- Diffusion Cell,
Many independent studies have conclusively demonstrated that fiber reinforced polymers (FRP) slow down chloride-induced corrosion of steel in concrete. The mechanism for this slow down is not well understood but it has been hypothesized that FRP serves as a barrier to the ingress of chloride, moisture, and oxygen that sustain electrochemical corrosion of steel.
This dissertation presents results from an experimental study that determined the oxygen permeation rates of materials used in infrastructure repair. In the study, the oxygen permeation constants for epoxy, carbon and glass fiber laminates, concrete, epoxy-concrete and FRP-concrete systems were determined and a method developed to use these results for designing the corrosion repair of FRP-concrete systems.
A new diffusion cell was developed that could be used to test both thin polymer specimens and much thicker FRP-concrete specimens. Concentration gradients were introduced by exposing one face of the specimen to air and the other face continuously to 100% oxygen for the duration of the test to achieve steady state conditions. Partial pressures on the two surfaces were measured using electronic sensors and oxygen permeation constants extracted from the data using a quasi-steady state theoretical model based on Fick's law. Results obtained using this system were in agreement with published data for specimens such as Teflon and Polyethylene Terephthalate (PET) Mylar whose oxygen permeation constant is available in the published literature.
Following the successful calibration of the system, oxygen permeation constants for epoxy, Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) laminates were determined. It was found that the oxygen permeation constant for epoxies was an order of magnitude lower than that for FRP. Furthermore, two layer FRP laminates were found to be more permeable than single layer laminates. This finding had been reported previously in the literature but had been considered anomalous. Scanning electron micrographs showed that this was due to the wet layup process that inevitably trapped air between the multiple FRP layers.
The oxygen permeability of FRP-concrete systems was evaluated for three different water-cementitious ratios of 0.4, 0.45 and 0.50 for both CFRP and GFRP materials. Results showed that the performance of CFRP and GFRP were comparable and the best results were obtained when FRP was used with concrete with the highest water-cementitious ratio. A simple design method is proposed to apply the findings from the research. This uses the concept of an equivalent FRP thickness derived following Fick's law.
The findings from the research can be used to optimize FRP applications in corrosion repair. The experimental set up can easily be adapted to measure diffusion of carbon dioxide through FRP and other materials. This has potential applications in other disciplines, e.g. climate change.
Available at: http://works.bepress.com/chandra_khoe/1/