Consistent distribution of air voids and asphalt and random orientation of aggregates by flipping specimens during gyratory compaction process

Abstract

The current Superpave mix design determines the optimum asphalt content that would produce asphalt specimens with total air voids of 4.0% without considering their sizes and distribution within the specimens. In addition, the current Superpave gyratory compaction equipment may produce inconsistent specimens with higher air voids on the top layer than the middle and bottom layers of the specimen. To produce more consistent gyratory specimens, a new approach of compacting both ends of the specimen, rather than the one side, is presented. Based on the automated image analysis of twenty-four specimens, the difference in air voids between top and bottom layers decreased when specimens were compacted on both ends. In addition, the standard deviations of both air voids and asphalt contents throughout the specimen decreased when the specimens were compacted on both ends. Therefore, it can be concluded that the air voids and asphalt contents were more uniformly distributed throughout the specimen when the gyratory specimens were compacted on both ends. Based on the angles between major axes of aggregates and horizontal plane, the aggregates were more randomly oriented when compacted on the both ends.