattered modes that are generated from the edges of the corroded region. It is found that when the damage is placed at the centre of the rebar, several scattered wave modes superimpose to form two distinct wave packets in the received signal. A damage index is proposed by using these two distinct wave packets. It is shown that the proposed damage index method can be used successfully to monitor the axial extent and intensity of pitting corrosion in rebars. However, for the pitting corrosion that is situated at an arbitrary position, a different methodology, which utilises the differential time of arrival of various scattered wave modes, is proposed to identify the location of the pitting corrosion. Finally, a non-dimensional parameter, namely the scatter coefficient, is defined to analyse the energy contributions of various scatter modes. It is found that this scatter coefficient gradually increases with the mass loss and that the increment is pronounced when the corrosion pit is closer to the receiver location. The findings of the study can be used to identify the pitting corrosion in bare rebars.