Behaviour of CFRP composites and epoxy adhesives after long-term exposure to outdoor and laboratory-controlled environments

Abstract

Carbon fiber reinforced polymer (CFRP) composites have shown desirable properties in aerospace, automotive, and construction industries. Focusing on the latter and in the context of strengthening existing structures, CFRP composites are typically bonded to concrete structures using epoxy adhesive as a bonding agent. To date, there is a lack of literature on the durability of both the CFRP composite and epoxy adhesive. In this regard, the durability of two different commercially available CFRP laminates and epoxy adhesives was assessed after exposure to different indoor and outdoor environments for up to 4 years. Experimental, numerical, and analytical studies were conducted. In the latter, a new formulation was introduced to model water diffusion through the epoxy adhesive. The results from the experimental tests showed that water immersion substantially affected the two studied epoxy adhesives, resulting in a reduction of approximately 60–66 % and 70–75 % of their tensile strengths and elastic moduli, respectively. In contrast, the CFRP laminates improved both tensile strengths and elastic moduli in outdoor environments, with the highest increases being approximately 16 % and 10 %, respectively. Furthermore, both the developed numerical and analytical models for epoxy adhesives corroborated well with the experimental results. In particular, the former revealed that water diffusion through the adhesive was faster and reached its maximum in less than a year, and the proposed formulation in the latter led to a promising prediction.