Bond-slip behavior of lapped sand-coated deformed GFRP rebars in UHPC under double-row splice test

Novel Ultra-High-Performance-Concrete (UHPC) structures reinforced with Fiber-Reinforced Polymer (FRP) rebars are promising candidates for applications in important infrastructures under exposed environments where normal concrete and steel rebars may falter. This paper aims to assess the bond-slip behavior between lapped sand-coated deformed Glass FRP (GFRP) rebars and UHPC using double-row splice tests, with parameters including bar diameter, splice length and lap clearance. Failure modes including the pullout of GFRP rebars and the splitting of UHPC were identified. For cases of pullout failure, the average bond strengths in samples with splice lengths of 5d_b were reduced by 17.6–22.1 % compared to those of 2.5d_b. Increasing the lap clearance from 0 to 1d_b and 2d_b led to 11.1 % and 30.2 % increases in average bond strengths. Furthermore, average bond-slip models for lapped sand-coated deformed GFRP rebars in UHPC were developed. The predicted curves matched the experimental ones, showing errors within 20 % for both average bond stresses and slips. When the cover is not less than 2d_b, the splice length is recommended to be at least 15d_b for sand-coated deformed GFRP rebars with diameters of 10 mm–16 mm in UHPC, approximately 1.25 times the corresponding development length proposed by the existing research.