DESIGN OF SUPERPAVE HMA FOR LOW VOLUME ROADS

The Superpave mix design system is being adopted by most of the states in the United 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 research was carried out to develop a proper mix design system for low volume roads from the standpoint of durability 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. Three 9.5 mm Nominal Maximum Aggregate Size (NMAS) and two 12.5 mm NMAS fine graded mixes were tested during this research. Based on the results from performance testing, film thickness of 11 microns in samples compacted to 7% voids were found to be desirable from a stability and durability standpoint. A design voids in mineral aggregate (VMA) of 16% was determined to be optimum value 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% for mixes with gradations close to the maximum density line.

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