Establishment of the Precision of a Rapid-Angle Measurement Device for Superpave Gyratory Compactors

Abstract

Superpave^® hot-mix asphalt (HMA) specimens are compacted in the laboratory with the Superpave gyratory compactor (SGC) through pressure and an applied angle of gyration. The original compaction specification for the SGC requires the angle of gyration to be 22 ± 0.35 mrad (1.25 ± 0.02 degrees), measured externally to the compaction mold. Questions concerning the ability of different compactors to produce HMA specimens of the same mix with the same density led to the development of the dynamic angle validation (DAV) kit, which measures the angle of gyration internally (on the inside of the mold). The DAV procedure requires the use of HMA to measure the internal angle of gyration. Because of practical limitations of performing measurements with HMA and questions concerning the “proper” HMA mix to use in the measurements, a device–-the rapid-angle measurement (RAM)–-was introduced to simulate effectively the load placed on the SGC by an HMA specimen. An interlaboratory study was conducted in accordance with ASTM E691-99 to establish the precision of the internal angle measurement provided by the RAM. A total of 11 RAM units and five SGC models were included in the study. On the basis of the study data, estimates were developed of both repeatability (within lab) and reproducibility (between lab) for the RAM device for all five SGC models. It is recommended that all devices with the reported ability to measure internal angle of gyration be subjected to a similar interlaboratory study to compare devices on an equal basis.

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