Concrete structures in the atmosphere are continuously subjected to thermal cycle (TC) induced by varying environmental temperature. However, the influencing mechanism of thermal cycling fatigue on the mechanical properties and microstructure of cement-based materials has not been thoroughly documented. To address this issue, the relationship between the macro-properties and microstructure of cement paste under TC was analyzed using micro-properties measurement and quantitative microcrack evaluation. In this work, ordinary Poland cement pastes with three different water-to-cement (w/c) ratios (0.4, 0.5, and 0.6) were exposed to TC in the range of 5–45 °C. The mechanical properties, pore structures, and micromorphology of cement pastes after different cycle times were measured. The result indicated that as the number of cycles increased, TC negatively affected the macro-mechanical characteristics, pore structure, and micromorphology of cement pastes. Cement pastes with greater w/c ratios were more susceptible to TC-induced deterioration. In addition, thermal cycling fatigue caused the propagation of microcracks including crack width, length, and density. Thermal cycling fatigue also coarsened the pore structure of cement pastes, especially the large pores (i.e., diameter > 100 nm). The underlying damage mechanism caused by TC is the coupled actions of fluid flow, thermal deformation, and thermal fatigue. Moreover, a negative linear relationship was established between microcrack density and Vickers hardness of cement pastes.

大气中的混凝土结构不断受到热循环 (TC) 的影响 通过改变环境温度。然而，热循环疲劳对水泥基材料力学性能和微观结构的影响机制尚未得到彻底的文献记载。为了解决这个问题，通过微观性能测量和定量微裂纹评估分析了TC下水泥浆体的宏观性能与微观结构之间的关系。在这项工作中，具有三种不同水与水泥 (w/c) 比（0.4、0.5 和 0.6）的普通波兰水泥浆暴露于 5-45°C 范围内的 TC。测量了不同循环时间后水泥浆体的力学性能、孔隙结构和微观形貌。结果表明，随着循环次数的增加，TC对宏观力学特性、孔结构、和水泥浆体的微观形貌。具有较大 w/c 比的水泥浆更容易受到 TC 引起的劣化。此外，热循环疲劳导致微裂纹的扩展，包括裂纹宽度、长度和密度。热循环疲劳也使水泥浆体的孔隙结构变粗，尤其是大孔隙（即直径> 100 nm）。TC 造成的潜在损害机制 是流体流动、热变形和热疲劳的耦合作用。此外，水泥浆体的微裂纹密度与维氏硬度之间存在负线性关系。