Detecting embedded rebar in cement mortar by frequency-difference electrical resistance tomography

Abstract

This study investigated frequency-difference electrical resistance tomography (ERT) using a 16-channel ERT system to detect rebar embedded in cement mortar. Two different data collecting methods (i.e., referencedifference and frequency-difference) were used for ERT image reconstruction, and the reconstructed ERT images were validated with binarized micro-CT images. As a result, the reference-difference ERT was not suitable for detecting rebar in cement mortar. This method generated incorrect ERT reconstruction images since the target specimen and reference specimen is different, and thus an inconsistent contact impedance, electrode position error, and different pore distributions between the samples could generate measurement errors affecting internal conductivity distribution. However, use of the frequency-difference method provided more accurate and reliable results for detecting rebar. The ERT images were well-matched with the binarized micro-CT images. In frequency-difference ERT, an identical specimen is used to obtain measurement data, and thus the experimental errors can be largely reduced. In particular, the reconstruction result was influenced by the range of the two used frequencies. In wide-ranging frequency-difference ERT, the rebar was better tracked regardless of distance from the electrodes than when using a narrow range of frequencies.