Elevated Temperature Response of RC Beams Strengthened with NSM FRP Bars Bonded with Cementitious Grout

Abstract

This paper presents the results of 12 tests on small-scale reinforced concrete beams strengthened in flexure with a single near surface mounted (NSM) carbon FRP bar. To improve the performance of the FRP strengthening system at elevated temperature, the specific FRP bar has high values of glass transition Tg and decomposition Td temperature. Tests are performed to define the resin behavior at elevated temperature. The FRP is bonded using a cementitious grout rather than an epoxy adhesive. Flexural tests have been performed at both ambient and elevated temperatures on both unstrengthened and strengthened beams. Tests at elevated temperature were performed using propane-fired radiant panels rather than a fire testing furnace. Two heating configurations were used: (1) localised heating near midspan only; and (2) global heating over the entire bonded length of the FRP systems. Thermo-structural response was investigated under loads that give typical (i.e. maximum permissible) FRP service loading strain conditions. Internal temperatures, beam displacements, and slip of the FRP strengthening were measured. Bonded foil strain gauges were used to measure the FRP bar strains prior to heating, and digital image correlation (DIC) was also used to study displacements. The tests demonstrated good performance of this novel FRP strengthening system, both under localized (non-bond critical) and global heating (bond critical), and also demonstrated the grout-bonded NSM CFRP strengthening system’s ability to maintain structural effectiveness at temperatures up to about 600°C with adequate anchorage. However, similar tests with an epoxy adhesive are needed before the novel system can be confidently stated as being vastly superior to epoxyadhered NSM systems.