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This spreadsheet pertains to report 2018-22, Balanced Design of Asphalt Mixtures, and can automatically calculate the CTindex.

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.

Incorporating cracking tests and criteria in binder acceptance, mix design, and construction quality control (QC and quality assurance (QA) offer a way to improve pavement performance. The objective of this research is to identify and, if necessary, refine binder and mixture tests capable of addressing asphalt cracking in Minnesota asphalt pavements. The tests/criteria selected for evaluation are the IDEAL-CT and the DCT for asphalt mixtures, and the (SE (BTc and the G-R parameter for binders. These tests are relatively simple to perform in standard agency and contractor laboratories, require minimal time to perform and produce results, are repeatable and reproducible, and provide a distinction between brittle and ductile behavior. Additionally, binders are tested using the multiple stress creep recovery procedure to characterize their elastic recovery. Mixtures and binders from projects constructed in the 2018 and 2019 construction seasons are tested using these methods. It is found that all the mixtures and binders exhibit good cracking resistance. The mixture results from 2018 are robust for periods of up to two weeks after mixing and molding, but the mixing and molding needs to take place at the same time for both QC and QA samples as reheating QA samples will lead to a degradation in cracking resistance. The main conclusion from the 2019 mixture testing is that cracking resistance is directly related to asphalt content. Binder testing shows that all of the sources used possess good aging properties.

A balanced mix design (BMD) sets a maximum asphalt content based on the rutting criterion and a minimum asphalt content based on cracking criterion. This project developed a BMD framework for the Minnesota Department of Transportation (MnDOT) and used it to evaluate materials from four Minnesota projects using the Illinois Flexibility Index; the IDEAL-CTAL-CT-CT Cracking Test Index by the Texas A&M Transportation Institute; and the Disk-shaped Compact Tension test for cracking and the Hamburg Wheel Tracking test for rutting. For the four test mixtures; the performance tests and the BMD procedure were successful in distinguishing the influence of asphalt content on cracking resistance and rutting resistance. There was fairly good agreement among the cracking tests for the asphalt content and only a slight deviation from volumetric asphalt content in most cases. The cracking and rutting performance criteria need to be refined for different applications based on characteristics such as climate; lift thickness; traffic level; and placement within the pavement structure.