Analysis of the Durability of the Bond between Masonry and FRP Sheets

The use of polymeric materials, such as thermosetting resins and their composites, for the repair and/or the strengthening of structures is attaining worldwide an increasing success. Among all the epoxy resins is widely employed in many structural applications, assuring good performance in terms of flexibility, effectiveness of repairing technique and moderate costs. When correctly formulated and cured, epoxy resins provide a high level of mechanical properties, excellent resistance to corrosion and to chemicals. Furthermore, the use of FRP (Fiber Reinforced Polymer) composites as reinforcement for masonry structures, to improve the strength and/or the stiffness of structural elements, is becoming very popular. The FRP composites, in fact, exhibit several advantages, such as: low weight, high strength, tailor-ability and corrosion resistance. The long-term durability of the thermosetting resins and of their FRP composites, especially when they are subjected to severe environmental conditions, is still not well known. This issue represents a strong limit for a wider spreading of these materials, since the acceptable lifetime of an effective repair should be in the order of 10-20 years. The performance and the long term behavior of these resins and of their composites depends on the chemical nature of the base materials, on the conditions in which they set and harden and, mainly, on the environmental conditions in which they “operate” (temperature, presence of water, moisture and chemicals, pollution, etc.). In the present paper the interface FRP-masonry has been analysed in terms of durability under specific environmental conditions, simulated in the laboratory by the following treatments: exposition in a climatic room at 40°C temperature and 90% humidity for about six months. Each utilized material (stones, adhesive, composite sheets) has been also conditioned following the same above-mentioned procedures in order to investigate the influence of the materials durability on the bond durability. Bond tests have been performed on conditioned specimens, while standard mechanical tests allowed evaluating the mechanical properties of conditioned materials. By bond tests the ultimate load and the kind of failure have been recorded, as well as the strains and stresses distribution within the reinforcement. In addition, displacement transducers have been used to measure the slip at the loaded end, between the stones and the FRP sheets; results are reported and discussed. In order to estimate the degradation caused by the conditioning procedures on the bond performance and on materials properties, the results obtained after conditioning have been compared with those referring to standard conditions.