Nonlinear Wave Modulation for the Evaluation of Corroded Steel Plates Embedded in Concrete

Corrosion of steel components embedded in concrete is detrimental to the structural integrity and their intrinsic function,such as the leak-tightness of containment liners in nuclear reactor containment buildings. Detection of embedded linercorrosion is a challenging task due to the concrete’s heterogeneity and the large dimensions of containment buildings.This initial study explores early-stage detection using nonlinear wave modulation on corroded liner plates embeddedinside small lab-scaled concrete cylinder specimens. The liners were corroded before being embedded in concrete tominimize the risk of concrete cracking, allowing for a focused exploration of early-stage detection capabilities. Impactbased modulation and Luxembourg-Gorky type cross-modulation techniques were employed. Impact-based modulationuses a hammer impact to introduce a strong perturbation on a weak probe signal, analyzed with the Hilbert-Huang transform. Cross-modulation uses a second amplitude-modulated ultrasound to transfer modulation onto the weaker probe,analyzed via spectral analysis. Initial results indicate that impact-based frequency modulation is not highly sensitive tocorrosion products alone and may not effectively identify specimens without concrete defects. However, impact-inducedamplitude modulation is more responsive to corrosion and cracks in concrete. Cross-modulation shows strong sensitivityto crack-like defects and embedded severe corrosion but may not be optimal for early-stage corrosion detection due tothe presence of inherent concrete cracks. Further research is needed to evaluate nonlinear ultrasonic techniques appliedto larger concrete specimens and under realistic conditions before making practical recommendations.