This paper aims to reveal the mechanical evolution and potential mechanism of Ultra-high Performance Concrete (UHPC) exposed to a complex temperature-variation environment typical of Liquefied Natural Gas storage tank. Herein, the effect of steel fiber geometries (straight and hooked-end) on flexural failure of UHPCs in the range of −170 °C ∼ 200 °C was studied, and dynamic fracture evolution during the loading process was tracked using acoustic emission (AE) test. Results indicated that the flexural strength of concrete specimen enhanced at −170 °C but diminished at 200 °C in the first cycle. For multiple cycles, its improved strength subsisted until the third cycle, after which gradually decreased. Moreover, the hooked-end fiber generally had superior strengthening and toughening effects than straight fiber, except for cryogenic temperature and third cycles tests. At cryogenic temperature, the freezing of pore moisture inside specimen enhanced the matrix strength and the interfacial bonding between the matrix and fibers. At elevated temperature, the thawing, diffusion and evaporation of moisture in concrete could induce matrix dehydration and weaken the bonding effect between interfaces. In varying exposure environments, the moisture migration would also undergo secondary hydration reactions with unreacted cement particles. Finally, using AE parameters to effectively record damage progression in UHPCs exposed to extreme temperatures was also highlighted.

中文翻译：

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通过声发射表征超高性能混凝土在低温和高温交替作用下的弯曲破坏


本文旨在揭示超高性能混凝土（UHPC）暴露于液化天然气储罐典型的复杂温度变化环境下的力学演化和​​潜在机制。在此，研究了钢纤维几何形状（直端和钩端）对 UHPC 在 -170 °C ~ 200 °C 范围内弯曲失效的影响，并使用声发射（AE）跟踪加载过程中的动态断裂演化。 ） 测试。结果表明，在第一个循环中，混凝土试件的弯曲强度在 -170 °C 时增强，但在 200 °C 时下降。对于多次循环，其强度的提高一直持续到第三次循环，之后逐渐下降。此外，除低温和第三次循环测试外，钩端纤维通常比直纤维具有更优异的增强和增韧效果。在低温下，样品内部孔隙水分的冻结增强了基体强度以及基体与纤维之间的界面结合。在高温下，混凝土中水分的融化、扩散和蒸发会引起基体脱水，削弱界面间的粘结作用。在不同的暴露环境下，水分迁移也会与未反应的水泥颗粒发生二次水化反应。最后，还强调了使用 AE 参数有效记录暴露在极端温度下的 UHPC 的损伤进展。