Packing Theory and Volumetrics-Based Aggregate Gradation Design Method

Current gradation design in Superpave mix design method is an empirical-based trial-and-error method, which is costly and time-consuming. Moreover, few mechanical properties have been evaluated during the mix design to assist the mix optimization. This paper describes a novel aggregate gradation and asphalt mixture design concept that estimates the target gradation and optimum asphalt content at an early stage. Voids in mineral aggregate (VMA) is used as a media to link the properties of aggregates and asphalt binder to their engineering properties based on an analysis of aggregate packing. A design example is provided to describe the new design method step by step. As a fast and simple design method, it helps to evaluate the quality of an existing gradation and mix design, and adjust the gradation to satisfy both volumetrics and mechanical properties. With local material calibration to take into account the variation in aggregate shape and angularity, and validated in seven different projects of Washington State, this method can be integrated together with the balanced mix design concept as a convenient practical and research tool to achieve better designs that not only satisfy the performance test but also meet the volumetrics criteria.