United States Department of Transportation
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Optimization of Asphalt Mixture Design for the Louisiana ALF Test Sections
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2018-05-01
[PDF-1.49 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance
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Abstract:This research presents an extensive study on the design and characterization of asphalt mixtures used in road pavements. Both mixture volumetrics and physical properties obtained from several laboratory tests were considered in optimizing the mixture design. The research was divided into two phases. Phase 1 included the design and detailed analysis of compaction and performance characteristics of asphalt concrete mixtures, where aggregate structures were designed using an analytical aggregate blending method. In this study, Bailey Method which is a comprehensive gradation based mixture design method was selected. Three types of aggregate (i.e., limestone, sandstone, and granite) were considered and three different aggregate structures for each aggregate type were designed using this Bailey Method. All the aggregates were crushed aggregates. Sandstone and granite mixtures had a nominal maximum aggregate size (NMAS) of 12.5 mm and were designed for high traffic level, while two types of limestone mixtures were designed (25.0-mm and 12.5-mm NMAS) for two traffic levels (high-and low-traffic volumes). For the heavy traffic mixtures, the asphalt binder type selected was PG 76- 22M while PG70-22M was used for low-volume mixtures. In Phase 2, further evaluation of the mixtures selected in Phase 1 was conducted with the consideration of specific attributes. The concept of locking point was adopted in modifying the current Superpave mixture design method, in order to improve the durability of the mixtures without compromising the stability. The outcome of this research suggests that suitable mixes with dense aggregate structures can be developed using the Bailey Method of aggregate gradation, providing good resistance to permanent deformation while still maintaining adequate levels of durability. A systematic and simplified design approach in which asphalt mixtures were designed based on the locking point concept, analytical aggregate gradation method, and fundamental mechanistic properties is also recommended.
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