The influence of the hygrothermal aging on the strength and stiffness of adhesives used for civil engineering applications with pultruded profiles: an experimental and numerical investigation

The use of the composite pultruded materials is increasing due to the particular characteristics of lightness, ease of installation, high corrosion resistance and, finally, lower maintenance costs. Even if the bolting technique is the most widely used, especially in the field of civil engineering, re-adapting the rules valid for steel structures, thanks to several studies on adhesives, there is reason to believe that the best connection technique for pultruded profiles is gluing (the continuity of the fibers is guaranteed). Current applications involving such materials, strictly related to the field of civil engineering, include bridges, pedestrian and the motorway bridges, roof structures, helipads, solar charging stations, offshore structures, cooling towers and lockgates. In some of these structures, the system (composite material and resin) is in contact with water. Even if there are several studies on the durability of composite pultruded material, current literature referring to adhesives between pultruded adherents needs further investigation. Within this framework, the paper aims to investigate, from an experimental and numerical point of view, the effect of the hygrothermal ageing on both the fracture energy in mode II as well as the strength and stiffness of two commercial epoxy resins taking into account the further effect of the desorption. Finally, in view of a safe design of a bonded joint, limiting its behaviour to only the elastic field, a lower fracture energy value is presented in relation to the classical one.