Non-destructive assessment of the adhesion at the interface between FRCM reinforcements and masonry substrates by non-linear ultrasonic technique

The strong diffusion of Fiber Reinforced Cementitious Matrix (FRCM) composites for the reinforcement of historic masonry 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 Side-band Peak Count (SPC) technique is proposed. This approach is discussed and validated through experimental tests made on tuff substrates reinforced with FRCM mortars embedding a basalt fibers grid and having known artificial defects at the adhesion between tuff and FRCM as well as in the fiber grid.