Bond behaviour of CFRP-steel double-lap shear joints exposed to marine atmosphere

Fibre reinforced polymer (FRP) materials are currently more and more widely applied in structural engineering attributed to the high strength-to-weight ratio and good resistance to environmental attack. Carbon FRP (CFRP) has been demonstrated great potential in fatigue strengthening of defected steel components, because it could help to share the far-field load, to constrain the crack opening, and to reduce the crack propagation rate. The strengthening efficiency relies on the load transfer between steel and CFRP and consequently the interfacial behaviour of CFRP-to-steel joints. Generally, a structural adhesive is adopted to attach CFRP to a steel substrate and it takes one to two weeks to achieve the full strength. However, the potential risk of environmental attack at the curing stage of the adhesive has not been well understood. In this paper, a series of experimental studies on the interfacial behaviour of CFRP-steel double-lap joints were carried out. The specimens were cured in different environmental conditions for two weeks and then statically loaded to failure. The performance of specimens subjected to room condition, salt fog and high relative humidity (RH) was compared. Effects of CFRP material type and surface treatment were also considered. The bond strength was decreased by 2-17% in comparison with the control specimens. Proper silane treatment could help to maintain the integrity of the specimen. This study extends the understanding of the environmental durability of CFRP-to-steel joints and provides some useful suggestions for the strengthening technique.