Diagnostic application of nonlinear ultrasonics to characterize degradation by expansive salts in masonry systems

An experimental study was conducted on lab-scale masonry systems constituted by traditional hand-made bricks coupled with external layers of de-humidifying mortar, damaged by means of salt crystallization. The evolution of damage was followed by means of a non-destructive technique denoted as scaling subtraction method (SSM), which is based on the detection and post-processing of the nonlinear response of the system to prescribed ultrasonic excitations. The experimental results obtained, further than providing a better understanding of the mechanical degradation process under consideration, highlight the effectiveness and potentialities of the non-destructive technique used.