Effect of Gradation Characteristics on Performance of Superpave Mixtures in the Field

Previous studies have indicated that existing mix design criteria, including voids in mineral aggregates, gradation control points, and effective asphalt content, do not capture all critical aspects of gradation and mixture volumetric properties found to be strongly related to rutting and cracking performance. The performance of Superpave^® mixtures varied significantly in mixtures that met all existing criteria. Therefore, there was a need to identify and verify additional criteria that could ensure better and more consistent performance of Superpave mixtures. Four parameters from the dominant aggregate size range (DASR)– interstitial component (IC) model have been determined to relate well to field performance of Superpave mixtures: DASR porosity, disruption factor (DF), effective film thickness (EFT), and the ratio of coarse portion to fine portion of fine aggregate (CFA/FFA). These four parameters were used in a field performance evaluation of rutting and cracking that was conducted to identify performance-related criteria. Results indicated that DASR porosity, which reflected the characteristics of coarse aggregate structure, was the most dominant parameter to control rutting performance. IC characteristics including DF, EFT, and CFA/FFA could not overcome the problems associated with a mixture that had DASR porosity outside the acceptable range. However, IC characteristics were more important than DASR porosity to differentiate clearly field cracking performance. The DF criteria should be considered in conjunction with EFT and CFA/FFA criteria to distinguish effectively the field cracking performance. Therefore, the introduction of DASR-IC criteria into current mix design guidelines and specifications will help to ensure good field rutting and cracking performance of Superpave mixtures.