Laboratory and Field Characterization of Additive-Modified Asphalt Concrete Mixtures

Abstract

There is a need for a more rapid system of evaluation and implementation for new and existing asphalt additives, especially due to 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. A comprehensive laboratory evaluation of six asphalt mixtures has been completed. Each mixture was modified with a popular additive type that was selected by the AG’s state DOT sponsors. Simultaneously, full-scale test sections were constructed at the NCAT Test Track to evaluate the field performance and structural behavior of each modified mixture. Trafficking of these test sections began in the Fall of 2021 and is currently underway at the writing of this thesis. Trafficking is estimated to be completed in 2024, at which point a framework for rapid additive evaluation, the primary goal of the AG experiment, will be developed. This thesis presents the completed laboratory evaluation of each AG mixture via dynamic modulus (E*), direct tension cyclic fatigue, and bending beam fatigue testing. Additionally, pavement layer strain response measurements, performance data (rutting, cracking, and ride quality), and backcalculated layer moduli gathered from the full-scale test sections are presented within this thesis. All Test Tack data presented was gathered from the beginning of trafficking through June 2023. Relevant links between the laboratory and field-testing results were established. Finally, a layered-elastic simulation tool was used to model strain responses of the pavement sections using their in-situ layer moduli and surveyed layer thicknesses. Key findings within this thesis included the following: For the AG mixtures, average initial flexural stiffness provided a better correlation with backcalculated pavement modulus and measured pavement strain response in comparison to average dynamic modulus (E*). WESLEA simulated strain responses (using the surveyed layer thicknesses and backcalculated layer moduli for each test section) closely approximated the measured strain responses (with the exception of the control section). Through June 2023, the Sapp parameters computed for each AG mixture have not provided good agreement with the observed levels of cracking in the field. However, computing the number of cycles to failure (Nf) for each mixture, using its individual fatigue life transfer function (from beam fatigue testing) and its average measured thickness- and temperature-corrected strain response (μecor), provided good agreement with the observed levels of cracking so far.