Environmental durability of a composite-to-composite adhesive bond in infrastructure applications

Fiber-reinforced composites have proven to be effective in the rehabilitation of concrete bridge beams as an externally-bonded tensile reinforcement. Practical requirements for bonding precured composite plates to large concrete beams in the field necessitate some form of composite joint to limit the size of the plates to be transported to the site. In earlier work to demonstrate the feasibility of this approach to strengthening concrete beams in bridge decks [I], the composite selected was a graphite/epoxy, AS4C/1919, bonded to the concrete with Hysol EA9460, a two-part ambient-cure epoxy adhesive. Composite joints were introduced at periodic intervals, both in the lab studies and in the field, to simulate techniques necessitated by the actual application. From tests conducted to date it appears that this joint is more susceptible to failure under mechanical loading than the composite itself or the composite-to-concrete adhesive bond. In the present study, therefore, the durability of such a composite-to-composite joint was evaluated under simulated outdoor environmental exposure using a double-lap shear test coupon. Specimens were subjected to various combinations of moisture, thermal cycling and fatigue, and the residual lap shear strengths determined at various temperatures. The results are compared with those of unaged specimens.