Fundamental Experiment on Invisible Crack Detection of Concrete Covered with Fiber Reinforced Polymer (FRP) through Electrical Impedance Variations and Phase Transition

Abstract

This study aims to develop a non-destructive test for the detection of invisible cracks in concrete covered with fiber reinforcement polymer (FRP) sheets using electrical impedance variation and phase transition. The fundamental test was performed considering the hypothesis that the concrete exhibits inductive and resistive properties. Some FRP-covered concrete specimens with an artificial crack were prepared. The study examined the frequency characteristics of impedance and phase under AC voltage with frequencies ranging from 1 kHz to 8 MHz. These frequency characteristics were examined using an impedance analyzer controlled by a computer. The impedance and phase were measured using a probe with two electrode terminals. The test results confirmed that in the range of approximately 3 MHz to 4 MHz, the capacitive phase property of cracked concrete changes to exhibit inductive characteristics. It was revealed that invisible cracks in FRP-covered concrete can be detected by measuring the frequency at the impedance local maximum value and the phase transition property.