Volumetric Properties of Superpave Mixtures with Reclaimed Asphalt Pavement

Abstract

The Superpave mix design process involves finding optimum asphalt content for a specified gradation that would result in desired percent air voids, voids in mineral aggregates (VMA), voids filled with asphalt (VFA), dust proportion, and percent maximum specific gravity (Gmm) at Nini and Nmax. The mix design criteria include a minimum VMA to ensure durability. The other related volumetric parameters are VFA and dust proportion. Bulk specific gravity (Gsb) of the blended aggregates is needed to calculate VMA and subsequently VFA, and dust proportion. With Reclaimed Asphalt Pavement (RAP) becoming more popular and with a higher and higher percentage of it being used in Superpave mixtures, precise RAP bulk specific gravity (GRAPsb) is essential for designing durable Superpave mixtures. The FHWA-recommended method for calculating RAP aggregate Gsb is based on a number of assumptions including asphalt absorption of the aggregates. In this study, Superpave mixtures with 20, 30, and 40 percent RAP and fractionated RAP were tested to find out how these assumptions can influence volumetric properties of the Superpave mixtures with high RAP content. In addition, Gsb tests were conducted on the aggregates obtained from the solvent extraction and ignition burn-off methods. The calculated volumetric properties were compared with the results from that obtained using GRAPsb from the FHWA-recommended method. The results show that volumetric properties obtained from two test methods can vary significantly.