Development of a Rational Method of Designing Hot Mix Asphalt (HMA) for Low Volume Roads

Nanagiri, Yamini Varma

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Development of a Rational Method of Designing Hot Mix Asphalt (HMA) for Low Volume Roads

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The Superpave mix design system is being adopted by most of the states in the Unites States. Since the Superpave system was developed on the basis of data mostly obtained from medium to high traffic volume roads, there is a need to develop criteria for mix design for Hot Mix Asphalt (HMA) mixes for low traffic volume roads. In this study funded by the six New England states, research was carried out to develop a proper mix design system for low volume roads from the standpoint of durability properties and then, once a good mix design system was available, check it to determine if it meets required strength properties. For low volume roads the performance is primarily affected by the environment and not by traffic, the approach in this study has been to determine the optimum value of a key volumetric property and an optimum number of design gyrations for producing compacted HMA mixes with adequate resistance against aging/high stiffness related durability problems. Six mixes were obtained in which only one can be characterized as a fine mix, and the remaining five were all relatively close to the maximum density line - three of them were with 9.5 mm Nominal Maximum Aggregate Size (NMAS), and the other two were with 12.5 mm NMAS. Based on the results from performance testing, film thickness of 11 microns in samples compacted to 7 percent voids was found to be desirable from considerations of stability and durability and a design VMA of 16 percent was determined to be optimum for producing durable and stable mixes for low volume roads. Results from testing of in-place mixes from good performing 10 to 12 year old low volume roads indicated a design gyration of 50 for obtaining a void content of 4 percent for mixes with gradations close to the maximum density line.

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