Volume 3, Issue 8 (September 2006)
Superpave and the Aggregate Industry
The Superior Performing Asphalt Pavement (Superpave) mix design system was developed under the Strategic Highway Research Program, which was completed in 1993. Superpave consists of new methodologies for evaluation and selection of hot mix asphalt (HMA) material constituents along with new laboratory compaction protocols. During Superpave development, significant research focused on the performance grade asphalt binder system and gyratory compaction development. In contrast, very little research was performed to determine those aggregate properties and specification requirements most closely related to HMA mix performance. In 2000, the aggregate industry prepared a white paper for, and at the request of, the Transportation Research Board Expert Task Group on Superpave Mixtures and Aggregates. The paper focused on discussion of aggregate related issues that presented challenges to the implementation and use of Superpave. Since the white paper was written, Superpave has undergone modifications (specifications and general use or practice) based on completed research and general knowledge obtained. Many Superpave modifications were addressed in varying degrees in the white paper, and it is now important to discuss the impact of these modifications on HMA performance and the aggregate industry. In addition, other aggregate related issues are presented and discussed, including inconsistent fine aggregate definition, influence of minus 0.075 mm sieve material on fine aggregate specific gravity determination, aggregate production and particle shape, and the influence of aggregate on dynamic modulus.