Interstitial component characterization to evaluate asphalt mixture performance

The importance of having an adequate aggregate particle distribution for asphalt mixture rutting and cracking performance has been well established on the basis of experience and is well documented in the literature. Typically, aggregate gradation is selected to meet Superior Performing Asphalt Pavements (Superpave) mix design specification however, many mixtures that meet Superpave criteria have not exhibited good field performance.Recently a conceptual and theoretical approach to evaluate coarse aggregate structure based on packing theory and particle size distribution was developed. The range of particle sizes determined to form an interactive network was referred to as the Dominant Aggregate Size Range (DASR) and its porosity must be no more than 50% for the particles to be in contact with each other. The material (asphalt, aggregate and air voids) that exists within the interstices of the DASR was referred to as the Interstitial Component (IC).The main purpose of this study was to enhance understanding of how asphalt mixture performance is affected by changes in IC. Two known good mixtures (according to DASR criterion) were selected as a reference and then modified to assess a broad range of IC gradations from very coarse IC to very fine IC.Laboratory results from Superpave Indirect Tension Test (IDT) and Asphalt Pavement Analyzer (APA) tests clearly showed that IC characteristics have a very significant effect on rutting and cracking performance of HMA even when both DASR porosity and the percentage passing Particle packing theory and volumetric properties of aggregates were used as the basis to define Disruption Factor (DF), which is the ratio between the volume of potentially disruptive IC particles and the volume of DASR voids. DF was conceived to evaluate the potential of IC aggregates to disrupt the DASR structure. DF was calculated for an extensive range of asphalt mixtures including laboratory mixtures and field sections from Superpave projects in Florida, National Center for Asphalt Technology NCAT, and Westrack. DF satisfactorily distinguished poor performing mixtures therefore, it may eventually be used as a design parameter for rutting and cracking resistant asphalt mixtures.