Effect of concrete composition on FRP/concrete bond behavior

External bonding of fibre reinforced plastics (FRP) has been proved to be an effective and efficient method in strengthening concrete members. For the strengthened member, failure may occur through FRP debonding that initiates from-the bottom of a major flexural crack in the concrete member, and propagates towards the free end of the plate. This failure mechanism is often studied with the direct shear test. Various analytical models have been established based on fracture mechanics and empirical study. In existing models, the bond capacity is considered to be strongly dependent on the compressive (or tensile strength) of the concrete itself. However, theoretical analysis indicates that the shear stress distribution along the FRP/concrete interface at ultimate debonding failure is usually dominated by friction, where cracking has already occurred in the concrete, and aggregate interlocking is leading to residual stress. It is therefore suspected that the content of aggregates, which may affect the interlocking effect, will also play important roles in determining the bond capacity.