In recent years, research on FRP strengthening RC beams has been one of the most popular topics due to the more rapid use of FRP composites for strengthening structures and in repair applications. The interface performance between FRP and concrete is one of the key factors affecting the behavior of the strengthened structure. Much research has been carried out using different test methods to study the behavior of FRP-concrete bonded joints. However, in spite the great number of research studies, only a small fraction of the research has considered the effect of adhesives and how their mechanical properties can affect the strengthened system.;In all tests the same CFRP laminate was used but the substrate material included both aluminum and concrete. The aluminum system was chosen to insure that the failure would occur in the adhesive layer to study the effects of different adhesive parameters on the bond strength. The concrete system is a more realistic case and is more representative of actual strengthening in the field.;The results of this research snow the impact of using different bonding widths and adhesive thickness on the bond strength. In addition, the results also show the effects of using different adhesive mechanical properties on the bond strength of the two bonding systems.;The main objective of this research was to perform experimental investigations on the effect of the mechanical and geometry properties of adhesives on the performance of bonded systems in direct shear. A special steel fixture was developed and designed to conduct all the tests reported in this research. Geometric parameters tested were the adhesive thickness and adhesive-concrete width ratio. Two different adhesives systems with different mechanical properties were tested. The results were compared against two existing theoretical models, one for linear elastic response and the other for ultimate strength.
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