Application of FRCM composites to masonry blocks manufactured with historical bricks: bond behaviour with and without salt contamination

The retrofitting interventions on historical masonry structures are still an open issue in the preservation field. Multiple aspects must be considered for the design of a strengthening intervention, such as compatibility and durability of materials. Fiber-reinforced composites with inorganic matrix (FRCM) have been recently proposed as a more compatible solution with respect to FRPs (fiber-reinforced polymers), but their application in aggressive environments is still a matter of investigation. In this study, the behaviour of historical masonry specimens subjected to salt conditioning and reinforced with externally bonded steel-fiber reinforced cementitious matrix (FRCM) is investigated. Specimens were tested in pure tension to direct shear tests. Material characterization tests were carried out to analyse the salt content and the porosity of the substrate and of the matrix. These data were contextualised to investigate the influence of the substrate properties on the mechanical behaviour of FRCM-masonry joints. Test results demonstrate that FRCM composite showed a good performance on different substrates, thus confirming its compatibility with ancient masonry typologies, but a more in-depth chemical-physical analysis is desirable to predict the mechanical behaviour on variable substrates such as historical masonries.