| Abstract: | This paper presents a methodology for assessing the bond strength of composite overlays to concrete utilizing a fracture toughness test. The principles and practices of existing ASTM standards for determining the fracture toughness of adhesive bonds between double cantilever beam (DCB) metallic and composite specimens (D 3433-93 and D 5528-94a) have been extended to cover the case of an elastic composite layer bonded to a rigid concrete/masonry substrate. In the theoretical section, the dominant loading conditions, relevant ASTM standards, and the development of energy release rate concepts for analyzing a disbonding composite layer modeled as an elastic cantilever beam are presented. The experimental section covers specimen fabrication and preparation, experimental setup, test procedures, post-test evaluation of the specimens, and data processing. The discussion of test results focuses on explaining the variability in measured strain energy release rate, and identifies trends between the measured strain energy release rate and the fraction of the fracture surface retaining cement paste after disbonding. It was found that good-quality composite-to-concrete bond is associated with high fracture toughness of the adhesive and location of the crack path in the concrete substrate. Strict enforcement of surface preparation and adhesive handling procedures was found to play an important role in promoting good bond strength and high fracture toughness. The fracture toughness test developed in this paper can be used for screening various composite-repair systems, to assess the effect of different environmental attacks, and as a quality control tool. |
