Fiber content optimization of UHPC and R-UHPC oriented to tensile behavior and cost reduction.

• Feasibility of reducing the cost of UHPC by decreasing the fiber content and adding steel rebars was explored. • Effects of varying fiber content and adding steel rebars on the tensile behavior of UHPC were evaluated. • Cracking behavior and mechanical response of UHPC including low fiber content were assessed in detail. • Fiber efficiency in UHPC with different parameter combinations was evaluated. • Impacts of adding steel rebars and varying the fiber content on the fiber dispersion and orientation of UHPC were evaluated. The excellent performance of Ultra-high performance concrete (UHPC) is widely recognized, but its high cost remains a hindrance to its more comprehensive application. This paper focuses on the effects on the tensile cracking behavior and mechanical response of UHPC when its cost is reduced by decreasing the fiber content and adding steel rebars. Twenty-four UHPC specimens with different fiber contents (0.5%, 1.0%, 2.0%, and 3.0%) and reinforcement ratios (0% and 3.0%) were tested by direct tensile tests. The effects of varying fiber content and adding steel rebars on the cracking behavior and mechanical response of UHPC were assessed. The fiber efficiency in UHPC with different parameter combinations was quantitatively evaluated in terms of the ability to control the main crack opening, improve ductility, and enhance load-bearing capacity. The results show that reducing the fiber content leads to a substantial degradation in the capacity to restrain the maximum crack opening, ductility, and load-bearing capacity of UHPC. However, the addition of steel rebars weakens or eliminates the negative effects induced by lowering the fiber content and even obtains a better capacity to restrain the maximum crack opening. With tensile properties and fiber efficiency as evaluation indicators, a fiber content of 2% is appropriate for UHPC, and a fiber content as low as 0.5% is recommended for steel rebar-reinforced UHPC. [ABSTRACT FROM AUTHOR]