Analysis of the bond between fabric reinforced cementitious mortar (FRCM) strengthening systems and masonry

The structural performances of masonry elements strengthened with externally bonded composites, is strongly governed by the bond between the strengthening system and the masonry substrate; the failure of strengthened masonry usually takes place with loss of bonding at the interface strengthening system /masonry substrate. Debonding has been widely studied in Fiber Reinforced Polymers (FRP) applied to concrete substrates but less in the case of masonry; very limited studies have been conducted to analyze the bond between Fiber Reinforced Cementitious Matrix (FRCM) strengthening systems and masonry. Due to the growing use of FRCM as strengthening systems of masonry structures, mainly historical and monumental masonry buildings, the analysis of the FRCM/masonry bond is essential for a reliable design of strengthening systems. In the present paper, results of an investigation, both experimental and theoretical, on bond between FRCM materials, made by Carbon fabric meshes embedded in a cement based matrix, and the masonry are presented and discussed. A total of eighteen clay brick specimens strengthened with a single layer of Carbon FRCM, were tested under single face shear tests under the ambient temperature of 20°C. In order to evaluate the influence of the bond length and to identify an effective anchorage length, different bond lengths (Lb=150, 200, 250 and 300 mm) of the C-FRCM reinforcement were considered. The width of reinforcement, bf, was equal to 50 mm for all tested specimens. Results of the analysis, presented and discussed in the paper, make possible: i) to determine the bond strength and the failure modes of the masonry strengthened by the FRCM system, ii) to evaluate the influence of mechanical and geometrical parameters involved in the masonry/reinforcing system transfer mechanism on the local bond-slip law.