Durability assessment of adhesives and reinforcement at the FRP-wood interface

Pultruded glass fibre reinforced composites can be used for reinforcing low-grade wood. In composite design, it is imperative that a successful bond is established between the component materials. This paper describes a test program to assess the bond quality between glass fibre reinforced polymers and spruce that contains large juvenile wood proportions. Durability testing involved cycling specimens five times by a vacuum-pressure-soak-drying procedure. Two pultruded reinforcing materials were selected for the study both comprising glass fibres aligned unidirectionally, one in a vinylester resin and the other, in an engineered thermoplastic polyurethane. Bond tests were executed using both wood laminating adhesives and two-part structural epoxies. The tests results show that the bond depends not only on the adhesive in question but also the FRP type. In general, the durability tested specimens failed at equal or lower shear strengths than solid control specimens, ambient tested wood-wood bond specimens or ambient tested FRP-wood bond specimens that were taken from the same plank. Failure modes included wood failure, reinforcement failure and adhesion failure.