Static and dynamic tensile properties of ultra-high performance concrete (UHPC) reinforced with hybrid sisal fibers

Abstract

Ultra-high performance concrete (UHPC) is widely applied in concrete structures against impact and explosive loads. To achieve a more eco-friendly and cost-effective UHPC material, mixed plant fibers instead of conventional steel fibers are considered in the present study. UHPC with single and hybrid long and short sisal fibers (12 mm long fibers and 6 mm short fibers) reinforcement (2% fiber content) were prepared and compared against UHPC with no fiber reinforcement. The quasi-static tensile and bending properties of these six types of UHPC specimens were investigated. A split Hopkinson pressure bar test has also been adopted to evaluate the dynamic tensile performance of UHPC specimens under five strain rates, the effect of strain rate has been investigated, and the failure process has been recorded with a high-speed camera. The experimental results showed that the UHPC containing 1% long sisal fibers (12 mm) and 1% short sisal fibers (6 mm) has optimum dynamic mechanical properties. Hybrid sisal fibers are more effective in strengthening UHPC specimens in dynamic tests than in static tests. A synergy effect is also introduced to further characterize the strengthening effect of hybrid sisal fibers. Finally, to more accurately predict the dynamic tensile strength of the specimens under various strain rates, an improved prediction model of the dynamic increase factor for tensile strength is proposed by combining the results of this experiment and previous experimental data.