Environmental Effects on Mechanical Properties of Wet Lay-Up Fiber-Reinforced Polymer

The demand for fiber-reinforced polymers (FRPs) in rehabilitation of infrastructure is increasing. New techniques use the light weight, high strength, and formability of FRP fabrics and laminates in various concrete retrofitting projects. This paper presents the results of studies on the long-term behavior of different types of FRP laminates produced using the wet lay-up technique. This technique is the most used in field application of FRPs on concrete structures. The scope of the paper is limited to only one mode of failure: laminate failure. It is noted that another form of failure is the bond at the interface. This mode of failure is currently under investigation at the University of Arizona. A total of 525 specimens were prepared using one type of epoxy and seven different types of fabrics. Unidirectional and bidirectional fabrics made from glass, carbon, and aramid were used in this study. The samples were exposed to nine different environments. These environments were simulated using four different chemical solutions with a pH of 12.5, 10, 7, and 2.5 and substitute seawater. Additional FRP samples were exposed to ultraviolet (UV) radiation, temperatures of 60 and 50°C (140 and 122°F) with 95% relative humidity (RH), and soil with 25% moisture content and active microorganisms in specially constructed chambers. Uniaxial tension tests were performed on the samples after 6000, 12,000, and 20,000 hours of exposure as well as on control samples; and tensile properties were measured for each specimen. The results showed a significant loss of strength and ultimate strain for glass FRP (GFRP), especially in environments with high pH values, while carbon and hybrid glass carbon laminates showed very little loss of mechanical properties.