United States Department of Transportation
i
Optimizing laboratory mixture design as it relates to field compaction to improve asphalt mixture durability.
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2015-11-01
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[PDF-8.87 MB]
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Edition:Final report
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Abstract:Most departments of transportation, including Indiana, currently use the Superpave mixture design method to design asphalt mixtures.
This method specifies that the optimum asphalt content for a given gradation be selected at 4 percent air voids. During construction,
these mixtures are typically compacted to 7‐8 percent air voids. If mixtures were designed to be more compactable in the field they
could be compacted to the same density as the laboratory mixture design, which would increase pavement durability by decreasing the
in‐place air voids. The objective of this research was to optimize the asphalt mixture design in order to increase in‐place asphalt
pavement durability without sacrificing the permanent deformation characteristics of the mixture.
Three asphalt mixtures were designed using the standard Superpave design method at 100 gyrations of the Superpave Gyratory
Compactor, suitable for traffic levels of 3 to 30 million Equivalent Single Axle Loads. Each mixture was then used as a starting point to
design three additional mixtures using 70, 50, and 30 gyrations, with optimum binder content chosen at 5 percent air voids, rather than
the currently specified 4 percent. The effective asphalt content was held constant for the original and redesigned mixtures. Permanent
deformation characteristics of the sets of four mixtures were determined by measuring the dynamic modulus and flow number. The
results suggest that the mixture designs produced using 70, 50, and 30 gyrations had permanent deformation characteristics equal to or
better than the original 100‐gyration mixtures.
Based on the laboratory test results, two field trials were placed evaluate the design method, ease of construction and to compare the
construction results of the re‐designed and original mixtures. Samples from both projects were collected during construction, test
specimens compacted, and additional physical testing completed. The field trial results suggest that it is possible to place a mixture at 5
percent air voids and that mixtures designed at 5 percent air voids should have equivalent performance to those designed at the
conventional 4 percent air voids.
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