Effect of Specimen Size on Compaction and Volumetric Properties in Gyratory Compacted Hot-Mix Asphalt Concrete Specimens

Abstract

Gyratory compaction is the centerpiece of the Strategic Highway Research Program asphalt mixture design procedure Superpave. A number of factors could potentially affect the behavior of asphalt mixes in the gyratory compactor. One of these is specimen size. Four specimen sizes each of one unmodified and two rubber-modified hot-mix asphalt concrete mixes were compacted in the Superpave gyratory compactor to determine the effect of specimen size on compaction and volumetric properties of the mixes. All specimens were compacted using a 150-mm-diameter mold. Specimens of each of the mix types were prepared using three gradations and three binder contents. Densification curves and plotting number of gyrations versus percent of theoretical maximum density were developed for each mix type/gradation/binder content combination. A strong trend in the densification data was observed, in which curves representing specimen sizes of 3500, 5000, and 6500 g were grouped together, apart from the curve representing a 2000-g specimen size. This trend, the grouping of larger specimen data apart from small specimen data, was also observed in volumetric data (optimum asphalt content, voids in mineral aggregate, and voids filled with asphalt). These trends were observed in most of the mix type/ gradation/binder content combinations. The data presented suggest that for specimens of sufficient size, for example, greater than 3500 g, specimen size does not significantly affect the volumetric or compaction properties of hot mix specimens, which supports the ruggedness of the gyratory compaction procedure.