Mechanochemical investigation into bond performance of an NSM CFRP strengthening system at elevated temperatures

Near surface mounted (NSM) fiber reinforced polymer FRP strengthening system is a promising strengthening technique that increases the flexural and shear strengths in concrete members. FRP rods or strips are embedded in concrete members using polymeric epoxy resin or cementitious materials. Polymeric materials are highly sensitive to high temperatures. Limited number of research studies have been conducted evaluating the bond performance of NSM FRP strengthened systems. Few references are available in the area of residual behavior of NSM System and fire protection systems for NSM strengthened concrete members. Two-phase experimental testing program was conducted to evaluate the mechanochemical performance of NSM CFRP strengthened concrete members. Material-level testing includes a Fourier transform infrared spectroscopy (FTIR) interpretation of bond degradation mechanism of polymeric adhesives and degradation of mechanical properties of polymeric materials. Used epoxy resin was exposed to elevated temperatures ranging from 25°C [77°F] to 200°C [392°F]. FTIR spectrums were collected for residual epoxy samples to examine the degradation of chemical bonds using a mid-range FTIR instrument. The effect of mechanical properties of epoxy resin was investigated from a coupon test. The element-level testing was conducted to investigate the bond performance of NSM CFRP strengthening system in fire. NSM CFRP strengthened concrete elements were exposed up to elevated temperatures of 200°C [392°F]. Monotonic tension test was conducted to evaluate the pull out strength, load-displacement behavior and different failure modes and cyclic loading was applied to examine the bond stiffness of NSM CFRP systems at elevated temperatures. Also, internal thermal propagation at the mid-span of the concrete element was examined using an Infrared (IR) thermal camera. Test results illustrate that the polymeric adhesives have significant influences on the mechanical properties of the epoxy resin that can reduced the overall strength of the NSM CFRP systems. Different failure modes were observed with decreased ultimate pull out strength at high temperatures. FTIR spectrums proved the effect on polymeric materials at high temperatures. Also, internal thermal propagation justify the observed failure modes and the strength degradation. This thesis presents the conducted experimental testing program and its results.