Concrete Confinement Using Carbon Fiber Reinforced Polymer Grid

Synopsis: Corrosion of prestressing steel in precast concrete is a significant problem for coastal bridges in Florida. Replacement of prestressing steel with carbon fiberreinforced polymer (CFRP) reinforcement provides a potential solution to this costly problem. The Florida Department of Transportation (FDOT) structures research center has teamed with the University of Florida (UF) to evaluate CFRP reinforced piles that employ two types of carbon reinforcement: (a) CFRP reinforcing bars and (b) CFRP grid. The CFRP bars act as flexural reinforcement while the CFRP grid provides confinement to the concrete core. The focus of this paper is on the confinement provided by the embedded CFRP grid, which is tied into a circular shape and cast into the concrete in a similar configuration to spiral ties. Existing confinement models are based on confinement provided by FRP wraps. Consequently, their use in predicting confinement must be validated with tests on embedded FRP grid. Standard (152 mm x 304 mm) concrete cylinders were cast both with and without the embedded CFRP grid. The cylinders were tested in compression to determine the effect of the CFRP grid on their strength and ductility. A significant improvement in ductility was observed for the cylinders with the embedded CFRP grid compared to the control cylinders.