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This research project investigates the level of Voids in the Mineral Aggregate (VMA) in Minnesota paving projects. Researchers analyzed 10 paving projects from 1996 to determine if a VMA decrease occurred, the magnitude of the decrease, and the potential causes of the decrease. Potential causes include the generation of fines, high-production temperatures, and long storage or cure times. Three of the 10 projects had a VMA decrease of 1.9 or more. These three projects also had the highest plant temperatures and fairly long storage times, which makes increased asphalt absorption a likely cause of the VMA decrease. Five projects showed a moderate drop in VMA. Most had some increases in fines, and some had moderately high plant temperatures and storage times. The two projects with little or no change in VMA had very little change in gradation, and moderate to low plant temperatures and storage times.

The research performed for this report was intended to recommend alternative mix design procedures and parameters for evaluation of asphalt mixture sensitivity, with more of an emphasis on volumetric relationships. Three Mn/DOT projects were selected to represent the following durability issues: 1) debonding of asphalt from aggregate, 2) cohesion problems, and 3) mix design problems. Materials were obtained from these construction projects and evaluated in the laboratory. Gradations were varied from the project specifications so that mixtures with more and less asphalt were evaluated along with the project mixture. Testing included the temperature susceptibility and moisture sensitivity of the mixtures, in addition to the net adsorption test on the aggregates. The results suggested means for identifying moisture sensitivity mechanisms in mixtures during the mixture design phase, although these need to be confirmed through more extensive investigation. Aggregate mineralogy, gradation, and mixture proportioning can all play a role in improving the durability characteristics of asphalt mixtures. Recommendations are made for continued research and implementation of an improved approach to asphalt mixture design.