ORIGINAL ARTICLE Shear bond of composites-to-brick applied with highly deformable, in relation to resin epoxy, interface materials Arkadiusz Kwiecien ´ Received: 14 October 2013 / Accepted: 13 June 2014 / Published online: 26 June 2014 Ó RILEM 2014 Abstract The paper presents comparison of a work of stiff and flexible bonds fastening composite strengthening to masonry. In the first approach (tra- ditional), barely deformable interface material made of stiff epoxy resin is used as shear bonds of composites-to-brick. In the second one (innovative), highly deformable interface material made of flexible polymer is used as repair shear bonds of composites- to-brick. Behavior of both materials was compared using single-lap shear tests made on four kinds of fiber fabrics (glass, carbon, basalt and steel) applied to clay brick units. The results indicated that highly deform- able interface materials allow increasing load capac- ity, because deformable adhesive layers reduce shear stress concentrations in bond, redistributing stress more evenly along the whole lap joint. Usefulness of the theory which allows calculating the bond shear stress–slip characteristic was also discussed in accor- dance to the highly deformable interface materials. Keywords Masonry  Deformable interface  FRP  SRP  Shear test 1 Introduction Rapid development of strengthening systems, based on the use of fibre reinforced polymers (FRP) mate- rials, is observed in strengthening of masonry struc- tures, especially in Italy. Various types of fibres are using: glass, carbon, basalt, aramid and steel fibers [4]. In the field of strengthening and repair of masonry buildings, externally bonded (EB) fiber-reinforced systems are mostly adopted: the fiber-reinforced polymer (FRP) and steel-reinforced polymer (SRP). They were tested and applied in various kinds of structural components [5, 11, 12, 18, 20, 24, 25] and on historical structures [6, 10], which showed their efficiency in practice. Unfortunately, possible advantages of these mate- rials are not fully utilized because of low tensile and shear surface strength of substrates [1, 3, 24]. Usually, laminates are fixed to masonry substrates using stiff epoxy resins or cement mortars of low deformability, but in many cases, especially referring to buildings made with weak lime mortars this materials are not so good and adequate [19] and do not ensure proper ductility and compatibility properties. Failure forms of masonries strengthened by FRP are brittle, very rapid (no warning) and demolish masonry substrates. These forms of failure are known from many laboratory tests especially, when stiff epoxy resin adhesives are used, which generate stress concentrations in masonry [14]. This is the reason why other bonding solutions, more compatible with masonry substrate, are tested. There A. Kwiecien ´(&) Faculty of Civil Engineering, Cracow University of Technology, ul. Warszawska 24, 31-155 Cracow, Poland e-mail: akwiecie@pk.edu.pl Materials and Structures (2014) 47:2005–2020 DOI 10.1617/s11527-014-0363-y