Optimized Mix Design Approach— Contractor’s Perspective

Abstract

Mix durability related performance issues have been observed in recent years with a commonly reported contributing factor being a deficiency in mix asphalt binder content. In many instances, these performance issues are occurring with mixes that have met all governing mix specifications. As a result, asphalt mix specifications are changing rapidly as agencies search for solutions to improve durability. Lower design gyrations (Ndesign), lower target air voids, and increased voids in the mineral aggregate (VMA) are among the implemented specification modifications. Often, individual specification changes are implemented without evaluating their potential conflict with other specification items or at a rate that makes establishing true “cause and effect†on mix performance difficult or impossible to determine. Oldcastle Materials recognizes the need for improved mix performance and has developed a framework for an Optimized Mix Design Approach (OMEGA) in which innovation and mix engineering efforts are emphasized. The ultimate design approach objective is determining the optimum mix binder content for the specific mix design application (e.g., design traffic, pavement layer location, climate, etc.). This is accomplished through an enhanced materials evaluation and selection process, along with appropriate performance testing (stability and durability/cracking) to help ensure the desired end result performance is provided by the designed mix.