Effect of rubber modifier on interlaminar fracture toughness of CFRP-concrete interface

Fibre reinforced plastic (FRP) strips bonded to the tension face of reinforced concrete (RC) beams are an effective means of rehabilitation and strengthening of concrete structures. Epoxy and vinylester resins have been widely used as structural adhesive for this purpose. Amongst various materials and design variables, the properties of adhesive play a significant role in controlling the efficiency of FRP strengthening, which in turn determines the durability of strengthened concrete structure. This paper presents an experimental investigation regarding the influence of reactive rubber modifier added in the adhesive on interlaminar fracture resistance between the CFRP strip and concrete. The interlaminar fracture toughness measured from the asymmetric double cantilever beam (ADCB) test showed significant improvements with 10 and 20% rubber modifier contents. This ameliorating effect is partly attributed to the ability of modified resin to penetrate deeper into the concrete than unmodified resin, as suggested by the micro-hardness measurements. Experiments in bending of RC beams showed substantially enhanced load carrying capacity and ductility for the CFRP plates bonded with modified resins.