Integrity of Precracked Reinforced Concrete Retrofitted with Composite Laminates

The objective of this proposed research is to provide a scientific basis for the underlying mechanisms of fracture and delamination of precracked reinforced concrete retrofitted using fiber-reinforced plastic (FRP) composite laminates, and to develop design guidelines for efficient applications and safe engineering designs of these systems. Laminated beams have been observed to fail through several mechanisms, including yielding of the laminate, crushing of the concrete, and brittle fracture through delamination of the composite from the concrete. Available experience has shown that fracture through delamination can occur at stress below material limits and under loads within normal service. The emphasis of this study will be on delamination and its causes, specifically, in the presence of combined flexural and shear cracks in the retrofitted concrete beam. Fracture mechanics based combined experimental and numerical studies of failure initiating from the concrete-adherent-laminate interface region will be performed on concrete beams laminated with fiber-reinforced plastics. Parametric investigations involving different materials and construction techniques will determine the optimum effectiveness of these combinations. Various criteria for conditions representing interface crack propagation, crack deflection into the laminate, and crack deflection into concrete will be established. The developed fracture criteria will then be used to investigate the effects of inherent defects in the retrofitted structure on the integrity of the composite system. The influence of existing cracks in the concrete beam on the concrete-laminate interfacial fracture toughness will be quantified and the results will be used to determine the flexural strength of the repaired system as affected by existing shear and flexural cracks. The research will be conducted in an evolutionary fashion using analytical and physical laboratory models, and tests on beams representing real-world applications with pre-existing cracks. The project will have the collaboration of Swiss Federal Laboratories for Materials Testing and Research (EMPA) in Switzerland where large scale tests will be conducted with consistent parameters as will be used in this proposed study.