A Basic Study on GMR Sensor-Based Eddy Current Nondestructive Testing Method for Corrosion Detection in Concrete Structures

Abstract

Steel corrosion in concrete structures adversely influences safety performance and durability. This study proposes a giant magnetoresistance (GMR) sensor-based eddy current nondestructive testing method to detect the decreasing steel area caused by corrosion under a 30 mm thick concrete cover. The 30 mm lift-off distance is a big challenge that many eddy current testing (ECT) methods can only perform with a lift-off distance of a few millimeters. As a primary step, artificial cutting flaws on the SPCC steel plate surfaces were used to simulate the material loss by corrosion. The GMR sensor-based eddy current detection probe succeeded in obtaining stable voltage data with a 30 mm lift-off distance by scanning perpendicular to the flaws, and the shape of the voltage amplitude with its gradient values was found to be effective in determining the flaw’s existence and position. The finite element simulation and experimental results verified the validity and feasibility of this method. Finally, the XY-direction scan was performed to provide 3D images to visualize the flaw location.