Flexural Performance of Pre-Cracked UHPC with Varying Fiber Contents and Fiber Types Exposed to Freeze–Thaw Cycles

Abstract

Ultra-high-performance concrete (UHPC) is an advanced cementitious composite material with high durability and the strength properties exceeding those of conventional concrete. This paper presents the results of experimental testing assessing the freeze–thaw durability of UHPC specimens with varying fiber types (13 mm straight microfibers and 30 mm hooked-end fibers) and fiber percentages, as well as pre-existing cracks. The performance of all specimens was evaluated by measuring resonant frequency at intervals during testing and residual flexural strength after the completion of 350 freeze–thaw cycles. All specimens showed no degradation of resonant frequency over time. However, the pre-cracked specimens showed an increase in resonant frequency over the course of testing. The uncracked straight fibers specimens exposed to freeze–thaw cycles had the highest flexural strength, but the flexural resistance of the pre-cracked straight fibers specimens increased compared to the control specimens after 350 freeze–thaw cycles. The pre-cracked hooked fiber specimens showed higher first cracking strength and similar ultimate strength to the uncracked specimens after freeze–thaw exposure.