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 $\mathrm{SGCs}$ are required to meet the American Association of State Highway and Transportation Officials (AASHTO) T312 specification parameter requirement of external gyration angle $(1.25\pm 0.02°)$. Numerous agencies have reported significant differences in the HMA bulk specific gravity $\left(G_{\mathrm{mb}}\right)$ of the same HMA mix compacted in different $\mathrm{SGCs}$. These differences are hypothesized to be, in part, due to different internal gyration angles between $\mathrm{SGCs}$. In response, a dynamic angle verification (DAV) procedure has been used to measure and verify the internal gyration angle during compaction. $\mathrm{SGCs}$ 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 $G_{\mathrm{mb}}$ 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 $\mathrm{SGCs}$ evaluated.