Early detection of corrosion in reinforced concrete using ultrasonic guided wave technique correlated with embedded fiber bragg grating strain sensors

Reinforced concrete (RC) is commonly utilized in construction, but corrosion, particularly in marine environments, causes considerable challenges, resulting in high maintenance costs. Non-destructive corrosion detection techniques are critical to ensure structural safety. This study aims to detect early corrosion in steel-reinforced concrete using leaking UGW. UGW propagation in steel bars embedded in concrete and energy leakage through the concrete medium were explored experimentally and numerically. The study also aims to provide passive corrosion monitoring using embedded Fiber Bragg Gratings (FBG) strain sensors. An accelerated corrosion setup using the impressed voltage technique was employed to simulate natural corrosion in RC specimens. The results reveal that the first longitudinal mode, L(0,1), is dominant and its amplitude is sensitive to corrosion, even when monitored away from the corrosion source. Different corrosion stages (initiation, progression, and diameter reduction) were distinguished by variations in signal strength and L(0,1) characteristics. The leaky wave observed from bar 2, which was subjected to corrosion and propagated to neighboring bars, showed sensitivity to the diameter reduction phase and crack propagation. This was indicated by a significant drop in amplitude during that phase. Additionally, the integration of FBG sensors provided further insights into the correlation between strain and GW readings, particularly during the diameter reduction phase. The results demonstrate the effectiveness of UGW for the detection and assessment of corrosion in steel-reinforced concrete structures.