Transitioning from Texas Gyratory Compactor to Superpave Gyratory Compactor

The Strategic Highway Research Program expended great effort in developing the Superpave^® gyratory compactor (SGC) as a modern, technologically advanced tool for the design of hot-mix asphalt (HMA) paving mixtures and for preparation of realistic test specimens for laboratory evaluation. Since the widely accepted SGC was designed to produce specimens similar to actual pavement layers and since the current series of Texas Department of Transportation (TxDOT) HMA paving mixtures have demonstrated acceptable performance, TxDOT wished to replace the Texas gyratory compactor (TGC) with the SGC for the design of its current repertoire of dense-graded mixtures. In the first phase of this study, the authors developed a specification for the number of design gyrations with the SGC to achieve the same optimum asphalt content (OAC) as that obtained with the TGC. However, on the basis of past experience, review of the literature, and feedback from TxDOT, the design OAC was considered to be too low; mixtures that may be susceptible to fatigue cracking resulted. To mitigate this problem, the authors revised the specification for use of the SGC so that the resulting mixtures had an increased OAC. This revision was done by comparing the rutting resistance of HMA mixtures designed at different numbers of gyrations with the Hamburg wheel-tracking device and then selecting the lowest number of gyrations that did not compromise rutting resistance of the mixture. Results show that it is possible to select a considerably lower number of design gyrations with the SGC without a significant decrease in rutting performance of the mixtures.