Investigation of the Gyration Angle of Superpave Gyratory Compactors

The superior performing asphalt pavement (Superpave) hot mix asphalt (HMA) mix design system was a principal development of the Strategic Highway Research Program (SHRP). In the Superpave mix design system, the Superpave gyratory compactor (SGC) was developed as a laboratory HMA compactor, targeted at better simulating the field compaction of HMA mixes. All SGCs are required to meet the American Association of State Highway and Transportation Officials (AASHTO) T312 specification parameter requirement of external gyration angle (1.25(plus_minus)0.02°). Numerous agencies have reported significant differences in the HMA bulk specific gravity (Gmb) of the same HMA mix compacted in different SGCs. These differences are hypothesized to be, in part, due to different internal gyration angles between SGCs. In response, a dynamic angle verification (DAV) procedure has been used to measure and verify the internal gyration angle during compaction. SGCs located in the central and district Mississippi Department of Transportation laboratories were evaluated with the DAV procedure to determine the internal gyration angle and the resulting Gmb values. Substantial differences in the internal and external gyration angles, as well as the top and bottom DAV determined internal angles, were found for many of the SGCs evaluated.