Bond properties between lapped steel rebars and UHPC under direct tension

Abstract

Ultra-High Performance Concrete (UHPC) is a highly advanced cement-based composite that offers higher mechanical properties and exceptional durability over Normal-Strength Concrete (NSC). Bond properties between steel rebars and UHPC are the key to designing reinforced UHPC structures. The goal of this study was to characterize the bond properties between lapped steel rebars (uncoated) and UHPC. A total of 20 modified pullout tests having two-row lap splices were performed to examine the variation of diameters of 10, 14, 20, 25 and 32 mm. It was shown that the splitting of UHPC covers was a dominant failure mode, and samples with smaller bar diameters exhibited good ductility. Higher bond strengths were found in samples with smaller bar diameters. Specifically, bond strengths in samples having diameters of 20 mm, 25 mm, and 32 mm showed reductions of 14.8 %, 27.6 %, and 35.2 % in comparison to those featuring a diameter of 10 mm. The distributed curves of bond stress with two peaks were identified when maintaining a lapped length of four times the bar diameter. Furthermore, the mechanical model for lapped steel rebars in UHPC and the theoretical equation for calculating the bond-splitting strength and minimum lapped length were presented and validated by the available studies.