Ultra-high performance concrete (UHPC) shows superior mechanical performance, which leads to increasing applications in infrastructure constructions that are subjected to different loading (i.e., flexure, tension, compression, etc.) and environmental conditions (ambient, freeze, etc.). Among them, the flexural performance of UHPC under low temperatures (i.e., sub-zero temperature) is still little understood especially under fatigue loading. To investigate the flexural fatigue properties of UHPC under low temperatures, eleven UHPC prisms are subjected to cyclic bending at different stress levels from 0.40 to 0.80 (the ratio between applied maximum fatigue stress and static flexural strength) and temperatures of 20 °C, -10 °C, and -20 °C. Results indicate that the fracture interfaces for specimens under static and fatigue loading exhibit distinct differences. No fiber buckling appears for the monotonically-loaded specimens, while for specimens under fatigue loading, fibers buckled and fractured. Low temperature improves the mechanical properties of UHPC under monotonic loading due to enhanced matrix strength. Conversely, low temperature adversely affects the flexural fatigue performance of UHPC due to the cold brittleness nature of matrix and steel fibers, leading to the accumulation of matrix deterioration and the fracture of steel fiber. When the temperature drops from 20 °C to -10 °C and -20 °C, there is a 15.0 % and 12.7 % decline in the flexural fatigue strength of UHPC, respectively. In addition, low temperature accelerates the degradation of UHPC, resulting in a larger and faster accumulation of fatigue deformation, including tensile strain, mid-span deflection, and fatigue deformation modulus.

中文翻译：

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超高性能混凝土低温弯曲疲劳性能

超高性能混凝土（UHPC）表现出优异的机械性能，这导致在承受不同载荷（即弯曲、拉伸、压缩等）和环境条件（环境、冷冻等）的基础设施建设中的应用不断增加。 。其中，UHPC在低温（即零下温度）下的弯曲性能仍然知之甚少，特别是在疲劳载荷下。为了研究 UHPC 在低温下的弯曲疲劳性能，将 11 个 UHPC 棱镜在 0.40 至 0.80（所施加的最大疲劳应力与静态弯曲强度之比）的不同应力水平和 20 °C、-10 的温度下进行循环弯曲。 °C 和-20 °C。结果表明，静态和疲劳载荷下试样的断裂界面表现出明显的差异。单调加载的试件没有出现纤维屈曲，而疲劳载荷下的试件则出现纤维屈曲和断裂。由于基体强度增强，低温提高了 UHPC 在单调载荷下的机械性能。相反，由于基体和钢纤维的冷脆性，低温会对UHPC的弯曲疲劳性能产生不利影响，导致基体劣化累积和钢纤维断裂。当温度从20℃降至-10℃和-20℃时，UHPC的弯曲疲劳强度分别下降15.0%和12.7%。此外，低温加速了UHPC的降解，导致疲劳变形积累得更大、更快，包括拉应变、跨中挠度和疲劳变形模量。