Experimental Study on Sprayed FRP System for Strengthening Reinforced Concrete Beams

Abstract

The purpose of this study is to develop a new technique for strengthening and repairing existing concrete structures with sprayed fiber-reinforced polymers (FRP) by mixing chopped carbon or glass fibers with epoxy or vinyl ester resins in open air and randomly spraying the mixture onto the concrete surface with compressed air. The use of sprayed FRP for repair and strengthening purposes using epoxy or vinyl ester resins has never been fully investigated. In this study, tensile testing was conducted on material specimens to determine the optimum length of chopped carbon or glass fibers and the mixture ratio of fiber, epoxy, and vinyl ester resin for sprayed FRP. These variables were adjusted to produce a material strength equivalent to that of one FRP sheet. The optimal length of glass and carbon chopped fibers was determined to be 38 mm, and the optimal mixture ratio of chopped fiber to resin was found to be 1:2. The thickness of sprayed FRP required to provide the same strengthening effect as one FRP sheet was also calculated. During this study, experiments were conducted to evaluate the strengthening/repair effects of the sprayed FRP on flexural beams, shear beams, and damaged beams. The results showed that the strengthening effect of sprayed FRP on the flexural and shear specimens was similar to those of one FRP sheet. The maximum strength of the damaged beams reinforced by sprayed FRP was approximately the same as that of the reinforced flexural and shear beams. Moreover, existing design equations for FRP sheets were found to be applicable to flexural beams reinforced with sprayed FRP. The shear beam specimens could be safely designed using the coefficient of shear strength reduction α= 0.18, determined to result in computed values that most closely approximate the experimental values. Overall, the sprayed FRP technique was found to be suitable for strengthening existing reinforced concrete buildings.