A new guided wave–based technique for corrosion monitoring in reinforced concrete

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.