Evaluation and Selection of Aggregate Gradations for Asphalt Mixtures Using Superpave

Abstract

The design of asphalt mixtures is a complex process that requires the proper proportioning of materials to satisfy mixture volumetric and mechanical properties. The majority of time spent in the mix design process is used in evaluating and selecting aggregate gradations to meet project requirements. The latest set of requirements for asphalt mixtures is the Superpave system, developed during the Strategic Highway Research Program. This system incorporates materials selection, evaluation of trial aggregate structures, selection of design asphalt binder content, moisture sensitivity, and, in some cases, determination of performance properties of the selected asphalt-aggregate blend. The selection of a design aggregate structure reduces to selecting an aggregate gradation that will meet minimum volumetric and densification criteria, and selecting an aggregate structure that will provide adequate resistance to permanent deformation, fatigue, and thermal cracking. In the Superpave volumetric mix design process, achieving voids in mineral aggregate (VMA) is the most difficult task facing the mix designer. One phase of this evaluation focuses on providing Guidelines to achieve VMA requirements with Superpave mix designs. This phase was accomplished by evaluating the existing database of information on Superpave mix designs at the Asphalt Institute. The second phase examines the relationship between properties determined during the Superpave volumetric mix design process, and material properties determined by mix analysis tests.