不同成型方法和级配的沥青混合料内部空隙特征

Air voids distribution of asphalt mixtures in different compaction methods and aggregate gradations

采用X-ray CT技术和数字图像处理技术研究两种成型条件下三种级配沥青混合料试件的内部空隙特征,并通过统计分析提出数学模型对其进行表征。结果表明,沥青混合料的空隙空间分布规律受试件成型方法及级配类型的影响较大。不同级配条件下,马歇尔试件内部空隙率分布沿着高度方向总体呈现对称形状,而静压试件内部空隙率分布则为'一端大,一端小'的形状,马歇尔试件的平均空隙率与目标空隙率差异较小,而静压试件的平均空隙率是目标空隙率的1.4倍以上;相同级配条件下,与马歇尔试件相比,静压试件的空隙空间分布离散性、平均空隙率和平均空隙数量均较大,但平均空隙等效直径相差较小;采用两参数数学模型能够较好地表征成型方法和集料级配对沥青混合料内部空隙空间分布规律的影响。

The air voids distribution of three gradations of aggregate is characterized using X-ray computed technology and digital image processing technology. Furthermore, a mathematic model is proposed to describe the air void distribution inside the asphalt mixtures by means of statistical analysis. The results show that both the gradations of aggregate and compaction methods have considerable influence on the air voids distribution within the specimens. Results also show that the voids distribution is symmetric along the depth of the Marshall specimens, whereby, the air voids distribution in the statically compacted specimens in nonsymmetrical along the depth that the number of air voids on the top part of the specimen is bigger than that at the bottom part. There is little difference between the target void fraction and the mean void fraction of the Marshall specimens; while the mean void fraction of the static compaction specimens is over 1.4 times of the target void fraction. In comparison with the Marshall specimens in uniform gradation of aggregate, in the statically compacted specimens, the number of air voids is bigger and the fluctuation along the depth is more remarkable, but the void size is almost consistent. Sstatistical analysis validates the applicability of the two parameter mathematical model to characterize air void distribution in asphalt mixture, and to quantify the effects of compaction methods and gradation of aggregate on air voids.