Strengthening of Reinforced Concrete Beams with Ultra-high Performance Fiber-Reinforced Concrete in Shear

Abstract

Ultra-high performance fiber-reinforced concrete (UHPFRC) exhibits high compressive and tensile strength together with outstanding durability. Due to these superior properties, UHPFRC is promising for retrofitting existing reinforced concrete (RC) bridges. While research and on-site applications show the significant improvement of RC structures strengthened with UHPFRC in flexure, information regarding the shear behavior of such UHPFRC composite structures is limited. Therefore, the primary objective of the present study is to investigate the efficiency of UHPFRC in enhancing the shear strength of RC beams. The material properties including the compressive and tensile strength, and shrinkage of UHPFRC are experimentally measured. The shear deficient reference beam (RB) is designed, and UHPFRC is applied on the lateral sides of the RB. Two different bonding techniques to apply UHPFRC are employed: (1) casting fresh UHPFRC in-situ; and (2) gluing precast UHPFRC plates with epoxy resin. The interface properties under each technique are examined. Results demonstrate that compared to RB, strengthened beam (ST) with bonded prefabricated UHPFRC using epoxy resin shows an around 110% and 60% enhancement in strength and ductility, respectively. However, with in-situ casting of UHPFRC, due to restrained shrinkage, the delamination between UHPFRC and concrete beam occurs and a negligible strengthening effect is observed. The findings indicate that the ability of UHPFRC can be fully utilized only provided that the interface strength is sufficient to prevent premature debonding for the hybrid UHPFRC-concrete structure.