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The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


Investigation of Optimized Mixture Design for Superpave Surface Mixtures
Year: 2010
VTRC No.: 11-R5

Since the adoption of the Superpave asphalt mixture design, it has been suspected that mixtures have been deficient in asphalt content, even though some changes have been made in the design specifications.  The primary purpose of this study was to determine if Virginia’s current Superpave mixtures are deficient in asphalt and if they are to determine ways to remedy the situation.

 Analysis of current 9.5 mm mixture production data and production data of similar mixtures produced prior to the adoption of Superpave revealed no significant difference in asphalt content.  Gradation differences may have affected these results.  Additional analysis of the production 12.5 mm mixtures possibly over certain time intervals is recommended.  Analysis of several mixtures in the laboratory revealed that some mixtures may be able to tolerate more asphalt, thereby improving durability; however, additional asphalt would be detrimental to the performance of other mixtures. 

 Based on the findings of this study, the Virginia Department of Transportation’s specifications regarding mixture design should not be changed at this time, but additional research work is justified.