Investigation of factors related to rutting of bituminous aggregate mixes

Soon after 1980, wheelpath rutting in asphalt pavements came to be recognized as a problem confronting the Montana Department of Highways. By 1982, it became clear that the rutting was not limited exclusively to older pavements, but was also occurring in a significant portion of the newer pavements, both overlays and new construction. To address this problem a number of improvements were implemented. Although these anti-rutting specifications reduced rutting, the problem of pavement rutting was still occurring in some of the newest pavements in 1985. Starting in 1986, several bituminous plant mixtures were tested to develop formulations for rut resistant bituminous pavements. Supplemental design criteria and construction specifications to eliminate or reduce rutting of future bituminous pavements were developed. The variables investigated were aggregate gradation and asphalt additives. Testing covered tensile strength, creep, binder properties, and Marshall stability. Results are presented in this report.