To study the effect of pore structure changes on the fatigue life of concrete in areas with large temperature differences, a concrete fatigue test program was designed after a temperature cycle of −50 to 70°C. Results show that temperature differences considerably influence pores with a size ranging from 0.1 to 27.98 nm. Furthermore, the fatigue life of concrete gradually decreases with the increase in the pore structure parameters of 0.1 to 27.98 nm. This result indicates that the effect of temperature difference on the fatigue life of concrete in areas with large temperature differences must not be ignored. The combined effect of temperature differences and load increases the coarsening rate of the pore structure, and the load remarkably affects pores with a size ranging from 524.26 to 10,000 nm. To characterize the pore structure of concrete under temperature cycling and fatigue load, two pore structure characteristic parameters, namely, comprehensive change rate of pore size (S_z) and pore structure complexity coefficient (C_z), are proposed. These parameters, together with the total porosity (P_total), form a three-dimensional pore structure characteristic parameter and establish the relationship expression between the three-dimensional pore structure parameters and the fatigue life of concrete (N); thus, they provide basis for the prediction of the fatigue life of concrete on the basis of pore structure.

中文翻译：

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温差大区疲劳荷载下混凝土的孔隙结构

为研究孔结构变化对温差较大区域混凝土疲劳寿命的影响，设计了-50～70℃温度循环后的混凝土疲劳试验方案。结果表明，温度差异显着影响孔径范围为 0.1 至 27.98 nm 的孔。此外，混凝土的疲劳寿命随着孔隙结构参数0.1~27.98 nm的增加而逐渐降低。这一结果表明，在温差较大的地区，温差对混凝土疲劳寿命的影响不容忽视。温差和载荷的共同作用增加了孔隙结构的粗化率，载荷显着影响孔径为524.26～10000nm的孔隙。提出了S _z ) 和孔结构复杂度系数 ( C _z )。这些参数与总孔隙率（P_总）共同构成三维孔隙结构特征参数，建立三维孔隙结构参数与混凝土疲劳寿命（N）的关系表达式；从而为基于孔隙结构的混凝土疲劳寿命预测提供依据。