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Characterization of Distributed Cracks in Concrete using Randomly Scattered Wavefield Extraction



This paper presents a fully contactless air-coupled ultrasonic scanning approach to characterize distributed cracks in concrete. The approach enables characterization of near-surface distributed cracks in concrete, for example that caused by alkali-silica reaction or freezing and thawing action. A series of numerical simulations are performed to understand surface wave scattering phenomenon caused by distributed cracks in concrete. The numerical simulation results reveal that incident surface waves undergo complicated random scattering within the cracked region. As a result of the random scattering, local wavefields having a broad wavenumber spectrum manifest. A frequency-wavenumber (f-k) domain signal filtering approach is applied to extract the randomly scattered wavefields set up by distributed cracks. The feasibility of the proposed approach is established using a series of experiments on laboratory-scale concrete specimens including simulated distributed cracks. The experimental wavefield data obtained by fully contactless ultrasonic scanning measurements is analyzed using the f-k domain signal filtering approach. The experimental results demonstrate that distributed cracks in concrete can be successfully characterized and further that the the extracted scattered wavefield energy is closely related to the crack density


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