Experimental Study on Properties of Sprayed Ultra-High-Strength Fiber-Reinforced Concrete with Mixed Copper and Polypropylene Fibers

Infrastructure constructed around 60 years ago during Japan’s postwar period of high economic growth (1955–1973) is now facing the problem of aging. As a consequence, an era of maintenance and repair is approaching. There is expectation that sprayed ultra-high-strength fiber-reinforced concrete (UFC) will be a suitable repair material in many cases. UFC generally offers high strength, toughness, and durability. However, there is a problem with the workability of UFC because of its high viscosity, leading to experimental efforts aimed at achieving high strength, durability, pumpability, and adhesion when spraying UFC. This paper presents research on the hardening properties and physical properties of sprayed ultra-high-strength fiber-reinforced mortar containing a mix of copper and polypropylene fibers. The results confirm that, even with the addition of chemical fibers, the fresh properties remain similar to those of formulations containing only copper fibers. It is also found that spraying can achieve sufficient cover thickness and that on-site application is possible.