不同强度等级混凝土遭受超低温冻融循环作用的受压强度试验研究

引气混凝土在自然环境下中的冻融损伤源于外部环境水分的侵入、混凝土的毛细孔-气孔系统的不断饱和。通过对气体分子扩散过程的讨论，修正了基于Fagerlund经典长期吸水理论的气孔饱水度变化预测模型，并采用引气砂浆的吸水实验结果证明了修正模型优于传统模型。结合自然条件下的干湿交替过程，提出了引气混凝土在自然条件下的吸水模型，包括两个阶段：自然环境中孔隙饱水度随环境干燥和降水作用而变化，以及外部侵入水分对毛细孔-气孔系统的饱和过程。前者利用干湿交替作用下混凝土表面湿润深度与平衡时间比的概念建立了自然条件吸水过程与连续吸水过程的联系，后者使用修正的气孔饱水度模型计算气泡持续饱水过程。将两阶段使用寿命模型应用于某大型铁路基建工程，结合当地气象数据与预设混凝土特性，得到了满足工程使用寿命的冻融耐久性关键设计参数。

Experimental study on the compressive strength of concrete of different strength grades experiencing ultralow temperature freeze-thaw cycle action

The freeze-thaw damage of air-entraining concrete in natural environment is caused by the intrusion of external water and the saturation process in the capillary pores and air-entraining voids. By discussing the process of air dissolution and diffusion, a revised absorption model is built based on Fagerlund's classic long-time absorption theory. The air-entraining mortar absorption test is performed to validate the improved model. Considering the drying–wetting actions, the absorption model of air-entraining concrete in natural environment is proposed. This model consists of two phases: the water intake in natural environment affected by drying and wetting; the saturation of pore-voids system by external water intake. The water intake under natural drying-wetting cycles is evaluated through the concepts of moisture influential depths and equilibrium drying–wetting time ratio. The pore-void saturation process employs the revised absorption model to predict the change of the saturation degree. Afterwards, the two-stage freeze-thaw service life model is applied to a major railway construction project. On the basis of the local meteorological data and of the predetermined characteristics of structural concrete, the key design parameters are obtained with respect to the frost actions and the expected service lives.