Fiber Reinforced Polymers in Civil Engineering: Durability Issues

In the last decades, the use of fiber reinforced polymers (FRP) composites to repair and/or upgrade existing buildings or infrastructure systems proved to be an effective solution as they are able to overcome some of the drawbacks experienced with traditional interventions. The knowledge of durability behavior of polymer composite materials in terms of their degradation/aging causes and mechanisms is a critical issue for safe and advantageous implementation of FRP. The durability of FRP employed in civil infrastructure applications mainly depends on the durability of every single component and the environment (service conditions) in which the system operates. The components of FRP are polymeric resins (more frequently thermosetting resins cured in service, i.e. at ambient temperature), fibers and the interface between them. Major concerns arise from the behavior of “Cold-cured” thermosetting resins (often epoxy) used as matrices to manufacture (through wet layup technique) and adhesives to apply and precured FRP. The experimental studies presented in current literature focus on the effects of environmental agents on FRP properties, highlighting the crucial role of the adhesive/matrix on the behavior of the whole system. Many other parameters (i.e. direction and disposition of fibers, direction of load application) are involved in the assessment of the durability of FRP. However, in the durability studies of FRP and their components, a lack of specific standards for such materials is recognized. In addition, the results of durability studies do not always agree, possibly due to different curing conditions employed. The aim of this work is to critically illustrate the durability studies carried out on FRP for civil engineering applications based on current literature, highlighting the issues that are not yet assessed and addressed.