Appendix E NCHRP Project Experimental Plans, Results, and Analyses

Transcription

1 Appendix E NCHRP Project Experimental Plans, Results, and Analyses E-1

2 Table of Contents Table of Contents... 3 List of Figures... 3 List of Tables... 6 E1. Introduction... 9 E2. Sample Reheating Study... 9 E3. Binder Grade Study E3.1 Analysis of High Temperature Properties E3.2 Analysis of Low Temperature Properties E4. Short-Term Oven Conditioning Study E5. RAP Study E5.1 Interfacial Mixing and Compatibility Experiment E5.2 Laboratory Mixing Experiment E6. Workability Study E6.1 UMass Workability Device E6.2 Gyratory Shear Stress E6.3 Nynäs Workability Device E6.4 University of New Hampshire Device E7. Mix Design Study E7.1 Experimental Design E7.2 Mixture Properties E7.3 Statistical Analysis E8. Field Validation Study E8.1 Validation Mixtures E8.2 Binder Grade Selection E8.3. RAP E8.4. Short-Term Oven Conditioning E8.5. Specimen Fabrication, Coating and Compactability E8.6 Moisture Sensitivity E8.7 Flow Number E9. Feasibility of Using a Two Step Aging Process for Performance Testing E10. Fatigue Study E11. Summary of Findings E11.1 Sample Reheating Study E11.2 Binder Grade Study E11.3 Short-Term Conditioning Study E11.4 Recycled Asphalt Pavement (RAP) Study E11.5 Workability Study E11.6 Mix Design Study E11.7 Field Validation Study E11.8 Fatigue Study E12. Production Records for Pennsylvania SR2006 WMA Demonstration Project References E-2

3 List of Figures Figure E1. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis HMA Control Mixture Figure E2. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis Aspha-Min Mixture Figure E3. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis Evotherm Mixture Figure E4. Effect of Sample Reheating of the Dynamic Modulus of the St. Louis Sasobit Mixture Figure E5. Effect of Sample Reheating on the Dynamic Modulus of the New York LEA Mixture Figure E6. Effect of RTFOT Temperature on the RTFOT High Temperature Continuous Grade Figure E7. Effect of Short-Term Aging Susceptibility on the Rate of Change of RTFOT High Temperature Grade with RTFOT Temperature Figure E8. Allowable Temperature Changes Figure E9. Effect of RTFOT Temperature on the Low Temperature Continuous Grade Figure E10. Effect of Low Temperature Binder Grade on the Rate of Change of Low Temperature Grade With RTFOT Temperature Figure E11. Maximum Specific Gravity for Colorado I-70 Mixtures Figure E12. Comparison of Tensile Strengths for Colorado I-70 Mixture Figure E13. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Control Mixture Figure E14. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Advera Mixture Figure E15. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Evotherm Mixture Figure E16. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Sasobit Mixture Figure E17. Projected Views (photograph-to-light microscope-to-afm image) of a Contact Interface Between New and RAP Binder Figure E18. AFM Scans at the Interfacial Contact Line (upper-left), at the New Binder Surface (upper-right), and the RAP Binder Surface (lower-left) After Annealing Figure E19. AFM Scan at the Interfacial Contact Line Between the New Binder Film and the RAP Binder Film After Annealing Figure E20 Photograph Image of Two Film-on-Film Slides. Left, Prior to Thermal Annealing. Right Thermally Annealed for F (130 C) Figure E21. Dynamic Modulus Master Curve for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F Figure E22. Dynamic Modulus Master Curve for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E23. Dynamic Modulus Master Curve for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F E-3

4 Figure E24. Dynamic Modulus Master Curve for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E25. Dynamic Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E26. Dynamic Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E27. Dynamic Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E28. Dynamic Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E29. Recovered Binder Modulus Master Curve for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F Figure E30. Recovered Binder Modulus Master Curve for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E31. Recovered Binder Modulus Master Curve for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E32. Recovered Binder Modulus Master Curve for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E33. Recovered Binder Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E34. Recovered Binder Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E35. Recovered Binder Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Figure E36. Recovered Binder Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Figure E37. Comparison of the Ratio of Measured to Fully Blended Dynamic Moduli Figure E38. Photograph of UMass Workability Device Figure E39. Paddles for UMass Workability Device Figure E40. Torque Versus Temperature for 12.5 mm, PG Mixture in the UMass Dartmouth Workability Device Figure E41. Repeatability of the UMass Workability Device Figure E42. Air Voids at N initial Figure E43. Gyratory Shear Stress at N initial Figure E44. Gyrations to 8 Percent Air Voids Figure E45. Gyratory Shear Stress at 8 % Air Voids Figure E46. Air Voids at N design Figure E47. Maximum Gyratory Shear Stress Figure E48. Photograph of Nynäs Workability Device Figure E49. Nynäs Force Versus Time Curves Figure E50. Early Portion of Nynäs Forces Versus Time Curves Figure E51. Nynäs Force at 1 sec Figure E52. Nynäs Initial Work Figure E53. Photograph of the University of New Hampshire Device Figure E54. Torque Setting Versus Temperature for the University of New Hampshire Device E-4

5 Figure E55. Dynamic Modulus Master Curves for the Colorado I-70 Project Figure E56. Dynamic Modulus Master Curves for the Yellowstone National Park Project Figure E57. Dynamic Modulus Master Curves for the New York Project Figure E58. Predicted Rutting for the Colorado I-70 Project Figure E59. Predicted Rutting for the Yellowstone National Park Project Figure E60. Predicted Rutting for the New York Project Figure E61. Comparison of Measured and Estimated Fully Blended Dynamic Modulus for the Monroe, North Carolina Mixture Produced with the Astec Double Barrel Green Process and 30 Percent RAP Figure E62. Differences in Indirect Tensile Strength Between Field Mixes and Laboratory Mixes Short Term Conditioned 2 Hours at the Compaction Temperature Figure E63. Introducing Foamed Asphalt to Mixing Bucket Figure E64. Foamed Asphalt on Before Mixing Figure E65. Foamed Asphalt Mixture after 90s Mixing Time Figure E66. Effect of Loose Mix Aging on Tensile Strength Figure E67. Comparison of Tensile Strengths for Loose Mix Aging Conditions Figure E68. Continuum Damage Analysis for 75 Gyration HMA Figure E69. Continuum Damage Analysis for 75 Gyration Advera WMA Figure E70. Continuum Damage Analysis for 75 Gyration Evotherm WMA Figure E71. Continuum Damage Analysis for 75 Gyration Sasobit WMA Figure E72. Continuum Damage Analysis for 100 Gyration HMA Figure E73. Continuum Damage Analysis for 100 Gyration Advera WMA Figure E74. Continuum Damage Analysis for 100 Gyration Evotherm WMA Figure E75. Continuum Damage Analysis for 100 Gyration Sasobit WMA Figure E76. Comparison of Continuum Damage Fatigue Curves for the 75 Gyration Mix Figure E77. Comparison of Continuum Damage Fatigue Curves for the 100 Gyration Mix E-5

6 List of Tables Table E1. Summary of the Sample Reheating Study Table E2. Comparison of Reheated to Immediate and Delayed Dynamic Moduli for 68 F, 0.1 Hz Loading Table E3. High Temperature Binder Properties From the RTFOT Temperature Experiment Table E4. Low Temperature Binder Properties From the RTFOT Temperature Experiment Table E5. Aging Index and Rate of Change of RTFOT High Temperature Grade with RTFOT Temperature Table E6. Effect of High Temperature Binder Grade on Pavement Rutting Resistance Table E7. Typical HMA Mixing Temperatures Table E8. Minimum WMA Production Temperatures Not Requiring a High Temperature PG Grade Increase Table E9. Recommended Improvement in Virgin Binder Low Temperature Continuous Grade for RAP Blending Chart Analysis for WMA Production Temperatures Table E10. Properties of Mixture Used in the Short-Term Oven Conditioning Study Table E11. Statistical Analysis of Tensile Strength Data for I-70 Mixtures Table E12. Statistical Analysis of the Dynamic Modulus Data for the I-70 Mixtures Table E13. Summary of Statistical Analysis of Short-Term Conditioning Table E14. Summary of Compatibility Testing Table E15. Hiethaus Compatibility Parameters for Sasobit RAP Blends Table E16. Hiethaus Compatibility Parameters for Advera RAP Blends Table E17. Experimental Design for the Laboratory RAP Mixing Experiment Table E18. Performance Grading Properties for Recovered RAP Binder Table E19. Fitted Christensen-Anderson Master Curve Parameters for Recovered Binders for the Laboratory RAP Mixing Study Table E20. Measured and Estimated Fully Blended Dynamic Modulus for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F Table E21. Measured and Estimated Fully Blended Dynamic Modulus for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Table E22. Measured and Estimated Fully Blended Dynamic Modulus for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Table E23. Measured and Estimated Fully Blended Dynamic Modulus for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Table E24. Measured and Estimated Fully Blended Dynamic Modulus for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Table E25. Measured and Estimated Fully Blended Dynamic Modulus for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Table E26. Measured and Estimated Fully Blended Dynamic Modulus for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Table E27. Measured and Estimated Fully Blended Dynamic Modulus for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F Table E28. Key Elements of Potential Workability Devices for WMA Table E29. Screening Experiment for Workability Tests Table E30. Mixture Used in the Workability Study E-6

7 Table E31. Summary of Torque From UMass Workability Device Table E32. Summary of Analysis of Variance for the UMass Workability Device Table E33. Summary of Results for the Gyratory Compactor Table E34. Summary of Analysis of Variance for the Gyratory Compactor Table E35. Summary of Data From Early Portion of the Nynäs Force Curves Table E36. Summary of Analysis of Variance for the Nynäs Device Table E37. Summary of Results Using the University of New Hampshire Device Table E38. Mix Design Experiment Table E39. Mixtures Used in the Mix Design Experiment Table E40. Properties of RAP Used in the Mixture Design Experiment Table E41. Mixture Design Properties for 50 Gyration Mixtures Table E42. Mixture Design Properties for 75 Gyration Mixtures Table E43. Mixture Design Properties for 100 Gyration Mixtures Table E44. Paired Difference Analysis for Design Air Voids, One Sided Test With Significance Level of 0.5 percent Table E45. Paired Difference Analysis for Design VMA, One Sided Test With Significance Level of 0.5 percent Table E46. Paired Difference Analysis for Design VBE, One Sided Test With Significance Level of 0.5 percent Table E47. Paired Difference Analysis for Binder Absorption, One Sided Test With Significance Level of 0.5 percent Table E48. Paired Difference Analysis for Design Binder Content, One Sided Test With Significance Level of 0.5 percent Table E49. Paired Difference Analysis for Effective Binder Content, One Sided Test With Significance Level of 0.5 percent Table E50. Paired Difference Analysis for Relative Density at N ini, One Sided Test With Significance Level of 0.5 percent Table E51. Paired Difference Analysis for Relative Density at N max, One Sided Test With Significance Level of 0.5 percent Table E52. Paired Difference Analysis for Gyrations to 92 Percent Relative Density at the Compaction Temperature, One Sided Test With Significance Level of 0.5 percent Table E53. Paired Difference Analysis for Percent Increase in Gyrations to 92 Percent Relative Density at 54 F (30 C) Below the Compaction Temperature, One Sided Test With Significance Level of 0.5 percent Table E54. Paired Difference Analysis for Dry Tensile Strength, One Sided Test With Significance Level of 0.5 percent Table E55. Paired Difference Analysis for Conditioned Tensile Strength, One Sided Test With Significance Level of 0.5 percent Table E56. Paired Difference Analysis for Tensile Strength Ratio, One Sided Test With Significance Level of 0.5 percent Table E57. Summary of Tensile Strength Ratios Table E58. Normalized Paired Difference Analysis for Flow Number, One Sided Test With Significance Level of 0.5 percent Table E59. Normalized Paired Difference Analysis for Allowable Traffic, One Sided Test With Significance Level of 0.5 percent E-7

8 Table E60. Summary of NCHRP 9-33 Rutting Resistance From Flow Number Testing Table E61. Field Validation Mixtures Table E62. Summary of Binder Grading Test Data Table E63. Summary of Continuous Grading of Recovered Binders Table E64. Summary of Average Difference in Continuous Grade Temperatures for WMA Compared to HMA Table E65. Input Data for MEPDG Spreadsheet Rutting Predictions Table E66. Measured and Estimated Fully Blended Dynamic Modulus for the Monroe, North Carolina Mixture Produced with the Astec Double Barrel Green Process and 30 Percent RAP Table E67. Verification Testing for Short-Term Oven Conditioning Table E68. Composition of Colorado I-70 Mixtures Table E69. Properties of Specimens Compacted to 75 Gyrations for the Colorado I-70 Mixtures Table E70. Composition of Yellowstone National Park Mixtures Table E71. Properties of Specimens Compacted to 75 Gyrations for the Yellowstone National Park Mixtures Table E72. Composition of Pennsylvania SR2007 Mixtures Table E73. Properties of Specimens Compacted to 50 Gyrations for the Pennsylvania SR2007 Mixtures Table E74. Composition of Pennsylvania SR2006 Mixtures Table E75. Properties of Specimens Compacted to 75 Gyrations for the Pennsylvania SR2006 Mixtures Table E76. Summary of Quality Control Test Results for Pennsylvania SR 2006 Project Table E77. Summary of Core Density Results for Pennsylvania SR 2006 Project Table E78. Composition of Monroe, North Carolina Mixture Table E79. Properties of Specimens Compacted to 75 Gyrations for the Monroe, North Carolina Mixture Table E80. Summary of Optimum Binder Content Determination for the Pennsylvania Foamed Asphalt Mixture Table E81. Summary of Optimum Binder Content Determination for the North Carolina Foamed Asphalt Mixture Table E82. Properties at the Optimum Binder Content Table E83. Summary of AASHTO T283 Results Table E84. Summary of Flow Number and Rutting Resistance Results Table E85. Summary of Average Difference in Allowable Traffic WMA Compared to HMA Table E86. Database of Dry Tensile Strengths Extracted from NCHRP Project Table E87. Two-Way Analysis of Variance for Loose-Mix Aging Tensile Strength Data Table E88. Significant Differences for Loose Mix Aging Effect Table E89. Experimental Design for the WMA Fatigue Study Table E90. Design Properties for Fatigue Study Mixtures Table E91. Summary of Continuum Damage Fatigue Parameters E-8

9 E1. Introduction National Cooperative Highway Research Program (NCHRP) Project 9-43 included the design and execution of eight laboratory studies addressing critical aspects of mixture design for warm mix asphalt (WMA): 1. Sample Reheating Study 2. Binder Grade Study 3. Short-Term Conditioning Study 4. Recycled Asphalt Pavement (RAP) Study 5. Workability Study 6. Mix Design Study 7. Field Validation Study 8. Fatigue Study This appendix discusses each of these studies in detail. All of the data presented in this section of the report are included on the NCHRP Project 9-43 Data CD. E2. Sample Reheating Study Since several of the experiments for NCHRP 9-43 used mechanical property tests on specimens prepared from loose mix, a study was conducted to determine if sample reheating significantly affected the mechanical properties of WMA. The response variable used in this study was the mixture dynamic modulus because it is very sensitive to changes in binder stiffness, and it was expected that sample reheating may result in additional stiffening of the binder in the mixture. The effect of sample reheating was evaluated for a control hot mix asphalt (HMA) and four WMA processes: Aspha-min, Evotherm ET, LEA, and Sasobit. The data for the control HMA, Aspha-min, Evotherm ET, and Sasobit mixtures were provided by the Federal Highway Administration (FHWA) Mobile Asphalt Laboratory. The FHWA provided data for a WMA project constructed in St. Louis, Missouri where modulus tests were performed for three conditions: (1) samples prepared at the time of construction and immediately tested, (2) samples prepared at the time of construction, but tested weeks later, and (3) reheated samples. McConnaughay Technologies prepared dynamic modulus specimens for the LEA process during E-9

10 construction and the research team prepared an additional set of dynamic modulus specimens after reheating. Both sets of LEA specimens were tested by the research team. All of the dynamic modulus tests were conducted with an Asphalt Mixture Performance Tester (AMPT) in accordance with AASHTO PP61. Table E1 summarizes the sample reheating study. The data analysis consisted of comparing dynamic modulus master curves for the various sample preparation and testing conditions. Table E1. Summary of the Sample Reheating Study. Mixture Immediate Delayed Reheated HMA Control X X X Aspha-min X X X Evotherm ET X X X LEA X X Sasobit X X X Figures E1 through E5 present comparisons of dynamic modulus master curves obtained from the various samples. The error bars in these figures represent 95 percent confidence intervals for the mean based on a typical coefficient of variation for the dynamic modulus test of 14 percent and the number of samples that were tested. When the confidence intervals do not overlap, there is a significant difference in the dynamic modulus for the various conditions. Reheating has similar effect on the stiffness of WMA as it does on HMA. There is a stiffening of the middle portion of the dynamic modulus master curve, which is most sensitive to changes in binder stiffness. Table E2 quantifies the stiffening caused by reheating. This table presents the ratio of the reheated modulus to the immediate modulus and the delayed modulus for tests at 68 F (20 C), 0.1 Hz loading, which corresponds to a reduced frequency of 0.1 Hz in Figures E1 through E5 and is near the maximum difference between the master curves. The modulus after reheating is 60 to 150 percent higher than the immediate modulus and 30 to 80 percent higher than the delayed modulus. When the immediate modulus is used as the basis, the Aspha-min mixture was more sensitive to reheating effects compared to the HMA control and the Evotherm and Sasobit mixtures. When the delayed modulus is used as the basis, the WMA mixtures and the HMA control have similar sensitivity to reheating. The reheating effect is probably the result of the E-10

11 additional aging that occurs when field samples are reheated to temperatures high enough to allow proper compaction. As with HMA, reheating times and temperatures for WMA should be limited to minimize this effect. The Aspha-min mixture also shows an increase in modulus for the delayed testing. This effect suggests a stiffening of this mixture upon curing at room temperature. Additional study of this effect is needed before firm conclusions can be drawn. Immediate Delayed Reheat Dynamic Modulus, MPa E E E E E+04 Reduced Frequency, Hz Figure E1. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis HMA Control Mixture. E-11

12 Immediate Delayed Reheat Dynamic Modulus, MPa E E E E E+04 Reduced Frequency, Hz Figure E2. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis Aspha- Min Mixture. Immediate Delayed Reheat Dynamic Modulus, MPa E E E E E+04 Reduced Frequency, Hz Figure E3. Effect of Sample Reheating on the Dynamic Modulus of the St. Louis Evotherm Mixture. E-12

13 Immediate Delayed Reheat Dynamic Modulus, MPa E E E E E+04 Reduced Frequency, Hz Figure E4. Effect of Sample Reheating of the Dynamic Modulus of the St. Louis Sasobit Mixture. Delayed Reheat Dynamic Modulus, ksi E E E E E+04 Reduced Frequency, Hz Figure E5. Effect of Sample Reheating on the Dynamic Modulus of the New York LEA Mixture. E-13

14 Table E2. Comparison of Reheated to Immediate and Delayed Dynamic Moduli for 68 F, 0.1 Hz Loading. Dynamic Modulus Ratio, Mixture 68 F, 0.1 Hz Reheat to Reheat to Immediate Delayed Control Aspha-min Evotherm LEA NT 1.49 Sasobit The primary finding from the sample reheating study is reheating has a similar effect on the mechanical properties of WMA and HMA. Mixture stiffness increases significantly upon reheating especially over the middle portion of the dynamic modulus master curve which is most sensitive to changes in binder stiffness. Reheating times and temperature for both WMA and HMA should be limited to minimize this effect. Additionally, the stiffening effect must be considered when drawing conclusions from tests on specimens produced using reheated samples. E3. Binder Grade Study The lower production temperatures used with WMA produce less aging of the binder during construction. This reduced aging may result in increased rutting of pavements produced using WMA processes and it may also result in improved resistance to fatigue and low temperature cracking. NCHRP Project 9-43 included analysis of an experiment conducted by the FHWA where the effects of WMA production temperatures were simulated using the Rolling Thin Film Oven Test (RTFOT), AASHTO T240. In this experiment, binders were short-term aged in the RTFOT, at temperatures of 325, 266, and 230 F (163, 130, and 110 C). The high temperature properties of the binders were then measured in accordance with AASHTO T315 at multiple temperatures to determine the continuous RTFOT high temperature grade of the binder. Table E3 summarizes the high temperature properties of the binders for the three short-term aging temperatures. Low temperature properties for several of the binders were measured during NCHRP Project 9-43 for RTFOT temperatures of 325 and 230 F (163 and 110 C). Low temperature properties were measured in accordance with AASHTO T313 at two temperatures to determine the continuous low temperature grade of the binder. The RTFOT aged binders were E-14

15 further aged in the pressure aging vessel (PAV) in accordance with AASHTO R28 at a temperature 100 C prior to bending beam rheometer testing. Table E4 summarizes the low temperature properties for the two short-term aging temperatures. Table E3. High Temperature Binder Properties From the RTFOT Temperature Experiment. Binder ID AAM1 B-6354 B-6272 B-6348 B-6328 AAM-2 AAG-1 AAD-1 B % Sasobit B % Sasobit RTFOT at 163 o C RTFOT at 130 o C RTFOT at 110 o C Continuous RTFOT Continuous RTFOT Continuous RTFOT Temperature, o C G*/sinδ, kpa Grade, o C G*/sinδ, kpa Grade, o C G*/sinδ, kpa Grade, o C E-15

16 Table E4. Low Temperature Binder Properties From the RTFOT Temperature Experiment. RTFOT at 163 o C, PAV at 100 o C RTFOT at 110 o C, PAV at 100 o C Binder ID Temperature, o C Continuous Low Continuous Low S m Temperature Grade, S m Temperature Grade, o C o C AAM-1 B-6354 B-6272 B-6348 B-6328 AAM AAG-1 Not Tested AAD B % Sasobit B % Sasobit Not Tested Not Tested E3.1 Analysis of High Temperature Properties The high temperature continuous grade data were analyzed to develop preliminary recommendations for WMA production temperatures below which consideration should be given to increasing the high temperature grade of the binder to minimize the potential for increased rutting due to the reduced aging of WMA. This was accomplished by: (1) determining the effect of temperature on the continuous high temperature grade properties, (2) selecting an allowable decrease in continuous grade based on a model of the effect of binder stiffness on rutting performance, and (3) estimating allowable decreases in production temperature from the allowable continuous high temperature grade change and the effect of temperature on the change in high temperature grade. Figure E6 presents a plot of the change in the RTFOT high temperature grade as a function of the RTFOT aging temperature. There is a nearly linear decrease in the RTFOT high temperature grade with decreasing aging temperature; however, the slope varies substantially for the binders tested. It ranges from approximately 0.01 per C to approximately 0.13 per C. E-16

17 0 Change in RTFOT Continuous Grade, o C B-6354 B-6348 B-6328 AAM-1 AAM-2 AAG-1 AAD-1 B6272 B % Sasobit B % Sasobit RTFOT Temperature, o C Figure E6. Effect of RTFOT Temperature on the RTFOT High Temperature Continuous Grade The effect of the aging temperature on the RTFOT high temperature grade should be related to the short-term aging susceptibility of the binder. An index of the short-term aging susceptibility can be obtained from normal binder grading data by dividing the G*/sinδ value after RTFOT aging by the G*/sinδ value for the tank binder. Because the index will vary with temperature, it should be computed using data at the high temperature grade temperature. Table E5 summarizes aging indices computed in this manner and the rate of change in RTFOT high temperature grade with RTFOT temperature for the binders included in the FHWA RTFOT experiment. These data are plotted in Figure E7 and show a good relationship between the aging susceptibility of the binder and the effect of RTFOT aging temperature on the RTFOT high temperature grade. This data shows that the effect of changes in production temperatures is more important for binders with greater aging ratios. E-17

18 Table E5. Aging Index and Rate of Change of RTFOT High Temperature Grade with RTFOT Temperature. Binder Source Aging Index G * / sin δ G * / sin δ RTFOT Tank Rate of Change of RTFOT High Temperature Grade with RTFOT Temperature, C/ C B-6354 Missouri WMA Demo Control PG B-6348 Hawaii PG B-6328 Venezuelan PG AAM-1 SHRP MRL AAM-2 SHRP MRL AAG-1 SHRP MRL AAD-1 SHRP MRL B6272 ALF PG Control B % Sasobit B % Sasobit ALF PG Control + Sasobit ALF PG Control + Sasobit Rate of Change of RTFOT High Temperature Grade With RTFOT Temperature, o C/ o C y = 0.085(x-1) R 2 = 0.97 Rate of High Temperature Grade Change ( o C/ o C) = 0.085(AI-1) Binder Aging Index Figure E7. Effect of Short-Term Aging Susceptibility on the Rate of Change of RTFOT High Temperature Grade with RTFOT Temperature. E-18

19 The relationship shown in Figure E7 was used to estimate the effect of WMA production temperature on the high temperature properties of the binder after mixing. To limit the change in high temperature grade to one grade level, divide 6 C by the slope obtained from the binder aging index. To limit the high temperature grade change to one-half grade level, divide 3 C by the slope obtained from the binder aging index. Equations E1 and E2 present the allowable temperature changes for one grade level and one-half grade level changes, respectively. These are plotted as a function of binder aging index in Figure E8. For a typical binder with an aging index of 2.4, the maximum allowable temperature changes are -140 F (-60 C) for a one grade level change and -54 F (-30) C for a one-half grade level change T full grade = (E1) ( AI 1) T grade = (E2) ( AI ) / 2 1 where: T full grade = maximum temperature change for a full grade change, C T 1/2 grade = maximum temperature change for a ½ grade change, C AI = binder aging index at the performance grade temperature E-19

20 300 Allowable Change in Production Temperature, o F /2 Grade Change Full Grade Change Binder Aging Index Figure E8. Allowable Temperature Changes. Based on the rutting model developed in NCHRP Projects 9-25 and 9-31, the rutting rate in a typical pavement is approximately inversely proportional to the high temperature stiffness of the binder (1). Using the rule of thumb that the 6 C interval used in the Performance Grading System is approximately equal to a doubling of the high temperature stiffness of a typical asphalt binder, an estimate of the effect of changing the high temperature binder grade on rutting rate can be made using Equation E3. 1 RRR = (E3) 2 T 6 where: RRR = relative rutting rate T = change in the high temperature continuous grade of the binder, C E-20

21 Table E6 summarizes approximate relative rutting rates for various allowable high temperature continuous grade changes based on Equation E3. Considering that the error in the rutting model developed in NCHRP Projects 9-25/9-31 is a factor of two limiting the allowable high temperature grade change due to a decrease in production temperature to 3 C is reasonable. This limit will limit the increase in rutting rate to approximately 40 percent. Therefore, when the WMA production temperature results in a decrease in the high temperature continuous grade of more than 3 C, the high temperature grade of the binder should be increased one grade to compensate for the decreased short-term aging of the binder. Table E6. Effect of High Temperature Binder Grade on Pavement Rutting Resistance. Change in Continuous High Temperature Grade, C Relative Pavement Rutting Rate Recommended plant mixing temperatures below which the binder grade should be increased can be obtained using Equation E2 and typical HMA production temperatures. Table E7 summarizes the typical plant mixing temperatures recommended by the Asphalt Paving Environmental Council (2) based on the high temperature performance grade of the binder. WMA production temperatures below which it is recommended to increase in the performance grade are obtained by combing the temperature change from Equation E2 with the typical mixing temperatures from Table E6. The results rounded to the nearest 5 F (2.8 C) are presented in Table E8 for various binder grades and levels of the aging index of the binder. If the proposed plant mixing temperatures are lower than those listed in Table E8, the performance grade of the binder should be increased one level above that normally used for hot mix asphalt. E-21

22 Table E7. Typical HMA Mixing Temperatures (2). Recommended PG High Mid-Point Temperature HMA Mixing Grade Temperature, F Table E8. Minimum WMA Production Temperatures Not Requiring a High Temperature PG Grade Increase. PG High Temperature Grade Aging Index Minimum WMA Mixing Temperature Not Requiring PG Grade Increase, F E3.2 Analysis of Low Temperature Properties The high temperature grade bumping recommended in Table E8 may increase the cost of binders for WMA, because when the high temperature grade is increased and the low temperature grade remains the same, the useable temperature range of the binder increases. The low temperature continuous grade data from the FHWA RTFOT experiment were analyzed to determine if the lower WMA temperatures improved the low temperature grade of binder sufficiently to warrant using a higher low temperature grade binder. E-22

23 Figure E9 presents a plot of the change in the low temperature grade of the binder as a function of the RTFOT aging temperature. Comparing Figure E9 with Figure E6, the low temperature continuous grade is much less sensitive to changes in the RTFOT aging temperature compared to the high temperature grade. The low temperature grade improves by only 0.5 to 2.0 C when the RTFOT aging temperature is reduced to from 325 to 230 F (163 to 110 C) compared to 4.0 to 7.0 C for the RTFOT high temperature grade of the same binders. The additional aging from the PAV that is included in the characterization of the low temperature properties of binders is the likely cause of this difference. Apparently improvements in low temperature binder properties resulting from lower short-term aging temperatures are offset by the simulated long-term aging from the PAV, resulting in little change in the low temperature grade of the binder. 0 Change in Low Temperature Continuous Grade, o C B-6354 B-6348 B-6328 AAM-1 AAM-2 AAD-1 B RTFOT Temperature, o C Figure E9. Effect of RTFOT Temperature on the Low Temperature Continuous Grade. E-23

24 Figure E10 shows that there appears to be a weak relationship between the rate of change in low temperature grade with RTFOT temperature and the low temperature grade of the binder. Binders with better low temperature properties tend to show more improvement in low temperature properties when the RTFOT temperature is decreased. The relatively small effect of RTFOT temperature on the low temperature binder grade does not warrant recommended changes in low temperature binder grade selection for WMA. For the binders tested, decreasing the production temperature by 95 F (53 C) only improved the low temperature grade of the binder by 1 to 2 C which is only 1/6 th to 1/3 rd of a grade level Rate of Change of Low Temperature Grade With RTFOT Temperature, o C/ o C y = x R 2 = Low Temperature Grade, o C Figure E10. Effect of Low Temperature Binder Grade on the Rate of Change of Low Temperature Grade With RTFOT Temperature. The low temperature grade improvement, however, can be significant when considering mixtures incorporating recycled asphalt pavement (RAP). When RAP blending charts are used (3), the low temperature continuous grade of the binder changes approximately 0.6 C for every 10 percent of the total binder in the mixture replaced with RAP binder. Thus, improving the low E-24

25 temperature properties of the virgin binder in the mixture 0.6 C by lowering the production temperature will allow 10 percent additional RAP binder to be added to the mixture. Using the relationship shown in Figure E10, for the middle of the low temperature binder grade temperature range, recommended improvements in virgin binder low temperature continuous grade for RAP blending chart analysis can be made as a function of WMA production temperature for mixtures incorporating PG XX-16, PG XX-22, and PG XX-28. These recommended improvements are summarized in Table E9 for some common binder grades. For a mixture using PG virgin binder and a WMA production temperature of 250 F, the virgin binder low temperature continuous grade would be improved 0.6 C to account for the lower WMA production temperature. Table E9. Recommended Improvement in Virgin Binder Low Temperature Continuous Grade for RAP Blending Chart Analysis for WMA Production Temperatures. Virgin Binder PG Grade Average HMA Production Temperature, o F Rate of Improvement of Virgin Binder Low Temperature Grade per o C Reduction in Plant Temperature Recommended Improvement in Virgin Binder Low WMA Production Temperature, o F Temperature Continuous Grade for RAP Blending Chart Analysis, o C 300 NA NA NA NA NA NA NA NA NA NA E-25

26 E4. Short-Term Oven Conditioning Study An important step in mixture design and analysis is short-term oven conditioning of laboratory prepared loose mix prior to compaction. Short-term oven conditioning simulates the binder absorption and aging that occurs during construction. The short-term oven conditioning recommended for HMA at the end of the Strategic Highway Research Program (SHRP) was 4 hours at 275 F (135 C) for both volumetric design and performance testing (4). This was included in AASHTO PP2, Practice of Short and Long Term Aging of Hot Mix Asphalt (HMA) which later became AASHTO R30 Mixture Conditioning of Hot-Mix Asphalt (HMA). To expedite the mixture design process and reduce the amount of ovens required for mixture design, the FHWA Mixtures and Aggregates Expert Task Group (ETG) reviewed data concerning the effect of conditioning time and temperature on the volumetric properties of asphalt mixtures. The ETG ultimately recommended that the short-term oven conditioning for mixture design be changed to 2 hours at the compaction temperature for aggregates with water absorption less than 4.0 percent. For aggregates with greater water absorption and for performance testing, the shortterm oven conditioning remained 4 hours at 275 F (135 C). AASHTO R30 was eventually modified to reflect the ETG s recommendation. Short-term conditioning of 2 hours at the compaction has been recommended by some WMA process developers for mixture design. No recommendations have been made for short-term conditioning of WMA for performance testing. The objective of the short-term oven conditioning study was to determine appropriate shortterm oven conditioning times for use in WMA mixture design and analysis. For convenience and to properly assess the effect of WMA process temperature, the short-term conditioning temperature was selected to be equal to the compaction temperature. Conditioning times of 2 hours and 4 hours were used in the experiment. The approach that was used was to compare the following properties of laboratory mixtures with those from field mixtures: Maximum specific gravity, AASHTO T209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures, Tensile strength at 77 F (25 C), AASHTO T322, Determining the Creep Compliance and Strength of Hot Mix Asphalt (HMA) Using the Indirect Tensile Test Device, E-26

27 Dynamic modulus at 39.2, 68, and 95 F (4, 20, and 35 C) using frequencies of 10, 1, and 0.1 Hz, AASHTO TP70, Determining the Dynamic Modulus and Flow Number for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT) The short-term oven conditioning experiment was completed for the mixture used in the field project from I-70 in Colorado, and a tentative short-term conditioning time was selected. This tentative conditioning time was then verified using the remaining field mixtures as discussed in Section E8 of this appendix. Pertinent properties of the mixture used in the short-term oven conditioning study are given in Table E10. Table E10. Properties of Mixture Used in the Short-Term Oven Conditioning Study. Property I-70 Sieve Size 1 in Colorado 100 3/4 in 100 1/2 in 100 3/8 in 95 Gradation, % passing #4 73 #8 54 #16 40 #30 29 #50 18 # # Asphalt Content, % 6.2 N design 75 Design Air Voids, % 3.9 Design VMA, % 16.9 Design VFA, % 77.0 Fines to Effective Asphalt Ratio 1.0 Fractured Faces (one face/two faces), % 100/99 FAA 48.6 Aggregate Water Absorption, % 0.8 Tensile Strength Ratio, % 91 Binder Grade PG E-27

28 Figures E11 through E16 compare the properties of laboratory prepared mixtures for the Colorado I-70 project for various conditioning times with those for field mixtures. Due to material limitations, data for the Evotherm mixture was only collected for a conditioning time of 2 hours. Figure E11 compares the maximum specific gravity. The error bars shown in Figure E11 are the acceptable range of maximum specific gravity measurements based on the single operator precision statement given in AASHTO T209. Figure E11 shows that for the aggregate used in the Colorado I-70 mixtures, the maximum specific gravity is essentially the same for all processes and all short-term aging conditions. The reported water absorption for the Colorado I- 70 job mix formula was 0.8 percent. Figure E11. Maximum Specific Gravity for Colorado I-70 Mixtures. E-28

29 Figure E12 compares the indirect tensile data. The error bars in Figure E12 are 95 percent confidence intervals for the average indirect tensile strength. The graphical analysis shown in Figure E12 suggests that two hours of conditioning at the compaction temperature provides tensile strengths for laboratory prepared specimens that are approximately equal those from field mixtures. Figure E12. Comparison of Tensile Strengths for Colorado I-70 Mixture. Table E11 presents the results of statistical hypothesis testing to compare the mean tensile strength for the various laboratory conditions with that for the field mixtures. For the control mixture and the Advera mixtures, there is no difference in mean tensile strength for 2 hours at the compaction temperature, while 4 hours at the compaction resulted in significantly higher tensile strengths. For the Evotherm mixture, 2 hours at the compaction temperature produced significantly lower tensile strengths. Finally, for the Sasobit mixture, 2 hours at the compaction temperature produced significantly lower tensile strength compared to the field mixture, while 4 E-29

30 hours at the compaction temperature produced significantly higher tensile strength compared to the field mixture. Table E11. Statistical Analysis of Tensile Strength Data for I-70 Mixtures. Mixture Conditioning Field Strength, psi Lab Strength, psi t t cr, α =0.05 Conclusion Control 4 hours at compaction Lab strength greater than field strength Control 2 hours at compaction Lab strength same as field strength Advera 4 hours at compaction Lab strength greater than field strength Advera 2 hours at compaction Lab strength the same as field strength Evotherm 4 hours at compaction 83.3 Not tested NA NA NA Evotherm 2 hours at compaction Lab strength less than field strength Sasobit 4 hours at compaction Lab strength greater than field strength Sasobit 2 hours at compaction Lab strength less than field strength Figures E13 through E16 compare the dynamic modulus data. The error bars in these figures are 95 percent confidence intervals for the average dynamic modulus for each testing condition. This graphical analysis indicates that two hours of conditioning at the compaction temperature provides dynamic moduli for laboratory prepared specimens that are similar to those from field mixtures. Table E12 summarizes a statistical analysis of the dynamic modulus data using a paired t-test. A paired t-test can be used to investigate the significance of differences between two treatments. The null hypothesis is the mean difference between the two treatments is zero. The alternative hypothesis is the mean difference is greater than zero. A negative mean difference indicates the laboratory conditioning results in lower dynamic moduli compared to the field mixture. For the control and Advera and Evotherm mixtures, 2 hours at the compaction temperature produced modulus values that were the same as those obtained for the field mixtures. For the Sasobit mixture, 2 hours at the compaction temperature produced modulus values that were greater than those obtained for the field mixtures. Four hours at the compaction temperature produced modulus values that were greater than the field mixture for the control, Advera, and Sasobit mixtures. E-30

31 Figure E13. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Control Mixture. Figure E14. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Advera Mixture. E-31

32 Figure E15. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Evotherm Mixture. Figure E16. Effect of Short-Term Conditioning on Dynamic Modulus Data for the I-70 Sasobit Mixture. E-32

33 Table E12. Statistical Analysis of the Dynamic Modulus Data for the I-70 Mixtures. 4 Hours at Compaction 2 Hours at Compaction 4 Hours at Compaction 2 Hours at Compaction Mixture Temp., F Freq, Hz Field Avg Avg Difference, % Avg Difference, % Mixture Temp., F Freq, Hz Field Avg Avg Difference, % Avg Difference, % % % NT NA % % % NT NA % % % NT NA % % % NT NA % % % NT NA % % % NT NA % % % NT NA % Control % % Evotherm NT NA % % % NT NA % Average Difference 39.64% 0.53% Average Difference NA NA 0.76% Standard Deviation of Differences 32.78% 18.01% Standard Deviation of Differences NA NA 20.94% t t NA NA t cr α = t cr α =0.05 NA NA Conclusion Lab Greater Same Conclusion NA Same Temp., F Freq, Hz Field Avg Avg Difference, % Avg Difference, % Temp., F Freq, Hz Field Avg Avg Difference, % Avg Difference, % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Advera % % Sasobit % % % % % % Average Difference 17.44% 5.49% Average Difference 34.79% 23.93% Standard Deviation of Differences 22.21% 21.94% Standard Deviation of Differences 16.64% 7.34% t t t cr α = t cr α = Conclusion Lab Greater Same Conclusion Lab Greater Lab Greater Table E13 summarizes the results of the analysis for 2 hours and 4 hours at the compaction temperature for all three parameters: maximum specific gravity, indirect tensile strength, and dynamic modulus. Statistically significant differences are shown in bold in Table E13. Table E13 also presents the average difference for the data from the four mixtures. Based on the summary data presented in Table E13 and the finding from the sample reheating study that reheating increases the stiffness of WMA and HMA mixtures, 2 hours at the compaction temperature was tentatively selected for short-term conditioning of WMA mixtures. This conditioning should be used for volumetric mixture design, moisture sensitivity testing, flow number testing, and dynamic modulus testing for structural analysis. E-33

34 Table E13. Summary of Statistical Analysis of Short-Term Conditioning. Mixture Control Advera Evotherm Sasobit Average Conditioning Time, hours Percent Difference (Lab-Field)/Field Theoretical Indirect Tensile Maximum Strength Specific Gravity Dynamic Modulus NA NA NA E5. RAP Study The primary concern when using RAP in WMA is whether the RAP and new binders mix at the lower temperatures used in WMA. Two experiments were conducted in NCHRP Project 9-43 to determine if RAP binder mixes at lower WMA production temperatures and to establish appropriate conditioning time for WMA mixtures incorporating RAP. E5.1 Interfacial Mixing and Compatibility Experiment The first experiment included measurements of interfacial mixing to determine if thin films of new binder on RAP binder actually mix and measurements of binder compatibility to determine the effect of mixing on the properties of the combined binder. The interfacial mixing measurements used atomic force microscope imaging of film-on-film interface contact lines. Asphalt binders including Advera and Sasobit WMA additives were used in the interfacial mixing measurements. Thin films of these WMA binders were cast onto a film of binder that was previously aged in the PAV to simulate an aged RAP binder. The specific procedures for the film-on-film imaging were developed by the Western Research Institute during NCHRP Project The compatibility measurements were performed in accordance with ASTM D6703 Standard Test Method for Automated Heithaus Titrimetry. As the compatibility of an asphalt binder changes, the physical properties change. Less compatible binders tend to have E-34

35 more structure and more elastic properties. Compatibility measurements were made for three neat asphalt binders, two WMA additives (Advera and Sasobit), one RAP binder, and four RAP percentages. Table E14 summarizes the compatibility testing. RAP Content, % Table E14. Summary of Compatibility Testing. AAB-1 AAG-1 Yellowstone National Park Neat 1.5 % Sasobit 5 % Advera Neat 1.5 % Sasobit 5 % Advera Neat 1.5 % Sasobit 0 X X X X X X X X 5 X X 15 X X 25 X X X X X 50 X X X X X 5 % Advera The interfacial mixing of RAP and new binders in WMA was investigated by solvent casting a thin film of new binder on a thin film of simulated RAP binder and performing atomic force microscopy (AFM) imaging of the film-on-film interface contact lines. In this procedure, 1.0 g samples of both the RAP binder and the new binder were dissolved in solvents, (toluene in the case of RAP, and cyclohexane in the case of the new binder). Film-on-film systems were developed by solvent spin casting solutions of the new binder onto RAP binder that was previously spin cast onto glass microscope slides. These samples were imaged via AFM in the center of the new binder film, at the contact line between the two films, and toward the edge of the RAP binder film where the new binder had not coated this film. All sample films were imaged after casting, then periodically imaged after being thermally conditioned in a 266 F (130 C) oven for minute intervals Figure E17 shows a projection of views (photograph-to-light microscope-to-afm image) of a contact interface between the new binder and RAP binder after casting. Note the distinct interface between the new binder and RAP binder in the AFM image at the upper right. Figure E18 shows AFM scans at the interfacial contact line between the new and RAP binder (upperleft), the new binder surface (upper-right), and the RAP binder surface after annealing the film in a 266 F (130 C) oven for 60 minutes. The material toward the center of the top film has the appearance of naturally waxy (2-4%) asphalt, in this case AAB-1 with Sasobit added, as indicated by the bumble-bee shaped microstructures depicted in the upper-right hand image. E-35

36 The more subtle microstructures depicted in the lower left hand image are indicative of a moderately waxy (1-3%) asphalt, in this case PAV aged AAD-1 used to simulate a RAP binder. Finally, the image of the thermally mixed interfacial contact line, upper left hand image, depicts a transition in structuring between that of the new binder surface, and the RAP binder surface. This transitional (diffuse) interface is better illustrated in Figure E19. This figure clearly shows that a complex reordering of materials is taking place at the interfacial contact line as the filmon-film is thermally treated. Figure E17. Projected Views (photograph-to-light microscope-to-afm image) of a Contact Interface Between New and RAP Binder. E-36

37 Figure E18. AFM Scans at the Interfacial Contact Line (upper-left), at the New Binder Surface (upper-right), and the RAP Binder Surface (lower-left) After Annealing. Figure E19. AFM Scan at the Interfacial Contact Line Between the New Binder Film and the RAP Binder Film After Annealing. E-37

38 Figure E20, shows photographs of film-on-film slides before and after thermal annealing. It was observed that as film-on-film samples were thermally annealed several times, the two films would eventually appear to mix. This experiment provides evidence that RAP and new binder do mix at elevated temperatures. The likely mechanism is that during plant mixing, the new binder coats the RAP, and then while the mixture remains at an elevated temperature further mixing of the RAP and new binders occurs as simulated in this experiment. Figure E20 Photograph Image of Two Film-on-Film Slides. Left, Prior to Thermal Annealing. Right Thermally Annealed for F (130 C). When a new binder mixes with an aged RAP binder, its properties change. One way to measure this change is by measuring the compatibility of the binder. Historically asphalt binders have been modeled as colloidal suspensions in which a polar associated asphaltene fraction is suspended in a maltene solvent fraction (5). The extent to which these two fractions remain in a given state of dispersion is a measure of the compatibility of the suspension. Based on this model, asphalt binders may be classified as exhibiting gel-type (less compatible) to sol-type E-38

39 (more compatible) characteristics in terms of their material flow properties. In more compatible asphalt binders, the asphaltene fraction is usually smaller and better dispersed or peptized by the maltene solvent fraction. Compatible asphalt binders exhibit more Newtonian-like flow properties, are less sensitive to variation in viscosity due to temperature change, and are generally more ductile than less compatible asphalt binders (6). Conversely, less compatible asphalt binders, often exhibit more elastic properties and are usually less ductile than compatible asphalt binders, possibly due to their higher asphaltene fraction (6). The compatibility of an asphalt binder is measured by the Heithaus parameter, P, referred to as the state of peptization and is measured by ASTM D6703, Standard Test Method for Automated Heithaus Titrimetry. The value of P varies from approximately 2.5 to 10 for neat asphalt binders. The compatibility of the asphalt binder increases with increasing value of P. In this project the compatibility of asphalt binders containing Advera and Sasobit, and blends of simulated RAP were measured in accordance with ASTM D6703 for various percentages of RAP. Representative WMA binders were prepared by adding low concentrations of two types of WMA modifiers, Advera at 5 percent by weight of binder and Sasobit at 1.5 percent by weight of binder to three asphalt binders: SHRP binder AAB-1, SHRP binder AAG-1, and the binder used in the Yellowstone National Park project, designated YNP. The WMA binders were all prepared in a laboratory mix oven at low shear for 1 hour, each mixed at approximately 266 F (130 C). RAP-WMA binder blends were then prepared by combining approximately 10 g of total materials, containing simulated RAP binder (PAV aged SHRP binder AAA or AAD) along with WMA binder materials in 50 ml sample tins. Both the WMA binder and the simulated RAP were weighed into a sample tin at room temperature, then placed in a 266 F (130 C) mix oven and mixed for 1 hour after the sample was observed to soften in the oven. Sample mixtures were stored by purging the sample tins under an argon gas and capping the tins for future analyses. Compatibility test samples were performed on the RAP-WMA binder blends by transferring three ± g samples into 40 ml reaction vials and dissolving them in 3.00 ± 0.01 ml of HPLC grade toluene. Sample solutions were allowed to stand overnight prior to testing in accordance with ASTM D6703 to determine Heithaus compatibility parameters. E-39

40 Tables E15 and E16 present the Heithaus compatibility parameters measured for the two WMA binders. The following observations were made based on the data in these tables: 1. The addition of the Sasobit decreased the compatibility of both SHRP binders. The effect of the Advera additive is not clear. The compatibility of the SHRP binder AAB remained the same while the compatibility of SHRP binder AAG decreased. 2. The compatibility of the RAP-WMA blends generally decrease with increasing RAP contents. Recall that less compatible asphalt binders exhibit more elastic behavior and are less ductile compared to more compatible binders. 3. The 50 percent RAP-WMA blends have compatibility parameters that are well within the range expected for neat asphalt binders, indicating that these blends are relatively stable materials. In summary, the interface mixing and compatibility experiment demonstrated that thin films of new asphalt binder and RAP binder do mix when subjected to elevated temperatures. This suggests that mixing of new and RAP binders continues to occur after plant mixing is completed and that the overall time a RAP mixture is exposed to elevated temperatures may be an important consideration. Second, the addition of RAP decreases the compatibility of the new binder when the RAP and new binders mix. Less compatible asphalt binders exhibit more elastic behavior and are less ductile compared to more compatible binders. This finding supports current practice of selecting new binders for RAP mixtures based on the properties of the blended RAP and new binders. In some cases, this may require using a softer, more compatible new binder to obtain the desired properties. E-40

41 Table E15. Hiethaus Compatibility Parameters for Sasobit RAP Blends. Binder/RAP Blend % RAP Asphaltene Peptizability Parameter (p a ) Maltene Peptizing Power Parameter (p o ) State of Peptization (P) AAB-1-Sasobit/AAA-1-(RAP-1) AAB AAB-1-Sasobit AAB-1-Sasobit/5%RAP-AAA AAB-1-Sasobit/15%RAP-AAA AAB-1-Sasobit/25%RAP-AAA AAB-1-Sasobit/50%RAP-AAA RAP-AAA AAB-1-waxWMA/AAD-1-(RAP-2) AAB AAB-1-Sasobit AAB-1-Sasobit/5%RAP-AAD AAB-1-Sasobit/15%RAP-AAD AAB-1-Sasobit/25%RAP-AAD AAB-1-Sasobit/50%RAP-AAD RAP-AAD AAG-1-Sasobit/AAD-1-(RAP-2) %rap Pa = po = P = AAG AAG-1-Sasobit AAB-1-Sasobit/5%RAP-AAD AAB-1-Sasobit/15%RAP-AAD AAB-1-Sasobit/25%RAP-AAD AAB-1-Sasobit/50%RAP-AAD RAP-AAD YNP-Sasobit/AAD-1-(RAP-2) %rap Pa = po = P = YNP-Sasobit YNP-Sasobit-repeat YNP-Sasobit/25%RAP-AAD YNP-Sasobit/25%RAP-AAD-1-repeat RAP-AAD RAP-1 = AAA-1 RTFO-PAV aged 20 hr 100 C RAP-2 = AAD-1 PAV aged 144 hr 80 C E-41

42 Table E16. Hiethaus Compatibility Parameters for Advera RAP Blends. Binder/RAP Blend % RAP Asphaltene Peptizability Parameter (p a ) Maltene Peptizing Power Parameter (p o ) State of Peptization (P) AAB-1-Advera/AAD-1(RAP-2) AAB AAB-1-Asphamin AAB-1-Advera/25%RAP AAB-1-Advera/50%RAP RAP-AAD AAG-1- Advera/AAD-1(RAP-2) AAG AAG-1-Advera AAG-1-Advera/25%RAP AAG-1-Advera/50%RAP RAP-AAD YNP-Advera/AAD-1(RAP-2) YNP-Advera YNP-Advera/25%RAP YNP-Advera/50%RAP RAP-AAD RAP-2 = AAD-1 PAV aged 144 hr 80 C E5.2 Laboratory Mixing Experiment The second experiment in the RAP study was a laboratory mixing experiment designed to assess the degree of mixing between RAP and new binders at WMA process temperatures. This experiment used an approach that was developed by Advanced Asphalt Technologies, LLC for the Maryland State Highway Administration and the Pennsylvania Department of Transportation to evaluate the acceptability of plant mixing of mixtures containing RAP and recycled asphalt shingles (RAS) (7). It involves comparing dynamic moduli measured on mixture samples with dynamic moduli estimated using the properties of the binder recovered from the mixture samples. The dynamic modulus test is very sensitive to the stiffness of the binder in the mixture, and adding RAP will increase the dynamic modulus significantly when the RAP is properly mixed with the new materials. The dynamic modulus for the as-mixed condition was measured in accordance with AASHTO PP61. The dynamic modulus for the fully blended condition was estimated using the Hirsch model (8) from the shear modulus of binder recovered from the dynamic modulus specimens. E-42

43 Table E17 summarizes the experimental design for the laboratory mixing experiment. The experimental design included testing a control HMA and three WMA processes: Advera, Evotherm, and Sasobit. Each of the four mixtures was tested at two temperatures and three aging times. Each mixture was mixed at the mixing temperatures listed in Table E17, then short-term oven aged at the compaction temperature listed in Table E17 prior to compaction. Duplicate dynamic modulus specimens were prepared and tested for each mixture in accordance with AASHTO PP61. The binder from one of the specimens was recovered in accordance with ASTM D5404. Dynamic shear rheometer (DSR) frequency sweep tests were performed on the recovered binders in accordance with AASHTO T315 to determine binder modulus input vales for the Hirsch model. Table E17. Experimental Design for the Laboratory RAP Mixing Experiment. Process Control Advera Evotherm Sasobit Mixing/Compaction Conditioning Time, hrs Temperatures, F /255 X X X 248/230 X X X 248/230 X X X 230/212 X X X 248/230 X X X 230/212 X X X 248/230 X X X 230/212 X X X The Colorado I-70 mixture that was described earlier in Section E4, Short-Term Oven Conditioning Study, was used with 25 percent RAP containing a very stiff binder. Table E18 presents high and low temperature performance grading properties for the recovered RAP binder. The recovered RAP binder has a continuous grade of PG This RAP source was selected because it was extremely stiff and likely represented a worst case scenario. Typical RAP binders have a high temperature continuous grade ranging from PG 88 to PG 100. The continuous low temperature grade was extrapolated because of the temperature control limits on the bending beam rheometer. Low temperature continuous grades for typical RAP binders are approximately 3 to 6 C lower than the specified performance grade. E-43

44 Table E18. Performance Grading Properties for Recovered RAP Binder. Property Temperature, C Value G*/sinδ, 10 rad/sec, kpa Creep Stiffness, MPa/Slope, / sec / / Continuous Grade Laboratory mixtures were produced to simulate four processes: (1) HMA, (2) WMA using Advera at 0.3 percent by weight of mix, (3) WMA using Evotherm DAT at 0.5 percent by weight of total binder (new binder + RAP binder), and (4) WMA using Sasobit at 1.5 percent by weight of total binder (new binder + RAP binder). The new binder was a PG obtained from NuStar Asphalt Refining, LLC in Paulsboro, NJ. In preparing the mixtures, the virgin aggregate and the RAP were heated separately to approximately 30 F (15 C) above the mixing temperature given in Table E17. The virgin aggregates were usually heated overnight. The RAP was heated for approximately 2 hours. The new binder was heated to the mixing temperature, added to the aggregate plus RAP, and the mixture was mixed in a Blakeslee planetary mixer with a wire whip for 60 sec. The mixture was then short-term oven aged at the compaction temperature listed in Table E17 for the times listed in Table E17 prior to compaction. Sufficient mix for duplicate dynamic modulus specimens and a maximum specific gravity test were prepared for each mixture. After conditioning, dynamic modulus specimens were prepared in accordance with AASHTO PP60. The dynamic modulus of each specimen was measured using an AMPT at 39.2, 68, and 95 F (4, 20, and 35 C) in accordance with AASHTO PP61. Figures E21 through E28 present dynamic modulus master curves for the four mixtures and two aging conditions. These master curves exhibit similar behavior for the control HMA, Advera WMA, and Sasobit WMA. At both temperatures, the master curves for 0.5 and 1.0 hours of short-term conditioning are very similar, while the master curve for 2.0 hours of short-term conditioning is significantly stiffer for intermediate and low reduced frequencies. The master curves for the Evotherm WMA are different. They have similar stiffness for all aging times at both temperatures. E-44

45 0.5 Hours 1.0 Hours 2.0 Hours Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E21. Dynamic Modulus Master Curve for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F Hours 1.0 Hours 2.0 Hours 1000 Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E22. Dynamic Modulus Master Curve for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. E-45

46 0.5 Hours 1.0 Hours 2.0 Hours Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E23. Dynamic Modulus Master Curve for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Hours 1.0 Hours 2.0 Hours 1000 Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E24. Dynamic Modulus Master Curve for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-46

47 0.5 Hours 1.0 Hours 2.0 Hours Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E25. Dynamic Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Hours 1.0 Hours 2.0 Hours 1000 Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E26. Dynamic Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-47

48 0.5 Hours 1.0 Hours 2.0 Hours Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E27. Dynamic Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F Hours 1.0 Hours 2.0 Hours 1000 Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency at 20 o C Figure E28. Dynamic Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-48

49 The differences shown in Figures E21 through E28 may be caused by blending of the RAP and new binders or by changes in the binder stiffness due to the WMA additives or the different aging times and temperatures. To address these potential differences, the binder from one of the dynamic modulus specimens was recovered and a partial binder shear modulus master curve was developed over the range of reduced frequencies used in the dynamic modulus testing. These binder shear modulus values were then used with the Hirsch model and volumetric properties of the dynamic modulus test specimens to estimate the dynamic modulus that would be expected for the fully blended binder. Equation E4 presents the Hirsch model, which can be used to estimate the dynamic modulus of the mixture knowing the binder modulus and the VMA and VFA of the mixture (8). E* mix VMA = P 4,200,000 1 c + 3 G* 100 where: binder E* mix = mixture dynamic modulus, psi VFA xvma 1 Pc + 10,000 VMA VMA + 4,200,000 3VFA G* binder (E4) VFA x 3 G* 20 + VMA Pc = VFA x 3 G* VMA binder binder 0.58 VMA = Voids in mineral aggregates, % VFA = Voids filled with asphalt, % G* binder = shear complex modulus of binder, psi 0.58 Data for the Hirsch model predictions of the fully blended condition were obtained from the volumetric properties of the dynamic modulus specimens and a partial shear modulus master curve for the recovered binder. The binder was extracted in accordance with Method A of AASHTO T164 using trichloroethylene as the solvent and then recovered using a rotary evaporator in accordance with ASTM D5404. The binder shear modulus was measured in accordance with AASHTO T315 over the range of reduced frequencies used in the mixture E-49

50 dynamic modulus test. Binder DSR frequency sweep tests were conducted at temperatures of 50, 71.6, 93.2, and F (10, 22, 34, and 46 C) over the frequency range from 0.1 to 100 rad/sec with 5 measurements per decade. A partial master curve was constructed by fitting the binder shear modulus data to the Christensen-Anderson model (9). Equation E5 presents the Christensen-Andersen model for the frequency dependency of the binder complex shear modulus. R log 2 log 2 R c G *( ) G ω ω = g 1+ (E5) r ω where: G*(ω) = complex shear modulus G g = glass modulus assumed equal to 1GPa ω r = reduced frequency at the reference temperature, rad/sec ω c = cross over frequency at the reference, rad/sec R = rheological index The shift factors relative to the defining temperature are given by Equation E6 for temperatures above the defining temperature. The temperatures used in the binder testing are well above the defining temperature of typical binders. ( T T ) 19 = 92 + T T d log a( T ) (E6) d where: a(t) = shift factor T = temperature, K T d = defining temperature, K E-50

51 The three unknown parameters, ω c, R, and T d, were obtained through non-linear least squares fitting of Equations E5 and E6 using the DSR data collected for each binder. Table E19 presents the fitted master curve parameters and Figures E29 through E36 present the recovered binder shear modulus master curves over the reduced frequency range of the mixture dynamic modulus test data for the four mixtures and three aging conditions. The recovered binder master curves are very similar for the Control HMA, Advera WMA, and Sasobit WMA. For these mixtures the stiffness of the recovered binder increases with increasing aging time at both temperatures. For the Evotherm WMA, the stiffness of the recovered binder is approximately the same for all aging times. Table E19. Fitted Christensen-Anderson Master Curve Parameters for Recovered Binders for the Laboratory RAP Mixing Study. Mixture Control Advera Evotherm Sasobit Mixing/Compaction Temperatures, F 280/ / / / / / / /212 Time, hrs T d, C ω c, rad/sec R E-51

52 0.5 Hours 1.0 Hours 2.0 Hours 1.0E E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E29. Recovered Binder Modulus Master Curve for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F. 1.0E Hours 1.0 Hours 2.0 Hours 1.0E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E30. Recovered Binder Modulus Master Curve for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. E-52

53 0.5 Hours 1.0 Hours 2.0 Hours 1.0E E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E31. Recovered Binder Modulus Master Curve for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. 1.0E Hours 1.0 Hours 2.0 Hours 1.0E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E32. Recovered Binder Modulus Master Curve for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-53

54 0.5 Hours 1.0 Hours 2.0 Hours 1.0E E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E33. Recovered Binder Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. 1.0E Hours 1.0 Hours 2.0 Hours 1.0E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E34. Recovered Binder Modulus Master Curve for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-54

55 0.5 Hours 1.0 Hours 2.0 Hours 1.0E E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E35. Recovered Binder Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. 1.0E Hours 1.0 Hours 2.0 Hours 1.0E E+05 Binder G*, Pa 1.0E E E E E E E E E E E E+00 Reduced Frequency at 20 o C, rad/sec Figure E36. Recovered Binder Modulus Master Curve for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. E-55

56 Tables E20 through E27 summarize estimates of the dynamic modulus for fully blended conditions obtained from the Hirsch model using the recovered binder shear moduli discussed above. These tables also include the average measured dynamic moduli and the ratio of the measured to the estimated fully blended moduli for each temperature and frequency combination. When the ratio of the measured to fully blended moduli approaches 1.0, there is good mixing of the new and recycled binders. Figure E37 shows the effect of time, temperature and process on the ratio of the measured to fully blended moduli averaged over the temperatures and frequencies used in the dynamic modulus testing. At conditioning times of 0.5 and 1.0 hours, there is little blending of the new and recycled binders. For all process at both temperatures, the ratio ranges from about 0.35 to At the 2 hour conditioning time, the ratio of the measured to estimated fully blended moduli reaches values approaching 1.0 for the Control HMA, Advera WMA, and Sasobit WMA. The effect of temperature is also evident for these processes, with the higher conditioning temperature resulting in somewhat improved blending. The ratio of the measured to estimated fully blended moduli for the Evotherm WMA remained low even at the 2 hour conditioning time. This suggests that either the particular form of Evotherm used in this study retards the mixing of the new and recycled binders or that the extraction and recovery process stiffens the Evotherm modified binder. As will be discussed later in Section E7 Mixture Design Study, RAP and new binders do mix well for the Evotherm G3 process for 2 hours of conditioning time. In the mixture design study, mixtures with and without RAP were designed as HMA, Advera WMA, Evotherm WMA, and Sasobit WMA. The optimum binder content of the RAP mixtures was found to be the same for all processes. If the Evotherm process did not result in blending of the new and recycled binders, then the binder content for these mixtures would be significantly higher. Therefore, after this additional testing it was concluded that the apparent lack of blending observed with the Evotherm DAT formulation used on the Colorado I-70 project when comparing measured dynamic moduli with dynamic moduli estimated from recovered binder properties is an artifact of the binder extraction and recovery process. E-56

57 Table E20. Measured and Estimated Fully Blended Dynamic Modulus for the Control HMA for Mixing Temperature of 280 F and Compaction Temperature of 255 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,861 2,190 1, ,507 2,215 1, ,788 2,048 2, ,599 1,753 1, ,913 1,782 1, ,644 1,655 1, ,992 1, ,112 1, ,886 1,207 1, ,571 1, ,616 1, ,668 1,150 1, E-57

58 Table E21. Measured and Estimated Fully Blended Dynamic Modulus for the Control HMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,089 2,224 1, ,903 2,285 1, ,813 2,214 2, ,610 1,742 1, ,017 1,860 1, ,712 1,837 1, ,756 1, ,499 1, ,758 1,378 1, ,662 1, ,843 1, ,288 1,287 1, E-58

59 Table E22. Measured and Estimated Fully Blended Dynamic Modulus for the Advera WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,020 2,302 1, ,613 2,289 1, ,077 2,222 2, ,978 1,870 1, ,881 1,862 1, ,801 1,795 2, ,441 1, ,451 1, ,114 1,279 1, ,783 1, ,773 1, ,768 1,195 1, E-59

60 Table E23. Measured and Estimated Fully Blended Dynamic Modulus for the Advera WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,646 2,256 1, ,620 2,289 1, ,394 2,305 2, ,242 1,811 1, ,772 1,854 1, ,311 1,917 1, ,135 1, ,358 1, ,890 1,433 1, ,556 1, ,744 1, ,226 1,304 1, E-60

61 Table E24. Measured and Estimated Fully Blended Dynamic Modulus for the Evotherm WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,093 2,260 1, ,239 2,308 1, ,024 2,325 1, ,292 1, ,424 1, ,367 1, ,300 1, ,772 1, ,776 1, ,733 1, ,054 1, ,111 1, E-61

62 Table E25. Measured and Estimated Fully Blended Dynamic Modulus for the Evotherm WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,091 2,357 1, ,867 2,327 1, ,764 2,348 1, ,854 1, ,799 1,928 1, ,813 1, ,942 1, ,950 1, ,990 1, ,090 1, ,141 1, ,096 1, E-62

63 Table E26. Measured and Estimated Fully Blended Dynamic Modulus for the Sasobit WMA for Mixing Temperature of 248 F and Compaction Temperature of 230 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,785 2,187 1, ,050 2,235 1, ,214 2,241 2, ,579 1,751 1, ,243 1,811 1, ,484 1,831 1, ,991 1, ,268 1, ,439 1,329 1, ,817 1, ,779 1, ,020 1,239 1, E-63

64 Table E27. Measured and Estimated Fully Blended Dynamic Modulus for the Sasobit WMA for Mixing Temperature of 230 F and Compaction Temperature of 212 F. Temp, F Freq, Hz Recovered Binder G*, psi Conditioned 0.5 Hours Conditioned 1.0 Hours Conditioned 2.0 Hours Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,773 2,225 1, ,308 2,207 1, ,245 2,223 2, ,050 1,794 1, ,788 1,771 1, ,107 1,817 1, ,167 1, ,051 1, ,344 1,325 1, ,651 1, ,736 1, ,981 1,244 1, E-64

65 Control 255 Control 230 Advera 230 Advera 212 Evotherm 230 Evotherm 212 Sasobit 230 Sasobit Average Ratio of Measured Modulus to Estimated Fully Blended Modulus Conditioning Time, Hours Figure E37. Comparison of the Ratio of Measured to Fully Blended Dynamic Moduli. The laboratory mixing study showed that it is reasonable to expect that significant mixing of RAP and new binders will occur at WMA production temperatures when the mixture is held at elevated temperatures for approximately 2 hours. Clearly the mixing is time dependent indicating that the new binder coats the virgin aggregate and RAP then during storage at elevated temperature, the two binders continue to mix. The RAP used in this study was very stiff, and likely represents a worst case scenario. Considering the results of the interface mixing study that shows that mixing of the RAP and new binders continues at elevated temperature without mechanical mixing, the compaction temperature is probably the critical temperature in the mixing study. It is likely that the minimum temperature that can be used is related to the viscosity of the RAP binder at that temperature. The RAP binder used in this study had a viscosity of approximately 22,000 P (220 Pa s) at the average compaction temperature of 221 F (105 C) used in this study suggesting that a reasonable tentative requirement for RAP in WMA is that the RAP have a viscosity less than 22,000 P (220 Pa s) at the proposed compaction temperature. This is approximately equivalent to requiring the proposed compaction temperature E-65

66 to be greater than the temperature where the as-recovered RAP binder meets the AASHTO M320 requirement of G*/sinδ =2.20 kpa. E6. Workability Study Viscosity based mixing and compaction temperatures cannot be used to address coating, workability, and compactability for the wide range of WMA processes currently available and expected in the future. Coating can be evaluated during the mixture design process using AASHTO T195, Determining Degree of Particle Coating of Bituminous-Aggregate Mixtures, but there are no standard procedures to evaluate workability and compactability of asphalt concrete mixtures. Table E28 summarizes the characteristics of several workability tests that were considered for use in the WMA mixture design procedure. After careful review of the workability devices in Table E28, the following devices were selected for consideration in NCHRP Project 9-43: UMass Workability Device, Gyratory Shear Stress, Nynäs Workability Device, and University of New Hampshire Workability Device A screening study was conducted with the objective of selecting an appropriate test to evaluate workability during WMA mixture design. The primary concern in the screening study was the effect of temperature and WMA additive on the workability of the mixture. The screening experiment is summarized in Table E29. It consisted of performing workability tests on a single mixture produced with three binders: Control PG 64-28, PG with Sasobit, and PG with Advera. Table E30 presents pertinent properties of the mixture used in the experiment. Sasobit and Advera were selected as the warm mix additives because these additives are easiest to use in the laboratory. Duplicate workability tests were made with each device at three temperatures. Analysis of variance was used to evaluate the sensitivity of the test to changes in temperature and WMA additive. The sensitivity of the test along with ease of integration into the WMA design procedure were the factors considered in the final selection. E-66

67 Table E28. Key Elements of Potential Workability Devices for WMA. Device Measurement Modification Needed of Procedure Needed for WMA NCAT Prototype Workability Device UMass Prototype Workability Device Modified Nynäs Workability Device ASTM D6704 Gyratory Shear Stress University of New Hampshire Torque to rotate paddle at constant speed. Torque to rotate an auger at constant speed. Force to blade loose mix sample. Force to push a blade into a loose mix sample. Shear stress during gyratory compaction. Torque using blade attached to hand drill with adjustable torque settings. Advantages None Measure workability during mixing. Previous research. None Measure workability during mixing. Augur may better represent field movement. Temperature control at WMA placement and compaction temperatures. Temperature control at WMA placement and compaction temperatures. None for gyratory compactors with this capability. Simulates screed action. Relatively inexpensive. Simple and inexpensive. Uses existing equipment Measure workability during compaction. None Simple and inexpensive. Can easily be performed after mixing or prior to compaction. Disadvantages Requires new mixer. Requires new mixer. Requires new device. May not represent field conditions. Requires gyratory compactor with shear stress measurement. Blade and drill torque settings need to be standardized. E-67

68 Table E29. Screening Experiment for Workability Tests. Factor Levels Details Mixtures mm Binders 3 Control PG PG with Sasobit PG with Advera Workability Tests 5 UMass Prototype (auger) Modified Nynäs Gyratory Shear Stress University of New Hampshire Temperatures F 245 F 190 F Replicates 2 Table E30. Mixture Used in the Workability Study. Property Gradation, % Passing Value Sieve Size 3/4 in 100 1/2 in 99 3/8 in 86 #4 57 #8 40 #16 28 #30 20 #50 12 #100 6 # Asphalt Content, % 5.4 N design 75 Design Air Voids, % 3.7 Design VMA, % 14.6 Design VFA, % 74.5 Fines to Effective Asphalt Ratio 0.69 E6.1 UMass Workability Device The UMass workability device is similar to the prototype workability device developed at the National Center for Asphalt Technology NCAT (10). It measures the torque exerted on a paddle E-68

69 by mixture in a rotating bucket. Figure E38 is a photograph of the device. An infrared sensor monitors the temperature of the mixture as the testing progresses. Different shape paddles can be used with the device as shown in Figure E39. In this study the auger shaped paddle circled in Figure E39 was used. For each test, approximately 33 lbs (15 kg) of mixture was placed in the mixing bucket and the bucket was rotated at 15 rpm. The temperature and torque were monitored as the test progressed. Figure E38. Photograph of UMass Workability Device. E-69

70 Used in NCHRP 9-43 Figure E39. Paddles for UMass Workability Device. Figure E40 presents a plot of torque as a function of temperature for the three mixtures used in the study. The data shown in Figure E40 are the average of duplicate tests for each mixture that have been smoothed using a moving average filter. Several interesting observations can be made based on the data shown in this plot Control Advera Sasobit Torque (in-lb) Temperature (F) Figure E40. Torque Versus Temperature for 12.5 mm, PG Mixture in the UMass Dartmouth Workability Device. E-70

71 1. The greatest difference in torque for the WMA mixtures relative to the control HMA occurs at temperatures that are lower than those normally associated with mixture production. 2. The rate of increase in torque with decreasing temperature is much lower for the Advera mixture compared to the control HMA. At HMA production temperatures, the workability of this mixture is similar to the HMA control, but as the temperature decreases, this mixture remains more workable than the HMA control. 3. The Sasobit mixture is more workable than the HMA control over the entire temperature range tested. The rate of increase in torque with decreasing temperature is only slightly less than that of the HMA control. 4. This device may be able to quantify the effect of different WMA processes on workability. Sasobit appears to primarily displace the workability curve downward, while Advera appears to flatten the workability curve, particularly in the lower temperature region. Table E31 summarizes the torque at selected temperatures. These data are shown graphically in Figure E41. The error bars shown are 95 percent confidence intervals for the mean based on the pooled standard deviation from the three mixtures tested. The trends shown in Figure E41 are rational. The torque increases with decreasing temperature. The torque is generally less for the WMA additives compared to the control. Table E31. Summary of Torque From UMass Workability Device. Torque, in lb Sample Control Advera Sasobit 300 F 250 F 190 F 150 F 300 F 250 F 190 F 150 F 300 F 250 F 190 F 150 F Sample Sample Average σ E-71

72 Figure E41. Repeatability of the UMass Workability Device. A one way analysis of variance was conducted for the data at each temperature and the results are summarized in Table E32. For a level of significance of 5 percent, this analysis concluded that the torque for the control is significantly higher than both WMA additive at 150 F (66 C) and significantly higher that the Sasobit mixture at 190 F (88 C). This analysis confirms that the effect of the WMA additives is most significant at lower temperatures. Table E32. Summary of Analysis of Variance for the UMass Workability Device. Temperature, F p-value Planned Comparisons Differences not significant Differences not significant Sasobit < Advera=Control Advera = Sasobit < Control E-72

73 E6.2 Gyratory Shear Stress Some gyratory compactors are equipped with devices that measure the force required to apply the gyratory compaction angle. This measurement may be provided as a force, or converted to stress based on the geometry of the equipment. The specific compactor used in the workability screening study was an Intensive Compaction Tester Model ICT 150R/RB manufactured by Invelop Oy of Finland. This compactor has a variable gyratory angle and the capability to measure and record the stress required to maintain the angle during compaction. In this work, air voids and shear stress were considered as potential indicators of the workability. Test were conducted using an external angle of 1.25 degrees with a limited amount of additional testing using an external angle of 1.0 degrees. The lower gyratory angle is that used in the French gyratory compactor, which is used to assess the compactability of mixtures (11). The limited testing at 1.0 degrees did not show improvement in the sensitivity of the data to changes in temperature. The results of the gyratory shear stress testing using an external angle of 1.25 degrees are summarized in Table E33 for selected parameters including: Air Voids at N initial, Gyratory shear stress at N initial, Gyrations to 8 % air voids, Gyratory shear stress at 8 % air voids, and Air voids at N design, Maximum gyratory shear stress. Figures E42 through E47 present bar charts for each of these parameters. In each of these figures the error bars indicate 95 percent confidence intervals based on the pooled standard deviation for the three mixtures at the three temperatures. E-73

74 N ini 8 % Voids N design Table E33. Summary of Results for the Gyratory Compactor. Properties Sample Control Advera Sasobit 300 F 250 F 190 F 300 F 250 F 190 F 300 F 250 F 190 F Sample Voids, % Sample Average σ Sample Shear Stress, Sample psi Average σ Sample Gyrations Sample Average Shear Stress, psi Voids Max Shear Stress, psi σ Sample Sample Average σ Sample Sample Average σ Sample Sample Average σ E-74

75 Figure E42. Air Voids at N initial. Figure E43. Gyratory Shear Stress at N initial. E-75

76 Figure E44. Gyrations to 8 Percent Air Voids. Figure E45. Gyratory Shear Stress at 8 % Air Voids. E-76

77 Figure E46. Air Voids at N design. Figure E47. Maximum Gyratory Shear Stress. E-77

78 The gyratory shear stress measurements generally show irrational results. The gyratory shear stress for the control mixture decreases with increasing temperature at all levels, N initial, 8 percent air voids, and maximum gyrator shear stress. The air voids at N initial and N design gyrations are somewhat sensitive to temperature, but not sensitive to the warm mix additive. Air voids at N design generally increase with decreasing temperature. At the lowest temperature, the air voids at N design for the warm mix additives are slightly less than that for the control. The most promising parameter is the number of gyrations to reach 8 percent air voids. As shown in Figure E44, the number of gyrations to reach 8 percent air voids is sensitive to temperature and at the lowest temperature sensitive to the warm mix additive. The number of gyrations to 8 percent air voids has also been investigated by NCAT as a possible measure of compactability (12). The number of gyrations required to reach 8 percent air voids generally increases with decreasing temperature. At the lowest temperature, the number of gyrations to reach 8 percent air voids for the warm mix additives appear to be less than that for the control. Table E34 summarizes the results of one way analyses of variance for the air voids at N initial, and the number of gyrations to 8 percent air voids at each temperature for a level of significance of 5 percent. This analysis confirms that the number of gyrations to 8 percent air voids is sensitive to the WMA additives at the lowest temperature. Table E34. Summary of Analysis of Variance for the Gyratory Compactor. Parameter Air Voids at N initial Gyrations to 8 % Air Voids 300 F 250 F 190 F P value Planned Comparisons p value Planned Comparisons p - value Planned Comparisons 0.22 Not significant 0.26 Not significant 0.17 Not significant 0.34 Not significant 0.08 Not significant Control > Sasobit=Advera Based on the screening study, it appears that the number of gyrations to 8 percent air voids may serve as a measure of compactability. It is sensitive to the effects of temperature and the warm mix additives. The gyratory shear stress provided irrational effects for the control mixture and is relatively insensitive to temperature changes. Like the UMass, Dartmouth workability device, the improvement in workability and compactability resulting from the use of warm mix processes appears to occur at temperatures well below the starting field compaction temperature. E-78

79 E6.3 Nynäs Workability Device The Nynäs workability device was developed to evaluate the workability of cold mixes (13). This device measures the force required to push a blade through the mixture. Figure E48 is a photograph of the Nynäs device fabricated at the University of Massachusetts, Dartmouth for use with WMA and HMA mixtures. It includes a box that contains approximately 30 lb (13 kg) of mixture heated to the desired temperature. The box has end gates that open to allow the blade to pass through the loose-mix sample. The blade is pushed through the mixture by a hydraulic actuator mounted above the sample. A pressure transducer measures the hydraulic pressure as the blade moves through the mixture. The speed of the blade was 0.4 in/sec (10 mm/sec). Figure E48. Photograph of Nynäs Workability Device. Figure E49 presents the data collected with the Nynäs device. The maximum force occurs in the 10 to 20 sec range. The maximum force appears to be sensitive to temperature but not sensitive to the warm mix additive. The force in this area is likely dominated by the mass of the mixture that builds up in front of the blade. Figure E50 shows the early portion of the force E-79

80 versus time data. This area of the curve appears to be sensitive to temperature and at the lowest temperature, to the effect of the WMA additives. Two parameters were computed for this portion of the curve: (1) force at 1 sec, (2) area under the curve out to 2 sec. The second represents the work done during the initial portion of the test. The data for these parameters are summarized in Table E35 and shown graphically in Figures E51 and E52. In each of these figures the error bars indicate 95 percent confidence intervals based on the pooled standard deviation for the three mixtures at the three temperatures. 90 Control Advera Sasobit F Pressure, psi F 300 F Time, Sec Figure E49. Nynäs Force Versus Time Curves. E-80

81 Control Advera Sasobit F 60 Pressure, psi F F Time, Sec Figure E50. Early Portion of Nynäs Forces Versus Time Curves. Table E35. Summary of Data From Early Portion of the Nynäs Force Curves. Properties Force at 1 sec Work to 2 sec Sample Control Advera Sasobit 300 F 250 F 190 F 300 F 250 F 190 F 300 F 250 F 190 F Sample Sample Average σ Sample Sample Average σ E-81

82 Figure E51. Nynäs Force at 1 sec. Figure E52. Nynäs Initial Work. E-82

83 Table E36 summarizes the results of one way analyses of variance for the Nynäs parameters at each temperature for a level of significance of 5 percent. This analysis concludes that there are no significant differences between the WMA mixtures and the control at all temperature levels. This is the result of relatively high variability of the Nynäs measurements. Table E36. Summary of Analysis of Variance for the Nynäs Device. 300 F 250 F 190 F Parameter P value Planned Comparisons p value Planned Comparisons p value Planned Comparisons Force at 1 sec 0.87 Not significant 0.45 Not significant 0.15 Not significant Initial Work 0.88 Not significant 0.50 Not significant 0.16 Not significant E6.4 University of New Hampshire Device The University of New Hampshire workability device uses a cordless drill with multiple torque settings to measure the torque required to turn blade through the mixture (14). The mixture workability is defined as the lowest torque setting that moves the blade. Initial testing with the device at the University of New Hampshire showed it to be sensitive to both temperature and the presence of warm mix additive (14). Figure E53 shows the set-up that was used in the screening study. Table E37 summarizes the data that were collected with the University of New Hampshire workability device. The experimental design called for collecting data on duplicate specimens at temperatures of 300, 250, and 190 F (149, 121, and 88 C); however, difficulties with this device precluded collecting the data as planned. The torque available from the cordless drill that was used would not allow data to be collected below about 240 F (116 C) for the mixture tested. As shown in Figure E54, at this temperature and higher this device like the other devices is not sensitive to the effect of the WMA additives. Therefore, only one sample was tested rather than two as planned. Since only one sample was tested, a statistical analysis could not be performed. E-83

84 Figure E53. Photograph of the University of New Hampshire Device. Table E37. Summary of Results Using the University of New Hampshire Device. Temperature, F Lowest Torque Setting to Turn Paddle Control Advera Sasobit Sample 1 Sample 2 Sample 1 Sample 2 Sample 1 Sample E-84

85 Lowest Drill Clutch Setting to Rotate Paddle In Mix (0-24) Control ADVERA Sasobit Power (Control) Power (Sasobit ) Power (ADVERA) Temperature (F) Figure E54. Torque Setting Versus Temperature for the University of New Hampshire Device. The workability study demonstrated that it is possible to measure differences in the workability and compactability of WMA compared to HMA. The differences, however, are only significant at temperatures that are below typical WMA discharge temperatures. This suggests that it is not be necessary to evaluate workability at the proposed production temperature. The evaluation of coating at the proposed production temperature should suffice. It appears that workability and compactability can be evaluated by using the gyratory compactor to determine the gyrations to 8 percent air voids at the proposed compaction temperature and a second temperature that is approximately 54 F (30 C) lower than the proposed compaction temperature. This will permit an assessment of the effect of temperature on the workability and compactability of the mixture. E-85

86 E7. Mix Design Study E7.1 Experimental Design The objective of the mix design study was to compare properties of properly designed WMA and HMA mixtures. Recall, the underlying principal for the mixture design and analysis procedure for WMA is to produce mixtures with similar strength and performance properties as HMA. The experimental design for the mix design study was a paired difference experiment. This design is commonly used to compare population means, in this case the properties of properly designed WMA and HMA mixtures for the same traffic level, using the same aggregates with the same gradation. In this design, differences between the properties for WMA and HMA are computed for each mixture included in the experiment. If the two design procedures produce mixtures with the same properties, then the average of the differences will not be significantly different from zero. The difference for an individual mixture may be positive or negative, but the average difference over several mixtures should be zero. A t-test is used to assess the statistical significance of the average difference as summarized below. Null hypothesis: µ WMA - µ HMA = 0 Alternative hypothesis: Test statistic: Rejection region: µ WMA - µ HMA > 0 or µ WMA - µ HMA < 0 (as appropriate) d t = s d n Reject the null hypothesis and accept the alternative hypothesis if t > t α for n-1 degrees of freedom. where: µ WMA = population mean for WMA mixtures µ HMA = population mean for HMA mixtures d = average of the differences between WMA and HMA mixtures s d = standard deviation of the differences n = number of mixtures compared E-86

87 Table E38 presents the experimental design for the mix design experiment. In this experiment various properties for WMA and corresponding HMA mixtures were evaluated using paired difference comparisons. Comparisons were made for Advera, Evotherm, and Sasobit. For the WMA processes, two mixing and compaction temperatures were used: one above the recommended grade bumping temperature from the binder grade study described earlier in Section E2, and one below. The HMA mixtures and the WMA mixtures above the grade bumping temperature were made with PG binder. Also, the WMA mixtures with RAP and Sasobit below the grade bumping temperature were made with PG because, both RAP and Sasobit increase the high temperature grade of the binder. The Advera and Evotherm WMA mixtures below the grade bumping temperature were made with PG binder. All mixtures were short-term conditioned for 2 hours at the compaction temperature. The six mixtures were selected to provide a range of gyratory compaction levels and aggregate absorptions. One half of the mixtures included RAP at 25 percent. A total of 24 mixture designs were prepared using either AASHTO R35 for HMA mixtures or the WMA mixture design procedure presented in Appendix A. No. N design Table E38. Mix Design Experiment. Mixture Identification Aggregate Absorption RAP HMA Advera WMA Process Evotherm G3 WMA Sasobit WMA 1 50 High Yes 320/ / / / Low No 320/ / / / Low Yes 320/ / / / High No 320/ / / / High Yes 320/ / / / Low No 320/ / / /260 Notes: 1. XXX/XXX denotes Mixing/Compaction temperatures, F 2. All HMA mixtures use PG binder 3. Low temperature Advera and Evotherm WMA use PG All other mixtures use PG Low absorption < 1.0 percent 6. High absorption > 2.0 percent 7. All mixtures short-term conditioned 2 hours at the compaction temperature 8. RAP content 25 percent in all mixtures containing RAP E-87

88 For the experimental design in Table E38, separate comparisons can be made between the properties of HMA and each of the WMA processes. Comparisons can be made for the following properties: 1. Design air voids, vol % 2. Design VMA, vol %, 3. Effective binder content (VBE), vol %, 4. Binder absorption, wt% 5. Design binder content, wt %, 6. Effective binder content, wt %, 7. Coating 8. Gyrations to 8 % air voids at the compaction temperature, 9. Gyrations to 8% air voids at the compaction temperature minus 54 F (30 C), 10. Density at N max, 11. Dry tensile strength, 12. Conditioned tensile strength, 13. Tensile strength ratio, 14. Flow number, and 15. Rutting resistance. These properties are all obtained as part of the WMA mixture design process. The HMA mixtures required design in accordance with AASHTO R35, flow number testing, and assessment of compactability at the lower temperature as proposed in the WMA design process. E7.2 Mixture Properties Table E39 presents the six mixtures that were included in the mix design study. The volumetric properties presented for these mixtures were those obtained from an HMA mixture design in accordance with AASHTO R35 and AASHTO M323. The low absorption mixtures were composed of limestone or diabase aggregate from Virginia. The high absorption mixtures were composed of gravel and limestone from Pennsylvania. Unfortunately the absorption of the gravel aggregate as supplied was lower than reported in PennDOT s Aggregate Producers E-88

89 Bulletin 14 (15) resulting in lower water absorptions for the high absorption mixtures. For the 50 and 75 gyration designs, the high absorption mixtures have approximately twice the water absorption compared to the low absorption mixtures. For the 100 gyration design, the planned low absorption mixture actually has higher absorption. This difference was taken into account when performing statistical analysis of the results of the experiment. Table E39. Mixtures Used in the Mix Design Experiment. Mix Number Design Gryations Aggregate Water Absorbtion, % RAP NMAS Coarse Aggregate Sources Fine Gradation Aggregate Properties Yes No Yes No Yes No 9.5 mm 9.5 mm 9.5 mm 9.5 mm 9.5 mm 9.5 mm PA Gravel VA Diabase PA Gravel VA Limestone PA Gravel RAP RAP RAP VA Diabase PA Limestone VA Diabase PA Limestone PA Limestone VA Diabase PA Gravel VA Limestone Natural Sand PA Gravel RAP Natural Sand RAP RAP RAP LCA, Leesburg, VA None LCA, Leesburg, VA None LCA, Leesburg, VA None Sieve Size, mm FAA CAA 98/95 100/ /99 98/95 98/95 100/100 Flat & Elongated Sand Equivalent Binder Content, wt % Effective Binder Content, wt % Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Voids Filled With Asphalt, % Dust to Effective Asphalt Ratio The same RAP was used in the three mixtures that incorporated RAP. Table E40 presents the gradation and binder content of the RAP material that was used. The RAP binder had a continuous performance grading of PG 95.9 (33.9) The RAP was obtained from Loudoun County Asphalt in Leesburg, VA. All of the RAP mixtures used 25 percent RAP resulting in a RAP binder contribution of approximately 1.1 percent by weight. NuStar Asphalt Refining, LLC provided the binders for this study from their Paulsboro, NJ refinery. The dosage rate of the Sasobit was 1.5 percent by weight of the total binder (virgin plus RAP) in the mixture. The dosage rate of the Advera was 0.25 percent by total mix weight. Binders containing the Evotherm G3 were provided premixed by NuStar Asphalt Refining, LLC. E-89

90 For the Evotherm RAP mixtures, the Evotherm G3 dosage rate was not adjusted to account for the RAP binder. The mixtures incorporating gravel required an anti-strip additive. Akzo-Nobel WETFIX 312 was used in the HMA, Sasobit, and Advera mixtures. The dosage rate for the anti-strip additive was 0.25 percent by weight of the total binder in the mixture. Representatives of Evotherm recommended that the anti-strip not be added when using the Evotherm G3 additive. Table E40. Properties of RAP Used in the Mixture Design Experiment. Property Sieve Size, mm Value Gradation, % Passing Asphalt Content, wt % 4.4 Continuous Performance Grade PG 95.9 (33.9) Aggregate Bulk Specific Gravity Aggregate Water Absorption, % 1.01 Fine Aggregate Angularity, % 44.4 Crushed Aggregate Fractured Faces (1 Face), % 99.3 Crushed Aggregate Fractured Faces (2 Faces), % 94.3 Flat and Elongated Particles, % 0.5 Tables E41, E42, and E43 presents HMA and WMA design properties for 50, 75, and 100 gyration mixtures, respectively. All of the mixtures meet the volumetric requirements contained in AASHTO M323; however, the design VMA for Mixture 2 at approximately 18 percent is somewhat high, and the design VMA for Mixture 6 at approximately 15 is at the minimum allowable in AASHTO M323. The HMA design for Mixture 6 fails the AASHTO M323 moisture resistance requirement, having an AASHTO T283 tensile strength ratio of 70 percent without an anti-strip additive. The rutting resistance given in Tables E41, E42, and E43 is based on the following relationship between flow number and rutting resistance developed in NCHRP Project 9-33 (16). E-90

91 where: F n MESAL = (E7) MESAL = estimated traffic to 12 mm rutting, million ESAL F n = flow number per NCHRP 9-33 test conditions, cycles The estimated rutting resistance for Mixture 6 is somewhat low considering its design gyration level and the angularity of the aggregates. Although Mixture 2 and Mixture 6 would probably be redesigned in practice, the analysis in this experiment is based on differences between the WMA mixtures and the corresponding HMA mixtures and was completed with the mixtures as designed. Table E41. Mixture Design Properties for 50 Gyration Mixtures. Property Mixture 1 50 Gyrations With RAP 1.5 % Water Absorption Mixture 2 50 Gyrations Without RAP 0.8 % Water Absorption HMA Advera Evotherm Sasobit HMA Advera Evotherm Sasobit N ini N design N max Mixing Temperature, F Compaction Temperature, F Design Binder Content, wt % Gmm Gsb % Gmm at N ini % Gmm at N design % Gmm at N max Design VMA, vol. % Design VBE, vol % Design VFA, % Effective Binder Content, wt % Adbsorbed Binder, wt % Coating, % Gyrations to 92 % of Gmm at Compaction Temperature Gyrations to 92 % of Gmm at Compaction Temperature - 54 o F % Increase in Gmm Dry Tensile Strength, psi Wet Tensile Strength, psi Tensile Strength Ratio Flow Number NCHRP 9-33 Rutting Resistance, MESAL E-91

92 Table E42. Mixture Design Properties for 75 Gyration Mixtures. Property Mixture 3 75 Gyrations With RAP 1.0 % Water Absorption Mixture 4 75 Gyrations Without RAP 2.1 % Water Absorption HMA Advera Evotherm Sasobit HMA Advera Evotherm Sasobit N ini N design N max Mixing Temperature, F Compaction Temperature, F Design Binder Content, wt % Gmm Gsb % Gmm at N ini % Gmm at N design % Gmm at N max Design VMA, vol. % Design VBE, vol % Design VFA, % Effective Binder Content, wt % Adbsorbed Binder, wt % Coating, % Gyrations to 92 % of Gmm at Compaction Temperature Gyrations to 92 % of Gmm at Compaction Temperature - 54 o F % Increase in Gmm Dry Tensile Strength, psi Wet Tensile Strength, psi Tensile Strength Ratio Flow Number NCHRP 9-33 Rutting Resistance, MESAL Table E43. Mixture Design Properties for 100 Gyration Mixtures. Property Mixture Gyrations With RAP 1.2 % Water Absorption Mixture Gyrations Without RAP 1.3 % Water Absorption HMA Advera Evotherm Sasobit HMA Advera Evotherm Sasobit N ini N design N max Mixing Temperature, F Compaction Temperature, F Design Binder Content, wt % Gmm Gsb % Gmm at N ini % Gmm at N design % Gmm at N max Design VMA, vol. % Design VBE, vol % Design VFA, % Effective Binder Content, wt % Adbsorbed Binder, wt % Coating, % Gyrations to 92 % of Gmm at Compaction Temperature Gyrations to 92 % of Gmm at Compaction Temperature - 54 o F % Increase in Gmm Dry Tensile Strength, psi Wet Tensile Strength, psi Tensile Strength Ratio Flow Number NCHRP 9-33 Rutting Resistance, MESAL E-92

93 E7.3 Statistical Analysis The paired difference analysis was performed for several mixture properties using the entire data set and several subsets. Analyses were performed for mixture volumetric properties, coating, compactability, resistance to moisture damage, and rutting resistance. Analyses were performed for each of these properties using the entire data set and the following subsets: Low temperature WMA, High temperature WMA, With RAP, Without RAP, Lower absorption, Higher absorption, Advera WMA, Evotherm WMA, and Sasobit WMA. The lower absorption mixtures had binder absorption for the HMA design ranging from 0.6 to 0.7 percent while the higher absorption mixtures had binder absorption ranging from 0.8 to 1.0 percent. These differences were lower than originally planned, limiting the conclusions that could be drawn from the study to mixtures with binder absorption less than 1.0 percent. E7.4.1 Volumetric Properties The design binder content for all of the mixtures was selected from a plot of air voids as a function binder content using a target air void content of 4.0 percent. The air void content for specimens compacted to N design at the design binder content was not always 4.0 percent. For this experiment, a tolerance of 3.5 to 4.5 percent was used. Table E44 presents the paired difference statistical analysis for the design air void content. For the complete data set, the average air void content of the WMA designs was 0.02 percent higher than that for the HMA designs. This difference was not statistically significant. The highest differences in design air voids occurred for the mixtures without RAP. For this subset, the average air void content of the WMA designs was 0.17 percent higher than that for the HMA designs. This difference was statistically E-93

94 significant. The design air voids for the lower absorption mixtures were also significantly higher than that for the corresponding HMA. Table E44. Paired Difference Analysis for Design Air Voids, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature No High Temperature No With RAP No Without RAP Yes Lower Absorption Yes Higher Absorption No Advera No Evotherm No Sasobit No Table E45 presents the paired difference statistical analysis for the VMA. For the complete data set, the average VMA of the WMA designs was 0.23 percent higher than that for the HMA designs. This difference was statistically significant. Three subsets had even greater average differences. The VMA in the Low Temperature WMA mixtures was 0.33 percent higher; the VMA in the WMA mixtures Without RAP was 0.36 percent higher; and the VMA in the Advera WMA mixtures was 0.42 percent higher. All of these differences were statistically significant. Table E45. Paired Difference Analysis for Design VMA, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature No With RAP No Without RAP Yes Lower Absorption No Higher Absorption No Advera Yes Evotherm No Sasobit No E-94

95 The design of HMA and WMA mixtures is controlled by the volume of effective binder (VBE) in the mixture. VBE is equal to the VMA minus the air voids; therefore, for a fixed design air void content, the minimum VMA requirement sets the minimum VBE in the mixture. The maximum VBE is set by the maximum VFA requirement. For the 9.5 mm mixtures used in the mix design study, the minimum VBE is 11.0 percent and the maximum VBE is depends on the traffic level. The maximum VBE is 16.0 percent for less than 0.3 MESAL, 14.2 percent for 0.3 to 3.0 MESAL, and 12.7 percent for greater than 3.0 MESAL. For a given combination of aggregates, gradation, and binder, it should be expected that the HMA and WMA design procedures will produce the same design VBE. This is confirmed by the paired difference statistical analysis for design VBE shown in Table E46. For the complete data set, the average VBE for the WMA designs is only 0.09 percent higher than that for the HMA designs. This difference is not statistically significant. The difference in VBE is only statistically significant for the Advera subset of WMA mixtures; averaging 0.30 percent higher than the corresponding HMA. Since the air voids for the Advera WMA mixtures were not significantly different, the higher VMA and VBE are likely caused by lower levels of binder absorption. Table E46. Paired Difference Analysis for Design VBE, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature No High Temperature No With RAP No Without RAP No Lower Absorption No Higher Absorption No Advera Yes Evotherm No Sasobit No The paired difference statistical analysis for binder absorption is presented in Table E47. For the complete data set, binder absorption averaged 0.12 percent less in the WMA mixtures compared to the HMA mixtures. This difference is statistically significant. Binder absorption is E-95

96 also significantly less for all of the subsets except the RAP subset of mixtures where it is almost significant. These data clearly indicate a significant difference in binder absorption for WMA and HMA mixtures made with the same aggregates and binder. Table E47. Paired Difference Analysis for Binder Absorption, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP No Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm Yes Sasobit Yes The lower binder absorption for WMA compared to HMA translated into somewhat lower design binder contents for the WMA mixtures as shown by the paired difference analysis for the design binder content in Table E48. For the complete data set, the design binder content for the WMA mixtures was 0.06 percent less than that for the HMA. This difference was not statistically significant. The difference in design binder content between WMA and HMA was not significant for any of the mixture subsets. Table E48. Paired Difference Analysis for Design Binder Content, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature No High Temperature No With RAP No Without RAP No Lower Absorption No Higher Absorption No Advera No Evotherm No Sasobit No E-96

97 Table E49 presents the paired difference analysis for the effective binder content. For the complete data set, the effective binder content for the WMA mixtures was 0.06 percent higher than that for the HMA. This difference was not statistically significant. For the various subsets, the effective binder content for the WMA mixtures was generally higher than that for the HMA. The difference was statistically significant for the (1) Low Temperature, (2) Without RAP, and (3) Advera subsets. These differences ranged from 0.1 to 0.2 percent higher effective binder content. Table E49. Paired Difference Analysis for Effective Binder Content, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature Yes High Temperature No With RAP No Without RAP Yes Lower Absorption No Higher Absorption No Advera Yes Evotherm No Sasobit No In summary, the primary difference between mixtures composed of the same binder and aggregates designed as WMA following the proposed mixture design procedure and HMA following AASHTO R35 is lower binder absorption in the WMA mixtures. For HMA mixtures with less than 1.0 percent binder absorption, the lower absorption in the WMA mixtures does not result in a decrease in the design binder content. It does result in a small increase in the design VMA, particularly at the lower WMA temperature. E7.4.2 Coating Coating was evaluated for all of the mixtures in accordance with AASHTO T195, Determining Degree of Particle Coating of Asphalt Mixtures. The analysis was conducted on aggregates retained on the #4 (4.75 mm) sieve. The coating for all mixtures was found to be 100 percent. It should be noted that all of the laboratory mixing was done using Blakeslee 20 qt (22 E-97

98 l) planetary mixer with a wire whip. The coating analysis may have been different if a bucket mixer was used. E7.4.3 Compactability The WMA mixture design procedure provides several measures of the compactability of the mixture. These include: (1) the relative density at N ini at the proposed compaction temperature, (2) the relative density at N max at the proposed compaction temperature, (3) the number of gyrations to 92 percent relative density at the proposed compaction temperature, and (4) the number of gyrations to 92 percent relative density at 54 F (30 C) below the proposed compaction temperature. The increase in gyrations to reach 92 percent relative density when the compaction temperature is lowered 54 F (30 C) was included in the WMA mixture design procedure to evaluate the effectiveness of the WMA processes. Tables E50 and E51 present the results of the paired difference statistical analysis for relative density at the proposed compaction temperature at N ini and N max, respectively. The average relative density for both N ini and N max at the proposed compaction temperature is consistently lower for the WMA mixtures compared to HMA control. However, the average differences are small and not statistically significant for N ini. The average differences are statistically significant for N max, but they are still small and of no engineering significance because the current mix design places a maximum on the relative density at N max. Table E50. Paired Difference Analysis for Relative Density at N ini, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature No High Temperature No With RAP No Without RAP No Lower Absorption No Higher Absorption Yes Advera No Evotherm No Sasobit No E-98

99 Table E51. Paired Difference Analysis for Relative Density at N max, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP No Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera No Evotherm Yes Sasobit No In the WMA mixture design procedure, the number of gyrations to reach 92 percent relative density at the proposed compaction temperature and the increase in gyrations to reach 92 percent relative density when the compaction temperature is lowered 54 F (30 C) are used to evaluate the effectiveness of the WMA process. Tables E52 and E53 present the results of the paired difference statistical analysis for the number gyrations to reach 92 percent relative density at the proposed compaction temperature and the increase in gyrations to reach 92 percent relative density when the compaction temperature is lowered 54 F (30 C). The average difference in the number of gyrations to reach 92 percent relative density at the compaction temperature is small and not statistically significant, indicating that the WMA processes produce mixtures with similar compactability at the compaction temperatures. However, the average increase in the number of gyrations to reach 92 percent relative density when the compaction temperature is lowered 54 F (30 C) is significantly greater for the WMA mixtures compared to the HMA mixture in certain cases. These include the lower compaction temperature of 215 F (102 C), the mixtures containing RAP, and the Evotherm mixtures. For these conditions, the compactability of WMA mixtures would be more sensitive to temperature changes than the HMA mixture with a proposed compaction temperature of 310 F (154 C). E-99

100 Table E52. Paired Difference Analysis for Gyrations to 92 Percent Relative Density at the Compaction Temperature, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature No High Temperature No With RAP No Without RAP No Lower Absorption No Higher Absorption No Advera No Evotherm No Sasobit No Table E53. Paired Difference Analysis for Percent Increase in Gyrations to 92 Percent Relative Density at 54 F (30 C) Below the Compaction Temperature, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete No Low Temperature Yes High Temperature No With RAP Yes Without RAP No Lower Absorption No Higher Absorption No Advera No Evotherm Yes Sasobit No In summary, there is little difference in the compactability of WMA mixtures and HMA mixtures at the compaction temperatures used in the mix design study. However, the increase in gyrations to reach 92 relative density when the compaction temperature is lowered 54 F (30 C) increased significantly for WMA mixtures compared to the HMA mixtures for the following conditions: (1) WMA mixtures produced at the low mixing and compaction temperature of 225 F/215 F (107 C/102 C), (2) WMA mixtures with RAP, and (3) WMA mixtures produced with Evotherm. For these conditions, the compactability of WMA mixtures would be more sensitive to temperature changes than the HMA mixture with mixing and compaction temperature of 320/310 F (160 F /154 C). E-100

101 E7.4.4 Moisture Sensitivity Moisture sensitivity is evaluated using AASHTO T283, Resistance of Compacted Hot Mix Asphalt (HMA) to Moisture Induced Damage in both the WMA mixture design procedure and AASHTO R35 for HMA. For the mix design study, AASHTO T283 was conducted after shortterm oven conditioning for 2 hours at the compaction temperature. Three measurements from AASHTO T283 were compared using the paired difference analysis: (1) dry tensile strength, (2) conditioned tensile strength, and (3) tensile strength ratio. Table E54 presents the paired difference statistical analysis for the dry tensile strength. The dry tensile strength is consistently lower for the WMA mixtures compared to the HMA mixtures. The average difference is significant for the complete data set and all subsets. The lower dry tensile strength is due to the reduced aging in the WMA mixtures. Table E54. Paired Difference Analysis for Dry Tensile Strength, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP Yes Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm Yes Sasobit Yes Table E55 presents the paired difference statistical analysis for the conditioned tensile strength. Like the dry tensile strength the conditioned tensile strength is consistently lower for the WMA mixtures. The average difference is significant for the complete data set as well as all subsets. Comparison of the average differences for the dry and conditioned tensile strengths in Tables E54 and E55 show that the average difference for the conditioned tensile strength is generally larger than that for the dry tensile strength indicating that the conditioning imparts damage to the mixture. This is not the case for the Evotherm mixtures, which have approximately the same average difference for dry and conditioned tensile strengths. This is E-101

102 more clearly shown by the paired difference statistical analysis of the tensile strength ratio shown in Table E56. The tensile strength ratio is consistently lower for the WMA compared to HMA for the complete data set and all of the subsets. The average difference is significant in all comparisons except for the Evotherm mixtures and the mixtures without RAP. Table E55. Paired Difference Analysis for Conditioned Tensile Strength, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP Yes Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm Yes Sasobit Yes Table E56. Paired Difference Analysis for Tensile Strength Ratio, One Sided Test With Significance Level of 0.5 percent. Paired Differences (WMA-HMA) Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP Yes Without RAP No Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm No Sasobit Yes Table E57 summarizes the tensile strength ratios for all of the mixtures included in the study. Most of the WMA mixtures had tensile strength ratios below the AASHTO M323 minimum of 80 percent. Only mixtures produced with Evotherm had tensile strength ratios exceeding 80 percent. Mixture 2, made with Virginia limestone and having a very high binder content was highly resistant to moisture damage with tensile strength ratios exceeding 92 percent for HMA E-102

103 and all WMA processes. Had a more moisture sensitive mixture been used in this cell, the analysis for the mixtures without RAP would likely have also shown a significant difference. Table E57. Summary of Tensile Strength Ratios. Design HMA Advera Evotherm Sasobit Gyration Traffic Compaction Compaction Compaction Compaction Mixture Level MESAL RAP TSR, % Temp., F TSR, % Temp., F TSR, % Temp., F TSR, % Temp., F 1 50 < 0.3 Yes <0.3 No <3 Yes <3 No <10 Yes <10 No In summary, the tensile strength of the WMA mixtures was significantly lower than that for the corresponding HMA mixture due to the lower aging that occurs at the WMA mixing and compaction temperatures. In most cases, WMA mixtures have significantly lower tensile strength ratios when tested in accordance with AASHTO T283. Only the Evotherm WMA mixtures consistently yielded tensile strength ratios that were not significantly lower than the corresponding HMA mixture. This finding suggests that some WMA mixtures will require additional or a different anti-strip additive to meet the 80 percent tensile strength ratio included in the proposed WMA mixture design procedure. E7.4.5 Rutting Resistance Rutting resistance is evaluated in the WMA mixture design procedure using the flow number test, AASHTO TP79, Determining the Dynamic Modulus and Flow Number for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT). In NCHRP Project 9-33, the flow number has also been proposed as one performance test to evaluate rutting resistance for HMA (16). For the mixture design study, unconfined flow numbers were measured on specimens compacted to 7.0 ± 0.5 percent air voids using a repeated deviator stress of 87 psi (600kPa) and contact deviator stress of 4.4 psi (30 kpa). The test temperature was 130 F (54.5 C), which is the 50 percent reliability high temperature performance grade temperature obtained from LTPPBind 3.1 for a depth of 0.79 in (20 mm) for Dulles International Airport. As discussed earlier, the flow numbers were converted to allowable traffic to 0.5 in (12.5 mm) of E-103

104 rutting using the relationship between flow number and rutting resistance developed in NCHRP Project 9-33 (16). Because the flow number and estimated rutting resistance are significantly different for different gyration levels, the paired difference statistical analysis used normalized differences defined by Equation E8. Where: VWMA VHMA ND = *100 (E8) VHMA ND = normalized difference V WMA = value (either flow number of allowable traffic) for the WMA mixture V HMA = value (either flow number of allowable traffic) for the HMA mixture Normalized differences were used so that the mixtures with the higher flow numbers and allowable traffic would not dominate the analysis. The paired difference statistical analyses for the flow number and allowable traffic are presented in Tables E58 and E59, respectively. The WMA mixtures consistently produce lower flow numbers and lower allowable traffic compared to the corresponding HMA mixtures. The smallest average differences occurred for the mixtures without RAP, where the performance grade of the binder used in the WMA mixtures was increased by grade bumping or the addition of Sasobit. The average differences were significant for the complete data set and all of the subsets. E-104

105 Table E58. Normalized Paired Difference Analysis for Flow Number, One Sided Test With Significance Level of 0.5 percent. Normalized Paired Differences (WMA-HMA)/HMA*100 Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP Yes Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm Yes Sasobit Yes Table E59. Normalized Paired Difference Analysis for Allowable Traffic, One Sided Test With Significance Level of 0.5 percent. Normalized Paired Differences (WMA-HMA)/HMA*100 Statistical Analysis Data Set Standard Min Max Average Deviation t Critical t Significant? Complete Yes Low Temperature Yes High Temperature Yes With RAP Yes Without RAP Yes Lower Absorption Yes Higher Absorption Yes Advera Yes Evotherm Yes Sasobit Yes The rutting resistance for the WMA mixtures decreased approximately 40 percent for both the 260 F (154 C) and 215 F (102 C) compaction temperatures. The reason is the high temperature grade of the binder in the Evotherm and Advera mixtures without RAP was increased one grade for the lower compaction temperature mixes based on the findings of the binder grade study. The rutting resistance of the Sasobit mixtures compared to the HMA decreased somewhat less than the other WMA processes because Sasobit also increases the high temperature grade of the binder. The allowable traffic to a rut depth of 0.5 in (12.5 mm) of rutting from the NCHRP 9-33 analysis provides a means of quantifying the rutting resistance. Table E60 summarizes the E-105

106 allowable traffic for all of the mixtures included in the study. Based on the HMA data, the rutting resistance of the 50 gyration mixtures is significantly higher than required because both of these mixtures used aggregates that far exceeded the angularity requirements in AASHTO M323 for this traffic level. The rutting resistance from the HMA design for Mixture 4 is a little less than the design traffic level, while the rutting resistance and Mixture 6 is only one-half of the design traffic level. The rutting resistance of the mixtures with 25 percent RAP is significantly higher than the mixtures without RAP for all traffic levels. Based on the data in Table E60, it will be difficult to meet the flow number rutting resistance criteria developed in NCHRP Project 9-33 for WMA mixtures designed for 10 MESAL or greater. Table E60. Summary of NCHRP 9-33 Rutting Resistance From Flow Number Testing. Design HMA Advera Evotherm Sasobit Gyration Traffic Compaction Compaction Compaction Compaction Mixture Level MESAL RAP MESAL Temp., F MESAL Temp., F MESAL Temp., F MESAL Temp., F 1 50 < 0.3 Yes <0.3 No <3 Yes <3 No <10 Yes <10 No In summary, rutting resistance as measured by the flow number is significantly lower for WMA mixtures compared HMA. The flow number reduction is large enough that many WMA mixtures will fail the flow number criteria contained in the revised preliminary WMA procedure unless the high temperature grade of the binder is increased by grade bumping, adding RAP, or using a WMA additive that increases the high temperature grade of the binder. The lower flow numbers for WMA are the result of reduced aging from the lower compaction temperatures used with WMA. E8. Field Validation Study The objective of the field validation study was to use properties of laboratory and field produced WMA to validate selected parts of the revised preliminary WMA procedure. The parts of the procedure addressed by the validation included: Binder grade selection, E-106

107 RAP, Short-term oven conditioning, Specimen fabrication, Compactability, Moisture sensitivity, and Flow number. The following describes the mixtures that were included in the validation study and the testing and analysis that was performed in the validation effort for individual parts of the revised preliminary procedure. E8.1 Validation Mixtures Table E61 summarizes the mixtures that were included in the validation study. Materials from a total 16 mixtures in 6 projects were sampled. The validation mixtures included a wide range of processes. Four mixtures were HMA control; three mixtures used the Advera WMA process; two mixtures used the Evotherm WMA process; two mixtures used the LEA process; two mixtures used plant foaming processes; and three mixtures used Sasobit. The WMA production temperatures ranged from 210 to 275 F (99 to 135 C) and the WMA compaction temperatures ranged from 195 to 250 F (90 to 121 C). Most of the WMA mixtures were produced around 250 F (121 C) and compacted around 230 F (121 C). The mixes included PG 58 and PG 64 binders. Only one mixture included RAP. E-107

108 Project Colorado I-70 Yellowstone National Park Table E61. Field Validation Mixtures. Process Temperature, F Production Compaction Mix Type HMA Control mm, PG 58-28, 75 Advera gyrations Evotherm DAT Sasobit HMA Control mm, PG 58-34, Hveem Advera Sasobit NY Route 11 LEA mm, PG 64-22, 65 gyrations PA SR2007 HMA Control mm, PG 64-22, 50 PA SR2006 and PA SR2012 Monroe, North Carolina Evotherm DAT HMA Advera Gencor Ultrafoam GX LEA Sasobit Astec Double Barrel Green gyrations 9.5 mm, PG 64-22, 75 gyrations 9.5 mm, PG with 30 % RAP, 75 gyrations E8.2 Binder Grade Selection Initial validation of the findings from the RTFOT experiment was completed using recovered binder grading and estimates of rutting obtained from dynamic modulus tests on plant mixtures. Recovered binder grading data were collected on all of the 16 validation mixtures. Rutting estimates were made only for the mixtures included in the Colorado I-70, Yellowstone National Park, and New York Route 11 projects. E8.2.1 Recovered Binder Grading Continuous grading properties for the binder from each of the validations mixtures were determined in accordance with AASHTO R29, Grading or Verifying the Performance Grade (PG) of an Asphalt Binder. The binders were extracted in accordance with Method A of AASHTO T164, Quantitative Extraction of Asphalt Binder from Hot Mix Asphalt (HMA), using reagent grade trichloroethylene as the solvent. The binder was then recovered in accordance with ASTM D 5404, Recovery of Asphalt from Solution Using the Rotary Evaporator. The recovered binders were treated as Rolling Thin Film Oven conditioned and graded in accordance E-108

109 with AASHTO R29. Tank samples of the binder used in the HMA control sections were also graded in accordance with AASHTO R29. Table E62 summarizes the binder test data. Table E63 presents continuous grading results for the recovered binders and compares them to the binder grade specified for each project. In all cases, the low and intermediate temperature properties for the WMA processes comply with the binder grade specified for the project. There are three cases where the high temperature grade was lower than specified: Advera for the Yellowstone National Park project was 1.7 C lower, LEA for the NY Route 11 project was 3.5 C lower, and LEA for the Pennsylvania SR2006 project was 0.8 C lower. Table E64 summarizes the average difference in continuous grade temperatures for WMA compared to HMA. The high temperature grade changes are significantly less than estimated from the RTFOT experiment. From the RTFOT experiment the estimated reduction in high temperature grade for 50 and 100 F (28 and 56 C) reductions in production temperature for a typical asphalt binder having an aging index of 2.4 are 2.8 and 5.6 C, respectively. For the field data excluding Sasobit, which increases the high temperature grade of the binder, an approximately 50 F (28 C) reduction production temperature resulted in a small average decrease in the high temperature grade of 0.2 C, while an approximately 100 F (56 C) reduction in production temperature resulted in approximately a one-half grade decrease in the high temperature grade for one LEA project. The low temperature grade changes, on the other hand are greater than estimated from the RTFOT experiment. From the RTFOT experiment the estimated improvement in the low temperature grade for 50 and 100 F (28 and 56 C) reductions in production temperature are 0.5 and 1.0 C, respectively. For the field data excluding Sasobit, which increases the low temperature grade of the binder, an approximately 50 F (28 C) reduction production temperature resulted in an average improvement in the low temperature grade of binder of 1.5 C, while an approximately 100 F (56 C) reduction in production temperature resulted in 2.9 C improvement in the low temperature grade for one LEA project. Based on the recovered binder testing, it does not appear that the binder grade should be changed when using WMA as long as the production temperature is not decreased by more than 100 F (56 C). E-109

110 Table E62. Summary of Binder Grading Test Data. E-110

111 Table E63. Summary of Continuous Grading of Recovered Binders. Project Colorado I-70 Yellowstone National Park New York Route 11 Pennsylvania SR2007 Pennsylvania SR2006 Monroe, North Carolina Production Continuous Grade Temperature, C Process Temperature, F High Intermediate Low Specified NA Control Advera Evotherm Sasobit Specified NA Control Advera Sasobit Specified NA LEA Specified NA Control Evotherm Specified NA Control Advera Gencor LEA Sasobit Specified NA Astec Table E64. Summary of Average Difference in Continuous Grade Temperatures for WMA Compared to HMA. Process Number Average Difference in Production Temperature, F Average Difference in Continuous Grade Temperature, C High Intermediate Low Advera Evotherm LEA Plant Foaming Sasobit E-111

112 E8.2.2 Estimated Rutting Dynamic modulus master curves were developed for the Colorado I-70, Yellowstone National Park, and New York LEA projects on reheated samples of field mix compacted to a target air void content of 5.0 percent. The dynamic modulus master curves were developed using an AMPT in accordance with AASHTO TP61, Developing Dynamic Modulus Master Curves for Hot-Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester. Dynamic modulus measurements were made at 39.2, 68, and 95 F (4, 20, and 35 C) using frequencies of 10, 1, 0.1, and 0.01 Hz. For the New York LEA project, McConnaughay Technologies provided additional samples of a mixture produced using the LEA process and a PG binder. The master curves are shown in Figures E55 through E57. I70 Control I70 Sasobit I70 Asphamin I70 Evotherm Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency, Hz Figure E55. Dynamic Modulus Master Curves for the Colorado I-70 Project. E-112

113 YNP Control YNP Sasobit YNP Advera Dynamic Modulus, ksi E E E E E E E+06 Reduced Frequency, Hz Figure E56. Dynamic Modulus Master Curves for the Yellowstone National Park Project Control PG LEA PG LEA PG Dynamic Modulus, ksi E E E E E E E+06 Redeuced Frequency at 20 C, Hz Figure E57. Dynamic Modulus Master Curves for the New York Project. E-113

114 The dynamic modulus master curves are generally in agreement with the recovered binder test data. For the Colorado I-70 project, the Sasobit mixture is somewhat stiffer than the other WMA processes and the control. For the Yellowstone project, all mixtures have similar stiffness, while for the New York project, the LEA mixture produced with the control binder is significantly softer than the control. The LEA mixture produced with the PG binder is stiffer than the control suggesting that the needed grade change is less than one grade level. To further investigate the significance of the difference in the mixture moduli shown in Figures E55 through E57, rutting was predicted for the three projects using the Excel spreadsheet developed by the Arizona State University for the dynamic modulus Simple Performance Test (17). This spreadsheet rapidly performs asphalt layer rutting predictions using the calibrated rutting model contained in the MEPDG. The required inputs for this spreadsheet are summarized in Table E65. The required temperature data were obtained from the National Oceanic & Atmospheric Administration website (18). Table E65. Input Data for MEPDG Spreadsheet Rutting Predictions. Project Input Parameter Colorado I-70 Yellowstone National NY Route 11 Park Traffic Speed, mph Surface layer thickness, in Mean annual air temperature, F Standard deviation of mean annual air temperature, F Weather station Dillon, CO Lake Yellowstone, Syracuse, NY location WY Traffic Level, ESAL Varied Varied Varied Mixture dynamic modulus varied by mix type varied by mix type varied by mix type Figures E58, E59, and E60 present predicted surface course rutting for the three projects as a function of traffic level. The design traffic level for the Colorado I-70 and New York projects were 10 million and 3 million ESAL, respectively. A Hveem mixture design was used for the E-114

115 Yellowstone National Park project. It was assumed that the design traffic for this project was also 3 million ESAL. Several interesting observations were made based on Figures E58 through E The predicted rut depths for the control mixtures are reasonable considering the design traffic levels. Rut depths of 0.11, 0.09 and 0.09 in (2.8, 2.3, and 2.3 mm) were predicted for the control mixtures for the Colorado I-70, Yellowstone National Park, and New York projects at the design traffic levels. 2. For the I-70 project, the predicted rutting for the Advera and Evotherm DAT mixtures was slightly greater than the control while the predicted rutting for the Sasobit mixture was slightly less than the control. The predicted rutting for the Advera and Evotherm mixtures was only 0.13 in (3.3 mm). 3. For the Yellowstone National Park project, the predicted rutting of the Sasobit and Advera mixtures were essentially the same as the control at the design traffic level Control Sasobit Advera Evotherm 0.50 Predicted Rut Depth, in Traffic, Million ESALs Figure E58. Predicted Rutting for the Colorado I-70 Project. E-115

116 Control Sasobit Advera Predicted Rut Depth, in Traffic, Million ESALs Figure E59. Predicted Rutting for the Yellowstone National Park Project PG PG LEA PG LEA 0.50 Predicted Rut Depth, in Traffic, Million ESALs Figure E60. Predicted Rutting for the New York Project. E-116

117 4. For the New York project, the predicted rutting for the PG LEA mixture was 0.11 in (2.8 mm), while that for the PG LEA mixture is 0.05 in (1.3 mm). The differences in estimated rutting resistance from field mixed WMA do not support the binder grade bumping recommendations developed from the RTFOT experiment. For production temperature decreases as large as 100 F (56 ), the estimated rutting for a mixture produced as WMA only approximately 25 percent greater than that for the same mixture produced as HMA. E8.3. RAP Only one of the validation mixtures, the Monroe, North Carolina mixture, included RAP. This mixture used PG binder with 30 percent RAP to produce a mixture with meeting the requirements for PG binder. The mixture was produced at 275 F using the Astec Double Green process. For this mixture, the mixing analysis based on dynamic modulus testing of the plant mixture described earlier in the RAP Study (Section E5), was conducted to verify the degree of mixing of the RAP and new binders. The dynamic modulus for the plant mixed condition was measured on duplicate specimens in accordance with AASHTO TP61 at temperatures of 39.2, 68, and 104 F (4, 20, and 40 C) using test frequencies of 10, 1, and 0.1 Hz. The dynamic modulus for the fully blended condition was estimated from the modulus of binder recovered from the dynamic modulus specimens using the Hirsch model (8). The applicable volumetric properties for the Hirsch model predictions were: (1) air voids = 6.5 percent, (2) VMA = 19.6 percent, and (3) VFA = 66.8 percent. The results of this analysis are summarized in Table E66 and shown in Figure E61. The error bars in Figure E61 are 95 percent confidence intervals for the measured data and 95 percent prediction intervals for the Hirsch model predictions. Since the average of the measured data fall within the prediction intervals for the Hirsch model, the plant mixed modulus is not significantly different from the fully blended modulus indicating that the mixing of the RAP and new binders is acceptable. E-117

118 Table E66. Measured and Estimated Fully Blended Dynamic Modulus for the Monroe, North Carolina Mixture Produced with the Astec Double Barrel Green Process and 30 Percent RAP. Temp., F Freq., Hz Recovered Binder G*, psi Hirsch Estimated E*, ksi Measured E*, ksi Ratio of Measured to Estimated ,681 2, ,339 1, ,839 1, ,014 1, Figure E61. Comparison of Measured and Estimated Fully Blended Dynamic Modulus for the Monroe, North Carolina Mixture Produced with the Astec Double Barrel Green Process and 30 Percent RAP. E-118

119 E8.4. Short-Term Oven Conditioning For WMA and HMA, short-term oven conditioning of 2 hours at the compaction temperature was determined by comparing properties of field mixed, laboratory compacted specimens and laboratory mixed, laboratory compacted specimens for the mixtures from the Colorado I-70 project. The properties that were compared were maximum specific gravity, indirect tensile strength, and dynamic modulus. To validate this short-term conditioning, maximum specific gravity and indirect tensile strength measurements were made on all of the validation sections. The results are presented in Table E67. Table E67 also presents a paired difference statistical analysis of the maximum specific gravity and indirect tensile strength data. The statistical analysis shows that there is no difference in the maximum specific gravity measured on samples of the field mix and measured on samples of laboratory prepared mixture that has been shortterm oven conditioned for 2 hours at the compaction temperature. For the mixtures tested, the aggregate water absorptions ranged from 0.5 to 2.5 percent. The statistical analysis did, however, show a significant difference in the indirect tensile strengths, with the tensile strengths of the field mix averaging 9.1 psi (48 kpa) higher than that obtained from laboratory prepared mixture that has been short-term oven conditioned for 2 hours at the compaction temperature. Figure E62 shows the differences for the indirect tensile strengths for all of the projects. The field indirect tensile strengths for all of the mixtures from the Pennsylvania SR2006 were consistently 15 to 40 psi (103 to 207 kpa) higher than the laboratory prepared and conditioned mixtures. Since one third of the mixtures were from this project, this difference biased the results. The average difference for the mixtures from the other projects was very small and not significant. E-119

120 Project Colorado I-70 Yellowstone National Park Pennsylvania SR2007 Pennsylvania SR2006 and SR2012 Table E67. Verification Testing for Short-Term Oven Conditioning. Indirect Tensile Strength Water Compaction Maximum Specific Gravity (77 F, 2 in /min), psi Absorption, Process Temperature, Field Lab Difference Field Lab Difference Percent F 2 hours 2 hours Control Advera Evotherm Sasobit Control Advera Sasobit Control Evotherm Control Advera Gencor LEA Sasobit Monroe, NC 0.6 Astec Average Difference Standard Deviation of Differences Calculated t Critical t, 95 percent one sided Conclusion No difference Field significantly higher E-120

121 45 35 IDT Strength Differences, psi CO I-70 Control CO I-70 Advera CO I-70 Evotherm CO I-70 Sasobit YNP Control YNP Advera YNP Sasobit PA SR2007 Control PA SR2007 Evotherm Mixture/Process PA SR2006 Control PA SR2006 Advera PA SR2006 Gencor PA SR2006 LEA PA SR2006 Sasobit Monroe NC Astec Figure E62. Differences in Indirect Tensile Strength Between Field Mixes and Laboratory Mixes Short Term Conditioned 2 Hours at the Compaction Temperature. E8.5. Specimen Fabrication, Coating and Compactability The proposed specimen fabrication procedures and methods for evaluating coating and compactability were verified using the field validation mixtures. Laboratory specimens were prepared based on the approved job mix formula using the revised preliminary procedure for WMA and AASHTO R35 for HMA. The resulting properties were then compared. The sections that follow describe this analysis by project. E8.5.1 Colorado I-70 The composition of the laboratory mixtures for the Colorado I-70 project is presented in Table E68. Duplicate specimens for Advera WMA, Evotherm WMA, and Sasobit WMA were prepared per the revised preliminary WMA procedure and compared to the properties reported in the HMA mixture design approved for the project. The binder content was 6.2 percent and the specimens were compacted to 75 gyrations. E-121

122 Table E68. Composition of Colorado I-70 Mixtures. Properties Value Design Traffic Level, MESAL <10 Design Gyration Level 75 Sieve Size, mm Gradation Fine Aggregate Angularity, vol % 48.6 Crushed Aggregate Fractured Faces, % 99/99 Aggregate Bulk Specific Gravity Aggregate Water Absorption, % 0.8 Binder Content, wt % 6.2 The target mixing and compaction temperatures and properties of the mixtures are presented in Table E69. The volumetric properties of the Evotherm and Sasobit WMA mixtures are in extremely close agreement with those reported in the mixture design, indicating that the optimum binder content for these mixtures is the same as that reported in the approved HMA job mix formula. The Advera WMA mixture has lower air voids, and higher VBE indicating that there is less binder absorption and that the optimum binder content determined by the preliminary WMA mixture design procedure for this mixture would be closer to 6.0 percent. This difference in optimum binder contents is within the range observed in the mix design study described earlier in Section E7. Coating was 100 percent for all of the WMA mixtures when a Blakeslee planetary mixer with wire whip was used for specimen preparation. The Advera WMA was more compactable than the Evotherm and Sasobit WMA at the project compaction temperatures due to its higher VBE. The increase in the number of gyrations to reach 92 percent relative density when the compaction temperature was reduced 54 F (30 C) was similar for the three WMA mixtures ranging from 16 to 20 percent. There were no reports of workability or compaction issues for the WMA mixtures used on the Colorado I-70 project. E-122

123 Table E69. Properties of Specimens Compacted to 75 Gyrations for the Colorado I-70 Mixtures. Property HMA JMF Advera Evotherm Sasobit Mixing Temperature Compaction Temperature Binder Content, wt. % Bulk Specific Gravity of Mixture Maximum Specific Gravity of Mixture Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Effective Binder Content, wt. % Voids Filled with Asphalt, % Dust to Effective Binder Content Ratio Coating NR Gyrations to 92 % Gmm at Compaction Temp NR Gyrations to 92 % Gmm at Compaction Temp -54 F NR Gyration Increase, % NR Notes: 1 Mixed with Blakeslee planetary mixer with wire whip E8.5.2 Yellowstone National Park The mixture used in the Yellowstone National Park project was designed using the Hveem mixture design procedure. Table E70 presents the composition of the laboratory mixtures for this project. Duplicate specimens for the control HMA, Advera WMA, and Sasobit WMA were compacted using a binder content of 5.5 percent to 75 gyrations. The properties of the WMA mixtures were then compared to the properties of the control HMA. The target mixing and compaction temperatures and properties of the mixtures are presented in Table E71. The air void content for all of the mixtures was quite high indicating that the optimum binder content determined by the Hveem design procedure is much lower that would be obtained using the revised preliminary WMA procedure or AASHTO R35. The air voids for both WMA mixtures are higher than the control. The VBE for the Advera mixture is higher than that for the control HMA and the Sasobit WMA indicating that the binder absorption for this process is somewhat less. Using the rule of thumb that a 0.4 percent increase in binder content will result in a 1.0 percent decrease in air voids, the optimum binder content for the Advera E-123

124 WMA is estimated to be approximately 0.2 percent higher than the control while that for the Sasobit WMA is estimated to be approximately 0.4 percent higher than the control HMA. The estimated difference in the optimum binder content for the Sasobit mixture is somewhat higher than the range observed in the mix design study described earlier in Section E7. This may have been affected by the fact that the binder content for the Hveem mixture design is about 1 percent lower than would be obtained using AASHTO R35. Even at these low binder contents, coating was 100 percent for all three mixtures when a Blakeslee planetary mixer with wire whip was used for specimen preparation. Based on the number of gyrations to 92 percent relative density, the WMA mixtures are less compactable than the HMA control at the project compaction temperatures. The effect of decreasing temperature on the compactability of the WMA mixtures was not evaluate due to the high air void content of the mixtures at 75 gyrations. Table E70. Composition of Yellowstone National Park Mixtures. Properties Value Design Traffic Level, MESAL Not Given Design Gyration Level Hveem Sieve Size, mm Gradation Fine Aggregate Angularity, vol % NR Crushed Aggregate Fractured Faces, % 100/100 Aggregate Bulk Specific Gravity Aggregate Water Absorption, % 2.5 Binder Content, wt % 5.5 E-124

125 Table E71. Properties of Specimens Compacted to 75 Gyrations for the Yellowstone National Park Mixtures. Property HMA Advera Sasobit Mixing Temperature Compaction Temperature Binder Content, wt. % Bulk Specific Gravity of Mixture Maximum Specific Gravity of Mixture Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Effective Binder Content, wt. % Voids Filled with Asphalt, % Dust to Effective Binder Content Ratio Coating Gyrations to 92 % Gmm at Compaction Temp > 75 Gyrations to 92 % Gmm at Compaction Temp -54 F Gyration Increase, % Notes: 1 Mixed with Blakeslee planetary mixer with wire whip E8.5.3 Pennsylvania SR2007 The composition of the laboratory mixtures for the Pennsylvania SR2007 project is presented in Table E72. Duplicate specimens for Evotherm WMA were prepared using the revised preliminary WMA procedure and compared to the properties reported in the HMA mixture design approved for the project. The binder content was 6.4 percent and the specimens were compacted to 50 gyrations. The target mixing and compaction temperatures and properties of the mixtures are presented in Table E73. The volumetric properties of the Evotherm WMA mixture are in extremely close agreement with those reported in the mixture design, indicating that the optimum binder content for this mixture is the same as that reported in the approved HMA job mix formula. The binder absorption for this mixture is quite low at approximately 0.1 weight percent. Coating was 100 percent for the Evotherm WMA when a Blakeslee planetary mixer with wire whip was used for specimen preparation. Although this mixture was designed for low traffic using 50 gyrations, it was made using highly angular manufactured sand and crushed stone. The compactability as E-125

126 measured by the increase in the number of gyrations to reach 92 percent relative density when the compaction temperature was reduced 54 F (30 C) was 20 percent. There were no reports of workability or compaction issues for the WMA mixtures used on the Pennsylvania SR2007 project. Table E72. Composition of Pennsylvania SR2007 Mixtures. Properties Value Design Traffic Level, MESAL <0.3 Design Gyration Level 50 Sieve Size, mm Gradation Fine Aggregate Angularity, vol % 50 Crushed Aggregate Fractured Faces, % 100/100 Aggregate Bulk Specific Gravity Aggregate Water Absorption, % 0.5 Binder Content, wt % 6.4 E-126

127 Table E73. Properties of Specimens Compacted to 50 Gyrations for the Pennsylvania SR2007 Mixtures. Property HMA JMF Evotherm Mixing Temperature Compaction Temperature Binder Content, wt. % Bulk Specific Gravity of Mixture Maximum Specific Gravity of Mixture Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Effective Binder Content, wt. % Voids Filled with Asphalt, % Dust to Effective Binder Content Ratio Coating NA Gyrations to 92 % Gmm at Compaction Temp NA 20 Gyrations to 92 % Gmm at Compaction Temp 54 F NA 24 Gyration Increase, % NA 20 Notes: 1 Mixed with Blakeslee planetary mixer with wire whip E8.5.4 Pennsylvania SR2006 The Pennsylvania SR2006 project included a control HMA and four WMA processes: Advera, Gencor Ultrafoam GX, LEA, and Sasobit. Table E74 presents the approved job mix formula for the Pennsylvania SR2006 project, which was used in preparing laboratory mixtures for each process. Duplicate specimens for each mixture were prepared at the design binder content of 5.9 percent using 75 gyrations. Additionally, a WMA mixture verification was performed by the University of Wisconsin, Madison for the Gencor foaming process using a Wirtgen WLB 10 laboratory foaming plant. The water content used in the laboratory foaming plant was 1.25 percent by weight of binder. Details of the mix design verification are presented later in Section E E-127

128 Table E74. Composition of Pennsylvania SR2006 Mixtures. Properties Value Design Traffic Level, MESAL <3 Design Gyration Level 75 Sieve Size, mm Gradation Fine Aggregate Angularity, vol % 45.2 Crushed Aggregate Fractured Faces, % 100/100 Aggregate Bulk Specific Gravity Aggregate Water Absorption, % 0.6 Binder Content, wt % 5.9 The target mixing and compaction temperatures and properties of the mixtures at the job mix formula binder content are presented in Table E75. The air void content of the mixtures is significantly higher than the 4.0 percent reported in the approved job mix formula. Air voids for the HMA control at 6.2 percent are 2.2 percent higher than reported in the job mix formula. The paving contractor provided excellent records of the production and placement including quality control test results, in-place pavement density results, and production and compaction temperatures. These records, which are included in Section E11, show that the filler content and binder content varied somewhat between the sections and that the air voids of the plant mixtures typically exceeded the design target of 4.0 percent except for the cases when the filler content was more than one percent over the target value. Table E76 summarizes the average binder content, filler content, and air voids from the quality control tests for each of the test sections. This data suggests that the air void content obtained by the mix design laboratory at the job mix formula binder and filler contents is approximately 5.0 percent, which is in agreement with the value obtained by the University of Wisconsin, Madison for the laboratory reproduced Gencor foamed mixture. The difference between this value and that obtained in AAT s laboratory for E-128

129 the control HMA, and the Advera, LEA, and Sasobit WMA probably represents between laboratory differences in specimen compaction and measurements of bulk specific gravity. The reported multilaboratory precision for AASHTO T315 is 1.7 percent which is greater than the difference between the air voids reported in Table E75 and 5.0 percent for the mix design laboratory. Table E75. Properties of Specimens Compacted to 75 Gyrations for the Pennsylvania SR2006 Mixtures. Property HMA Advera Gencor LEA Sasobit Mixing Temperature Compaction Temperature Binder Content, wt. % Bulk Specific Gravity of Mixture Maximum Specific Gravity of Mixture Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Effective Binder Content, wt. % Voids Filled with Asphalt, % Dust to Effective Binder Content Ratio Coating Gyrations to 92 % Gmm at Compaction Temp Gyrations to 92 % Gmm at Compaction Temp F Gyration Increase, % Notes: 1 Mixed with Blakeslee planetary mixer with wire whip 2 Mixed with bucket mixer Table E76. Summary of Quality Control Test Results for Pennsylvania SR 2006 Project. Property HMA Advera Gencor LEA 1 Sasobit Control Average Binder Content, % Average Passing mm sieve, % Average Quality Control Air Voids, % Notes: 1 Outlier excluded The VBE for the HMA control and all of the WMA mixtures are very similar indicating that the binder absorption is similar, even for the very low mixing and compaction temperatures used E-129

130 in the LEA process. Coating was 100 percent for the control HMA, Advera, LEA, and Sasobit. These mixtures were produced in AAT s laboratory using a Blakeslee planetary mixer with wire whip. Coating was only 81 percent for the laboratory prepared foamed WMA (Gencor) produced at the University of Wisconsin, Madison using a bucket mixer. This suggests that if coating is used as a mixture design criterion, then better standardization of the mixing process is needed. At the compaction temperature, the compactability, measured by the number of gyrations to 92 percent relative density at the compaction temperature, was similar for the mixtures prepared in AAT s laboratory. The value obtained for the laboratory prepared foamed WMA (Gencor) should not be compared due to the between laboratory differences in compaction discussed earlier. The increase in the number of gyrations to reach 92 percent relative density when the compaction temperature was reduced 54 F (30 C) was 29 percent for the HMA and ranged from 2 to 16 percent for the WMA mixtures. This indicates that the compactability of the WMA mixtures was less sensitive to changes in compaction temperature. Table E77 presents in-place core density results that were reported. One less roller was used in the Advera section compared to the others. These data show that the WMA mixtures were as compactable as the HMA when the compaction temperatures were reduced 45 to 80 F (25 to 44 C). Table E77. Summary of Core Density Results for Pennsylvania SR 2006 Project. Section Target Compaction Temperature, F Average Standard Deviation HMA Control Advera Gencor LEA Sasobit Notes: 1 One less roller 2 Outlier excluded E8.5.5 Monroe, North Carolina The last verification mixture that was evaluated was a mixture produced with the Astec Double Barrel Green process that included 30 percent RAP. Table E78 compares the job mix E-130

131 formula for the Monroe, NC project with the composition used in the validation. The binder content for the validation work was obtained from a WMA mixture design verification performed by the University of Wisconsin, Madison using a Wirtgen WLB 10 laboratory foaming machine. The water content used in the laboratory foaming machine was 2.0 percent by weight of binder. Details of the mix design verification are presented later in Section E Table E78. Composition of Monroe, North Carolina Mixture. Properties JMF WMA Verification Design Traffic Level, MESAL <10 Design Gyration Level 75 Gradation Sieve Size, mm Fine Aggregate Angularity, vol % > 45 > 45 Crushed Aggregate Fractured Faces, % 100/ /100 Aggregate Bulk Specific Gravity Aggregate Water Absorption, % Total Binder Content, wt % Binder From RAP Anti-strip Additive (Ad Here LOF 6500), % of new binder The target mixing and compaction temperatures and properties of the laboratory designed WMA mixture and the approved job mix formula are presented in Table E79. The optimum binder content from the verification is 0.3 percent higher than the approved job mix formula. This difference is within the range observed in the mix design study described earlier in Section E7. The effective binder contents are approximately the same; therefore, there is greater binder absorption for the verification mixture. Coating was 65 percent for the laboratory prepared E-131

132 foamed WMA when a bucket mixer was used for specimen preparation. The number of gyrations to reach 92 percent relative density was the same at the compaction temperature and when the compaction temperature was reduced 54 F (30 C) indicating that the compactability of this mixture is not sensitive to temperature over the temperature range investigated. The contractor routinely uses this mixture and reported improved field compaction compared to similar HMA mixtures. Table E79. Properties of Specimens Compacted to 75 Gyrations for the Monroe, North Carolina Mixture. Property JMF Verification Mixing Temperature Compaction Temperature NR 260 Binder Content, wt. % Bulk Specific Gravity of Mixture Maximum Specific Gravity of Mixture Air Voids, vol % Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Effective Binder Content, wt. % Voids Filled with Asphalt, % Dust to Effective Binder Content Ratio Coating NA 65 Gyrations to 92 % Gmm at Compaction Temp NA 16 Gyrations to 92 % Gmm at Compaction Temp -54 F NA 16 Gyration Increase, % NA 0 Notes: 1 Mixed with bucket mixer E8.5.6 Evaluation of Warm Mix Asphalt Mix Design Procedures for Foamed Asphalt Mixes The validation effort included an evaluation of the feasibility and practicality of designing foamed asphalt WMA mixtures in the laboratory. This evaluation was performed at the University of Madison, Wisconsin using a modified Wirtgen WLB-10 asphalt foaming plant. The WLB-10 was modified by Wirtgen to produce foamed asphalt at the lower water contents used in production of WMA. The WLB-10 was designed for mixture design of foamed asphalt stabilized bases and in-place recycling where higher water contents are used. The evaluation was conducted for the Gencor WMA process from the Pennsylvania SR2006 project and for the Astec process from the Monroe, North Carolina project. Job mix formulas for these projects E-132

133 were presented in Tables E74 and E78, respectively. The water content used to simulate the Gencor process for the Pennsylvania mixture was 1.25 percent by weight of binder. For the North Carolina mixture, 2.0 percent water by weight of the new binder added to the mixture was used to simulate the Astec process. This mixture used 30 percent RAP, with approximately 17 percent of the total binder content being provided by the RAP. The mixing and compaction temperatures for the Pennsylvania mixture were 250 and 230 F (121 and 110 C), respectively. The North Carolina project used mixing and compaction temperatures of 275 and 260 F (135 and 127 C). For both mixtures, the Wirtgen WLB-10 foaming plant was used to reproduce the foamed asphalt in the laboratory. Laboratory mixtures were prepared for the following: Determination of optimum asphalt content, Evaluation of aggregate coating and mixture compactability, and Preparation of samples for moisture sensitivity and flow number testing. The WMA mixture design procedure uses process specific specimen fabrication procedures to simulate the WMA process. For plant foaming systems this requires the production of foamed asphalt in the laboratory. At the time NCHRP Project 9-43 was completed, the Wirtgen WLB-10 was the only commercially available laboratory foaming machine. The following describes the process used to fabricate foamed asphalt using this equipment. Operation of the Wirtgen WLB -10 foaming machine requires asphalt binder temperatures above 320 F (160 C), thus the mixing temperature of the foamed asphalt mixture is controlled by the temperature of the aggregates. It is assumed that the asphalt binder will quickly revert to the mixing temperature when it comes in contact with the aggregate. The mass of foamed asphalt that is required is calculated based on the weight of the aggregates. The aggregate and mixing bucket are placed under the foaming head and the foamed asphalt is shot into the bucket as shown in Figure E63. The flow of foamed asphalt into the mixing bucket is metered using a flow controller. Based on a known flow rate, the user prescribes the time required to obtain the appropriate quantity of asphalt binder. E-133

134 Figure E63. Introducing Foamed Asphalt to Mixing Bucket. The mixing bucket, with the foamed asphalt sitting on top of the aggregate is immediately transferred to the laboratory mixer, mixed for 90s, and transferred to a shallow pan. Illustrations of the foamed asphalt mixture before and after the 90s mixing time are provided in Figures E64 and E65, respectively. After mixing, the foamed mix is short term conditioned at the compaction temperature for two hours and compacted. Figure E64. Foamed Asphalt on Before Mixing. E-134

135 Figure E65. Foamed Asphalt Mixture after 90s Mixing Time. The operation of the foaming plant presents some practical concerns for use in laboratory WMA mixture design. The machine is intended for preparation of samples of foam stabilized asphalt base course and cold in-place recycling. These applications require foamed asphalt with water contents above 10 percent by weight of the asphalt binder. In contrast, the water contents for WMA applications range from 1.0 to 3.0 percent. To accommodate this difference the existing flow controller was replaced with one that was smaller and more precise. Operation of the machine for WMA applications was possible, however due to the low percentage of water required for WMA, the operation of the flow controller was approaching its minimum control tolerance. The more precise flow controller was selected with the intent of delivering a more consistent foam at the water contents used in the WMA field production. The machine is designed to produce large quantities of material. This was especially an issue in trying to prepare samples for evaluation of the maximum specific gravity. The sample size to conduct the maximum specific gravity test for 9.5 mm mixtures is 1000 g. E-135

136 A timer is used to control the amount of foamed asphalt shot into the bucket. Because of the flow rate of the foaming head, the machine provides the required 50 to 60 g of foamed asphalt in a fraction of a second. This amount of time is insufficient for the machine to produce a consistent asphalt foam, introducing potential reproducibility issues into the results. It is not recommended to use this machine for small batches of aggregate, instead large batch sizes should be produced then split for the various tests required. At times the air line in the machine becomes clogged, so instead of foamed asphalt, an asphalt/water mix is produced. This problem has been encountered with both the neat PG binders from the Pennsylvania and North Carolina projects and SBS modified PG binder used in another project. The valve that controls the flow of the air at the foaming head becomes clogged regularly, requiring disassembly and cleaning of the head. This issue occurred on three separate occasions while preparing samples for this project, each time resulting in a delay of 2 to 3 hours. The regularity with which this problem occurs suggests that redesign of the foaming head of the machine may be needed for continuous use as a mix design tool. The problem was more severe with the SBS modified binder. After production of approximately 20 samples the machine clogged and had to be taken apart a fully cleaned before further use. Finally, the preparation of the foamed mixes requires a significant amount of technician time and expertise. Each mix design evaluated for this project required three separate days for foamed mix production. For both mixtures, samples were prepared as described above at multiple binder contents to verify the mixture design. The results are summarized in Tables E80 and E81 for the Pennsylvania and North Carolina mixtures, respectively. Based on the air voids, an optimum binder content of 5.8 percent was selected for the Pennsylvania mixture; the selected optimum binder content was 6.1 percent for the North Carolina mixture. E-136

137 Table E80. Summary of Optimum Binder Content Determination for the Pennsylvania Foamed Asphalt Mixture. Binder Content, % % G ini Properties at N design Air Voids, % VMA, % VFA, % G mm Effective Binder Content, % Dust to Effective Binder Ratio Gyrations to 92% G mm (N 92 ) % % % % % % Table E81. Summary of Optimum Binder Content Determination for the North Carolina Foamed Asphalt Mixture. Binder Content, % % G ini Properties at N design Air Voids, % VMA, % VFA, % G mm Effective Binder Content, % Dust to Effective Binder Ratio Gyrations to 92% G mm (N 92 ) Specimens were then prepared at the optimum binder content to evaluate coating and compactability. The results are summarized in Table E82. The air void content of the North Carolina mixture at the optimum binder content agreed well with that estimated from the trial blends. However, the air void content of the Pennsylvania mixture at the optimum binder content was 0.8 percent higher than the target determined from the trial blends. This discrepancy indicates a potential for variability in the quality of foamed asphalt produced by the laboratory foaming machine. Trial blends and compactions at the design binder content were prepared on two separate days. Because of the high air voids at N design for the Pennsylvania mixture, the number of gyration to reach 92 percent relative density exceeded the maximum of 35 percent of N design included in the revised preliminary procedure. The North Carolina mixture failed the maximum relative density at N ini having a relative density at N ini of 89.7 percent. E-137

138 Table E82. Properties at the Optimum Binder Content. Property Pennsylvania North Carolina WMA Criteria Design Binder Content NA G mm NA Air Voids, % to 4.5 VMA, % VFA, % to 78 Coating, % % G N ini <89 N 92 at compaction temperature <26 N 92 at compaction temperature 54 F NA Gyration Increase, % % G N max 96.7 NT 98 Coating for both of the mixtures using a bucket mixture was much lower than observed when using a planetary mixer with wire whip. This difference indicates that if coating is to be used as a mixture design criteria, better standardization of the mixing process is needed. The laboratory foaming device and the bucket mixture were used to fabricate specimens at the optimum binder content for moisture sensitivity and flow number testing. The results of this testing are described in later sections of this report. E8.6 Moisture Sensitivity Moisture sensitivity was evaluated for all of the validation mixtures using AASHTO T283. Specimens were compacted to a target air void content of 7.0 percent ± 0.5 percent using either the job mix formula binder content or that determined from the mix design verification. Per the revised preliminary WMA procedure the mixture was conditioned 2 hours at the compaction temperature. Table E83 summarizes the results. Nine of the 11 WMA mixtures and 2 of the 4 HMA control mixtures have tensile strength ratios less than 80 percent. The effect of the WMA process on the moisture sensitivity is mixture and process specific. For the Colorado project, the tensile strength ratio was reduced by all of the WMA processes. For this project, the Advera specimens failed during the conditioning processes. The WMA processes had no effect on the tensile strength ratio for the Yellowstone National Park and PA SR2007 projects. For the PA SR2006 project, the Advera, Gencor, and Sasobit WMA processes reduced the tensile strength E-138

139 ratio, while the LEA process increased it. The LEA process includes an anti-strip additive that is added to the binder at the plant. For the plant foaming processes, the AASHTO T283 results may have been adversely affected by the poorer coating obtained with the bucket mixer when simulating these processes. Table E83. Summary of AASHTO T283 Results. Project Colorado I-70 Yellowstone National Park Pennsylvania SR2007 Pennsylvania SR2006 Monroe, North Carolina Process Production Temperature, F Compaction Temperature, F Dry Tensile Strength, psi Conditioned Tensile Strength, psi Tensile Strength Ratio, % Control Advera Evotherm Sasobit Control Advera Sasobit Control Evotherm Control Advera Gencor LEA Sasobit Astec E8.7 Flow Number Rutting resistance was evaluated for all of the validation mixtures using the flow number test in AASHTO TP 79. Specimens were compacted to a target air void content of 7.0 percent ± 0.5 percent using either the job mix formula binder content or that determined from the mix design verification. All of the specimens were within this tolerance except for the Gencor mixture for the PA SR2006 project, which were compacted to 4.5 percent. Per the preliminary WMA mixture design procedure the mixture was conditioned 2 hours at the compaction temperature. The flow number test was conducted at the 50 percent reliability high pavement temperature from LTPPBind 3.1 for the project location. As recommended in NCHRP 9-33, the flow number E-139

140 testing used unconfined specimens with a repeated deviatoric stress of 87 psi (600 kpa) and a contact deviatoric stress of 4.4 psi (30 kpa). Table E84 summarizes the results. The allowable traffic in Table E84 was calculated using the relationship between flow number and allowable traffic to an estimate rut depth of 0.5 in (12.5 mm) developed in NCHRP Project 9-33 (Equation E7) and discussed earlier in the mixture design study (Section E7). These are the criteria that were included in the revised preliminary WMA procedure. Three of the mixtures do not meet the rutting resistance criteria: the Advera and LEA mixtures for the PA SR2006 project and the Monroe, North Carolina mixture. The North Carolina mixture has very high design VMA of 17.6 percent indicating that the rutting resistance of this mixture could be improved by decreasing the design VMA. In NCHRP Project 9-33, a maximum VMA of 17 percent has been recommended for 9.5 mm mixtures to limit the effective binder content of the mixture and provide adequate rutting resistance. The rutting resistance of the Hveem designed mixtures from the Yellowstone project is very high. Also, the rutting resistance of the 50 gyration mixtures from the Pennsylvania SR2007 project is high considering the design traffic level. These mixtures were produced with highly angular manufactured sand and crushed stone. Project Table E84. Summary of Flow Number and Rutting Resistance Results. Design Traffic Level, MESAL Colorado I-70 < 10 Yellowstone National Park Pennsylvania SR2007 Pennsylvania SR2006 Monroe, North Carolina < 3 (estimated) Notes: < 0.3 < 3 Process Production Temperature, F Compaction Temperature, F Test Temperature, F Flow Number NCHRP 9-33 Allowable Traffic, MESAL Control Advera Evotherm Sasobit Control Advera Sasobit Control Evotherm Control Advera Gencor LEA Sasobit < 10 Astec Specimens compacted to 3.5percent air voids instead of 7.0 percent E-140

141 Table E85 compares the rutting resistance of the WMA mixtures to that of the HMA control mixtures. The Gencor mixture from the PA SR2006 project was not included in this analysis because the air void content of the specimens for this mixture were much lower than that of all of the others. The rutting resistance for all WMA processes except Sasobit is less than the HMA control due to the lower short-term conditioning temperatures. The rutting resistance decreases approximately 6 percent for every 10 F (5.5 C) reduction in compaction temperature. Sasobit increases the high temperature stiffness of the binder, resulting in improved rutting resistance. Table E85. Summary of Average Difference in Allowable Traffic WMA Compared to HMA. Process Number Average Difference in Compaction Temperature, F Average Difference is Allowable Traffic, % Advera Evotherm LEA Sasobit E9. Feasibility of Using a Two Step Aging Process for Performance Testing Criteria for evaluating rutting resistance using the flow number and other tests are generally based on mixtures that have been laboratory conditioned for 4 hours at 275 C (135 C) in accordance with AASHTO R30. Although it is generally accepted that this conditioning represents the binder stiffening that occurs during construction, it appears from the short-term conditioning study that this level of conditioning is more representative of the stiffness of the binder after some short period in service. To extend existing performance criteria to WMA, a two step loose mix conditioning procedure should be considered. This two step procedure would include two hours of conditioning at the compaction temperature to simulate the absorption and binder stiffening that occurs during construction, followed by aging at a representative high inservice pavement temperature to simulate early stiffening during the service life of the pavement. The representative in-service pavement temperature should be in the range of 120 to 150 F (50 to 65 C) depending on the project location based on the 50 percent reliability high pavement E-141

142 temperature from LTPPBind 3.1. The conditioning time should be selected such that typical HMA mixtures reach approximately the same stiffness after the two step conditioning procedure as they reach using 4 hours at 275 F (135 C). This additional study could not be performed within the time and funding available for NCHRP Project 9-43, but an analysis of the feasibility of the two step aging process was performed using loose-mix aging data collected during NCHRP Project 9-13 (19). NCHRP Project 9-13 included data that could be analyzed to investigate the effect of aging at in-service pavement temperatures compared to HMA mixing and compaction temperatures. With the database reported for this project, dry tensile strengths were collected on Superpave gyratory compacted samples for five mixtures that were aged using four loose-mix aging procedures: unaged, 2 hours at 275 F (135 C), 4 hours at 275 F (135 C), and 16 hours at 140 F (60 C). Dry tensile strengths were measured after two compacted sample conditioning periods: 0 hours and 96 hours at room temperature. The database extracted from this study is presented in Table E86. In analyzing this data, the data for the two compacted mix aging conditions were combined. Figure E66 shows plots of the ratio of the average strength of the conditioned specimens to the unaged specimens. From Figure E66, it appears that there is an error in the unaged data for the Maryland mixture because the ratio of the conditioned to unaged tensile strengths are always less than one indicating that the mixture softens upon loose-mix conditioning, which is not rational. Individual specimen air voids were not reported, but the text stated that the air void tolerance for specimen fabrication was 7.0 ± 1.0 percent. E-142

143 Table E86. Database of Dry Tensile Strengths Extracted from NCHRP Project 9-13 (19). Mix Nevada Alabama Colorado Maryland Texas Loose Mix Aging Unaged 16 Hours at 60 C 2 Hours at 135 C 4 hours at 135 C Unaged 16 Hours at 60 C 2 Hours at 135 C 4 hours at 135 C Unaged 16 Hours at 60 C 2 Hours at 135 C 4 hours at 135 C Unaged 16 Hours at 60 C 2 Hours at 135 C 4 hours at 135 C Unaged 16 Hours at 60 C 2 Hours at 135 C 4 hours at 135 C Compacted Mix Dry Tensile Strength, psi Aging, hours at Room Temperature Average Failed Failed Failed Standard Deviation E-143

144 1.8 Nevada Alabama Colorado Maryland Texas Aged/Unaged Tensile Strength Ratio Hours at 135 C 4 Hours at 135 C 16 Hours at 60 C Aging Condition Figure E66. Effect of Loose Mix Aging on Tensile Strength. Data From NCHRP Project 9-13 (19). Because of the questionable unaged data for the Maryland mixture, the unaged data were eliminated from the analysis. Figure E67 shows the average tensile strength for the remaining three loose mix aging conditions: 2 hours at 275 F (135 C), 4 hours at 275 F (135 C), and 16 hours at 140 F (60 C). The error bars in this figure are 95 percent confidence intervals based on the measured data for each mixture. Figure E67 shows that the tensile strengths for 16 hours at 140 F (60 C) are somewhat higher than the other aging conditions, indicating that this aging condition stiffens the mixture somewhat more than the shorter aging times at the higher temperatures. This was confirmed by a two-way analysis of variance. Table E87 summarizes the results of the two-way analysis of variance. This analysis shows that both the mixture and aging effects were significant. The aging effect was further investigated using the Scheffe test. The results are summarized in Table E88 and show that the dry tensile strength for the 16 hours at 140 F (60 C) aging condition is higher than that for the aging conditions of 2 hours at 275 F (135 C) and 4 hours at 275 F (135 C) which are not significantly different. E-144

145 Figure E67. Comparison of Tensile Strengths for Loose Mix Aging Conditions. Data From NCHRP Project 9-13 (19). Table E87. Two-Way Analysis of Variance for Loose-Mix Aging Tensile Strength Data. Data From NCHRP Project 9-13 (19). Source of Variance Degrees of Freedom Mean Square F P-value Conclusion Mixture Significant Aging Significant Interaction Not Significant Error Table E88. Significant Differences for Loose Mix Aging Effect. Condition Mean P-Value for Scheffe Test Tensile 2 Hours at 4 Hours at 16 Hours at Strength, psi 275 F 275 F 140 F 2 Hours at 275 F Hours at 275 F Hours at 140 F E-145

146 This analysis shows that it is possible to reach the level of binder stiffening caused by 4 hours of loose mix oven conditioning at 275 F (135 C) through loose mix oven conditioning at representative in-service temperatures. Since the suggested two step procedure would include two hours of conditioning at the compaction temperature to simulate the absorption and binder stiffening that occurs during construction, the in-service aging step will require less than 16 hours of loose mix aging at the representative in-service temperature. E9. Fatigue Study One of the potential benefits of WMA mixtures is improved fatigue characteristics compared to HMA mixtures due to the lower aging that occurs during plant mixing at the lower WMA process temperatures. Phase II included a brief study to evaluate the fatigue resistance of WMA compared to HMA. The experimental design for this study is presented in Table E89. No. Table E89. Experimental Design for the WMA Fatigue Study. Mixture Identification Aggregate RAP HMA WMA Absorption Organic N design Process WMA Foam WMA Chemical 4 75 High No 320/ / / / Low No 320/ / / /240 Notes: 1. Surface course mixtures either 12.5, 9.5, or 4.75 mm. 2. XXX/XXX denotes Mixing/Compaction temperatures, F 3. All mixtures use PG binder 4. All mixtures short-term conditioned 2 hours at the compaction temperature 5. All mixtures long-term conditioned 120 hours at 185 F Two of the mixtures from the mix design experiment were used in this study. Continuum damage fatigue tests were performed on the HMA control, and WMA mixtures produced using Advera, Evotherm, and Sasobit. All mixtures used PG binder. The HMA mixture was prepared at the recommended viscosity based mixing and compaction temperatures. The WMA mixtures were prepared at the midpoint of the temperatures used in the mix design study. After compaction, all specimens were long-term oven aged in accordance with AASHTO R30 to simulate the effects of long-term aging. E-146

147 Design properties for the two mixtures used in the fatigue study are summarized in Table E90. Although it was planned to have mixtures with significantly different binder absorption levels, the binder absorption was approximately the same for the two mixtures. The VMA and VBE for the 100 gyration mixture, Mix 6, are at approximately the minimum permitted by AASHTO M323 for 9.5 mm mixtures. The 75 gyration mixture, Mix 4, has somewhat higher VMA and VBE. Thus, the fatigue experiment compares the fatigue resistance of WMA mixtures to HMA mixtures for two VBE levels, 11.4 and 12.0 percent by volume. Table E90. Design Properties for Fatigue Study Mixtures. Mix Number Design Gryations Aggregate Water Absorbtion, % RAP NMAS Aggregate Sources Gradation Aggregate Properties No No 9.5 mm 9.5 mm Coarse PA Gravel VA Diabase Fine Binder Content, wt % Effective Binder Content, wt % Air Voids, vol % PA Limestone PA Gravel VA Diabase Natural Sand RAP None None Sieve Size, mm FAA CAA 98/95 100/100 Flat & Elongated Sand Equivalent Voids in Mineral Aggregate, vol % Effective Binder Content, vol % Voids Filled With Asphalt, % Dust to Effective Asphalt Ratio E-147

148 The fatigue resistance of the mixtures was evaluated using continuum damage theory. Continuum damage theory is a new, powerful tool for characterizing the fatigue behavior of asphalt concrete in a thorough and rational way with relatively limited amounts of testing. Continuum damage theory has recently been applied to the fatigue response of asphalt concrete mixtures by several researchers (20,21). Recently a practical approach for using continuum damage theory to quickly and accurately characterize the fatigue resistance of asphalt concrete mixtures was developed (22). In this approach, cyclic direct tension fatigue tests are performed at two strain levels and temperatures. For this study, the cyclic fatigue tests were performed 39.2 and 68 F (4 and 20 C) using a low strain level of approximately 150 µstrain, and at a high strain level of approximately 250 µstrain (peak-to-peak). The resulting data were analyzed using the concept of reduced cycles (22). In this approach, the damage ratio, C (damaged modulus divided by the linear viscoelastic modulus), for each specimen tested is plotted as a function of reduced cycles, N R, at the reference temperature of 39.2 F (4 C) and the reference strain of 200 µstrain using Equation E9. where N R = N R ini f + N f N R = reduced cycles 0 E * E * LVE LVE / 0 2α ε ε 0 2α a 1 / ( T T ) 0 N R-ini = initial value of reduced cycles, prior to the selected loading period N = actual loading cycles f 0 = reference frequency f = actual test frequency E* LVE = initial (linear viscoelastic or LVE) dynamic modulus under given conditions E* LVE/0 = reference initial (LVE) dynamic modulus (the LVE modulus at 4 C was used) α = continuum damage material constant ε= applied strain level (E9) E-148

149 ε 0 = reference effective strain level ( suggested) a(t/t 0 ) = shift factor at test temperature T relative to reference temperature T 0 The values of the continuum damage material constant, α, and the shift factor, a(t/t 0 ), are then varied until the C versus N R plots for the tests at different temperatures and strain levels converge into a single continuous function. Experience has shown that the damage ratio, C, follows the following function of N R : 1 C = (E10) 1+ K ( N ) 2 R K 1 where: C = damage ratio K 1 = cycles to 50 % damage at the reference effective strain K 2 = a model constant The values of α, a(t/t 0 ), K 1 and K 2 are best determined using numerical optimization. The optimization can be performed using the Solver function in Mircosoft EXCEL. This is done by setting up a spreadsheet to compute the sum of the squared errors between the measured damage ratio and the predicted damage ratio from Equations E9 and E10. The Solver function was used to minimize the sum of the squared errors by varying the four parameters. Figures E68 through E75 are summary plots of the continuum damage analysis for the 8 mixtures included in the fatigue study. The reference temperature for the analysis was 39 F (4 C), and the reference strain was 200 µstrain. The complete continuum damage fatigue data are presented on the NCHRP 9-43 Data CD. E-149

150 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E68. Continuum Damage Analysis for 100 Gyration HMA. E-150

151 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E69. Continuum Damage Analysis for 100 Gyration Advera WMA E-151

152 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E70. Continuum Damage Analysis for 100 Gyration Evotherm WMA. E-152

153 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E71. Continuum Damage Analysis for 100 Gyration Sasobit WMA. E-153

154 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E72. Continuum Damage Analysis for 75 Gyration HMA. E-154

155 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E73. Continuum Damage Analysis for 75 Gyration Advera WMA. E-155

156 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E74. Continuum Damage Analysis for 75 Gyration Evotherm WMA. E-156

157 Low Strain 20C High Strain 20 C Low Strain 4 C High Strain 4 C Fit Damage Ratio E E E E E E E E E+08 Reduced Cycles Low Strain 20 C High Strain 20 C Low Strain 4 C High Strain 4 C Equality Predicted C Measured C Figure E75. Continuum Damage Analysis for 75 Gyration Sasobit WMA. E-157

158 Table E91 summarizes the parameters from the reduced cycles continuum damage analysis for all of the mixtures. The reduced cycles continuum damage analysis was formulated to provide a direct measure of the fatigue resistance of the mixture. Substituting 0.5 for the damage ratio, C, in Equation E10 and solving for the reduced cycles, N R, gives the fatigue half-life, or the reduced cycles to reach 50 percent damage. The WMA mixture fatigue half-lives range from approximately 70 to 170 percent of the fatigue half-life of the control HMA for the 100 gyration mixture and 70 to 92 percent for the 75 gyration mixture. This indicates that the fatigue resistance of WMA and HMA mixtures produced from the same aggregates and binders are essentially the same. Figures E76 and E77 provide further evidence of the similarity of the WMA and HMA fatigue resistance. These figures compare the fitted reduced cycles damage curves for the 100 and 75 gyration mixtures, respectively. The reduced cycles damage curves are very similar for the WMA processes and the HMA controls providing further evidence that fatigue performance of WMA and HMA mixtures produced from the same aggregates and binders will essentially be the same. Process Table E91. Summary of Continuum Damage Fatigue Parameters. Mixture Gyration Level Reference Temperature Reference Modulus, ksi α Continuum Damage Shift Factor Fatigue Half-Life K 1, 10 7 K 2 Control E Advera E Evotherm E Sasobit E Control E Advera E Evotherm E Sasobit E E-158

159 Control Advera Evotherm Sasobit Damage Ratio E E E E E E E E E+08 Reduced Cycles Figure E76. Comparison of Continuum Damage Fatigue Curves for the 100 Gyration Mix Control Advera Evotherm Sasobit Damage Ratio E E E E E E E E E+08 Reduced Cycles Figure E77. Comparison of Continuum Damage Fatigue Curves for the 75 Gyration Mix. E-159

160 E10. Summary of Findings NCHRP Project 9-43 included the design and execution of eight laboratory studies addressing critical aspects of mixture design for WMA. The major finding of these studies are summarized below: E10.1 Sample Reheating Study In the sample reheating study, dynamic modulus data were analyzed for HMA and WMA specimens that were: (1) compacted during construction and tested immediately, (2) compacted during construction and tested weeks later, and (3) produced by reheating loose-mix sampled during construction. The sample reheating study found that WMA and HMA mixtures are similarly affected by reheating. Mixture stiffness increases significantly upon reheating especially over the middle portion of the dynamic modulus master curve, which is most sensitive to changes in binder stiffness. Reheating times and temperature for both WMA and HMA should be limited to minimize this effect. Additionally, the stiffening effect must be considered when drawing conclusions from tests on specimens produced using reheated samples. E10.2 Binder Grade Study The binder grade study used the RTFOT to simulate the effect that changes in production temperature have on the short-term aging of asphalt binder in mixtures. High and low temperature performance grading properties were measured on binder samples that were conditioned in the RTFOT at temperatures covering the range used in WMA and HMA production. The study found that the high temperature grade of the binder was significantly affected by the RTFOT temperature while the low temperature grade was only minimally affected. A reduction in the RTFOT temperature from 325 to 230 F (163 to 110 C) reduced the high temperature grade of the binder 4.0 to 7.0 C, but only improved the low temperature grade 0.5 to 2.0 C. The high temperature grade changes were large enough that high temperature grade bumping rules were developed. The rules considered the grade of binder specified, the planned WMA production temperature, and the sensitivity of the binder to aging. The low temperature grade improvements were not sufficient to warrant changes in low temperature binder grade selection for WMA. The low temperature grade improvement, however, can be significant when RAP blending charts are used. E-160

161 E10.3 Short-Term Conditioning Study In the short-term conditioning study properties of field mixed, laboratory compacted samples were compared to laboratory mixed, laboratory compacted samples that were conditioned for different times at the compaction temperature. The properties that were measured were: (1) maximum specific gravity, (2) dynamic moduli, and (3) tensile strength. The study found that 2 hours of oven conditioning at the compaction temperature reasonably reproduced the binder absorption and stiffening that occurs during construction in both WMA and HMA mixtures. E10.4 Recycled Asphalt Pavement (RAP) Study The RAP study investigated whether RAP and new binders mix at WMA process temperatures. The study included an interfacial mixing experiment that used atomic force microscopy to characterize thin films of new binder cast on thin films of aged binder and thermally cycled. This experiment found that the structure at interfacial contact lines between the new and aged binder changed with thermal cycling indicating that the two binders were mixing. This finding was confirmed through a laboratory mixing experiment. In the laboratory mixing experiment, HMA and WMA mixtures incorporating RAP were prepared at different temperatures and short-term conditioned for times ranging from 0.5 hours to 2.0 hours. The amount of mixing was quantified by comparing dynamic moduli measured on samples of the mixtures with dynamic moduli estimated using binder recovered from the mixtures. The measured dynamic moduli represented the as mixed condition, the estimated moduli represented the fully blended condition. A measured to estimated dynamic modulus ratio approaching one indicated a high degree of mixing of the RAP and new binders. This experiment found that time at elevated temperature is an important consideration in the mixing of RAP and new binders. For short-term conditioning at the compaction temperature for 0.5 and 1.0 hours, little mixing of the new and RAP binders occurred. However, for 2 hours of short-term conditioning at the compaction temperature, nearly complete mixing occurred even for WMA conditioned at 212 F, (100 C). E-161

162 E10.5 Workability Study The workability study evaluated the feasibility of using various workability devices and the gyratory compactor to measure WMA workability and compactability during the mixture design process. The workability study demonstrated that it is possible to measure differences in the workability and compactability of WMA compared to HMA. The differences, however, were only significant at temperatures that are below typical WMA discharge temperatures. Since the workability devices were not able to discriminate more precisely than compaction data obtained from a standard Superpave gyratory compactor, a method for evaluating the temperature sensitivity of the compactability of WMA was developed for assessing WMA workability and compactability. It involves determining the number of gyrations to 8 percent air voids at the proposed compaction temperature and a second temperature that is 54 F (30 C) lower than the proposed compaction temperature. A tentative limit allowing a 25 percent increase in the number of gyrations when the temperature is decreased was developed. E10.6 Mix Design Study In the mix design study, mixtures using the same asphalt binder and aggregate were designed as HMA and WMA and properties of the mixtures were compared. The HMA designs were done in accordance with AASHTO R35. The WMA designs followed the revised preliminary procedures developed in NCHRP The mix design study found little difference in the volumetric properties of WMA and HMA designed using the same asphalt binder and aggregates. However, the compactability, moisture sensitivity, and rutting resistance of the WMA may be significantly different than the HMA. Each of these properties is evaluated directly in the recommended WMA mixture design methods Field Validation Study The field validation study used mixtures from field WMA projects to assess several parts of the revised WMA procedures including: Binder grade selection, RAP, Short-term oven conditioning, E-162

163 Specimen fabrication, Coating and compactability, Moisture sensitivity, and Flow number. Grading of binders recovered from the field validation projects did not support that the high temperature grade changes developed from the binder grade selection study. The high temperature grade changes were significantly less than estimated from the RTFOT experiment while the low temperature grade improvement were somewhat greater than estimated by the RTFOT experiment. Based on the recovered binder testing, it does not appear that the binder grade should be changed when using WMA as long as the production temperature is not decreased by more than 100 F (56 C). Only one of the field validation mixtures incorporated RAP. This mixture was produced using the Astec Double Barrel Green process and included 30 percent RAP. The mixing analysis that was conducted for this mixture found that there was a high degree of mixing of the RAP and new binders. Comparisons of maximum specific gravity and tensile strength measurements for laboratory prepared mixtures with field mixed samples of WMA and HMA from the validation mixtures confirmed that 2 hours of conditioning at the compaction temperature reasonably simulates the binder absorption and stiffening that occurs during construction. Comparisons of volumetric properties of laboratory prepared WMA and HMA mixtures from the field validation mixtures demonstrated the engineering reasonableness of the WMA mixture design method developed in NCHRP Project Mixtures for several WMA processes including: (1) Advera synthetic zeolite; (2) Evotherm chemical additive; (3) the sequential mixing LEA process; and (4) two plant foaming processes, Astec Double Barrel Green and Gencor Ultrafoam GX were successfully produced and evaluated in the laboratory. For replicating the plant foaming processes a Wirtgen WLB-10 laboratory foaming device was used. Although it was possible to prepare foamed asphalt WMA mixtures in the laboratory using this E-163

164 device, several improvements are needed before it or similar devices can be used routinely in the laboratory. Coating for laboratory mixtures was found to sensitive to the type of mechanical mixer that was used. Most of the mixtures used in NCHRP Project 9-43 were prepared with a planetary mixer with wire whip, and the coating for all these mixtures was nearly 100 percent. A bucket mixer was used with two mixtures and the coating was significantly lower. The mixing times included in the Draft Appendix to AASHTO R35 are based on the planetary mixer. If a bucket mixer is used, appropriate mixing times need to be determined by evaluating coating of HMA mixtures produced at the appropriate viscosity based mixing temperature specified in Section of AASHTO T312. The compactability criteria developed in the workability study were found to be reasonable based on the reported compactability of the validation mixtures. The moisture sensitivity of WMA as measured by AASHTO T283 will likely be different for WMA and HMA mixtures produced using the same asphalt binder and aggregates. The effect of the WMA process on the moisture sensitivity is mixture and process specific. The tensile strength ratio relative to the HMA control decreased in 6 of 10 validation mixtures that included an HMA control. The tensile strength ratio remained the same for 3 of 10 mixtures. It increased for one of the 10 mixtures. Rutting resistance as measured by the flow number test on specimens of WMA prepared from laboratory mixtures that were conditioned for 2 hours at the compaction temperature was lower than that measured for HMA. The lower compaction temperature significantly reduces the flow number measured for WMA. Current criteria for the flow number and other rutting tests for HMA are based on 4 hours of short-term conditioning at 275 F (135 C). The short-term conditioning study completed in NCHRP Project 9-43 shows that this level of conditioning represents the stiffening that occurs during construction as well as some time in-service. Since it is inappropriate to condition WMA mixtures at temperatures exceeding their production temperature, the criteria for evaluating the rutting resistance of WMA mixtures were reduced compared to those currently recommended for HMA conditioned for 4 hours at 275 F (135 C). Based on an analysis of data from NCHRP Project 9-13, it appears feasible to reach E-164

165 approximately the same level of binder stiffening in HMA that occurs in 4 hours at 275 F (135 C) using a two step aging process: 2 hours at the compaction temperature to simulate construction effects, followed by extended loose mix conditioning at a representative high inservice pavement temperature to represent early in-service aging. E10.8 Fatigue Study The fatigue study used reduced cycles continuum damage analysis to evaluate differences in fatigue characteristics for WMA and HMA mixture produced with the same asphalt binder and aggregates. This study found that there was little difference in the fatigue characteristics of WMA and HMA mixtures having the same composition. E-165

166 E11. Production Records for Pennsylvania SR2006 WMA Demonstration Project E-166

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