Rebar Local Corrosion Monitoring of RC Structures Based on Fractal Characteristics of Piezoelectric Guided Waves

Abstract

In offshore reinforced concrete (RC) structures, how to monitor early occurrences and developments of rebar corrosion is of great significance. However, the rebar corrosion in RC structures is localized and developed along interfaces, having great challenges to evaluations of rebar corrosion levels. In this paper, the theoretical analysis, numerical calculation, and experiment validation are used to study the rebar local corrosion monitoring and evaluation of RC structures with piezoelectric ultrasonic guided waves (UGWs). A reasonable selection of the UGW excitation and reception method and corresponding experimental setup are studied. Frequency dispersion curves of the selected UGWs under different corrosion conditions are obtained by analyzing the wave dispersion and multimodal characteristics. Based on energy values and fractal dimension characteristic values of echo signals for different corrosion levels, a rebar corrosion evaluation index is proposed, and a corresponding evaluation algorithm is established. The effectiveness of the proposed algorithm is verified by a rebar corrosion monitoring test based on the accelerated corrosion and guided wave technologies. A fitting relationship between corrosion levels (length and thickness) and basic characteristics of sensing signals is established. A corrosion evaluation method is established based on the corrosion index and algorithm. The results show that rebar corrosions have a sensitive effect on the energy and fractal characteristics of longitudinal UGWs. The larger corrosion length and the thicker corrosion layer result in the smaller energy value of echo signal and the smaller fractal characteristic value, and the larger corrosion index value.