Investigation of large-stone mixtures

This report presents the results of a one-year study on large-stone asphalt mixtures (LSAM). A thorough review of the existing technology regarding materials, mix design, and performance is included. This study expanded upon the body of knowledge by exploring an easier means of mixture design and explaining the fundamental properties of large-stone mixtures with respect to the aggregate gradation. It was found that a dense LSAM gradation possesses better strength and durability properties than a more open LSAM gradation. Furthermore, a mix design methodology is presented wherein the optimum asphalt content for the mixture may be determined on the basis of aggregate and compacted sample properties. This eliminates the need for cumbersome Marshall stability and flow measurements. The frequency dependency of large-stone mixtures is more pronounced at low temperatures than that of a conventional mixture. The tendency for thermal cracking should be lower for a LSAM than for a conventional mixture. Finally, recommendations are made to develop a permissive specification for LSAM, and to adopt the volumetric mixture design procedure outlined in the report.