Evaluation of Simulated Load Techniques for Determining the Internal Angle of Gyration for the Superpave Gyratory Compactor

Abstract

Recently concerns have arisen regarding the inability of different Superpave gyratory compactors (SGC) to produce hot-mix asphalt (HMA) specimens with similar density. One proposed solution led to the development of the Dynamic Angle Validation (DAV) kit which measures the angle of gyration internally to the mold. DAV requires the use of HMA for the angle determination; logistical concerns and other issues led to the introduction of devices to mechanically simulate the load placed on the SGC by the mix being compacted. Two such devices – the Rapid Angle Measurement (RAM), which uses invelop load simulation (ILS) technology, and the Hot-Mix Simulator (HMS) – are described. Both simulation systems appear sound and applicable. Outstanding issues include SGC frame stiffness, the use of “cold” versus “hot” molds, comparisons of measurement systems, and the precision of internal angle measurements. Frame stiffness effects may require SGC calibration specifications to specify or reference the applied loading used. Internal angle measurements using simulated loading may be made with SGC molds at room temperature. The two proposed simulated loading methods may not yield the same value for internal angle on all SGC models. A definitive relationship between HMA stiffness and applied load to the SGC must be established to enable comparisons between internal angle measurements taken using hot-mix asphalt and taken using simulated loading.