Large-stone mixes are becoming a very popular means for reducing rutting in flexible pavements. Aggregate interlock in large-stone mixes provides for very efficient dissipation of compressive and shear stresses that are known to be responsible for rutting and shoving in flexible pavements. This report documents mix design procedures and laboratory testing for characterization of rutting potential of large-stone asphalt mixes (LSAM) in Kentucky and particularly the Louisa Bypass project.

A series of large-stone aggregate gradations were studied. A promising aggregate gradation was selected in cooperation with Kentucky Department of Highway officials and representatives of the asphalt industry. Based upon the findings of this study, several test sections were constructed on coal-haul corridors throughout the Commonwealth of Kentucky. LSAM sections have been in service for less than one year, and conclusions on the performance of these mixes would be premature. It is important, however, to note that conventional asphalt mixtures on pavements subjected to heavy tTuck traffic in Kentucky usually exhibit severe rutting after only a few months in service. In this respect, one may conclude that LSAM projects have performed well. Performance-oriented laboratory test results indicate that higher levels of structural capacity and rutting resistance, as compared to conventional hot mix asphalt, may be achieved by using the LSAM in flexible pavements. A field trial followed the laboratory investigations. Construction of the Louisa Bypass, which is located in the mountainous region of eastern Kentucky, was studied. Recommendations presented in this report for construction of Large-stone mixes in heavy haul roads are based upon information obtained from the Louisa Bypass.

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