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Suggested Citation:"Table of Contents." 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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Suggested Citation:"Table of Contents." 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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Suggested Citation:"Table of Contents." 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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Suggested Citation:"Table of Contents." 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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Suggested Citation:"Table of Contents." 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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Suggested Citation:"Table of Contents." 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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ii Table of Contents LIST OF FIGURES ..................................................................................................................................... IV  LIST OF TABLES ...................................................................................................................................... VII  SUMMARY .................................................................................................................................................. 1  CHAPTER 1 BACKGROUND .................................................................................................................. 3  PROJECT OBJECTIVES AND SCOPE ................................................................................................. 4  PREVIOUS RESEARCH INTO LONG-TERM AGING OF ASPHALT MIXTURES ............................ 5  Compacted Specimen Aging versus Loose Mixture Aging ......................................................... 5  Oven Aging versus Pressure Aging ................................................................................................ 6  Laboratory Aging Temperature ....................................................................................................... 7  Aging Index Properties ..................................................................................................................... 8  Modeling of Oxidative Aging ............................................................................................................ 9  CHAPTER 2 RESEARCH APPROACH ............................................................................................... 12  OVERVIEW OF RESEARCH APPROACH .......................................................................................... 12  AIP Selection .................................................................................................................................... 13  Sensitivity Study .............................................................................................................................. 14  Selection of the Proposed Aging Method .................................................................................... 14  Determination of Project-Specific Aging Durations .................................................................... 16  Climate-Based Determination of Predefined Aging Durations ................................................. 16  Development of Pavement Aging Model...................................................................................... 16  TEST MATERIALS AND FIELD PROJECTS ..................................................................................... 17  Group A Materials ............................................................................................................................ 17  Group B Materials/Projects ............................................................................................................ 18  SAMPLE PREPARATION METHODS ................................................................................................. 19  Asphalt Mastic Preparation ............................................................................................................ 19  Fine Asphalt Matrix (FAM) Preparation ........................................................................................ 19  Asphalt Mixture Aging ..................................................................................................................... 20  Asphalt Binder Aging....................................................................................................................... 23  Field Core Preparation .................................................................................................................... 24  Micro-Extraction and Recovery ..................................................................................................... 24  TEST METHODS .................................................................................................................................. 25  Asphalt Binders ................................................................................................................................ 25  Asphalt Mixtures .............................................................................................................................. 25  CHAPTER 3 FINDINGS AND APPLICATIONS .................................................................................. 27  FINDINGS .............................................................................................................................................. 27  Sensitivity Study .............................................................................................................................. 27  Selection of the Chemical and Rheological Aging Index Properties ....................................... 29  Selection of Long-Term Aging Method ......................................................................................... 32  Climate-Based Determination of Predefined Aging Durations ................................................. 67  Aging Model to Predict Field Aging throughout Pavement Depth ............................................ 90  APPLICATIONS .................................................................................................................................. 106  Integration of Pavement Aging Model in Mechanistic-Empirical Design ............................... 106  CONCLUSIONS ................................................................................................................................... 109 

iii Sensitivity Study ............................................................................................................................ 109  Selection of the Chemical and Rheological Aging Index Properties ..................................... 110  Selection of the Long-Term Aging Method ................................................................................ 110  Climate-Based Determination of Predefined Aging Durations ............................................... 112  Aging Model to Predict Field Aging ............................................................................................. 112  Integration of the Pavement Aging Model in Mechanical-Empirical Design ......................... 113  CHAPTER 4 SUGGESTED FUTURE RESEARCH ......................................................................... 114 REFERENCES ....................................................................................................................................... 115  APPENDIX .............................................................................................................................................. 122 

iv LIST OF FIGURES Figure 1. Damage contours from 10-cm thick asphalt pavements in California after 20 years of service: (a) no aging and (b) with aging. ........................................................................................ 4  Figure 2. Research approach flow chart. ...................................................................................... 13  Figure 3. Locations of materials/projects included in the study. .................................................. 19  Figure 4. (a) FAM plug with cored and cut sample and (b) instrumented FAM sample. ............. 20  Figure 5. Long-term aging of large and small specimens in the oven. ......................................... 21  Figure 6. WMA compacted specimens aging in an oven. ............................................................ 21  Figure 7. Simple set-up for holding large specimens during aging in the PAV. .......................... 22  Figure 8. Long-term aging of loose mix in thin layers for long-term aging in oven. ................... 22  Figure 9. Aging rack developed for long-term aging of loose mix in PAV. ................................ 23  Figure 10. Depiction of field core slices used to determine oxidation gradient with depth. ........ 24  Figure 11. Summary of results from the sensitivity study. ........................................................... 28  Figure 12. Sensitivity of different chemical AIPs to aging duration: (a) carbonyl area, (b) C+S area, and (c) C+S peaks. ............................................................................................................... 31  Figure 13. Correlation between G* at 64°C and 10 rad/s with C+S peaks for six mixtures. ....... 32  Figure 14. Dynamic modulus results: (a) log-log scale and (b) semi-log scale. ........................... 37  Figure 15. Comparison of damage characteristic curves for the NC mixes subjected to different aging conditions. ........................................................................................................................... 38  Figure 16. Illustration of summation of (1-C). ............................................................................. 39  Figure 17. DR failure criterion lines of NC mix subjected to different aging conditions. ............ 39  Figure 18. Schematic of components of small specimen (38 mm × 100 mm) used to evaluate oxidation gradients. ....................................................................................................................... 40  Figure 19. Schematic of components of large specimen (100 mm × 150 mm) used to evaluate oxidation gradients. ....................................................................................................................... 41  Figure 20. Comparison between C+S absorbance peaks and log G* at 64°C and 10 rad/s for extracted and recovered binders from different compacted specimen aging processes, loose mix aging trials, and aged binders. ....................................................................................................... 42  Figure 21. Comparison between field core aging gradient with respect to depth and long-term aging of loose mix in oven at 95°C. .............................................................................................. 46  Figure 22. Comparisons between C+S absorbance peaks and log G* at 64°C and 10 Hz for extracted and recovered binders from different loose mix aging trials, field core top layer surface slices, and aged binders (SBS-modified mixture). ........................................................................ 47  Figure 23. Dynamic modulus test results: (a) log-log scale and (b) semi-log scale. .................... 48  Figure 24. Comparison of damage characteristic curves from FHWA ALF SBS mixtures subjected to different aging conditions. ........................................................................................ 48  Figure 25. Comparison of DR failure criterion lines for SBS-modified mixtures. ........................ 49  Figure 26. Summary of experimental plan. .................................................................................. 50  Figure 27. SHRP AAD loose mix prepared for long-term aging. ................................................ 51  Figure 28. Determination of FHWA ALF SBS aging durations. ................................................. 52  Figure 29. Determination of SHRP AAG aging durations. .......................................................... 52  Figure 30. Determination of SHRP AAD aging durations. .......................................................... 53  Figure 31. FHWA ALF SBS mixture performance test results: (a) dynamic modulus curves, (b) C versus S curves, and (c) DR failure criterion lines. ................................................................... 54  Figure 32. Damage contours for FHWA ALF-SBS mixture aged at different conditions. .......... 57 

v Figure 33. Area for ‘percent damage’ definition. ......................................................................... 57  Figure 34. Comparison of fatigue damage area versus service life for FHWA ALF SBS mixture aged at different conditions. .......................................................................................................... 58  Figure 35. SHRP AAD mixture performance test results: (a) dynamic modulus curves, (b) C versus S curves, and (c) DR failure criterion lines. ........................................................................ 59  Figure 36. Damage contours for SHRP AAD mix aged under different conditions. ................... 60  Figure 37. Comparison of fatigue damage area versus service life for SHRP AAD mixture aged under different conditions. ............................................................................................................ 61  Figure 38. SHRP AAG mixture performance test results: (a) dynamic modulus curves, (b) C versus S curves, and (c) DR failure criterion lines. ...................................................................... 62  Figure 39. Damage contours for SHRP AAG mixture aged at different conditions. ................... 63  Figure 40. Comparison of fatigue damage area versus service life for SHRP AAG mixture aged at different conditions. .................................................................................................................. 64  Figure 41. G* values at 64°C and 10 rad/s versus depth for (a) MB field cores and (b) NCAT field cores. ..................................................................................................................................... 65  Figure 42. Laboratory aging G* evolution results for (a) MB mixtures and (b) NCAT mixtures. ....................................................................................................................................................... 66  Figure 43. Loose mix aging rates obtained from WesTrack Fine mix prepared with high (6.1%), optimum (5.4%), and low (4.7%) binder contents: (a) aging rates in terms of C+S absorbance peaks and (b) aging rates in terms of logarithm of binder shear modulus log G* at 64°C and 10 rad/s. .............................................................................................................................................. 70  Figure 44. Comparisons between measured and predicted log G* values for the calibration mixtures: (a) ALF-Control, (b) ALF-SBS, (c) SHRP AAD, (d) WesTrack Fine, and (e) WesTrack Coarse. ......................................................................................................................... 72  Figure 45. Comparisons between measured and predicted log G* values for the validation mixtures: (a) NCS9.5B, (b) LTPP-SD, (c) LTPP-NM, (d) LTPP-TX, and (e) LTPP-WI. ........... 73  Figure 46. Predictions of non-isothermal loose mixture oven aging: (a) non-isothermal laboratory aging history, (b) WesTrack, fine mix prediction, (c) ALF Control mix prediction, and (d) overall prediction quality. ......................................................................................................................... 74  Figure 47. Laboratory non-isothermal aging validation: (a) measured aging duration for non- isothermal aging of ALF Control and WesTrack Fine mixtures and (b) measured field aging for ALF Control and WesTrack Fine mixtures. ................................................................................. 76  Figure 48. FHWA ALF field case study validation: (a) FHWA ALF location in McLean, VA, (b) measured field aging at different depths, and (c) measured field aging for ALF Control and ALF SBS-modified mixtures. ................................................................................................................ 77  Figure 49. Fast and slow reaction rates at different temperatures. ............................................... 79  Figure 50. Climatic aging index (CAI) predictions: (a) overall CAI fitting without depth correction factor D, (b) CAI fitting based on layer depth without depth correction factor D, and (c) overall CAI fitting after applying depth correction factor (D). ............................................... 81  Figure 51. Required oven aging duration at 95°C to match level of field aging 6 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. .................................................................................................................................... 84  Figure 52. Required oven aging duration at 95°C to match level of field aging 20 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. .................................................................................................................................... 86 

vi Figure 53. Required oven aging duration at 95°C to match level of field aging 50 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. .................................................................................................................................... 88  Figure 54. Log G* values for measured field gradient throughout pavement depth compared to laboratory short-term aged materials for FHWA ALF-Control and WesTrack Fine section with optimum %ac and high %Va. ....................................................................................................... 89  Figure 55. Measured log G* values as a function of pavement depth for (a) field cores obtained from various locations in the USA and (b) field cores obtained from 19-year-old WesTrack Fine sections constructed with different binder contents and air voids. ............................................... 90  Figure 56. Predicted versus measured log G* values for (a) FHWA ALF-Control, (b) FHWA ALF-SBS, (c) LTPP South Dakota, (d) LTPP New Mexico, and (e) LTPP Wisconsin sections. 92  Figure 57. Predicted versus measured log G* values after 19 years of aging for WesTrack sections with fine gradation: (a) all sections, (b) extreme sections, (c) sections with optimum asphalt content, (d) sections with high asphalt content, and (e) sections with low asphalt content. ....................................................................................................................................................... 93  Figure 58. Calibration of kinetics prediction model of field aging by comparing predicted versus measured log G* values at a depth of 20 mm. .............................................................................. 94  Figure 59. Summary of experimental plan. .................................................................................. 97  Figure 60. Measured USAT binder aging rates and loose mix aging rates at 95°C for mixtures with hydrated lime: (a) ALF Control, (b) WesTrack Coarse, (c) WesTrack Fine, (d) SHRP AAD, and (e) SHRP AAG. ...................................................................................................................... 99  Figure 61. Measured USAT binder aging rates and loose mix aging rates at 95°C for mixtures without hydrated lime: (a) LTPP New Mexico, (b) LTPP South Dakota, (c) LTPP Texas, (d) LTPP Wisconsin, and (e) NCS9.5B. ........................................................................................... 100  Figure 62. Ranking comparisons: (a) loose mix aging rates and (b) USAT binder aging rates. 101  Figure 63. Relationship between slope correction factor and percentage passing No. 200 sieve. ..................................................................................................................................................... 102  Figure 64. Summary of developed empirical model to relate binder and loose mix aging rates.103  Figure 65. Predicted age hardening rates for loose mix aging at 95°C from USAT binder aging for mixtures with hydrated lime: (a) ALF Control, (b) WesTrack Coarse, and (c) WesTrack Fine. ..................................................................................................................................................... 104  Figure 66. Predicted age hardening rates for loose mix aging at 95°C from USAT binder aging for mixtures without hydrated lime: (a) LTPP New Mexico, (b) LTPP South Dakota, (c) LTPP Texas, and (d) LTPP Wisconsin. ................................................................................................ 105  Figure 67. Validation of predictive model: (a) SHRP AAD, (b) SHRP AAG, and (c) NCS9.5B mixtures....................................................................................................................................... 106  Figure 68. Comparison of dynamic modulus mastercurves at different aging levels for LTPP South Dakota mix. ...................................................................................................................... 108  Figure 69. Comparison between dynamic modulus values measured at 20°C and 10 Hz and predicted values based on extracted and recovered binder data measured at 20°C and 10 Hz. . 109 

vii LIST OF TABLES Table 1. Comparison between Loose Mix and Compacted Specimens in the Aging Procedure .... 6  Table 2. Comparison between Oven and PAV Aging Methods ..................................................... 7  Table 3. Summary of Group A Materials ..................................................................................... 18  Table 4. Selected Sections for Development of Long-Term Aging Protocol and Field Calibration under Group B Materials .............................................................................................................. 18  Table 5. Summary of Sensitivity Study Findings ......................................................................... 28  Table 6. Asphalt Mixtures Used for AIP Evaluation .................................................................... 30  Table 7. Summary of Findings from Level 1 Integrity Check of Compacted Specimen Long- Term Aging ................................................................................................................................... 36  Table 8. Average DR Values for NC Mix Subjected to Different Aging Conditions ................... 40  Table 9. Percentage Change in Chemical and Rheological AIPs According to the Different Aging Methods......................................................................................................................................... 43  Table 10. Statistical t-Test Analysis Outcomes for Dynamic Modulus and Cyclic Fatigue Test Results for FHWA ALF SBS Materials........................................................................................ 55  Table 11. Statistical t-Test Analysis Outcomes for Dynamic Modulus and Cyclic Fatigue Test Results for SHRP AAD Materials ................................................................................................ 60  Table 12. Statistical t-Test Analysis Outcomes for Dynamic Modulus and Cyclic Fatigue Test Results for SHRP AAG Materials ................................................................................................ 63  Table 13. Group B Materials Used for WMA Aging Evaluation ................................................. 65  Table 14. Laboratory Aging Durations Required to Match Four Years of In-Service Aging ...... 67  Table 15. Mixtures Used to Calibrate and Validate Kinetics Model for Loose Mix Oven Aging 69  Table 16. Kinetics Model Parameters Using a Single Fitting Parameter and Universal Reaction Rates .............................................................................................................................................. 71  Table 17. Climatic Aging Index (CAI) Fitting Coefficients ......................................................... 82  Table 18. Mixtures Used to Calibrate Field-Aging Kinetics Model Predictions .......................... 91  Table 19. WesTrack Fine Sections Used to Evaluate the Effects of Mixture Morphological Properties on Field Aging ............................................................................................................. 95  Table 20. Mixtures Used to Compare Binder Aging Rates Obtained from USAT Binder Aging and Loose Mix Aging ................................................................................................................... 98  Table 21. G* Results for Asphalt Binders Extracted and Recovered from Loose Mix Aged at Different Durations ..................................................................................................................... 108 

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TRB’s National Cooperative Highway Research Program has released a pre-publication, non-edited Report 871: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction. The report 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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