Elevated temperature response of RC beams strengthened with NSM FRP bars bonded with cementitious grout

•The FRP is bonded using a cementitious grout rather than an epoxy adhesive.•The flexural tests demonstrated good performance of the novel FRP strengthening system.•Thermo-structural response was investigated under typical serviceability loads.•Internal temperatures, beam displacements, and slip of the FRP strengthening were measured.•Digital image correlation (DIC) was also used to study displacements.