Bond Behavior of Carbon Fiber-Reinforced Polymers in Ultra-High-Performance Concrete

Presented by Nariman Khalil, University of Balamand The development of bond and transfer of stresses between ultra‐high performance concrete (UHPC) and fiber‐reinforced polymer (FRP) bars are not well understood. Unlike steel reinforcement, there is still no universal agreement on standard FRP type, roughness, and surface geometry, which requires proper understanding of the bond properties between both components including the behavior of structures in service and ultimate limit states. Different series of UHPC mixtures possessing 90 to 125 MPa compressive strengths are investigated in this study; the mixtures were modified using styrenebutadiene rubber (SBR) polymers and polypropylene fibers. The bond stress‐slip characteristics between UHPC and FRP bars was realized using the direct bond method. Test results showed that the incorporation of fibers leads to increased ultimate bond strengths recorded at failure, which can be attributed to higher UHPC mechanical properties. The initial tiffness of bond stress‐slip curves was considerably accentuated with SBR additions, reflecting improved interfacial shear stress between the FRP bars and surrounding UHPC. Also, the responses of ascending curves showed extended nonlinear regions, reflecting higher ductility due to the presence of SBR and polypropylene fibers. Such data can be of particular interest to concrete researchers and practitioners seeking improved performance of UHPC and FRP combinations for structural, repair, and precast applications.