Experimental study of post-fire bond strength between steel reinforcing bars and concrete using beam-end specimens

After exposure to high temperatures, the integrity of reinforced concrete structures depends on the residual bond strength between steel rebars and surrounding concrete. Most existing data on residual bond strength are based on pull-out tests, while beam-end tests provide a more realistic stress state condition around the rebar, leading to a more accurate assessment of residual bond strength. This study aims to investigate the temperature-induced degradation of bond strength by employing beam-end specimens. A series of experiments are conducted with target concrete-rebar interface temperatures of 20°C, 150°C, 200°C, 300°C, and 400°C, with two heating protocols. The beam-end tests used in this study follow ASTM A944 guidelines. This experimental setup provides a more realistic representation of bond behavior than traditional pull-out tests, which often overestimate bond strength due to uniform confinement. The findings indicate that residual bond strength measured through beam-end bond tests is generally lower than the values measured through pull-out tests reported in the literature. The study also highlights the impact of heating protocols, with uniform heating yielding slightly higher bond strengths than cases with thermal gradients within the cover. Finally, results from beam-end tests indicate that the reduction in residual bond strength after exposure to elevated temperatures is more significant than the decrease in compressive strength. Overall, the paper provides insights into the effects of test setup and different heating protocols on residual bond strength, as well as identifying gaps for further research.