Effect(s) of Concrete Strength and its Bond to CFRP sheets on the Ultimate Strength of Concrete Beams

Among the systems used for Retrofitting and Strengthening of structures، FRP systems seem to be more popular. When using FRP، the surface strength of concrete plays major role in producing sufficient adhesion between FRP laminates and concrete. Therefore، this paper is devoted to the findings of research on five different concrete strength that were used in manufacturing concrete beams for Retrofitting. In total twenty beams were prepared for studying the changes in adhesion between concrete and CFRP layers. While half of the beams were wrapped with CFRP''s، the other half were left as they were for comparative studies. The adhesion of CFRP layers on concrete beams were measured by new Twist-off method and the results were compared with those obtained from standard flexural testing of the beams. Finally، the effect of concrete surface strength and the bond strength of the CFRP on the ultimate strength of the strengthened beams have been assessed.