Contribution of Fine Aggregate Angularity and Particle Shape to Superpave Mixture Performance

Abstract

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.

Sensitivity of HMA Performance to Aggregate Shape Measured Using Conventional and Image Analysis Methods

“…Fine aggregate angularity test cannot always discern between poor and good performing aggregates (Huber et al, 1998). This is due to the fact that packing properties (i.e uncompacted voids) of aggregate are not only a function of angularity, but are also affected by surface texture, gradation, and aggregate specific gravity.…”

Unified Imaging Approach for Measuring Aggregate Angularity and Texture

“…Recent experience with the current FAA criteria indicates that there are cases where the test does not discern poor-quality from high-quality fine aggregate. 14 There are crushed fine aggregates that fail to meet the FAA criteria. 9 Therefore, it is of importance to develop methods that can accurately and rapidly quantify fine aggregate properties.…”

Avaliação do método Bailey de seleção granulométrica de agregados para misturas asfálticas

“…Desenvolveu métodos de análises de materiais betuminosos e misturas asfálticas com base em propriedades fundamentais, diretamente relacionadas com o desempenho dos pavimentos em serviço. As misturas Superpave são dosadas volumetricamente, sendo controladas por propriedades dos agregados e pelo equilíbrio dos volumes de vazios, de asfalto e de agregados (HUBER et al, 1998). et al, 1995).…”