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The procedure proposed in the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures (referred to as MEPDG) heavily depends on the characterization of the fundamental engineering properties of paving materials. This paper presents the results of a project aimed at the characterization of hot-mix asphalt (HMA) in accordance with the procedure established by MEPDG to support its implementation in Virginia. The project examined the dynamic modulus, the main HMA material property required by MEPDG, as well as creep compliance and tensile strength, which are needed to predict thermal cracking. Loose samples of 11 mixes (four base, four intermediate, and three surface mixes) produced with PG 64-22 binder were collected from different plants across Virginia. Representative samples underwent testing for maximum theoretical specific gravity, asphalt content by the ignition oven method, and gradation of the reclaimed aggregate. Specimens for the various tests were then prepared by use of the Superpave® gyratory compactor. The test results showed that the dynamic modulus is sensitive to the mix constituent properties (aggregate type, asphalt content, percentage of recycled asphalt pavement, etc.) and that even mixes of the same type (SM-9.5A, IM-19.0A, and BM-25.0) had different measured dynamic modulus values. The Level 2 dynamic modulus prediction equation reasonably estimated the dynamic modulus measured; however, it did not capture some of the differences between the mixes found in the measured data.

Performance mix design (PMD) of asphalt mixtures, often referred to as balanced mix design, is a design methodology that incorporates performance testing into the mix design process. The Virginia Department of Transportation (DOT), like many owner agencies, is interested in ways to specify asphalt mix designs better in an effort to make its roadway network more sustainable, longer lasting, and more economical. By adding performance criteria through a PMD framework, that goal can be achieved. Further, a PMD framework should allow for the development of new, innovative methods to increase pavement recyclability, new performance additives, and other means to enhance pavement performance. This paper provides details and documentation of the approach being taken by the Virginia DOT in their efforts to develop a PMD specification. Aspects of development presented include PMD method options, selection of performance tests, and determination of acceptance criteria. A discussion about validating specifications with in-service performance data and addressing quality control and quality assurance is also provided. Although additional work is needed for full development and implementation, the methodology being applied has been found to provide useful outcomes for the Virginia DOT even in the initial stages of development.

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This study evaluated the rutting resistance of plant-produced asphalt concrete (AC) mixtures in the laboratory. Nineteen plant-produced AC mixtures were used; these mixtures contained reclaimed asphalt pavement (RAP) amounts that ranged from 0% to 25%. Tests on the mixtures included the dynamic modulus (|E*|) test at multiple temperatures and the flow number (FN) test at 54°C to characterize stiffness and rutting resistance, respectively. Mixtures that contained no RAP showed |E*| values comparable to those that contained 25% RAP in most cases. For most of the 19 mixtures tested, mixtures with lower FNs either contained no RAP, contained 25% RAP, or had PG 64-22 as the design binder grade. Mixtures that contained moderate amounts of RAP (10% and 15%), regardless of design binder grade, had higher FNs than mixtures with either high or low RAP amounts. Statistical analysis showed that the RAP amount was the most significant factor to affect rutting resistance in the mixtures studied. A linear inverse relationship between RAP and FN appeared to describe the data well. As the RAP amount increased, a downward trend occurred in both effective binder content (Pbe) and rutting parameter (G*/sin δ). The effect of RAP on FN was unexpected, because it showed the rutting resistance to decrease with increased RAP. Possible reasons might have been the use of softer asphalt binder in mixtures with higher RAP and the observed decrease in both Pbe and G*/sin δ with increased RAP amounts. More rutting-related mechanistic studies are needed of AC mixtures that contain RAP.