Three-dimensional in-situ imaging of cracks in concrete using diffuse ultrasound

Locadiff, an innovative imaging technique based on diffuse waves, has recently been developed in order to image mechanical changes in heterogeneous, geological, or man-made materials. This manuscript reports the on-site application of Locadiff to locate several pre-existing cracks on an aeronautical wind tunnel made of pre-stressed concrete. Using 32 transducers working at ultrasonic frequencies (80–220 kHz) where multiple scattering occurs, we monitor during 15 min an area of 2.5 m×2.5 m of a 35-cm-thick wall. With the wind tunnel in its routine operation, structural changes around the cracks are detected, thanks to their closing or opening due to slight pressure changes. By mapping the density of such microstructure changes in the bulk of the material, locating three pre-existing cracks is properly performed in three dimensions.