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

The application of Ultra High‐Performance Fiber Reinforced Concrete (UHPFRC) is increasing worldwide to repair and strengthen existing structures. One of the main applications is in bridge components, e.g., to repair bridge decks and piers, but also to strengthen existing floors in residential or industrial buildings and to realize construction joints in prefabricated members. To properly design a strengthening intervention with UHPFRC, bond between the existing structure and the new layer of reinforcing material should be properly developed. In this work, a review about the interface behavior between UHPFRC and concrete is carried out, analyzing in detail the available test methods, and the variables influencing the bond behavior between the two materials. Among them, the role of moisture exchanges, the material properties of the concrete, the surface roughness, and the effect of bonding agents are discussed in 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 behaves monolithically.