Impact of Gyration Reduction and Design Specification Changes on Volumetric Properties of Virginia Dense-Graded Asphalt Mixtures

Abstract

In 2015, the Virginia Department of Transportation (VDOT) proposed changes to their specification for asphalt mix design. The changes incorporated a reduction of design gyrations from 65 to 50; the addition of constraints on the No. 4 (4.75 mm) and No. 30 (600 µm) sieves; and adjustments to the production value for voids filled with asphalt and minimum voids in mineral aggregate. Before these modifications were fully adopted, a study was performed to assess the effect of the changes on mixture properties and laboratory performance. Eleven pairs of asphalt mixtures were evaluated; the pairs consisted of a typical VDOT 65-gyration mixture produced under the specification current at the time and a companion 50-gyration mixture designed and produced in accordance with the proposed specification. Mixtures were evaluated to determine the effect of the design parameters on volumetric properties, gradation, and permeability. The changes had very little effect on volumetric properties or gradation. Permeability effects were mixed, with 9.5 mm nominal maximum aggregate size mixtures requiring greater compaction to meet permeability requirements and 12.5 mm nominal maximum aggregate size mixtures showing improved permeability even at higher air-void contents. For the 50-gyration mixtures, core air voids were reduced, indicating the potential for increased durability attributable to improved densification in the field.