Analysis of coherent surface wave dispersion and attenuation for non-destructive testing of concrete

Extracting non-propagating oscillatory fields in concrete to detect distributed cracking

Work to detect and locate distributed subsurface cracks in concrete by extracting non-propagating oscillatory fields is presented. The medium of interest is concrete, but the approach also applies to other types of inhomogeneous media. The theoretical basis of the work is first presented through a one-dimensional point-scatterer model that considers the wavefield set up by multiple distinct scatterers. More complex scattering scenarios are then investigated using numerical simulation. The numerical models consider two types of scatterers: elliptic large-scale particles distributed throughout a medium, and small-sized cracks localized within a damage zone. The theoretical and numerical analyses show that forward propagating waves undergo distinct scattering behavior within the crack damaged zone: non-propagating resonance-like oscillatory fields are set up within the cracked zone, and are distinct from the scatter caused by the large-scale particles. Frequency-wavenumber (f-k) domain analyses to extract the energy of non-propagating oscillatory fields and thus to detect and locate zones of distributed cracking are employed. The proposed approach is evaluated using numerical simulation and experimental data collected from concrete specimens that contain simulated distributed cracks. The results demonstrate that the location of distributed crack zones in discrete random media, such as concrete, can be successfully detected.

Contactless Ultrasonic Wavefield Imaging to Visualize Near-Surface Damage in Concrete Elements

We present work to detect and visualize near-surface damage in concrete using contactless ultrasonic wavefield imaging technology. A fully contactless ultrasonic scanning system that utilizes a micro-electro-mechanical systems (MEMS) ultrasonic microphone array is used to collect ultrasonic surface wave data from a concrete sample. The obtained wavefield data sets are processed with a frequency-wavenumber (f-k) domain wavefield filtering approach to extract non-propagating oscillatory fields set up by near-surface concrete cracking damage. The experimental results demonstrate that near-surface concrete damage can be detected and visualized using the proposed ultrasonic wavefield imaging approach.