Design of TxDOT Asphalt Mixtures Using the Superpave Gyratory Compactor (0-4203-1)

The primary objective of this project was to develop laboratory protocols for nusing the Superpave gyratory compactor (SGC) in place of the Texas gyratory compactor (TGC) to design essentially all of the Texas Department of Transportation (TxDOT) dense-graded hot mix asphalt (HMA) paving mixtures. The specific goal was to recommend a design number of gyrations (Ndesign) using the SGC for each TxDOT mixture type that will most closely simulate a mixture formerly designed using the TGC (Tex-204-F). TxDOT HMA mixtures included Type A, Type B, Type C, Type D, Type Course Matrix High Binder CMHB-C, and Type CMHB-F. Researchers conducted the experiment in four steps including 1) SGC compaction of plant mixed materials, 2) SGC compaction of laboratory mixed materials, 3) determination of optimum asphalt content using the SGC, and 4) indirect tension testing of mixtures. The number of SGC gyrations that most closely simulated the TGC design for each mixture type was recommended. Researchers discovered that the TGC and the number of SGC gyrations to match the TGC were producing mixtures with comparatively low asphalt contents that may yield poor performance. Therefore, Phase II was developed and implemented to determine an acceptable SGC design procedure using fewer gyrations than those proposed following Phase I. In both phases, more than 60 HMA mixture designs with related materials that had been designed by TxDOT personnel using the TGC were studied using the SGC. Phase II determined that mixtures indicating good performance in the Hamburg test can be designed using a considerably lower number of SGC gyrations than the number that will match optimum asphalt contents from the TGC. The final recommended SGC design gyrations should accommodate adequate asphalt in the mixture to improve resistance to cracking, raveling, and aging as well as decrease permeability while providing acceptable rutting resistance.