Project No. 9-58 Copy No.__

THE EFFECTS OF RECYCLING AGENTS ON ASPHALT

MIXTURES WITH HIGH RAS AND RAP BINDER RATIOS

PHASE II DRAFT INTERIM REPORT

Prepared for

National Cooperative Highway Research Program Transportation Research Board

of The National Academies

TRANSPORTATION RESEARCH BOARD OF THE NATIONAL ACADEMIES

PRIVILEGED DOCUMENT

This report, not released for publication, is furnished only for review to members of or participants in the work of the CRP. This report is to be regarded as fully

privileged, and dissemination of the information included herein must be approved by the CRP.

Amy Epps Martin

Fujie Zhou Edith Arambula Eun Sug Park

Arif Chowdhury Fawaz Kaseer

Fan Yin Juan Carvajal Munoz

Avery Rose Elie Hajj Jo Daniel

Charles Glover

Texas A&M Transportation Institute The Texas A&M University System

College Station, Texas

March 2016

ACKNOWLEDGMENT OF SPONSORSHIP

This work was sponsored by one or more of the following as noted:

X American Association of State Highway and Transportation Officials, in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program,

Federal Transit Administration and was conducted in the Transit Cooperative Research Program,

Federal Aviation Administration and was conducted in the Airport Cooperative Research Program,

Research and Innovative Technology Administration and was conducted in the National Cooperative Freight Research Program,

Pipeline and Hazardous Materials Safety Administration and was conducted in the Hazardous Materials Cooperative Research Program, which is administered by the Transportation Research Board of the National Academies.

DISCLAIMER

This is an uncorrected draft as submitted by the research agency. The opinions and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the Transportation Research Board, the National Academies, or the program sponsors.

Project No. 9-58 Copy No.__

THE EFFECTS OF RECYCLING AGENTS ON ASPHALT

MIXTURES WITH HIGH RAS AND RAP BINDER RATIOS

PHASE II DRAFT INTERIM REPORT

Prepared for

National Cooperative Highway Research Program Transportation Research Board

of The National Academies

Amy Epps Martin Fujie Zhou

Edith Arambula Eun Sug Park

Arif Chowdhury Fawaz Kaseer

Fan Yin Juan Carvajal Munoz

Avery Rose Elie Hajj Jo Daniel

Charles Glover

Texas A&M Transportation Institute College Station, Texas

March 2016

iii

TABLE OF CONTENTS

LIST OF FIGURES ........................................................................................................................ v LIST OF TABLES ......................................................................................................................... ix ACKNOWLEDGMENTS ............................................................................................................. xi ABSTRACT .................................................................................................................................. xii Chapter 1  INTRODUCTION .................................................................................................... 13 

1.1 NCHRP Research on Recycled Materials in Asphalt Mixtures ............................. 14 1.2 Scope of the Interim Report .................................................................................... 15 1.3 Key Results from Phase I ........................................................................................ 17 1.4  Recent Relevant Literature .................................................................................. 21 

1.4.1  Binder Characterization ................................................................................. 21 1.4.2  Mixture Characterization ............................................................................... 25 

Chapter 2  Revised Phase II Laboratory Experiment Designs ................................................... 28 2.1 Field Projects and Expanded Materials .................................................................. 28 2.2 Field Activities ........................................................................................................ 32 

2.2.1  Material Sampling during Production and Construction ............................... 32 2.2.2  Coring Plan after Construction ...................................................................... 33 2.2.3  Post-Construction Assessment and Pavement Design Data .......................... 33 

2.3 Laboratory Testing .................................................................................................. 33 2.3.1  Binder and Mortar Testing ............................................................................ 36 2.3.2  Mixture Testing ............................................................................................. 38 

2.4 Binder and Mortar Experiments ............................................................................. 48 2.5 Mixture Experiments .............................................................................................. 53 

Chapter 3  Binder and Mortar Results and Analysis .................................................................. 57 3.1  Binder Blend Rheology Results .......................................................................... 57 

3.1.1  RA Dosage and Tc ....................................................................................... 57 3.1.2  G-R with Aging ............................................................................................. 67 3.1.3  FT-IR CA with Aging ................................................................................... 72 

3.2  Binder Aging Results .......................................................................................... 75 3.2.1  Preliminary Aging Analysis .......................................................................... 75 3.2.2  DSR Function Maps and Black Space Analysis ........................................... 80 

3.3  Binder Compatibility Results .............................................................................. 88 3.4  Mortar Results ..................................................................................................... 92 

Chapter 4  Mixture Results and Analysis ................................................................................. 104 4.1  Specimen Fabrication ........................................................................................ 104 4.2  Stiffness ............................................................................................................. 106 

4.2.1  MR ................................................................................................................ 106 4.2.2  E* ................................................................................................................ 108 

4.3 Cracking Resistance .............................................................................................. 110 4.3.1  IFIT (SCB) .................................................................................................. 110 4.3.2  S-VECD ...................................................................................................... 113 4.3.3 UTSST ........................................................................................................... 118 

Chapter 5  Phase II DELIVERABLES and key findings ......................................................... 123 5.1 RA Dosage Selection ............................................................................................ 123 5.2 Specimen Fabrication ........................................................................................... 123 5.3 Key Findings ......................................................................................................... 123 

iv

5.4 Recommended Binder and Mixture Characterization Tools toward Phase III ..... 126 Chapter 6  Phase III Field Experiment Designs ....................................................................... 129 

6.1 Laboratory Testing ................................................................................................ 129 6.2 Binder Experiments .............................................................................................. 131 6.3 Mixture Experiments ............................................................................................ 131 6.4 Binder Contribution from Recycled Materials ..................................................... 137 

6.4.1 Binder Contribution Methodology ................................................................. 138 6.4.2 Preliminary Verification ................................................................................ 139 

6.5 Mixture Master Curve Analysis ............................................................................ 139 6.6 Aging Analysis ..................................................................................................... 140 6.7 Final Report .......................................................................................................... 143 

REFERENCES ........................................................................................................................... 144 LIST OF ACRONYMS .............................................................................................................. 153 APPENDIX A NEVADA CONSTRUCTION REPORT ........................................................... A-1 APPENDIX B INDIANA CONSTRUCTION REPORT ........................................................... B-1 APPENDIX C ADDITIONAL BINDER AND MORTAR INFORMATION ........................... C-1 APPENDIX D ADDITIONAL MIXTURE INFORMATION ................................................... D-1

v

LIST OF FIGURES

Figure 1.1. NCHRP 9-58 Project Overview. ................................................................................ 16 

Figure 1.2. Oxidation Kinetics Measures. .................................................................................... 21 

Figure 1.3. Oxidation Rates (TR=Tire Rubber; PM=Polymer; HPM=High Polymer loading) ... 22 

Figure 1.4. G-R Parameters in Black Space. ................................................................................ 24 

Figure 2.1. SHRP-LTPP Environmental Zones and Constructed and Probable Field Projects. ... 30 

Figure 2.2. Aggregate with Incomplete Coating. .......................................................................... 39 

Figure 2.3. LTRC-SCB Approach Force-Deflection Plot (left) and Test Set Up (right). ............. 41 

Figure 2.4. LTRC-SCB Approach Gf -Notch Depth Plot (calculation of slope “m” using linear fit is also shown). ................................................................................................................ 41 

Figure 2.5. Fracture Energy and Post Peak Slope for IFIT SCB Method. .................................... 43 

Figure 2.6. Uniaxial Thermal Stress and Strain Test (UTSST) Setup. ........................................ 44 

Figure 2.7. Determination of Thermo-Volumetric Properties from Thermal Strain Measurements. .............................................................................................................................. 45 

Figure 2.8. (a) Measured Thermal Stress and Strain; (b) Calculated UTSST Modulus and Associated Characteristic Stages. ................................................................................................. 46 

Figure 2.9. UTSST Resistance Index. .......................................................................................... 47 

Figure 3.1. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-22 and T1 in TX (Expanded) Materials Cluster. ...................................................................................................... 60 

Figure 3.2. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-22 and A1 in TX (Expanded) Materials Cluster. ...................................................................................................... 60 

Figure 3.3. RA Dosage Selection for 0.4 Binder Blend with PG 64-22 and T1 in TX (Expanded) Materials Cluster. ...................................................................................................... 61 

Figure 3.4. RA Dosage Selection for 0.4 Binder Blend with PG 64-22 and A1 in TX (Expanded) Materials Cluster. ...................................................................................................... 61 

Figure 3.5. RA Dosage Selection for 0.5 Binder Blend with PG 64-22, MWAS, and T1 in TX (Expanded) Materials Cluster. ................................................................................................ 62 

Figure 3.6. RA Dosage Selection for 0.5 Binder Blend with PG 64-22, TOAS, and T1 in TX (Expanded) Materials Cluster. ...................................................................................................... 62 

Figure 3.7. RA Dosage Selection for 0.4 Binder Blend with PG 64-28 and A1 in TX (Expanded) Materials Cluster. ...................................................................................................... 63 

Figure 3.8. RA Dosage Selection for 0.5 Binder Blend with PG 64-28, TOAS, and T1 in TX (Expanded) Materials Cluster. ...................................................................................................... 63 

Figure 3.9. RA Dosage Selection for 0.5 Binder Blend with PG 64-28P, TOAS, and T1 in TX (Expanded) Materials Cluster. ................................................................................................ 64 

vi

Figure 3.10. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-28P and T2 for NV Field Materials. ...................................................................................................................... 64 

Figure 3.11. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-28P and A2 for NV Field Materials. ...................................................................................................................... 65 

Figure 3.12. Effect of Base Binder Type on RA Dosage and Tc for TX (Expanded) Materials Cluster. .......................................................................................................................... 65 

Figure 3.13. Effect of RA Type on RA Dosage and Tc for TX (Expanded) Materials Cluster. .......................................................................................................................................... 66 

Figure 3.14. Effect of RAS Type on RA Dosage and Tc for TX (Expanded) Materials Cluster. .......................................................................................................................................... 66 

Figure 3.15. G-R Parameter Results; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blends .......................................................................................... 68 

Figure 3.16. G-R Parameter Results in Black Space Diagram; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blends ..................................................... 69 

Figure 3.17. PAV Aging Durations to Reach G-R Damage Curves; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blends ........................................ 70 

Figure 3.18. Schematic Definition of Rejuvenating Effectivenss Parameter ............................... 71 

Figure 3.19. Evolution of RE values with PAV Aging ................................................................. 72 

Figure 3.20. FT-IR CA Increase with PAV Aging; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blend. .................................................................. 73 

Figure 3.21. G-R Parameter versus CA; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blend. ........................................................................... 74 

Figure 3.22. Graphical Relationship between PAV CA Growth Rate, PAV Eac, and POV Eac. .. 76 

Figure 3.23. Comparison of Measured Virgin/Target and Control Binder CA Growth Rates and Eac with Predicted Growth Rate for Binder from Same Manufacturer with Same PG Grade as Virgin/Target Binder (and previously reported PAV Eac). ............................................ 77 

Figure 3.24. Carbonyl (CA) Growth with Time (60 °C, 20.7 atm. gauge, and 120 hr. total aging time). ................................................................................................................................... 78 

Figure 3.25. CA Growth with Time (60 °C, 20.7 atm. gauge, and 120 hr. total aging time). [Unaged blend CA value shown as marker without fill at zero aging time.] ................................ 79 

Figure 3.26. CA growth rate (60 °C, 20.7 atm. gauge, and 24–120 hr. aging). ........................... 80 

Figure 3.27. DSR Map at 15°C for PG64-22 Base Binder (TX (Expanded) Material Cluster). .. 81 

Figure 3.28. DSR Map at 15°C for PG64-28 Base Binder (TX (Expanded) Material Cluster). .. 82 

Figure 3.29. Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-22 Base Binder (TX (Expanded) Material Cluster). ................................................................................... 83 

Figure 3.30. Black Space of Glover-Rowe Parameter at 15°C for PG64-28 Base Binder (TX (Expanded) Material Cluster). ...................................................................................................... 84 

vii

Figure 3.31. Summary Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-22 Base Binder (TX (Expanded) Material Cluster). ..................................................................... 85 

Figure 3.32. Summary Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-28 Base Binder (TX (Expanded) Material Cluster). ..................................................................... 85 

Figure 3.33. Glover-Rowe Parameter at 15°C for PG64-22 Base Binder Aged at 100°C (TX (Expanded) Material Cluster). ...................................................................................................... 87 

Figure 3.34. Glover-Rowe Parameter at 15°C for PG64-28 Base Binder Aged at 100°C (TX (Expanded) Material Cluster). ...................................................................................................... 87 

Figure 3.35. (a) Control Samples Under Natural Light Before Incubation (b) Control Samples Under Natural Light After Incubation (c) Control Samples Under UV Light After Incubation. .................................................................................................................................... 90 

Figure 3.36. (a) Texas (Expanded) Samples Under Natural Light Before Incubation (b) Texas (Expanded) Samples Under Natural Light After Incubation (c) Texas (Expanded) Under UV Light After Incubation................................................................................................. 91 

Figure 3.37. Florescent Ring Widths from Exudation Droplet Test. ............................................ 92 

Figure 3.38. RAP and MWAS Materials (Passing Sieve #50 and Retained on Sieve #100) from Mortar Experiment for TX (Expanded) Materials Cluster. .................................................. 93 

Figure 3.39. Effect of Recycling and RA on Continuous Grades Based on Mortar Test Results for PG70-22 Target Binder (TX (Expanded) Materials Cluster). .................................... 95 

Figure 3.40. Effect of Recycling and RA on Continuous Grades Based on Mortar Test Results for PG64-22 Base Binder (TX (Expanded) Materials Cluster). ....................................... 96 

Figure 3.41. Effect of Recycling and RA on Continuous Grades Based on Mortar Test Results for PG64-28 Base Binder (TX (Expanded) Materials Cluster). ....................................... 97 

Figure 3.42. Effect of Recycling and RA on Continuous Grades Based on Mortar Test Results for PG64-28P Target Binder (NV Field Materials). ........................................................ 98 

Figure 3.43. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG70-22 Target Binder (TX (Expanded) Materials Cluster). ....................................................................................................................................... 101 

Figure 3.44. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG64-22 Base Binder (TX (Expanded) Materials Cluster). . 102 

Figure 3.45. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG64-28 Base Binder (TX (Expanded) Materials Cluster). . 102 

Figure 3.46. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG64-28P Target Binder (NV Field Materials). ................... 103 

Figure 4.1. Coatability Results for Various RA Blending Methods. .......................................... 105 

Figure 4.2. LMLC MR Stiffness at 25⁰C for STOA and LTOA Specimens for TX (Expanded) Materials Cluster. .................................................................................................... 106 

Figure 4.3. MR Stiffness at 25⁰C for Different Specimen Types for TX (Expanded) Materials Cluster. ........................................................................................................................................ 107 

viii

Figure 4.4. LMLC E* Stiffness (at 4, 20, 40⁰C and 10Hz) for STOA and LTOA Specimens for TX (Expanded) Materials Cluster. ........................................................................................ 109 

Figure 4.5. RPMLC E* Stiffness (at 4, 20, 40⁰C and 10Hz) for STOA and LTOA Specimens for TX (Expanded) Materials Cluster. ........................................................................................ 110 

Figure 4.6. LTRC Jc Results for Two Thicknesses and Two RAP Contents. ............................. 111 

Figure 4.7. Flexibility Index Values (a) without Thickness Adjustment and (b) with Thickness Adjustment. ................................................................................................................ 112 

Figure 4.8. LMLC-SCB results at 25⁰C for STOA and LTOA Specimens for TX (Expanded) Materials. .................................................................................................................................... 113 

Figure 4.9. SVECD Analysis C-S Plot for TX Mixtures. ........................................................... 114 

Figure 4.10. SVECD Analysis Nf -GR Plot for TX Mixtures. ..................................................... 115 

Figure 4.11. Predicted Number of Cycles to Failure from SVECD Analysis for TX Mixtures. 115 

Figure 4.12. Pavement Cross-Section for LVECD Analysis of TX Mixtures. ........................... 116 

Figure 4.13. LVECD Damage Factor (N/Nf) Contour Plots at 20 Years for TX Mixtures. ....... 117 

Figure 4.14. Number of Failure Points (N/Nf=1) Over Time from LVECD Analysis for TX Mixtures. ..................................................................................................................................... 118 

Figure 4.15. UTSST Modulus Curves for TX Field Mixtures. .................................................. 119 

Figure 4.16. TX Field Mixtures UTSST Resistance Index. ....................................................... 121 

Figure 5.1.  Recommended Recycling Agent Dosage Selection Method. ............................... 124 

Figure 5.2. Example Mix Design and Performance Evaluation Guidelines and Evaluation Tools. .......................................................................................................................................... 128 

Figure 6.1. Sample Plot of Log Inflection Point Frequency Versus Log-Log Difference of Glassy Modulus and Inflection Point Modulus. ......................................................................... 140 

Figure 6.2. Sample Mixture-Based Black Space Plot with Low Temperature Failure Threshold. ................................................................................................................................... 140 

Figure 6.3. Cumulative Degree Days for NCHRP 9-52 Field Projects. ..................................... 141 

Figure 6.4. MR Ratio versus CDD for NCHRP 9-52 Post-Construction Cores and Correlation of LTOA Protocols with Field Aging. ........................................................................................ 142 

ix

LIST OF TABLES

Table 2.1. RA Categories and Types (NCAT 2014a). .................................................................. 29 

Table 2.2. Constructed and Potential Field Projects. .................................................................... 31 

Table 2.3. Material Combinations in Revised Phase II Experiments. .......................................... 34 

Table 2.4. Laboratory Tests (S=short-term aging, L=long-term aging). ...................................... 36 

Table 2.6. Summary of the SCB Test Parameters for the LTRC-SCB Approach. ....................... 40 

Table 2.7. Summary of the SCB Test Parameters for the IFIT Approach. ................................... 42 

Table 2.8. Revised Binder Blend Experiment for TX (Expanded) Materials Cluster. ................. 49 

Table 2.9. Revised Binder Blend Experiment for NV Field Materials. ........................................ 49 

Table 2.10. Revised Binder Aging Experiment for TX (Expanded) Materials Cluster. ............... 50 

Table 2.11. Revised Preliminary Aging and Binder Compatibility Experiment for TX (Expanded) Materials Cluster. ...................................................................................................... 51 

Table 2.12. Mortar Experiment for TX (Expanded) Materials Cluster. ....................................... 52 

Table 2.13. Mortar Experiment for NV Field Materials. .............................................................. 52 

Table 2.14. Factors Evaluated in Revised Phase II Experiments. ................................................ 52 

Table 2.15. Revised Mixture Stiffness Experiment for TX (Expanded) Materials Cluster. ......... 54 

Table 2.16. Revised Mixture Performance Experiment for TX (Expanded) Materials Cluster. .. 55 

Table 2.17. Factors Evaluated in TX (Expanded) Mixture Experiments. .................................... 56 

Table 3.1 Recycling Agent Dosage Results. ................................................................................. 59 

Table 3.2. G-R HS Summary for Recycled Blends. ..................................................................... 75 

Table 3.3. Effect of Recycling and RA on Asphalt Binder Grade Change Rate for TX (Expanded) Materials Cluster (Mortar Test Results). ................................................................... 93 

Table 3.4. Effect of Recycling and RA on Asphalt Binder Grade Change Rate for NV Field Materials (Mortar Test Results). ................................................................................................... 94 

Table 4.1. LVECD Analysis Input Values for TX Mixtures. ..................................................... 116 

Table 4.2. UTSST Thermo-viscoelastic Properties for TX Field Mixtures. .............................. 120 

Table 5.1. Specimen Fabrication Protocol for Preparing High RBR Mixtures. ......................... 125 

Table 5.2. NCHRP 9-58 Key Findings through Phase II. ........................................................... 126 

Table 6.1. Revised Component Binders and RAs Experiment. .................................................. 130 

Table 6.2. Proposed Binder Blend Experiment for NV Field Materials. .................................... 132 

Table 6.3. Proposed Binder Blend Experiment for IN Field Materials. ..................................... 133 

Table 6.4. Proposed Binder Blend Experiment for MO Field Materials. ................................... 134 

Table 6.5. Proposed Mixture Experiment for NV Field Materials. ............................................ 135 

x

Table 6.6. Proposed Mixture Experiment for IN Field Materials. .............................................. 136 

Table 6.7. Proposed Mixture Experiment for MO Field Materials. ............................................ 137 

Table 6.8. Correlation of Field Aging in Terms of In-Service Time and Laboratory LTOA Protocol of 5 days at 85°C (185°F) for NCHRP 9-52 Field Projects. ........................................ 143 

xi

ACKNOWLEDGMENTS

The research reported herein was performed under NCHRP Project 9-58 by the Texas A&M Transportation Institute with the Texas A&M Sponsored Research Services serving as fiscal administrator. Dr. Amy Epps Martin, P.E., Professor of civil engineering at Texas A&M University, was the project director and principal investigator. Dr. Fujie Zhou, P.E., Research Engineer with the Texas A&M Transportation Institute, was the co-principal investigator. Other authors of this report are Dr. Edith Arambula, Dr. Eun Sug Park, Mr. Arif Chowdhury, Mr. Fawaz Kaseer, Mr. Fan Yin, Mr. Juan Carvajal, Mr. Avery Rose, Dr. Elie Hajj, Dr. Jo Daniel, and Dr. Charles Glover. The field projects required for the success of this study are realized based on the cooperation of state DOTs, contractors, and asphalt paving associations; and their participation is recognized and appreciated.

xii

ABSTRACT

This draft interim report documents the results of NCHRP Project 9-58 Phase II and describes the Phase III work plan based on laboratory experiments and results to date. Binders, mortars, and mixtures from a field project in Texas along with an expanded set of materials and binder materials from a second field project in Nevada were tested to develop a proposed recycling agent dosage selection method and recommended laboratory characterization tools, including determination of mixture stiffness and cracking resistance after long-term aging. All of these results were synthesized and used to develop the Phase III work plan also described in this draft report.

13

CHAPTER 1 INTRODUCTION

More than 90 percent of highways and roads in the United States are built using hot-mix asphalt (HMA) or warm-mix asphalt (WMA) mixtures. In the early 1990s, the Federal Highway Administration (FHWA) estimated that more than 90 million tons of asphalt pavements are milled off roads each year during resurfacing projects, and over 80 percent of reclaimed asphalt pavement (RAP) is recycled in new asphalt mixtures (FHWA 1993). Following studies showed that this trend is continuously increasing (Copeland 2011).

The use of RAP in HMA dates back to the early 1900s with renewed focus on research and implementation in the 1970s and 1980s due to dramatic increases in the cost of oil and thus asphalt binders and fuel needed to produce asphalt pavements. Newcomb and Epps (1981) reviewed the technologies developed during this early period of recycling, which included drum mix plants, cold milling machines, vibratory compaction rollers, cold and hot in-place recycling techniques, and mix design methods toward high RAP contents to maximize economic and environmental benefits. These symbiotic benefits are substantial and include: conservation of natural resources (aggregate, binder, fuel, etc.), reduction in energy consumption, and reduction in emissions (including greenhouse gases). For example for a relatively high 25 percent RAP content HMA mixture, Robinett and Epps (2010) indicated 10 percent energy savings, 10 percent emissions reductions, and 20–25 percent conservation of natural resources that translated into reduced production and construction costs.

Interest in recycling waned during the 1990s and was not considered in the Strategic Highway Research Program (SHRP), and these technologies remained largely unchanged until 2008, when the cost of petroleum products significantly increased again. So highway agencies and the paving industry have developed a renewed interest in achieving higher recycled binder ratios (RBRs) in asphalt mixtures through the use of larger percentages of RAP and/or the addition of recycled asphalt shingles (RAS) from either manufacturer waste asphalt shingles (MWAS) or tear-off asphalt shingles (TOAS) for the same economic and environmental benefits described previously. To provide an overall indication of the possible binder contribution from these recycled materials, RBR is defined as follows:

100

where PbRAP is the binder content of the RAP, PRAP is the percentage of RAP by weight of mix, PbRAS is the binder content of the RAS, PRAS is the percentage of RAS by weight of mix, and Pbtotal is the binder content of the combined mixture.

In spite of the symbiotic benefits, state departments of transportation (DOTs) limit the use of RAP and/or RAS in asphalt mixtures for reasons that include variability of the recycled materials and concerns about the long-term performance of the asphalt mixtures that contain these materials. In addition, the mix design of these mixtures is more complicated and more time consuming, particularly with high RBRs between 0.3 and 0.5. The potential for the following construction and performance issues is also increased as RBRs increase and corresponding mixtures become stiffer and more brittle:

Compactibility/workability in cool weather. Low-temperature cracking with accumulation of thermally induced stresses.

14

Fatigue cracking and microdamage accumulation leading to crack initiation and propagation with repeated loading.

Reflection cracking with repeated loading and daily/seasonal thermal stresses. Raveling with subsequent aging or moisture damage.

Thus, the environmental and economic benefits must be compared to the potential increased risks associated with construction and performance to ensure engineering benefits can also be realized. Mitigation of these construction and performance issues can be addressed through mix design with the use of higher binder contents, material selection with the use of softer binders that may be polymer modified, or additives such as reclying agents (RAs), as long as there are not compatibility concerns and binder resistance to bleeding and mixture resistance to rutting/permanent deformation is maintained. Mitigation by the use of RAs includes (Tran et al., 2012; Mogawer, Booshehrian, et al. 2013; Im and Zhou, 2014):

Partial restoration of stiffness caused by the addition of recycled materials at high RBRs.

Improvement in cracking resistance of mixtures with high RBRs without adversely affecting their resistance to rutting/permanent deformation and moisture damage.

Improvement in compactibility/workability (in some cases).

Utilizing lower production temperatures through the use of WMA technologies will also affect these construction and performance issues and possibly offset benefits from reduced aging with decreased blending of virgin/target, base, and recycled binders and/or possible compatibility concerns with WMA additives, RAs, and virgin/target, base, and recycled binders.

RAs were utilized in HMA in the early period of widespread recycling in the 1970s and 1980s for the purpose of realizing all three types of benefits—environmental, economic, and engineering. As RBRs continue to increase in the current period of widespread recycling, the use of RAs holds promise once again with proper understanding of their effectiveness in partially restoring binder rheology, its evolution with aging in HMA and WMA mixtures in both the laboratory and the field, and stiffness and cracking resistance of these binder blends and corresponding mixtures. Mix design procedures, including component material characterization to ensure the recycled binders are restored as much as possible rheologically, specimen fabrication protocols to simulate field conditions, and production and construction best practices (including handling of recycled materials—fractionation and drying, for example), are needed to ensure adequate performance when using RAs. Guidelines developed in the 1970s and 1980s, such as those by Epps et al. (1980) and, more recently, Copeland (2011), can be utilized as a starting point to produce high-quality asphalt mixtures with high RBRs and adequate performance.

1.1 NCHRP Research on Recycled Materials in Asphalt Mixtures

In addition to this study, the National Cooperative Highway Research Program (NCHRP) has funded the following four research projects to address the use of recycled materials in asphalt mixtures (McDaniel and Anderson 2001; Advanced Asphalt Technologies 2011; West et al. 2013):

15

NCHRP Project 9-12 (NCHRP Web Document 30 and Report 452): Incorporation of Reclaimed Asphalt Pavement in the Superpave System. The final report for this project is NCHRP Web Document 30, Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method, that addresses the use of RAP in the Superpave mix design method based on: (1) an investigation of whether blending occurs between RAP and virgin/target binders or if RAP acts like a Black rock in the mixture; (2) an examination of RAP binder tests, including RAP binder extraction and recovery procedures, and the effect of RAP content and stiffness on the properties of the blended binder; and (3) an evaluation of the effect of RAP addition on the properties of asphalt mixtures by conducting shear, indirect tensile, and beam fatigue tests. NCHRP Report 452, Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual, corresponds to the appendix of the final report and provides a detailed description of the steps involved in designing and testing HMA mixtures with RAP, including determining properties of RAP binder, developing RAP mix design, and conducting field quality-control testing for RAP mixtures.

NCHRP Project 9-33 (Report 673): A Manual for Design of Hot Mix Asphalt with Commentary. This report includes recommendations for RAP handling, RAP sampling, RAP blending and variability, RAP properties, and design of HMA mixtures with RAP.

NCHRP Project 9-46 (Report 752): Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content. This report provides documentation of the development of a mix design and evaluation procedure for asphalt mixtures containing high RAP contents, up to 50 percent, to achieve acceptable long-term performance. Changes to existing American Association of State Highway and Transportation Officials (AASHTO) standards were also proposed to allow the design of asphalt mixtures with high RAP content.

NCHRP Project 9-55: Recycled Asphalt Shingles in Asphalt Mixtures with Warm Mix Asphalt Technologies. This project is currently ongoing with an expected completion date of fall 2016. The goal of this project is to develop a mix design and evaluation procedure that provides satisfactory performance of WMA mixtures with RAS for project-specific service conditions.

1.2 Scope of the Interim Report

This interim report completes Phase II of NCHRP Project 9-58. Phase II covers Tasks 4 through 5, which includes conducting the laboratory experiments, designing the field experiments, and documenting results. Figure 1.1 illustrates how Phase II contributes substantially to the overall study.

16

Figure 1.1. NCHRP 9-58 Project Overview.

17

Chapter 1 includes a brief history of the use of recycled materials in HMA and WMA mixtures, construction and performance challenges associated with using high percentages of these materials, the use of RAs to overcome these challenges, the scope of this interim report, and a summary of key results from Phase I and recent literature.

Chapter 2 provides the revised laboratory experiment designs for Phase II that evolved based on a continual review of results to select material and testing combinations that most efficiently meet the study objectives while considering the limitations of materials, time, and budget. Chapter 2 includes the following in separate sections: (a) descriptions of field projects in TX and NV and expanded materials from those used in the field projects; (b) field activities; (c) laboratory tests that include binder and mortar rheological characterization, binder chemical characterization, and mixture stiffness and cracking resistance evaluation; (d) binder and mortar experiments to assess RA type, RA dosage, RBR (RAP/RAS combination), base binder type, and RAS type; and (e) mixture experiments to assess RA type, RA dosage, RBR (RAP/RAS combination), and base binder type.

Chapter 3 and Chapter 4 present the results and analysis from the binder and mortar experiments and the mixture experiments, respectively. The binder results include: (1) rheological characterization including a method for selecting RA dosage and cracking resistance in terms of Tc and the Glover-Rowe (G-R) parameter with aging, (2) compatibility evaluation by exudation droplet, and (3) aging characterization in terms of the G-R parameter and carbonyl area by Fourier Transform-Infrared (FT-IR) analysis. The mortar experiment results that provide more realistic blending of base and recycled binders and RAs are also compared to the binder rheological results. The mixture results include: (1) validation of aging protocols for specimen fabrication, (2) stiffness evaluation by MR and E* with aging, and (3) cracking resistance characterization by semi-circular bending (SCB), simplified viscoelastic continuum damage (S-VECD), and Unixial Thermal Stress and Strain Test (UTSST).

Chapter 5 provides conclusions and recommendations from Phase II including a proposed method for selecting RA dosage and recommended binder and mixture charactization tools for mixtures with high RBRs.

Finally, Chapter 6 presents the proposed field experiments for Phase III to gather additional knowledge toward characterizing the effectiveness of RAs, its evolution with aging, and the performance of binders and mixtures with high RBRs through incorporation of RAP, RAS, or a combination of RAP and RAS materials from various sources. The results from Phase II were utilized to select the laboratory tests and material combinations to evaluate the performance of the binders and mixtures with high RBRs from the additional field projects. Chapter 6 includes descriptions of laboratory tests diferent from those included in Phase II; binder experiments for the three field projects; mixture experiments for the three field projects; and additional analyses. And construction reports for the NV and IN field projects are provided in appendices.

With approval of the Phase III work plan proposed in this interim report (Task 5), Phase III will begin with Task 6 (conduct field experiments). Identification of field projects and materials procurement for Phase III was conducted partially in Phase II to tie the laboratory results to field performance.

1.3 Key Results from Phase I

The use of RAP and/or RAS as components of new asphalt mixtures reduces construction costs, maintains dwindling natural resources, conserves valuable landfill space, protects the

18

environment, and improves sustainability. As the percentage of RAP and/or RAS increases in asphalt mixtures, these benefits also increase. State DOTs and contractors alike have recognized these benefits. For example, more than 71 million tons of RAP and almost 2 million tons of RAS were used in asphalt mixtures in 2014 (Hansen 2015).

However, since State DOTs and other highway agencies require mixtures containing RAP and/or RAS to meet the same mix design standards as mixtures with all virgin materials, maximum RAP/RAS contents are usually specified, or some adjustments are considered to accommodate the severely aged and substantially stiffer binder in these recycled materials, which exhibit lower mixture cracking resistance. These adjustments take into account the PG grade of the aged recycled binder and the recycled materials content. To improve cracking resistance of asphalt mixtures with high RBRs, a softer base binder grade (in terms of a lower high PG grade or PGH and/or a lower low PG grade or PGL) can be utilized, a RA can be added, or a combination of these two approaches can be used. This study aims to explore the use of RAs with or without adjustments in the base binder grade. This section provides a summary of the following key results and remaining issues identified in the literature review and surveys in Phase I that will be addressed to some extent in this study:

Separation of RAP and RAS Contributions to RBR

The revised Phase II laboratory experiment designs described in Chapter 2 builds on these issues and includes specification of an overall RBR and the contribution from RAP and RAS separately as RAP binder ratio (RAPBR) and RAS binder ratio (RASBR) according to the following (NCAT 2014b):

100

100

100

where PbRAP is the binder content of the RAP, PRAP is the percentage of RAP by weight of mix, PbRAS is the binder content of the RAS, PRAS is the percentage of RAS by weight of mix, and Pbtotal is the binder content of the combined mixture.

Predominant Use of RAP at High RBRs

Despite the widespread acceptance across States DOTs of the use of recycled materials in asphalt mixtures, survey results indicated that most DOTs do not commonly use a high percentage of RAP (60% utilize 11-20% and 23% utilize 21-30%) and do not commonly use a high percentage of RAS (65% utilize 0-3% and 29% utilize 4-6%). Surveys also indicated that State DOTs and contractors predominantly use RAP in mixtures with high RBRs, as this recycled material is more readily available as compared to RAS, but concerns remain with respect to variability.

19

Increased Use of Recycling Agents at High RBRs

RAs were utilized in HMA in the early period of widespread recycling in the 1970’s and 1980’s toward realizing the environmental, economic, and engineering benefits. Despite this long history of RA use, survey results indicated that more than 80 percent of State DOTs did not use, or do not allow the use of RAs in asphalt mixtures. According to these DOTs, the main barriers to utilizing RAs in asphalt mixtures with RAP and/or RAS are the lack of experience in using RAs, and most importantly, the absence of tests and criteria to determine dosage rates and/or to assess the performance of asphalt mixtures containing RAs. As RBRs increase, this shortcoming becomes more pronounced. Thus, as State DOTs consider the use of mixtures with high RBRs, they are predominantly exploring the use of tall oil (T) type RAs.

Characterization of Binder Blend Rheology

With aging, the stiffness of a binder increases and the phase angle decreases. With the addition of RAs that partially restore or rejuvenate aged binder rheology, and not just soften the material, the aging process is expected to be reversed with the stiffness decreasing and phase angle increasing. Both of these processes (aging and rheology restoration) can be seen by plotting the G-R parameter in Black space. Other chemical and rheological parameters provide additional tools for assessing the effectiveness of RAs in restoring rheology and evaluating aging characteristics of binder blends. FT-IR spectroscopy and determination of carbonyl area (CA) can be used to track oxidative aging of the binder blend. Binder blend master curves, determined through DSR isothermal frequency sweeps tests, can also be used to determine other rheological indices such as low shear viscosity (LSV), crossover frequency and modulus (ωc and G*c), and rheological index R-value.

More Realistic Characterization of Binder Blends

In order to characterize the aged, recycled binder in RAP and RAS and to quantify the effect of these recycled binders on the continuous PG grade profile of a base binder, extraction and recovery is required. However, this process alters the recycled binder properties due to incomplete extraction, remaining solvent, possible binder-solvent reaction, and binder aging due to high temperatures during the process. The mortar procedure defined by the latest draft of AASHTO T XXX-12, Estimating Effect of RAP and RAS on Blended Binder Performance Grade without Binder Extraction (www.arc.unr.edu/Outreach.html), provides a more realistic method for characterizing the effect of the aged, recycled binders on a base binder with or without RA. The mortar procedure is also more realistic than characterizing the binder blend where complete blending is realized. Mortar results were verified by Bahia et al. (2011) within 2.5 °C for PGL and 6 °C for PGH, and Hajj et al. (2012) indicated that mortar results agreed with mixture TSRST results and field performance when recovered PG binder grades did not.

20

Primary Concern of Mixture Cracking Resistance

As expected, survey results indicated that rutting resistance of recycled asphalt mixtures is not a concern, unless higher RA doses were used. Of greater concern in recycled asphalt mixtures is fatigue, reflective, and thermal cracking, since cracking resistance decreases with aging, and asphalt mixtures with high RBRs are expected to have lower cracking resistance initially due to their aged, stiff binders. Most existing models/tests to predict crack growth in asphalt mixtures are generally empirical or phenomenological in nature and include indirect tensile (IDT) strength, TSRST, beam fatigue, and the overlay test. More recent mechanistic-based approaches/tests; such as the Uniaxial Thermal Stress and Strain Test (UTSST), the Simplified Viscoelastic Continuum Damage (S-VECD) approach, and the energy-based mechanistic (EBM) method; provide improved chacterization tools for evaluating cracking resistance of mixtures with high RBRs. These approaches can be utilized along with the semi-circular bend (SCB) test recommended through NCHRP 9-57 (Zhou and Newcomb 2015) after long-term aging to evaluate the effectiveness of RAs in improving cracking resistance for mixtures with high RBRs. In addition, differences in laboratory specimen fabrication and field production and construction of mixtures with RAs must be considered with respect to short-term laboratory aging protocols for use in mix design and quality assurance testing.

Evolution of RA Effectiveness

Although many studies have shown the effect of RAs in improving the cracking resistance of mixtures with high RBRs, state DOTs remain concerned with the evolution of RA effectiveness and the resulting long-term performance of these mixtures. Surveys indicated that unknown long-term performance of asphalt mixtures with RAP and/or RAS is one of the main barriers to using higher RBRs. Binder and mortar rheology and mixture stiffness and cracking resistance results after laboratory long-term aging can be subsequently tied to field project locations in terms of environment and construction date that play a role in the blending of the binder components through diffusion. This is one approach to evaluating long-term performance of mixtures with high RBRs and RAs. A companion approach towards predicting long-term performance uses a computational pavement oxidation model that is based on fundamentals of heat and mass transfer together with measured binder oxidation kinetics and rheological hardening properties to provide changes in binder rheology as a function of time and depth below the surface. The model is founded on local climate and weather data as well as parameters for the specific binder used in the pavement. For sufficiently oxidized binder blends, data suggest that the model also provides meaningful durability calculations for polymer-modified binders. This model provides a tool to capture the unknown effect of RAs on binder oxidation kinetics and resulting evolution of RA effectiveness.

21

1.4 Recent Relevant Literature

A comprehensive literature review was presented in the first interim report, and a summary and update of some of the key tools utilized in Phase II are described in this section.

1.4.1 Binder Characterization

Although there are aging protocols and measurement techniques being used in practice to conduct oxidative aging studies, the most common procedures use FT-IR spectroscopy measurements to characterize the oxidation level of asphalt binders following multiple aging durations and temperatures. Although the aging procedures, specific measurement techniques, and quantifiable parameters may differ with respect to each developed protocol, the FT-IR spectral measurements are used to indicate the level of oxidation through quantification of the carbonyl (C=O) functional groups (Lau et al., 1992; Liu et al., 1998). Some methods also use sulfoxide (S=O) (Petersen and Harnsberger, 1998; Petersen and Glaser, 2011) and other chemical species as additional indicators of aging (Zofka et al., 2013; Yut and Zofka, 2014).

The benefit of providing such stringent chemical analyses arise from the resulting kinetics modeling available through these evaluations. One exemplary model is provided in Figure 1.2 which presents the Texas A&M kinetics model (Glover et al., 2005; Prapaitrakul, 2009; Han, 2011) along with example binder measurements representing aging in terms of a carbonyl area (CA) measurement.

Considerations of these measures permit the evaluation of the fast-rate (kf) and constant-rate (kc) oxidation parameters as a function of temperature. Consideration of the oxidation rates is a more pragmatic method of comparison between different binders. As an example, Figure 1.3 presents the relative comparison of the constant-rate oxidation measures of several binders beginning with the base binder (Base B) and three different modified versions of it. The base

Figure 1.2. Oxidation Kinetics Measures.

22

asphalt (Base B) remained unmodified, while each of the other three contained a terminally blended rubber product, i.e. not particulate or crumb rubber. The binder B_TR only contained the rubber (40% concentration), while the other two PM versions were also modified with an SBS-modified asphalt which reduced the rubber concentration down to 10%. The B_TR_PM binder is commercially available as a PG64-28NVTR, while the B_TR_HPM contained significantly more SBS in a different formulation, i.e. 7.5% polymer.

The significance of such comparisons is the relative differences observed in the oxidation rates between the different versions of modified binders. While there may be a great deal of information to be interpreted from such figures, such as the influence of the rubber concentration, changes in oxygen diffusivity with binder stiffness, etc., the key point is that the rate of oxidation changes with modification and binder formulation. However, these changes may be readily observed and combined with rheological valuations to address the relative change in the physical characteristics of the evaluated binders.

The physical characterization of the binders corresponding to the same aging levels as the kinetics measures are often accomplished through rheological techniques of varying levels of robustness and complexity. Fully developed rheological evaluations including stiffness master curves may be developed utilizing the DSR and even the BBR measurements which permits multiple parameters to be readily evaluated; provided the input data and calculation procedures are technically sound and maintain validity throughout the process. If care is taken to maintain the validity of the selected rheological index, a great deal of information may be gleaned from these evaluations.

Common indices from these master curve evaluations include parameters such as zero-shear viscosity (Anderson et al., 2002), low-shear viscosity (Lunsford, 1994; Morian et al., 2013;

Figure 1.3. Oxidation Rates (TR=Tire Rubber; PM=Polymer; HPM=High Polymer loading)

23

Morian, 2014; Morian et al., 2015), and crossover modulus (Farrar et al., 2013) including several variations such as the rheological index (R) from the Christensen and Anderson family of master curve models (Christensen and Anderson, 1992a, 1992b; Anderson et al., 1994). Other parameters have been and will continue to be explored (Christensen and Anderson, 1992b; Farrar et al., 2013; Rowe, 2014a, 2014b). However, certain parameters have been gaining popularity and are currently perceived as some of the most readily used in practice.

Two versions of the same parameter are represented by the DSR function (DSRFn) that was originally defined by Ruan et al. (2003) as (G’/(η’/G’)) and reformulated for greater practical use by Rowe (2011) in a discussion of Anderson et al. (2011) as the Glover-Rowe (G-R) parameter: G’/(η’/G’) = G* x (cos δ)2/(sin δ). These measures have been shown to correlate well with ductility and thus cracking resistance as well as binder oxidation levels (Ruan et al., 2003). The G-R parameter captures both rheological parameters needed to characterize binder viscoelastic behavior: stiffness (G* at high and intermediate temperatures or S at low temperatures) and phase angle (δ at high and intermediate temperatures or m-value at low temperatures). These two parameters can be used to capture embrittlement by plotting them on a Black space diagram (Figure 4.5) with each point representing an aging state and further aging moving the binder rheologically from the lower right to the upper left of the diagram by increasing G* and decreasing δ.

However, there have also been limitations observed with the G-R parameter measured in the DSR at intermediate temperatures, particularly when correlations were attempted with modified binders (Glover et al., 2005). Traditionally, the DSRFn is reported as a single point measurement at 15°C and a frequency of 0.005 rad/s (Ruan et al., 2003) as is the corresponding G-R parameter (Rowe, 2011). It has been proposed that the original DSRFn correlation to ductility measures (Kandhal, 1977) were based upon the Pennsylvania climate using a PG58-28 binder and thus have inherent assumptions. It has been proposed that the original DSRFn and the subsequent G-R evaluation temperature of 15°C can appropriately be considered as either a constant offset of 43°C from the low temperature PG grade (King et al., 2012; King, 2013) or as the midpoint of the PG binder grade (King, 2013). Both interpretations yield the original 15°C evaluation temperature for the climate and materials used in the early development of the DSRFn and G-R parameters, but will necessitate temperature adjustment for many of the modified binders as well as binders not matching the original PG58-28 grade.

As an example comparison, Figure 1.4 presents the G-R parameter of six binders, four of which are the Base B and rubber modified versions discussed previously. The other two consist of a different binder (Base A) as well as the SBS modified version (A_PM) that meets the requirement of a PG64-28NV. Figure 1.4 also shows a damage zone where cracking likely begins due to brittle rheological behavior defined by G-R parameter values between 180 and 450kPa that correlates to low ductility values of 5cm to 3cm, respectively. These limits were previously related to surface raveling and cracking by Kandhal (1977).

24

Figure 1.4 readily presents the differences between the physical characteristics of the respective binders noting that each of the binders were tested over the same aging states, i.e. same temperature and duration intervals. This figure highlights the effect of the respective modification processes (e.g. rubber and polymer modification) that significantly influences the results by increasing the elastic component (e.g. reducing the phase angle). It further exemplifies through a comparison of the base binders (Base A and B) that these types of characteristic behaviors are binder source dependent, with binders having the same PG grade shown further to the right if they are S-controlled for low temperature PG grade or further to the left if they are m-controlled. Different rates of aging from the lower right of the diagram to the upper left are also shown in agreement with work done by Juristyarini et al. (2011), Ruan et al. (2003), and Jin et al. (2011). Noting the initial difference in the base binders compared to the relative similarities in the polymer modified versions of each (A_PM and B_TR_PM), highlight the fact that the addition of the SBS polymer may have varying levels of influence dependent upon the characteristics of the base binder, the modifiers/additives themselves, and the process utilized to obtain the composite blend of the final product.

Another parameter gaining popularity due to the availability of data from traditional PG binder grading is ΔTc used by Anderson et al. (2011) and Hanson et al. (2010) and which is defined as the difference between the low temperatures where binders reach their respective limits of 300 MPa stiffness (S) and 0.30 m-value. This parameter recognizes the importance of phase angle for cracking resistance, and although BBR test temperatures are almost 35°C below the temperature where ductility and G-R parameters are measured, Anderson et al. (2011) showed that ΔTc correlates well with both.

Figure 1.4. G-R Parameters in Black Space.

25

1.4.2 Mixture Characterization

In NCHRP Project 9-57: Experimental Design for Field Validation of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures, existing cracking tests, that are currently used by state highway agencies, are being evaluated with respect to their ability to assess the cracking potential of asphalt mixtures in the field (Zhou and Newcomb, 2014). The first interim report documented the findings of an extensive literature review on cracking mechanisms, factors affecting cracking development, and most importantly existing cracking tests for routine use. In order to select, or recommend, a particular cracking test for routine use by any state highway agency, the following aspects are under consideration: sensitivity to mix design parameters, correlations to field performance, test simplicity, test variability, availability of test standards, and other factors. In a workshop held in Irvine, CA, two to three tests each were recommended for thermal, reflective, bottom-up fatigue cracking, and top-down fatigue cracking (Zhou and Newcomb, 2015). The Semi-Circular Bending test (SCB) is the only test that was recommend in all cracking categories. This highlighted the fact that the SCB test is favored due to sensitivity to different mixture variables, ease of sample preparation, quick and simple testing procedure, availability and low cost of test equipment, ability to test extracted field cores, and good correlation to field performance (Wu et al. 2005; Kim et al. 2012; Zhou and Newcomb 2015; and Mogawer et al 2015). Therefore, the SCB test (at intermediate temperature) was proposed by the panel of this study to characterize asphalt mixtures with high RBRs with RAs.

The SCB test at intermediate temperature for characterization of fatigue cracking of asphalt mixtures was proposed by Mohammad and co-workers at the Louisiana Transportation Research Center (LTRC) (Wu et al. 2005), and the LTRC-SCB test is similar to the SCB test for low temperature cracking described in AASHTO TP105-13 but with differences in specimen geometry, testing temperature, loading rate, and output parameters. An asphalt pavement core or laboratory compacted specimen is trimmed and cut in half to create a semicircular test specimen with a thickness of 57 mm, and a notch is introduced along the axis of symmetry. Three different notch depths are introduced: 25.4 mm, 31.8 mm, and 38.1 mm. The test is a three-point bending test typically run at 25°C (77°F), and it is performed by applying the load in displacement control at a rate of 0.5 mm/min. The load-deformation curve is plotted, and the strain energy to failure (U) [the area under the load-deformation curve up to the maximum load] and the critical J-integral (Jc) [the slope of U versus notch size divided by the specimen thickness] are recorded. According to the LTRC-SCB method, a higher Jc values indicates better cracking resistance, and a threshold of a minimum Jc of 0.65 kJ/m2 has been suggested as a failure criterion (Wu et al., 2005). The LTRC-SCB test is sensitive to binder PG grade and the nominal maximum aggregate size (NMAS) used in Superpave mixtures, and a fair correlation with field cracking data is reported by Wu et al. (2005) and Kim et al. (2012). However, some limitations exist with the LTRC-SCB method.

Wu et al. (2005) reported that when testing the SCB specimens at a single notch size, the test results (peak load, vertical displacement, or U) were not consistently sensitive to mix design parameters, but the Jc (calculated using the data of three notches) was found to be fairly sensitive to all mixture variables selected, including binder type, NMAS, and compaction effort (Ndesign). Furthermore, Kim et al. (2012) evaluated the effect of RAP content and oven aging on LTRC-SCB results. They compared different mixtures with different RAP contents (15%, 20%, and 30%). The Jc value comparisons showed mixed trends. In comparing two mixtures, higher RAP content yielded lower Jc values as expected, but in comparing the other two mixtures, higher RAP content resulted in higher Jc values, which indicate better cracking resistance. As for the

26

aging comparison, the Jc values of unaged and oven aged specimens of the same mixture were compared for three different mixtures type with PG 64-22, polymer-modified PG 70-22, and polymer-modified PG 76-22. They found that the difference in the Jc values as a result of aging is insignificant, which contradicts the expected negative effect of aging on cracking resistance of HMA mixtures.

Mogawer et al (2015) also evaluated the use of the LTRC-SCB test to evaluate the effect of long-term aging on the fatigue performance of high RAP mixtures with and without RAs. Asphalt mixtures with PG 58-28 + 50% RAP with and without RA (either an aromatic oil or an organic blend) showed similar fracture resistance as compared to a control mixture containing PG 64-28. Thus the test was not capable of capturing either the effect of using 50% RAP or the inclusion of RA. Adding a paraffinic oil RA or a second organic blend RA to the PG 58-28 + 50% RAP resulted in less fracture resistance as compared to the same mixture without RA, again against expectations. However, the Jc value decreased for all mixtures (except one mixture with PG58-28) after long-term oven aging (5 days @85⁰C), which suggests that the LTRC-SCB test is sensitive to this effect.

Based on the comparisons described, there are concerns with the ability of the LTRC-SCB test to consistently capture the effect of RAP inclusion, RA inclusion, and aging on the cracking resistance of asphalt mixtures. Thus, a second SCB test utilized by others was explored in recent literature.

Al-Qadi and co-workers at the Illinois Center for Transportation (ICT) developed and verified the Illinois Flexibility Index Test (IFIT) that also utilizes a modified SCB test to rank and quantify intermediate temperature cracking potential of asphalt mixtures and proposed an AASHTO specification for the test. Before they developed the IFIT method, they evaluated other existing cracking tests including the indirect tensile (IDT) strength test, the Texas overlay test (OT), the disk-shaped compact tension (DCT) test, the push-pull fatigue test, the complex modulus (E*) test, and the low-temperature SCB test (AASHTO TP 105-13). They concluded that none of these tests was appropriate to accurately, and consistently predict and rank an asphalt mixture based on its cracking resistance with the established test methods’ criteria except for the Texas OT. The comparison of fatigue cracking resistance between IFIT and OT indicated a good correlation between these tests at intermediate temperature (25°C [77°F]). Both tests were able to distinguish the performance of asphalt mixtures with different recycled materials content and binder PG grade. However, the Texas OT suffers from issues with repeatability and time-consuming specimen preparation and testing.

The new IFIT is similar to the LTRC-SCB mentioned previously for intermediate temperature cracking but with a few differences in specimen geometry, loading rate, and output parameters. An asphalt pavement core or laboratory compacted specimen is trimmed and cut in half to create a semicircular test specimen with a thickness of 50 mm, and a notch is introduced along the axis of symmetry 15 mm in depth and 1.5 mm in width. The three-point bending test is also run at 25°C (77°F) but with a loading head displacement rate of 50 mm/min (2 in/min). From the load and displacement history recorded from the test, a number of parameters can be extracted such as work of fracture and fracture energy (area under load-displacement curve), peak load, displacement at the peak load, and post-peak slope or the slope at the inflection point (Al-Qadi et al, 2015). In addition, the flexibility index (FI) was introduced to capture cracking resistance of different mixtures with different binder PG grade and recycled materials content. FI is calculated by dividing the fracture energy by the absolute value of the post-peak slope.

27

According to Al-Qadi et al (2015), the developed FI provides greater separation between asphalt mixtures to capture the effects of different mixture variables that could not be captured by the previous parameters alone, particularly the fracture energy. For instance, they found a consistent reduction trend in FI with increasing RAP content in the mixture (from 0 to 60%). In addition, mixtures with the same RAP content and stiffer binder (PG 70-22) had significantly lower FI values as compared to mixtures having the same RAP content and softer binder (PG58-22).

Zhou et al (2016) also investigated the sensitivity of a number of cracking tests to several mixture parameters which have a significant impact on performance. The cracking tests utilized were the Texas OT, the DCT test, the LTRC-SCB test, and the IFIT. The key components evaluated were binder PG grade, binder content, and RAP/RAS content. The following five dense-graded asphalt mixtures were designed and prepared: (1) virgin/target mix with 5% PG 70-22, (2) virgin/target mix with 5.5% PG 70-22, (3) 20% RAP mixture with 5% PG 64-22, (4) 20% RAP mixture with 5% PG 64-34, and (5) 5% RAS mixture with 5% PG 64-22. The following results were expected:

Mix 2 would have better cracking resistance than Mix 1 due to a higher binder content.

Mix 3 would have worse cracking resistance than Mix 1 due to the high RAP content even though a softer base binder was used.

Mix 4 would have significantly better cracking resistance than Mix 3 due to the modified binder.

Mix 5 would have worse cracking resistance than Mix 4 due to the RAS binder even though both mixtures have an RBR of 0.2.

Test results showed that both the LTRC-SCB test and the IFIT were sensitive to the softer binder (PG 64-22 vs PG 64-34). However, only the LTRC-SCB test was sensitive to the increase in binder content. As for RAP/RAS utilization, both tests were sensitive to RAP inclusion, in which adding 20% RAP reduced cracking resistance of the asphalt mixtures. However, only the IFIT was sensitive to RAS inclusion in which a decrease in cracking resistance was observed. LTRC-SCB results showed that the addition of RAS improves cracking resistance, which is contrary to expected performance.

Field cores taken from field test sections were used to compare LTRC-SCB test and IFIT results with the performance of the mixtures in the field. Two test sections were constructed with two different mixtures: a virgin/target mixture (PG 70-28) and a recycled mixture (PG 70-28 plus 5%RAP and 5%RAS). Several performance surveys were conducted after the construction and used to compare the tests results. It was found that IFIT results matched the field observation in which the virgin/target mixture is better than the recycled mixture. LTRC-SCB results showed the recycled mixture had better cracking resistance than the virgin/target mixture, which is not consistent with field observations of performance.

The comparisons described highlighted the fact that even though the LTRC-SCB test is sensitive to the change in binder content and PG grade, there are concerns with its ability to consistently capture the effect of RAP/RAS inclusion, RA inclusion, and aging on the cracking resistance of asphalt mixtures. The IFIT appears to provide a better way to evaluate the effect of these variables on asphalt mixtures.

28

CHAPTER 2 REVISED PHASE II LABORATORY EXPERIMENT DESIGNS

This chapter provides the revised laboratory experiment designs for Phase II that evolved based on a continual review of results to select material and testing combinations that consider the limitations of materials, time, and budget and meet the study objectives to:

Assess the effectiveness of RAs in partially restoring blended binder rheology through selection of an optimum RA dosage based on binder testing and validation by a more representative mortar evaluation.

Assess the effectiveness of RAs in improving mixture cracking performance at optimum dosage rates using selected laboratory tests.

Evaluate the evolution of RA effectiveness. Recommend evaluation tools for assessing the effectiveness of RAs and their

evolution for specific material combinations at specific locations.

Based on Phase I and laboratory results to date, the revised Phase II laboratory experiment designs detailed in this chapter focus on the following:

High 0.4 or 0.5 RBRs with all RAP and balanced RAP/RAS combinations. Traditional aromatic and greener alternative tall oil RAs. TX (expanded): PG 70-22, PG 64-22 + PG 64-28 (NH) + PG 64-28P (NV) with TX

RAP, TX TOAS, and TX MWAS NV: PG 64-28P with NV RAP for binder and mortar experiments only

2.1 Field Projects and Expanded Materials

In selecting field projects to be associated with the Phase II laboratory experiments and the Phase III field experiments, consideration was given to obtaining a range in each of the following factors to make the conclusions of this study as comprehensive as possible:

RA by category as defined in Table 2.1 for comparison of traditional aromatic agents with alternative green tall oil technologies.

RA handling procedure including temperature of mixing, time of mixing, and location where it is introduced in the production process.

Environment by SHRP-LTPP zones of Wet-Freeze, Dry-Freeze, Wet-No Freeze, and Dry-No Freeze (Figure 2.1).

Traffic volume.

29

Table 2.1. RA Categories and Types (NCAT 2014a).

Category Types Description

Paraffinic Oils

Waste Engine Oil (WEO) Waste Engine Oil Bottoms (WEOB) Valero VP 165® Storbit®

Refined used lubricating oils

Aromatic Extracts

Hydrolene® Reclamite® Cyclogen L® ValAro 130A®

Refined crude oil products with polar aromatic oil components

Napthenic Oils SonneWarmix RJ™ Ergon HyPrene®

Engineered hydrocarbons for asphalt modification

Triglycerides & Fatty Acids

Waste Vegetable Oil Waste Vegetable Grease Brown Grease Oleic Acid

Derived from vegetable oils

Tall Oils Sylvaroad™ RP1000 Hydrogreen®

Paper industry by-products Same chemical family as liquid antistrip agents and emulsifiers

30

Figure 2.1. SHRP-LTPP Environmental Zones and Constructed and Probable Field

Projects.

Since the laboratory experiments are tied to actual field projects to facilitate Phase III, selection of a field project in a specific environment simultaneously resulted in selection of the aggregate and binder types (and additives, including RAs) based on the materials selected by the respective DOT. Other eligibility requirements for field projects include:

Include a high RBR between 0.3 and 0.5. Located on a highway, arterial, or collector facility in North America. Include a virgin/target section (with no recycled materials) if possible. Include a control section (with recycled materials but without RA). Include multiple RAs if possible. With a minimum number of WMA and anti-stripping additives. Not yet constructed with materials available for testing.

New construction was required for this study, as it provides the only opportunity for fabrication of reheated plant-mixed, laboratory-compacted (RPMLC) specimens that capture field blending of base binders, recycled materials, and RAs and a starting point for tracking performance of cores to validate laboratory aging protocols critical to evaluating mixture cracking resistance and its evolution.

31

Table 2.2 provides details for the field projects constructed to date in TX, NV, and IN which include those utilized in Phase II from TX and NV. Also shown is the best information to date for the probable field project in MO where most of the eligibility requirements are met. In the MO potential field project, there are two different base binder grades. Two other potential field projects are also being pursued in WI/MI and NJ/NY. It is likely that two of these three potential field projects will be utilized in Phase III. The RAs for each field project were selected based on the interests of the state DOTs and/or contractors in consultation with the research team.

Table 2.2. Constructed and Potential Field Projects.

$Not true control as it contains less recycled materials

Field Project w/Environment & Construction

Date Mix Type RBR RAPBR | RASBR RA Texas SH 31

Wet, No-Freeze 6/2014

Target 0.0 — —

Recycled Control 0.3 0.1 | 0.18 —

Recycled w/T1 0.3 0.1 | 0.18 T1

Nevada Matterhorn Blvd

Dry, Freeze 9/2015

Target 0.0 — — Recycled Control 0.3 0.3 | 0.0 — Recycled w/T2 0.3 0.3 | 0.0 T2 Recycled w/A2 0.3 0.3 | 0.0 A2

Indiana Co Rd W2100 Wet, Freeze

9/2015

Target 0.0 — — Recycled Control$

0.3 0.25 | 0.07 —

Recycled w/T2 0.4 0.14 | 0.27 T2

Missouri City Street

Wet, Freeze 2016

Target 0.0 — — Recycled Control1

0.45 0.35 | 0.1 —

Recycled Control2

0.45 0.35 | 0.1 —

Recycled1 w/T1 0.45 0.35 | 0.1 T1 Recycled2 w/T1 0.45 0.35 | 0.1 T1

32

The materials from the TX field project included a target PG 70-22 binder, a control PG 64-22 binder, TX RAP, TX MWAS, and a tall oil (T1) RA added at a field RA dosage of 2.65%. These materials from the TX field project were expanded with the following supplemental materials to develop the revised Phase II laboratory experiments:

An unmodified PG 64-28 (S-controlled) binder from NH. A polymer-modified PG 64-28P binder from NV. TX TOAS. Three RAs: an aromatic extract (A1), a paraffinic oil (P), and a re-refined lube oil (R).

And the following materials from the NV field project were utilized in the binder blend and mortar experiments in Phase II: a PG 64-28P target and base binder, NV RAP, and two RAs (a tall oil T2 and an aromatic extract A2).

Thus, the materials used in Phase II were selected based on input from panel comments and careful selection of efficient material and testing combinations to focus on commonly used and available TOAS in addition to MWAS; four types of rejuvenating RAs including traditional aromatic extract and paraffinic oil RAs to compare with alternative re-refined lube oil and green tall oil RAs; base binder type; and 0.3, 0.4, and 0.5 RBR values with all RAP or RAP/RAS combinations.

2.2 Field Activities

Field activities for the constructed field projects in TX, NV, and IN included gathering original component materials and plant mix for fabrication of laboratory-mixed, laboratory-compacted (LMLC) and RPMLC specimens, respectively, and procuring cores at construction and after approximately 1 year to verify specimen fabrication and aging protocols and validate relationships between binder and mixture properties. These materials were available through cooperation with the state DOTs, contractors, and state asphalt paving associations. General field performance assessment by visual survey is also planned in cooperation with the associated DOTs. In addition, cumulative degree days (CDDs, 0°C base) based on daily average temperatures since construction was gathered for each field project location for use in Phase III to quantify field aging and normalize data with respect to both environment and date of construction as in NCHRP Project 9-52 and discussed in Chapter 6. Construction reports for the NV and IN field projects are provided in Appendix A and Appendix B. The construction report for the TX field project was provided in an appendix to the first interim report. And additional details on these field activities are discussed in the following subsections.

2.2.1 Material Sampling during Production and Construction

The sampling plan followed the guidelines established in Research Results Digest 370, Guidelines for Project Selection and Materials Sampling, Conditioning, and Testing in WMA Research Studies that was established and utilized by multiple recent NCHRP projects. The following general procedures were utilized:

Asphalt binders, WMA additives, RAS, RAP, any other additives (anti-stripping, etc.), and low-viscosity RAs if used were sampled at the plant location during

33

production of the mixtures for the field sections for subsequent production of LMLC specimens.

Plant mix was sampled at the plant location for subsequent production of RPMLC specimens after reheating at a central laboratory prior to compaction.

Plant production information such as plant type and characteristics, baghouse fines handling, production rate, mixture design inputs, plant temperatures, silo storage times, and haul times were recorded.

Field laydown and compaction process information was recorded, including equipment, rolling pattern, mat thickness, mat temperature, temperature uniformity, and climate conditions at the time of construction.

2.2.2 Coring Plan after Construction

To define the evolution of stiffness and cracking resistance of high RBR mixtures with RAs over time in Phase III, pavement cores will be obtained from the field sections associated with each field project throughout the duration of this study to the extent possible considering time, resource, and budget constraints. At a minimum, cores will be taken from the field projects at two different times—immediately after construction and after 1 year. Three coring periods are possible for the field projects constructed in 2014 and 2015 in TX, NV, and IN.

2.2.3 Post-Construction Assessment and Pavement Design Data

After construction, two visual condition surveys by the Long-Term Pavement Performance (LTPP) methodolody are planned for field projects constructed in 2014 and 2015 in TX, NV, and IN after 1 and 2 years of service. And other available pavement design information (e.g., pavement structure layer thickness, modulus, and traffic data) was collected for use in a layered viscoelastic continuum damage (LVECD) analysis to supplement the fatigue cracking resistance characterization with the S-VECD approach.

2.3 Laboratory Testing

The results from Phase I and continuous review of the results generated in this study were also utilized to select the laboratory tests to evaluate the performance of binders and mixtures with high RBRs for the selected materials described in the previous section in the combinations presented in the following sections for the revised Phase II laboratory experiment designs. Different tests will be utilized in the different experiment designs for binders, mortars, and mixtures as shown in Table 2.3 and described in the following sections. Further details on the selected laboratory tests shown in Table 2.4 are included subsequently.

34

Table 2.3. Material Combinations in Revised Phase II Experiments.

Materials Mortar

Virgin RBR RAP RAS RA Dosage Rheology Coating Compatibility Aging Stiffness SCB EBM SVECD UTSST HWTT

70-22 TX 0 - - - √ √ √ √ √ √ √70-22 TX 0 - - T1 √70-22 TX 0.3 0.1 TX 0.2 TX MWAS - √70-22 TX 0.3 0.1 TX 0.2 TX MWAS T1 √64-22 TX 0 - - - √ √ √ √64-22 TX 0 - - T1 √ √ √64-22 TX 0 - - A1 √64-22 TX 0 - - R √64-22 TX 0 - - P √64-22 TX 0.3 0.1 TX 0.2 TX MWAS - √ √ √ √ √ √ √ √ √64-22 TX 0.3 0.1 TX 0.2 TX MWAS T1 √ √ √ √ √ √ √ √ √ √ √64-22 TX 0.3 0.1 TX 0.2 TX MWAS A1 √ √ √ √ √64-22 TX 0.3 0.1 TX 0.2 TX MWAS R √64-22 TX 0.3 0.1 TX 0.2 TX MWAS P √64-22 TX 0.4 0.4 TX - - √ √64-22 TX 0.4 0.4 TX - T1 √ √64-22 TX 0.4 0.4 TX - A1 √ √ √64-22 TX 0.5 0.25 TX 0.25 TX MWAS - √ √64-22 TX 0.5 0.25 TX 0.25 TX MWAS T1 √ √64-22 TX 0.5 0.25 TX 0.25 TX TOAS - √ √64-22 TX 0.5 0.25 TX 0.25 TX TOAS T1 √ √ √64-28 NH 0 - - - √ √ √64-28 NH 0 - - T1 √ √64-28 NH 0 - - A1 √64-28 NH 0.3 0.1 TX 0.2 TX MWAS - √64-28 NH 0.3 0.1 TX 0.2 TX MWAS T1 √ √ √64-28 NH 0.4 0.4 TX - - √64-28 NH 0.4 0.4 TX - A1 √ √ √64-28 NH 0.5 0.25 TX 0.25 TX TOAS - √ √64-28 NH 0.5 0.25 TX 0.25 TX TOAS T1 √ √ √ √ √ √ √64-28P NV 0 - - - √ √64-28P NV 0 - - T1 √64-28P NV 0.5 0.25 TX 0.25 TX TOAS - √ √64-28P NV 0.5 0.25 TX 0.25 TX TOAS T1 √ √ √64-28P NV 0 - - - √ √ √64-28P NV 0.15 0.15 NV - -64-28P NV 0.3 0.3 NV - - √ √64-28P NV 0.3 0.3 NV - T2 √ √ √ √64-28P NV 0.3 0.3 NV - A2 √ √ √ √

10% RA at TX field

Mixture Binder

35

For all tests, a minimum of two replicate specimens was utilized with at least three replicates for MR testing. Air voids (AV) for all mixture specimens were determined by AASHTO T 166.

As shown in Table 2.4, critical representative aging states were utilized for each laboratory test across the pavement temperature spectrum, with short-term (S) aged binders (RTFO) or mixtures (short-term oven aging [STOA]) evaluated for stiffness at high temperatures and long-term (L) aged binders (RTFO and PAV) or mixtures (STOA and long-term oven aging [LTOA]) for cracking resistance or stiffness at intermediate and low temperatures. Short-term and long-term aging protocols for mixtures were first verified based on a preliminary specimen fabrication experiment as described in the first interim report. Results from ongoing NCHRP Project 9-54 with respect to the aging protocols will also be considered in Phase III as described in Chapter 6.

36

Table 2.4. Laboratory Tests (S=short-term aging, L=long-term aging).

Performance Property Binder Test Mortar Test Mixture Test

Compatibility Exudation Droplet Test

Tc SAR-AD (Phase III)

NA NA

Rheology Evolution with Aging

G*, @ Thigh after S Aging G*, @ Tint after L Aging

S, m-value @ Tlow after L Aging

Tc G-R @ Tint with Aging

CA by FT-IR with Aging Oxidation Kinetics

DSR MC

PGH after S Aging

PGI, PGL after L Aging

Tc

MR @ Tint & Tlow after S, L Aging

E* @ Thigh, Tint & Tlow after S, L Aging @ Thigh, Tint & Tlow

after S, L Aging (Phase III)

Specimen Fabrication Protocol

NA NA MR @ Tint

Rutting Resistance G*/sin @ Thigh & PGH after S Aging

PGH after S Aging

HWTT^ (Phase III)

Fatigue Resistance after Aging

G-R @ Tint with Aging PGI after L Aging SCB after L Aging

S-VECD after L Aging

Low-Temperature Cracking Resistance

after Aging

S, m-value @ Tlow & PGL after L Aging

Tc

PGL after L Aging

UTSST after L Aging

^For limited number of mixtures

2.3.1 Binder and Mortar Testing

For binder testing, the RTFO was utilized for short-term (S) aging. A single long-term (L) aging protocol of 20 hr in the PAV was used for the PG grading tests, and two long-term (L) aging protocols of 20 hr in the PAV and 40 hr in the PAV (based on recent results by Reinke et al. (2015)) was used for determination of the G-R parameter for Black space analysis. Recent work by Ryan et al. (2014) suggested that 40 hr might be sufficient in extreme climates such as Minnesota.

Traditional DSR and BBR binder testing was used to determine rheological parameters of stiffness (G* and S) and phase angle or stress relaxation ability ( and m-value) and the associated PG grade at high temperatures (PGH) and low temperatures (PGL) (AASHTO M 320 with AASHTO T 315 and AASHTO T 313).

The influence of RAs on the rheology restoration and aging characteristics of binders was assessed using chemical (carbonyl area (CA) by FT-IR) and physical (rheology) parameters. As part of the binder compatibility experiment, CA growth rates for binders with and without RAs were evaluated at a single temperature of 85°C selected as the farthest from the isokinetic temperature but practical in terms of the capabilities of the equipment and time required to obtain results. In the more extensive binder aging experiment, the binder blends were aged in a forced draft oven at different temperatures and for multiple durations and were evaluated again with CA

37

growth rate. The binders were also tested in a DSR to determine the master curves of G* and by conducting isothermal frequency sweeps at different temperatures. Rheological indices such as low shear viscosity (LSV), G-R parameter, crossover frequency and modulus (c and G*c), and rheological index R-value were calculated as a function of aging for the various binders to study the effect of RAs. Furthermore, the results were also utilized to develop and assess the effects of RAs on binder oxidative aging kinetics and resulting hardening susceptibility, which are key inputs for the modeling of binder aging during the in-service life of a pavement. In addition, a shortcut method with faster PAV oxidative aging of binders, rather than the longer testing at atmospheric pressure, was also evaluated.

The intermediate-temperature DSR parameter, called the G-R parameter (G* x (cos δ)2/(sin δ)), as originally defined by Glover et al. (2005) and reformulated for greater practical use by Rowe (2011), in a discussion of Anderson et al. (2011), was utilized to assess the effectiveness of RAs in partially restoring aged recycled binders. This G-R parameter is ideal for this purpose because it measures both fundamental rheological properties using a DSR at an intermediate temperature. The results can be compared on Black space diagrams to determine cracking resistance as defined by inadequate ductility of 5 cm to 3 cm that correlates to G-R parameter values between 180 and 450 kPa, respectively, and relates to surface raveling and cracking (Kandhal 1977). At low temperatures, the difference between the m-controlled and S-controlled PGL grades ( Tc) that Anderson et al. (2011) found correlated with the G-R parameter was also determined as an indicator of compatibility and brittleness.

The binder compatibility experiment utilizes an exudation droplet test recently used by Glaser and Porot (2014) and originally developed by Shell Bitumen as a screening test and SAR-AD analysis for more complete characterization of binder blends. The exudatioh droplet test utilizes a marble slab (with 10 mm diameter indentations) to simulate an aggregate, and blended binder droplets are placed in the indentations and kept in an oven at 60°C for 4 days under a nitrogen blanket. After aging, the width of any light-colored ring is measured under ultraviolet light and a microscope. If the ring width is greater than 1.5 mm, the binder blend is considered incompatible. The SAR-AD technique was recently developed to provide a more complete picture of binder blend chemical composition in a short period of time, with a small amount of material, and in an automated fashion. This technique provides an expanded 8 chemical fractions (2 saturates, 3 asphaltenes, 2 aromatics, and resins) as compared to the traditional ASTM D4124 (Boysen and Schabron 2013, Boysen and Schabron 2015). This technique can be utilized to examine the effect of adding RA. This more detailed compatibility analysis is planned for Phase III when results will be compared to corresponding rheological properties determined from DSR master curves and PG grading (Tc). Recent research by Ryan et al. (2014) has shown that Tc is able to screen for compatibility, and this same rheological parameter is tied to cracking resistance in MN with a threshold of approximately 5 based on work by Anderson et al. (2011). With the ultimate goal of acceptable mixture performance, incompatible binder blends will be examined to determine if binder rheological properties can preclude their use and limited mixture testing will be considered in Phase III to define inadequate mixture performance.

For mortars, the laboratory testing procedure followed the latest draft of test method AASHTO T XXX-12, Estimating Effect of RAP and RAS on Blended Binder Performance Grade without Binder Extraction (www.arc.unr.edu/Outreach.html). In this procedure, mortar and binder samples are tested in the DSR and BBR to quantify the effect of recycled binder on the continuous grade profile of base binder, allowing for an estimation of blended binder properties at critical pavement temperatures with commonly available equipment and without the

38

need for the time-consuming and hazardous binder extraction and recovery process that may impact binder properties. The following three samples are each tested at low, intermediate, and high critical PG temperatures after appropriate or critical aging in the RTFO or PAV: (a) base binder; (b) void-less Mortar A with the same base binder and a single size RAP (or RAS) from a single source; and (c) void-less Mortar B with the same base binder, the same total binder content as Mortar A, and recovered aggregate from the same RAP (or RAS) material (using the ignition oven). With known base binder properties, this procedure determines the change in continuous PG grade of the composite binder with the addition of recycled materials, which then allows for an estimation of mixture performance for a specific RBR. The effect of RAs on selected binder properties was also evaluated by adding this component to the base binder and both mortars.

2.3.2 Mixture Testing

Prior to mixture performance testing, specimen fabrication and aging protocols were established for use in the laboratory to simulate blending of the RA, recycled binder, and base binder that occurs in the field during early life of the pavement. These protocols developed and verified in NCHRP Projects 9-49 and 9-52, respectively, by Epps Martin et al. (2014, Yin et al. (2013), Yin and Garcia Cucalon et al. (2014), and Yin et al. (2015) were validated in this study for mixtures with RAs. Results and analyses were presented in the first interim report for the following selected protocols:

2 hr at 135°C (275°F) for STOA for HMA, all mixtures with RAs, and all mixtures prior to LTOA.

2 hr at 116°C (240°F) for STOA for WMA without RAs. 5 days at 85°C for LTOA for all mixtures.

Long-term aging protocol results from ongoing NCHRP Project 9-54 will also be considered in Phase III as described in Chapter 6.

During specimen fabrication of mixtures with RAS and RA dosage rates as low as 5.5% by weight of binder, incomplete aggregate coating was observed (Figure 2.2). Thus RA blending methods that ranged from 100% replacement to 100% addition were characterized in terms of aggregate coatability using a modified water absorption method developed in NCHRP Project 9-53 (Newcomb et al., 2015). The modified water absorption method is based on the assumption that a completely coated aggregate submerged in water for a short period cannot absorb water because water cannot penetrate through the binder film covering the aggregate surface. Conversely, a partially coated aggregate is expected to have detectable water absorption since water is able to penetrate and be absorbed by the uncoated area. The resulting coatability index (CI) is calculated as the relative difference in saturated surface dry (SSD) water absorption for a defined coarse aggregate fraction and the same fraction mixed with the binder blend. A higher CI indicates better aggregate coating.

39

Figure 2.2. Aggregate with Incomplete Coating.

Mixture rheology and its evolution with aging was evaluated through the use of resilient modulus (MR) and dynamic modulus (E* and ) stiffness testing. The nondestructive MR (ASTM D7369) test utilized successfully in NCHRP Projects 9-49 and 9-52 was used to measure stiffness at 25°C to assess performance for comparison with binder and mortar results. In addition, MR at 25°C was utilized to validate specimen fabrication protocols for STOA of loose-mix prior to compaction of mixtures and LTOA of compacted mixtures by comparing mixture stiffness for STOA LMLC, LTOA LMLC, reheated PMLC (RPMLC), and LTOA reheated PMLC specimens and field cores at construction and after 1 year of field aging. The MR test was selected in addition to the commonly used E* because it provides a repeatable, cost-effective measurement of tensile stiffness that is likely more sensitive to binder properties and is of great concern in mixtures with high RBRs as compared to the compressive E* stiffness. Dynamic modulus characterization, however, is required for the S-VECD and the Uniaxial Thermal Stress and Strain Test (UTSST) mixture cracking tests and provides both rheological parameters (stiffness E* and ) needed to completely assess the effectiveness of RAs in these mixtures with high RBRs. In addition, E* master curve parameters may be utilized in Phase III analyses in Black space to provide an analogous evaluation to that conducted for the binder blends.

For mixtures with high RBRs, cracking resistance is critical, and two approaches were selected to analyze mixture fatigue resistance. The first approach is the semi-circular bend (SCB) test. This approach was utilized for all mixtures and was selected based on ongoing results from NCHRP Project 9-57. Two procedures that utilize the SCB test are currently available, the LTRC-SCB test and the IFIT as compared in the literature in Chapter 1. These two procedures as described in this section were compared, and the results are shown in Chapter 4. The IFIT was then used to evaluate the evolution of RA effectiveness in improving mixture cracking resistance.

The LTRC-SCB approach conducts the SCB test on three half disc specimens with different notch depths. To conduct an SCB test, a specimen is placed with its flat side on two rollers and a cross-head controlled load at a constant deformation rate is applied. Table 2.5 summarizes all the parameters regarding geometry of specimen, notch depths, test temperature, and loading rate for the SCB test with the LTRC-SCB approach.

40

Table 2.5. Summary of the SCB Test Parameters for the LTRC-SCB Approach.

Diameter (mm)

Thickness (mm)

Notch depths (mm)

Displacement Rate

(mm/min)

Temperature (ºC)

150 57 25.4

0.5 25 31.8 38.1

Fracture energy (U) is calculated by measuring the area under load versus deflection

curve up to peak load for each notch depth (Figure 2.3). Fracture energy (U) versus notch depth is plotted to determine the rate of change in the fracture energy as a function of notch depth (Figure 2.4). JC is calculated by dividing the absolute slope of fracture energy versus notch plot (kJ/m) by the thickness of specimen.

JC=-( )

where: JC= critical strain energy release rate (kJ/m2) b = specimens thickness (m) a = notch depth (m) U= strain energy to failure (kJ) dU/da= change of strain energy with notch depth, kJ/m

41

Figure 2.3. LTRC-SCB Approach Force-Deflection Plot (left) and Test Set Up (right).

Figure 2.4. LTRC-SCB Approach Gf -Notch Depth Plot (calculation of slope “m” using

linear fit is also shown).

42

Generally, the higher the value of JC, the better mixture is expected to perform with

respect to fatigue cracking. In order to obtain sufficient fracture resistance of the mixture, JC values of at least 0.65 kJ/m2 are recommended.

The Illinois Flexibility Indext Test (IFIT) includes SCB testing of a half disc specimen with only one specific notch depth. To conduct an SCB test, a specimen is placed with its flat side on two rollers and a cross-head controlled load at a constant deformation rate is applied. Table 2.6 summarizes all the parameters regarding geometry of specimen, notch depth, test temperature, and loading rate for the SCB test with the IFIT approach.

Table 2.6. Summary of the SCB Test Parameters for the IFIT Approach. Diameter

(mm) Thickness

(mm) Notch Depths

(mm) Loading Rate

(mm/min) Temperature

(ºC) 150 50 15 50 25

The IFIT uses a flexibility index (FI) parameter to evaluate fatigue cracking (Figure 2.5).

Flexibility Index is calculated by dividing fracture energy, calculated as the area under the entire load-displacement curve, by the slope of the post peak curve at the inflection point:

FI= | |

∗A

where:

Gf = fracture energy m = the post peak slope at the inflection point A = a unit and thickness adjustment constant The area under the curve is obtained analytically using the raw data. In order to

determine m (slope at inflection point), the data after the peak is fitted using an exponential form:

P2(u) = ∑ d exp

where: P2(u) = the fitted equation after the peak; d, e, and f = regression constants n = number of the exponential terms The inflection point is determined using P”2(u) =0, and the slope (m) is quantified as

P’2(u); the regression is performed so that the Sum of Squared Differences (SSD) is minimized using the solver function in excel. Analysis of up to 6 exponential terms was conducted and based on SSD comparisons and the shape of the curve, it was determined that 2 terms (as shown below) is sufficient to model the data:

y a e a e

43

The accuracy of the fitted equation and the resulting slope was also evaluated using a six term polynomial fit as follows:

y a a a a a a a

Slope and peak load are directly related to the thickness of the specimen, so the slope values

were normalized based on the thickness (standard thickness of 50 mm) in order to obtain an adjusted flexibility index.

FIadjusted= FI

∗ Thickness

Generally, the higher the value of FI, the better mixture is expected to perform with

respect to fatigue cracking. There is not a threshold value in the proposed standard, however the FHWA-ICT-15-017 (December 2015) report states that FI values greater than 6 are expected to have better fatigue performance.

Figure 2.5. Fracture Energy and Post Peak Slope for IFIT SCB Method.

The second approach is the S-VECD approach developed originally by Kim and Little (1990) and extended for both controlled stress and strain cyclic loading conditions and to include the effects of healing (Lee and Kim 1998a, 1998b), temperature, and monotonic loading (Daniel and Kim 2002). This approach was utilized on a limited basis to characterize RPMLC specimens. The viscoelastic continuum damage model produces a damage characteristic curve for a mixture that can be used to determine mixture response to any uniaxial loading history. Testing time was reduced when several researchers (Chehab et al. 2002; Underwood et al. 2009) confirmed the validity of the time-temperature superposition principle that allows characterization at a single temperature. Recently, the S-VECD approach was developed to reduce analysis time and establish compatibility with the AMPT (Underwood et al. 2010). This approach that includes the E* measurement is now AASHTO TP 107. This second approach may also provide low temperature mixture cracking resistance when used with E* characterization at low temperatures.

The evolution of RA effectiveness in improving mixture cracking resistance will also be evaluated with respect to low-temperature cracking since these mixtures with high RBRs will be

44

stiff and exhibit significant brittle behavior with an inability to relax stress. A complete characterization of the mixture properties can be obtained with the measurements of both the thermal strain and thermal stress, and through the examination and interpretation of the relationship between these two measurements. For this purpose the Uniaxial Thermal Stress and Strain Test (UTSST) has recently been developed through enhancement of the traditional TSRST setup that measures thermal stress build-up under a constant cooling rate in a restrained mixture specimen until fracture. The UTSST test allows reliable and repeatable measurements of thermal stress and strain from restrained and unrestrained asphalt mixture specimens, respectively. The UTSST specimens can be easily obtained from Superpave gyratory compacted specimens or field cores with a lift thickness of at least 65 mm. More detailed information regarding the test setup and sample fabrication can be found in the literature (Alavi et al., 2013a, Hajj et al., 2013).

The UTSST test has been used in several recent studies to investigate the thermo-viscoelastic (i.e., stiffness-temperature relationship) and fracture properties of asphalt mixtures including mixtures with high RAP contents (Menching et al., 2014) and select WMA mixtures (Hajj et al., 2013). Moreover, the evolution of the stiffness-temperature curve calculated using the UTSST results with oxidative aging of asphalt binder has been observed and described recently (Alavi et al., 2013b, Morian et al., 2014; Morian, 2014).

Figure 2.6 presents the layout of the UTSST apparatus. The thermal stress and thermal strain were measured, respectively, from the restrained and unrestrained asphalt mixture specimens using the UTSST device. Briefly, the measurements were obtained while the restrained and unrestrained specimens were simultaneously subjected to a cooling rate of 10°C/hr starting from an initial temperature of 20°C. Detailed information regarding the effect of cooling rate on UTSST results can be found in literature (Alavi and Hajj, 2014). A minimum of two replicates for the restrained specimen were tested for each evaluated mixture. In the case of thermal strain, the same unrestrained specimen was tested twice, once for each of the corresponding retrained specimen replicate tests.

Figure 2.6. Uniaxial Thermal Stress and Strain Test (UTSST) Setup.

The thermal contraction strain of the unrestrained specimen caused by constant cooling rate, as shown in Figure 2.7, can be fitted with the following proposed model (Bahia, 1991) to obtain the thermo-volumetric properties of the asphalt mixture.

45

Figure 2.7. Determination of Thermo-Volumetric Properties from Thermal Strain

Measurements.

∆ 1

where:

∆ ⁄ : relative change of length or thermal strain; C: fitted intercept;

: liquid coefficients of thermal contraction; : glassy coefficient of thermal contraction;

: temperature; and : glass transition temperature.

The measured thermal build-up stress can be related to the corresponding measured

thermal strain using the uniaxial constitutive equation for linear viscoelastic materials, i.e., Boltzmann’s equation (Christensen, 2003). These conditions are considered to be met for uniform and undamaged specimens. By considering the synchronized thermal stress and thermal strain measurements, the UTSST modulus of an asphalt mixture at each temperature (corresponding to testing time t ) can be calculated from the discrete form of the Boltzmann’s equation as follows:

∑

where: E: asphalt mixture UTSST modulus

: thermal stress : thermal strain

: testing temperature as a function of testing time tn: testing time n and i: time indices (i changes from 0 to n+1)

Five characteristic stages of material behavior are then identified from the developed

stiffness-temperature curve relationship and thermal build-up stress curve (Figure 2.8). A brief description for these behaviors is listed subsequently. In this study, the main evaluation was performed by examining the stresses and temperatures corresponding to fracture, crack initiation,

-0.0015

-0.001

-0.0005

0

-50 -40 -30 -20 -10 0 10 20Th

erm

al S

train

(mm

/mm

)

Temperature (°C)

CTCl

CTCg

Tg

46

and viscous softening stages. Further information regarding the thermo-viscoelastic properties and the stiffness-temperature relationship can be found in the literature (Alavi et al., 2013a; Hajj et al., 2013; Morian, et al., 2014; Alavi and Hajj, 2014; Menching et al., 2014).

Viscous softening: From this stage the relaxation modulus of the asphalt mixture increases rapidly with decreasing temperature.

Viscous-glassy transition: At this stage the glassy properties of the material overcome the viscous properties.

Glassy hardening: At this stage the behavior of the material is pure glassy. Crack initiation: In this stage micro-cracks occur in the specimen due to the induced

thermal stresses when the material behavior is glassy. Fracture: At this stage the asphalt mixture specimen breaks due to the propagation of

micro-cracks by the induced thermal stresses, i.e. macro failure.

(a)

(b)

Figure 2.8. (a) Measured Thermal Stress and Strain; (b) Calculated UTSST Modulus and Associated Characteristic Stages.

-0.0012

-0.001

-0.0008

-0.0006

-0.0004

-0.0002

0

0

0.5

1

1.5

2

2.5

-40 -30 -20 -10 0 10 20 The

rmal

Str

ain

(mm

/mm

)

The

rmal

Str

ess

(MP

a)

Temperature (°C)

Thermal Stress Thermal Strain

Fracture

-100

-80

-60

-40

-20

0

20

0

1,000

2,000

3,000

4,000

5,000

6,000

-40 -30 -20 -10 0 10 20

2nd

deri

vati

ve

UT

SS

T m

odul

us (

MP

a)

Temperature (°C)

Relaxation Modulus 2nd derivative of Relaxation Modulus

Crack initiation

Glassy hardening

Viscous-glassy transition

Viscous softening

Fracture

UTSST Modulus

47

Based on five characteristic stages of material behavior (Alavi 2014, Morian 2014), a UTSST resistance index is calculated as follows based on the predefined areas (Av = area to viscous softening; Ai = Area to cracking initiation; and Ap = area to ultimate fracture) above the thermally-induced stress-strain curve and below the fracture stress limit (Figure 2.9). These predefined areas along with their interactions can provide a better indication of the relaxation properties of the asphalt mixture and its response to thermally-induced stresses. A higher resistance index is expected for asphalt mixtures with higher relaxation properties; hence, a better thermal cracking resistance.

Figure 2.9. UTSST Resistance Index.

istance

where:

Av: area to viscous softening Ai: area to crack initiation Ap: area to ultimate fracture v: stress at viscous softening F: fracture stress

While mixture cracking resistance is the biggest concern with high RBRs and is thus the focus of this study, addition of RAs to address this issue must be balanced by ensuring adequate mixture resistance to rutting and moisture susceptibility during early life. In Phase III for a limited number of mixtures with a high RA dosage, the HWTT (AASHTO T 324) with traditional parameters of rut depth at a specific number of load cycles and stripping inflection point will be utilized to check mixture resistance to rutting and moisture susceptibility,

48

respectively. In addition, three new parameters defined by Yin and Arambula et al. (2014) that separate mixture resistance to these two forms of distress will be determined from the same set of laboratory results.

2.4 Binder and Mortar Experiments

The binder experiment designs combine the selected laboratory tests and materials in different combinations described previously in three different experiments: binder blend rheology, binder aging, and binder compatibility. These binder experiment designs are shown in Table 2.7, Table 2.8, Table 2.9, and Table 2.10 with the shaded combinations indicating those associated with the corresponding field project. Table 2.7 and Table 2.8 are used to select the optimum RA dosage used when assessing the G-R parameter with aging and mixture performance properties. And the mortar experiment designs shown in Table 2.11 and Table 2.12 were used to verify the binder blend rheology results. The comparison of material combinations included in all of the revised Phase II experiments is shown in Table 2.3, and the factors evaluated in these experiments are highlighted in Table 2.13.

49

Table 2.7. Revised Binder Blend Experiment for TX (Expanded) Materials Cluster.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

PGH, PGL, Tc

0% RA

Low %

RA$

High%

RA$

G-R, FT-IR

CA @ Opt with

Aging 70-22 0 — — — NA NA

64-22

0 — — — NA NA 0.3 0.1 TX 0.18 TX MWAS T1 0.3 0.1 TX 0.18 TX MWAS A1 0.4 0.4 TX 0.0 T1 0.4 0.4 TX 0.0 A1 0.5 0.25 TX 0.25 TX MWAS T1 0.5 0.25 TX 0.25 TX TOAS T1

64-28 0 — — — NA NA

0.4 0.4 TX 0.0 A1 0.5 0.25 TX 0.25 TX TOAS T1

64-28P 0 — — — NA NA

0.5 0.25 TX 0.25 TX TOAS T1 $ Dosages for T1 = 2 and 10%; for A1 = 5 and 10%

Table 2.8. Revised Binder Blend Experiment for NV Field Materials.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

PGH, PGL, Tc G-R, FT-IR CA

@ Opt with Aging

0% RA

Low %

RA$

High%

RA$

64-28P 0 — — — NA NA Phase III

0.3 0.3 NV 0.0 T2 Phase III 0.3 NV 0.0 A2 Phase III

$ Dosages for T2 = 1, 3, and 5%; for A2 = 1.5, 2, and 3%

50

Table 2.9. Revised Binder Aging Experiment for TX (Expanded) Materials Cluster.

Base Binder RBR

RAPBR &

Source RASBR &

Source RA

Aging FT-IR

CA DSR MC

w/G-R

64-22

0 — — — PAV

20, 40

Pha

se I

II

Phase III

Oven

0 0.0 0.0 T1# PAV

20, 40 Phase III

Oven

0.3 0.1 TX 0.18 TX MWAS T1# Oven

64-28

0 — — — PAV

20, 40

Pha

se I

II

Phase III

Oven

0 0.0 0.0 T1# PAV

20, 40 Phase III

Oven

0 0.0 0.0 A1* PAV

20, 40 Phase III

Oven 0.4 0.4 TX 0.0 A1* Oven 0.5 0.25 TX 0.25 TX TOAS T1* Oven Phase III

64-28P

0 — — — PAV

20, 40 P

hase

III

Phase III Oven

0 0.0 0.0 T1# PAV

20, 40 Oven

0.5 0.25 TX 0.25 TX TOAS T1* Oven # At TX field RA dosage * At optimum by binder blend testing

51

Table 2.10. Revised Preliminary Aging and Binder Compatibility Experiment for TX (Expanded) Materials Cluster.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

FT-IR Exudation

Droplet SAR-AD

(Phase III)

64-22

0 — — — 0 — — T1 $ $ — 0 — — A1 $ $ — 0 — — P $ $ — 0 — — R $ $ —

0.3 0.1 TX 0.18 TX MWAS — 0.3 0.1 TX 0.18 TX MWAS T1 $ $ # 0.3 0.1 TX 0.18 TX MWAS A1 $ $ # 0.3 0.1 TX 0.18 TX MWAS P $ $ — 0.3 0.1 TX 0.18 TX MWAS R $ $ — 0.5 0.25 TX 0.25 TX MWAS — — — 0.5 0.25 TX 0.25 TX MWAS T1 — — # 0.5 0.25 TX 0.25 TX TOAS — — — 0.5 0.25 TX 0.25 TX TOAS T1 #

64-28 0 — — — — —

0.5 0.25 TX 0.25 TX TOAS — — — 0.5 0.25 TX 0.25 TX TOAS T1

$ 10% RA Dosage # Optimum RA Dosage

52

Table 2.11. Mortar Experiment for TX (Expanded) Materials Cluster. Base

Binder RAP RAS RA# Mortar Testing

— TX — — PGH — TX MWAS — PGH — TX TOAS — PGH

70-22 TX TX MWAS T1 Calculated PG Grade & Tc from PGH, PGI, PGL of Base;

Base+ RA; Base+RAP, Base+RAS;

Base+RA+RAP, Base+RA+RAS

64-22 TX TX MWAS T1

64-28

TX TX MWAS T1 TX TX TOAS T1 TX TX MWAS A1

#At Texas field dosage for T1 and optimum by binder blend testing for A1.

Table 2.12. Mortar Experiment for NV Field Materials. Base

Binder RAP RAS RA# Mortar Testing

64-28P

NV — — PGH, PGL NV — T2 Calculated PG Grade & Tc

from PGH, PGI, PGL of Base; Base+ RA;

Base+RAP, Base+RAS; Base+RA+RAP, Base+RA+RAS

NV A2

#At Nevada field dosages for T2 and A2.

Table 2.13. Factors Evaluated in Revised Phase II Experiments. Experiment Mortar Binder Blend Mixture

Factor TX

(Expanded) NV TX

(Expanded) NV

(field) TX

(Expanded) RAS Type X X Base Binder Type

X X X

RBR X X RA Type X X X X RA Dosage X X

53

2.5 Mixture Experiments

The mixture experiment designs combine the selected laboratory tests and TX (Expanded) materials in different combinations described previously in two different experiments: stiffness and performance. These mixture experiment designs are shown in Table 2.14 and Table 2.15 with the shaded combinations indicating those associated with the corresponding field project. Table 2.14 and Table 2.15 utilize the selected optimum RA dosage from binder blend testing unless otherwise noted. Expanded material combinations for mixture testing were selected based on the results of the binder and mortar experiments toward efficient use of materials, time, and budget in this study. Resilient Modulus (MR) tests, Dynamic Modulus (E*) tests, Illinois Flexibility Index Tests (IFIT) using modified Semi-Circular Bending (SCB) tests, and Simplified Viscoelastic Continuum Damage (S-VECD) tests were performed on a combination of laboratory-mixed, laboratory-compacted (LMLC) specimens, reheated plant-mixed, laboratory-compacted (RPMLC) specimens, field cores extracted immediately after construction and approximately 1 year after construction. LMLC and RPMLC specimens were short-term oven aged (STOA) for 2 hours at the compaction temperature and long-term oven aged (LTOA) for 5 days at 85⁰C (185⁰F) prior to testing. MR and SCB tests were performed at 25⁰C (77⁰F), and the E* test was performed at 4, 20, and 40⁰C (40, 68, and 104⁰F) at five frequencies (0.1, 0.5, 1, 5, 10, and 25 Hz).

In the first interim report, the energy-based mechanistic (EBM) approach that utilizes a repeated uniaxial direct tension (RDT) test was proposed as candidate test to evaluate the effect of aging on cracking resistance of RPLMLC specimens with and without RAs. In this approach based on controlled-strain RDT testing and analysis, the evolution of cracking damage density index is determined and then used to formulate a modified Paris’ law to calculate some fracture parameters that can discriminate the fatigue resistance of different types of mixtures. However, during testing of LTOA RPMLC specimens due to very high stiffness, inconsistent data were collected from the three LVTDs attached to the side of the specimen. Thus the controlling LVDT had a lot of noise and could not control the test to the desired strain. The test was repeated on a number of RPMLC specimens, but without success. Therefore, the use of this test and approach was discontinued.

The comparison of material combinations included in all of the revised Phase II experiments is shown in Table 2.3, and the factors evaluated in these experiments are highlighted in Table 2.13. Table 2.16 shows the factors investigated specifically in the mixture experiments for the TX (Expanded) materials cluster. By measuring the stiffness and intermediate temperature cracking resistance of LMLC and RPMLC specimens and field cores for the TX (Expanded) materials cluster with different levels for each of these factors, the following evaluations were completed: (1) the effectiveness of RAs in mixtures with high RBRs, (2) the effect of binder PG, RA type, and dosage on the performance of these mixtures, and (3) the stiffness and cracking resistance evolution with aging.

A statistical analysis at a 95% confidence level was performed on MR, E*, and SCB test results using analysis of variance (ANOVA) plus Tukey’s honest significant differences (HSD) to explore the effect of different factors such as binder PG grade, RA type, and RA dosage on the mixture stiffness and cracking resistance.

54

Table 2.14. Revised Mixture Stiffness Experiment for TX (Expanded) Materials Cluster.

Mix Label Base

BinderRBR

RAPBR & Source

RASBR & Source

RA MR E*

Specimen Type LMLC RPMLC

Cor

es X

2 LMLC RPMLC

Aging State

ST

OA

LT

OA

ST

OA

LT

OA

ST

OA

LT

OA

ST

OA

LT

OA

Target 70-22 0.0 --- --- --- Recycled Control

64-22 0.3 0.1 TX

0.18 TX MWAS

---

Recycled w/ T1 @ FLD 0.3 0.1 TX

0.18 TX MWAS

T1#

Recycled w/ T1 @ FLD (64-28)

64-28 0.3 0.1 TX 0.18 TX MWAS

T1# --- --- --- --- ---

Recycled w/ T1 @ 3.5%

64-22

0.3 0.1 TX 0.18 TX MWAS

T1 --- --- --- --- ---

Recycled w/ T1 @ OPT 0.3 0.1 TX

0.18 TX MWAS

T1* --- --- --- --- ---

Recycled w/ A1 @ OPT 0.3 0.1 TX

0.18 TX MWAS

A1* --- --- --- --- ---

Recycled w/ T1 @ OPT (TOAS)

64-28 0.5 0.25 TX 0.25 TX TOAS

T1* --- --- --- --- ---

#At TX field dosage (2.65% of total binder)

*At the optimum dosage by binder blend testing

55

Table 2.15. Revised Mixture Performance Experiment for TX (Expanded) Materials Cluster.

Mix Label Base

Binder RBR

RAPBR & Source

RASBR & Source

RA IFIT (SCB)

SV

EC

D

UTSST

Specimen Type LMLC

RP

ML

C

Cor

es X

2

RP

ML

C

LM

LC

RP

ML

C

Aging State

ST

OA

LT

OA

LT

OA

LT

OA

LT

OA

LT

OA

Target 70-22 0.0 --- --- ---

Pha

se I

II

Pha

se I

II

Recycled Control

64-22 0.3 0.1 TX

0.18 MWAS

---

Recycled w/ T1 @ FLD 0.3 0.1 TX

0.18 MWAS

T1#

Recycled w/ T1 @ FLD (64-28)

64-22

0.3 0.1 TX 0.18

MWAS T1# --- --- ---

Ph III

---

Recycled w/ T1 @ 3.5% 0.3 0.1 TX

0.18 MWAS

T1 --- --- --- --- ---

Recycled w/ T1 @ OPT 0.3 0.1 TX

0.18 MWAS

T1* --- --- ---

Pha

se I

II

---

Recycled w/ A1 @ OPT 0.3 0.1 TX

0.18 MWAS

A1* --- --- --- ---

Recycled w/ T1 @ OPT (TOAS)

64-28 0.5 0.25 TX 0.25 TOAS T1* --- --- --- --- ---

#At Texas field dosage

*At the optimum dosage (by binder blend testing)

56

Table 2.16. Factors Evaluated in TX (Expanded) Mixture Experiments. Factor

Mix Label Target/Base Binder

Type RA

Type RA

Dosage STOA/LTOA Specimen

Type Target X X Recycled Control X X X Recycled w/T1 @ FLD X X X X

Recycled w/T1 @ FLD (64-28) X

X

Recycled w/T1 @ 3.5% X X Recycled w/T1 @ OPT X X X Recycled w/A1 @ OPT X X Recycled w/T1 @ OPT (TOAS) X

57

CHAPTER 3 BINDER AND MORTAR RESULTS AND ANALYSIS

Chapter 3 presents the binder and mortar results and analysis, including determination of RA dosage and the effects of different factors on Tc, G-R parameters and FT-IR CA values and their evolution with aging, a preliminary aging analysis to examine the effects of RA on oxidation kinetics and a more detailed examination of the effect of aging on binder blend rheology, a preliminary examination of compatability, and the more realistic PG grades based on the mortar procedure. Appendix C provides additional binder and mortar information including refinement of the exudation droplet test method, G-R and FT-IR CA results, and mortar contour plots.

3.1 Binder Blend Rheology Results

3.1.1 RA Dosage and Tc

Binder blends at multiple RA dosages (0% or recycled control, low%, and high%) shown in Table 2.7 and Table 2.8 were characterized in terms of PG grade determination at high (PGH) and low (PGL) temperatures according to AASHTO M320. Using the following draft RA dosage selection method, these results were plotted for each blend on a comprehensive RA dosage selection graph as shown in Figure 3.1, Figure 3.2, Figure 3.3, Figure 3.4, Figure 3.5, Figure 3.6, Figure 3.7, Figure 3.8, Figure 3.9, Figure 3.10, and Figure 3.11 and the selected RA dosage was added to Table 3.1:

Plot original PGH, RTFO PGH, S-controlled PGL, and m-controlled PGL values versus RA dosage

Establish linear regression equations for each value versus RA dosage Select initial RA dosage rate in 0.5% increments to restore target binder PGL using

warmer PGL regression line Check PGH at initial RA dosage versus target binder PGH using colder PGH

regression line If required, increase/decrease RA dosage in 0.5% increments to meet target binder

PGH while maintaining target binder PGL

The dosage selection graphs indicate the change in PGH and PGL with RA dosage, the properties controlling PGH and PGL, and Tc. All of the PG grade determinations showed that the linear regional concept holds for the all material combinations tested in Phase II and thus allowed for determining the RA dosages to partially restore to a PG 70-22 required for the TX field project or a PG 64-28 required for the NV field project.

The optimum RA dosages shown in Table 8 were used to evaluate the evolution of RA effectiveness with the carbonyl area (CA) growth rate by FT-IR and the change in the Glover-Rowe parameter for unaged and aged binder blends and examine the effects of imperfect and more realistic blending with mortars and mixture performance properties. All nine blends shown in Table 3 were prepared at the optimum RA dosages shown in Table 8 for aging by RTFOT followed by 0, 20, and 40hrs in the PAV prior to additional rheological (Glover-Rowe) and chemical (CA by FT-IR) characterization. In addition, RA dosages greater than 5.5% resulted in coatability issues during mixture preparation and thus an evaluation of a combination of addition and replacement as discussed subsequently.

58

The effects of base binder type, RA type, and RAS type on optimum RA dosage are shown in Figure 3.12, Figure 3.13, and Figure 3.14, respectively. For RAP only combinations, Figure 3.12 highlights the importance of selecting a softer base binder to help as much as possible in restoring the phase angle as shown subsequently in Black space. For the blends with RAS, the effect of base binder type is not shown with respect to optimum RA dosage, but the effect is seen in lowering Tc. Figure 3.13 shows that the aromatic RA (A1) requires a higher optimum RA dosage to restore the target binder grade. And at higher RBR, the effect appears to be larger. However, in all cases the A1 RA provides a lower Tc. And Figure 3.14 shows that TOAS requires a higher RA dosage but does not appear to effect Tc when compared to the same blend utilizing MWAS.

59

Table 3.1 Recycling Agent Dosage Results.

Field Project Target

Base Binder

& Source RBR

RAPBR &

Source RASBR &

Source RA

% RA Dosage Restore

PGL Reduce PGH

Optimum (Field) Tc@ Opt

TX 70-22

64-22 TX

0.3 0.1 TX 0.2 TX MWAS T1 4.5

73-22 NA

4.5 (2.65)

10

64-22 TX

0.3 0.1 TX 0.2 TX MWAS A1 5.5

72-22 NA 5.5 9

64-22 TX

0.4 0.4 TX 0.0 T1 7.5

69-22 NA 7.5 8

64-22 TX

0.4 0.4 TX 0.0 A1 9.5

74-22 NA 9.5 7

64-22 TX

0.5 0.25 TX 0.25 TX MWAS T1 7.5

73-22 NA 7.5 9

64-22 TX

0.5 0.25 TX 0.25 TX TOAS T1 9.5

79-22 11.5

75-26 11.5 9

64-28 NH

0.4 0.4 TX 0.0 A1 3.5

79-22 6.0

75-24 6.0 4

64-28 NH

0.5 0.25 TX 0.25 TX TOAS T1 8.0

84-22 12.5

76-27 12.5 5

64-28P NV

0.5 0.25 TX 0.25 TX TOAS T1 7.0

89-22 11.0

81-27 11.0 7

NV 64-28

64-28P 0.3 0.3 NV 0.0 T2 1.5

68-29 NA

1.5 (2.0)

3

64-28P 0.3 0.3 NV 0.0 A2 2.0

69-30 NA 2.0 2

60

Figure 3.1. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-22 and T1 in

TX (Expanded) Materials Cluster.

Figure 3.2. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-22 and A1 in TX

(Expanded) Materials Cluster.

61

Figure 3.3. RA Dosage Selection for 0.4 Binder Blend with PG 64-22 and T1 in TX

(Expanded) Materials Cluster.

Figure 3.4. RA Dosage Selection for 0.4 Binder Blend with PG 64-22 and A1 in TX

(Expanded) Materials Cluster.

62

Figure 3.5. RA Dosage Selection for 0.5 Binder Blend with PG 64-22, MWAS, and T1 in TX

(Expanded) Materials Cluster.

Figure 3.6. RA Dosage Selection for 0.5 Binder Blend with PG 64-22, TOAS, and T1 in TX

(Expanded) Materials Cluster.

63

Figure 3.7. RA Dosage Selection for 0.4 Binder Blend with PG 64-28 and A1 in TX

(Expanded) Materials Cluster.

Figure 3.8. RA Dosage Selection for 0.5 Binder Blend with PG 64-28, TOAS, and T1 in TX

(Expanded) Materials Cluster.

64

Figure 3.9. RA Dosage Selection for 0.5 Binder Blend with PG 64-28P, TOAS, and T1 in

TX (Expanded) Materials Cluster.

Figure 3.10. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-28P and T2 for NV

Field Materials.

65

Figure 3.11. RA Dosage Selection for 0.3 RBR Binder Blend with PG 64-28P and A2 for

NV Field Materials.

Figure 3.12. Effect of Base Binder Type on RA Dosage and Tc for TX (Expanded)

Materials Cluster.

66

Figure 3.13. Effect of RA Type on RA Dosage and Tc for TX (Expanded) Materials

Cluster.

Figure 3.14. Effect of RAS Type on RA Dosage and Tc for TX (Expanded) Materials

Cluster.

67

3.1.2 G-R with Aging

Figure 3.15 presents the comparison of G-R parameter results for nine Texas recycled binder blends at the optimum RA dosage versus the target binder and the recycled control blends. The G-R parameter values of both the target binder and the recycled blends increased with aging, indicating increased cracking potential. For all three aging states (RTFO, RTFO plus 20-hour PAV, and RTFO plus 40-hour PAV), the recycled control blends showed the highest G-R parameter values, followed by the recycled blends at the optimum RA dosage and the target binder, respectively. These results illustrated that adding RA partialy restored the properties of aged recycled materials. Figure 3.16 shows a similar trend in terms of the G-R parameter results in Black space. The recycled blends at the optimum RA dosage were located closer to the bottom right corner than the corresponding recycled control blends, indicating improved cracking resistance. However, the improvement due to the addition of RA at the optimum dosage was not as pronounced in terms of stiffness but more significant in terms of phase angle as compared to using the target binder with no aged recycled materials. Additionally, the recycled blends at the optimum RA dosage still showed high cracking potential after 40-hour PAV aging based on the two damage curves also shown in Figure 3.16 that indicate brittle rheological behavior at G-R parameter values of 180kPa and 450kPa for the onset of cracking and significant cracking, respectively. These two G-R parameter thresholds correlate to ductility values of 5cm and 3cm, respectively, for field sections located in a PG 58-28 climate (Kandhal 1977 and Glover et al. 2005). Thus, there is a need to adjust the G-R parameter tresholds for different climates. Development of these thresholds is planned for Phase III. Based on the current thresholds, however, the PAV aging duration (in hours) required to reach the G-R damage curves were determined and the results are summarized in Figure 3.17. Given that the recycled control blends had high G-R parameter values after RTFO aging, they showed high cracking potential even before PAV aging. As compared to the recycled control blends, the recycled blends with the optimum RA dosage exhibited significant improvements in cracking resistance, with the ability to endure approximately 8 and 19 hours of PAV aging before cracking onset and significant cracking, respectively. Therefore, it was further validated that the addition of RA at the optimum dosage was able to improve the cracking ressitance of high RBR mixtures by partially restoring the rheological properties of the overaged recycled materials.

68

(a)

(b)

(c) Figure 3.15. G-R Parameter Results; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR Recycled

Blends, (c) 0.5 RBR Recycled Blends

69

(a)

(b)

(c) Figure 3.16. G-R Parameter Results in Black Space Diagram; (a) 0.3 RBR Recycled Blends,

(b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blends

70

(a)

(b)

(c) Figure 3.17. PAV Aging Durations to Reach G-R Damage Curves; (a) 0.3 RBR Recycled

Blends, (b) 0.4 RBR Recycled Blends, (c) 0.5 RBR Recycled Blends

71

In order to quantify the long-term effectiveness of RA on binder blends with high RBRs, the Rejuvenating Effectiveness (RE) parameter was proposed. The RE is schematically illustrated in Figure 3.18 and defined as follows as the normalized difference in the logarithm of the G-R parameter of the recycled blend at the optimum RA dosage versus the target binder and the recycled control blends:

100%

where: T = logarithm of G-R parameter of the target binder; RnoRA = logarithm of G-R parameter of the recycled control blend;

RRA = logarithm of G-R parameter of the recycled blend at the optimum RA dosage.

A RE value of 100% indicated an equivalent G-R parameter for the recycled blends at the optimum RA dosage as compared to the target binder; while a RE value of 0% indicated an equivalent property to the recycled control blends.

Figure 3.19 presents the evolution of RE values with PAV aging for five Texas recycled blends. At 0-hour PAV aging (i.e., right after RTFO aging), the RE values of all recycled blends were above 80%, indicating that similar G-R parameter values were achieved by those recycled blends as compared to the target binder. However, a substantial reduction in the RE values was observed after long-term PAV aging. The reduction was possibly due to the fact that a significant amount of large-size molecular asphaltenes were formed as the oxidation products during the aging process, which the RA was not able to dissociate. The RE value for 0.3 RBR and 0.5 RBR recycled blends at the optimu RA dosage dropped to 40% after 40-hour PAV aging, and a 60% RE value was observed for the 0.4 RBR recycled blends. The poorer long-term rejuvenating effect observed for the 0.3 RBR and 0.5 RBR recycled blends was likely due to the inclusion of over-aged RAS in these blends. The RE results shown in Figure 3.19 indicated that the rejuvenating effect of RA at the optimum dosage diminished with aging.

Figure 3.18. Schematic Definition of Rejuvenating Effectivenss Parameter

72

Figure 3.19. Evolution of RE values with PAV Aging

3.1.3 FT-IR CA with Aging

Figure 3.20 presents the FT-IR CA increase with PAV aging for five Texas recycled blends; the detailed results are summarized in Appendix C. As shown, all the recycled blends showed significant increase in FT-IR CA with PAV aging, indicating a continuous formation of C=O bonds due to oxidation. In addition, the recycled blends at the optimum RA dosage exhibited similar CA increase rates as compared to those of the recycled control blends. Therefore, the inclusion of RA at the optimum dosage had no effect on the oxidation kinetics of the recycled blends. According to Glover et al. (2005), the hardening effect on binder rheological properties due to oxidation can be characterized with hardening susceptibility. In this study, the G-R hardening susceptibility (G-R HS) was utilized to identify the effect of oxidation on binder rheologial properties. This G-R HS was defined as the ratio of changes in logarithm of G-R parameters over changes in FT-IR CA with aging as follows:

∆∆

where: Δ(G-R) = changes in logarithm of G-R parameter with aging; ΔCA = changes in FT-IR CA with aging. Figure 3.21 presents the G-R parameter versus the FT-IR CA results for the five Texas

recycled blends, and the G-R HS results are summarized in Table 3.2. The recycled blends at the optimum RA dosage had higher G-R HS values than the corresponding recycled control blends, which indicated that the addition of RA increased the hardening susceptibility of the recycled blends in terms of the changes in rheological properties in response to oxidation.

73

(a)

(b)

(c) Figure 3.20. FT-IR CA Increase with PAV Aging; (a) 0.3 RBR Recycled Blends, (b) 0.4

RBR Recycled Blends, (c) 0.5 RBR Recycled Blend.

74

(a)

(b)

(c) Figure 3.21. G-R Parameter versus CA; (a) 0.3 RBR Recycled Blends, (b) 0.4 RBR

Recycled Blends, (c) 0.5 RBR Recycled Blend.

75

Table 3.2. G-R HS Summary for Recycled Blends. RBR RA Dosage G-R HS

Target Binder, 70-22 8.5

0.3 RBR No RA (Control) 5.1

4.5% T1 8.5 5.5% T1 10.1

0.4 RBR No RA (Control) 4.7

7.5% T1 6.7 9.5% T1 11.3

0.5 RBR No RA (Control) 4.9

7.5% T1 6.1

3.2 Binder Aging Results

This section includes a preliminary aging to examine the effects of RA on oxidation kinetics and a more detailed examination of the effect of aging on binder blend rheology.

3.2.1 Preliminary Aging Analysis

Before looking at a detailed comparison including recycling agent effects, the aging rate of the virgin/target and control binders was compared to the predicted aging rate; the comparison emphasizes the relationship between binder activation energy (Eac) and aging rate, and further shows that two binders coming from a single manufacturer and having the same PG grade may, nonetheless, age very differently. As shown in Table 2.10, the virgin/target binder is a PG 64-22 from a given manufacturer, and for estimation purposes, kinetics parameters for a binder from the same manufacturer and having the same PG grade were used to estimate oxidation rate as shown in Figure 3.22. Further, using relations proposed by Cui et al. (2014) and Glover (presentation, 2014), it is possible to relate PAV CA growth rate to PAV Eac and POV Eac. Key equations are presented as follows, and the above-described relations are presented graphically in Figure 3.22.

CA Constant-Rate Growth Rate Equation (Arrhenius Form)

Rate A ∙ e∙

where

Rate: CA growth Rate [CA/hr]

A: Pre-exponential Factor [ CA/hr]

PAV Eac: PAV Constant Rate Activation Energy [kJ/mol]

R: Ideal gas constant [kJ/mol·K]

T: Temperature [K]

76

Relationship Between PAV Eac and PAV Pre-exponential Factor

A C ∙ e ∙ where

C1: Constant, 0.0103 [CA/hr]

C2: Constant, 0.3276 [mol/kJ]

Relationship Between PAV Eac and POV Eac

PAVEac 1.89 ∙ POVEac 91.5

where

POV Eac: POV Constant Rate Activation Energy [kJ/mol]

Figure 3.22. Graphical Relationship between PAV CA Growth Rate, PAV Eac, and POV

Eac.

Figure 3.23 shows that the virgin/target and (recycled) control binder CA growth rates are slower than the predicted CA growth rate. Although, the (recycled) control best-fit CA growth line is shifted above the virgin/target line, the virgin/target and (recycled) control binder growth rates are similar (0.0023 and 0.0021 [CA/hr], respectively) and probably cannot be statistically distinguished. The faster (0.007 [CA/hr]) predicted virgin/target growth rate is based on a PAV Eac value of 14.4 [kJ/mol] (same PG grade, same manufacturer from TxDOT Project 0-6009). In contrast, the virgin/target and (recycled) control binder PAV Eac values were calculated to be 45 and 48 [kJ/mol] respectively. POV Eac values were also calculated and are shown.

77

Figure 3.23. Comparison of Measured Virgin/Target and Control Binder CA Growth Rates

and Eac with Predicted Growth Rate for Binder from Same Manufacturer with Same PG Grade as Virgin/Target Binder (and previously reported PAV Eac).

Figure 3.24 and Figure 3.25 show the individual, measured, PAV-aged CA values with best fit regression lines for each binder virgin/target blend and (recycled) control blend, respectively, with a combined graphs also provided (with the T1 line shifted down for comparison). Each graph represents a single binder blend. The significant increase in measured CA seen with the addition of T1 RA results from the high CA content in the T1 RA rather than an increased aging rate.

78

Figure 3.24. Carbonyl (CA) Growth with Time (60 °C, 20.7 atm. gauge, and 120 hr. total

aging time).

Unaged blend CA value shown as marker without fill at zero aging time. aVirgin/Target asphalt is PG 64-22 from the Texas project. bThe T1 blend best-fit regression line has been shifted down by 1.23 for better visualization of the relative

slopes.

79

Figure 3.25. CA Growth with Time (60 °C, 20.7 atm. gauge, and 120 hr. total aging time).

[Unaged blend CA value shown as marker without fill at zero aging time.]

aControl asphalt is Virgin/Target PG 64-22 from the Texas project with a RBR of 30% (10% RAP/20%RAS).

bThe T blend has been shifted down by 1.23 for better visualization of the relative slopes. Figure 3.26 presents the CA growth rates (slopes of regression lines from graphs in

Figure 3.24 and Figure 3.25) for all of the binder blends. A statistical comparison was made to compare the grow rate of each blend with RA to the corresponding virgin/target or (recycled) control blend growth rate. Using a 90% confidence level, there is evidence that addition of P and TI RAs to the virgin/target binder reduces the CA growth rate. There is no evidence that any of

80

the RAs increase the CA growth rate of the virgin/target binder. The CA values are shifted up for the recycled (control) binder blends as expected. For the (recycled) control blends at a 90% confidence level, there is evidence that the A1, P, and T1 RAs decrease the CA growth rate. Again, there is no evidence that any of the RAs increase the CA growth rate of the recycled (control) blend. In addition, the RAs exhibit a stronger influence on the (recycled) control blend than on the virgin/target binder, as they are designed to. Alternatively, the data can be interpreted as a dilution effect with CA growth in the recycled binders may be slower than in the virgin/target binder and therefore the reduced CA growth rates are explained simply by a fraction of the blend being recycled material.

Figure 3.26. CA growth rate (60 °C, 20.7 atm. gauge, and 24–120 hr. aging).

aVirgin/Target PG 64-22 from the Texas project . bControl asphalt is virgin/target PG 64-22 from the Texas project with a RBR of 30% (10%

RAP/20%RAS).

3.2.2 DSR Function Maps and Black Space Analysis

As a portion of the binder aging study, interim results from the Texas (Base PG 64-22) and New Hampshire (Base PG 64-28) binders with various additions of the recycled materials and RAs are presented. Example results of those measures are summarized in this section where plots present the rheological measures in terms of the DSR function and Glover-Rowe parameters. In these example plots, measures of the two respective binders were determined following the isothermal aging at 60, 85, and 100°C over the temperature-specific durations.

81

Each data point indicates the respective rheological measure at one aging duration for one temperature. The determination of each respective measurement has been identified utilizing the full dynamic shear modulus (G*) master curve.

Figure 3.27 and Figure 3.28 present the comparison between the DSR function of the PG 64-22 and PG 64-28 binders and a few blends containing recycled materials and the RAs included in this study. Note that the measurements of the binders considered are specific to the testing conditions of 0.005 rad/s at 15°C.

Figure 3.27. DSR Map at 15°C for PG64-22 Base Binder (TX (Expanded) Material Cluster).

1 cm

2 cm

4 cm

6 cm8 cm

10 cm

5 cm

3 cm

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

0 250 500 750 1,000 1,250 1,500

G' (

MP

a) [

15°C

, 0.0

05 r

ad/s

]

ɳ'/G' [15°C, 0.005 rad/s]

Base (64-22)Base w/T1 @ FLD (64-22)Recycled w/T1 @ FLD (64-22/RAP+MWAS)180kPa = 5cm Duct.450kPa = 3cm Duct.

82

Figure 3.28. DSR Map at 15°C for PG64-28 Base Binder (TX (Expanded) Material

Cluster).

Initial observations of the DSR maps in Figure 3.27 and Figure 3.28 indicate the expected outcome. The younger or lesser aged binders initially start in the lower right hand corner of the DSR map and progress toward the upper left corner with increased aging. This migration across the plot indicates the loss of flexibility and increased brittleness in the binders as identified by the reduction in the correlated ductility measures on the right hand margin of the plots.

Considering the different blends of each respective base binder indicates fairly similar paths within the respective base binder, e.g. PG 64-22 or PG 64-28. This suggests that for these particular binder blends the overall behavior, i.e. the path of the DSR function, of the blended binders are heavily influenced by the base asphalt somewhat irrespective of the RAs or the recycled materials. In other words, the overall shape of the DSR map is substantially similar to the base binder in each case. However, this should not be misinterpreted to indicate that the aged properties or more specifically the rate of progression are the same with the blended materials. Specifically, the range or distances travelled across the DSR map are substantially different between the base and blended materials.

For both base binders considered and shown by the blue data points, there is a distinct increase in the flexibility noted by the addition of either RA shown by the red data points, as depicted by the substantial shift to the lower right corner of the DSR map. However, this shift does not remain constant, noting that at the more aged conditions the binders with and without the RAs are quite similar nearing the upper left of the plots. Additionally, the binder blends including the recycled materials present a marked shift back toward the left despite the inclusion of RA. This loss in ductility extends past that of each respective base binder for the lesser aged conditions, e.g. the green data points are further along the path (higher and to the left) than the base binders. Given that the aging durations of these binders are nearly the same, this finding suggests differences in the aging rate of the blended materials, at least so far as the rheological

1 cm

2 cm

4 cm

6 cm8 cm

10 cm

5 cm

3 cm

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

0 250 500 750 1,000 1,250 1,500

G' (

MP

a) [

15°C

, 0.0

05 r

ad/s

]

ɳ'/G' [15°C, 0.005 rad/s]

Base (64-28)Base w/T1 @ FLD (64-28)Base w/A1 @ OPT (64-28)Recycled w/A1 @ OPT (64-28/RAP)180kPa = 5cm Duct.450kPa = 3cm Duct.

83

properties of the DSR map indicate. Additional considerations of this fact will be further explored in the subsequent discussions as well as in Phase III which will also include oxidation measurements.

An alternative representation of the rheological measures shown on the DSR map may be considered on a Black space diagram with dynamic shear modulus (G*) plotted as a function of phase angle () as presented in Figure 3.29 and Figure 3.30. To be clear, the measures reported on the Black space diagrams are the same measures, more specifically at the same condition of 0.005 rad/s and 15°C, as were shown in the DSR map comparisons. The Glover-Rowe (G-R) parameter at the established limits of 180 and 450 kPa corresponds to the 5 and 3 cm ductility limits noted in the DSR maps. Additional conditions are noted with three levels of the rheological index (R), which has long been utilized as an aging index. Specifically, the value of R has been determined from the difference between the glassy modulus (G*g, taken as a constant 1x109 Pa) and the crossover modulus (G*c) following the Christensen-Anderson master curve methodology.

Figure 3.29. Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-22 Base

Binder (TX (Expanded) Material Cluster).

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 10 20 30 40 50 60 70 80 90

|G*|

(kP

a) [

15°C

, 0.0

05 r

ad/s

]

Phase Angle (°)

Base (64-22)

Base w/T1 @ FLD (64-22)

Recycled w/T1 @ FLD (64-22/RAP+MWAS)

G-R = 180 kPa

G-R = 450 kPa

R = 1R = 2R = 3

84

Figure 3.30. Black Space of Glover-Rowe Parameter at 15°C for PG64-28 Base Binder (TX

(Expanded) Material Cluster).

Initial considerations of the Black space diagram for the respective binder highlight similar behavioral traits as were observed in the DSR map. For each of the base binders, the lesser aged binders begin at the lower right side of the plots and progress toward the upper left with increased levels of oxidation. The progression of the binders with aging, i.e. the path of embrittlement, is quite similar, again within each respective base binder. Once more, the overall aging characteristics seem to be predominantly influenced by the base binder.

However, in agreement with the DSR map comparison, the similarities in the aging path do not directly indicate the same aging characteristics. This aspect is more clearly represented by Figure 3.31 and Figure 3.32, which are the same fitted relationships shown in Figure 3.29 and Figure 3.30, but with the individual data points removed for clarity.

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 10 20 30 40 50 60 70 80 90

|G*|

(kP

a) [

15°C

, 0.0

05 r

ad/s

]

Phase Angle (°)

Base (64-28)Base w/T1 @ FLD (64-28)Base w/A1 @ OPT (64-28)Recycled w/A1 @ OPT (64-28/RAP)G-R = 180 kPaG-R = 450 kPa

R = 1R = 3 R = 2

85

Figure 3.31. Summary Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-

22 Base Binder (TX (Expanded) Material Cluster).

Figure 3.32. Summary Black Space Diagram of Glover-Rowe Parameter at 15°C for PG64-

28 Base Binder (TX (Expanded) Material Cluster).

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 10 20 30 40 50 60 70 80 90

|G*|

(kP

a) [

15°C

, 0.0

05 r

ad/s

]

Phase Angle (°)

Base (64-22)

Base w/T1 @ FLD (64-22)

Recycled w/T1 @ FLD (64-22/RAP+MWAS)

G-R = 180 kPa

G-R = 450 kPa

R = 1R = 2R = 3

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 10 20 30 40 50 60 70 80 90

|G*|

(kP

a) [

15°C

, 0.0

05 r

ad/s

]

Phase Angle (°)

Base (64-28)Base w/T1 @ FLD (64-28)Base w/A1 @ OPT (64-28)Recycled w/A1 @ OPT (64-28/RAP)G-R = 180 kPaG-R = 450 kPa

R = 1R = 3 R = 2

86

When the Black space diagram is summarized without the data points, the relationship between the blended materials becomes more clear. Figure 3.31 indicates similar behavior with the addition of the RAs to the base binders resulting in a slight reduction in the binder stiffness but also a shift to the right, or increased phase angle. Both findings indicate an increase in flexibility as noted in the DSR map previously. By similar comparison, the addition of the recycled materials also indicated a substantial reduction in the flexibility noting both an increase in stiffness (G*) and a reduction in for a given oxidation state. Thus far, the two comparisons agree and support one another.

However, additional information may observed in the Black space representations by considering the magnitude in the change of both G* and . By comparing the range of the G* values between the unaged and highly aged binders, the two datasets can be considered fairly similar, e.g. between the base PG 64-22 and PG 64-28. However, the observed phase angle indicate a substantial change with the PG 64-28 and corresponding blends. Specifically, the binders containing the PG 64-22 binder initially begin with in the range of about 70 to 80 degrees. At the longest aged condition, those binders indicate values of nearly 30° for all three respective binder blends. Conversely, the PG 64-28 and corresponding blends initially exhibit phase angles two degrees higher, but end up over 40° after the same age conditioning. This retention in highlights the perceived benefit of utilizing the softer base PG 64-28 binder with recycled materials.

In addition to the strict rheological observations, it is also of interest to consider the rate at which to the observed changes take place within the respective materials. Commonly these rates are evaluated as a hardening susceptibility (HS), which represents the rheological indices (RI) as a function of oxidation, e.g. carbonyl content by CA and similar measures as discussed previously. However, it is considered insightful as an interim step to consider an example RI as a function of real time as well.

Thus, the G-R parameter was considered as a function of aging time utilizing the 100°C aging conditions for brevity. The 100°C aging state was selected as it represents the widest range of oxidation level, identified by the nearly unaged to the highest level of the determined G-R measures. For the sake of consistency, the G-R parameters considered here are based upon the 0.005 rad/s and 15°C evaluation conditions as were utilized previously. The G-R parameter for the PG 64-22 and PG 64-28 base binders with their respective blended materials are provided as a function of aging time at 100°C in Figure 3.33 and Figure 3.34, respectively.

87

Figure 3.33. Glover-Rowe Parameter at 15°C for PG64-22 Base Binder Aged at 100°C (TX

(Expanded) Material Cluster).

Figure 3.34. Glover-Rowe Parameter at 15°C for PG64-28 Base Binder Aged at 100°C (TX

(Expanded) Material Cluster).

0.1

1

10

100

1000

10000

0 2 4 6 8 10 12 14 16 18 20

G-R

(kP

a) [

15°C

, 0.0

05 r

ad/s

ec]

Aging (days) [100°C]

Base (64-22)

Base w/T1 @ FLD (64-22)

Recycled w/T1 @ FLD (64-22/RAP+MWAS)

G-R = 180 kPa

G-R = 450 kPa

0.01

0.1

1

10

100

1000

10000

0 2 4 6 8 10 12 14 16 18 20

G-R

(kP

a) [

15°C

, 0.0

05 r

ad/s

ec]

Aging (days) [100°C]

Base (64-28)

Base w/T1 @ FLD (64-28)Base w/A1 @ OPT (64-28)

Recycled w/A1 @ OPT (64-28/RAP)G-R = 180 kPaG-R = 450 kPa

88

Considering the G-R parameters as a function of aging time for the respective binders at a single temperature readily permits the direct comparison of the stiffening effect and subsequent loss of flexibility in the materials as they age. Based on Figure 3.33, it is evident that the addition of the RA to the base PG 64-22 increases the flexibility of the binder resulting in lower G-R values at a given aging duration. However, after substantial aging, e.g. eight or more days in this particular case, the G-R values are quite similar for the base and RA blended materials. Similar trends are observed at the lower aging temperatures; however, the collapse of the G-R at longer durations is not as pronounced. From this particular set of data, it cannot be clearly determined whether or not the base and the RA blended binder will eventually converge with that containing the recycled materials. However, the level of oxidation required to evaluate this potential is considered extremely high and may not be practically achieved in an in-service setting. This is particularly true when considering the reduced level of convergence observed with the reduced aging temperatures. Conversely, the addition of the recycled materials increases the brittleness resulting in higher G-R values again for nearly all aging durations.

An alternative way to interpret this information is to consider the duration to meet the established cracking thresholds associated with the G-R parameter, e.g. initial cracking at 180 kPa and severe distresses at 450 kPa. As an example, the base PG 64-22 binder reaches the 180 kPa cracking susceptibility indicator after approximately 4 days of aging at 100°C. The same binder blended with the T1 RA extends that duration to 4.5 days, while the addition of the RA and MWAS reduces that duration to about 2 days. Initial considerations of the base PG 64-28 binder presented in Figure 3.34 indicate quite similar comparisons noting a similar convergence at the higher levels of aging as well as the systematic deviations at lesser oxidized stages.

Comparison of the two base binders produces an interesting set of data as well. The duration for each of the base binders to reach the 180 kPa limit yields is 8 days for the base PG 64-28 binder and 4 days for the base PG 64-22 binder. When these two base binders were blended with the same dosage of the T1 RA, the durations were extended by 0.5 and 1.5 days for the PG 64-22 and PG 64-28 base binders, respectively. These durations equate to reasonably similar levels of 13 and 19 percent of the base binder durations for that particular brittleness level. Subsequently, the direct comparison of the influence of the T1 on these particular materials requires a more in-depth evaluation of the respective oxidation rates, which will be evaluated in Phase III upon completion of the infrared measurements.

Once the oxidation kinetics are determined and are assembled with the rheological indices into the hardening susceptibility relationships, it will be possible to conduct simulated aging conditions for varying environmental conditions, specifically in-service temperature fluctuations, that will permit more comprehensive evaluations of how these particular materials can be expected to perform under field conditions. Such considerations are expected to highlight the different influences of the blended materials on the overall aging and condition of the binders in-service.

3.3 Binder Compatibility Results

Preliminary exudation droplet testing for the binder compatibilty experiment was completed, and the improved test and evaluation method using 0.01 g samples was used for the control blends (TX 64-22 binder with 10 wt.% TX RAP and and 20 wt.% TX MWAS and this control binder plus 10 wt.% of each of four RAs (R, P, A1, T1)) and two binder blends from the TX (Expanded) materials cluster as shown in Table 2.10. Results for the control blends are shown in Figure 3.35, and results for the TX (Expanded) blends are shown in Figure 3.36 with a

89

summary provided in Figure 3.37. Figure 3.35(a) illustrates the binder blend samples in the marble recesses prior to any aging and under natural light. Figure 3.35(b) shows the samples after aging and under natural light, and Figure 3.35(c) shows the samples after aging under UV light. Florescent bands and an indication of their width are shown for all samples. As expected based on their chemical components, control blends with the RA P and RA R appear to have the widest and second widest bands, respectively. The control blend with the RA P is at approximately the 1.5mm band threshold utilized by other researchers to distinguish blends having potential compatibility issues from blends considered compatible. The TX (Expanded) blends exhibited less exudation than the control blends even though they contained a little more RAS and the more heavily aged TOAS instead of the MWAS. Replicate testing performed on the TX (Expanded) blends (along with the control plus T1 and virgin/target plus T1 blends previously tested) confirmed that the TX (Expanded) blends exhibit less exudation than the control blends, and additionally demonstrated that the improved exudation droplet test method is reasonably repeatable.

To better understand the exudation droplet testing results, abridged exudation droplet tests were conducted on the four RAs (i.e. the pure RA materials) and on four selected paraffinic (P) materials. The RAs were ranked by fluorescence as follows: A1, P, R, and T1, with A1 fluorescing notably more than the others. They were ranked by diffusion as follows: P, A1, T1, and R. The selected P materials showed limited florescence and substantial diffusion, comparable to the P RA. Considering these results along with the binder blend results, the P materials may cause phase separation that, in turn, causes exudation of the aromatic materials. Another possibility, although less likely, is that the P materials are exuded, but their diffusion is limited, resulting in a ring of highly concentrated P material that produces a relatively bright fluorescence under UV light.

90

Figure 3.35. (a) Control Samples Under Natural Light Before Incubation (b) Control Samples Under Natural Light After Incubation (c) Control Samples Under UV Light After

Incubation.

91

Figure 3.36. (a) Texas (Expanded) Samples Under Natural Light Before Incubation (b) Texas (Expanded) Samples Under Natural Light After Incubation (c) Texas (Expanded)

Under UV Light After Incubation.

92

Figure 3.37. Florescent Ring Widths from Exudation Droplet Test.

3.4 Mortar Results

The influence of recycled materials and RA on the blended binder continuous PG grade was evaluated using the mortar procedure for the TX (Expanded) and NV field materials. The mortar procedure followed the latest draft AASHTO T XXX-12 standard test method for Estimating Effect of RAP and RAS on Blended Binder Performance Grade without Binder Extraction (www.arc.unr.edu/Outreach.html). The effect of RAP and RAS on the blended binder continuous grade was first identified separately, then the combined effect for the RAP and RAS blend was estimated from the linear combination of the RAP-alone and RAS-alone blends (Bahia and Swiertz, 2011). A selected blend of RAP and RAS materials was also created and tested in the mortar procedure to verify the predictions for the blended binder performance grade using the linear combination of the RAP-alone and RAS-alone blends.

Figure 3.38 shows, as an example, the R100 (passing sieve #50 and retained on sieve #100) RAP and MWAS materials from the Texas field project used in the TX (Expanded) mortar experiment. The estimated influence of each of the RAP and MWAS binders on the high, intermediate, and low temperature blended binder properties was determined in terms of the grade change rate which is defined as the change in the binder grade in degrees Celsius with respect to the percent recycled binder ratio. The grade change rate is calculated as follows:

%

Table 3.3 and Table 3.4 indicate the RBRs for the RAP and MWAS used in the actual mortars as the highest percentages that allowed for sufficient workability to cast specimens free of air voids and allow sufficient total mortar asphalt contents of at least 30% by total weight that facilitate DSR and BBR testing. Table 3.3 and Table 3.4 also summarize, at each of the high, intermediate, and low temperatures, the determined grade change rate for the TX (Expanded) materials and the NV field materials, respectively.

93

Figure 3.38. RAP and MWAS Materials (Passing Sieve #50 and Retained on Sieve #100)

from Mortar Experiment for TX (Expanded) Materials Cluster.

Table 3.3. Effect of Recycling and RA on Asphalt Binder Grade Change Rate for TX (Expanded) Materials Cluster (Mortar Test Results).

Asphalt Binder

PG

RAP Binder Ratio# (%)

MWAS Binder Ratio# (%)

RA

Grade Change Rate (°C/%Recycled Binder Ratio)

High Temperature Intermediate Temperature

Low Temperature

Original RTFO S-

Controlled m-

Controlled

70-22

9.2 — — 0.28 0.28 0.33 0.29 0.42

10.1 — T1* 0.09 0.38 0.27 0.19 0.32

— 20.7 — 0.20 0.17 0.05 0.04 0.26

— 25.0 T1* 0.24 0.34 0.38 0.06 0.22

64-22

10.1 — — 0.28 0.12 0.26 0.26 0.42

10.1 — T1* 0.26 0.22 0.46 0.16 0.38

— 25.0 — 0.25 0.27 0.15 0.06 0.39

— 25.0 T1* 0.29 0.28 0.17 0.08 0.18

64-28

11.4 — — 0.41 0.49 0.27 0.22 0.10

10.1 — T1* 0.31 0.36 0.43 0.31 0.28

— 20.7 — 0.30 0.28 0.14 0.12 0.32

— 25.0 T1* 0.31 0.26 0.22 0.15 0.15 # TX RAP or TX MWAS binder ratio used during mortar testing experiment. * Binder replacement of 2.65% by total weight of binder.

94

Table 3.4. Effect of Recycling and RA on Asphalt Binder Grade Change Rate for NV Field Materials (Mortar Test Results).

Asphalt Binder

PG

RAP Binder Ratio# (%)

RA

Grade Change Rate (°C/%Recycled Binder Ratio)

High Temperature Intermediate Temperature

Low Temperature

Original RTFO S-

Controlled m-

Controlled

64-28P

12.4 — 0.07 0.15 0.12 0.09 0.32

12.4 A2* 0.09 NA@ 0.26 0.02 0.19

12.4 T2$ 0.09 0.30 0.13 0.07 0.23 # NV RAP binder Ratio used during mortar testing experiment. * Binder addition of 2.0% by total weight of binder per manufacturer’s recommendation. $ Binder replacement of 2.0% by total weight of binder. @ Not Available

Appendix C shows the various surface plots for the expected effect of the RAP and

MWAS combination as well as the T1 RA on the high, intermediate and low temperature continuous grades of the blended binders for the TX (Expanded) materials cluster. The horizontal and vertical axis of the surface plots represent the percent binder ratio for RAP and MWAS, respectively. Accordingly, the shaded area represents the resulting continuous grades of the base binders blend based on the determined grade change rates (Table 3.3).

Using the determined grade change rates with and without RA (shown in Table 3.3 and Table 3.4), the expected high, intermediate and low temperature continuous grades for the various blended binders were calculated at the following recycling binder ratios consistent with the ones used in the respective field projects. The results are shown in Figure 3.39, Figure 3.40, Figure 3.41, and Figure 3.42.

TX (Expanded) materials cluster: RAP binder ratio of 0.10, MWAS Binder ratio of 0.18, and a combined recycling binder ratio of 0.28.

NV field materials: RAP binder ratio of 0.30.

95

Figure 3.39. Effect of Recycling and RA on Continuous Grades Based on Mortar Test

Results for PG70-22 Target Binder (TX (Expanded) Materials Cluster).

108.6

133.9

74.868.7

77.569.6

78.373.1

81.173.9

73.669.9

76.4 73.7 76.7 75.979.5 79.8

21.116.8

24.519.5 22.1 23.6 25.4 26.3

-29.4 -29.1 -26.5 -27.2 -28.7 -27.9 -25.8 -26.0-24.5 -26.3-20.3 -23.2 -19.7 -22.4

-15.6-19.2

-36

-24

-12

0

12

24

36

48

60

72

84

96

108

120

132

144

RA

P

RA

S

Tar

get

70-2

2

Tar

get

70-2

2 +

T1

Tar

get

70-2

2 +

0.1

RB

R (

TX

RA

P)

Tar

get

70-2

2 +

T1

+ 0

.1 R

BR

(T

X R

AP

)

Tar

get

70-2

2 +

0.1

8 R

BR

(T

X M

WA

S)

Tar

get

70-2

2 +

T1

+ 0

.18

RB

R (

TX

MW

AS

)

Tar

get

70-2

2 +

0.2

8 R

BR

(0.

1 T

X R

AP

+ 0

.18

TX

MW

AS

)

Tar

get

70-2

2 +

T1

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.1

8 T

X M

WA

S)

Binder Testing Mortar Testing

Tem

per

atu

re (

°C)

High_Original High_RTFO Intermediate_PAV Low_PAV (S-Controlled) Low_PAV (m-Controlled)

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

96

Figure 3.40. Effect of Recycling and RA on Continuous Grades Based on Mortar Test Results for PG64-22 Base Binder (TX (Expanded) Materials Cluster).

108.6

133.9

67.662.9

81.476.8

70.465.5

72.268.1

75.070.6

68.364.6

85.480.6

69.5 66.873.2

69.674.4 71.8

18.8 17.121.4 21.7 21.5 20.1

24.1 24.7

-29.1 -30.0-26.6

-30.5-26.5 -28.4 -28.1 -28.5 -25.5 -26.9

-24.5 -25.2-15.6

-19.5 -20.3 -21.4-17.5

-21.9

-13.3-18.1

-36

-24

-12

0

12

24

36

48

60

72

84

96

108

120

132

144

TX

RA

P

TX

MW

AS

Bas

e 64

-22

Bas

e 64

-22

+ T

1

Bas

e 64

-22

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.1

8 T

X M

WA

S)

Bas

e 64

-22

+ T

1 +

0.2

8 R

BR

(0.

1 T

X R

AP

+ 0

.18

TX

MW

AS

)

Bas

e 64

-22

+ 0

.1 R

BR

(T

X R

AP

)

Bas

e 64

-22

+ T

1 +

0.1

RB

R (

TX

RA

P)

Bas

e 64

-22

+ 0

.18

RB

R (

TX

MW

AS

)

Bas

e 64

-22

+ T

1 +

0.1

8 R

BR

(T

X M

WA

S)

Bas

e 64

-22

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.1

8 T

X M

WA

S)

Bas

e 64

-22

+ T

1 +

0.2

8 R

BR

(0.

1 T

X R

AP

+ 0

.18

TX

MW

AS

)

Binder Testing Mortar Testing

Tem

per

atu

re (

°C)

High_Original High_RTFO Intermediate_PAV Low_PAV (S-Controlled) Low_PAV (m-Controlled)

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

Not

mea

sure

d.

Not

mea

sure

d.

97

Figure 3.41. Effect of Recycling and RA on Continuous Grades Based on Mortar Test

Results for PG64-28 Base Binder (TX (Expanded) Materials Cluster).

108.6

133.9

66.062.6

70.165.6

71.468.1

75.571.1

66.062.2

70.965.7

71.066.8

75.970.3

20.3 20.1 22.9 24.4 22.8 24.1 25.5 28.4

-29.7 -29.1 -27.6 -26.1 -27.5 -26.4 -25.4 -23.3

-31.2-27.2 -30.1

-24.4 -25.5 -24.4 -24.5 -21.7

-36

-24

-12

0

12

24

36

48

60

72

84

96

108

120

132

144

RA

P

RA

S

Bas

e 64

-28

Bas

e 64

-28

+ T

1

Bas

e 64

-28

+ 0

.1 R

BR

(T

X R

AP

)

Bas

e 64

-28

+ T

1 +

0.1

RB

R (

TX

RA

P)

Bas

e 64

-28

+ 0

.18

RB

R (

TX

MW

AS

)

Bas

e 64

-28

+ T

1 +

0.1

8 R

BR

(T

X M

WA

S)

Bas

e 64

-28

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.1

8 T

X M

WA

S)

Bas

e 64

-28

+ T

1 +

0.2

8 R

BR

(0.

1 T

X R

AP

+ 0

.18

TX

MW

AS

)Binder Testing Mortar Testing

Tem

per

atu

re (

°C)

High_Original High_RTFO Intermediate_PAV Low_PAV (S-Controlled) Low_PAV (m-Controlled)

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

98

Figure 3.42. Effect of Recycling and RA on Continuous Grades Based on Mortar Test

Results for PG64-28P Target Binder (NV Field Materials).

89.4

67.0

73.4 71.9

66.969.0 69.2

64.3

84.4

65.6

72.3 68.766.9

70.2

60.5

69.8

25.8

13.4

19.0 17.5 15.9 17.019.1

13.4

-23.8

-34.3-30.6 -32.2 -32.4 -31.6

-34.2 -33.7

-20.4

-30.7

-26.1-29.8 -29.5

-21.1

-27.1 -27.9

-36

-24

-12

0

12

24

36

48

60

72

84

96

RA

P

Tar

get

64-2

8P

Tar

get

64-2

8P +

0.3

0 R

BR

Tar

get

64-2

8P +

A2

+ 0

.30

RB

R

Tar

get

64-2

8P +

T2

+ 0

.30

RB

R

Tar

get

64-2

8P +

0.3

0 R

BR

Tar

get

64-2

8P +

A2

+ 0

.30

RB

R

Tar

get

64-2

8P +

T2

+ 0

.30

RB

RBinder Testing Mortar Testing

Tem

per

atu

re (

°C)

High_Original High_RTFO Intermediate_PAV Low_PAV (S-Controlled) Low_PAV (m-Controlled)

99

Examination of the mortar test results data presented in Figure 3.39, Figure 3.40, and

Figure 3.41 for the TX (Expanded) materials cluster leads to the following observations:

Using the PG70-22 target binder grade as a base binder (Figure 3.39): o The influence of T1 RA was more significant on the high original critical

temperature when compared to the low critical temperature of the blend binder.

o In all cases, the low temperature grade of the blend binder was m-controlled similar to the PG70-22 binder used.

o In general, the influence of T1 RA was more significant on the m-value critical temperature in comparison to the stiffness critical temperature.

o The use of T1 RA at the selected dosage rate helped restoring the low temperature grade of the blend binder to the target performance grade of -22C when either RAP or MWAS were separately used at the respective RBR values.

o The use of T1 RA at the selected dosage rate did not fully restore the low temperature grade of the blend binder to the target performance grade of -22C when the 0.28 RBR value was used (0.1 RAP and 0.18 MWAS). Hence, suggesting the need for a different dosage rate for the T1 RA.

Using the PG64-22 base binder (Figure 3.40): o The influence of T1 RA was similar on the high original and RTFO critical

temperatures of the blend binder performance grade. o In all cases, the low temperature grade of the blend binder was m-controlled

similar to the PG64-22 base binder used. o In general, the influence of T1 RA was more significant on the m-value low

critical temperature in comparison to the stiffness low critical temperature. o The use of T1 RA at the selected dosage rate hardly helped restoring the low

temperature grade of the blend binder to the target performance grade of -22C when either RAP or MWAS were separately used at the respective RBR values.

o The use of T1 RA at the selected dosage rate did not fully restore the low temperature grade of the blend binder to the target performance grade of -22C when the 0.28 RBR value was used (0.1 RAP and 0.18 MWAS). Hence, suggesting the need for a different dosage rate for the T1 RA.

Using the PG64-28 base binder (Figure 3.41): o The influence of T1 RA was similar on the high original and RTFO critical

temperatures of the blend binder performance grade. o In all cases, the low temperature grade of the blend binder met the target

performance grade of -22C when RAP, MWAS, or the combination of both recycled materials were used at the respective selected RBR values regardless of the use of T1 RA.

In all cases, the use of T1 RA at the selected dosage rate had a negative impact on both the m-value and stiffness low critical temperatures.

100

Examination of the mortar test results data presented in Figure 3.42 for the NV field materials leads to the following observations:

Using the PG64-28P target binder grade as a base binder (Figure 3.42): o The use of A2 RA at the selected respective dosage rate resulted in an

estimated high performance for the blend binder softer that the target high temperature performance grade of 64C.

o The use of T2 RA at the selected respective dosage rate was effective in restoring the high temperature performance grade of the blend binder.

o The use of A2 and T2 RAs at the selected respective dosage rates was effective in restoring the low temperature grade of the blend binder to the target performance grade of -28C when 0.30 RAP binder ratio was used.

o The influence of A2 and T2 RAs was more significant on the m-value low critical temperature in comparison to the respective stiffness low critical temperature.

Figure 3.43, Figure 3.44, Figure 3.45, and Figure 3.46 show the binder critical temperature difference, Tc, defined as the m-value low critical temperature minus the stiffness low critical temperature. Examination of the data leads to the following observations:

In the case of the PG70-22 target binder, the T1 RA was effective in reducing the Tc of the blend binder when RAP, MWAS, or the combination of both recycled materials were used at the respective selected RBR values.

In the case of the PG64-22 base binder, the T1 RA was effective in reducing the Tc of the blend binder when MWAS or the combination of both recycled materials were used at the respective selected RBR values. No significant effect for the T1 RA was observed on the Tc of the blend binder when RAP material was used.

In the case of the PG64-28 base binder, no significant effect for the T1 RA was observed on the Tc of the blend binder when the MWAS or the combination of both recycled materials were used at the respective selected RBR values. On the other hand, the T1 RA when used with RAP materials resulted in a change in the sign of the Tc of the blend binder indicating the shift from an S-control low critical temperature to an m-control low critical temperature.

In the case of the PG64-28P target binder, both A2 and T2 RAs resulted in a decrease in the Tc of the blend binder when RAP material was used at 0.30 RBR.

101

Figure 3.43. Effect of Recycling and RA on Asphalt Binder Critical Temperature

Difference Based on Mortar Test Results for PG70-22 Target Binder (TX (Expanded) Materials Cluster).

4.9

2.7

6.2

4.0

9.0

5.6

10.2

6.9

-3

0

3

6

9

12

15

RA

P

RA

S

Tar

get

70-2

2

Tar

get

70-2

2 +

T1

Tar

get

70-2

2 +

0.1

RB

R (

TX

RA

P)

Tar

get

70-2

2 +

T1

+ 0

.1 R

BR

(T

XR

AP

)

Tar

get

70-2

2 +

0.1

8 R

BR

(T

XM

WA

S)

Tar

get

70-2

2 +

T1

+ 0

.18

RB

R (

TX

MW

AS

)

Tar

get

70-2

2 +

0.2

8 R

BR

(0.

1 T

XR

AP

+ 0

.18

TX

MW

AS

)

Tar

get

70-2

2 +

T1

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.1

8 T

X M

WA

S)

Binder Testing Mortar Testing

ΔT

C (

°C)

[m-v

alu

e C

riti

cal T

emp

-S

tiff

nes

s C

riti

cal T

emp

]

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

4.6 4.8

11.0 11.0

6.26.9

10.5

6.6

12.2

8.8

-3

0

3

6

9

12

15

TX

RA

P

TX

MW

AS

Bas

e 64

-22

Bas

e 64

-22

+ T

1

Bas

e 64

-22

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.18

TX

MW

AS

)

Bas

e 64

-22

+ T

1 +

0.2

8 R

BR

(0.

1 T

XR

AP

+ 0

.18

TX

MW

AS

)

Bas

e 64

-22

+ 0

.1 R

BR

(T

X R

AP

)

Bas

e 64

-22

+ T

1 +

0.1

RB

R (

TX

RA

P)

Bas

e 64

-22

+ 0

.18

RB

R (

TX

MW

AS

)

Bas

e 64

-22

+ T

1 +

0.1

8 R

BR

(T

XM

WA

S)

Bas

e 64

-22

+ 0

.28

RB

R (

0.1

TX

RA

P +

0.18

TX

MW

AS

)

Bas

e 64

-22

+ T

1 +

0.2

8 R

BR

(0.

1 T

XR

AP

+ 0

.18

TX

MW

AS

)

Binder Testing Mortar Testing

ΔT

C (

°C)

[m-v

alu

e C

riti

cal T

emp

-S

tiff

nes

s C

riti

cal T

emp

]

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

102

Figure 3.44. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG64-22 Base Binder (TX (Expanded)

Materials Cluster).

Figure 3.45. Effect of Recycling and RA on Asphalt Binder Critical Temperature

Difference Based on Mortar Test Results for PG64-28 Base Binder (TX (Expanded) Materials Cluster).

-1.4

1.9

-2.6

1.6 2.0 1.90.9 1.6

-6

-3

0

3

6

9

12

15

RA

P

RA

S

Bas

e 64

-28

Bas

e 64

-28

+ T

1

Bas

e 64

-28

+ 0

.1 R

BR

(T

X R

AP

)

Bas

e 64

-28

+ T

1 +

0.1

RB

R (

TX

RA

P)

Bas

e 64

-28

+ 0

.18

RB

R (

TX

MW

AS

)

Bas

e 64

-28

+ T

1 +

0.1

8 R

BR

(T

XM

WA

S)

Bas

e 64

-28

+ 0

.28

RB

R (

0.1

TX

RA

P+

0.1

8 T

X M

WA

S)

Bas

e 64

-28

+ T

1 +

0.2

8 R

BR

(0.

1 T

XR

AP

+ 0

.18

TX

MW

AS

)

Binder Testing Mortar Testing

ΔT

C (

°C)

[m-v

alu

e C

riti

cal T

emp

-S

tiff

nes

s C

riti

cal T

emp

]

Cou

ld n

ot b

e te

sted

.

Cou

ld n

ot b

e te

sted

.

103

Figure 3.46. Effect of Recycling and RA on Asphalt Binder Critical Temperature Difference Based on Mortar Test Results for PG64-28P Target Binder (NV Field

Materials).

The estimated PGH and PGL values based on the mortar procedure as compared to those from the binder blending results can be compared in Figure 3.40 and Figure 3.42 for the TX and NV field materials. In all cases, the effect of the RA is shown in reducing both the PGH and PGL. And in general, the complete blending from the binder results results in over-estimation of the PGH (warmer by 3-8 °C for NV and 6-7 °C for TX) and the PGL (colder by 2-5 °C for NV and 2-3 °C for TX). When comparing mortar and binder results in terms of Tc in Figure 3.44 and Figure 3.46, the RA at the optimum dosage in the NV field sections results in a decrease in Tc according to both the binder and mortar results, but the low RA dosage in th TX field section only shows a decrease in Tc based on the mortar results. These differences are likely related to the base binder grades (PG 64-28P for NV and PG 64-22 for TX), the presence of the polymer NV only), the presence of RAS (TX only), the difference between the field RA dosage and the optimum RA dosage as determined by the method described previously, and/or compatibility of the base binder, recycled binder(s), and the RA that may be indicated by Tc. These results also suggest that the effect of RA may only be captured at optimum dosage or with the mortar procedure that may also capture the effect of polymer modification.

3.43.6

4.5

2.4 2.9

10.5

7.15.8

-3

0

3

6

9

12

15

RA

P

Tar

get

64-2

8P

Tar

get

64-2

8P +

0.3

0 R

BR

Tar

get

64-2

8P +

A2

+ 0

.30

RB

R

Tar

get

64-2

8P +

T2

+ 0

.30

RB

R

Tar

get

64-2

8P +

0.3

0 R

BR

Tar

get

64-2

8P +

A2

+ 0

.30

RB

R

Tar

get

64-2

8P +

T2

+ 0

.30

RB

R

Binder Testing Mortar Testing

ΔT

C (

°C)

[m-v

alu

e C

riti

cal T

emp

-S

tiff

nes

s C

riti

cal T

emp

]

104

CHAPTER 4 MIXTURE RESULTS AND ANALYSIS

Chapter 4 presents the mixture results and analysis; including coatability results to provide guidance on RA blending methods; stiffness (MR and E*) results to examine RA effectiveness and its evolution with aging for the TX (Expanded) materials cluster; and cracking resistance results after long-term aging to compare SCB methods (LTRC-SCB and IFIT) and assess cracking resistance using IFIT results for the TX (Expanded) materials cluster and S-VECD/LVECD and UTSST results for the TX field materials. Appendix D provides additional mixture information including specimen fabrication protocols, MR, E*, and SCB test procedures, results, and statistical analyses and a comparison of SCB analysis approaches including their ability to accommodate different specimen thicknesses.

4.1 Specimen Fabrication

The optimum RA dosage was determined by following the recommended RA dosage selection method described in Chapter 3 and then used to fabricate mixture specimens for stiffness and performance testing. The RA was blended with the base binder by direct addition (100% addition) if the RA dosage was less than or equal to 2% or by replacement of the base binder (100% replacement) if the RA dosage was greater than 2%. This practice worked well for low RBR mixtures (i.e., 0.3 RBR), for which the optimum RA dosage varied between 2% and 5%. However, for high RBR mixtures (i.e., 0.4 to 0.5 RBR), a significant amount of uncoated coarse aggregate particles were observed after mixing and STOA at RA dosages as low as 5.5%. The poor aggregate coating was due to the reduction in total binder content resulting from the base binder being replaced by RA.

To address the problem, a preliminary laboratory experiment was completed. Two high RBR mixtures (the 0.4 RBR PG 64-22 blend with 9.5% A1 and the 0.5 RBR PG 64-28 blend with 12.5%T1) were prepared with various RA blending methods, including 100% addition, 50% addition plus 50% replacement, and 100% replacement, and characterized in terms of aggregate coatability using a modified water absorption method developed in NCHRP Project 9-53 (Newcomb et al., 2015).

Figure 4.1 presents the coatability index (CI) results for the selected high RBR mixtures. For the 0.4 RBR mixture, the CI values for the three different blending methods were equivalent and above 90%. However, a different trend was observed for the 0.5 RBR mixture; the CI value decreased significantly as the replacement RA dosage increased from 0% to 100%. In addition, the CI value for the 100% replacement blending method was lower than the minimum threshold of 70% established in NCHRP Project 9-53. A significant number of uncoated or partially coated aggregates were also observed in the mixture. The poor aggregate coating was likely attributed to the incomplete blending of RAS and the significant reduction in total binder content (from 4.9% to 4.3%) due to the 100% replacement of the base binder by RA. Based on the results shown in Figure 4.1, the following procedure was proposed to add RA in high RBR mixtures and address potential aggregate coating issues: if RAS was used and the optimum RA dosage was higher than 5.5%, add RA to the base binder at 50% addition plus 50% replacement; otherwise, directly add RA to the base binder by 100% addition.

105

Figure 4.1. Coatability Results for Various RA Blending Methods.

106

4.2 Stiffness

4.2.1 MR

MR results for the LMLC specimens are shown in Figure 4.2 for both STOA and LTOA specimens. MR results for STOA LMLC specimens showed that the target mixture, the recycled mixtures with T1 and A1 at their respective optimum dosages, and the recycled mixture with TOAS and optimum T1 dosage exhibited statistically equivalent stiffnesses that were statistically less than that of the recycled control mixture. These results indicate the effectiveness of RAs (at the optimum dosage) in restoring the PG grade of the aged recycled binders from the RAP and RAS (MWAS or TOAS) when used with the same base binder (PG 64-22) or a softer base binder (PG 64-28) when the very stiff TOAS is utilized at a high 0.5 RBR. After LTOA, the same trends were observed with the exception of the TOAS mixture with a softer binder PG grade (PG 64-28) that had statistically higher stiffness equivalent to that of the recycled control mixture. This result indicates that the advantage of using a softer binder PG grade reduces with aging at high RASBR with very stiff TOAS. In contrast, the advantage of using the softer binder (PG 64-28) was shown for the MWAS mixtures at lower 0.3 RBR after LTOA only. And the T1 field dosage was shown to be ineffective for both STOA and LTOA specimens with statistically equivalent stiffnesses for the recycled control and recycled with T1 at field dosage mixtures. Adding T1 at higher dosages (3.5% and 4.5% [optimum]) than the field dosage effectively reduced the stiffness of these recycled mixtures to be statistically equivalent to that of the target mixture for both STOA and LTOA specimens.

0

200

400

600

800

1000

1200

Target RecycledControl

Recycledw/ T1 @ FLD

Recycledw/ T1 @

FLD (64‐28)

Recycledw/ T1 @3.5%

Recycledw/ T1 @OPT

Recycledw/ A1 @OPT

Recycledw/T1 @ OPT

(TOAS)

Resilient Modulus (ksi)

LTOA STOA

Figure 4.2. LMLC MR Stiffness at 25⁰C for STOA and LTOA Specimens for TX (Expanded) Materials Cluster.

107

Figure 4.3 shows MR results for LMLC and RPMLC specimens and field cores for TX field project materials combinations. The numbers on the bars represent the AV% for the cores. As explained in the first interim report, the specimen fabrication protocol (conditioning time and temperature) was established for preparing LMLC specimens in the laboratory to match the initial stiffness of field cores. The statistical analysis (Appendix D) verified these protocols by indicating no statistical difference between the stiffness of LMLC specimens after STOA and field cores at construction except for the target mixture where the stiffness of the field cores was less than that of the LMLC specimens after STOA possibly due to higher AV content and low variability.

RPMLC specimens always exhibited higher stiffness, regardless of mixture type, due to the reheating of loose mixtures. For RPMLC specimens and field cores, the recycled control mixture has higher stiffness than the target mixture, but less than the recycled mixture with RA. For the LMLC specimens, this same result is not shown. These results correspond well with E* results discussed subsequently. This might be due to several reasons including less than optimum RA dosage in the TX field sections or incomplete blending between the base binder, aged recycled binder, and the RA. More than likely, however, the use of warm mix asphalt (WMA) additive in the recycled control mixture and corresponding lower mixing and compaction temperatures resulted in the reduced stiffnesses. This WMA additive was used to alleviate compaction concerns during construction.

Interestingly, after 1 year the stiffness of field cores is statistically higher than the LMLC specimens after LTOA, regardless of mixture type. Therefore, the LTOA protocol (5 days at 85°C) may not be adequate to test the specimens for the long-term performance.

0

300

600

900

1200

1500

1800

2100

Target RecycledControl

Recycledw/ T1 @FLD

Resilient Modulus (ksi)

Cores ‐ 1 Year Cores ‐  @ const. RPMLC ‐ LTOARPMLC ‐ STOA LMLC ‐ LTOA LMLC ‐ STOA

9. 3

%8.

7%

9.8%

10.4

%

9.6%

8.9%

Figure 4.3. MR Stiffness at 25⁰C for Different Specimen Types for TX (Expanded) Materials Cluster.

108

4.2.2 E*

E* results for LMLC specimens are shown in Figure 4.4 for STOA and LTOA specimens. E* results are shown here at only 10Hz for comparison purposes, and the detailed results for all test frequencies are provided in Appendix D. In agreement with the MR results, E* results for STOA LMLC specimens showed that the target mixture, the recycled mixtures with T1 and A1 at their respective optimum dosages, and the recycled mixture with TOAS and optimum T1 dosage exhibited statistically equivalent stiffnesses at intermediate and high temperatures that were all statistically lower than that for the recycled control mixture. These results indicate the effectiveness of RAs (at the optimum dosage) in restoring the PG grade of the aged recycled binders from the RAP and RAS (MWAS or TOAS) when used with the same base binder (PG 64-22) or a softer base binder (PG 64-28) when the very stiff TOAS is utilized at a high 0.5 RBR. But at low and intermediate temperatures for these same mixtures after STOA, the recycled mixture with TOAS exhibited a stiffness that was also statistically equivalent to that for the recycled control mixture. And after LTOA, the stiffnesses for all mixtures were statistically equivalent at low temperature, with the recycled mixture with TOAS again exhibiting higher stiffness equivalent to that for the recycled control mixture at intermediate and high temperatures. These results indicate that the advantage of using a softer binder PG grade reduces with aging or at colder temperatures at high RASBR with very stiff TOAS. The advantage of using the softer binder (PG 64-28) was also not realized for the MWAS mixtures at lower 0.3 RBR for both aging conditions and all temperatures except after STOA at high temperature. These results may be related to the greater sensitivity of the tensile MR stiffness results to binder properties as compared to the compressive E* stiffness results. As for the MR results, the T1 field dosage was shown to be ineffective for both STOA and LTOA specimens with statistically equivalent stiffnesses for the recycled control and recycled with T1 at field dosage mixtures across the temperature spectrum. The effect of T1 dosage and the effect of RA type, however, was not shown with the compressive E* stiffness results across the temperature spectrum and for both STOA and LTOA specimens.

109

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C

Target Recycled Control Recycledw/ T1 @ FLD

Recycledw/ T1 @ FLD

(64‐28)

Recycledw/ T1 @ 3.5%

Recycledw/ T1 @ OPT

Recycledw/ A1 @ OPT

Recycledw/ T1 @ OPT

(TOAS)

Dynam

ic M

odulus (ksi)

LTOA STOA

Figure 4.4. LMLC E* Stiffness (at 4, 20, 40⁰C and 10Hz) for STOA and LTOA Specimens for TX (Expanded) Materials Cluster.

110

E* results for the RPMLC specimens are shown in Figure 4.5 for the STOA and LTOA specimens. For both the STOA and LTOA specimens, the recycled mixture with T1 at the field dosage had statistically higher stiffness than the recycled control mixture at all temperatures. These results correspond with MR results for the RPMLC specimens and field cores, and likely result from the WMA additive and lower mixing and compaction temperatures utilized for the recycled control mixture as explained previously. For the LTOA results at low temperature, results indicated that the stiffness of the recycled control mixture is statistically lower than that of the target mixture. This may be attributed to different base binders used in these mixtures (PG 70-22 polymer modified for the target mixture versus PG 64-22 for the recycled control mixture).

4.3 Cracking Resistance

4.3.1 IFIT (SCB)

The Louisiana Transportation Research Center (LTRC) and the Illinois Flexibility Index Test (IFIT) procedure that both use the SCB test to evaluate fatigue cracking were conducted to evaluate the effect of specimen thickness and compare the two different procedures. Three 12.5 mm NMSA mixtures with PG 64-28 base binder and RAP contents of 0%, 20%, and 40% by total weight were tested.

The results of the LTRC-SCB testing for the 20% and 40% RAP mixtures are shown in Figure 4.6. Both mixtures show an impact in the calculated Jc value due to specimen thickness, and the relative ranking of the two mixtures reverses with the two different thicknesses. Both mixtures are below the recommended Jc range of 0.5-0.6 kJ/m2 for adequate fatigue performance.

0

500

1000

1500

2000

2500

3000

4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C 4⁰C 20⁰C 40⁰C

Target Recycled Control Recycled  w/ T1 @ FLD

Dynam

ic M

odulus (ksi)

LTOA STOA

Figure 4.5. RPMLC E* Stiffness (at 4, 20, 40⁰C and 10Hz) for STOA and LTOA Specimens for TX (Expanded) Materials Cluster.

111

Figure 4.6. LTRC Jc Results for Two Thicknesses and Two RAP Contents.

The flexibility index (FI) values calculated using the IFIT approach are shown in Figure 4.7. The unadjusted values determined using a 2nd order exponential and a 6th order polynomial fit of the raw data are shown in Figure 4.7a; there is a high dependency on the thickness for the RAP mixtures, but not for the target mixture. The thickness adjusted FI (Figure 4.7b) has less dependency on thickness for the RAP mixtures, but more for the target mixture.

Statistically, there is no significant difference in the exponential and polynomial fitting methods. There is a significant difference in the FI values for the RAP mixtures due to thickness, but not for the adjusted FI values. There is no significant difference for the target mixture for adjusted or unadjusted FI values. Both adjusted and unadjusted FI values indicate that the virgin mixture is the most crack resistant and the two RAP mixtures would be expected to have similar performance; all meet the recommended minimum FI threshold of 6.0. The RAP mixtures have relatively high binder content with a soft RAP (PG 74-25), so it is not unexpected that there is little difference in performance between the two RAP mixitures. These results agree with other cracking resistance tests (OT, beam fatigue) performed on these mixtures as part of the TPF 5(230) Pooled Fund Study (Daniel et al. 2014).

0.0

0.1

0.2

0.3

0.4

0.5

20% RAP 40% RAP

Jc' (

kJ/m

2 )

Mixture Type

38 mm 61 mm

112

Figure 4.7. Flexibility Index Values (a) without Thickness Adjustment and (b) with

Thickness Adjustment.

Based on the comparisons of the LTRC-SCB test and the IFIT as described previously in this chapter and in Chapter 1 through literature by other researchers, the IFIT was selected for use in evaluating RA effectiveness and its evolution in improving mixture cracking resistance. This IFIT is most promising in terms of practicality and its ability to distinguish different mixture behavior.

IFIT testing was next conducted for the TX (Expanded) materials cluster on LMLC specimens, with the results shown in Figure 4.8 for STOA and LTOA specimens. FI results for STOA LMLC specimens showed that the recycled control mixture, the recycled mixtures with lower than optimum RA dosage, and the recycled mixture with TOAS and optimum T1 dosage exhibited statistically equivalent behavior with low FI values. By increasing the T1 dosage to optimum for STOA specimens, the FI increased and was statistically higher than that for the recycled control mixture but still lower than that for the target mixture. And utilizing A1 at the

0.0

5.0

10.0

15.0

20.0

25.0

0% Exp 20% Exp 20% Poly 40% Exp 40% Poly

FI (Gf/m

)

Mixture type

38 mm 50mm 61 mm

0.0

5.0

10.0

15.0

20.0

25.0

0% Exp 20% Exp 20% Poly 40% Exp 40% Poly

Adjusted

 FI (Gf /m

)

Mixture type

38 mm 50mm 61 mm

113

optimum dosage resulted in a statistically equivalent FI as compared to the recycled mixture with T1 at optimum for both STOA and LTOA specimens. After LTOA, all the mixtures exhibited statitiscally equivalent FI values (even the target and the recycled control mixtures) with the exception of the recycled mixture with T1 and the softer binder (PG 64-28). However, the positive effect on FI of the softer binder was not shown for either STOA or LTOA specimens. In addition, the effect of LTOA on FI for the target mixture was more pronounced than that for the recycled control mixture based on the error bars representing plus or minus one standard deviation in the results. This may be due to the fact that the recycled control mixture is already stiff and aged, and thus there is little further aging as compared to the target mixture. And the effect of STOA on FI due to RA dosage was more pronounced than that due to LTOA, possibly due to the loss of RA effectiveness with aging.

4.3.2 S-VECD

The S-VECD approach, specified by AASHTO TP107, comprises two material properties: the damage characteristic curve (C vs. S) that defines how fatigue damage evolves in a mixture and failure criterion (GR) that defines an existing characteristic relationship between the rate of change of the average released pseudo strain energy (GR) during fatigue testing and the final fatigue life, defined as the number of cycles to failure (Nf). Generally, a mixture further towards the upper right corner in either plot would be expected to have better fatigue performance, recognizing that actual field performance will also depend on the structure in which the mixture is placed.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Target RecycledControl

Recycledw/ T1 @FLD

Recycledw/ T1 @

FLD (64‐28)

Recycledw/ T1 @3.5%

Recycledw/ T1 @OPT

Recycledw/ A1 @OPT

Recycledw/T1 @

OPT (TAOS)

Flexibility In

dex (FI)

STOA LTOA

Figure 4.8. LMLC-SCB results at 25⁰C for STOA and LTOA Specimens for TX (Expanded) Materials.

114

Figure 4.9 shows the average C-S curves for three of the TX mixtures. The Target and Recycled Control have similar curves. The Recycled w/T1 @ FLD curve is above the other two, indicating that mixture will have higher stiffness at the same level of damage. Figure 4.10 shows the Nf -GR relationship for all three mixtures. Recycled Control and Recycled with T1@ FLD mixtures show similar behavior. The slope of the Target mixture is shallower than the other two, indicating that mixture would be expected to have better performance at lower strain levels. However, there is a significant amount of scatter in the fatigue data due to the brittle nature of the materials and the average trends observed may not be significantly different.

Since the S-VECD approach is based on the viscoelastic damage mechanism and the Nf -GR relationship is not restricted to one specific temperature, it can be used to predict the fatigue life of asphalt mixtures at other loading conditions and temperatures. Figure 4.11 shows the predicted fatigue life of all three mixtures at 21°C and 10 Hz frequency at different strain levels. At lower strain levels, the Target mixture would be expected to perform best, while the Recycled Control and Recycled with T1@ FLD mixtures would be expected to have better performance at the higher strain levels.

Figure 4.9. SVECD Analysis C-S Plot for TX Mixtures.

115

Figure 4.10. SVECD Analysis Nf -GR Plot for TX Mixtures.

Figure 4.11. Predicted Number of Cycles to Failure from SVECD Analysis for TX

Mixtures.

The output from the SVECD testing can also be used in the Layered Viscoelastic for Critical Distress (LVECD) pavement evaluation software to evaluate the amount of damage accumulation in a pavement structure over time, combining the material properties with the impact of layer thickness and type. The LVECD software is not yet calibrated to actual distress levels in the field (e.g. length of cracking), however it can be used for comparative assessment.

116

The LVECD analysis was performed for the three TX field mixtures using a specific cross section (Figure 4.12) to directly compare performance of the three mixtures. Table 4.1 summarizes the LVECD inputs used in the analysis.

The damage factor distribution at the end of 20 years of traffic loading is shown for all three mixtures in Figure 4.13. The damage factor is the ratio of the current number of cycles of loading to the number of cycles of loading that would cause failure (N/Nf). A particular element is considered to be completely cracked when the damage factor reaches a value of 1.0. The Target mixture shows the best performance while the Recycled Control mixture shows extensive cracking at the end of the 20 year life. Figure 4.14 shows the number of failure points (N/Nf =1.0) over time for the three mixtures; there are no completely failed elements in the Target mixture, while the Recycled Control mixture shows that cracking failure begins rapidly after construction. The response of the Recycled w/T1 @ FLD mixture shows that cracking begins to initiate in a similar timeframe as the Recycled Control mixture, but progresses much slower, indicating the addition of the T1 RA is effective in mitigating some of the cracking susceptibility of the Recycled Control material, but does not bring it to the level of the Target mixture.

Figure 4.12. Pavement Cross-Section for LVECD Analysis of TX Mixtures.

Table 4.1. LVECD Analysis Input Values for TX Mixtures.

General Information

Pavement Type New

Analysis Option Performance/ Fatigue

Construction Date June 2014

Traffic Opening Date August 2014

Design life 20 years

Project Name SH 31

City/State Tyler, Texas

Lane width, in 3.65

Climate Data

Temperature Profile Input EICM

117

State/ City TX/ Tyler

Traffic Data

Vehicle New vehicle

Axle Type Single Axle

Wheel Type Single Tire

AADTT 490

Growth Type No Growth

Lane Distribution Factor 1

Monthly Adjustment Factor 1

Hourly Truck Distribution, % 4.1667

Outputs and Analysis Options

Output Option Contour, Fatigue cracking results

Figure 4.13. LVECD Damage Factor (N/Nf) Contour Plots at 20 Years for TX Mixtures.

Target RecycledControl 

Recycled w/T1@FLD 

118

Figure 4.14. Number of Failure Points (N/Nf=1) Over Time from LVECD Analysis for TX

Mixtures.

4.3.3 UTSST

The UTSST testing protocol was utilized to evaluate the thermal characteristics of the mixtures obtained from the Texas field project which have been identified previously as Target, Recycled Control, and Recycled with T1. Each of these mixtures was prepared as both LMLC specimens as well as RPMLC specimens using the Superpave gyratory compactor. Each of the respective test specimens were cored to the appropriate test geometry then aged for 5 days at 85°C prior to UTSST testing. Figure 4.15 presents the average UTSST modulus curves for the respective mixtures, and Table 4.2 presents the thermos-viscoelastic properties determined from the curves.

119

Figure 4.15. UTSST Modulus Curves for TX Field Mixtures.

0

2,000

4,000

6,000

8,000

10,000

12,000

-40 -30 -20 -10 0 10 20

Mod

ulu

s, E

(UT

SS

T)(M

Pa)

Temperature (°C)

TX Target LMLC

TX Target RPMLC

TX Recycled Control LMLC

TX Recycled Control RPMLC

TX Recycled w/T1 LMLC

TX Recycled w/T1 RPMLC

120

Table 4.2. UTSST Thermo-viscoelastic Properties for TX Field Mixtures.

TX

Target LMLC

TX Target

RPMLC

TX Recycled Control LMLC

TX Recycled Control RPMLC

TX Recycled

w/T1 LMLC

TX Recycled

w/T1 RPMLC

Temperature (°C) Fracture -27.3 -28.1 -19.0 -18.7 -22.8 -4.0

Crack Initiation -27.2 -26.2 -18.9 -10.1 -17.7 -1.6 Glassy Hardening -15.7 -11.4 -7.9 -1.3 -6.3 4.4

Visc.-Glassy Trans. 0.2 1.4 3.0 5.7 3.6 8.2 Viscous Softening 15.2 14.2 14.0 12.4 12.5 11.7

Modulus (MPa) Crack Initiation 11,839 8,242 5,197 5,376 5,407 3,898

Glassy Hardening 7,804 5,355 3,530 3,898 3,593 3,429 Visc.-Glassy Trans. 2,260 2,232 1,643 2,392 1,630 3,038 Viscous Softening 406 713 660 1,564 844 2,752

Stress (kPa) Fracture 3,302 3,659 2,266 2,367 2,591 1,414

Crack Initiation 3,297 3,369 2,263 1,639 2,007 1,224 Glassy Hardening 1,466 1,333 1,064 815 827 772

Visc.-Glassy Trans. 266 403 373 395 284 538 Viscous Softening 14 55 73 147 64 347

Beginning with general observations of the UTSST modulus curves initially

acknowledges a marked increase in the modulus values and a decrease in the cold temperature region, e.g. crack initiation and fracture temperatures with the TX Control Mixtures compared to the two Recycled mixtures. Previous efforts have observed such reductions in the UTSST modulus corresponding to increased brittleness within the mixtures which may be the result of increased oxidation (Morian 2014) or increased levels of damage within the specimen (Alavi et al. 2015). In either case, the corresponding decrease in temperatures of the respective behavior zones combine to indicate decreased thermal cracking resistance of the mixture containing the recycled materials. It is also suspected that these influences are compounded by the polymer modification of the PG70-22 binder utilized in the TX Target Mixture compared to the unmodified PG64-22 binder used in both of the Recycled mixtures. These observations were focused primarily on the LMLC measurements, but are even more pronounced with the respective RPMLC mixtures.

Additional considerations of Figure 4.15 and Table 4.2 enable the differentiation between the LMLC and RPMLC specimens for each mixture type. Beginning with the warmer temperature range of the TX Target mixtures, the two production methods yielded fairly similar modulus properties until the Glassy Hardening point. At temperatures below that (i.e., colder temperatures), the RPMLC mixtures exhibited much lower UTSST modulus values coupled with slightly warmer temperatures. Given the partial similarities and the systematic deviation in the colder temperature region between these two mixtures, it is likely that there may be a difference

121

in the binder or at least the level of aging between the two mixtures. This finding is not unreasonable acknowledging the generally accepted differences between plant and laboratory produced mixtures.

Observations of the modulus curves produced with the TX Recycled Control Mixtures discover further discrepancies, but over the entire range of the calculated UTSST modulus values despite the fracture temperatures being very similar to one another. In this case the RPMLC mixture exhibited higher modulus values almost immediately which also correspond to the slightly warmer temperature compared to the LMLC for the Recycled Control Mixture. Of particular significance is the difference between the crack initiation temperatures, indicating a more brittle RPMLC mixture.

A much more substantial change in behavior is noted with the TX Recycled w/T1 mixtures. The LMLC mixture is noted to be comparable to that of the Recycled Control; however, the RPMLC mixture was found to be very different from all the other mixtures in this evaluation set. The modulus is much higher for the duration of the test, but also the phase transitions are identified much earlier (i.e., at warmer temperatures) throughout the thermal loading conditions of the test. The much warmer temperatures, in this case even the fracture temperature, coupled with the increased modulus values indicate a much stiffer and more brittle mixture with the RPMLC mixture. This result agrees with other mixture tests including MR and S-VECD.

In both cases with the RPMLC materials, there was an observed decrease in the cracking resistance and observable increase in the stiffness of the mixtures. Portions of the observed differences may be attributed to discrepancies in the age conditioning between plant produced and laboratory produced mixtures. However, the more substantial differences noted with the Recycled mixtures is more appropriately understood to be the combined effect of the aging and potential differences in the component materials and/or the efficiency of the blending of the component materials.

A more abbreviated evaluation of the cracking resistance of the different TX field mixtures can be undertaken utilizing the UTSST Resistance Index as presented in Figure 4.16.

Figure 4.16. TX Field Mixtures UTSST Resistance Index.

388

118

4617

78

20

50

100

150

200

250

300

350

400

450

TX TargetLMLC

TX TargetRPMLC

TX RecycledControlLMLC

TX RecycledControlRPMLC

TX Recycledw/T1 LMLC

TX Recycledw/T1 RPMLC

UT

SS

T R

esis

tan

ce I

nd

ex

122

Quite similar findings to the full UTSST modulus evaluation can be observed with the UTSST Resistance Index (UTSST RI) noting that larger values of the RI represent increased resistance to thermal cracking. By a significant margin, the LMLC TX Target Mixture presents the highest UTSST RI, thereby indicating the greatest resistance to thermal cracking. The mixture with the second highest index was the RPMLC TX Target, again noting the apparent benefit of the polymer modification of the target 70-22 binder. The next lowest index values are the LMLC TX Recycled Control and Recycled w/T1 mixtures. However, once the UTSST RI reaches such low levels, the actual discrimination between individual mixtures becomes less significant compared to the overall magnitude of the respective indices indicating low cracking resistant properties. With that in perspective, the RPMLC mixtures were observed to have even lower UTSST RI values, which corroborate with the observation noted previously.

123

CHAPTER 5 PHASE II DELIVERABLES AND KEY FINDINGS

Chapter 5 presents the Phase II deliverables that have been produced to date toward meeting the goals of this study, including a RA dosage selection method and a summary of specimen fabrication aging protocols and RA blending method guidelines. Key findings that span across the different laboratory experiments are also highlighted. And preliminary recommendations for binder and mixture characterization tools are provided.

5.1 RA Dosage Selection

Figure 5.1 shows a flowchart of the recommended RA dosage selection method based on the results presented in Chapter 3. This comprehensive methodology requires materials selection, materials preparation, laboratory measurements, dosage selection, and dosage verification with both binder and mixture characterization.

5.2 Specimen Fabrication

Table 5.1 provides a summary of the specimen fabrication aging protocols and guidelines for RA blending by addition or replacement or a combination of both methods.

5.3 Key Findings

Table 5.2 provides a summary of the key findings and cross-references all of the laboratory experiments that provide justification of these findings.

124

Figure 5.1. Recommended Recycling Agent Dosage Selection Method.

125

Table 5.1. Specimen Fabrication Protocol for Preparing High RBR Mixtures.

Mixing

Dry RAP and RAS for 6 to 8 hrs at 60°C

Dry virgin aggregates overnight at mixing temperature

Mix RAP and RAS with virgin aggregates

Heat base binder and RAP/RAS/aggregate blend at mixing temperature 2 hrs before mixing

Blend RA with base binder using the 50% addition & 50% replacement method when RA dosage is greater than 5.5% and RAS is used; otherwise, use the 100% replacement method

Heat base binder/RA blend at mixing temperature for 10 min before mixing

Mix RAP/RAS/aggregate blend with base binder/RA blend

Short-Term Conditioning

Condition the loose mix for 2 hrs at 135°C for HMA and WMA with RA or 2 hrs at 116°C for WMA without RA

Compaction Compact the loose mix to the target AV at 135°C

Long-Term Aging Age the compacted specimens for 5 days at 85°C

126

Table 5.2. NCHRP 9-58 Key Findings through Phase II.

5.4 Recommended Binder and Mixture Characterization Tools toward Phase III

Based on the Phase II laboratory experiments, the following recommendations are provided for characterizing binders and mixtures with high RBRs and RAs with additional tasks to be included in Phase III:

The DSR and BBR can be utilized to select the RA dosage. Binder blend characterization with complete blending overestimates both the PGH and PGL, but this is likely the recommended, practical solution over the mortar procedure that provides a more realistic PG grade that accounts for incomplete blending. The mortar procedure may be warranted for high risk projects. The RA dosage selection method

Mortar Results

DSRFn G-R

RA dosage selection method was developed √

RA dosage selection method was validated by partially restoring the properties of recycled materials (field < optimum)

√ √ √ √

RA was more effective in rejuvenating RAP than RAS

√ √

RA was more effective in rejuvenating MWAS than TOAS

√

RA effectiveness (reducing stiffness and improving cracking resistance) decreased with aging

√ √ √

RA had no effect on oxidation kinetics but increased hardening susceptibility

√ √ √

RA, recycled materials, or aging temperature had no substantial effect on the rheological aging path which was largely dictated by the base binder

√ √

RA initially improved cracking resistance but was not able to completely counter act the brittlness added by the recycled materials

√ √

Use of softer base binders improved the stiffness and cracking resistance of high RBR mixtures

√ √ √ √ √

RA type affected compatibility and mechanical properties of high RBR mixtures

√ √ √

Mortar procedures provided realistic assessment of binder blending

√ √

Specimen fabrication protocols from 9-49 & 9-52 were applied successfully to high RBR mixtures

√

50% addition & 50% replacement was recommended to add RA at dosages > 5.5% in mixtures with RAS

√

Test modifications were needed for high RBR mixtures

√ √ √

RPMLC specimens from the Texas field project were very stiff

√ √ √

Mixture Results

Key Findings Extended Aging Analysis

Binder Results

EDCAG-R PG&ΔTc PG&ΔTc MR E* SCB UTSST SVECD CI

127

by binder blend characterization does require extraction and recovery of the recycled binders from the RAP and RAS. The contribution of binder from these materials will be further defined in Phase III as discussed in Chapter 6.

RA effectiveness and its evolution with aging in binders can be quantified by the G-R parameter in Black space that provides a complete characterization in terms of stiffness (G*) and phase angle () at intermediate temperatures. And RA effectiveness evolution with aging can be quantified by the Rejuvenating Effectiveness (RE) parameter introduced in Chapter 3. The Tc value is also critical in defining RA effectiveness. As described in Chapter 6, further development to define G-R thresholds in different climates will be completed. Based upon the inputs obtained in the binder aging experiment, the detailed aging analysis will be expanded to estimate the binder aging state in the field as a function of time for a given project location.

RA effectiveness in mixtures can be quantified by stiffness (either MR or E*) and cracking resistance (IFIT or S-VECD at intermediate temperatures and UTSST at low temperatures) after long-term aging. RA effectiveness evolution with aging can be quantified using the practical MR and IFIT SCB tests that can be conducted on the same specimen. These parameters will be utilized in an aging analysis to tie laboratory results to field performance as described in Chapter 6. Similar to the G-R parameter for binders, characterization of E* in Black space is also planned for Phase III as discussed in Chapter 6. Further examination of long-term aging will also be completed in Phase III. And other IFIT parameters for stiff, brittle mixtures will also be explored since this tool is the most practical of the cracking tests. The UTSST analysis will also be expanded to incorporate the estimated aging state which adds to the mixture characterization that correlates to field performance.

The proposed evaluation tools in the form an overall mix design and performance evaluation guidelines that accounts for the evolution of RA effectiveness will be a detailed version of the example shown in Figure 5.2.

128

Figure 5.2. Example Mix Design and Performance Evaluation Guidelines and Evaluation

Tools.

129

CHAPTER 6 PHASE III FIELD EXPERIMENT DESIGNS

Chapter 6 presents the Phase III field experiment designs and additional analyses to allow the following objectives of this study to be met:

Assess the effectiveness of RAs in partially restoring blended binder rheology through selection of an optimum RA dosage based on binder testing and validation by a more representative mortar evaluation.

Assess the effectiveness of RAs in improving mixture cracking resistance at optimum dosage rates using selected laboratory tests.

Evaluate the evolution of RA effectiveness. Recommend evaluation tools for assessing the effectiveness of RAs and their

evolution for specific material combinations at specific locations.

The three constructed and potential field projects for Phase III in NV, IN, and MO are listed in Table 2.2, and the field activities will be the same as for Phase II as described in Chapter 2. These field projects were coordinated during Phase II, and selection of material combinations to explore further in Phase III as shown in this chapter was based on the results from Phase II contained in this second interim report.

6.1 Laboratory Testing

The laboratory testing for Phase III will include the same methods used in Phase II as listed in Table 2.4 and shown in the binder and mixture experiments in this chapter.

A few tests or sets of specimens originally included in Phase II will be completed in Phase III as shown in Table 2.8 (G-R and FT-IR CA for NV field binders), Table 2.9 (FT-IR CA and some DSR master curves including G-R) Table 2.10 (SAR-AD), and Table 2.15 (some IFIT and UTSST).

Table 6.1 will be utilized to characterize the component binders and RAs and identify key properties that produce optimal binder blends. PGH and PGL results for the target, base, and recycled binders are provided in Chapter 3. These key properties include those currently contained in ASTM D4552, which defines six RA grades based on viscosity at 60°C and DSR master curve parameters (including G-R parameter, rheological index R-value, G*c, and c), where larger DSR plates of 50 mm in diameter are needed to characterize the RAs. Preliminary results by Zhou et al. (2015) indicate that the RA T1 utilized in the Texas field project is an RA1 grade by this specification. Results from the experiment shown in Table 6.1 and the compatibility experiment will be utilized to propose modifications to ASTM D4552.

130

Table 6.1. Revised Component Binders and RAs Experiment.

Base Binder RAP

Binder RAS Binder Recycling Agents

Tes

t

Agi

ng

Sta

te%

TX

PG

70-

22

TX

PG

64-

22

NH

PG

64-

28

NV

PG

64-

28P

TX

RA

P

NV

RA

P

TX

MW

AS

TX

TO

AS

CA

TO

AS

Tal

l Oil

T1

Tal

l Oil

T2

Aro

mat

ic O

il A

1

Aro

mat

ic O

il A

2

Par

affi

nic

Oil

P

Re-

Re

fin

ed L

ub

e O

il R

PGH U -- -- -- -- -- -- S -- -- -- -- -- --

PGL & Tc L -- -- -- -- -- -- -- -- -- --

@ 60°C U -- -- -- -- -- -- -- -- --

Phase III

S -- -- -- -- -- -- -- -- -- DSR Master Curve with 50 mm plates

U -- -- -- -- -- -- -- -- --

S -- -- -- -- -- -- -- -- --

%U = original, unaged; S = short-term aged in lab; L = long-term aged in laboratory.

131

In addition to the traditional G-R parameter determined at one temperature and frequency, the DSR frequency sweep test will be performed on recycled binder blends at the optimum RA dosage and binders extracted and recovered from LMLC specimens and field cores at multiple aging states. The test will be performed at three temperature isotherms of 41°F (5°C), 59°F (15°C), and 77°F (25°C) and 16 angular frequency values in the range of 0.1 to 100 rad/s. The test results in terms of G* and δ at different temperature-frequency combinations will be used to construct a limited master curve, from which the G-R parameter thresholds and/or testing conditions for different climates will be developed.

And additional mixture parameters for the IFIT approach with the SCB test will be explored for the stiff, brittle RPMLC specimens.

6.2 Binder Experiments

Table 6.2, Table 6.3, and Table 6.4 show the binder experiments for the NV, IN, and MO field projects, respectively. The optimum RA dosage for the A2 RA in the NV field project is 2.0% by weight of total binder, and the field RA dosage is the same for this RA. The additional material combination selected for the NV field project for both RAs is to add CA TOAS at 0.2 RASBR but keep the same total 0.3 RBR, similar to the combination used in the TX field project. Thus, the optimum RA dosages must be determined for use with the G-R parameter, FT-IR CA, and Tc, and for additional mixtures. For the field material combinations, the field dosage will be utilized for all three field projects. For the IN field project, a true control with the same recycled materials content as the recycled w/T2 will be utilized for the mixtures, and thus this materials combinations is included in the binder experiments. The optimum RA dosage for the IN recycled blend with T2 will also be determined by the recommended method presented in Chapter 5. For the MO field project, no additional materials combinations are proposed, but the optimum RA dosages will be determined by the recommended method presented in Chapter 5. A tie to the field will also be realized through characterization of extracted and recovered binders by the G-R parameter, FT-IR CA, and Tc testing from cores at construction and after one year.

6.3 Mixture Experiments

Table 6.5, Table 6.6, and Table 6.7 show the mixture experiments for the NV, IN, and MO field projects, respectively, combining both stiffness and cracking resistance tests. For the field material combinations, the field dosage will be utilized for all three field projects. For any additional mixtures (with RAS for NV and the true control for IN) will be fabricated with optimum RA dosages determined from the binder blend experiments in this chapter. A tie to the field will also be realized through MR and IFIT SCB testing of cores at construction and after one year.

132

Table 6.2. Proposed Binder Blend Experiment for NV Field Materials.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

PGH, PGL, Tc G-R,

FT-IR CA, Tc

0% RA

Low %

RA$

High%

RA$

PAV (hrs)

AL

ML

C

AR

PM

LC

Cores

0 20 40 Const 1 yr

64-28P 0 — — —

Completed in Phase II

0.3 0.3 NV 0.0 T2 # # # # # # # 0.3 NV 0.0 A2 *# *# *# *# *# *# *#

64-28P 0.3 0.1 NV 0.2 CA TOAS T2 * * * * — — — 0.1 NV 0.2 CA TOAS A2 * * * * — — —

$ Dosages for T2 = 1, 3, and 5%; for A2 = 1.5, 2, and 3% #At NV field dosage (2% of total binder) with T2 by Replacement and A2 by Addition

*At the optimum dosage by binder blend testing

133

Table 6.3. Proposed Binder Blend Experiment for IN Field Materials.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

PGH, PGL, Tc G-R,

FT-IR CA, Tc

0% RA

Low % RA

High% RA

PAV (hrs)

AL

ML

C

AR

PM

LC

Cores

0 20 40 Const 1 yr 64-22 0 — — — NA NA

58-28 0.3

0.25 IN 0.07 IN MWAS

— NA NA — — — — — — —

0.4 0.14 IN 0.28 IN MWAS

T2 #* #* #* #* # # #

58-28 0.4 0.14 IN 0.28 IN MWAS

— NA NA — — —

#At IN field dosage (3% of total binder) by Replacement

*At the optimum dosage by binder blend testing

134

Table 6.4. Proposed Binder Blend Experiment for MO Field Materials.

Base Binder RBR

RAPBR & Source

RASBR & Source RA

PGH, PGL, Tc G-R,

FT-IR CA, Tc

0% RA

Low %

RA$

High%

RA$

PAV (hrs)

AL

ML

C

AR

PM

LC

Cores

0 20 40 Const 1 yr 64-22 0 — — — NA NA

58-28P 0.45 0.35 MO 0.1 MO TOAS

T1 To be Completed

by Contractor

# # # # # # #

52-34P 0.45 0.35 MO 0.1 MO TOAS

T1 # # # # # # #

#At MO field dosage (8.7% of total binder)

135

Table 6.5. Proposed Mixture Experiment for NV Field Materials.

Mix Label

Base Binder R

BR

RAPBR &

Source

RASBR &

Source RA

MR & IFIT (SCB) @ 25 °C

E* & UTSST

S-V

EC

D

Specimen Type

LM

LC

RP

ML

C

Cor

es X

2

LM

LC

RP

ML

C

RP

ML

C

Aging State

ST

OA

LT

OA

ST

OA

LT

OA

LT

OA

LT

OA

LT

OA

Target 64-28P 0.0 --- --- --- Recycled Control

64-28P

0.3 0.3 NV 0.0 ---

Recycled w/ T2

0.3 0.3 NV 0.0 T2 # # # # # # # #

Recycled w/ A2

0.3 0.3 NV 0.0 A2 *# *# *# *# *# *# *# *#

Recycled RAP/RAS

w/ T2 64-28P

0.3 0.1 NV 0.2 CA TOAS

T2 * * --- --- --- * --- ---

Recycled RAP/RAS

w/ A2 0.3 0.1 NV

0.2 CA TOAS

A2 * * --- --- --- * --- ---

#At NV field dosage (2% of total binder) with T2 by Replacement and A2 by Addition

*At the optimum dosage by binder blend testing

136

Table 6.6. Proposed Mixture Experiment for IN Field Materials.

Mix Label

Base Binder R

BR

RAPBR &

Source

RASBR &

Source RA

MR & IFIT (SCB) @ 25 °C

E* & UTSST

S-V

EC

D

Specimen Type

LM

LC

RP

ML

C

Cor

es X

2

LM

LC

RP

ML

C

RP

ML

C

Aging State

ST

OA

LT

OA

ST

OA

LT

OA

LT

OA

LT

OA

LT

OA

Target 64-22 0.0 --- --- --- Recycled Control$

58-28 0.3 0.25 IN

0.07 IN MWAS

--- --- --- --- --- --- --- --- ---

Recycled w/ T2

0.4 0.14 IN 0.27 IN MWAS

T2 #* #* # # # #* # #

True Recycled Control

58-28 0.4 0.14 IN 0.28 IN MWAS

--- --- --- --- --- ---

$ Not true control as it contains less recycled materials

#At IN field dosage (3% of total binder) by Replacement

*At the optimum dosage by binder blend testing

137

Table 6.7. Proposed Mixture Experiment for MO Field Materials.

Mix Label

Base Binder R

BR

RAPBR &

Source

RASBR &

Source

RA

MR & IFIT (SCB) @ 25 °C

E* & UTSST

S-V

EC

D

Specimen Type

LM

LC

RP

ML

C

Cor

es X

2

LM

LC

RP

ML

C

RP

ML

C

Aging State

ST

OA

LT

OA

ST

OA

LT

OA

LT

OA

LT

OA

LT

OA

Target 64-22 0.0 --- --- --- Recycled Control1

58-28P 0.45 0.35 MO0.1 MO TOAS

---

Recycled Control2

52-34P 0.45 0.35 MO0.1 MO TOAS

---

Recycled1 w/ T1

58-28P 0.45 0.35 MO0.1 MO TOAS

T1 #

# # # # #

Recycled2 w/ T1

52-34P 0.45 0.35 MO0.1 MO TOAS

T1 #

# # # # #

#At MO field dosage (8.7% of total binder)

In addition, for a limited number of mixtures with a high RA dosage, the HWTT (AASHTO T 324) with traditional parameters of rut depth at a specific number of load cycles and stripping inflection point will be utilized to check mixture resistance to rutting and moisture susceptibility, respectively.

6.4 Binder Contribution from Recycled Materials

Currently, most DOTs design RAP/RAS mixtures by assuming 100% binder contribution from the recycled materials, and reducing the base binder content in the mixture by the recycled binder amount. However, this is not realistic as part of the recycled binder is not available during mixing, particularly for stiffer materials such as those containing RAS. Therefore, these mixtures will have less available binder content than the one specified as optimum in the mix design, and coatability problems may arise, which could eventually affect the cracking resistance of the mixture.

A methodology to estimate the binder contribution of different RAPs and RASs is proposed for Phase III. With this experiment, the effect of RAs in increasing the binder contribution or improving the degree of blending (DOB) will also be evaluated, as well as the method of adding the RAs in the mixture (i.e., incorporating the RA in the base binder or adding the RA directly to the RAP/RAS). The methodology will provide a tool for adjusting the binder contribution from RAP/RAS during mix design.

138

6.4.1 Binder Contribution Methodology

The methodology described herein will first be applied to estimate the binder contribution from RAP; later, the binder contribution from RAS will be evaluated in the same fashion. The method utilizes virgin aggregate and RAP of specific sieve sizes, and consists of the following steps:

1. Prepare the asphalt mixture using base binder, virgin aggregate, and RAP at a selected binder content.

2. Condition the loose mix using the standard STOA protocol. 3. Separate the coated virgin aggregate from the coated RAP by sieving. 4. Determine the binder content in the coated virgin aggregate and the coated RAP using

the ignition oven. The differences in binder content in the coated virgin aggregate versus the coated RAP

will be used to estimate the binder contribution in the RAP. The binder contribution will likely depend on the stiffness of the RAP binder. Assuming a case in which the RAP binder content is 5 percent and the total binder content in the asphalt mixture is also 5 percent, three outcome scenarios are plausible:

Scenario 1: the binder content is equal in the coated virgin aggregate and the coated RAP (i.e., 5 percent in each). This would imply that the RAP binder was fully mixed with the base binder, and the total binder was evenly distributed within the mixture. This scenario would represent a case of 100 percent binder contribution from the RAP.

Scenario 2: the binder content in the coated RAP is 5 percent higher than the binder content in the coated virgin aggregate. This would imply that the coated RAP binder is acting as a “black rock”, and the recycled binder is not available during mixing. In other words, only the base binder was evenly distributed between the virgin aggregate and the RAP. This scenario would represent 0 percent binder contribution from the RAP.

Scenario 3: the difference in binder content from the coated RAP and the coated virgin aggregate is between scenario 1 and 2 (which is the expected outcome). This scenario would represent a partial binder contribution from the RAP.

Therefore, if the is no difference in binder contents between the coated RAP and the coated virgin aggregate, the binder contribution from the RAP binder would be 100 percent. If the difference is equal to the RAP binder content, the binder contribution would be null (i.e., 0 percent). Values in between these two extremes, would allow estimating the binder contribution.

The binder contribution methodology described in this section will be revised to take into account the surface area of the virgin and RAP aggregates.

139

6.4.2 Preliminary Verification

The binder contribution methodology was verified in a preliminary experiment using artificial RAP (i.e., laboratory aged). The following conditions were used to prepare the artificial RAP in the laboratory by mixing base binder and aggregate retained in sieve No.4:

RAP 1 (soft RAP): no STOA. RAP 2 (stiff RAP): aging for 5 days at 110°C. RAP 3 (very stiff RAP): aging for 5 days at 110°C plus 2 days at 150°C.

The binder contribution of each RAP was determined using the proposed methodology. The results were reasonable and showed that the method was able to capture the effect of RAP stiffness. The binder contribution of RAP 1 was around 95 percent; a high value was expected since the binder in RAP 1 is not aged. The binder contribution of RAP 2 was around 60 percent; a lower value than RAP 1 was expected. The binder contribution in RAP 3 was around 50 percent; the binder contribution of this RAP was expected to have the lowest value since the binder in this RAP is very stiff.

The binder contribution methodology was also used to estimate the binder contribution of TX RAP and the effect of a type of RA. Three mixture were prepared: mixture with TX RAP only, mixture with TX RAP and T1 RA (the RA was added to the base binder prior mixing with the aggregate and RAP), and a mixture with T1 RA (the RA was added directly to the RAP prior mixing with virgin aggregate and base binder).

The results showed that the binder contribution of the mixture with TX RAP was around 40 percent, lower than the values obtained with the artificial RAP. Adding the RA to the base binder yielded a binder contribution of 50 percent, while adding the RA directly to the RAP increased the binder contribution to 60 percent. This was also expected since the RA will diffuse into the recycled binder when it is in direct contact with RAP, and therefore, will be more effective than incorporating the RA into the base binder prior mixing with the RAP.

6.5 Mixture Master Curve Analysis

In Phase III, the E* dynamic modulus and phase angle master curves will be evaluated using two parameters which were recently presented by Mensching et al. (2016) to assess general cracking resistance and susceptibility to aging with changes in recycled content, as well as RA type and dosage. The first plot (Figure 6.1) shows the log of the inflection point frequency (-β/γ) against the log of the distance between the glassy modulus and the inflection point modulus (γ) in a fashion similar to that of the crossover frequency-rheological index plot being used for rheological analysis of binders. The -β/γ term describes the elastic-viscous transition properties of the binder, while the γ term describes the width of the relaxation spectra. Both of these values are influenced by the presence of RAP or RAS and are expected to illustrate the changes in stiffness and relaxation associated with embrittlement or crack-susceptible mixtures, and to identify benefits of RAs. The second plot (Figure 6.2) utilizes a modified Glover-Rowe function to evaluate |E*| and phase angle in Black space with a defined failure threshold relating to low temperature performance using TSRST results. This diagram is also capable of describing the stiffness and relaxation changes that typically occur with decreases in cracking resistance, but is calibrated to laboratory low temperature fracture results.

140

Figure 6.1. Sample Plot of Log Inflection Point Frequency Versus Log-Log Difference of

Glassy Modulus and Inflection Point Modulus.

Figure 6.2. Sample Mixture-Based Black Space Plot with Low Temperature Failure

Threshold.

6.6 Aging Analysis

Cumulative degree days (0°C base) are proposed for use in this study to provide a quantitative basis for field aging that accounts for differences in construction dates and

141

environments at different field projects. As an example, the CDD values for seven field projects from NCHRP 9-52 are presented in Figure 6.3 with coring dates indicated by a Black point. Differences between field projects are shown with:

Steeper overall slopes for warmer climates (Texas I, New Mexico, and Florida) as compared to colder climates (Wyoming, South Dakota, Iowa, and Indiana).

Flat initial slopes for fall or winter construction (as shown for South Dakota, which was constructed in the fall).

A similar plot will be formulated for the field projects in this study to provide a distinct indication of the individual climate and its cumulative effect since construction.

Figure 6.3. Cumulative Degree Days for NCHRP 9-52 Field Projects.

Figure 6.4 shows the CDD values for post-construction cores of 33 mixtures from NHCRP Project 9-52 over a wide range of mixture components and production parameters versus their associated average MR ratios (aged/unaged) and an exponential trendline with a high coefficient of determination (R2). Figure 6.4 also shows the corresponding average (1.76) MR ratio value for all LMLC specimens with an STOA protocol of 2 hrs at 135°C (275°F) plus LTOA protocol of 5 days at 85°C (185°F) plotted as a marker where this value crosses the exponential trendline for MR ratio versus CDD values. The vertical and horizontal error bars represent one standard deviation from the average MR ratio values and corresponding CDD values, respectively. A laboratory STOA protocol of 2 hrs at 135°C (275°F) plus LTOA protocol of 5 days at 85°C (185°F) was able to produce mixture aging equivalent to an average of 16,000 CDD in the field. Based on the CDD curves shown in Figure 6.3, the in-service time for each field project corresponding to 16,000 CDD was determined and summarized in Table 6.8. As shown, the laboratory STOA protocol of 2 hrs at 135°C (275°F) plus LTOA protocol of 5 days at 85°C (185°F) was equivalent to approximately 11 months in service in warmer climates and 22 months in service in colder climates.

Based on the data from NCHRP 9-52 discussed, a more significant laboratory LTOA protocol as compared to the 5 days at 85°C (185°F) is needed in order to simulate approximately

0

5000

10000

15000

20000

25000

30000

35000

40000

Dec-11 Jul-12 Jan-13 Aug-13 Mar-14 Sep-14 Apr-15

Cu

mu

lati

ve D

egre

e D

ays

(°F

-day

s)

Coring Date

Texas I New Mexico Wyoming South Dakota

Iowa Indiana Florida

142

7 to 10 years of field aging, when asphalt pavements are most vulnerable to cracking. Recently, several studies have evaluated additional laboratory LTOA protocols, and the findings from these studies are summarized as follows:

Reinke (2015): LTOA protocol of 12 to 24 hours of loose mix aging at 135°C (275°F) was representative of approximately 8 years in Minnesota.

Blankenship and Zeinali (2016): LTOA protocol of 24 hours of loose mix aging at 135°C (275°F) was equivalent to 5 to 7 years of field aging.

Elwardany et al. (2016): oven aging of loose mix was more promising than aging compacted specimens; LTOA protocol of 13 to 21 days of loose mix aging at 95°C (203°F) was equivalent to approximately 8 years in Virginia.

Hanz et al. (2016): LTOA protocol of 12 hours of loose mix aging at 135°C (275°F) was equivalent to that of 5 days at 85°C (185°F) for compacted specimens.

Therefore, in this study, the LTOA protocols of 24 hours and 48 hours of loose mix aging at 135°C (275°F) prior to compaction will be explored. Plots similar to Figure 6.4 will be generated for high RBR mixtures using the MR and SCB test results of the post-construction field cores. In addition, binders extracted and recovered from the long-term aged LMLC specimens and post-construction field cores will be tested to determine the G-R parameter and FT-IR CA and then compared against those aged using the PAV. The results obtained will be utilized to determine the correlation between field aging, laboratory LTOA protocols for mixtures, and PAV aging of binders.

Figure 6.4. MR Ratio versus CDD for NCHRP 9-52 Post-Construction Cores and

Correlation of LTOA Protocols with Field Aging.

143

Table 6.8. Correlation of Field Aging in Terms of In-Service Time and Laboratory LTOA Protocol of 5 days at 85°C (185°F) for NCHRP 9-52 Field Projects.

Field Project Climate MR Ratio for 2 hr at 135°C (275 °F) + 5 days at 85°C

(185°F) Texas I

Warmer Climate

10 months New Mexico 12 months

Florida 11 months Average 11 months

Wyoming Colder Climate

22 months South Dakota 22 months

Iowa 22 months* Indiana 21 months*

Average 22 months *Predicted in-service time based on historical climatic information.

In addition to the tie of laboratory long-term aging to specific field projects/locations and construction dates, binder kinetics measured for blends used in field projects will be utilized to predict mixture stiffness (E*) through a relationship between E* master curve parameters and CA growth from kinetics (Alavi et al. 2013). E* will be measured at a minimum of three different aging levels: after short-term aging, after 5 days at 185F, and after a longer duration at 185F determined from the binder kinetics data for the location of interest. The binder will also be extracted and recovered from the E* samples for carbonyl measurements. Using the measured data, the E* will be determined following the 2S2P1D (2 springs, 2 parabolic, 1 dashpot) model (Olard and Benedetto 2003). Consequently, the relationship between the 2S2P1D model parameters and the increase in CA will be developed, hence allowing for the prediction of the E* at any oxidative aging level. Predicted E* values will then be validated using measured E* for aged cores (at approximately 1 year after construction). For target mixtures, binders will be extracted and recovered to validate the CA growth predictions. Finally, the CDD estimates for laboratory aging will be validated using these same relationships.

6.7 Final Report

Based on the results produced throughout the project, a final draft report will be developed to document the extensive experiments described in both interim reports and the associated results, recommendations, and tools. End products from this study are envisioned to include the following:

A RA dosage selection method Evaluation tools, including aging protocols and RA blending methods, for assessing

the effectiveness of RAs and its evolution in partially restoring blended binder rheology and improving mixture cracking resistance for specific material combinations at high RBRs and at specific field locations.

Better understanding of the contribution of recycled binders from RAP and RAS to mixture cracking resistance.

The draft final report will be submitted to the NCHRP panel for review and approval, and the revised final report will be submitted for publication.

144

REFERENCES

Advanced Asphalt Technologies (2011) NCHRP 9-33: A Manual for Design of Hot Mix Asphalt with Commentary, NCHRP Report 673, Transportation Research Board, National Research Council, Washington, DC.

Alavi, M.Z. (2014) “Comprehensive Methodologies for Analysis of Thermal Cracking in Asphalt Concrete Pavements,” Ph.D. Dissertation, University of Nevada, Reno, UMI Number: 3638109, ProQuest UMI Dissertation Publishing, Ann Arbor, MI.

Alavi, M.Z., and E.Y. Hajj (2014) “Effect of Cooling Rate on the Thermo-Volumetric, Thermo-Viscoelastic, and Fracture Properties of Asphalt Mixtures.” 12th ISAP Conference on Asphalt Pavement, International Society for Asphalt Pavements, Raleigh, NC (June).

Alavi, M.Z., E.Y. Hajj, and N.E. Morian (2013) “Approach for Quantifying Effect of Binder Oxidative Aging on Viscoelastic Properties of Asphalt Mixtures.” Transportation Research Record No. 2373, Transportation Research Board, National Research Council, Washington, DC, pp. 109-120.

Alavi, M.Z., E.Y. Hajj, N.E., Morian, and P.E. Sebaaly (2013) “Low Temperature Characterization of Asphalt Mixtures by Measuring Visco-Elastic Properties under Thermal Loading,” ISCORD 2013: Proceeding of International Symposium on Cold Regions Development, American Society of Civil Engineering, pp. 404-415.

Alavi, M.Z., N.E. Morian, E.Y. Hajj, and P.E. Sebaaly (2015) “Influence of Asphalt Binder Oxidative Aging on Critical Thermal Cracking Characteristics of Asphalt Mixtures,” Journal of the Association of Asphalt Paving Technologist, Vol. 84, pp. 115-142.

Al-Qadi, I.L., H. Ozer, J. Lambros, A. El Khatib, P. Singhvi, T. Khan, J. Rivera-Perez, and B. Doll (2015) “Testing Protocols to Ensure Performance of High Asphalt Binder Replacement Mixes Using RAP and RAS”, Report No. FHWA-ICT-15-017, Illinois Center for Transportation, Urbana, IL (December) 80 pp.

Anderson, D.A., D.W. Christensen, H.U. Bahia, R. Donger, M.G. Sharma, C.E. Antle, and J. Button (1994) “Binder Characterization and Evaluation, Volume 3: Physical Characterization.” SHRP Report A-369, National Research Council, Washington, DC, 475 p.

Anderson, R.M., G.N. King, D.I. Hanson, and P.B. Blankenship (2011) “Evaluation of the Relationship between Asphalt Binder Properties and Non-Load Related Cracking.” Journal of the Association of Asphalt Paving Technologists, Vol. 80, pp. 615-649.

Anderson, D.A., Y. Le Hir, J.P. Planche, and D. Martin (2002) “Zero Shear Viscosity of Asphalt Binders.” Transportation Research Record: Journal of the Transportation Research Board, No. 1810, Transportation Research Board of the National Academies, Washington D.C., pp. 54-62.

Bahia, H.U. (1991) “Low-Temperature Isothermal Physical Hardening of Asphalt Cements.” Ph.D. thesis, Pennsylvania State University, University Park, PA.

145

Bahia, H., and D. Swiertz (2011) “Design System for HMA Containing a High Percentage of RAS Material.” Final Report for RMRC Project 66, Recycled Materials Resource Center, Madison, WI, 40 p.

Blankenship, P.B., and A. Zeinali (2016) “Evaluation of the DC(t) Test in Discerning the Variations in Cracking Properties of Asphalt Mixtures.” Journal of the Association of Asphalt Paving Technologiests, Vol. 85.

Booshehrian, A., W.S. Mogawer, and R. Bonaquist (2013) “How to Construct an Asphalt Binder Master Curve and Assess the Degree of Blending between RAP and Virgin Binders.” Journal of Materials in Civil Engineering, Vol. 25, No. 12, pp. 1813-1821 (December).

Boysen, R.B., and J.F. Schabron (2013) “The Automated Asphaltene Determinator Coupled with Saturates, Aromatics, and Resins Separation for Petroleum Residua Characterization” Energy and Fuels, Vol. 27, No. 8, pp. 4654–4661, (August), http://www.pubs.acs.org/doi/abs/10.1021/ef400952b. (As of February 24, 2015).

Boysen, R., and J. Schabron (2015) “Automated HPLC SAR-AD Separation: Fundamental Properties of Asphalts and Modified Asphalts III Product: FP 01.” Western Research Institute, Laramie, WY, 13 p (March), Technical White Paper.

Chehab, G.R., Y.R. Kim, R.A. Schapery, M. Witczack, and R. Bonaquist (2002) “Time-Temperature Superposition Principle for Asphalt Concrete Mixtures with Growing Damage in Tension State.” Journal of the Association of Asphalt Paving Technologists, Vol. 71, pp. 559-593.

Christensen, R. (2003) “Theory of Viscoelasticity,” Dover Publication incorporation, New York.

Christensen, D.W., and D.A. Anderson (1992a). “Chemical-Physical Property Relationships for Asphalt Cements and the Dispersed Polar Fluid Model.” Proceedings 204th American Chemical Society National Meeting, Washington, D.C., Vol. 37, No. 3-4, pp. 1279-1291.

Christensen, D.W., and D.A. Anderson (1992b). “Interpretation of Dynamic Mechanical Test Data for Paving Grade Asphalt Cements.” Journal of the Association of Asphalt Paving Technologists, Vol. 61, pp. 67-116.

Copeland, A. (2011) Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice, Report No. FHWA-HRT-11-021, Federal Highway Administration, Washington, DC.

Cui, Y., X. Jin, R. Han, and C.J. Glover (2014). “An Accelerated Method for Determining Asphalt Oxidation Kinetics Parameters for Use in Pavement Oxidation and Performance Modeling.” Petroleum Science and Technology, Vol. 32, pp. 2691-2699.

Daniel, J.S., T. Bennert, Y.R. Kim, and W. Mogawer (2014). “TPF 5(230): Evaluation of Plant Produced RAP Mixtures in the Northeast Phase I Interim Report”, Transportation Pooled Fund Study Report.

146

Daniel, J.S., and Y.R. Kim (2002) “Development of a Simplified Fatigue Test and Analysis Procedure Using a Viscoelastic Damage Model.” Journal of the Association of Asphalt Paving Technologists, Vol. 71, pp. 619-650.

Elwardany, M.D., F.Y. Rad, C. Castorena, and Y.R. Kim (2016) “Evaluation of Asphalt Mixture Laboratory Long-Term Aging Methods for Performance Testing and Prediction.” Journal of the Association of Asphalt Paving Technologiests, Vol. 85.

Epps, J.A., D.N. Little, R.J. Holmgreen, and R.L. Terrel (1980) Guidelines for Recycling Pavement Materials, NCHRP Report 224, National Cooperative Highway Research Program, Washington, DC (September).

Epps Martin, A., E. Arambula, F. Yin, L. Garcia Cucalon, A. Chowdhury, R. Lytton, J. Epps, C. Estakhri, and E.S. Park (2014) NCHRP 9-49: Evaluation of the Moisture Susceptibility of WMA Technologies, NCHRP Report 763, Transportation Research Board, National Research Council, Washington, DC.

Farrar, M.J., T.F. Turner, J.P. Planche, J.F. Schabron, and P.M. Harnsberger (2013). “Evolution of the Crossover Modulus with Oxidative Aging, Method to Estimate Change in Viscoelastic Properties of Asphalt Binder with Time and Depth on the Road.” Transportation Research Record, Journal of the Transportation Research Board, No. 2370, Transportation Research Board of the National Academies, Washington, D.C., pp. 76-83.

FHWA (1993) A Study of the Use of Recycled Paving Materials: A Report to Congress, Report No. FHWA-RD-93-147, Federal Highway Administration, Washington, DC.

Glaser, R., and L. Porot (2014) “Miscibility and Microstructure Property Changes in RAP Binder /Rejuvenator Blends.” International Society for Asphalt Pavements Workshop, Raleigh, NC (June), Technical Presentation.

Glover, C.J., R.R. Davison, C.H. Domke, Y. Ruan, P. Juristyarini, D.B. Knorr, and S.H. Jung (2005) Development of a New Method for Assessing Asphalt Binder Durability with Field Evaluation. Report No. FHWA/TX/05-1872-2, Texas Transportation Institute, College Station, TX, 334 pp (August).

Glover, C.J., R. Han, X. Jin, N. Prapaitrakul, Y. Cui, A. Rose, J.J. Lawrence, M. Padigala, E. Arambula, E.S. Park, and A. Epps Martin (2014a). “Evaluation of Binder Aging and its Influence in Aging of Hot Mix Asphalt Concrete.” Technical report. FHWA/TX-14/0-6009-2. College Station, TX: Texas Transportation Institute.

Hajj, E.Y., M.Z. Alavi, N.E. Morian, and P.E. Sebaaly (2013) “Effect of Select Warm-Mix Additives on Thermo-Viscoelastic Properties of Asphalt Mixtures.” Journal of Road Material and Pavement Design, Vol. 14, Special Issue: EATA 2013, pp. 175-186.

147

Hajj, E.Y., L.G. Loria Salazar, and P.E. Sebaaly (2012) “Methodologies for Estimating Effective Performance Grade of Asphalt Binders in Mixtures with High Recycled Asphalt Pavement Content: Case Study.” Transportation Research Record No. 2294, Transportation Research Board, National Research Council, Washington, DC, pp. 53-63 (Nominated for the K.B. Woods Award).

Hajj, E.Y., M.I. Souliman, M.Z. Alavi, and L.G.L. Salazar (2013) “Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures.” Transportation Research Record No. 2371, Transportation Research Board, National Research Council, Washington, DC, pp. 13-22.

Han, R. (2011). “Improvement to a Transport Model of Asphalt Binder Oxidation in Pavements: Pavement Temperature Modeling, Oxidation Diffusivity in Asphalt Binders and Mastics, and Pavement Air Void Characterization.” Ph.D. Dissertation, Texas A&M University.

Hanson, D.I., P.B. Blankenship, G.N. King, and R.M. Anderson (2010). “Techniques for Prevention and Remediation of Non-Load-Related Distresses on HMA Airport Pavements – Phase II.” Final Report, Airfield Asphalt Pavement Technology Program, Project 06-01.

Hanson, K.R., and A. Copeland (2014) “Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage: 2014.” National Asphalt Pavement Association, Lanham, MD.

Hanz, A., E. Dukatz, and G. Reinke (2016) “Use of Performance Based Testing for High RAP Mix Design and Production Monitorning.” Journal of the Association of Asphalt Paving Technologiests, Vol. 85.

Im, S., and F. Zhou (2014) Field Performance of RAS Test Sections and Laboratory Investigation of Impact of Rejuvenators on Engineering Properties of RAP/RAS Mixes. Report No. FHWA/TX-14/0-6614-3, Texas A&M Transportation Institute, College Station, TX (April), 102 pp.

Im, S., F. Zhou, R. Lee, and T. Scullion (2014) “Impacts of Rejuvenators on Performance and Engineering Properties of Asphalt Mixtures Containing Recycled Materials.” Construction and Building Materials, Vol. 53, pp. 596-603 (February).

Jin, X., R. Han, Y. Cui, and C.J. Glover (2011) “Fast-Rate-Constant-Rate Oxidation Kinetics Model for Asphalt Binders.” Industrial and Engineering Chemistry Research, Vol. 50, pp. 13373-13379.

Juristyarini, P., R.R. Davison, and C.J. Glover (2011) “Oxidation Hardening Kinetics of the Rheological Function G′/(η′/G′) in Asphalts.” Petroleum Science and Technology, Vol. 29, pp. 2027-2036.

Kandhal, P.S. (1977) “ASTM STP 628: Low-Temperature Properties of Bituminous Materials and Compacted Bituminous Paving Mixtures.” C.R. Marek (Ed.), American Society for Testing and Materials, Philadelphia, PA.

148

Kandhal, P.S. (1977) Low-Temperature Ductility in Relation to Pavement Performance. In ASTM STP 628: Low-Temperature Properties of Bituminous Materials and Compacted Bituminous Paving Mixtures, C.R. Marek (Ed.), American Society for Testing and Materials, Philadelphia, PA, pp. 95-106.

Kim, Y.R., and D.N. Little (1990) “One-Dimensional Constitutive Modeling of Asphalt Concrete.” Journal of the Engineering Mechanics, Vol. 116, No. 4, pp. 619-650 (April).

Kim, M., L.N. Mohammad, and M.A. Elseifi (2012). “Characterization of Fracture Properties of Asphalt Mixtures as Measured by Semicircular Bend Test and Indirect Tension Test.” Transportation Research Record No. 2296, Transportation Research Board, National Research Council, Washington, DC, pp. 115-124.

King, G. (2013). “WRI Pavement Preservation Symposium.”

King, G., M. Anderson, D. Hanson, and P. Blankenship (2012) “Using Black Space Diagrams to Predict Age-Induced Cracking.” 7th RILEM International Conference on Cracking in Pavements, Vol. 4, pp. 453-463, Delft, Netherlands (June).

King, G., G. Rowe, and G. Reinke (2013) “Newark Airport Runway: A Forensic Study Revisited.” Transportation Research Record No. 2372, Transportation Research Board, National Research Council, Washington, DC, pp. 9-16.

Lau, C.K., K.M. Lunsford, C.J. Glover, R.R. Davison, and J.A. Bullin (1992). “Reaction Rates and Hardening Susceptibilities as Determined from POV Aging of Asphalts.” Transportation Research Record: Journal of the Transportation Research Board, No. 1342, Transportation Research Board of the National Academies, Washington D.C., pp. 50-57.

Lee, H.J., and Y.R. Kim (1998a) “A Uniaxial Viscoelastic Constitutive Model for Asphalt Concrete under Cyclic Loading.” Journal of the Engineering Mechanics, Vol. 124, No. 1, pp. 32-40 (January).

Lee, H.J., and Y.R. Kim (1998b) “A Viscoelastic Continuum Damage Model of Asphalt Concrete with Healing.” Journal of the Engineering Mechanics, Vol. 124, No. 41, pp. 1224-1232 (November).

Liu, M., M.A. Ferry, R.R. Davison, C.J. Glover, and J.A. Bullin (1998). “Oxygen Uptake as Correlated to Carbonyl Growth in Aged Asphalts and Asphalt Corbett Fractions.” Industrial & Engineering Chemistry Product Research and Development, Vol. 37.

Lunsford, K.M. (1994). “The Effect of Temperature and Pressure On Laboratory Oxidized Asphalt Films with Comparison to Field Aging.” Ph.D. Dissertation, Texas A&M University, University Microfilms International.

McDaniel, R., and R.M. Anderson (2001) Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual, NCHRP Report 452, National Cooperative Highway Research Program, Washington, D.C. 49 p.

149

Mensching, D.J., J.S. Daniel, T. Bennert, M.S. Medeiros Jr., M.D. Eleaednay, W. Mogawer, E.Y. Hajj, and M.Z. Alavi (2014) “Low Temperature Properties of Plant-Produced RAP Mixtures in the Northeast,” Journal of Road Materials and Pavement Design, Vol. 15, Supplement 1, Special Issue: 89th Association of Asphalt Paving Technologists, pp. 1-27.

Mensching D.J., G.M. Rowe, J.S. Daniel (2016) “A Mixture-Based Black Space Parameter for Low Temperature Performance of Hot Mix Asphalt,” Journal of Road Materials and Pavement Design, 91st Association of Asphalt Paving Technologists’ Annual Meeting Special Issue.

Mogawer, W.S., A. Austerman, R. Roque, S. Underwood, L. Mohammad, and J. Zou (2015) “Aging and Rejuvenators: Evaluating Their Impact on High RAP Mixtures Fatigue Cracking Characteristics Using Advanced Mechanistic Models and Testing Methods.” 2015 Annual Meeting of the Association of Asphalt Paving Technologists, Proceedings.

Mogawer, W.S., A. Booshehrian, S. Vahidi, and A.J. Austerman (2013) “Evaluating the Effect of Rejuvenators on the Degree of Blending and Performance of High RAP, RAS, and RAP/ RAS Mixtures.” Journal of the Road Materials and Pavement Design, Vol. 14, Supplement 2, pp. 193-213.

Mooney, K. (2015) “Re-Refined Engine Oil Bottoms: Don’t Jump on the “Banned”-wagon Too Quickly.” The Association of Modified Asphalt Producers, AMAP Newsletters and Bulletins, February 2015, http://www.modifiedasphalt.org/news-bulletin-reob. (As of February 24, 2015).

Morian, N.E. (2014) “Influence of Mixture Characteristics on the Oxidative Aging of Asphalt Binders.” Ph.D. Dissertation, University of Nevada, Reno, UMI Number: 3626103, ProQuest UMI Dissertation Publishing, Ann Arbor, MI.

Morian, N.E., M.Z. Alavi, E.Y. Hajj, and P.E. Sebaaly (2014) “Evolution of Thermo-viscoelastic Properties of Asphalt Mixtures with Oxidative Aging.” Transportation Research Record No. 2447, Transportation Research Board, National Research Council, Washington, DC, pp. 1-12.

Morian, N., E.Y. Hajj, and P.E. Sebaaly (2013). “Significance of Mixture Parameters on Binder Aging in HMA Mixtures.” Transportation Research Record No. 2370, Vol. 1, Journal of the Transportation Research Board, Washington, D.C.

Morian, N., C. Zhu, and E.Y. Hajj (2015). “Rheological Indices: Phenomenological Aspects of Asphalt Binder Aging Evaluations” Transportation Research Record: Journal of the Transportation Research Board, Transportation Research Board of the National Academies, Washington, D.C.

NCAT (2014a) “How Should We Express RAP and RAS Contents?” Asphalt Technology News, Vol. 26, No. 2 (Fall), http://www.eng.auburn.edu/research/centers/ncat/info-pubs/newsletters/fall-2014/recycledcontents.html. (As of February 24, 2015).

NCAT (2014b) “NCAT Researchers Explore Multiple Uses of Rejuvenators.” Asphalt Technology News, Vol. 26, No. 1 (Spring), http://www.ncat.us/info-pubs/newsletters/spring-2014/rejuvenators.html. (As of February 24, 2015).

150

Newcomb, D.E., E. Arambula, F. Yin, J. Zhang, A, Bhasin, W. Li, and Z. Arega (2015). “Properties of Foamed Asphalt for Warm Mix Asphalt Applications.” NCHRP Report 807, National Cooperative Highway Research Program, Washington, D.C.

Newcomb, D.E., and J.A. Epps (1981) Asphalt Recycling Technology: Literature Review and Research Plan. Report No. ESL-TR-81-42, Air Force Engineering and Services Center, Florida, (June).

Newcomb, D.E., A. Epps Martin, F. Yin, E. Arambula, E.S. Park, A. Chowdhury, R. Brown, C. Rodezno, N. Tran, E. Coleri, D. Jones, J.T. Harvey, and J.M. Signore (2015). “Short-Term Laboratory Conditioning of Asphalt Mixtures.” NCHRP Report 815, National Cooperative Highway Research Program, Washington, D.C.

Olard, F., and H. Benedetto (2003) “General ‘2S2P1D’ Model and Relation Between the Linear Viscoelastic Behaviours of Bituminous Binders and Mixes.” Road Materials and Pavement Design, Vol. 4, No. 2, pp. 185-224.

Prapaitrakul N., X., R. Han, and C.J. Glover (2009) “A Transport Model of Asphalt Binder Oxidation in Pavements.” Road Materials and Pavement Design, 10 (Special Issue), 95-113.

Petersen, J.C., and R. Glaser (2011). “Asphalt Oxidation Mechanisms and the Role of Oxidation Products on Age Hardening Revisited.” Road Materials and Pavement Design, Vol. 12, Issue 4, Taylor & Francis, London, UK.

Petersen, J.C., and P.M. Harnsberger (1998). “Asphalt Aging, Dual Oxidation Mechanism and Its Interrelationships with Asphalt Composition and Oxidative Age Hardening.” Transportation Research Record: Journal of the Transportation Research Board, No. 1638, Transportation Research Board of the National Academies, Washington, D.C.

Read, J., and D. Whiteoak (2003). The Shell Bitumen Handbook, 5th. Ed. Marsh Wall, London: Thomas Telford Publishing.

Reinke, G.M. (2015). “Some Properties of Binders with and without REOB with RAP & RAP+RAS NHDOT and Data from Vermont Cores.” FHWA Binder ETG.

Reinke, G., A. Hanz, D. Herlitzka, S. Engber, and M. Ryan (2015) “Further Investigations into the Impact of Reob & Paraffinic Oils on the Performance of Bitiuminous Mixtures” FHWA Asphalt Mix Expert Task Group (ETG), Fall River, MA, Technical Presentation, (April).

Robinett, C.J., and J.A. Epps (2010) “Energy, Emissions, Material Conservation, and Prices Associated with Construction, Rehabilitation, and Material Alternatives for Flexible Pavement.” Transportation Research Record No. 2179, Transportation Research Board, National Research Council, Washington, DC, pp. 10-22.

151

Rowe, G.M. (2011) “Prepared Discussion for the AAPT Paper by Anderson et al.: Evaluation of the Relationship between Asphalt Binder Properties and Non-Load Related Cracking.” Journal of the Association of Asphalt Paving Technologists, Vol. 80, pp. 649-662. Rowe, G.M. (2014a). “Assessment of Parameters for Asphalt Cracking Using Linear Visco-Elastic Properties.” Presented at the Pavement Performance Prediction (P3) Symposium, Western Research Institute, Laramie, Wyoming.

Rowe, G.M. (2014b). “Interrelationships in Rheological Parameters.” Presented at the 51st Petersen Asphalt Research Conference, Western Research Institute, Laramie, Wyoming.

Ruan, Y., R.R. Davison, and C.J. Glover (2003) “An Investigation of Asphalt Durability: Relationships between Ductility and Rheological Properties for Unmodified Asphalts.” Petroleum Science and Technology, Vol. 21, pp. 231-254.

Ryan, M., D. Herlitzka, S. Engber, A. Engstler, S. Veglahn, A. Hanz, and G. Reinke (2014) “A Discussion of Some Factors Impacting Performance of Binders Blended With Additives for Reducing Low Temperature Properties of Asphalt Binders and Their Impact on Mix Performance” FHWA Asphalt Mix Expert Task Group (ETG), Technical Presentation.

Tran, N.H., A. Taylor, and R. Willis (2012) Effect Of Rejuvenator on Performance Properties of HMA Mixtures with High RAP and RAS Contents. NCAT Report 12-05, National Center for Asphalt Technology, Auburn, AL, 70 pp.

Underwood, B.S., Y.R. Kim, M. Guddati, S. Thirunavukkarasu, and S. Savadatti (2009) “Response and Fatigue Performance Modeling of ALF Pavements Using 3-D Finite Element Analysis and a Simplified Viscoelastic Continuum Damage Model.” Journal of the Association of Asphalt Paving Technologists, Vol. 78, pp. 743-776.

Underwood, B.S., M.N. Guddati, and Y. R. Kim (2010) “Improved calculation method of damage parameter in viscoelastic continuum damage model” International Journal of Pavement Engineering, Vol. 11, No. 6, pp. 459-476.

Van Gooswilligen, G., F.T. De Bats, and T. Harrison (1989). “Quality of Paving Grade Bitumen – A Practical Approach in terms of Functional Tests.” Proc 4th Eurobitume Symp, Madrid, pp 290–297.

West, R., J.R. Willis, and M. Marasteanu (2013) NCHRP 9-46: Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content, NCHRP Report 752, Transportation Research Board, National Research Council, Washington, DC.

Wu, Z., L. Mohammad, L.B. Wang, and M. Mull (2005) “Fracture Resistance Characterization of Superpave Mixtures Using the Semi-Circular Bending Test.” Journal of ASTM International, Vol. 2, No. 3, (March).

152

Yin, F., E. Arambula, R. Lytton, A. Epps Martin, and L. Garcia Cucalon (2014) “A Novel Method to Evaluate Moisture Susceptibility and Rutting Resistance of Asphalt Mixtures Using the Hamburg Wheel Tracking Test.” Transportation Research Record, Transportation Research Board, National Research Council, Washington, DC, in press.

Yin, F., A. Epps Martin, E. Arambula, and D.E. Newcomb (2015) “Short-Term Aging of Asphalt Mixtures.” Journal of the Association of Asphalt Paving Technologists, Vol. 84, in press.

Yin, F., L. Garcia Cucalon, A. Epps Martin, E. Arámbula, A. Chowdhury, and E.S. Park (2013) “Laboratory Conditioning Protocols for Warm-Mix Asphalt.” Journal of the Association of Asphalt Paving Technologists, Vol. 82, pp. 177-211.

Yin, F., L. Garcia Cucalon, A. Epps Martin, E. Arámbula, and E.S. Park (2014) “Performance Evolution of Hot-Mix and Warm-Mix Asphalt with Field and Laboratory Aging.” Journal of the Association of Asphalt Paving Technologists, Vol. 83, pp. 109-142.

Yut, I., and A. Zofka (2014). “Correlation between rheology and chemical composition of aged polymer-modified asphalts.” Construction and Building Materials, Vol 62, Elsevier, Ltd., pp. 109-117.

Zhou, F., S. Im, S. Hu, D. Newcomb, and T. Scullion (2016) “Selection and Preliminary Evaluation of Laboratory Cracking Tests for Routine Asphalt Mix Designs.” 2016 Annual Meeting of the Association of Asphalt Paving Technologists, Proceedings.

Zhou, F., S. Im, D. Morton, R. Lee, S. Hu, and T. Scullion (2015) “Rejuvenator Characterization, Blend Characteristics, and Proposed Mix Design Method.” Journal of the Association of Asphalt Paving Technologists, accepted for publication.

Zhou, F., and D. Newcomb (2015) NCHRP Project 9-57: Experimental Design For Field Validation Of Laboratory Tests To Assess Cracking Resistance Of Asphalt Mixtures. Interim Report, National Cooperative Highway Research Program, Washington, D.C.

Zofka, A., M. Chrysochoou, I. Yut, C. Johnston, M. Shaw, S. Sun, J. Mahoney, S. Farquharson, and M. Donahue (2013). “Evaluating applications of field spectroscopy devices to fingerprint commonly used construction materials.” Report S2-R06B-RW-1,Strategic Highway Research Program 2, Transportation Research Board, Washington, D.C.

153

LIST OF ACRONYMS

AASHTO American Association of State Highway and Transportation Officials ALMLC Aged Laboratory Mixed Laboratory Compacted AMPT Asphalt Mixture Performance Tester ANOVA Analysis of Variance ARPMLC Aged Reheated Plant Mixed Laboratory Compacted ASTM American Society for Testing and Materials AV Air Voids BBR Bending Beam Rheometer CA Carbonyl Area CDD Cumulative Degree Days CI Coatability Index DCT Disk-Shaped Compact Tension DOB Degree of Blending DOT Department of Transportation DSR Dynamic Shear Rheometer DSRFn Dynamic Shear Rheometer Function EBM Energy-Based Mechanistic E* Dynamic Complex Modulus FHWA Federal Highway Administration FI Flexibility Index FT-IR Fourier Transform Infrared G* Shear Complex Modulus G-R Glover-Rowe Parameter HMA Hot-Mix Asphalt HS Hardening Susceptibility HWTT Hamburg Wheel Tracking Test ICT Illinois Center for Transportation IDT Indirect Tensile Strength IFIT Illinois Flexibility Index Test LMLC Laboratory Mixed Laboratory Compacted LSV Low Shear Viscosity LTOA Long-Term Oven Aging LTPP Long-Term Pavement Performance Program LTRC Louisiana Transportation Research Center LVECD Layered Viscoelastic Continuum Damage MR Resilient Modulus MWAS Manufacturer Waste Asphalt Shingles NCAT National Center for Asphalt Technology NCHRP National Cooperative Highway Research Program NMAS Nominal Maximum Aggregate Size OT Overlay Test PAV Pressure Aging Vessel PG Performance Grade PGH High-Temperature PG PGI Intermediate-Temperature PG

154

PGL Low-Temperature PG PMLC Plant Mixed Laboratory Compacted POV Pressure Oxidation Vessel RA Recycling Agent RAP Reclaimed Asphalt Pavement RAPBR RAP Binder Ratio RAS Recycled Asphalt Shingle RASBR RAS Binder Ratio RBR Recycled Binder Ratio RDT Repeated Uniaxial Direct Tension RE Rejuvenating Effectiveness RI Rheological Indices RPMLC Reheated Plant Mix Laboratory Compacted RTFO Rolling Thin Film Oven SARA Saturate, Aromatic, Resin, and Asphaltene Analysis SCB Semi-Circular Bending SHRP Strategic Highway Research Program SSD Saturated Surface Dry STOA Short-Term Oven Aging S-VECD Simplified Viscoelastic Continuum Damage TOAS Tear-Off Asphalt Shingles Tukey’s HSD Tukey’s Honest Significant Differences TSRST Thermal Stress Restrained Specimen Test TxDOT Texas Department of Transportation UTSST Uniaxial Thermal Stress and Strain Test WMA Warm-Mix Asphalt δ Binder Phase Angle c Crossover Frequency