No abstract

Guided waves have been used in the past for monitoring corrosion and other damages in plates, rods, pipes, and reinforced concrete structures. Past investigations tried to relate the recorded signal strength to the extent of corrosion or other damage. The main disadvantage of this approach is that the signal strength is also affected by the bonding condition between the sensors and the structure. Over time, this bonding condition is bound to deteriorate, and therefore, one cannot say for sure if the change in the signal strength is due to corrosion or because of the deterioration of the attachment of the sensors to the structure. A new guided wave-based technique is proposed here, which investigates the change in the time of flight of the propagating wave in loaded reinforced concrete structures at various levels of corrosion. Corrosion affects the bonding strength between concrete and reinforcing steel altering the stress level in the reinforcing steel bar in a loaded beam. Since the wave speed is affected by the internal stress, an increase in corrosion level should affect the wave speed in a steel bar and the wave's time of flight through the bar. The main advantage of the proposed approach is that this result should not be affected by the bonding condition between the sensor and the structure. How delamination at the bar-concrete interface affects the signal strength and the effect of induced corrosion in free bars as well as in bars embedded in the concrete are also investigated.

This paper explores the feasibility of detecting and quantifying corrosion and delamination at the interface between reinforcing steel bar and concrete using ultrasonic guided waves. The problem of corrosion and delamination of the reinforcing steel in the aging infrastructure has increased significantly in the last three decades and is likely to keep on increasing. Ultrasonic cylindrical guided waves that can propagate a long distance along the reinforcing steel bar are found to be sensitive to the interface conditions between steel bar and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar. The traditional ultrasonic testing methods, for instance the pulse-echo method, where reflection, transmission, and scattering of longitudinal waves are used for detecting large voids in concrete, are not very efficient for detecting corrosion and delamination at the interface between concrete and steel bar. For this study four sets of specimens were prepared. They are rebars and plain steel bars with corrosion and physical separation. Transducers used during the experiment are the Electromagnetic Acoustic Transducer (EMAT) and the Piezoelectric Transducer (PZT). The experiment suggests that the guided wave inspection technique is feasible for the health monitoring of reinforced concrete structures. It also reveals that the ultrasonic guided waves are sensitive to the type of steel used and to the rib patterns on the reformed steel bars.

This paper explores the feasibility of detecting and quantifying corrosion and delamination (separation) at the interface between reinforcing steel bars and concrete using ultrasonic guided waves. The problem of corrosion of the reinforcing steel in structures has increased significantly with time. Concrete is strengthened by the inclusion of the reinforcement steel such as deformed or corrugated steel bars. Bonding between the two materials plays a vital role in maximizing performance capacity of the structural members. Corrosion of reinforcing steel has led to premature deterioration of many concrete members before their design life is attained. It is therefore, important to be able to detect and measure the level of corrosion in reinforcing steel or delamination at the interface. The development and implementation of damage detection strategies, and the continuous health assessment of concrete structures then become a matter of utmost importance. The ultimate goal is to develop a nondestructive testing technique to quantify the amount of corrosion in the reinforcing steel. The guided mechanical wave approach has been explored towards the development of such methodology. The ultrasonic waves, specifically cylindrical guided waves, can propagate a long distance along the reinforcing steel bars and have been found to be sensitive to the interface conditions between steel bars and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar.