Abstract: To analyze the effect of compaction methods and aggregate gradations on air voids distribution in asphalt mixtures, the air voids distribution of three gradations of aggregate was characterized using x-ray computed technology and digital image processing technology. Furthermore, a mathematic model was made an attempt to present for describing the air voids distribution in internal structure of asphalt mixtures by means of statistical analysis. The results show that the gradation of aggregate and compaction methods had considerable influence on air voids distribution in the specimens, and that was found to be symmetrical along the depth of Marshall specimen, whereby distribution of air voids in the static compacted specimen is nonsymmetrical along the depth, and the number of air voids on top part of a specimen was bigger than at bottom part. The target volume of air voids and mean of air voids of Marshall specimen had little difference, the mean volume of air voids is more than 1.4 times beyond target volume of air voids of static compacted specimen. The number of air voids was more bigger and the fluctuations along the depth was more remarkable, the air voids size was almost consistent in static compacted specimens compared with the Marshall specimens in uniform gradation of aggregate. The statistical analysis performed validated the applicability of a two parameters mathematics model for characterizing air voids distribution of asphalt mixture, and the model could quantify the effect of compaction methods and gradation of aggregate on air voids.

Key words: Road engineering, Air voids, X-ray CT, Asphalt mixture, Compaction methods