Mechanical Mixture Simulation Devices for Determining and Calibrating Internal Angle of Gyration in Superpave Gyratory Compactor

Since 1993, asphalt technologists have recognized the importance of maintaining a tight tolerance on the angle of gyration used in the Superpave^® gyratory compactor. Small changes in angle were shown to affect significantly the percentage of air voids in a compacted mix specimen and, in the design phase, to affect the design asphalt binder content. Through the years since its implementation, there have been significant advancements in the understanding of the Superpave gyratory compactor. Implementation research indicated that the internal angle of gyration was the compaction parameter of importance and that it did not directly relate to the measured external angle of gyration. Continuing to seek improvements in reproducibility of test results, the industry developed several devices that mechanically simulate the stiffness of an asphalt mixture so that determination and calibration of the internal angle of gyration can be accomplished without the necessity of compacting mixture specimens. The purpose of this research was to improve the determination and subsequent calibration of the dynamic internal angle of gyration for the Superpave gyratory compactor by evaluating the use of the mechanical mixture simulation devices. The results of the research indicate that mechanical mixture simulation devices can be used to effectively determine and calibrate the internal angle of gyration. By streamlining and standardizing the process for determining and calibrating the internal angle, it is expected that the variation in the bulk specific gravity (or percentage of air voids) of a compacted mixture specimen between user agencies and producers will be significantly reduced.