Improvements of the Ultrasonic Tomography for Applications to Historical Masonry Constructions

Non-destructive tests play a crucial role for rehabilitation, restoration and strengthening of historical masonry constructions: this justifies increasing research interests on this issue. In particular, sonic and ultrasonic tomography are among the most used NDT techniques for applications to historical constructions since they are relatively fast, reliable and inexpensive. Anyway, the resolution and the capability of those techniques in assessing hidden defects, voids, damage, the masonry layout and the mechanical properties of masonry can be further substantially improved. To this aim, several issues about the experimental setup, the modeling of propagation phenomena of acoustic waves, and the inversion algorithms should be addressed. In this paper some improvements of the ultrasonic tomography for masonry constructions are proposed, based on the implementation of advanced inversion algorithms, on the use of the information about wave attenuation (attenuation tomography) in addition to those related to the time of flight of acoustic waves, and on the enhancement of the experimental setup, in particular for what concerns the coupling between probes and masonry. With reference to tuff samples having known internal defects like holes, cuts and inclusions, the capability of the proposed approach is compared with the standard ultrasonic tomography. The experimental results show the effectiveness of the proposed approach, and suggest some directions for further improvements.