Application of Full Waveform Inversion to Ultrasonic Data Acquired on Concrete

Summary Ultrasonic testing is a key method in non-destructive testing (NDT) and structural health monitoring (SHM) of concrete structures. It provides information on the structure’s internal geometry, built-in components, and material quality. However, concrete’s highly heterogeneous and multiphase nature causes challenges such as strong dispersion, scattering, and attenuation. These effects complicate defect detection and imaging, particularly for features with dimensions comparable to the wavelength. Conventional ray-based method, such as the Synthetic Aperture Focusing Technique (SAFT), rely on simplified assumptions about wave propagation and only exploit part of the recorded wavefield. In contrast, full-wave-equation-based approaches, such as full-waveform inversion (FWI), utilise information from the entire wavefield and have the potential to improve the recovery of material properties and the imaging of complex internal structures. This study demonstrates the feasibility of applying elastic FWI to ultrasonic testing of concrete. For synthetic datasets, FWI produced stable results, reliably reconstructing steel reinforcement bars with diameters of 20 mm or larger and recovering strong material contrasts. Application of FWI to real data also demonstrated the ability to identify steel bars in the upper part of the test sample and to reconstruct elastic properties. However, further investigation is required.