Energy Based Ultrasonic Techniques for Earlystage Damage Detection in Concrete Structures

Abstract

During the service life, concrete structures undergo several adversities that lead to weakening in concrete and results in crack initiation. At initial stage of damage, breathing /clapping effect prevails inside the material. It results in additional nonlinearity, called as contact acoustic nonlinearity (CAN) in the structure which is often subsumed due to the material nonlinearity and leads to unidentified progression of damage inside structure. In the present study, ultrasonic investigations have been carried out to detect the flexural cracks in a scaled model of a reinforced concrete (RC) girder-deck system under four-point bending where the damage stages can be categorized as, undamaged (Stage 0), crack initiation (Stage I), crack propagation (Stage II), and severe damage (Stage III). Data acquired from ultrasonic actuation-sensing at different damage stages are processed in time-frequency domain and frequency domain using energy based ultrasonic parameters, such as, wavelet packet energy and spectral energy distribution. Further, a new energy based nonlinear acoustic parameter (ENAP) is introduced that works on the harmonic phenomenon induced by the breathing cracks. The proposed energy based methods (especially nonlinear methods) are found to be very efficient for detecting all the damage levels successfully.