Feasibility of passive intermodulation test for detecting corrosion in reinforcing bars

Abstract

The passive intermodulation (PIM) test is a nondestructive test utilizing the nonlinear reflections of electromagnetic (EM) waves to identify material deterioration. This study explored the feasibility of the PIM test for detecting corrosion in reinforced concrete (RC) structures. First, the principle of the PIM was explained, and the devised PIM test equipment was described. Subsequently, the PIM test was performed on rebar, plain concrete, and RC specimens with various corrosion degrees. The results indicated that plain concrete generated large PIM signals, attributed to a nonuniform permittivity distribution, whereas the rebar specimens exhibited small or no PIM signals, resulting from relatively linear reflections. The RC specimens exhibited smaller PIM signals than plain concrete, suggesting that the rebar inside the concrete reduced the PIM signals by linearly reflecting a part of EM waves. Rebar corrosion further reduced the PIM signals owing to the scattering of EM waves. Therefore, rebar corrosion can be identified through smaller PIM signals compared with the surrounding region. Furthermore, the effect of rebar contact nonlinearity on the PIM signals was investigated using contacted rebars. The results indicated that corrosion reduced the PIM signals even with the contacted rebars. Therefore, the PIM test is feasible for detecting rebar corrosion.