Laboratory Characterization of Additive-Modified Asphalt Concrete Mixtures

There is a need for a more rapid system of evaluation and implementation for new and existing asphalt additives, especially because of the prohibitive cost of full-scale performance evaluations. To help to meet this need, the Additive Group (AG) experiment at the National Center for Asphalt Technology (NCAT) was developed and began in 2021. A comprehensive laboratory evaluation of six mixtures, each modified with a popular additive type selected by the AG state DOT sponsors, was conducted. Simultaneously, full-scale test sections were constructed at the NCAT test track to evaluate the field performance and structure behavior of each modified mixture. Trafficking of these test sections is currently underway, and estimated to be completed in 2024, at which point an investigation linking the laboratory and field results will be done. This paper presents the completed laboratory evaluation of each AG mixture via complex dynamic modulus (E*), direct tension cyclic fatigue, and bending beam fatigue testing. The wet-process rubber modified mixture was found to have reduced E* and initial flexural stiffness, but increased fatigue resistance, relative to the styrene-butadiene-styrene (SBS)-modified control mixture. The dry-process rubber-modified mixture displayed similar trends, though to a lesser degree. Conversely, the dry-process plastic-modified mixture was found to have increased E* and initial flexural stiffness, but reduced fatigue resistance, relative to the SBS-modified control mixture. The other AG mixtures-a dry-process fiber and a wet-process plastic-modified mixture-were found to display E*, initial flexural stiffness, and fatigue resistance similar to that of the SBS-modified control mixture.