The evaluation of the adhesion defects in FRCM reinforcements for masonry constructions by Sideband Peak Count based nonlinear acoustic technique

Fabric-reinforced cementitious matrix (FRCM) composites have emerged as reliable strengthening materials especially for historical masonry constructions. Their strengthening effectiveness strongly depends on the bond at the matrix-fibers interface and at the matrix-substrate interface; thus, the analysis of FRCM bond behavior is of crucial relevance. The strong diffusion of the FRCM composites for the reinforcement of masonry and concrete constructions requires suitable experimental techniques for assessing possible defects in the adhesion between FRCM and masonry, and between FRCM layers. To this aim, in this paper, an innovative nonlinear ultrasonic approach based on the sideband peak count technique is proposed. This approach is discussed and validated through acoustic (sonic and ultrasonic) tests performed on masonry tuff substrates reinforced with FRCM mortars embedding a basalt fibers grid and having known artificial defects at the adhesion between masonry and the reinforcement as well as in the fiber grid.