Sensitivity of longitudinal guided wave modes to pitting corrosion of rebars embedded in reinforced concrete

The detection of incipient pitting corrosion in rebars that are embedded in reinforced concrete is an important area of research currently. Similar damages in metallic and composite structures are effectively uncovered using guided waves; however, their application in the identifying of defects in concrete remains elusive. In this paper, the influence of longitudinal guided wave modes on pitting corrosion is explored in detail to identify specific phases of corrosion, namely; corrosion initiation, corrosion progression, and diameter reduction. An impressed-current-based accelerated corrosion setup is designed to induce pitting corrosion in reinforced concrete (RC) beams. These beams are continuously monitored using longitudinal guided wave modes that are generated and captured by contact transducers. Theoretical dispersion curves are generated using an approximate concrete model to recognise the guided wave modes. The effectiveness of this model is examined by comparison with a full-scale numerical model. A pitting corrosion identification strategy is then devised using a non-dimensional parameter that is termed relative amplitude (RA), and the group velocity extracted from wavelet analysis of a guided wave mode. We demonstrate that the RA values and the group velocities of the higher longitudinal wave modes, L(0,3) and L(0,4), have the potential to decipher the various phases of pitting corrosion.