Bond between Ultra High‐Performance Fiber Reinforced Concrete and existing concrete: a review

The application of UltraHigh-PerformanceFiberReinforced Concrete (UHPFRC) is increasingworldwide to repair and strengthen existing structures. One of the main applications is in bridgecomponents, e.g., to repair bridge decks and piers, but also to strengthen existing floors in residentialor industrial buildings and to realize con-struction joints in prefabricated members. To properly designa strengthening inter-vention with UHPFRC, bond between the existing structure and the new layer ofreinforcing material should be properlydeveloped. In this work, a review about the interface behaviorbetween UHPFRC and concrete is carried out, analyzing in detail the available test methods, and thevariables influencing the bond behavior between the two materials. Among them, the role of moistureexchanges, the material prop-erties of the concrete, the surface roughness, and the effectof bonding agentsare discussedin detail.This work shows only proper surface treatments can enhance bond strength, otherwise they could be detrimental. In most previous experiences, UHPFRC bond efficiently with the substrate, resulting in composites that behave monolithically.