Understanding and Improving Heterogeneous, Modern Recycled Asphalt Mixes

2021PDFTech ReportButtlar, William G.Abdelrahman, MagdyMajidifard, HamedDeef, EslamUniversity of Missouri--Columbia. Department of Civil and Environmental EngineeringMissouri University of Science and TechnologyMissouri. Department of Transportation. Construction and Materials DivisionUnited States. Department of Transportation. Federal Highway AdministrationMissouri. Department of Transportation. Construction and Materials DivisionMissouriUnited StatesAsphalt mixturesPavement performanceRecycled materialsTestingSpecificationsPerformance testsPavementsModern recycled asphalt mixescmr 21-007MoDOT project # TR201807Final Report (March 2018 \u2013 August 2021)A comprehensive research investigation was carried out to investigate the use of recycled materials in Super-pave asphalt mixtures in Missouri. The investigation involved sampling of aggregates, binders, plant-produced mixtures, and field cores followed by a rigorous lab testing program. Lab testing included an extensive binder extraction and recovery (E & R) experiments, followed by a comprehensive suite of advanced binder tests. An attempt was made to shed light on effective strategies to iterate existing mix designs into more \u2018balanced mix designs\u2019 for modern, heterogeneous recycled mixtures in the Midwest. Different strategies were employed, such as the use of a softer virgin binder, the addition of a rejuvenator, and the employment of 5% to 20% of dry-process, engineered crumb rubber by weight of total binder. These mixes were subjected to a suite of cracking and rutting mixture performance tests to establish baseline performance, followed by four additional mix design iterations per mix (for a total of 10investigated mixtures). The DC(T), I-FIT, IDEAL-CT, and Hamburg wheel tracking tests were used in the performance testing suite. Based on the results of the study, it was found that RAP, and particularly RAS, drive the need for the use of softer virgin binders to be used in modern, recycled asphalt mixtures in Missouri. Recommendations are provided with respect to the selection of softer virgin binder grades based on recycled material type and amount. Recommendations for balancing mixes with the use of rejuvenators and ground tire rubber are also provided.122