The paper concerns bond behavior between composite carbon fibre reinforced polymer (CFRP) materials and concrete in externally bonded (EB) and near surface mounted (NSM) FRP strengthened reinforced concrete (RC) beams. Bond mechanism was investigated on the modified bond test in aspect of six parameters: beam's span and depth, longitudinal steel reinforcement ratio, type of the CFRP strips/sheets, CFRP bond length, and concrete compressive strength. In order to confirm the influence of the

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... ing steel reinforcement ratio on the FRP-to-concrete bond conditions, the longitudinal steel bars in some beams were cut through at the mid-span. The test confirmed an important rule of the internal steel bars on the FRP-toconcrete interfaces and the final failure modes.