Bond strength evaluation between steel rebars and carbon nanotubes modified concrete

In the present study, the effect of multi-walled carbon nanotubes (CNTs) on the mechanical strengths of concrete as well as on the pullout bond behavior between steel rebars and concrete were experimentally investigated. Compressive and tensile strengths of concrete with varied dosages of CNTs (0 %, 0.05 %, 0.1 %, and 0.2 %) were measured. Twenty seven pullout specimens were prepared with various embedded length (100 mm, 150 mm, 200 mm) and bar diameter (12 mm, 14 mm, 16 mm, 18 mm), and tested to evaluate the influence CNTs on the bond-slip behavior. The morphology at the steel/concrete interaction transition zone (ITZ) was explored using scanning electron microscopy (SEM) imaging. Adding 0.2 wt.% CNTs improved the compressive and tensile strengths of concrete by 23 % and 22 %, respectively. Presence of CNTs also enhanced the bond strength and bond stiffness, and changed the failure mode from splitting to pullout failure. According to the SEM images, the CNTs uniformly distributed at the steel/ concrete ITZ. Finally, an empirical model was developed to predict the bond strength between steel rebars and CNTs-modified concrete. The model reflected the influence of the confinement and the bar diameter to the embedded length ratios on the predicted strength.