Compressive strength of concrete damaged by elevated temperature and confined by CFRP fabrics

In general, concrete structures have high fire-resistance. When exposed to fire, however, the strength and stiffness of the concrete and reinforcing steel deteriorate significantly. Fibre-reinforced polymer (FRP) wraps are an excellent material for strengthening concrete to increase its axial load capacity. This paper describes an experimental study on fourteen concrete cylinders after exposure to 500oC for one hour and cooling to room temperature which were then wrapped and tested under axial compression to failure to determine the ultimate axial strength. The purpose of the study was to extend the Carbon fiber reinforced polymer (CFRP) confinement technique to investigate the residual concrete strength of post-heated RC cylinders strengthened/confined with CFRP fabrics. The experimental parameters included type of reinforcement and number of CFRP fabric layers. It was found that repairing heat-damaged cylinders with 1, 2 and 3 layers of unidirectional CFRP can be highly effective for enhancing the compressive strength of concrete damaged by high temperature. The residual concrete strength of post-heated cylinders can be restored to the original level or higher than that of unwrapped cylinders. The failure mode of the confined concrete was predominantly rupture of the CFRP sheets.