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In this study, the recently-proposed adaptive wavelet transform (AWT) and synchro-squeezed adaptive wavelet transform (SSAWT) are introduced with their optimum transformation parameters automatically searched to derive at a desirable time-frequency representation of any dynamic response. The AWT enables the selectivity of time and frequency resolution in a domain of interest and the synchro-squeezing algorithm reduces the dispersion of a scalogram of the AWT, facilitating an accurate extraction of frequency features over time. The effectiveness of AWT is first demonstrated with an illustrative signal of four time segments covering various frequency distribution cases. In comparison with conventional wavelet transform, the AWT can clearly separate time-varying frequency features from the signal. Accordingly, the SSAWT is at least 5 times more accurate with a 1.1% error than conventional synchro-squeezed wavelet transform. The AWT is then applied to the impact echo (IE) responses experimentally recorded from a 60"×36"×7.25" concrete slab for potential pavement applications. The time-frequency resolution and corresponding frequency spectra led to the successful detections of deep pavement defect, shallow pavement defect or no pavement defect from 40 sets of experimental data. The SSAWT results in a 1.5% estimation error in the identification of deep pavement defect depth and a 5% estimation error in slab thickness, both being twice more accurate than the AWT in terms of estimation error. The selection process of time-varying central frequencies, scaling factors, and window lengths proves robust.

This study is intended to assess the integrity of a reinforced concrete bridge deck at the Missouri S&T campus using non-destructive testing (NDT) methods performed at top and bottom surfaces of the bridge deck. These utilized methods are named ground generating radar (GPR), impact echo (IE), and ultrasonic surface waves (USW). GPR was applied using 1.6 GHz and 2.5 GHz antennas to transmit and receive electromagnetic radio waves at embedded concrete reinforcement or distinct contacts between solid and loose concrete materials with different dielectric properties. Due to significant variations of the apparent depth to top of the embedded reinforcing steel bars, it was difficult to interpret the GPR results for the bridge deck assessment. Therefore, GPR results are often calibrated in application with ground truth data from either borehole tests or other nondestructive methods, such as IE and USW. IE and USW are based on the reflection of the acoustic waves at discontinuity (e.g., delamination). Both IE and USW data were acquired using portable seismic property analyzer (PSPA) device. USW is used to measure the variations of Young’s modulus of concrete deck and IE is used to measure depth to possible embedded defects in concrete deck. Eventually, USW and IE results were used as an indicative of the concrete quality of the bridge deck. An approximately 10 x 9 ft. sections were surveyed at the top and the bottom surfaces of the bridge deck in order to evaluate and correlate the three NDTs results for the bridge deck assessment.