Effects of content and length/diameter ratio of PP fiber on explosive spalling resistance of hybrid fiber-reinforced ultra-high-performance concrete

Ultra-high-performance concrete (UHPC) is prone to explosive spalling at high temperatures, which compromises the load-bearing capacity of the structures. In this paper, the effects of the content and length/diameter ratio of polypropylene (PP) fibers on the explosive spalling resistance of the steel and PP hybrid fiber-reinforced UHPC were investigated utilizing experimental method. First, the UHPC specimens were prepared using the conventional curing method. Second, the UHPC specimens were heated using the ISO-834 standard heating curve. Thirdly, the appearances, the first spalling time, the first spalling temperature, and the mass loss of the specimens were used to evaluate the explosive spalling resistance of the UHPC. The results demonstrated that the steel and PP hybrid fiber-reinforced UHPC has much greater explosive spalling resistance than the steel fiber-reinforced UHPC. The explosive spalling resistance of the hybrid fiber-reinforced UHPC is strongly influenced by the content and length/diameter ratio of the PP fibers. Generally, the explosive spalling resistance of the hybrid fiber-reinforced UHPC increases with the increase of the PP fiber content and length/diameter ratio.