Reference free imaging of subsurface cracks in concrete using Rayleigh waves

One of the major reasons of deterioration in reinforced concrete structures is cracking of the concrete cover. In contrast to bulk waves, ultrasonic Rayleigh waves are more sensitive to such near-surface cracks. This paper presents an imaging technique for nondestructive evaluation of the concrete cover area using the scattered Rayleigh wave field. The proposed imaging methodology acts as a useful diagnostic tool to detect the existence of subsurface cracks in concrete. An added advantage of the technique is that it is reference free and does not require information regarding the pristine condition of the structure. A wedge-based technique that maximizes the propagating Rayleigh wave amplitude in the concrete cover is developed. A variant of the synthetic aperture focusing technique (SAFT) named as Planar SAFT is used for imaging. The number of scanning points has been minimized by scanning with the transmitter and the receiver in tied-together mode. Numerical simulations and experimental investigations are reported to demonstrate the capability and potential of the proposed technique.