Detecting delamination of concrete cover using movable PZT sensors and baseline-free electromechanical impedance techniques

Concrete spalling, which typically develops from crack initiation to delamination in concrete cover, is usually caused by the corrosion of steel rebars. It reduces the capacity of concrete structures, and falling concrete pieces also directly threaten the safety of occupants. Early detection of concrete cover delamination is crucial for timely repair to avoid severe concrete spalling. Although techniques for detecting large-size delamination are available for bridges, their effectiveness in reinforced concrete buildings is limited because of relatively smaller delamination sizes. The baseline-free electromechanical impedance (EMI) technique, which utilizes the resonant frequencies of a target object for material characterization and delamination detection, has the great potential to detect near-surface concrete delamination in small sizes. However, the limited detected range of traditional fixed sensors cannot cover sufficiently large areas in actual practice. To address this critical deficiency, this study improves baseline-free EMI techniques by using a movable sensor to detect concrete delamination, which, to the best of our knowledge, has not been reported in the literature. Numerical and experimental studies on a laboratory-scale slab with corrosion-induced delamination were conducted to examine the proposed method. Results show that the proposed method can detect, localize, and assess concrete delamination effectively. Moreover, the successful detection of concrete delamination was realized in the on-site tests, showing the practicality of the proposed method.