Detection and Characterization of Distributed Micro-Cracking in Steel Reinforced Structural Concrete Using Nonlinear Ultrasonic Guided Waves

The present study focusses on detecting and characterizing distributed micro-cracking in a steel reinforced structural concrete (RSC) specimen caused by static and dynamics loadings using a second order nonlinear parameter (SONP). The SONP was evaluated using the spectral amplitudes of fundamental and second harmonics obtained through the three-dimensional (3D) numerical modeling of ultrasonic guided waves. Firstly, the dispersion curves of the concrete were evaluated to determine the range of excitation frequencies and the wave modes that could be used in simulation. Secondly, a 3D finite element (FE) simulation model was developed to study the wave propagation in the RSC specimen with and without micro-cracking. The desired wave modes are generated with a wedge sensor arrangement and the propagated wave is sensed with the normal contact sensor. Moreover, simulations were conducted in presence and absence of steel reinforcement to verify whether the reinforcement contributes to generation of higher harmonics. It is found that the generation of harmonics is purely limited to the distributed micro-cracking and the intensity of harmonics increases with an increase in micro-cracking. This eventually leads to an increase in SONP. Thus, the present study shows that the use of a combination of two ultrasonic guided wave modes could facilitate a reasonable evaluation of the structural health of RSC. The results could be helpful in the development of Digital transformation in non-destructive testing (NDT) integrated with BIM systems for better understanding the status of concrete structures.