Lab Variability of the Marshall Test Method


Download Lab Variability of the Marshall Test Method


Preview text

Inter Laboratory Variability of the Marshall Test Method
for Asphalt Concrete
FINAL REPORT WVDOH RP #137
By John P. Zaniewski, Ph.D.
Michael Hughes
Harley O. Staggers National Transportation Center Department of Civil and Environmental Engineering
West Virginia University PO Box 6103
Morgantown, WV 26506
Submitted to: West Virginia Department of Transportation
Division of Highways And
U.S. Department of Transportation Federal Highway Administration
June 2003 Revised June 2006

NOTICE The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the State or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Trade or manufacturer names which may appear herein are cited only because they are considered essential to the objectives of this report. The United States Government and the State of West Virginia do not endorse products or manufacturers. This report is prepared for the West Virginia Department of Transportation, Division of Highways, in cooperation with the US Department of Transportation, Federal Highway Administration.
i

Technical Report Documentation Page

1. Report No.

2. Government Accociation No.

3. Recipient's catalog No.

4. Title and Subtitle
Inter Laboratory Variability of the Marshall Test Method for Asphalt Concrete

5. Report Date June 2006
6. Performing Organization Code

7. Author(s)
John P. Zaniewski, Michael Hughes

8. Performing Organization Report No.

9. Performing Organization Name and Address
Harley O. Staggers National Transportation Center Department of Civil and Environmental Engineering West Virginia University P.O. Box 6103 Morgantown, WV 26506-6103

10. Work Unit No. (TRAIS) 11. Contract or Grant No.

12. Sponsoring Agency Name and Address

13. Type of Report and Period Covered

West Virginia Division of Highways 1900 Washington St. East Charleston, WV 25305

14. Sponsoring Agency Code

15. Supplementary Notes
Performed in Cooperation with the U.S. Department of Transportation - Federal Highway Administration
16. Abstract
Statistical quality control measures, such as used by the West Virginia Division of Highways (WVDOH), require quantification of the variability of the test methods to set meaningful material acceptance parameters. The Division currently uses the Marshall method for asphalt concrete mix design and quality control. The objective of this project was to determine multi-laboratory precision statements for the Marshall method that the WVDOH can use in developing statistically based quality acceptance specifications.
An inter-laboratory study was performed in accordance with ASTM standards to evaluate the multilaboratory variability of test methods. All WVDOH laboratories, two contractor laboratories and the Asphalt Technology Laboratory at West Virginia University (WVU) participated in the study. The experiment included three WVDOH asphalt concrete types. All samples were mixed at the WVU laboratory and shipped to the laboratories for compaction and testing using the Marshall method. From the results of these tests, within-laboratory and between laboratory precision statements were developed for 102mm and 152mm Marshall test specimens.

17. Key Words

Marshall Variability, Asphalt mix design

19. Security Classif. (of this 20. Security Classif. (of

report)

this page)

Unclassified

Unclassified

18. Distribution Statement

21. No. Of Pages

22. Price

126

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized

ii

Table of Contents
CHAPTER 1 INTRODUCTION ........................................................................................................ 1 1.1 Introduction ................................................................................................................................... 1 1.2 Problem Statement ....................................................................................................................... 1 1.3 Objectives ....................................................................................................................................... 2 1.4 Report Summary ........................................................................................................................... 3
CHAPTER 2 LITERATURE REVIEW .............................................................................................. 5 2.1 Introduction ................................................................................................................................... 5 2.2 Single Laboratory Variability....................................................................................................... 6 2.3 Inter-Laboratory Variability ........................................................................................................ 7 2.4 Calibration of Marshall Hammer ............................................................................................... 9 2.5 Summary ....................................................................................................................................... 11
CHAPTER 3 BUCKET MIXER TESTING .................................................................................... 12 3.1 Introduction ................................................................................................................................. 12 3.2 Mixer Description ....................................................................................................................... 13 3.3 Mixer Evaluation......................................................................................................................... 13 3.4 Mixer Capacity ............................................................................................................................. 18 3.5 Temperature Tests ...................................................................................................................... 19 3.6 Conclusion.................................................................................................................................... 21
CHAPTER 4 MIX DESIGN PROCEDURE AND SAMPLE PREPARATION................... 22 4.1 Introduction ................................................................................................................................. 22 4.2 Aggregate Preparation................................................................................................................ 22 4.3 Specimen Fabrication ................................................................................................................. 28 4.4 Specimen Testing ........................................................................................................................ 30 4.4.1 Specific Gravity ................................................................................................................. 30 4.4.2 Stability and Flow ............................................................................................................. 30 4.4.3 Maximum Theoretical Specific Gravity........................................................................ 31 4.4.4 Voids Analysis ................................................................................................................... 32 4.5 Mix Design Results ..................................................................................................................... 33 4.6 Sample Fabrication ..................................................................................................................... 37 4.7 Specimen Distribution ............................................................................................................... 38
CHAPTER 5 DATA ANALYSIS AND RESULTS ........................................................................ 40 5.1 Introduction ................................................................................................................................. 40 5.2 Test for Outliers .......................................................................................................................... 40 5.3 Preliminary Data Analysis ......................................................................................................... 40 5.4 Precision Parameters for All Data ........................................................................................... 56 5.5 Data Analysis and Precision Parameters without District 3 ............................................... 59 5.6 Analysis of Other Studies .......................................................................................................... 65 5.7 Evaluation of Questionaire Information ................................................................................ 66 5.8 Precision Statements................................................................................................................... 66 5.9 Summary of Analysis.................................................................................................................. 70
CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS .............................................. 71 6.1 Conclusions.................................................................................................................................. 71 6.2 Recommendations ...................................................................................................................... 72
Appendix A Procedure for Developing Precision Statements ....................................................... 74 Appendix B Data From Previous Studies........................................................................................... 80 Appendix C bucket Mixer Instructions.............................................................................................. 84
iii

Appendix D Mix Design Charts........................................................................................................... 85 APPENDIX E Laboratory Data........................................................................................................... 94 APPENDIX F Laboratory Instructions, Questionnaire and Data Sheets................................ 101
Questionnaire ................................................................................................................................... 103 APPENDIX G Variability Analysis Tables....................................................................................... 107
List of Figures
Figure 3.1. Diagram of Bucket Mixer .................................................................................................. 13 Figure 3.2. Isometric Drawing of Paddle ............................................................................................ 14 Figure 3.3. First Bucket Mixer Configuration .................................................................................... 15 Figure 3.5. Segregation of Aggregates with Mixer Tilted Away from Lock Stops...................... 17 Figure 4.1. Three Methods for Determining Dense Gradation Line ............................................ 24 Figure 4.2. Gradation of First Wearing 1 Sample.............................................................................. 26 Figure 4.3. Gradation for First Base 2 Sample................................................................................... 27 Figure 4.4. Base 1 Gradation ................................................................................................................. 27 Figure 4.5. Temperature-viscosity Curve for Asphalt Cement Used in the Research................ 29 Figure 4.6. Second Gradation Attempt for Wearing 1 ..................................................................... 34 Figure 4.7. Third Gradation Attempt for Wearing 1 (Greer Gradation) ...................................... 34 Figure 4.8. Forth Gradation Attempt for Wearing 1 ........................................................................ 35 Figure 4.9. Gradation for Second Base 2 Mixture (Greer Gradation)........................................... 36 Figure 5.1. Base 1 Rice Specific Gravity Variance versus Laboratory. .......................................... 46 Figure 5.2. Base 2 Rice Specific Gravity Variance versus Laboratory ........................................... 46 Figure 5.3. Wearing 1 Rice Specific Gravity Variance versus Laboratory .................................... 46 Figure 5.4. Base 1 Marshall Stability Variance versus Laboratory .................................................. 47 Figure 5.5. Base 2 Marshall Stability Variance versus Laboratory .................................................. 47 Figure 5.6. Wearing 1 Marshall Stability Variance versus Laboratory ........................................... 47 Figure 5.7. Base 1 Marshall Flow Variance versus Laboratory ....................................................... 48 Figure 5.8. Base 2 Marshall Flow Variance versus Laboratory ....................................................... 48 Figure 5.9. Wearing 1 Marshall Flow Variance versus Laboratory ................................................ 48 Figure 5.10. Base 1 Bulk Specific Gravity Variance versus Laboratory ........................................ 49 Figure 5.11. Base 2 Bulk Specific Gravity Variance versus Laboratory ........................................ 49 Figure 5.12. Wearing 1 Bulk Specific Gravity Variance versus Laboratory ................................. 49 Figure 5.13. Wearing 1 Percent Air Voids Variance versus Laboratory ....................................... 50 Figure 5.14. Base 1 Percent Air Voids Variance versus Laboratory .............................................. 50 Figure 5.15. Base 2 Percent Air Voids Variance versus Laboratory .............................................. 50 Figure 5.16. Chart of Interactions in Maximum Theoretical Specific Gravity ............................ 53 Figure 5.17. Chart of Interactions in Marshall Stability.................................................................... 54 Figure 5.18. Chart of Interactions in Marshall Flow......................................................................... 54 Figure 5.19. Chart of Interactions in Bulk Specific Gravity ............................................................ 55 Figure 5.20. Chart of Interactions in Percent Air Voids .................................................................. 55 Figure 5.21. Re-heat Temperature versus Base 1 Stability............................................................... 67 Figure 5.22. Re-heat Temperature versus Wearing 1 Stability ........................................................ 67 Figure 5.23. Plot of Re-heat Temperature versus Base 2 Stability ................................................. 67
iv

Figure D.1. Percent Air Voids Versus Asphalt Content for Base 1 .............................................. 85 Figure D.2. Stability Versus Asphalt Content for Base 1................................................................. 85 Figure D.3. Flow Versus Asphalt Content for Base 1...................................................................... 86 Figure D.4. Unit Weight Versus Asphalt Content for Base 1......................................................... 86 Figure D.5. Percent VMA Versus Asphalt Content for Base 1...................................................... 87 Figure D.6 Percent VMA Versus Asphalt Content for Base 1....................................................... 87 Figure D.7. Percent Air Voids Versus Asphalt Content for Base 2 .............................................. 88 Figure D.8. Stability Versus Asphalt Content for Base 2................................................................. 88 Figure D.9. Flow Versus Asphalt Content for Base 2...................................................................... 89 Figure D.10. Unit Weight Versus Asphalt Content for Base 2 ...................................................... 89 Figure D.11. Percent VMA Versus Asphalt Content for Base 2 ................................................... 90 Figure D.12. Percent VFA Versus Asphalt Content for Base 2..................................................... 90 Figure D.13. Percent Air Voids Versus Asphalt Content for Wearing 1...................................... 91 Figure D.14. Stability Versus Asphalt Content for Wearing 1........................................................ 91 Figure D.15. Flow Versus Asphalt Content for Wearing 1............................................................. 92 Figure D.16. Unit Weight Versus Asphalt Content for Wearing 1................................................ 92 Figure D.17. Percent VMA Versus Asphalt Content for Wearing 1............................................. 93 Figure D.18. Percent VFA Versus Asphalt Content for Wearing 1 .............................................. 93
List of Tables
Table 3.1. Temperature at Completion of Mixing for Different Bucket Configurations in Celsius........................................................................................................................................... 20
Table 4.1. Specific Gravity of Individual Aggregate Sizes ............................................................... 23 Table 4.2. Superpave Specifications for 37.5 mm Nominal Aggregate Size Mix (Wearing 1)
(Roberts, 96) ................................................................................................................................ 24 Table 4.3. Superpave Specifications for 19 mm Nominal Aggregate Size Mix (Base 2)
(Roberts, 96) ................................................................................................................................ 25 Table 4.4. Superpave Specifications for 37.5 mm Nominal Aggregate Size Mix (Base 1)
(Roberts, 96) ................................................................................................................................ 25 Table 4.5. WVDOH Master Ranges for Base 1, Base 2, and Wearing 1 ...................................... 26 Table 4.6. Gradations Used in Study ................................................................................................... 37 Table 5.1. Base 1 Within-laboratory Averages and Variances ........................................................ 42 Table 5.2. Base 2 Within-laboratory Averages and Variances ........................................................ 43 Table 5.3. Wearing 1 Within-laboratory Averages and Variances.................................................. 44 Table 5.4. Test for High and Low Variability .................................................................................... 45 Table 5.5 Precision of Maximum Theoretical Specific Gravity (all data)....................................... 57 Table 5.6 Precision of Stability (all data) .............................................................................................. 57 Table 5.7. Precision of Flow (all data) ................................................................................................. 58 Table 5.8. Precision of Bulk Specific Gravity (all data) .................................................................... 58 Table 5.9. Precision of Percent Air Voids (all data) .......................................................................... 59 Table 5.10. Test for High and Low Variability without District 3 ................................................. 60 Table 5.11 Precision of Maximum Theoretical Specific Gravity without District 3.................... 61 Table 5.12 Precision of Stability without District 3 ........................................................................... 62 Table 5.13 Precision of Flow without District 3 ................................................................................ 62 Table 5.14 Precision of Bulk Specific Gravity without District 3 ................................................... 63 Table 5.15 Precision of Percent Air Voids without District 3 ......................................................... 63
v

Table Table Table
Table
Table Table Table Table
Table
Table Table Table Table Table Table Table Table Table
Table
Table
Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table

5.16 Percent change in precision statements without District 3 .......................................... 64 5.17. Standard Deviations of Average Laboratory Results from Inter-laboratory Studies66 A.1 Approximate Values (Upper 5 percent Level) for the Ratio of the Largest Variance
to the Sum of the Variances ..................................................................................................... 77 A.2 Approximate Values (Upper 5 percent Level) for the Ratio of the Highest to Lowest Variance ......................................................................................................................... 77 A.3. Example Calculation of Components of Variance ....................................................... 78 B.1. Precision Summary of Study by ASTM (Kanhdal, 96) ................................................. 80 B.2. Georgia Laboratory Comparison Study (Siddiqui, 95) ................................................. 81 B.3. Utah-Marshall Study, Same Operator, Different Equipment at Various Laboratories (Siddiqui, 95)........................................................................................................ 82 B.4. Utah-Marshall Study, Different Operator and Equipment at Various Laboratories (Siddiqui, 95)................................................................................................................................ 82 B.5. Canadian Mix Exchange, .................................................................................................... 83 E.1. Compacted Base 1 Samples Raw Data ............................................................................ 94 E.2. Compacted Base 2 Samples Raw Data ............................................................................ 95 E.3. Compacted Wearing 1 Samples Raw Data ..................................................................... 96 E.4. Base 1 Maximum Theoretical Specific GravitySamples Raw Data ............................ 97 E.5. Base 2 Maximum Theoretical Specific GravitySamples Raw Data ............................ 98 E.6. Wearing 1 Maximum Theoretical Specific Gravity Samples Raw Data .................... 99 E.7. Questionnaire Results ....................................................................................................... 100 G.1. Base 1, Maximum Theoretical Specific Gravity, Within-Laboratory Average and Variance...................................................................................................................................... 107 G.2. Base 2, Maximum Theoretical Specific Gravity, Within-Laboratory Average and Variance...................................................................................................................................... 107 G.3. Wearing 1, Maximum Theoretical Specific Gravity, Within-Laboratory Average and Variance .............................................................................................................................. 108 G.4. Base 1, Stability, Within-Laboratory Average and Variance ..................................... 108 G.5. Base 2, Stability, Within-Laboratory Average and Variance ..................................... 109 G.6. Wearing 1 Stability, Within-Laboratory Average and Variance................................ 109 G.7. Base 1, Flow, Within-Laboratory Average and Variance .......................................... 110 G.8. Base 2, Flow, Within-Laboratory Average and Variance .......................................... 110 G.9. Wearing 1, Flow, Within-Laboratory Average and Variance.................................... 111 G.10. Base 1, Bulk Specific Gravity, Within-Laboratory Average and Variance ........... 111 G.11. Base 2, Bulk Specific Gravity, Within-Laboratory Average and Variance ........... 112 G.12. Wearing 1, Bulk Specific Gravity, Within-Laboratory Average and Variance .... 112 G.13. Base 1, Percent Air Voids, Within-Laboratory Average and Variance ................. 113 G.14. Base 2, Percent Air Voids, Within-Laboratory Average and Variance ................. 113 G.15. Wearing 1, Percent Air Voids, Within-Laboratory Average and Variance .......... 114 G.16. Outlying Percentile for Maximum Theoretical Specific Gravity Specific Gravity115 G.17. Outlying Percentile for Marshall Stability................................................................... 116 G.18. Outlying Percentile for Marshall Flow........................................................................ 117 G.19. Outlying Percentile for Bulk Specific Gravity ........................................................... 118 G.20. Outlying Percentile for Percent Air Voids ................................................................. 119

vi

CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION In the late 1860’s the first bituminous pavements were placed in Washington D.C. These pavements were a significant improvement over the common earth road surfaces of the day. However, with continuous growth in traffic, particularly during World War II, the need to improve pavement quality became an important issue to highway agencies and the Department of Defense. As a result, mix design methods were developed for improving the quality of asphalt concrete. One of these methods, developed by Bruce Marshall, has been widely adopted by state highway agencies, including West Virginia.
The West Virginia Division of Highways, WVDOH, uses statistical quality control methods. Under these methods, the precision of all test procedures must be known in order to ensure equitable evaluation of contractors’ products. Although the Marshall method has been in use for approximately 50 years, the precision of the method is not quantified in the ASTM standard test method. Hence, the WVDOH needs to quantify the precision of the Marshall method as it is implemented in the state. This need defined the primary objective of this research. In essence, this requires performing a test method precision experiment as described in ASTM Standard C 802 “Standard Practice for Conducting and Inter-laboratory Test Program to Determine the Precision of Test Methods for Construction Materials.” The standard requires preparing and distributing at least 3 replicate samples of 3 material types to a minimum of 10 laboratories. Obviously, sample preparation is a significant effort during this type of experiment.
1.2 PROBLEM STATEMENT Even though the Superpave procedures will eventually replace the Marshall procedure for mix design and quality control, in the interim, WVDOH will continue to use the Marshall method. For quality control, the inter-laboratory precision and variance in the Marshall method must be
1

quantified for statistical based quality control methods. In a previous project, single laboratory precision of the Marshall method was evaluated (Head, 93). The current project expands on the work of Head to include inter-laboratory precision.
1.3 OBJECTIVES The objective of this research was to develop precision statements for Marshall parameters. The Marshall parameters evaluated during this project were stability, flow, air void, maximum theoretical specific gravity, and bulk specific gravity.
The precision statements must apply to all laboratories working for and with WVDOH, therefore, all WVDOH district laboratories and the central laboratory participated in the study. In addition, since contractors have a direct responsibility for quality control, contractors laboratories were included in the study. The precision statements must be valid for all asphalt concrete types, so three mix types were included in the research. To ensure the experiment design and analysis fulfilled these objectives, ASTM standard practices for performing precision statements were used during the research.
The Marshall method was developed to accommodate mixes with relatively small maximum size aggregates. This permitted the use of a 102 mm diameter mold, which can accommodate a 25 mm maximum aggregate size. Recently, in response to heavier traffic loads, highway agencies have introduced mixes with larger maximum aggregate sizes to improve mix durability. Consequently, there is a need to increase the Marshall sample size to accommodate the larger size aggregates. The use of larger sample molds is also accommodated in more modern mix design methods, such as the Superpave system developed during the Strategic Highway Research Program. Both the large Marshall mold and the mold used for the Superpave system require approximately 4,000 g of aggregate as opposed to the 1,200 g sample needed for the standard Marshall mold.
Increasing the sample size significantly affects laboratory sample preparation. Due to the mass of material required, it is difficult to prepare samples using traditional methods. In response to this need, industry has introduced a large capacity mixer for asphalt concrete. Since the
2

objective of this project required preparation of many samples, the large capacity mixer was evaluated.
1.4 REPORT SUMMARY This report is organized into six chapters and seven appendices. Following the introduction chapter is a summary of the literature. Given the fact that the Marshall method was developed 50 years ago and was the standard method for approximately seventy-five percent of the stated highway agencies, the lack of information on the test method precision seems unusual. The literature survey found two studies covering single-laboratory precision and two reports on inter-laboratory precision. The studies indicate the variability of the Marshall method is relatively high. Others have recognized this fact and studies of methods for reducing the variability have been conducted. One such study was reviewed to highlight the difficulty in reducing the variability of the seemingly simple Marshall mix design method.
One aspect of the standard Marshall test method is the small mold size which limits the maximum aggregate size that can be considered for mix design. To overcome this limitation, an ASTM test method for using a 152 mm diameter mold was developed. In addition, the Superpave method uses large sample sizes. Chapter 3 outlines a method for mixing large samples.
Chapter 4 presents the process used to select the specific aggregate gradations and asphalt contents for the mixture types used during this research. The types of mixtures were selected in concert with the project sponsor. Once the mixture types were selected, samples of aggregate were obtained from Greer Industries. A Marshall mix design was preformed to determine the optimum asphalt content. However, mixes with the Greer aggregates failed to meet all the WVDOH Marshal criteria. Therefore the mix designs used by the Greer plant for DOH projects were used for the research.
The samples were prepared in the WVU Asphalt Technology Laboratory and distributed to the 10 WVDOH district laboratories, the WVDOH central laboratory, two contractor laboratories, and the WVU Asphalt Technology Laboratory. The samples were tested using
3

Preparing to load PDF file. please wait...

0 of 0
100%
Lab Variability of the Marshall Test Method