Evaluation of the AIMS-II and Micro-Deval for Friction Characteristics of Aggregates by Mary Greer A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Master of Science Auburn, Alabama May 10, 2015 Key Words: AIMS, Micro-Deval, Skid Resistance, Surface Texture, Pavement Friction, Hot-Mix Asphalt Copyright 2015 by Mary Greer Approved by Richard Willis, Chair, Associate Research Professor for Civil Engineering Michael Heitzman, Co-chair, Assistant Director of the National Center for Asphalt Technology David Timm, Brasfield & Gorrie Professor for Civil Engineering Mary Robbins, Assistant Research Professor for Civil Engineering ABSTRACT There is a need for a rapid quantitative way to evaluate the quality of aggregate friction properties for use in an asphalt surface (wearing) course. Aggregates that are resistant to polishing and capable of retaining their shape characteristics are desirable in the asphalt wearing course. The wearing course should be capable of maintaining an adequate amount of friction when subjected to polishing due to heavy traffic in order to ensure the safety of the roadway. Current laboratory procedures used to evaluate the friction properties of aggregates are said to be time consuming and subjective. The purpose of this research study was to evaluate the correlation between aggregate performance in a laboratory test consisting of the second generation Aggregate Imaging Measurement System (AIMS-II) and Micro-Deval to field friction performance. The AIMS-II device was used to quantify aggregate shape characteristics (angularity, texture, and form) before conditioning (polishing) and after conditioning in the Micro-Deval at different increments of time. The aggregates used for testing were selected based on their friction performance in surface courses at the National Center for Asphalt Technology (NCAT) Pavement Test Track. Field friction performance data for the selected test sections was obtained using the locked-wheel skid trailer. Aggregate shape indexes, more specifically, angularity and texture, were compared with the results obtained from the skid trailer in the field to see if a correlation could be established. ii The results showed the AIMS-II device was capable of detecting changes in aggregate shape characteristics when subjected to conditioning in the Micro-Deval. However, the analysis showed a good correlation between the AIMS-II indexes and the field friction data could not be established with the procedure that was used in this research study. This research study was a useful step in working towards developing a test method that may use the AIMS-II in conjunction with the Micro-Deval to predict the skid resistance of an asphalt wearing course mixture in the field. Future research is needed to enhance the test method used in this research study and take other factors into consideration that affect field friction performance. iii ACKNOWLEDGEMENTS The author would like to thank Dr. Richard Willis and Dr. Michael Heitzman for all of their guidance and support throughout writing this thesis. Their dedication and patience throughout the process were greatly appreciated, and this research would not have been possible without their assistance. The author would also like to thank all of the committee members, including Dr. David Timm and Dr. Mary Robbins, for their feedback with this thesis as well as their valued guidance throughout graduate school and Dr. Saeed Maghsoodloo for his help with the statistical analysis. Also, the author greatly appreciates the National Center for Asphalt Technology laboratory personnel for completing any work asked of them that was needed to complete this research study. Lastly, a special thanks to Dr. Randy West for giving the author the opportunity to work at NCAT and complete a Master’s Degree with their program. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................................. ii ACKNOWLEDGEMENTS ...................................................................................................... iv LIST OF TABLES ..................................................................................................................... xi LIST OF FIGURES ................................................................................................................. xiv LIST OF ABBREVIATIONS .................................................................................................. xx CHAPTER 1 INTRODUCTION ............................................................................................... 1 1.1 Background ......................................................................................................................... 1 1.2 Project Objectives ............................................................................................................... 2 1.3 Scope of Work .................................................................................................................... 2 CHAPTER 2 LITERATURE REVIEW ................................................................................... 4 2.1 Pavement Friction Overview .............................................................................................. 4 2.2 Factors Affecting Pavement Friction .................................................................................. 6 2.3 Pavement Texture ............................................................................................................... 6 2.4 Measuring Friction .............................................................................................................. 7 v 2.4.1 British Pendulum Tester (BPT) ................................................................................... 8 2.4.2 Dynamic Friction Tester (DFT) ................................................................................... 9 2.4.3 Locked-Wheel Skid Trailer ........................................................................................ 11 2.4.4 Lab Test Correlations with Locked-Wheel Skid Trailer ............................................ 14 2.5 Measuring Mixture Surface Texture ................................................................................. 17 2.5.1 Volumetric Sand Patch Test ....................................................................................... 17 2.5.2 Circular Texture Meter (CTM) .................................................................................. 18 2.5.3 Laser Texture Scanner (LTS)..................................................................................... 21 2.6 Existing Laboratory Conditioning Devices ...................................................................... 23 2.6.1 Los Angeles (L.A.) Abrasion Test ............................................................................. 24 2.6.2 Micro-Deval Aggregate Conditioning Test ............................................................... 26 2.6.3 L.A. Abrasion and Micro-Deval Test Differences ..................................................... 29 2.6.4 British Polishing Wheel ............................................................................................. 30 2.6.5 NCAT Three Wheel Polishing Device (TWPD) ....................................................... 31 2.7 Aggregate Imaging Systems ............................................................................................. 32 2.7.1 The second generation Aggregate Imaging Measurement System (AIMS-II) .......... 32 vi 2.7.2 The Enhanced University of Illinois Aggregate Image Analyzer (E-UIAIA) ........... 34 2.8 Relevant Research on AIMS ............................................................................................. 35 2.9 Summary of Literature Review ......................................................................................... 44 CHAPTER 3 AIMS-II TEST DESCRIPTION ...................................................................... 45 3.1 AIMS-II Coarse Aggregate Testing .................................................................................. 46 3.2 AIMS-II Fine Aggregate Testing ...................................................................................... 50 3.3 AIMS-II Shape Properties................................................................................................. 52 3.3.1 Aggregate Angularity................................................................................................. 52 3.3.2 Surface Micro-texture ................................................................................................ 54 3.3.3 Aggregate Form ......................................................................................................... 55 3.3.4 Flat and Elongated Properties .................................................................................... 57 CHAPTER 4 EXPERIMENTAL PLAN ................................................................................ 59 4.1 Research Plan .................................................................................................................... 59 4.2 Material Selection ............................................................................................................. 59 4.2.1 Field Data ................................................................................................................... 61 4.2.1.1 Selection of NCAT Test Track Pavement Sections ............................................ 62 vii 4.2.1.2 Locked-Wheel Skid Trailer Measurements ........................................................ 63 4.3 Test Procedure .................................................................................................................. 64 4.3.1 Coarse Aggregate Micro-Deval/ AIMS-II Testing Procedure ................................... 64 4.3.2 Fine Aggregate Micro-Deval/ AIMS-II Testing Procedure ....................................... 66 4.3.3 Selection of Sample Size ........................................................................................... 68 4.4 Data Quality Control ......................................................................................................... 73 4.4.1 Defining Outliers ....................................................................................................... 73 4.4.2 Test Repeatability ...................................................................................................... 76 CHAPTER 5 LABORATORY RESULTS AND DISCUSSION .......................................... 78 5.1 Micro-Deval Aggregate Mass Loss .................................................................................. 78 5.2 AIMS-II Aggregate Angularity......................................................................................... 81 5.3 AIMS-II Coarse Aggregate Texture ................................................................................. 87 5.4 AIMS-II Aggregate Form ................................................................................................. 91 5.4.1 AIMS-II Coarse Aggregate Sphericity ...................................................................... 91 5.4.2 AIMS-II Coarse Aggregate Flatness and Elongated (F&E) Ratios ........................... 92 5.4.3 AIMS-II Fine Aggregate Two-Dimensional Form (Form2D) ................................... 93 viii 5.5 Summary of Lab Results ................................................................................................... 97 CHAPTER 6 COMPARISON OF AIMS-II LAB RESULTS AND FIELD FRICTION .. 99 6.1 Field Results...................................................................................................................... 99 6.1.1 Defining “Terminal Friction” .................................................................................. 101 6.2 Comparing AIMS-II Aggregate Angularity to Field Friction Performance ................... 102 6.2.1 AIMS-II Coarse Aggregate Angularity and SN40R ................................................ 103 6.2.2 AIMS-II Fine Aggregate Angularity and SN40R .................................................... 107 6.3 Comparing AIMS-II Texture to Field Friction Performance .......................................... 110 6.4 Comparing Micro-Deval Mass Loss to Field Friction Performance .............................. 113 6.5 Statistical Analysis for Comparison Results ................................................................... 114 6.6 Summary of Comparison Results ................................................................................... 126 CHAPTER 7 CONCLUSION AND RECOMMENDATIONS .......................................... 128 REFERENCES ........................................................................................................................ 132 APPENDICES ......................................................................................................................... 136 Appendix A: Minitab Graphical Summaries of AIMS-II Index Distributions after each Micro-Deval Conditioning Interval ................................................................ 137 ix Appendix B: AIMS-II Test Repeatability for Angularity, Texture, and Two-Dimensional Form Results ................................................................................................... 171 Appendix C: Cumulative Distribution Trends for AIMS-II Results .................................... 177 Appendix D: Kolmogorov-Smirnov Test Results for AIMS-II Cumulative Distributions .. 188 Appendix E: Detailed Statistical Output ............................................................................... 191 x