Durability of CFRP/Steel Bond in Natural Weather

Abstract

Fiber reinforced polymers (FRP) are increasingly being used for infrastructure strengthening and repair of steel structures. Though there have been several durability studies, exposures used are not representative of outdoor service conditions. Fewer studies have explored the effect of changing outdoor conditions typical in infrastructure use. The goal of the research is addressing this gap by evaluating the performance of commercially available CFRP systems under natural weather characteristic of hot, humid tropical conditions mainly and cold weather secondary in three different locations. Thirty CFRP/steel joint specimens were prepared in laboratory conditions and exposed to ambient temperature on the Engineering building roofs in Tampa FL, Knoxville TN, and Hamilton Ontario for a year. The steel surface temperatures were monitored. The durability of CFRP/steel bond was evaluated by pull-off adhesion test. MTS machine was used, and special fixture was designated to test six pull-off points in one specimen. The CFRP/steel bond was tested after 63, 120, 181, 250, and 398 days of exposure in Tampa, and it was tested after 365 days of exposure in Knoxville. The time series was considered to determine degradation with time. In addition, two specimens were painted by reflective paint to investigate the effect of reflective paint on the steel surface temperature and CFRP/steel bond strength for 250 days of exposure in Tampa. The loading fixtures were attached to steel plates without CFRP to conduct the best practice of pull-off test to evaluate the efficacy of pull-off test. The specimens were cured in laboratory conditions for 1, 2, 3, 7, 14, 28 days and tested. The significant variability in the pull-off test is caused by two major reasons; testing error that comes from imperfect cured epoxy dolly or eccentricity that comes from uneven CFRP surface or roughness of the steel surface. The second reason is the construction flaw that comes from entrained air bubbles at epoxy mixing or poorly fiber saturated due to high viscosity. However, after refining the result and analyzing the good tests, the degradation of CFRP/steel bond strength after one year exposure is minimal and no significant difference between Tampa, Knoxville, and Hamilton.