Oxygen Permeability of Fiber-Reinforced Polymers

Several independent studies have confirmed that fiber-reinforced polymers (FRP) used for repairing corrosion-damaged concrete structures slow down the corrosion rate. This suggests that in this application, FRP serves as a barrier to the ingress of moisture and oxygen that are critically important for sustaining electrochemical corrosion of steel in concrete. Because oxygen molecules are smaller than both water and chloride molecules, they diffuse faster. Therefore, their permeation through FRP is more critical. This paper presents results from an experimental study that determined the oxygen permeability of FRP laminates. Four different commercially available carbon-fiber-reinforced polymer (CFRP) and glass-fiber-reinforced polymer (GFRP) systems were investigated, and four different fiber orientations were evaluated for one-layer and two-layer configurations. The results showed that the oxygen permeability of FRP was somewhat poorer than the epoxy used for its fabrication. Single-layer FRP laminates were less permeable than two-layer laminates, a finding that had previously been reported but considered anomalous. Scanning electron micrographs indicated that this could be attributed to voids between the layers. The nonzero oxygen permeability of FRP explains why it can slow down but cannot completely stop chloride-induced corrosion of concrete.