Durability of concrete beams externally reinforced with composite fabrics

Abstract

This study represents the second half of a research project at the University of Delaware concerning the flexural strengthening of concrete beams using externally applied composite fabrics. Initial results showed that significant increases in flexural capacity can be achieved by epoxy-bonding composite fabrics to the tension face of reinforced concrete beams. This paper deals with the environmental durability of the concrete-epoxy fabric system. The three types of fabric studied are made of aramid, E-glass and graphite fibres. To determine the durability of this type of strengthening procedure under aggressive environments, 48 small-scale reinforced-concrete beams were exposed to freezethaw or wet/dry cycling in a calcium chloride solution, and an additional 12 beams were left in a control environment. Of the 60 beams, 45 were reinforced with aramid, E-glass, and graphite composite fabrics (15 with each type), and 15 had no external reinforcement (unwrapped). By varying the time of exposure to the different conditions and loading the beams to failure following the environmental testing, the durability of the externally reinforced beams was assessed. The tests indicate that chloride exposure in both wet/dry and freezeAhaw environments causes degradation to the beams' strength, with the wet/dry condition being slightly more severe. Both conditions led to some deterioration of the bond between the composite fabric and the concrete. Of the three types investigated, the graphite-reinforced beams proved to be the most durable, losing less than 15% of their 140% strength increase over the unwrapped beams after 100 cycles of exposure.