Experimental Fatigue Behavior of NSM CFRP-Strengthened RC Beams Under High Service Temperature

Fiber-Reinforced Polymer (FRP) materials have been widely used to strengthen reinforced concrete (RC) structures due to unique characteristics. In this sense, different strengthening techniques exist to enhance the load-carrying capacity of RC structures, being the Near-Surface Mounted (NSM) one of the foremost options. The performance of the NSM strengthening system relies, among other parameters, on the mechanical properties of the involved materials (i.e. concrete, FRP and bonding agent, typically consisting on epoxy adhesives). In this regard, the efficiency of the strengthening system may be limited if the service temperature of the strengthened component approaches the glass transition temperature (Tg) of the epoxy. Several RC structures, particularly bridges, are not limited to static loads but they also face dynamic loading, which can compromise the safety of these structures, when not properly addressed. Although the effect of repetitive (fatigue) loads on RC elements is of great importance in their designing process, little literature exists on the flexural behavior of FRP-strengthened RC elements under fatigue loading and, especially under high service temperature. In this work, an experimental program to study the effect of fatigue loading and high service temperature on the performance of NSM Carbon FRP (CFRP)-strengthened RC beams is presented. The test matrix consists of six beams, three unstrengthened and three NSM CFRP-strengthened, under two different test set-ups: instantaneous loading and fatigue loading with and without temperature. Experimental results are discussed in terms of cyclic load-deflection curves. The residual strength of the beams in post-fatigue stage is also presented. Experimental results show that high service temperature resulted in an increase in the deflection of the specimens. However, all the beams (unstrengthened and strengthened) survived to the programed 2 million fatigue cycles.