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Publication Number: FHWARD03041 
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This report documents a comprehensive review and evaluation of the Long Term Pavement Performance (LTPP) pavement layer thickness data. Pavement layer thickness data are very important for many types of analyses, including backcalculation of pavement moduli, mechanistic analysis of pavement structures, and performance modeling. The accuracy of layer thickness data has a great impact on the outcome of practically all analyses of performance. The report contains an assessment of the LTPP layer thickness data and recommendations for resolution of anomalous data. Results of the statistical analyses documented in this report provide insights into the characteristics of withinsection layer thickness variability. The results of the comparison between asdesigned and asconstructed layer thickness data provide useful estimates of the expected constructionrelated variability. These results can serve as a very important input to pavement engineering applications involving the reliability of pavement design and also for quality assurance construction specifications.
This report will be of interest to highway agency engineers involved in pavement analysis, design, construction, and data collection, as well as future researchers who will use LTPP data to improve on the design procedures and standards for constructing pavements.
T. Paul Teng, P.E.

This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.
The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein only because they are considered essential to the objective of this document.
Technical Report Documentation
Page 

1. Report No. FHWARD03041 
2. Government Accession No.  3. Recipient's Catalog No.  
4. Title and Subtitle EVALUATION AND ANALYSIS OF LTPP PAVEMENT LAYER THICKNESS DATA 
5. Report Date July 30, 2002  
6. Performing Organization  
7. Author(s) Olga I. Selezneva, Y. Jane Jiang, and Goran Mladenovic 
8. Performing Organization Report No. 

9. Performing Organization Name and Address ERES Division of Applied Research Associates, Inc. 9030 Red Branch Road, Suite 210 Columbia, Maryland 21045 
10. Work Unit No.  
11. Contract or Grant No. DTFH6196C00003 

12. Sponsoring Agency Name and Address Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, Virginia 221012296 
13. Type of Report and Period Covered Final Report 

14. Sponsoring Agency Code  
15. Supplementary Notes Contracting Officer's Technical Representative (COTR): Cheryl Allen Richter, HRDI Work was conducted as part of the LTPP Data Analysis Technical Support Contract. 

16. Abstract In addition, layer thickness variability indicators, withinsection material type consistency, and material type and thickness reasonableness were evaluated. In the cases where there were inconsistencies in the data, the data were reviewed and reported to the LTPP data managers along with recommendations for data anomaly resolution. In addition, the layer thickness data from Specific Pavement Studies (SPS) experiments were analyzed to determine characteristics of withinsection layer thickness variation. The analysis included layers with different material and functional types. Descriptive statistics such as mean, standard deviation, skewness, and kurtosis were computed for each section. The statistical analysis results for 1,034 SPS layers indicated that 84 percent of all layers thickness variations within LTPP section follow a normal distribution. The extent of differences between asdesigned (inventory) and asconstructed (measured) layer thickness data was also investigated for the SPS sections. The results of analysis indicate that about 60 percent of all section/layers have mean thicknesses within 6.35 mm (0.25 in) of the target thickness. For a tolerance level of 25.4 mm (1 in), this percentage is above 90 for most layer types and target thickness values. For the same layer and material type, the mean constructed layer thicknesses tend to be above the designed value for the thinner layers and below the designed value for the thicker layers. One important product from this study is the Researcher's Guide to LTPP Layer Thickness Data. The main purpose of this guide is to provide guidance for the selection of layer material type and thickness data from the LTPP database. The guide also contains a discussion about withinsection layer thickness variability and comparison between asdesigned and asconstructed layer thickness. The guide is available as a separate publication. 

17. Key Words Pavements, LTPP, layer thickness, material type, variability, deviations 
18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. 

19. Security Classif. (of this report) Unclassified 
20. Security Classif. (of this page) Unclassified 
21. No. of Pages 159 
22. Price 
SI* (Modern Metric) Conversion Factors
APPENDIX A  CORRELATED MATERIAL CODES
APPENDIX B  SKEWNESS AND KURTOSIS TEST
Statistical Formulations Used in the Skewness and Kurtosis Test
APPENDIX C  KOLMOGOROVSMIRNOV GOODNESSOFFIT TEST
Procedures for the KolmogorovSmirnov Goodnessoffit Test
Results of the KolmogorovSmirnov Goodnessoffit Tests
LIST OF TABLES
Table 1. Data availability assessment of the regular sections for layer thickness related tables.
Table 2. Data availability assessment for layer thickness related tables for supplemental sections.
Table 3. List of pavement structures that do not have any data in either the TST_L05B table or the TST_L05A table at any QC level.
Table 4. Level E data availability for layer thicknessrelated tables for LTPP experiments.
Table 5. Evaluation of layer numbering correspondence between the INV_LAYER and TST_L05B tables.
Table 6. Summary of the number of records used in the crosstable pavement layering analysis.
Table 7. LTPP layer function description codes.
Table 8. Summary of the layer functional description consistency evaluation.
Table 9. Criteria for evaluation of material code validity.
Table 10. Summary of the records with erroneous material codes.
Table 11. Material type consistency criteria.
Table 12. Summary of the layer material type consistency evaluation.
Table 13. Summary of the layer material type consistency evaluation along the LTPP section length (TST_L05A table).
Table 14. Thickness ranges used for reasonableness checks.
Table 15. Summary of the layer thickness reasonableness evaluation results^{1}.
Table 16. Criteria used for evaluation of layer thickness consistency between different tables.
Table 17. Summary of the layer thickness consistency evaluation results^{1}.
Table 18. Summary of layering data consistency evaluation for each LTPP experiment.
Table 19. Summary of projectlevel layer thickness variability evaluation using core data.
Table 20. Core data availability in tables TST_AC01_LAYER and TSTPC06.
Table 21. Summary of the elevation thickness measurements in the SPS*_LAYER_THICKNESS tables.
Table 22. The distribution of the elevation thickness records not used in the analysis.
Table 23. Distribution of the outliers by layer type.
Table 24. Summary of projectlevel layer thickness variability evaluation using elevation grid data.
Table 25. Summary of layer thickness COV and standard deviations based on core measurements.
Table 26. Summary of layer thickness COV and standard deviations based on SPS elevation measurements.
Table 27. Summary of layers with both elevation and core data available.
Table 28. Comparison of variances (Ftest, 99 percent confidence level) obtained from elevation and core thickness measurements.
Table 29. Results of the comparison of means (ttest, 95 % confidence level) for elevation and core thickness measurements.
Table 30. Pavement layer and material type identifiers available in the SPS*_LAYER_THICKNESS tables.
Table 31. Design thicknesses for different SPS experiments sorted by layer and material type.
Table 32. Multiplier for the standard deviation used in the outlier criterion based on tdistribution.
Table 33. Descriptive statistics for the binder course layer, SPS6 section 40_0608.
Table 34. Identified outlier points.
Table 35. Evaluation summary of the goodnessoffit testing methods.
Table 36. Kurtosis and skewness test results summary for binder course layer, SPS6 Section 40_0608.
Table 37. Summary of the normality evaluation results.
Table 38. Design layer thicknesses for the SPS1 experiment.
Table 39. Design layer thicknesses for the SPS2 experiment.
Table 40. Design layer thicknesses for the SPS5 experiment.
Table 41. Design layer thicknesses for the SPS6 experiment.
Table 42. Design layer thicknesses for the SPS7 experiment.
Table 43. Design layer thicknesses for the SPS8 experiment.
Table 44. Summary of differences between mean elevation thickness measurements and target thicknesses.
Table 45. Summary of differences between mean core thickness measurements and target thicknesses.
Table 46. Distribution of the mean thickness deviations from the design thickness based on kurtosis and skewness tests.
Table 47. Percentage distribution summary of the elevation thickness measurements.
Table 48. Percentage distribution of individual elevation measurements by layer type and design thickness for a tolerance level of 6.35 mm (0.25 in).
Table 49. Percentage distribution of individual elevation measurements by layer type and design thickness for a tolerance level of 12.7 mm (0.5 in).
Table 50. Percentage distribution of individual elevation measurements by layer type and design thickness for a tolerance level of 25.4 mm (1 in).
Table 51. Summary of the results of the twosided ttests (95 percent confidence level) using elevation measurements.
Table 52. Results of the twosided ttest for different material types (95 percent confidence level) by layer type and design thickness using elevation measurements.
Table 53. Summary of the results of onesided ttests using elevation measurements.
Table 54. Results of onesided ttest for tolerance level of 6.35 mm (0.25 in) by layer type and design thickness using elevation measurements.
Table 55. Results of onesided ttests for tolerance level of 12.7 mm (0.5 in) by layer type and design thickness using elevation measurements.
Table 56. Results of onesided ttest for tolerance level of 25.4 mm (1 in) by layer type and design thickness using elevation measurements.
Table 57. Summary of the percentage distribution of the individual core thickness measurements versus the design thickness.
Table 58. Percentage distribution of core thickness measurements by layer type and design thickness for a tolerance level of 6.35 mm (0.25 in).
Table 59. Percentage distribution of core thickness measurements by layer type and design thickness for a tolerance level of 12.7 mm (0.5 in).
Table 60. Percentage distribution of core thickness measurements by layer type and design thickness for a tolerance level of 25.4 mm (1 in).
Table 61. Summary of the results of the twosided ttest (95 percent confidence level) using core thickness data.
Table 62. Distribution of differences by layer type and design thickness (twosided ttest, 95 percent confidence level) using core thickness data.
Table 63. Summary of the results of the onesided ttests using core thickness data.
Table 64. Results of the onesided ttest (95 percent confidence level) by layer type and design thickness for tolerance level of 6.35 mm (0.25 in) using core thickness data.
Table 65. Results of the onesided ttest (95 percent confidence level) by layer type and design thickness for tolerance level of 12.7 mm (0.5 in) using core examination data.
Table 66. Results of the onesided ttest (95 percent confidence level) by layer type and design thickness for tolerance level of 25.4 mm (1 in) using core examination data.
Table 67. Correlated material codes.
Table 68. Number of pavement layers and number of layer thickness measurements per layer grouped by material and layer type.
Table 69. Summary of the goodnessoffit results using KolmogorovSmirnov test with 1 percent level of significance.
LIST OF FIGURES
Figure 1: Graph. LTPP data sources containing pavement layering data.
Figure 2: Graph. Four essential pavement layering characteristics.
Figure 3: Chart. Flowchart for pavement layering data evaluation.
Figure 4: Graph. Example of layer functional description consistency evaluation.
Figure 5: Chart. Results of layer functional description consistency evaluation.
Figure 6: Graph. Example of evaluation of layer material type consistency between different tables.
Figure 7: Chart. Results of layer material type consistency evaluation between different data sources.
Figure 8: Graph. Example of evaluation of layer material type consistency along the section.
Figure 9: Chart. Results of layer material type consistency evaluation along the section.
Figure 10: Graph. Example of evaluation of layer thickness consistency between different data tables.
Figure 11: Chart. Results of layer thickness consistency evaluation between different data sources.
Figure 12: Graph. Location of core sampling and elevation measurement areas along the LTPP section.
Figure 13: Equation. Definition of coefficient of variation.
Figure 14: Equation. The null and alternative hypotheses for the Ftest.
Figure 15: Equation. The null and alternative hypotheses for the ttest.
Figure 16: Chart. Comparison of the standard deviation for core thickness and elevation measurements.
Figure 17: Chart. Comparison of the COV for core thickness and elevation measurements.
Figure 18: Chart. Results of the statistical analysis of differences between elevation and core thickness measurements.
Figure 19: Chart. Example of the binder course thickness measurements along SPS6 Section 40_0608 with an apparent outlier.
Figure 20: Equation. Outlier definition criterion.
Figure 21: Chart. Example of the AC surface and binder layer thickness distribution with clear outlier detection for the SPS1 Section 300112.
Figure 22: Chart. Example of dense graded aggregate base layer thickness distribution with questionable outlier detection for the SPS2 Section 200210.
Figure 23: Chart. Example of the dense graded aggregate base layer thickness distribution skewed to the left for the SPS1 Section 200101.
Figure 24: Chart. Example of the normal layer thickness distribution for PCC surface layer, SPS2, Section 10_0211.
Figure 25: Chart. Example of the uniform layer thickness distribution for dense graded aggregate base, SPS1, Section 12_0101.
Figure 26: Chart. Example of the layer thickness distribution skewed to the right for PCC surface layer, SPS2, Section19_0213.
Figure 27: Chart. Flowchart of the kurtosis and skewness test procedures used for the test of layer thickness distribution normality.
Figure 28: Equation. Definition of pvalues.
Figure 29: Chart. Example distribution of layer thickness measurements along the section for the DGAB layer for the SPS1 Section 350108.
Figure 30: Chart. Example distribution of layer thickness measurements along the section for the DGAB layer for the SPS2 Section 190214.
Figure 31: Chart. Example distribution of layer thickness measurements along the section for the DGAB layer for the SPS8 Section 080811.
Figure 32: Chart. Example distribution of layer thickness measurements along the section for the DGATB layer for the SPS1 Section 220118.
Figure 33: Chart. Example distribution of layer thickness measurements along the section for the LC base layer for the SPS2 Section 530207.
Figure 34: Chart. Example distribution of layer thickness measurements along the section for the PATB layer for the SPS1 Section 200112.
Figure 35: Chart. Example distribution of layer thickness measurements along the section for the PATB layer for the SPS2 Section 080224.
Figure 36: Chart. Example distribution of layer thickness measurements along the section for the PCC surface layer for the SPS2 Section 080215.
Figure 37: Chart. Example distribution of layer thickness measurements along the section for the PCC surface layer for the SPS8 Section 390809.
Figure 38: Chart. Example distribution of layer thickness measurements along the section for the PCC surface layer for the SPS7 Section 190706.
Figure 39: Chart. Example distribution of layer thickness measurements along the section for the surface and binder layer for the SPS1 Section 550118.
Figure 40: Chart. Example distribution of layer thickness measurements along the section for the surface and binder layer for the SPS8 Section 480802.
Figure 41: Chart. Example distribution of layer thickness measurements along the section for the surface layer for the SPS5 Section 350507.
Figure 42: Chart. Example distribution of layer thickness measurements along the section for the surface layer for the SPS6 Section 420603.
Figure 43: Chart. Example distribution of layer thickness measurements along the section for the AC binder course for the SPS5 Section 240504.
Figure 44: Chart. Example distribution of layer thickness measurements along the section for the binder course for the SPS6 Section 290607.
Figure 45: Equation. The null and alternative hypotheses for twosided ttest.
Figure 46: Equation. The null and alternative hypothesis for onesided ttest.
Figure 47: Chart. The Frequency distribution of mean thickness deviations for all four target thicknesses of the DGAB layer.
Figure 48: Chart. Frequency distribution of elevation and core thickness measurements deviations for DGATB with 102mm (4in) target thickness.
Figure 49: Chart. Frequency distribution of elevation and core thickness measurements deviations for DGATB with 203mm (8in) target thickness.
Figure 50: Chart. Frequency distribution of elevation and core thickness measurements deviations for DGATB with 305mm (12in) target thickness.
Figure 51: Chart. Frequency distribution of elevation and core thickness measurements deviations for LC with 152mm (6in) target thickness.
Figure 52: Chart. Frequency distribution of elevation and core thickness measurements deviations for PATB with 102mm (4in) target thickness.
Figure 53: Chart. Frequency distribution of elevation and core thickness measurements deviations for PCC with 76mm (3in) target thickness.
Figure 54: Chart. Frequency distribution of elevation and core thickness measurements deviations for PCC with 127mm (5in) target thickness.
Figure 55: Chart. Frequency distribution of elevation and core thickness measurements deviations for PCC with 203mm (8in) target thickness.
Figure 56: Chart. Frequency distribution of elevation and core thickness measurements deviations for PCC with 279mm (11in) target thickness.
Figure 57: Chart. Frequency distribution of elevation and core thickness measurements deviations for SB with 51mm (2in) target thickness.
Figure 58: Chart. Frequency distribution of elevation and core thickness measurements deviations for SB with 102mm (4in) target thickness.
Figure 59: Chart. Frequency distribution of elevation and core thickness measurements deviations for SB with 127mm (5in) target thickness.
Figure 60: Chart. Frequency distribution of elevation and core thickness measurements deviations for SB with 178mm (7in) target thickness.
Figure 61: Chart. Frequency distribution of elevation and core thickness measurements deviations for SB with 203mm (8in) target thickness.
Figure 62: Chart. Example of normally distributed thickness deviations (elevation data, LC, target thickness 152 mm [6 in]).
Figure 63: Chart. Example of a skewed distribution for layer thickness deviation (core data, PCC, target thickness 279 mm [11 in]).
Figure 64: Chart. Percentage distribution of the elevation measurements for a tolerance level of 6.35 mm (0.25 in) for different material types and design thicknesses.
Figure 65: Chart. Percentage distribution of the elevation measurements for a tolerance level of 12.7 mm (0.5 in) for different material types and design thicknesses.
Figure 66: Chart. Percentage distribution of the elevation measurements for a tolerance level of 25.4 mm (1 in) for different material types and design thicknesses.
Figure 67: Chart. Results of onesided ttests for the differences between mean elevation and design thicknesses for a tolerance level of 6.35 mm (0.25 in).
Figure 68: Chart. Results of onesided ttests for the differences between mean elevation and design thicknesses for a tolerance level of 12.7 mm (0.5 in).
Figure 69: Chart. Results of onesided ttests for the differences between mean elevation and design thicknesses for a tolerance level of 25.4 mm (1 in).
Figure 70: Chart. Percentage distribution of core measurements by layer type and design thickness for a tolerance level of 6.35 mm (0.25 in).
Figure 71: Chart. Percentage distribution of core measurements by layer type and design thickness for a tolerance level of 12.7 mm (0.5 in).
Figure 72: Chart. Percentage distribution of core measurements by layer type and design thickness for a tolerance level of 25.4 mm (1 in).
Figure 73: Chart. Results of onesided ttests for the differences between core measurements and design thicknesses for tolerance level of 6.35 mm (0.25 in).
Figure 74: Chart. Results of onesided ttests for the differences between mean core and design thicknesses by layer type and design thickness for tolerance level of 12.7 mm (0.5 in).
Figure 75: Chart. Results of onesided ttests for the differences between mean core and design thicknesses by layer type and design thickness for tolerance level of 25.4 mm (1 in).
Figure 76: Equation. Skewness definition.
Figure 77: Equation. Kurtosis definition.
Figure 78: Equation. Nondimensional skewness coefficient definition.
Figure 79: Equation. Nondimensional kurtosis coefficient definition.
Figure 80: Equation. Definition of statistic.
Figure 81: Equation. Definition of b2 statistic.
Figure 82: Equation. Definition of intermediate parameter A.
Figure 83: Equation. Definition of intermediate parameter B.
Figure 84: Equation. Definition of intermediate parameter C.
Figure 85: Equation. Definition of intermediate parameter D.
Figure 86: Equation. Definition of intermediate parameter E.
Figure 87: Equation. Definition of skewness test statistic z1.
Figure 88: Equation. Definition of the mean of intermediate parameter meanb^{2}.
Figure 89: Equation. Definition of the variance of intermediate parameter varb^{2}.
Figure 90: Equation. Definition of intermediate parameter F.
Figure 91: Equation. Definition of intermediate parameter G.
Figure 92: Equation. Definition of intermediate parameter H.
Figure 93: Equation. Definition of kurtosis test statistic z2.
Figure 94: Equation. Cumulative frequencies definition.
Figure 95: Equation. Dmax statistic definition.
Figure 96: Equation. Critical value definition.
Figure 97: Equation. KolmogorovSmirnov test evaluation criteria.
Figure 98: Chart. Example of KolmogorovSmirnov normal distribution goodnessoffit test (DGAB layer SPS1 LTPP section 01_0101).
LIST OF ABBREVIATIONS
AC = Asphalt concrete (surface course).
AGG = Aggregate base (identical to densegraded aggregate base).
AASHTO = American Association of State Highway and Transportation Officials.
ASTM = American Society for Testing and Materials.
ATB = Asphalttreated base (densegraded, generally similar to the AC surface course).
COV = Coefficient of variation.
CRCP = Continuously reinforced concrete pavement.
CTB = Cementtreated base.
DGAB = Densegraded aggregate base (unbound).
DGATB = Densegraded asphalttreated base (bound).
FHWA = Federal Highway Administration.
GB = Granular base.
GPR = Ground Penetrating Radar.
GPS = General Pavement Studies.
HMAC = Hotmix asphalt concrete.
JCP = Jointed concrete pavement.
JPCP = Jointed plain concrete pavement.
JRCP = Jointed reinforced concrete pavement.
LC = Lean concrete (base).
LTPP = Long Term Pavement Performance (program).
PCC = Portland cement concrete.
PATB = Permeable asphalttreated base.
QA = Quality assurance.
QC = Quality control.
RSC = Regional Support Contractor.
SHRP = Strategic Highway Research Program.
SB = Surface and binder (layer).
SPS = Specific Pavement Studies.