Improved bond behavior between FRP reinforcing bars and concrete with carbon nanotubes

This study investigates the pullout bond behavior between fiber reinforced polymer (FRP) reinforcing bars and concrete with carbon nanotubes (CNTs). Fifty four pullout specimens were prepared and tested to investigate the effect of CNTs content (0%, 0.05%, 0.1%, and 0.2% by weight of cement), FRP bar diameter (10 mm and 12 mm), embedded length (100 mm, 150 mm, and 200 mm), and type of FRP bar on the bond behavior. The development length was calculated based on both experimental results and ACI standards. Effect of CNTs on the mechanical strengths of concrete was also investigated. The results showed that adding 0.2% CNTs significantly enhanced the compressive and splitting tensile strengths of concrete. During the pullout bond test, three main failure modes were observed: splitting, pullout, and bar fracture. The failure mode was affected by the bar diameter but not by the CNTs content or the embedded length. Experimental results revealed that CNTs enhanced the bond strength and reduced the development length. The enhancement increased with increasing the CNTs content. Scanning electron microscopic images showed the CNTs well distributed within the concrete at the interfacial zone with the FRP bars. (C) 2020 Elsevier Ltd. All rights reserved.