Combining Ultrasonic and Electromagnetic Techniques for Early Detection of Corrosion Damage in Reinforced Concrete Structures

Corrosion of reinforcing bars has been established as a primary contributor to the deterioration of reinforced concrete (RC) structures. As corrosion products accumulate and expand, they generate tensile stresses within the concrete, ultimately leading to cracking and spalling of the concrete cover. Additionally, the reduction of cross-sectional area in reinforcing bars undermines the bonding strength of RC structures. To prolong the service life of RC structures, it is crucial to develop a robust monitoring system for early-stage corrosion damage assessment. Ultrasonic waves are sensitive to cracks and voids due to the large contrast in acoustic impedance between air and the background material, while electromagnetic waves are sensitive to metallic structures due to the substantial contrast in dielectric permittivity and conductivity. Therefore, this work studies the feasibility of combining ultrasonic and electromagnetic techniques for detecting early signs of corrosion damage, including cracks and reductions in the cross-sectional area of reinforcing bars. Ultrasonic coda wave interferometry method is used to monitor the growth of internal cracks in the reinforcing bar. A linear multiple-input-multiple-output (MIMO) GPR array is employed to image reinforcing bars in the concrete. In the early stages of corrosion, rust and small cracks grow, leading to changes in the GPR image. The performance of the proposed ultrasonic and electromagnetic methods has been demonstrated by the accelerated corrosion monitoring test in the lab.