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

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.