Advances in adhesive joining of dissimilar materials with special reference to steels and FRP composites

Generally, it is relatively easy to obtain a high joint strength with most modem bonding systems if these are cured under ideal conditions. However, civil engineering construction joints generally are cured on site and are required for the lifetime of the structural member. This implies that the joint might not be as well constructed and cured as in a factory and, in addition, will be under harsh site environmental exposure. Consequently, the joint should be post cured on site and the free surfaces protected from the environmental influences. The paper discusses the advantages and limitations of a proposed partially cured carbon fibre composite prepreg and a compatible film adhesive both developed specifically for the construction industry. The system has been developed from one used in the aircraft industry. Two types of carbon fibre will be considered: an ultra high stiffness and a high stiffness carbon fibre. The technique is compared to that of a more conventional bonding two part system used in civil engineering. Two test techniques will be used to characterise the proposed structural material namely, the double shear butt test and a flexural test using the composite material as rehabilitation for an artificially degraded structural member. In the latter test, two geometric shapes have been used to investigate any advantage that may be gained in shaping the upgrading composite. The paper has shown that a partially cured prepreg manufactured in the factory, shaped geometrically on site, incorporating a film adhesive and applying a low elevated temperature cure under pressure to the prepreg and film adhesive has an advantage over other adhesives particularly when using ultra high carbon fibre composites but the strain to failure of these fibres is relatively low and must be carefully considered. Moreover, the thinness of the film adhesive will reduce to a minimum the ingress of any harsh environments onto its free surface; this will improve the durability of the adhesive over that of the two part adhesive.