Influence of Hybrid Fibers on Workability, Mechanical and Dynamic Properties of Ultra-High Performance Concrete

Ultra-high performance concretes (UHPCs) have been widely used in the construction industry due to their high strength and long-term performance. The purpose of this article is to review the literature on UHPC that contained at least two types of hybrid fiber with different lengths, diameters, and volumetric contents. The results show that the type of fiber, its geometry, including length, diameter, and shape, as well as volumetric content, affect the properties of the concrete, not only in the hardened state, but also in the fresh state. The compressive and flexural strength results increase with higher impact velocity and steel fiber content, with a higher content of shorter fibers contributing to increased strength and energy absorption. Tensile strength increases with the length of the steel fibers and the higher content of polyolefin, polyoxymethylene, and polyester fibers. Investigating new types of fiber, various shape factors, geometries, and anchoring mechanisms of hybrid fibers is essential to improve the workability, adhesion, and strength of the material.