Bond behavior of steel reinforcement in alkali-activated slag concrete exposed to ambient and elevated temperatures

The bond between steel bars and concrete is critical to the structural performance of reinforced concrete yet remains unexamined in alkali-activated slag concrete (AASC), with slag (GGBS) as the sole precursor. This study presents the first application of ASTM A944–10 beam-end test to investigate the bond behavior of AASC through 14 beam-end specimens, offering a more realistic assessment than the conventional pull-out test. The effects of embedment length, concrete cover, and macro polypropylene (PP) fibers were examined, along with bond degradation after exposure to elevated temperatures up to 800 °C. Results revealed that AASC exhibited comparable failure modes and load–slip responses to OPC concrete in the literature. Incorporating PP fibers enhanced bond strength by up to 14 % and increased post-splitting characteristic energy by 33–50 %, particularly with larger embedment lengths. After thermal exposure, AASC retained 70–88 % of its ambient bond strength up to 400 °C but dropped to 25 % at 600 °C, confirming 400 °C as a critical threshold. The applicability of OPC concrete models [Orangun et al. (1977), ACI 408R-03 (2003), and Darwin et al. (1992)] to AASC was validated via predictive error metrics, including average predicted/experimental ratio and root mean square error (RMSE), with Orangun et al. providing the closest prediction (predicted/experimental ratio = 1.00 ± 0.07, NRMSE = 7.1 %). These results offer vital quantitative data for reinforced concrete design, demonstrating the structural viability of AASC and promoting its sustainable adoption in future reinforced concrete construction.