Contribution of fine aggregate angularity and particle shape to Superpave mixture performance

The Superpave system is being implemented by state highway agencies. Many states implemented the asphalt binder specification during 1997. The volumetric mix design system, however, is being actively implemented. By the end of 1997, more than 200 Superpave projects had been built in the United States. As states consider specification changes necessitated by Superpave implementation, some questions are being raised. Fine aggregate angularity (FAA) requirements, one of the aggregate consensus properties, has generated considerable debate in some areas of the country. Adopting an FAA requirement of 45 percent for high traffic pavements has changed the number of sources available for asphalt mixtures. Superpave also provides a limit on flat and elongated particles. The aggregate properties requirements have increased interest regarding the basis of the specification and the values specified. The results of a limited cooperative study by industry and agencies to evaluate the role of FAA and particle shape on asphalt mixture properties are presented. A Superpave mixture design for high equivalent single-axle loads was evaluated. The fine aggregate used in the mixture design, with an FAA of 48, was replaced by other fine aggregates with lower FAA values. Properties of the mixtures containing the different fine aggregates were evaluated by using the asphalt pavement analyzer, the couch wheel tracker (a variation of the Hamburg rut tester), and the Superpave simple shear tester. A study to evaluate the sensitivity of the Superpave gyratory compactor and the Superpave mixture design system to differences in particle shape also is presented.