Caratterizzazione dell'aderenza di materiali compositi per il rinforzo di strutture in muratura

Fibre-reinforced composite materials have become, in the last years, one of the most popular solutions to strengthen and repair also masonry structures, especially in seismic areas where the behaviour against typically brittle failure mechanisms should be improved. In particular, the application of Externally Bonded (EB) composite materials, made of fabrics embedded in epoxy resin, can increase the performance of masonry, providing tensile resistance and avoiding or retarding certain collapse mechanisms. The effectiveness of those solutions, however, are closely related also to the transfer of bond stresses at the interface between reinforcement and substrate. Based on an extensive experimental campaign carried out at the University of Padova, Italy, this paper discusses the main aspects that influence the adhesion of EB Fibre-Reinforced Polymers (FRP) to brick masonry substrates. The work deals with the evaluation of the bond strength of EB FRP applied to single solid clay bricks, and then investigates the adhesion in presence of mortar joints perpendicular to the reinforcement axis. Various test methods and setups were adopted and compared, in order to identify adequate procedures to characterize the adhesion by means of shear bond tests, and to obtain results aimed at improving the calibration of design parameters. Overall forty single-brick specimens and thirty masonry prisms (i.e. samples with mortar joints) specimens were tested, and four types of unidirectional reinforcements, namely carbon (CFRP), glass (GFRP), basalt (BFRP) and steel (SRP), were applied to them. Single-lap and Double-lap setups were adopted for brick specimens, while all prism specimens had a Single-lap layout. In order to deepen the investigation of the role of mortar joints, the bonded length for GFRP prism samples varied from 65 mm (corresponding to one brick and one mortar joint) to 195 mm (three bricks and three mortar joints), while the bonded length of brick specimens was kept constant and equal to 160 mm.