Static and dynamic mechanical properties of ultra-high-performance concrete (UHPC) by replacing steel fibers with plastic steel fibers

To solve the problems of corrosion and explosive spalling of traditional steel fiber ultra-highperformance concrete (UHPC) in practical applications, this study prepared UHPC by replacing steel fibers with plastic steel fibers (UHP-PRSC) and the static and dynamic mechanical behaviors had been investigated by carrying out the static tests and split Hopkinson pressure bar (SHPB) tests. The results show that under static loading, when the volume fraction of plastic steel fibers is 0.1 %-0.5 % (substitution rate 5 %-25 %), UHP-PRSC exhibits better mechanical properties than normal steel fiber UHPC. The strength of UHP-PRSC is the highest when the volume fraction of plastic fibers is 0.5 % and gradually decreases with the increasing volume content of plastic steel fibers. Under dynamic loading, the dynamic mechanical properties of UHP-PRSC are enhanced due to the reinforcing effect of plastic steel fibers at strain rates of 48.8 s_ 1-62.0 s_ 1, with a 25.4 % increase in the dynamic compressive strength of UHP-PRSC compared to normal steel fiber UHPC at a volume fraction of 0.5 % (substitution rate 25 %) of plastic steel fibers. At higher strain rates, the enhancement effect of plastic steel fibers on UHPC is weakened and even brings negative improvement. The microstructural analysis found that the replacement of steel fibers with plastic steel fibers with a volume content of 0.1 %-0.5 % (substitution rate 5 %-25 %) could produce a synergistic effect to improve the mechanical properties of UHPC and with the increase in the volume content of plastic steel fibers, the interaction between the two fibers weakened, and the mechanical properties of UHPC decreased. Based on the experimental results, an optimal replacement rate of steel fibers by plastic steel fibers was determined and the fitting parameters of the constitutive model were obtained. This study provides a reference for the feasibility of replacing steel fibers with plastic steel fibers for the preparation of UHPC.