Moraes, Raquel

This project aimed to validate loose mix aging procedures for cracking resistance evaluation of asphalt mixtures in balanced mix design (BMD) with a broad range of field projects covering various mixture components, pavement ages, and climatic conditions. To that end, a two-phase research approach was followed, with Phase I focusing on a literature review, research gap analysis, and development of Phase II work plan. The literature review topics included development and preliminary field validation of existing loose mix aging procedures; the impact of loose mix aging on asphalt binder and mixture properties; and effects of silo storage, mix hauling, mix reheating, specimen storage, and asphalt weathering on asphalt binder and mixture properties. The literature was then critically reviewed to identify research gaps that might hinder the implementation of loose mix aging for cracking resistance evaluation in BMD, including lab-to-field aging correlation, applicability to asphalt mixtures containing additives, selection of laboratory tests and parameters to assess loose mix aging, and implementation of loose mix aging into BMD. Finally, a Phase II work plan was developed to address the knowledge gaps identified through the literature review and research gap analysis, which include two major tasks: 1) further validation of 95°C loose mix aging maps, and 2) conversion of different loose mix aging procedures based on a kinetics aging model.

This study evaluated the impact of polymer modification, without changing the base binder, on the intermediate-temperature cracking resistance of asphalt mixtures characterized using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and the Illinois Flexibility Index Test (I-FIT). Twelve asphalt mixtures prepared with two mix designs and six virgin binders (including two unmodified and four polymer-modified asphalt binders per mix design) were evaluated. Each mixture was tested at three binder contents and two temperatures: 25°C and an equal stiffness temperature (T=G*). In almost all cases, the polymer-modified asphalt (PMA) and unmodified mixtures with the same base binder had statistically equivalent IDEAL-CT and I-FIT results, indicating a lack of sensitivity to polymer modification. Increasing the binder content or adjusting the test temperature to T=G* did not discriminate the PMA and unmodified mixtures in the two tests. Interaction diagram analysis of the IDEAL-CT and I-FIT results showed that polymer modification generally affected the toughness and post-peak behavior of the mixture, but these effects tended to offset each other on the final cracking index parameters. Unlike the IDEAL-CT and I-FIT, the two cyclic loading tests evaluated in the study demonstrated the benefits of polymer modification. This discrepancy highlighted the potential limitation of the monotonic loading tests in assessing the fatigue cracking resistance of PMA binders and mixtures. Finally, asphalt binders extracted from the PMA versus unmodified mixtures with the same base binder showed distinctly different rheological properties, but these differences were not captured in the IDEAL-CT or I-FIT when the test variability was considered.

The overall objective of this study was to explore three novel rejuvenator application methods using the emulsion and foaming technologies and determine their impacts on the workability and long-term cracking resistance of high-reclaimed asphalt pavement (RAP) asphalt mixtures. To that end, a comprehensive experimental plan was developed, which consisted of four supplementary experiments focusing on rejuvenator characterization, foaming measurements of rejuvenators and rejuvenated asphalt binders, RAP pretreatment and marination evaluations, and mixture performance testing, respectively. Test results indicated that adding rejuvenators for RAP pretreatment improved the overall quality characteristics of RAP. Among the three rejuvenator application methods evaluated for RAP pretreatment, the emulsion method was found more effective than the spray-on and foaming methods. Marinating the pretreated RAP had a notable impact on the rheological and chemical properties of the extracted RAP binders, but it did not significantly affect the workability, appearance, and color consistency of RAP. Adding rejuvenators, in general, improved the workability and cracking resistance of high-RAP mixtures, although the improvement in mixture performance test results, in some cases, was not statistically significant. Among the different rejuvenator application methods, pre-blending the rejuvenator into the virgin binder (with or without foaming) provided slightly better or equivalent rejuvenating effectiveness and thus, mixture performance properties, than adding the rejuvenator for RAP pretreatment. Based on the findings of the study, it was recommended that asphalt contractors continue to use the pre-blending method of adding rejuvenators for the design and production of high-RAP mixtures due to performance and ease of operation considerations.