沥青混合料冻融劈裂微观结构损伤特性分析

Analysis of Micro Structural Damage Characteristics of Freeze-thaw Split Asphalt Mixtures

量化研究了沥青混合料冻融劈裂试件微观结构的损伤特性。基于冻融劈裂前后试件的CT图像,以CT值和损伤变量为基础,根据试件内部损伤特征,借助损伤力学基本概念,通过适当的数学假设,建立了冻融劈裂前后沥青混合料试件内部结构CT值分布规律的数学模型。利用CT值和损伤变量实现了对冻融劈裂前后试件内部微观损伤的量化。以损伤力学概念为基础,给出了沥青混合料损伤密度的定义,推导了以CT值表示的混合料密度损伤变量表达式,从而将CT值和损伤变量联系起来。利用损伤变量可以对混合料试件冻融劈裂前后内部微观结构的变化进行对比分析,实现了试件内部微观损伤特性变化的定量对比。对冻融劈裂前后试件上中下3个层位损伤变量的计算结果表明,冻融劈裂后试件各层位相应的损伤变量均有不同程度的增加,与CT图像表明的试件内部损伤明显加剧相吻合。

The purpose of the study is to quantify the micro structure damage characteristics of the freeze-thaw split specimens of asphalt mixture. Based on the original CT images of specimens and CT images after the freeze-thaw split test, and also based on the basic concepts of damage mechanics, the mathematic distribution models of CT values of the freeze-thaw split specimens were constructed by using CT value and damage variable and suitable mathematic assumption according to its inner damage characteristics. Then, the quantification of micro damages before and after freeze-thaw split test were perform by utilizing CT values and damage variables. On the basis of concepts of damage mechanics, the definition of damage density of asphalt mixture was given and a damage density formula expressed by CT value for asphalt mixture was derived. In this way, the CT value and damage variable were connected. The damage variable can be utilized to contrast and analyze the inner micro structure change of asphalt mixture specimens before and after freeze-thaw split test. Therefore, the damage characteristic changes inside the specimens can be quantified. The calculation results of upper, middle and lower scanning sections of freeze-thaw split specimens show that the damage variables of each section in the specimens are all increased to certain degree after the freeze-thaw split test. The increases inosculate the apparent aggravation of damage inside the specimens reflected by CT images.