The study of interface characteristics between two dissimilar materials and its size effect are of interest in many engineering applications in order to predict the performance of the structure. This paper studies the boundary effect on fracture energy of concrete-concrete interfaces. It is assumed that the interface is weaker than the material on either side with respect to its fracture toughness of the interface. The bilinear local fracture energy model is used to characterize the back boundary effect on fracture energy of concrete-concrete interfaces, so that the size-independent fracture energy can be derived, which otherwise can only be measured using very large specimens. The experimental results available in literature and results from finite element(FE) analysis using ATENA software are used in this study. The fracture energy values calculated by using bilinear model are in a good agreement with the experimental and FE results of interfacial beams. It is shown that the boundary effect is significant in weaker interfaces. This implies that greater the difference in compressive strength or elastic moduli at the interface, greater is the vulnerability to cracking and failure for the same loading configuration.

Keywords: Fracture energy, Size effect, Boundary effect, Concrete-Concrete interfaces.