Influence of fibers on fresh and hardened properties of Ultra High Performance Concrete (UHPC)—A review

Ultra High Performance Concrete (UHPC) is one of the recently emerging technologies in the construction industry. The strain hardening behavior, ductility, and toughness in UHPC are primarily contributed by the presence of the fibers. The major considerations adopted for the selection of fiber are: material properties should be compatible; fiber–matrix interaction must be sufficient to transmit stresses, and the aspect ratio must be optimal to ensure efficient post-cracking behavior. The efficiency of fibers is mainly dependent on their nature, fiber combination, fiber orientation, fiber mechanical properties, and fiber geometry. As detailed aforementioned, multiple criteria need to be satisfied for judicious selection of fibers. In view of the same, a critical review is presented in this study to provide a ready reference to the stakeholders regarding the effect of the fiber on the fresh and hardened properties of UHPC. In the first part, the fiber-to-binder interaction mechanism, geometrical and strength properties of metallic, inorganic, polymeric, carbon, and hybrid fibers adopted in UHPC are detailed. In the second part, the impact of fibers dosage and geometry is studied on workability, rheology, microstructure, compressive strength, tensile strength, and durability properties. Based on the findings, future potential applications, current challenges, and an overall summary are presented.