Effects of Hygrothermal Environments on Epoxy
- Paige Blackburn, Graduate Student, University of Florida
- H. R. Hamilton, Professor of Civil Engineering, University of Florida
The use of fiber reinforced polymer composites to repair and strengthen bridges and buildings has increased significantly over the last twenty years. FRP composites are composed of synthetic carbon fibers bound together and adhered to concrete with epoxy. Because of their outdoor exposure, the resistance of epoxy to the detrimental effects of moisture is an important aspect of these repair systems. The effect of moisture on epoxy is sometimes tested by exposure to moisture at high temperatures, which affects the relative cure and glass transition temperature (Tg). Because these systems are cured at ambient conditions and not at elevated temperatures, exposure to both moisture and high temperatures will affect the properties of the epoxy. The objective of this work was to determine the effect of moisture on the percent cure of the epoxy when exposed to high temperatures and moisture. Four epoxies from commercially available systems were tested; eight samples were prepared for each epoxy. One of the eight was used as a control sample, which was placed in air at room temperature. The remaining samples were exposed to either water immersion or 100% relative humidity at 30oC or 60oC for up to eight weeks. When the samples came out of exposure, data on their percent cure and water absorption was obtained using Fourier Transform Infrared Spectroscopy (FTIR). It was found that the moisture exposure techniques had no differing effects on the percent cure of epoxy. After two weeks of exposure, there were no differences in the amounts of water absorbed either. Increased temperatures, however, directly caused an increase in percent cure of epoxy, and had no effect on the amount of water absorbed.