Preparation and characterization of steel surfaces for adhesive bonding

In fiber-reinforced polymer (FRP) strengthened steel structures, debonding of the bonded FRP reinforcement from the steel substrate may result from adhesion failure at the steel/adhesive interface or the FRP/adhesive interface, cohesion failure in the adhesive, or a combination of these two modes. Of these failure modes, cohesion failure in the adhesive is the preferred mode of failure as it facilitates the development of a design theory based on the adhesive properties; the other two failure modes should be avoided if at all possible. This paper presents a systematic experimental study to identify a surface-adhesive combination that will avoid adhesion failure at the steel/adhesive interface. Different steel surface preparation methods, including solvent cleaning, hand grinding, and grit blasting, and different commonly used adhesives were examined in the study. Surface characterization using three key parameters (namely surface energy, surface chemical composition, and surface roughness and topography) was investigated. The test results showed that adhesion failure at the steel/adhesive interface can be avoided if the steel surface is properly grit blasted before bonding and a suitable adhesive is used, and that the treated surface can be characterized using the three key surface parameters mentioned previously.