Cryogenic pullout behavior of steel fibers from ultra-high-performance concrete under impact loading

This study investigates the effect of impact loading condition on the pullout property of steel fibers from ultra-high-performance concrete (UHPC) under various temperatures. For this, static and impact loads, ambient and cryogenic (−170 °C) temperatures, three steel fiber types, i.e., straight, half-hooked, and twisted, and two inclination angles of 0° and 45° were considered. From the test results and analysis, it was found that the steel fibers mostly had positive values of dynamic increasing factor (DIF) for the average bond strength at ambient temperature, but these were significantly reduced when the fibers were geometrically deformed, inclined, or tested under cryogenic temperature. Slip capacities generally decreased under the influence of the impact loading condition, and this effect was more severe at cryogenic temperature. There was no obvious impact loading rate effect on the probabilities of fiber and UHPC matrix damages at both ambient and cryogenic temperatures. The DIF values for pullout energies normally decreased or even became negative when the fibers were inclined, geometrically deformed, or tested at cryogenic temperature.