Bonding Behavior of Rebar and Concrete Reinforced with Steel–PVA Hybrid Fiber after Exposure to High Temperatures

To investigate the bonding behavior of rebar and concrete reinforced with steel–polyvinyl alcohol (steel–PVA) hybrid fiber after exposure to high temperatures, 30 normal concrete specimens and 60 specimens of concrete reinforced with steel–PVA hybrid fiber were subjected to pullout tests. The apparent characteristics and mass loss rate after high-temperature exposure were observed, and the failure modes of two different rebar diameters, three hybrid fiber volume ratios, and five temperature grades were analyzed. The results indicated that as the temperature increased, the specimen surface color changed to grey-white, and the mass loss increased. At the same time, the ultimate bond strength decreased and the ultimate slip value increased. The incorporation of steel–PVA hybrid fiber significantly improved the production of cracks and spalling of concrete after high temperatures and increased the ultimate bond strength and ultimate slip value of concrete. The increase in ultimate bond strength of specimens with P1S14 (0.1% PVA fibers and 1.4% Steel fibers) and 16 mm rebar diameter was more significant, with the largest influence rate of about 37.23%.