Investigating the Relationship of As-Constructed Asphalt Pavement Air Voids to Pavement Performance (2021)

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4 C O N T E N T S PART I: RESEARCH OVERVIEW ..........................................................................................11 Summary ...................................................................................................................................... 13 Background ................................................................................................................................. 17 Research Approach .................................................................................................................... 19 Objective and Scope ............................................................................................................................. 19 Methodology ......................................................................................................................................... 19 Overview of the LTPP Dataset ........................................................................................................................... 19 Overview of Datasets for Validation .................................................................................................................. 24 Initial LTPP Data Extraction .............................................................................................................................. 24 Additional LTPP Data for Analysis Methods 2 and 3 ....................................................................................... 25 Analysis ................................................................................................................................................. 38 Analysis Method 1: Common Data Subgroups ................................................................................................. 39 Analysis Method 2: Regression Modeling ............................................................................................. ...........52 Analysis Method 3: Artificial Neural Network Modeling ................................................................................. 79 Validation of Analysis Methods .......................................................................................................... 95 Validation of Analysis Method 1 Using Pavement ME Design ........................................................................ 95 Assembling MnROAD and NCAT Validation Datasets ................................................................................... 98 Validation of Analysis Method 1 Using MnROAD and NCAT Datasets ....................................................... 113 Validation of Analysis Method 2 Using MnROAD and NCAT Datasets ....................................................... 123 Validation of Analysis Method 3 Using MnROAD and NCAT Data ............................................................. 129 Findings and Applications ....................................................................................................... 132 Conclusions and Suggested Research ..................................................................................... 135 User Guide ................................................................................................................................. 138 Implementation Plan ................................................................................................................ 139 References .................................................................................................................................. 141 Appendix .................................................................................................................................... 142 LTPP Data Set .................................................................................................................................... 142 LTPP Expanded Data Set .................................................................................................................. 142 Pavement ME Design Validation Data Set ...................................................................................... 142 MnROAD Validation Data Set ......................................................................................................... 142 NCAT Validation Data Set ................................................................................................................ 142 PART II: USER GUIDE ........................................................................................................... 143 Preface ........................................................................................................................................ 144 Acknowledgments ..................................................................................................................... 145 List of Abbreviations ................................................................................................................ 146

5 Background .............................................................................................................................. 147 Study Conclusions .................................................................................................................................. 150 USER INSTRUCTIONS ......................................................................................................... 153 Local Validation ..................................................................................................................................... 154 Using the Models .................................................................................................................................... 155 Analysis Method 1 Subgroup Scatter Plots ..................................................................................... ................156 Analysis Method 2 Regression Models ........................................................................................................... 158 Using Analysis Method 3 ANN Models .......................................................................................................... 168 Methods Summary Chart ................................................................................................................................. 177 Regional Analysis Approach .................................................................................................................. 178 Analysis Method 1 Subgroup Scatter Plots ..................................................................................................... 179 Using Analysis Method 2 Regression Models ................................................................................................. 180 Analysis Method 3 ANN Models .................................................................................................................... 182 Appendix – Analysis Method 1 Subgroup Performance Trend Charts............................... 184

6 T A B L E S P A R T I : R E S E A R C H O V E R V I E W Table 2-1. LTPP sections used in this study. .............................................................................................................. 19 Table 2-2. Summary statistics of complete section attributes dataset for all analysis periods. ................................... 35 Table 2-3. Main characteristics of the data tables developed for Analysis Methods 2 and 3. .................................... 37 Table 2-4. Comparison of abbreviations used in Analysis Methods 2 and 3 .............................................................. 38 Table 2-5. Distribution of LTPP sections into subgroups for new and rehab pavements. .......................................... 43 Table 2-6. Comparing ride and wheel path cracking trends. ...................................................................................... 50 Table 2-7. Summary of as-constructed air voids impact on rutting performance. ...................................................... 50 Table 2-8. Summary of as-constructed air voids impact on fatigue cracking performance. ....................................... 51 Table 2-9. Summary of as-constructed air voids impact on thermal cracking performance. ...................................... 51 Table 2-10. Summary of as-constructed air voids impact on ride performance. ........................................................ 52 Table 2-11. List of variables used for Analysis Method 2 regression models. ........................................................... 52 Table 2-12. Summary statistics of data used for estimating rutting model for new pavements. ................................. 57 Table 2-13. Estimated parameters of rutting model for new pavements. ................................................................... 58 Table 2-14. Summary statistics of data used for estimating rutting model for rehabilitated pavements. ................... 59 Table 2-15. Estimated parameters of rutting model for rehabilitated pavements. ...................................................... 60 Table 2-16. Summary statistics of data used for estimating fatigue cracking model for new pavements................... 63 Table 2-17. Estimated parameters of fatigue cracking model for new pavements. .................................................... 64 Table 2-18. Summary statistics of data used for estimating fatigue cracking model for rehabilitated pavements. .... 65 Table 2-19. Estimated parameters of fatigue cracking model for rehabilitated pavements. ....................................... 66 Table 2-20. Summary statistics of data used for estimating thermal cracking after crack initiation model for new pavements. ................................................................................................................................................................... 70 Table 2-21. Estimated parameters of thermal cracking model for new pavements. ................................................... 71 Table 2-22. Summary statistics of data used for estimating thermal cracking model for rehabilitated pavements. ... 72 Table 2-23. Estimated parameters of thermal cracking model for rehabilitated pavements. ...................................... 73 Table 2-24. Summary statistics of data used for estimating ride model for new pavements. ..................................... 75 Table 2-25. Estimated parameters of ride model for new pavements. ........................................................................ 76 Table 2-26. Summary statistics of data used for estimating ride model for rehabilitated pavements. ........................ 77 Table 2-27. Estimated parameters of ride model for rehabilitated pavements. ........................................................... 78 Table 2-28. Number of pavement sections and data sets development of ANN models. ........................................... 80 Table 2-29. Input variables of ANN performance models. ......................................................................................... 81 Table 2-30. Input variables required for each ANN performance model. .................................................................. 82 Table 2-31. Architecture of ANN performance models. ............................................................................................ 82 Table 2-32. LTPP sections selected for PaveME software assessment. ..................................................................... 95 Table 2-33. Comparison of PaveME predicted trends to Analysis Method 1 observed trends. .................................. 97 Table 2-34. MnROAD’s available databases. ............................................................................................................. 99 Table 2-35. MnROAD flexible pavement test sections used for validation. .............................................................. 99 Table 2-36. MnROAD’s weather and traffic data. ................................................................................................... 100 Table 2-37. MnROAD’s pavement sections input data. ........................................................................................... 101 Table 2-38. Ride quality and rutting at MnROAD. .................................................................................................. 104 Table 2-39. Cracking parameters at MnROAD. ....................................................................................................... 106 Table 2-40. NCAT’s available flexible pavement test sections. ............................................................................... 107 Table 2-41. NCAT’s available database sources. ..................................................................................................... 107 Table 2-42. NCAT’s weather data. ........................................................................................................................... 108 Table 2-43. Summary of NCAT’s pavement sections. ............................................................................................. 110 Table 2-44. Summary of NCAT’s ride quality and rutting performance. ................................................................. 112 Table 2-45. NCAT’s wheel path cracking performance. .......................................................................................... 113 Table 2-46. New pavements ride F-test results. ........................................................................................................ 125 Table 2-47. Rehabilitated pavements ride F-test results. .......................................................................................... 126 Table 2-48. New pavements rutting F-test results. ................................................................................................... 127 Table 2-49. Rehabilitated pavements rutting F-test results. ...................................................................................... 128 Table 2-50. New pavements wheel path cracking F-test results. .............................................................................. 128

7 Table 2-51. New pavements transverse cracking F-test results. ............................................................................... 129 Table 2-52. Artificial neural network F-test results .................................................................................................. 131 Table 4-1. Summary of all analysis methods. ........................................................................................................... 135 Table 4-2. Summary of the validation. ..................................................................................................................... 136 P A R T I I : U S E R G U I D E Table 1. Input and Output Dataset Summary ............................................................................................................. 148 Table 2. Summary Statistics of Pavement Section Input Datasets ............................................................................. 149 Table 3. Subgroup Parameters and Ranges................................................................................................................ 156 Table 4. Performance Criteria Used for Analysis Method 1 ...................................................................................... 156 Table 5. Input Variables Used for Analysis Method 2 Regression Models ............................................................... 158 Table 6. Required User Input Dataset for All Models ............................................................................................... 159 Table 7. Model Parameters for Each Performance Characteristic and Pavement Type .......................................................................................................................................................... 159 Table 8. Input Variables for ANN Pavement Performance Models .......................................................................... 169 Table 9. Input Variables of ANN Performance Models ............................................................................................ 169 Table 10. ANN Model Inputs for LTPP Section 01-0105 ......................................................................................... 170 Table 11. ANN Model Inputs for LTPP Section 09-0960. ........................................................................................ 170 Table 12. ANN Model Inputs for LTPP Section 05-0115 ......................................................................................... 171 Table 13. ANN Model Inputs for LTPP Section 09-0902 ......................................................................................... 172 Table 14. ANN Model Inputs for LTPP Section 31-0122 ......................................................................................... 173 Table 15. ANN Model Inputs for LTPP Section 53-6056 ......................................................................................... 174 Table 16. ANN Model Inputs for LTPP Section 31-0122 ......................................................................................... 175 Table 17. ANN Model Inputs for LTPP Section 53-6020 ......................................................................................... 176 Table 18 Summary of All Analysis Methods ............................................................................................................ 178 Table 19. Generic Dataset Format Sorted into Eight Analysis Subgroups ................................................................ 180 Table 20. Architecture of ANN Performance Models for The NCHRP Study .......................................................... 182

8 F I G U R E S P A R T I : R E S E A R C H O V E R V I E W Figure 1-1. Availability of LTPP data. ....................................................................................................................... 18 Figure 2-1. Geographic distribution of selected LTPP sections (green=active, red=out of study). ............................ 20 Figure 2-2. Distribution of selected LTPP sections in each LTPP climate zone. ....................................................... 21 Figure 2-3. Distribution of selected LTPP sections by pavement structure. ............................................................... 21 Figure 2-4. Distribution of selected LTPP sections by traffic. ................................................................................... 22 Figure 2-5. Correlation of pavement structure and traffic for selected LTPP sections. .............................................. 22 Figure 2-6. Distribution of selected LTPP sections by as-constructed air voids. ....................................................... 23 Figure 2-7. Distribution of selected LTPP sections by duration of monitoring period. .............................................. 23 Figure 2-8. Distribution of selected LTPP sections by number of performance measures. ........................................ 24 Figure 2-9. Location of LTPP sections initially selected for analysis. ....................................................................... 26 Figure 2-10. Percent of missing data for each variable. .............................................................................................. 31 Figure 2-11. Distribution of original values and with imputed values for selected variables. .................................... 33 Figure 2-12. Timeline of construction events and milestone dates for Kansas LTPP section 20-0110. ..................... 34 Figure 2-13. Distribution of LTPP sections by LTPP and study climate zones. ......................................................... 41 Figure 2-14. Distribution of LTPP section by average annual temperature. ............................................................... 41 Figure 2-15. Distribution of LTPP section by average annual precipitation. ............................................................. 42 Figure 2-16. Distribution of LTPP sections by traffic for new and rehab pavements................................................. 42 Figure 2-17. Distribution of LTPP sections by pavement structure for new and rehab pavements. ............................ 43 Figure 2-18. Examples of influence of as-constructed air voids on rutting performance. .......................................... 45 Figure 2-19. Examples of the influence of as-constructed air voids on fatigue performance. .................................... 46 Figure 2-20. Years of performance monitoring for LTPP sections with no transverse cracking. ............................... 47 Figure 2-21. Distribution of time to initial transverse crack. ...................................................................................... 47 Figure 2-22. Examples of influence of as-constructed air voids on thermal cracking performance. .......................... 48 Figure 2-23. Examples of the influence of as-constructed air voids on ride performance. ......................................... 49 Figure 2-24. Boxplots of scaled variables considered for ride performance models. ................................................. 54 Figure 2-25. Median rutting versus age grouped by surface air voids quintiles. ........................................................ 55 Figure 2-26. Comparison of new pavement rutting performance between LTPP measurements and regression model predictions. .................................................................................................................................................................. 58 Figure 2-27. Comparison of rehabilitated pavement rutting performance between LTPP measurements and regression model predictions. ...................................................................................................................................... 61 Figure 2-28. Median scaled cracking percent versus age grouped by mean air voids quintiles. ................................ 62 Figure 2-29. Comparison of new pavement fatigue cracking performance between LTPP measurements and regression model predictions. ...................................................................................................................................... 65 Figure 2-30. Comparison of rehabilitated pavement fatigue cracking performance between LTPP measurements and regression model predictions. ...................................................................................................................................... 67 Figure 2-31. Probability of zero surface thermal cracking over time grouped by surface air voids quintiles............. 68 Figure 2-32. Median thermal cracking after crack initiation versus age grouped by surface air voids quintiles. ....... 69 Figure 2-33. Comparison of new pavement thermal cracking performance between LTPP measurements and regression model predictions. ...................................................................................................................................... 71 Figure 2-34. Comparison of rehabilitated pavement thermal cracking performance between LTPP measurements and regression model predictions. ............................................................................................................................... 73 Figure 2-35. Median IRI versus age grouped by surface air voids quintiles............................................................... 74 Figure 2-36. Comparison of new pavement ride performance between LTPP measurements and regression model predictions. .................................................................................................................................................................. 76 Figure 2-37. Comparison of rehabilitated pavement ride performance between LTPP measurements and regression model predictions. ....................................................................................................................................................... 79 Figure 2-38. Illustration of four-layered neural network architecture. ....................................................................... 81 Figure 2-39. Comparisons of rutting performance between LTPP measurements and ANN model predictions. ...... 83 Figure 2-40. Comparisons of fatigue cracking performance between LTPP measurements and ANN model predictions. .................................................................................................................................................................. 84

9 Figure 2-41. Comparisons of transverse cracking performance between LTPP measurements and ANN model predictions. .................................................................................................................................................................. 85 Figure 2-42. Comparisons of ride performance between LTPP measurements and ANN model predictions. ........... 85 Figure 2-43. Prediction accuracy of ANN rutting models using test data. ................................................................. 86 Figure 2-44. Prediction accuracy of ANN fatigue cracking models using test data. .................................................. 87 Figure 2-45. Prediction accuracy of ANN transverse cracking models using test data. ............................................. 88 Figure 2-46. Prediction accuracy of ANN ride models using test data. ...................................................................... 89 Figure 2-47. ANN model predicted influence of air voids on rut depth. .................................................................... 90 Figure 2-48. ANN model predicted influence of air voids on fatigue cracking. ......................................................... 91 Figure 2-49. ANN model predicted influence of air voids on transverse cracking. .................................................... 92 Figure 2-50. ANN model predicted influence of air voids on ride performance. ....................................................... 93 Figure 2-51. ANN model predicted influence of air voids on ride performance at the 10th year. .............................. 94 Figure 2-52. Example of actual rutting performance curves of LTPP pavement sections. ......................................... 95 Figure 2-53. Example of MnROAD’s 1993 cycle typical ride performance curve. ................................................. 102 Figure 2-54. Example of MnROAD’s 2008 cycle typical ride performance curve. ................................................. 102 Figure 2-55. Example of MnROAD’s 1993 cycle typical rutting performance. ....................................................... 103 Figure 2-56. Example of MnROAD’s 1993 Cycle Typical Rutting Performance Curve. ........................................ 103 Figure 2-57. Example of MnROAD’s typical wheel path cracking performance curve. .......................................... 105 Figure 2-58. Example of MnROAD’s typical thermal cracking performance curve. ............................................... 105 Figure 2-59. NCAT Test Track original pavement layers. ....................................................................................... 109 Figure 2-60. Example of new sections built after 2003. ........................................................................................... 109 Figure 2-61. Example of time shift on NCAT rutting performance curves. ............................................................. 110 Figure 2-62. Cumulative ESALs on NCAT sections over an adjusted 10-year cycle. ............................................. 111 Figure 2-63. Example of NCAT section typical ride quality performance. .............................................................. 111 Figure 2-64. Example of NCAT section typical wheel path cracking performance curves. ..................................... 112 Figure 2-65. MnROAD versus LTPP rutting tendencies CL1-LOW-THIN. ............................................................ 114 Figure 2-66. MnROAD versus LTPP rutting tendencies CL1-HIGH-THK. ............................................................ 114 Figure 2-67. MnROAD rutting tendencies CL1-HIGH-MED. ................................................................................. 114 Figure 2-68. MnROAD versus LTPP wheel path cracking tendencies CL1-LOW-THIN. ...................................... 115 Figure 2-69. MnROAD versus LTPP wheel path cracking tendencies CL1-HIGH-THK. ....................................... 115 Figure 2-70. MnROAD wheel path cracking tendencies CL1-HIGH-MED. ........................................................... 116 Figure 2-71. MnROAD versus LTPP thermal cracking tendencies CL1-LOW-THIN............................................. 116 Figure 2-72. MnROAD versus LTPP thermal cracking tendencies CL1-HIGH-THK. ............................................ 117 Figure 2-73. MnROAD thermal cracking tendencies CL1-HIGH-MED. ................................................................. 117 Figure 2-74. MnROAD versus LTPP ride tendencies CL1-LOW-THIN. ................................................................ 118 Figure 2-75. MnROAD versus LTPP ride tendencies CL1-HIGH-THK. ................................................................. 118 Figure 2-76. MnROAD ride tendencies CL1-HIGH-MED. ..................................................................................... 118 Figure 2-77. NCAT versus LTPP rutting tendencies CL4-HIGH-MED. ................................................................. 119 Figure 2-78. NCAT rutting tendencies CL4-HIGH-THK. ....................................................................................... 119 Figure 2-79. NCAT rutting tendencies CL4-HIGH-LOW. ....................................................................................... 120 Figure 2-80. NCAT rutting tendencies CL4-HIGH-THK (rehabilitation). ............................................................... 120 Figure 2-81. NCAT versus LTPP wheel path cracking tendencies CL4-HIGH-MED. ............................................ 121 Figure 2-82. NCAT wheel path cracking tendencies CL4-HIGH-THK. .................................................................. 121 Figure 2-83. NCAT versus LTPP ride tendencies CL4-HIGH-MED. ...................................................................... 122 Figure 2-84. NCAT ride tendencies CL4-HIGH-THK. ............................................................................................ 122 Figure 2-85. NCAT ride tendencies CL4-HIGH-LOW. ........................................................................................... 122 Figure 2-86. NCAT ride tendencies CL4-HIGH-THK (rehabilitation). ................................................................... 123 Figure 2-87. Observed versus predicted validation ride data (new pavements). ...................................................... 124 Figure 2-88. Box-plots of observed and predicted ride data (new pavements). ........................................................ 124 Figure 2-89. Observed versus predicted validation ride data, filtered (new pavements). ......................................... 125 Figure 2-90. Observed versus predicted validation ride data (rehabilitated pavements). ......................................... 126 Figure 2-91. Ride data error distribution. ................................................................................................................. 126 Figure 2-92. Observed versus predicted validation rutting, filtered (new pavements). ............................................ 127 Figure 2-93. Observed versus predicted validation rutting, filtered (rehabilitated pavements). ............................... 127 Figure 2-94. Observed versus predicted validation wheel path cracking, filtered (new pavements). ....................... 128 Figure 2-95. Observed versus predicted validation transverse cracking, filtered (new pavements). ........................ 129

10 Figure 2-96. Observed versus ANN predicted validation ride data. ......................................................................... 130 Figure 2-97. Observed versus ANN predicted validation rutting data. ..................................................................... 130 Figure 2-98. Observed versus ANN predicted validation wheel path cracking data. ............................................... 130 Figure 2-99. Observed versus ANN predicted validation transverse cracking data. ................................................ 131 P A R T I I : U S E R G U I D E Figure 1. Summary Flow Chart for Applying the User Guide ................................................................................... 154 Figure 2. Example of Analysis Method 1 Subgroup Summary Graphic ................................................................... 157 Figure 3. Example Influence of As-Constructed Air Voids on Predicted Rutting for New Pavements .................... 161 Figure 4. Example Influence of as-constructed air voids on predicted rutting for rehabilitated pavements .............. 162 Figure 5. Example Influence of As-Constructed Air Voids on Predicted Fatigue Cracking for New Pavements ..... 163 Figure 6. Example Influence of As-Constructed Air Voids on Predicted Reflected Fatigue Cracking for Rehabilitated Pavements .................................................................................................................................................................. 164 Figure 7. Example Influence of As-Constructed Air Voids on Predicted Thermal Cracking After Crack Initiation for New Pavements ......................................................................................................................................................... 165 Figure 8. Example Influence of As-Constructed Air Voids on Predicted Reflected Thermal Cracking After Crack Initiation for Rehabilitated Pavements ...................................................................................................................... 166 Figure 9. Example Influence of As-Constructed Air Voids on Predicted Ride for New Pavements ......................... 167 Figure 10. Example of Influence of As-Constructed Air Voids on Predicted Ride for Rehabilitated Pavements ..... 168 Figure 11. Influence of As-Constructed Air Voids on Rut Depth for LTPP Section 01-0105 .................................. 170 Figure 12. Influence of As-Constructed Air Voids on Rut Depth for LTPP Section 09-0960 .................................. 171 Figure 13. Influence of As-Constructed Air Voids on Fatigue Cracking for LTPP Section 05-0115 ....................... 172 Figure 14. Influence of As-Constructed Air Voids on Reflected Fatigue Cracking for LTPP Section 09-0902 ....... 173 Figure 15. Influence of As-Constructed Air Voids on Thermal Cracking for LTPP Section 31-0122 ...................... 174 Figure 16. Influence of As-Constructed Air Voids on Reflected Thermal Cracking for LTPP Section 53-6056 ...... 175 Figure 17. Influence of As-Constructed Air Voids on Ride for LTPP Section 31-0122 ........................................... 176 Figure 18. Influence of As-Constructed Air Voids on Ride for LTPP Section 53-6020 ........................................... 177

11 A B B R E V I A T I O N S This list does not include standard units of measure, LTPP database variable names, or equation variables. AADTT annual average daily truck traffic AASHTO American Association of State Highway and Transportation Officials AC asphalt concrete AIC Akaike information criterion ANN Artificial Neural Network AV air voids AVw or AV_m as-constructed air voids weighted average for all asphalt layers combined, computed from %Gmm, also expressed as %Gmm_m AVt or AV_s as-constructed air voids for the surface (top) asphalt layer, computed from %Gmm, also expressed as %Gmm_s BSB base and subbase DRY FRZ climate zone with low precipitation and low temperatures DRY NO climate zone with low temperature and high temperatures ESAL equivalent single axle load FHWA Federal Highway Administration FI freezing index Gmm asphalt mixture maximum specific gravity GPS LTPP general pavement study HPMS Highway Performance Monitoring System ID LTPP test section identification code consisting of the State number and test section number IRI international roughness index kESAL equivalent single axle loads reported in thousands LTPP Long-Term Pavement Performance program MESAL equivalent single axle loads reported in millions MnROAD Minnesota Department of Transportation pavement research test track NCAT National Center for Asphalt Technology PaveME AASHTOware Pavement ME Design software package R R Programming language for statistical computing by the R Foundation for Statistical Computing SG subgrade SN structural number, related to pavement structure stiffness SPS LTPP specific pavement study WET FRZ climate zone with high precipitation and low temperatures WET NO climate zone with high precipitation and high temperatures WIM weigh-in-motion method of measuring traffic axle weight