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Suggested Citation:"Appendices A I." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. Washington, DC: The National Academies Press. doi: 10.17226/24959.
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Page 116
Page 117
Suggested Citation:"Appendices A I." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. Washington, DC: The National Academies Press. doi: 10.17226/24959.
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Page 117
Page 118
Suggested Citation:"Appendices A I." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. Washington, DC: The National Academies Press. doi: 10.17226/24959.
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Page 118

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116 Appendices A though I are not printed herein but are available for download from the TRB website (trb.org) by searching for “NCHRP Research Report 871.” The appendices include the following: Appendix A: Previous Studies of Laboratory Aging of Compacted Specimens and Loose Mixtures Appendix B: Previous Studies of Modeling Asphalt Binder Aging in Pavements Appendix C: Evaluation of the Sensitivity of the Mechanical Properties of Asphalt Concrete to Asphalt Binder Oxidation Appendix D: Evaluation of Different Chemical and Rheological Aging Index Properties Appendix E: Factors Affecting Oxidation Reaction Mechanisms in Asphalt Concrete Appendix F: Evaluation of Asphalt Mixture Laboratory Long-Term Aging Appendix G: Investigation of Proper Long-Term Aging Temperature Appendix H: Climatic Aging Index Appendix I: Performance Testing of Field Cores Appendices A–I

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

111  The application of pressure in the compacted specimen aging process expedites oxidation. However, the performance test results indicate that the application and/or release of pressure damages specimens.  The aging gradient observed in large compacted specimens that were subjected to oven aging was eliminated by the use of small specimens (38-mm diameter with 100-mm height) due to their shortened lateral diffusion paths. Therefore, the oven aging of small compacted specimens is the most promising compacted specimen aging procedure, as no integrity issues were observed.  Aging asphalt mixtures in a loose mix state expedites oxidation compared to compacted specimen aging under the same conditions.  The compactive effort required to compact long-term aged loose mixes is comparable to that required for short-term aged mixes, with no adjustment to the compaction temperature needed based on the results for two mixtures, PG 64-22 and PG 70-28 SBS- modified, the latter of which is known to be difficult to compact.  The performance test results indicate no problems with loose mixtures compacted after long-term aging.  Pressure expedites the aging of loose mix. However, the size of the standard binder PAV prohibits the generation of enough aged material for performance testing. If the pressure aging of loose mix were to be selected as the best aging procedure, then a larger PAV would need to be developed.  Loose mix aging in an oven is the most promising aging procedure to produce mixture specimens for performance testing in terms of efficiency and integrity, without the need to develop costly new equipment. In addition, any specimen geometry (e.g., beams) can be produced using aged loose mix, also making this procedure the most versatile option.  The results indicate that loose mix aging at 95°C is the optimal procedure for the long- term aging of asphalt concrete for performance testing. The literature indicates that the disruption of polar molecular associations and sulfoxide decomposition become critical at temperatures that exceed 100°C (Petersen 2009). In this study, 95°C was selected as the aging temperature instead of 100°C in order to avoid the aging temperature reaching close to 100°C due to possible temperature fluctuations in the oven. Aging at lower temperatures precludes reaching field levels of oxidation within a reasonable time.  A significant change in the relationship between binder rheology and chemistry can occur for certain asphalts when the aging temperature is increased from 95°C to 135°C. This change implies corresponding changes in the kinetics and mechanisms of the oxidation reactions that are associated with an increase in temperature from 95°C to 135°C, which is consistent with findings described in the literature.  Asphalt mixture performance can be negatively impacted by long-term aging at 135°C. Despite having matching rheological characteristics, two of the three mixtures evaluated in this study exhibited decreases in both dynamic modulus values and fatigue resistance. These results suggest that aging at 135°C for performance assessment and prediction should be avoided.  When the loose mix laboratory aging temperature is at or below 95°C, the relationship between binder chemistry and rheology is unaffected by the aging temperature, based on all three mixtures evaluated, indicating that the aging temperature does not affect the oxidation reaction mechanism.

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 871: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction presents a proposed standard method for long-term laboratory aging of asphalt mixtures for performance testing. The method is intended for consideration as a replacement for the method in AASHTO R 30, “Mixture Conditioning of Hot Mix Asphalt (HMA),” which was the most commonly used method for aging asphalt materials for performance testing for input to prediction models for the past 25 years. The method improves on R 30 in that the laboratory aging time is specifically determined by the climate at the project location.

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