dot/faa/ar-06/56 comparative design study for airport pavement · the faa design procedure requires...

DOT/FAA/AR-06/56 Air Traffic Organization Operations Planning Office of Aviation Research and Development Washington, DC 20591

Comparative Design Study for Airport Pavement May 2007 Final Report This document is available to the U.S. public through the National Technical Information Service (NTIS), Springfield, Virginia 22161.

U.S. Department of Transportation Federal Aviation Administration

NOTICE

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents or use thereof. The United States Government does not endorse products or manufacturers. Trade or manufacturer's names appear herein solely because they are considered essential to the objective of this report. This document does not constitute FAA certification policy. Consult your local FAA airports office as to its use.

This report is available at the Federal Aviation Administration William J. Hughes Technical Center’s Full-Text Technical Reports page: actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF).

Technical Report Documentation Page

1. Report No. DOT/FAA/AR-06/56

2. Government Accession No. 3. Recipient's Catalog No.

5. Report Date May 2007

4. Title and Subtitle

COMPARATIVE DESIGN STUDY FOR AIRPORT PAVEMENT 6. Performing Organization Code AJP-6310

7. Author(s) Lia Ricalde, Navneet Garg, and Izydor Kawa

8. Performing Organization Report No.

10. Work Unit No. (TRAIS)

9. Performing Organization Name and Address SRA International, Inc. 3120 Fire Road Egg Harbor Township, NJ 08234

11. Contract or Grant No. DTFACT-05-D-00012

13. Type of Report and Period Covered Final Report

12. Sponsoring Agency Name and Address U.S. Department of Transportation Federal Aviation Administration Air Traffic Organization Operations Planning Office of Aviation Research and Development Washington, DC 20591

14. Sponsoring Agency Code AAS-100

15. Supplementary Notes The Federal Aviation Administration Airport and Aircraft Safety R&D Division COTR was Dr. Satish Agrawal. 16. Abstract A comparative analysis of the results of different design methods is a powerful tool for evaluating and developing new pavement design procedures. A sensitivity, or comparative, analysis was employed during the development of Federal Aviation Administration (FAA) Advisory Circular (AC) 150.5320-16 and its computer program LEDFAA. The FAA is currently developing a new Portland cement concrete design procedure based on the three-dimensional finite element method (FEDFAA) and has modified the original subgrade vertical strain-based failure criteria used for flexible pavement design. This report includes a comparison and evaluation of both new construction and overlay designs over a broad range of input conditions. Since the FAA design procedure requires the use of a stabilized base and subbase for airport pavements accommodating aircraft heavier than 100,000 lb, the sensitivity of a stabilized base/subbase on the pavement life or thickness was also studied. Design thickness comparisons, using different models, are provided to show how the sensitivity analysis results influence the design model. This report focuses on the results of the comparative analyses for both new and overlay pavements. Other parameters analyzed in this report include subgrade strength, aircraft type, annual departure levels for single aircraft, narrow- and wide-body aircraft traffic mixes, and thickness and strength of stabilized and aggregate base and subbase layers. Numerical sensitivity comparisons among different failure models included in conventional design methods (AC 150.5320-6D) and standard LEDFAA (AC 150.5320-6D, Change 3) were also conducted. It has been found that, under certain conditions, computational results can differ, depending on the model and the range of input parameters that were evaluated. The comparative analysis results will be used to calibrate the parameters to be used in the new failure models and to provide guidance on the selection of design inputs. 17. Key Words

Pavement, design, Portland concrete cement, Three-dimensional finite element model, FAArfield, Stabilized base, Sensitivity, Comparative, Strength, Failure model, Overlay, Calibration, Flexible pavement.

18. Distribution Statement

This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161.

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 70

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

TABLE OF CONTENTS Page

EXECUTIVE SUMMARY x 1. INTRODUCTION 1

2. COMPARATIVE ANALYSIS TEST MATRIX 1

2.1 New Flexible Pavement Test Structures 2 2.2 New Rigid Pavement Test Structures 3 2.3 Rigid Over Rigid Pavement Test Structures 3 2.4 Aircraft Traffic Mixes 6 2.5 Single Aircraft Traffic 6 2.6 Pavement Design Methods 12

3. NEW RIGID PAVEMENT DESIGN RESULTS 13

3.1 Single Aircraft Traffic 13

3.1.1 Subbase Effect on Pavement Structures 13 3.1.2 Effect of Departure Level 18 3.1.3 Subgrade Effect on Pavement Structures 19 3.1.4 Correlation Between Design Procedures 21

3.2 Aircraft Traffic Mixes 27

3.2.1 Conventional Pavement Structures 27 3.2.2 Pavement Structures With Stabilized Subbase 29

4. NEW FLEXIBLE PAVEMENT DESIGN RESULTS 33

4.1 Single Aircraft Comparisons 33 4.2 Traffic Mix Comparisons 36

5. PCC ON RIGID OVERLAY DESIGN RESULTS 41

5.1 Single Aircraft Traffic 41 5.2 Aircraft Traffic Mixes 49

6. FLEXIBLE-OVER-RIGID OVERLAY DESIGN RESULTS 54

6.1 Single Aircraft 54 6.2 Aircraft Traffic Mixes 57

7. REFERENCES 59

iii

LIST OF FIGURES

Figure Page 1 Conventional Pavement Structures for Single Aircraft (PCC R = 500 psi) 15

2 Conventional Pavement Structures for Single Aircraft (PCC R = 650 psi) 15

3 Conventional Pavement Structures for Single Aircraft (PCC R = 700 psi) 16

4 Stabilized Base (Item P-301) Pavement Structures With Single Aircraft Traffic (PCC R = 650 psi) 17



7 Slab Thickness Differences for Single Aircraft Traffic (Effect of Departure Level) 19

8 Effect of Subbase Strength on FEDFAA Design Thickness for Single Aircraft Traffic 20

9 Effect of Stabilized Base Modulus on FEDFAA Design Thickness for Single Aircraft Traffic 20

10 B727 FEDFAA-6D Correlation, Wheel Load 49,638 lb 22


12 DC10 FEDFAA-6D Correlation, Wheel Load 54,625 lb 24



15 Results of Design Comparison for New Conventional Rigid Pavements (R = 500 psi) Under Mixed Aircraft Traffic 27



18 Results of Design Comparison for New Rigid Pavements With Stabilized Base, Item P-301, SCB (Mixed Aircraft Traffic) 29

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19 Results of Design Comparison for New Rigid Pavements With Stabilized Base, Item P-304, CTB (Mixed Aircraft Traffic) 30

20 Results of Design Comparison for New Rigid Pavements With Stabilized Base, Item P-306, Econocrete Base (Mixed Aircraft Traffic) 30

21 Slab Thickness Correlation for Structures With Conventional Subbase, Grouped by Subgrade E-Modulus 31

22 Slab Thickness Correlation for All Structures, Grouped by Subbase E-Modulus 32

23 Slab Thickness Correlation for All Structures With Stabilized Subbase, Grouped by Subgrade E-Modulus 32

24 Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 8-Inch-Thick P-209 Crushed Stone Base 33

25 Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 12-Inch-Thick P-209 Crushed Stone Base 34

26 Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 5-Inch-Thick P-401 ASB 35

27 Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 8-Inch-Thick P-401 ASB 36

28 Thickness Comparisons for Mix 1 37







35 Thickness Calculated by LEDFAA 1.3 for Mix 8 41

36 Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 50 on Conventional Subbase 42

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40 Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 50 on Stabilized Subbase 44




44 Average PCC Overlay Comparison for Single Aircraft 46

45 PCC Overlay Correlation for B727 (GW 209,000 lb) 47


47 PCC Overlay Correlation for DC10 (460,000 lb) 48






53 Rigid Overlay Comparison: 10-inch Base Slab With Initial SCI = 75 on Stabilized Subbase 51


vi




58 Average Rigid Overlay Differences for All Traffic Mixes 54

59 Flexible-Over-Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 75 on Conventional Subbase 55


61 Flexible-Over-Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 75 on Stabilized Subbase 56






vii

LIST OF TABLES Table Page 1 Pavement Structural Data (New Flexible Pavement Design) 3

2 Pavement Structural Data (New Rigid Pavement Design) 4

3 Pavement Structural Data (Overlay Pavement Design) 5

4a Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 1, Sarasota-Bradenton Airport 7

4b Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 2, Washington-Dulles International Airport, Taxiway W-1 7

4c Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 3, Washington-Dulles International Airport, Runway 1L 8

4d Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 4, Memphis Airport, Runway 18R 8

4e Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 5, Charlotte Airport, Runway 18R-36L 9

4f Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 6, Charlotte-Douglas Airport 9

4g Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 7, Philadelphia Airport, 1993 Traffic 9

4h Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 8, J. F. Kennedy International Airport, Runway 13R-31L 10

5 Single Aircraft Traffic Data for Analysis of New Rigid Pavement and Overlays on Existing Rigid Pavements 11

6 Single Aircraft Traffic Data for Analysis of New Flexible Pavements and Overlays on Existing Flexible Pavements 12

viii

LIST OF ACRONYMS

2D Dual-tandem gear 3D Triple dual-tandem gear AC Advisory Circular ASB Asphalt stabilized base CBR California Bearing Ratio COE U.S. Army Corps of Engineers CTB Cement-treated base D Dual FAA Federal Aviation Administration FAArfield FAA Rigid and Flexible Interactive Elastic Layer Design FEDFAA Finite Element Design—Federal Aviation Administration GW Gross weight LEAF Layered Elastic Analysis—FAA (Computer Program) LEDFAA Layered Elastic Design—Federal Aviation Administration NAPTF National Airport Pavement Test Facility NF New flexible PCC Portland cement concrete PCI Pavement Condition index psi Pounds per square inch SCB Soil cement base SCI Structural Condition Index

ix

EXECUTIVE SUMMARY

The Federal Aviation Administration (FAA) has developed a new Portland cement concrete design procedure based on the three-dimensional finite element method (FEDFAA) and a layered elastic design method for flexible pavement design (LEDFAA). The integrated design procedures will be incorporated in the FAA Rigid and Flexible Interactive Elastic Layer Design (FAArfield) program expected to be released in 2008. The new rigid pavement design procedure has been compared to the conventional Westergaard-based FAA design method, as described in Advisory Circular (AC) 150.5320-6D, Chapter 3, for different structures under single aircraft load and various traffic mixes. For flexible pavement design, the LEDFAA version 1.3 program, as described in AC 150.5320-6D, Chapter 7, has been compared to the previous version, LEDFAA 1.2. The main difference between the two versions is the modification of the original subgrade vertical strain-based failure criterion. This report focuses on the results of the comparative analyses for both new and overlay pavements. Other parameters analyzed in this report include subgrade strength, aircraft type, annual departure levels for single aircraft, narrow- and wide-body aircraft traffic mixes, and thickness and strength of stabilized, and aggregate, base and subbase layers. For airport pavements accommodating aircraft heavier than 100,000 lb, the FAA design procedure requires the use of a stabilized base and subbase. The sensitivity of a stabilized base/subbase on the pavement life or thickness has also been studied. The comparative analysis results will be used to calibrate the parameters in the new failure criterion to be implemented for rigid pavement design in FAArfield.

x

1. INTRODUCTION.

The Federal Aviation Administration (FAA) is currently focusing the development of its new design procedures for airport pavements on mechanistic analytical methods. As discussed by Brill, et al. [1], the new design procedures will employ layered elastic design methods for flexible pavements and finite element methods for rigid pavements. The integrated design procedures will ultimately be incorporated in the FAA Rigid and Flexible Interactive Elastic Layer Design (FAArfield) program, scheduled for completion in 2006. The Layered Elastic Design Federal Aviation Administration (LEDFAA) program discussed in Chapter 7 of Advisory Circular (AC) 150.5320-6D, Change 3 [2] currently uses layered elastic design as an optional design procedure for both rigid and flexible pavements. The advisory circular still allows the use of the California Bearing Ratio (CBR) and Westergaard-based design procedures for flexible and rigid pavements respectively, provided there are no triple dual-tandem (3D) gears in the mix. In 2003, the FAA modified the subgrade strain failure model for flexible pavement design and incorporated the new model, as well as other changes, in version 1.3 of LEDFAA. Hayhoe [3] discussed the modifications to the flexible pavement failure model using the results of full-scale flexible pavement tests at the FAA National Airport Pavement Test Facility (NAPTF). The Finite Element Design Federal Aviation Administration (FEDFAA) software program is the beta version of the FAA’s new design procedure for airport pavements. FEDFAA version 1.4 includes the improved layered elastic analysis routine for flexible pavement design (LEAF) used in LEDFAA 1.3, and a three-dimensional finite element structural analysis routine for rigid pavement design, but maintains LEDFAA’s failure model. FEDFAA overcomes one of the major disadvantages associated with rigid pavement design inherent in the LEDFAA program by allowing direct computation of slab edge stresses. Data from historical full-scale tests conducted by the U.S. Army Corps of Engineers (COE) were used to develop the current performance/failure models in the FAA’s rigid pavement design procedures. These models and the new NAPTF full-scale tests have been fully integrated into the historical full-scale test results. After comparing the results from FEDFAA 1.4 and current FAA pavement design standards contained in AC 150.5320-6D [2], a new performance/failure model and calibration factor was developed. The new failure model and calibration factor have been incorporated into FEDFAA 2.0. The results of FEDFAA 2.0 are compared in this report to current FAA pavement design standards and earlier versions of FEDFAA. The approach for this sensitivity/comparative study is similar to the one taken by McQueen, et al. [4] during the development of the LEDFAA program. 2. COMPARATIVE ANALYSIS TEST MATRIX.

A standard set of pavement structures and traffic mixes was developed to fully exercise the new design procedures over a wide range of design conditions for both new and overlay flexible and rigid pavements. The comparative results were recorded in a spreadsheet program.

1

An eight-character naming convention was developed to identify the general characteristics of the pavement structure and the traffic mix (or single aircraft type) used in the present study. The naming convention is as follows: • The first character indicates the type of pavement (Rigid or Flexible).

• The second character indicates New, Flexible Overlay, Rigid Unbonded Overlay, or

Rigid Partial Bond Overlay.

• The third character indicates the type of base/subbase layer (Granular, Stabilized).

• The fourth character indicates the subgrade strength (Very Low, Low, Medium, and High).

• The fifth character indicates the number of base/subbase layers (1 or 2).

• The last three characters indicate the Single aircraft type or Traffic mix number.

As an example, structure RUGL1T01 indicates a rigid unbonded overlay on rigid pavement, with one granular subbase layer, on a low-strength subgrade. The loading applied is traffic mix 1. The particular structures used in the present study were used previously by McQueen, et al. [5] to calibrate LEDFAA 1.2 using AC 150.5320-6D design charts. This approach provides continuity in the sensitivity of the FAA design procedures. 2.1 NEW FLEXIBLE PAVEMENT TEST STRUCTURES.

Twelve pavement structures were selected for the new flexible pavement design testing and are presented in table 1. These 12 structures were chosen as representative of the range of flexible structures found in practice. Conventional structures have a minimum 8-inch item P-209 crushed aggregate base, per AC 150.5320-6D. Conversion between the subgrade elastic modulus E and CBR follows the formula E = 1500 CBR, where E is in pounds per square inch (psi).

2

3

Table 1. Pavement Structural Data (New Flexible Pavement Design)

P-401 Surface Base Subgrade PavementStructure

Thickness (inches)

E (psi)

Thickness (inches)

E (psi)

Design Layer(Subbase) CBR E

(psi) Comments1 5 200,000 8 * P-154 4 6,000 2 5 200,000 12 * P-154 4 6,000 3 5 200,000 5 400,000 P-209 4 6,000 ASB 4 5 200,000 8 400,000 P-209 4 6,000 ASB 5 5 200,000 8 * P-154 8 12,000 6 5 200,000 12 * P-154 8 12,000 7 5 200,000 5 400,000 P-209 8 12,000 ASB 8 5 200,000 8 400,000 P-209 8 12,000 ASB 9 5 200,000 8 * P-154 15 22,500 10 5 200,000 12 * P-154 15 22,500 11 5 200,000 5 400,000 P-209 15 22,500 ASB 12 5 200,000 8 400,000 P-209 15 22,500 ASB

* Modulus calculated by LEDFAA ASB - Asphalt stabilized base

2.2 NEW RIGID PAVEMENT TEST STRUCTURES.

Twenty-seven pavement structures were selected for the comparative study for new rigid pavement design testing and are summarized in table 2. Pavement structures 1 to 10 and 15 to 17 have concrete flexural strengths of 650 and 500 psi for structures 21 to 27, with the remainder of the structures designed with flexural strength of 700 psi. The effect of the concrete strength (R) in the failure model for rigid pavements is evaluated in this study following the approach used by McQueen during the LEDFAA sensitivity study [4]. 2.3 RIGID OVER RIGID PAVEMENT TEST STRUCTURES.

For the comparative study, 24 structures were selected, and their characteristics are shown in table 3. The subgrade strength varies from low (E = 7,500 psi) to high (E = 25,000 psi). A single concrete strength for the existing slab was tested (R = 715 psi). Two different condition levels for the existing slab were selected: Structural Condition Index (SCI) 50 and 75. The SCI definition is related to the Pavement Condition Index (PCI) contained in Chapter 6 of AC 150.5320-6D. The 24 structures were divided in two groups of 12 structures. In the first group, the existing Portland concrete cement (PCC) slabs are 10 inches thick. In the second group, the existing slabs are 14 inches thick. For each group, the first six structures have a conventional subbase layer and the other six a stabilized subbase layer. The last column in the table shows the k value at the top of the foundation (which includes the effect of any subbase layer on top of the subgrade). The conversions between subgrade elastic modulus E and modulus of subgrade reaction k were based on the formula E = 26 k1.284 (E in psi, k in pci).

Table 2. Pavement Structural Data (New Rigid Pavement Design)

Subbase 1 Subbase 2 Subgrade

Pavement Structure

Run No.

Flexural Strength

R (psi)

Thickness (inches)

E (psi)

Poisson’s Ratio

Thickness (inches)

E (psi)

Poisson’s Ratio

E (psi)

Poisson’s Ratio

k (pci)

Top of Subbase

Effective k (pci)

1 A 650 6 14,474 0.35 0 N/A N/A 4,500 0.35 55 85 2 22 650 6 21,404 0.35 0 N/A N/A 7,500 0.35 82 124 3 23 650 6 250,000 0.25 6 21,404 0.35 7,500 0.35 82 241 4 26 650 6 500,000 0.25 6 21,404 0.35 7,500 0.35 82 241 5 29 650 6 35,429 0.35 0 N/A N/A 15,000 0.35 141 199 6 30 650 6 250,000 0.25 6 35,429 0.35 15,000 0.35 141 304 7 33 650 6 500,000 0.25 6 35,429 0.35 15,000 0.35 141 304 8 36 650 6 49,985 0.35 0 N/A N/A 25,000 0.35 210 264 9 37 650 6 250,000 0.25 6 49,985 0.35 25,000 0.35 210 340

10 40 650 6 500,000 0.25 6 49,985 0.35 25,000 0.35 210 340 11 B 700 6 14,474 0.35 0 N/A N/A 4,500 0.35 55 85 12 22A 700 6 21,404 0.35 0 N/A N/A 7,500 0.35 82 124 13 29B 700 6 35,429 0.35 0 N/A N/A 15,000 0.35 141 199 14 36B 700 6 49,985 0.35 0 N/A N/A 25,000 0.35 210 264 15 23A 650 6 700,000 0.25 6 21,404 0.35 7,500 0.35 82 241 16 30A 650 6 700,000 0.25 6 35,429 0.35 15,000 0.35 141 304 17 37A 650 6 700,000 0.25 6 49,985 0.35 25,000 0.35 210 340 18 23B 700 6 700,000 0.25 6 21,404 0.35 7,500 0.35 82 241 19 30B 700 6 700,000 0.25 6 35,429 0.35 15,000 0.35 141 304 20 37B 700 6 700,000 0.25 6 49,985 0.35 25,000 0.35 210 340 21 C 500 6 14,474 0.35 0 N/A N/A 4,500 0.35 55 85 22 22C 500 6 21,404 0.35 0 N/A N/A 7,500 0.35 82 124 23 29C 500 6 35,429 0.35 0 N/A N/A 15,000 0.35 141 199 24 36C 500 6 49,985 0.35 0 N/A N/A 25,000 0.35 210 264 25 23C 500 6 700,000 0.25 6 21,404 0.35 7,500 0.35 82 241 26 30C 500 6 700,000 0.25 6 35,429 0.35 15,000 0.35 141 304 27 37C 500 6 700,000 0.25 6 49,985 0.35 25,000 0.35 210 340

4

pci = pounds per cubic inch

Table 3. Pavement Structural Data (Overlay Pavement Design)

5

Pavement Structures Existing PCC Stabilized Base Subbase Subgrade

No. Original No.

Thickness (inches)

R (psi) PCC SCI Cb Cr μ Thickness

(inches) E,

(psi) μ Thickness (inches)

E (psi) μ E

(psi) μ k (pci)

Top of Subgrade, Effective

k (pci) 1 22 10 715 50 0.75 0.50 0.15 0 N/A N/A 6 21,404 0.35 7,500 0.35 82 124

2 22 10 715 75 0.95 0.80 0.15 0 N/A N/A 6 21,404 0.35 7,500 0.35 82 124

3 29 10 715 50 0.75 0.50 0.15 0 N/A N/A 6 35,429 0.35 15,000 0.35 141 199

4 29 10 715 75 0.95 0.80 0.15 0 N/A N/A 6 35,429 0.35 15,000 0.35 141 199

5 36 10 715 50 0.75 0.50 0.15 0 N/A N/A 6 49,985 0.35 25,000 0.35 210 264

6 36 10 715 75 0.95 0.80 0.15 0 N/A N/A 6 49,985 0.35 25,000 0.35 210 264

7 23 10 715 50 0.75 0.50 0.15 6 250,000 0.25 6 21,404 0.35 7,500 0.35 82 241

8 23 10 715 75 0.95 0.80 0.15 6 250,000 0.25 6 21,404 0.35 7,500 0.35 82 241

9 33 10 715 50 0.75 0.50 0.15 6 500,000 0.2 6 35,429 0.35 15,000 0.35 141 304

10 33 10 715 75 0.95 0.80 0.15 6 500,000 0.2 6 35,429 0.35 15,000 0.35 141 304

11 37A 10 715 50 0.75 0.50 0.15 6 700,000 0.2 6 49,985 0.35 25,000 0.35 210 340

12 37A 10 715 75 0.95 0.80 0.15 6 700,000 0.2 6 49,985 0.35 25,000 0.35 210 340

13 22 14 715 50 0.75 0.50 0.15 0 N/A N/A 6 21,404 0.35 7,500 0.35 82 124

14 22 14 715 75 0.95 0.80 0.15 0 N/A N/A 6 21,404 0.35 7,500 0.35 82 124

15 29 14 715 50 0.75 0.50 0.15 0 N/A N/A 6 35,429 0.35 15,000 0.35 141 199 16 29 14 715 75 0.95 0.80 0.15 0 N/A N/A 6 35,429 0.35 15,000 0.35 141 199

17 36 14 715 50 0.75 0.50 0.15 0 N/A N/A 6 49,985 0.35 25,000 0.35 210 264

18 36 14 715 75 0.95 0.80 0.15 0 N/A N/A 6 49,985 0.35 25,000 0.35 210 264

19 23 14 715 50 0.75 0.50 0.15 6 250,000 0.25 6 21,404 0.35 7,500 0.35 82 241

20 23 14 715 75 0.95 0.80 0.15 6 250,000 0.25 6 21,404 0.35 7,500 0.35 82 241

21 33 14 715 50 0.75 0.50 0.15 6 500,000 0.2 6 35,429 0.35 15,000 0.35 141 304

22 33 14 715 75 0.95 0.80 0.15 6 500,000 0.2 6 35,429 0.35 15,000 0.35 141 304

23 37A 14 715 50 0.75 0.50 0.15 6 700,000 0.2 6 49,985 0.35 25,000 0.35 210 340

24 37A 14 715 75 0.95 0.80 0.15 6 700,000 0.2 6 49,985 0.35 25,000 0.35 210 340

pci = pounds per cubic inch

2.4 AIRCRAFT TRAFFIC MIXES.

Tables 4a through 4h show the eight different traffic mixes used to design the new rigid and overlay pavement structures. The traffic mixes are actual aircraft mixes obtained from civil airports in the United States. They include both exclusively narrow-body and narrow- and wide-body aircraft mixes as follows: • Mix 1—Sarasota-Bradenton Airport (narrow-body) (table 4a) • Mix 2—Washington-Dulles International Airport, Taxiway W-1 (wide-body) (table 4b) • Mix 3—Washington Dulles International Airport, Runway 1L (wide-body) (table 4c) • Mix 4—Memphis International Airport, Runway 18R (wide-body) (table 4d) • Mixes 5 and 6—Charlotte-Douglas Airport (narrow-body) (tables 4e and 4f) • Mix 7—Philadelphia International Airport (wide-body) (table 4g) • Mix 8—J. F. Kennedy International Airport (wide-body) (table 4h) Mixes 3, 4, and 8 include B777 aircraft, and mix 8 includes A380 aircraft. To gauge the contribution of different single aircraft gear configurations and operational frequencies, additional comparisons were performed for dual (D)-wheel (B727 and B737), dual-tandem (2D) (DC10, A340, B747-400), and triple dual-tandem (3D) (B777 and A380) gears at varying annual departure levels. Tables 5 and 6 show the list of aircraft, gross weight (GW), and departure levels used to evaluate rigid and flexible pavements, respectively. Although the FEDFAA traffic model requires the user to input a traffic mix and therefore these comparisons are most useful, evaluation of differences in thickness from single aircraft will be useful in program calibration. 2.5 SINGLE AIRCRAFT TRAFFIC.

Table 5 shows five single aircraft with different loads and gear configurations at three different departure levels (1,200, 6,000, and 25,000 passes) for new rigid and rigid-over-rigid pavement analysis. In table 6, four single aircraft at three different departure levels (120, 1,200, and 12,000 passes) are shown for new and flexible overlay pavement analysis.

6

Table 4a. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 1, Sarasota-Bradenton Airport

Aircraft GW (lb) Departures

DC9-30 90,700 24 B737-200 115,000 979 DC9-50 121,000 282 B737-300 140,000 304 B727 169,000 319 B727* 209,000 1572 B757 255,000 72 DC8 276,000 10 BAE-146 70,000 51

*Design Aircraft for FAA AC 150.5320-6D Conventional Design Procedure

Table 4b. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 2, Washington-Dulles International Airport, Taxiway W-1


B757 255,000 127 B767-200 315,000 237 DC9-50 135,000 855 B727* 209,500 2011 DC10-10 443,000 827 B737-100 110,000 3726 B747-200 600,000 280 DC8 325,000 852 B707 257,000 1730


7

Table 4c. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 3, Washington-Dulles International Airport, Runway 1L


Sngl Whl-30 35,000 17,850 Sngl Whl-60 55,000 164,599 B727* 210,000 7,965 B737-700 160,000 86,053 B737-800 173,000 17,064 B757 250,000 22,021 DC8 355,000 260 B767-200 350,000 10,433 B777-200 ER 634,500 11,102 B777-300 750,000 996 B747-400 873,000 5,990 DC10-10 460,000 4,135 MD11 621,000 3,693 MD11 Belly 621,000 3,693 A340-200/300 621,000 2,065 A340-2/3 Belly 621,000 2,065


Table 4d. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 4,

Memphis Airport, Runway 18R

Aircraft GW (lb) Departures Sngl Whl-45 45,000 20,432 DC9-30 100,000 2,578 B707 350,000 203 B737-400 150,000 11,663 MD90-30 160,000 3,184 B727 169,000 19 B727* 210,000 13,367 B757 255,000 2,321 B767-200 350,000 669 B747-400 870,000 311 MD11 607,000 3,915 MD11 Belly 607,000 3,915 A300-600 364,000 4,632 A330 467,000 4,072 B777-200A 590,000 156 C-141 343,000 1,030


8

Table 4e. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 5, Charlotte Airport, Runway 18R-36L


B737-300* 150,000 12,775 B737-400 140,000 3,650 B737-700 160,000 183 Fokker F100 100,000 1,095 A320 160,000 2,372


Table 4f. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 6, Charlotte-Douglas Airport


DC-8* 350,000 411 B707 312,000 91 B767-200 300,000 365 B757 220,000 639 MD82/88 140,000 1,825 B737-200 130,000 12,365 DC9-50 121,000 2,829


Table 4g. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 7, Philadelphia Airport, 1993 Traffic


B727* 209,500 4,958 B737-400 150,000 23,356 B747-200 870,000 832 B757 255,500 3,427 B767-200 350,000 5,061 DC10-30 590,000 2,263 DC10-30 Belly 590,000 2,263 DC8 350,000 1,000 DC9-50 121,000 6,086 MD82/88 160,000 13,756


9

Table 4h. Air Traffic Mixes for Rigid and Flexible Pavement Structures—Mix 8, J. F. Kennedy International Airport, Runway 13R-31L


A300-600 375,900 3,838 A320 162,000 15,101 A330 507,000 1,015 B757 270,000 7,544 B737-800 174,200 1,561 B747-200 833,000 2,207 B747-400 873,000 8,519 B767-200 335,000 6,178 B767-300 ER 409,000 9,635 B777-200 A 632,500 3,111 Concorde 410,000 406 Fokker F100 100,000 12,117 DC9-30 121,000 569 DC9-50 121,000 488 A340-500/600* 750,000 2,441 A340 Belly 750,000 2,441 A380-800 1,340,000 5,475 B747-SP 696,000 3 DC8 358,000 504 MD11 621,000 3,315 MD11 Belly 621,000 3,315


10

Table 5. Single Aircraft Traffic Data for Analysis of New Rigid Pavement and Overlays on Existing Rigid Pavements

Reference No. Aircraft

Gear Configuration

Gross Weight (lb)

Annual Passes

S01 B727 D 209,000 1,200

S02 B727 D 209,000 6,000

S03 B727 D 209,000 25,000

S04 DC10-10 2D 460,000 1,200

S05 DC10-10 2D 460,000 6,000

S06 DC10-10 2D 460,000 25,000

S07 B737-800 D 173,000 1,200

S08 B737-800 D 173,000 6,000

S09 B737-800 D 173,000 25,000

S10 B777-200 B 3D 653,000 1,200

S11 B777-200 B 3D 653,000 6,000

S12 B777-200 B 3D 653,000 25,000

S25 B747-400 2D 873,000 1,200

S26 B747-400 2D 873,000 6,000

S27 B747-400 2D 873,000 25,000

11

Table 6. Single Aircraft Traffic Data for Analysis of New Flexible Pavements and Overlays on Existing Flexible Pavements

Reference No. Aircraft

Gear Configuration

Gross Weight (lb)

Annual Passes

S13 A380-800 3D 1,239,000 120

S14 A380-800 3D 1,239,000 1,200

S15 A380-800 3D 1,239,000 12,000

S16 A340 BELLY 2D 600,000 120

S17 A340 BELLY 2D 600,000 1,200

S18 A340 BELLY 2D 600,000 12,00

S19 B777-200 A 3D 537,000 120

S20 B777-200 A 3D 537,000 1,200

S21 B777-200 A 3D 537,000 12,000

S22 B747-400 2D 873,000 120

S23 B747-400 2D 873,000 1,200

S24 B747-400 2D 873,000 12,000

2.6 PAVEMENT DESIGN METHODS.

In this study, the comparison of design thicknesses for rigid pavements used the following design methods: • Conventional FAA method based on Westergaard theory, as described in AC 150.5320-

6D, Chapter 3. COMFAA, the FAA program for computing flexible and rigid aircraft classification numbers and pavement thickness, was used to calculate design thicknesses, as described by AC 150.5320-6D for new pavements.

• Three-Dimensional Finite Element FAA:

a. FEDFAA 1.4 program, using the existing LEDFAA failure model including stabilized base compensation.

b. FEDFAA 1.4 program, using the LEDFAA failure model without stabilized base

compensation (parameter Fslope is set to the default value of 1.0, Fs = 1).

12

c. FEDFAA 2.0 program, using a revised failure model and calibration factor. For flexible pavements, the comparison uses: • Conventional FAA method based on CBR method, as described in AC 150.5320-6D,

Chapter 3 (COMFAA). • Layered elastic design, as described in AC 150.5320-6D, Chapter 7 (LEDFAA). The nomograms used in the conventional FAA pavement design method, as described in AC 150.5320-6D Chapters 3 and 4, have been incorporated in spreadsheet format and made official FAA standards in Change 3. The FAA spreadsheet programs are designated R805FAA (rigid) and F806FAA (flexible). COMFAA and the spreadsheets produced nearly identical solutions for pavement thickness design in cases where the spreadsheets include appropriate aircraft loads. The original nomograms in the FAA pavement design method did not include gears with six-wheel configuration. Therefore, for the six-wheel gear case (B777 and A380), COMFAA extrapolates the original nomograms and the calculated thicknesses are only approximations of the conventional method. The comparative study used the calculated pavement thicknesses by the original FAA design method described in AC 150.5320-6D as a baseline to calibrate the new FEDFAA method for rigid pavements. LEDFAA results have not been included since the calculated thicknesses by this method are not relevant for the rigid pavement calibration.

3. NEW RIGID PAVEMENT DESIGN RESULTS.

The PCC slab thicknesses for new rigid pavements have been calculated using the methods described in section 2.5 for the 27 pavement structures shown in table 2, the single aircraft traffic listed in table 5, and the eight traffic mixes listed in table 4. The calculated slab thicknesses comparison was analyzed in two groups: pavement structures under single aircraft traffic and pavement structures under aircraft traffic mixes. 3.1 SINGLE AIRCRAFT TRAFFIC.

Figures 1, 2, and 3 compare the conventional pavement structures with PCC strengths of 500, 650, and 700 psi, respectively. The comparisons in figures 4 to 6 are substantially the same except for the material assumed for the stabilized subbase layer (item P-301, soil cement; item P-304, cement-treated base (CTB); and item P-306, econocrete, respectively). 3.1.1 Subbase Effect on Pavement Structures.

The conventional rigid pavement structures compared in figures 1, 2, and 3 are identical except for the difference in design concrete strength 500, 650, and 700 psi. They are compared using the four different design procedures discussed in section 2.5 under single aircraft traffic. The

13

departure level and subgrade strength are varied. The following are some preliminary observations based on figures 1, 2, and 3: • The pavement structures appear to be more sensitive to the departure levels than any

other parameter. For example using COMFAA, the average thickness difference between structures:

a. by departure levels is between 1.8 to 1.9 inches for 1,200 passes, reducing to 1.1

to 1.7 inches for 6,000 passes and 0.4 to 1.3 inches for 25,000 passes;

b. by concrete R = 500 psi is between 0.4 to 1.8 inches for all departure levels and 1.3 to 1.9 inches when R = 650 psi or 700 psi for all departure levels;

c. by aircraft type is between 0.6 to 1.1 inches for two-wheel gear, 1.5 to 1.7 inches for four-wheel gear, and 2.3 inches for six-wheel gear for all departure levels.

• For the dual-wheel gear aircraft using COMFAA, thickness is less sensitive to the subgrade strength. The slab thickness is approximately 0.5 inch thicker when the subgrade E value is 4,500 psi than when the subgrade has an E = 7,500 psi; and 0.8 inch thicker between subgrade E values of 7,500 and 15,000 psi. The slab thickness difference reduces to 0.6 inch between 15,000 and 25,000 psi.

• In general, FEDFAA 2.0 produces thicker slabs than those calculated by COMFAA.

Exceptions occur for lower values of R and higher departure levels. Also, it is important to point out that AC 150.5320-6D does not have nomograms for newer aircraft like the B777. Therefore, the calculated thicknesses by COMFAA for the B777 are not necessarily reliable.

• For single aircraft with dual-wheel gears, the thicknesses calculated using COMFAA

seem to be most sensitive to departure levels, second-most sensitive to concrete R value, and less sensitive to subgrade strength. Thickness computed using FEDFAA 2.0 seems to be equally sensitive to departure levels and subgrade strength, and less sensitive to concrete R value.

• For single aircraft with 2D and 3D gears, the subgrade strength seems to be the most

sensitive factor for both COMFAA and FEDFAA 2.0. For the subgrade strength comparison, the slab thickness differences calculated by COMFAA increase with the departure levels, but decrease when calculated by FEDFAA 2.0. The other factors (departure level and concrete R value) have a similar effect as with the dual-wheel gear.

14

0

5

10

15

20

25

30

C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C

Section Code

Slab

Thi

ckne

ss, i

nche

s

AC 150/5320-6D (COMFAA)FEDFAA BETA 1.4FEDFAA BETA 1.4 (Fs=1)FEDFAA 2.0

Es =

450

0Es

=75

00Es

= 1

5000

Es =

2500

0

B727 B737-800 DC10-10 B747-400 B777-200

Subgrade 4,500; 7,500;

15,000; 25,000 psi

PCC R =500 psi

6" P-209 Cr Ag

Annual Departures1200 | 6000 | 25000

Figure 1. Conventional Pavement Structures for Single Aircraft (PCC R = 500 psi)

0

5

10

15

20

25

30

A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36

Section Code

Slab

Thi

ckne

ss, i

nche

s


Es =

450

0Es

=75

00Es

= 1

5000

Es =

2500

0

B727 B737-800 DC10-10 B747-400 B777-200

Subgrade 4,500; 7,500; 15,000; 25,000 psi

PCC R = 650 psi

6" P-209 Cr Ag



15

0

5

10

15

20

25

30

B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B

Section Code

Slab

Thi

ckne

ss, i

nche

sAC 150/5320-6D (COMFAA)FEDFAA BETA 1.4FEDFAA BETA 1.4 (Fs=1)FEDFAA 2.0

Es =

450

0Es

=75

00Es

= 1

5000

Es =

2500

0

B727 B737-800 DC10-10 B747-400 B777-200

Subgrade 4,500; 7,500; 15,000; 25,000 psi

PCC R = 700 psi

6" P-209 Cr Ag



Pavements with PCC R = 650 psi and different stabilized base conditions have been analyzed. Figure 4 shows pavement structures with a soil cement base (SCB) (item P-301) stabilized layer, with an elastic modulus of 250,000 psi. Figure 5 shows pavement structures with a CTB (item P-304) stabilized layer (E = 500,000 psi). Figure 6 shows pavement structures with an econocrete subbase (item P-306, E = 700,000 psi). The following observations are related to figures 4 to 6:

• The slab thickness, as calculated by COMFAA, is the same for all the examples with

identical loads, if the only difference in the structure is the stabilized base material. This is because COMFAA does not differentiate between different types of stabilized bases. In other words, for COMFAA, any stabilized subbase will make the same contribution to the pavement structure. By contrast, the FEDFAA 2.0 structural model incorporates the E modulus of the stabilized base layer directly into the stress computation. Thus, there is an effect on the thickness calculation whether or not stabilized subbase compensation is included.

• The slab thickness calculated by FEDFAA 2.0 with the new failure model and calibration

factor seems to be always thicker than the thicknesses calculated by COMFAA regardless of the aircraft type, subgrade strength, and departure level. However, when the subgrade strength and departure level combined are high, then the calculated thicknesses for both methods are similar.

16

0

5

10

15

20

25

30

23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37

Section Code

Slab

Thi

ckne

ss, i

nche


B727 B737-800 DC10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

6" P-301 SCB

6" P-209 Cr Ag

PCC R = 650 psi

Subgrade 7,500; 15,000; 25,000 psi

Figure 4. Stabilized Base (Item P-301) Pavement Structures With Single Aircraft Traffic

(PCC R = 650 psi)

0

5

10

15

20

25

30

26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40

Section Code

Slab

Thi

ckne

ss, i

nche

s


B727 B737-800 DC10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

6" P-304 CTB

6" P-209 Cr Ag

PCC R = 650 psi

Subgrade 7,500; 15,000; 25,000 psi

Figure 5. Stabilized Base (Item P-304) Pavement Structures With Single Aircraft Traffic

(PCC R = 650 psi)

17

0

5

10

15

20

25

30

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

Section Code

Slab

Thi

ckne

ss, i

nche


B727 B737-800 DC10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

PCC R = 650 psi

6" P-306 Econocrete

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

Figure 6. Stabilized Base (Item P-306) Pavement Structures With Single Aircraft Traffic (PCC R = 650 psi)

3.1.2 Effect of Departure Level.

Figure 7 shows FEDFAA 2.0 results for single aircraft traffic at three departure levels. Results are presented as the difference (in inches) in PCC thickness between pavements designed using FEDFAA 2.0 and pavements designed using the COMFAA program. A positive value in figure 7 indicates that FEDFAA requires a thicker slab than required by the AC 150.5320-6D design method. A negative value means that the FEDFAA design is thinner than AC 150.5320-6D. For all single aircraft regardless of the gear configuration, the thickness differences decrease with the increase of annual departures. The thickness differences for all single aircraft are positive except for the B727 under 25,000 passes. Also, the thickness differences increase when the number of wheels in the gear increases.

18

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

B727 B737 DC10-10 B747 B777

Single Aircraft Type

Thic

knes

s U

sing

FED

FAA

2.0

- Th

ickn

ess

Usi

ng

CO

MFA

A, i

nche

s1,200 Annual Passes6,000 Annual Passes25,000 Annual Passes

Figure 7. Slab Thickness Differences for Single Aircraft Traffic (Effect of Departure Level)

3.1.3 Subgrade Effect on Pavement Structures.

Figure 8 compares FEDFAA 2.0 results to COMFAA for single aircraft traffic for three different subgrade strengths. As in figure 7, the results are presented as the difference in design thickness between FEDFAA 2.0 and COMFAA. For all the pavement structures with conventional subbase for the five single aircraft, the slab thickness differences are larger when the subgrade strength increases, as shown in figure 8. This is true for all the cases except for the B777. In most cases, the calculated thicknesses by FEDFAA 2.0 are thinner than by COMFAA. Figure 9 shows the effect of the stabilized subbase strength on the average slab thickness differences as calculated by FEDFAA 2.0 and COMFAA. As the stabilized subbase strength increases, the slab thickness differences increase for the D and 2D aircraft. In these cases, the thickness differences are less for structures that do not include stabilized base, i.e., aggregate base only. For the 3D, the opposite occurs.

19

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

B727 B737 DC10-10 B747 B777


Thic

knes

s U

sing

FED

FAA

2.0

- T

hick

ness

Usi

ng C

OM

FAA

, inc

hes

E = 7,500 psi

E = 15,000 psi

E = 25,000 psi

PCC R = 650 psi

6" P-209 Cr Ag

Subgrade E=7,500; 15,000; 25,000 psi

Figure 8. Effect of Subbase Strength on FEDFAA Design Thickness for Single Aircraft Traffic

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

B727 B737 DC10-10 B747 B777


Thic

knes

s U

sing

FED

FAA

2.0

- T

hick

ness

Usi

ng C

OM

FAA

, inc

hes

No Stabilized SubbaseE = 250,000 psiE = 500,000 psiE = 700,000 psi

PCC R = 650 psi

6" Stabilized Base0; 250,000; 500,000; 700,000 psi

6" P-209 Cr Ag

Subgrade E=7,500 psi

Figure 9. Effect of Stabilized Base Modulus on FEDFAA Design Thickness for Single

Aircraft Traffic

20

3.1.4 Correlation Between Design Procedures.

Figures 10 through 14 show the design thickness as computed by FEDFAA 2.0 on the vertical scale, against the corresponding thickness as computed by COMFAA on the horizontal scale. Plots were prepared for five single aircraft types: B727, B737, DC10-10, B747, and B777. In each case, two graphs were prepared. The plots shown in (a) segregate the data points by traffic levels; (b) combine all the data for each aircraft type into a single scatter plot. The following observations are made on the correlation of the data: • For dual-wheel gears, the data falls into three distinct groups according to departure

level, as shown in figures 10(a) and 11(a). The correlation coefficients (R2) are between 0.91 and 0.94 with a difference of about 2.5 inches. However, if the data are not segregated by departure levels (see figures 10(b) and 11(b)), then R2 is reduced (to 0.9088 for the B727 and 0.8943 for the B737), and the difference is also reduced (to 1.5 inches).

• For 2D gears, the correlation is about the same as for dual-wheel gears for the three

departure levels (figures 12(a) and 13(a)). Figures 12(b) and 13(b) show R2 values of 0.8839 and 0.8846 respectively for all three departure levels.

• Finally, the weakest correlation between COMFAA and FEDFAA 2.0 is obtained for the

3D aircraft (figures 14(a) and 14(b)). Although the R2 value from these plots is only 0.8399, the correlation difference is almost 5 inches.

21

y = 1.0563x + 0.2758R2 = 0.9132

y = 0.9628x + 1.2783R2 = 0.9332

y = 0.8911x + 2.1414R2 = 0.9462

0

5

10

15

20

25

30

0 5 10 15 20 25 30Thickness by COMFAA, inches

Thic

knes

s by

FED

FAA

, inc

hes

Annual Passes = 1,200



Linear (Annual Passes = 1,200)



(a) Segregated by Departure Level

y = 0.8568x + 3.2006R2 = 0.9088

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes

(b) All Departure Levels

Figure 10. B727 FEDFAA-6D Correlation, Wheel Load 49,638 lb

22

y = 1.2037x - 1.4678R2 = 0.9126

y = 1.0857x - 0.342R2 = 0.9302

y = 0.9963x + 0.6276R2 = 0.9413

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes








y = 0.9388x + 2.0725R2 = 0.8943

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes

(b) All Departure Levels


23

y = 0.9884x + 2.0734R2 = 0.8676

y = 0.8693x + 3.7031R2 = 0.8777

y = 0.7842x + 5.0063R2 = 0.8861

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes








y = 0.8513x + 3.9647R2 = 0.8839

0

4

8

12

16

20

24

28

0 4 8 12 16 20 24 2Thickness by COMFAA, inches

Thic

knes

s by

FED

FAA

, inc

hes

8

-

(b) All Departures Levels

Figure 12. DC10 FEDFAA-6D Correlation, Wheel Load 54,625 lb

24

y = 0.9647x + 2.6474R2 = 0.8747

y = 0.8452x + 4.4009R2 = 0.8913

y = 0.7639x + 5.7368R2 = 0.8995

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes








y = 0.8308x + 4.6184R2 = 0.8946

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes



25

y = 0.8056x + 5.5299R2 = 0.8187

y = 0.6924x + 7.4754R2 = 0.8302

y = 0.6374x + 7.4722R2 = 0.8308

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes








y = 0.7133x + 7.0799R2 = 0.8399

0

5

10

15

20

25

30


Thic

knes

s by

FED

FAA

, inc

hes



26


In this section, PCC thickness designs using COMFAA and FEDFAA 2.0 were compared for the eight traffic mixes shown in table 4. Figures 15, 16, and 17 show comparisons for conventional rigid pavement structures, i.e., slab on aggregate base. Thickness comparisons for structures with stabilized subbases are shown in figures 18 to 20. 3.2.1 Conventional Pavement Structures.

The preliminary observations from figures 15 and 17 follow: • For the structures in table 2, COMFAA calculates thicker slabs than FEDFAA 2.0 for

mixes with wide-body aircraft and thinner slabs for mixes with narrow-body aircraft, when the concrete strength is between 500 and 700 psi (see figures 15 to 17).

• For higher concrete R values, the thickness difference is significantly smaller than for

lower R values, in particular, for wide-body aircraft mixes, when thickness differences are significantly larger.

• For the traffic mixes in this study, the slab thickness difference is less sensitive to

subgrade strength when calculated by COMFAA than FEDFAA, except for traffic mixes 6 and 8. The concrete R value effect is higher for FEDFAA than COMFAA.

0

5

10

15

20

25

30

35

C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C C22

C29

C36

C

Section Code

Slab

Thi

ckne

ss, i

nche

s

AC 150/5320-6D (COMFAA)FEDFAA BETA 1.4FEDFAA BETA 1.4 Fs=1FEDFAA 2.0

Traffic Mix 1 Traffic Mix 2 Traffic Mix 3 Traffic Mix 4 Traffic Mix 5 Traffic Mix 6 Traffic Mix 7 Traffic Mix 8

Subgrade 4,500; 7,500; 15,000; 25,000 psi

PCC R = 500 psi

6" P-209 Cr Ag

Figure 15. Results of Design Comparison for New Conventional Rigid Pavements (R = 500 psi)

Under Mixed Aircraft Traffic

27

0

5

10

15

20

25

30

35

A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36 A 22 29 36

Section Code

Slab

Thi

ckne

ss, i

nche

s



Subgrade 4,500; 7,500; 15,000; 25,000 psi

PCC R = 650 psi

6" P-209 Cr Ag



0

5

10

15

20

25

30

35

B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B B22

A29

B36

B

Section Code

Slab

Thi

ckne

ss, i

nche

s



Subgrade 4,500; 7,500; 15,000; 25,000 psi

PCC R = 700 psi

6" P-209 Cr Ag



28

3.2.2 Pavement Structures With Stabilized Subbase.

Figures 18 through 20 show pavement structures with stabilized subbase layers: soil cement base (P-301 SCB), cement-treated base (P-304 CTB), and econocrete subbase (P-306 econocrete), respectively. Preliminary observations from figures 18 through 20 are as follows: • The slab thicknesses calculated by COMFAA have the same value regardless of the

stabilized subbase type, elastic modulus, and aircraft mix body type. • FEDFAA requires, on average, thinner slabs for the pavements with econocrete subbase

than with CTB or SCB. • An increase in subgrade strength results in a significantly larger reduction in PCC

thickness for stabilized base structures designed in FEDFAA compared to COMFAA for the same structures.

0

5

10

15

20

25

30

35

23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37 23 30 37

Section Code

Slab

Thi

ckne

ss, i

nche

s



6" P-301 SCB

6" P-209 Cr Ag

PCC R = 650 psi

Subgrade 7,500; 15,000; 25,000 psi

Figure 18. Results of Design Comparison for New Rigid Pavements With Stabilized Base,

Item P-301, SCB (Mixed Aircraft Traffic)

29

0

5

10

15

20

25

30

35

26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40 26 33 40

Section Code

Slab

Thi

ckne

ss, i

nche

sAC 150/5320-6D (COMFAA)FEDFAA BETA 1.4FEDFAA BETA 1.4 Fs=1FEDFAA 2.0


6" P-304 CTB

6" P-209 Cr Ag

PCC R = 650 psi

Subgrade 7,500; 15,000; 25,000 psi

Figure 19. Results of Design Comparison for New Rigid Pavements With Stabilized Base,

Item P-304, CTB (Mixed Aircraft Traffic)

0

5

10

15

20

25

30

35

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

23A

30A

37A

Section Code

Slab

Thi

ckne

ss, i

nche

s



PCC R = 650 psi

6" P-306 Econocrete

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

Figure 20. Results of Design Comparison for New Rigid Pavements With Stabilized Base, Item

P-306, Econocrete Base (Mixed Aircraft Traffic)

30

The thickness correlation between COMFAA and FEDFAA for structures with a conventional subbase and all concrete flexural strengths (R = 500, 650, and 700 psi) is shown in figure 21. • For low- to high-strength subgrade, the trend line falls about 2 inches above and up to 6

inches below the line of equality, but are roughly parallel to each other, except for the very low-strength line (E = 4500 psi).

• The correlation coefficients (R2) are between 0.8628 and 0.8821 for E = 4,500 psi to E =

25,000 psi, respectively.

y = 0.4788x + 10.283R2 = 0.8628

y = 0.5232x + 9.3705R2 = 0.8769

y = 0.5658x + 8.0678R2 = 0.8775

y = 0.6055x + 6.5974R2 = 0.8821

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35Slab Thickness by COMFAA, inches

Slab

Thi

ckne

ss b

y FE

DFA

A, i

nche

s

E = 4,500 psi

E = 7,500 psi

E = 15,000 psi

E = 25,000 psi

Linear (E = 4,500 psi)




PCC Modulus R = 500, 650 &

700 psi

6" P-209 Cr Ag

Subgrade 4,500; 7,500; 15,000; 25,000

psi

Figure 21. Slab Thickness Correlation for Structures With Conventional Subbase, Grouped by

Subgrade E-Modulus Figure 22 shows the correlations for all structures grouped by stabilized subbase. The different types of stabilized subbases are characterized by E value in FEDFAA. As stated above, the COMFAA program does not differentiate between different types of stabilized subbases. The trend lines for the three stabilized subbase types are roughly parallel and do not vary by more than 1 inch. Finally, figure 23 shows the correlation for all structures with stabilized subbases organized by subgrade strength. Once again, all three trend lines are approximately parallel. The correlation spreads approximately 2 inches above and below the equality line.

31

y = 0.6407x + 6.3786R2 = 0.8237

y = 0.6354x + 6.1568R2 = 0.7067

y = 0.6354x + 5.9835R2 = 0.6704

y = 0.6454x + 5.702R2 = 0.666

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35Slab Thickness by COMFAA, inches

Slab

Thi

ckne

ss b

y FE

DFA

A, i

nche

s

No Stab. Subbase

E = 250,000 psi

E = 500,000 psi

E = 700,000 psi

Linear (No Stab.Subbase)Linear (E = 250,000 psi)



PCC Modulus R = 650 psi

6" Stabilized Subbase 250; 500 & 700 ksi

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

Figure 22. Slab Thickness Correlation for All Structures, Grouped by

Subbase E-Modulus

y = 0.5574x + 8.4013R2 = 0.9266

y = 0.5778x + 7.2459R2 = 0.8692

y = 0.583x + 6.1223R2 = 0.8167

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Slab Thickness by COMFAA, inches

Slab

Thi

ckne

ss b

y FE

DFA

A, i

nche

s

E = 7,500 psi

E = 15,000 psi

E = 25,000 psi




PCC Modulus R = 650 psi

6" Stabilized Subbase 250; 500 & 700 ksi

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

Figure 23. Slab Thickness Correlation for All Structures With Stabilized Subbase, Grouped by

Subgrade E-Modulus

32

4. NEW FLEXIBLE PAVEMENT DESIGN RESULTS.

Pavement design thicknesses were computed using the COMFAA, LEDFAA 1.2, and LEDFAA 1.3 programs for various single aircraft and traffic mixes. 4.1 SINGLE AIRCRAFT COMPARISONS.

Three different annual departure levels were used: 120, 1,200, and 12,000. The results shown in this report are for 1200 annual departures. In figure 24, design thicknesses from LEDFAA 1.2 and COMFAA are both referenced to LEDFAA 1.3. Bars represent the percentage difference between the total thicknesses obtained from the two programs. A positive value in figure 24 indicates that LEDFAA 1.3 produces a thicker design than the program in question. Results are reported for pavement structures with an 8-inch-thick crushed stone (item P-209) subbase, for the various aircraft types shown in the figure. The results in figure 24 show that for very low- to medium-strength subgrades, LEDFAA 1.3 computed pavement thicknesses that, on the whole, were thinner than either version 1.2 of the same program or COMFAA. Note that the flexible pavement models in LEDFAA 1.3 are identical to those in FEDFAA 2.0.

-30

-20

-10

0

10

20

30

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

Aircraft

Thic

knes

s Diff

eren

ce, p

erce

nt

COMFAALEDFAA-1.2

SUBGRADE CBR - 3 SUBGRADE CBR - 15SUBGRADE CBR - 8SUBGRADE CBR - 4

Figure 24. Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 8-Inch-Thick P-209 Crushed Stone Base

For wide-body aircraft, LEDFAA 1.3 thicknesses are up to 17 percent lower than AC 150.5320-6D thicknesses and are up to 14 percent lower than LEDFAA 1.2 thicknesses. For the narrow-body aircraft (B727 and B737), the LEDFAA 1.3 thicknesses are up to 30 percent higher than

33

AC 150.5320-6D thicknesses, but up to 10 percent less than LEDFAA 1.2 thicknesses. For the high-strength subgrades (CBR = 15), LEDFAA 1.3 thicknesses are higher than those of the other two design procedures (AC 150.5320-6D and LEDFAA 1.2) for the majority of the aircraft considered. A similar trend was observed when the thickness of the P-209 crushed stone base was increased to 12 inches (figure 25).

-25

-20

-15

-10

-5

0

5

10

15

20

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

Aircraft

Thic

knes

s Diff

eren

ce, p

erce

nt

COMFAALEDFAA-1.2


Figure 25. Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 12-Inch-Thick P-209 Crushed Stone Base

Figures 26 and 27 show the thickness difference results obtained for pavements with stabilized (P-401) bases of 5 and 8 inches, respectively. For the very low- to medium-strength subgrades (CBR = 3, 4, and 8) and for wide-body aircraft, the LEDFAA 1.3 thicknesses are less than the COMFAA and LEDFAA 1.2 thicknesses. For the narrow-body aircraft (B727, B737), the LEDFAA 1.3 thicknesses are higher than the COMFAA thicknesses and lower than LEDFAA 1.2 thicknesses. For high-strength subgrade (CBR = 15), the LEDFAA 1.3 thicknesses are higher than the COMFAA and LEDFAA 1.2 thicknesses.

34

-20

-15

-10

-5

0

5

10

15

20

25

30

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

Aircraft

Thic

knes

s Diff

eren

ce, p

erce

nt

COMFAALEDFAA-1.2


Figure 26. Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 5-Inch-Thick P-401 ASB

35

-20

-15

-10

-5

0

5

10

15

20A

-380

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

A-3

80

A-3

40

B-7

77

B-7

47

B-7

27

B-7

37

Aircraft

Thic

knes

s Diff

eren

ce, p

erce

nt

COMFAALEDFAA-1.2


Figure 27. Difference Between Pavement Thicknesses Computed From LEDFAA 1.3, COMFAA, and LEDFAA 1.2 for Pavements With 8-Inch-Thick P-401 ASB

4.2 TRAFFIC MIX COMPARISONS.

The FAA design procedure is intended for designing airport pavements for traffic mixes. Aircraft traffic data from eight different airports were used for pavement thickness comparison. The traffic mixes consisted of both wide- and narrow-body aircraft. As previously discussed, of the eight traffic mixes, five were classified as wide-body mixes (wide-body aircraft dominate) and three were classified as narrow-body mixes (narrow-body aircraft dominate). Pavement thicknesses were computed from COMFAA, LEDFAA 1.2, and LEDFAA 1.3. Table 4 lists the traffic mixes used in the analysis. Figures 28, 32, and 33 show the thickness comparisons for narrow-body aircraft traffic mixes. Figures 29, 30, 31, 34, and 35 show the thickness comparisons for wide-body aircraft traffic mixes. In these figures, the x-axis gives the pavement structure identification number. The first two characters denote the type of pavement (NF = new flexible), the third character specifies the base type (G = P-209 base, S = P-401 ASB), the number after G or S denotes thickness of the base in inches, the character after the thickness denotes subgrade CBR (V = 3, L = 4, M = 8, H = 15), and the last three characters denote the mix number (in figure 28, T01 means traffic mix 1, and in figure 29, T07 means traffic mix 7, etc.).

36

0

10

20

30

40

50

60

70N

FG8V

T01

NFG

12V

T01

NFS

5VT0

1

NFS

8VT0

1

NFG

8LT0

1

NFG

12LT

01

NFS

5LT0

1

NFS

8LT0

1

NFG

8MT0

1

NFG

12M

T01

NFS

5MT0

1

NFS

8MT0

1

NFG

8HT0

1

NFG

12H

T01

NFS

5HT0

1

NFS

8HT0

1

Pave

men

t Thi

ckne

ss, i

nche

s

LEDFAA-1.2LEDFAA-1.3AC-150-5320-6D

Figure 28. Thickness Comparisons for Mix 1

For the narrow-body aircraft mixes (figures 28, 32, and 33), the LEDFAA 1.3 thicknesses are lower than LEDFAA 1.2 thicknesses for CBRs = 3 and 4 and are similar to CBRs = 8 and 15. No significant difference is observed between LEDFAA 1.3 and AC 150.5320-6D thicknesses. For the wide-body aircraft traffic mixes (figures 29, 30, 31, and 34), the LEDFAA 1.3 thicknesses are less than AC 150.5320-6D thicknesses for low- and medium-subgrade strengths. No significant difference is observed for the high-strength subgrade. LEDFAA 1.3 thicknesses are lower than LEDFAA 1.2 thicknesses for CBRs = 3, 4, and 8, and higher for CBR 15. Figure 35 shows the LEDFAA 1.3 thicknesses for traffic mix 8. Traffic mix 8 includes A380 and hence no thicknesses from LEDFAA 1.2 and AC 150.5320-6D are shown.

37

0

10

20

30

40

50

60

70

80

NFG

8VT0

2

NFG

12V

T02

NFS

5VT0

2

NFS

8VT0

2

NFG

8LT0

2

NFG

12LT

02

NFS

5LT0

2

NFS

8LT0

2

NFG

8MT0

2

NFG

12M

T02

NFS

5MT0

2

NFS

8MT0

2

NFG

8HT0

2

NFG

12H

T02

NFS

5HT0

2

NFS

8HT0

2

Pave

men

t Thi

ckne

ss, i

nche

s



0

10

20

30

40

50

60

70

80

90

100

110

NFG

8VT0

3

NFG

12V

T03

NFS

5VT0

3

NFS

8VT0

3

NFG

8LT0

3

NFG

12LT

03

NFS

5LT0

3

NFS

8LT0

3

NFG

8MT0

3

NFG

12M

T03

NFS

5MT0

3

NFS

8MT0

3

NFG

8HT0

3

NFG

12H

T03

NFS

5HT0

3

NFS

8HT0

3

Pave

men

t Thi

ckne

ss, i

nche

s

LEDFAA-1.2LEDFAA-1.3


38

0

10

20

30

40

50

60

70

80

90

100

NFG

8VT0

4

NFG

12V

T04

NFS

5VT0

4

NFS

8VT0

4

NFG

8LT0

4

NFG

12LT

04

NFS

5LT0

4

NFS

8LT0

4

NFG

8MT0

4

NFG

12M

T04

NFS

5MT0

4

NFS

8MT0

4

NFG

8HT0

4

NFG

12H

T04

NFS

5HT0

4

NFS

8HT0

4

Pave

men

t Thi

ckne

ss, i

nche

s

LEDFAA-1.2LEDFAA-1.3


0

10

20

30

40

50

60

70

NFG

8VT0

5

NFG

12V

T05

NFS

5VT0

5

NFS

8VT0

5

NFG

8LT0

5

NFG

12LT

05

NFS

5LT0

5

NFS

8LT0

5

NFG

8MT0

5

NFG

12M

T05

NFS

5MT0

5

NFS

8MT0

5

NFG

8HT0

5

NFG

12H

T05

NFS

5HT0

5

NFS

8HT0

5

Pave

men

t Thi

ckne

ss, i

nche

s



39

0

10

20

30

40

50

60

70

80

NFG

8VT0

6

NFG

12V

T06

NFS

5VT0

6

NFS

8VT0

6

NFG

8LT0

6

NFG

12LT

06

NFS

5LT0

6

NFS

8LT0

6

NFG

8MT0

6

NFG

12M

T06

NFS

5MT0

6

NFS

8MT0

6

NFG

8HT0

6

NFG

12H

T06

NFS

5HT0

6

NFS

8HT0

6

Pave

men

t Thi

ckne

ss, i

nche

sLEDFAA-1.2LEDFAA-1.3AC-150-5320-6D


0

10

20

30

40

50

60

70

80

90

100

NFG

8VT0

7

NFG

12V

T07

NFS

5VT0

7

NFS

8VT0

7

NFG

8LT0

7

NFG

12LT

07

NFS

5LT0

7

NFS

8LT0

7

NFG

8MT0

7

NFG

12M

T07

NFS

5MT0

7

NFS

8MT0

7

NFG

8HT0

7

NFG

12H

T07

NFS

5HT0

7

NFS

8HT0

7

Pave

men

t Thi

ckne

ss, i

nche

s



40

0

10

20

30

40

50

60

70

80

90

100

110

NFG

8VT0

8

NFG

12V

T08

NFS

5VT0

8

NFS

8VT0

8

NFG

8LT0

8

NFG

12LT

08

NFS

5LT0

8

NFS

8LT0

8

NFG

8MT0

8

NFG

12M

T08

NFS

5MT0

8

NFS

8MT0

8

NFG

8HT0

8

NFG

12H

T08

NFS

5HT0

8

NFS

8HT0

8

Pave

men

t Thi

ckne

ss, i

nche

s

LEDFAA-1.3

Figure 35. Thickness Calculated by LEDFAA 1.3 for Mix 8 5. PCC ON RIGID OVERLAY DESIGN RESULTS.

Reference PCC slab thicknesses for overlay rigid pavements have been calculated using the method described in AC 150.5320-6D, Chapter 4. Comparisons with FEDFAA 1.4 and FEDFAA 2.0 for the 24 reference pavement structures are shown in table 3. Following AC 150.5320-6D, the minimum rigid overlay thickness is 5 inches as indicated in paragraph 409 (page 112). For beta testing purposes, FEDFAA 1.4 allows a less conservative minimum overlay thickness of 3 inches to be computed. This report does not intend to resolve the minimum rigid overlay thickness issue. The purpose of the comparisons between AC 150.5320-6D and FEDFAA 2.0 is to evaluate the overlay thickness calculation independent of the minimum thickness constraints. 5.1 SINGLE AIRCRAFT TRAFFIC.

Overlay thicknesses were calculated for the five single aircraft presented in table 5 for several annual departure levels: 1,200, 6,000, and 25,000 passes. Figures 36 and 37 show the comparison of structures with conventional subbase and two different initial SCI values, 50 and 75, respectively. The structures in figure 36 (SCI = 50) indicate thicker overlays than the structures in figure 37 (SCI = 75). Also, FEDFAA 2.0 for both cases calculates a thicker overlay

41

than AC 150.5320-6D, except for the B777-200, especially when the pavement structure has a high-strength subgrade and SCI = 50.

0

5

10

15

20

25

1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5 1 3 5

Structure Number

Ove

rlay

Thic

knes

s, in

ches

AC 150/5320-6D Chapter 4FEDFAA BETA 1.4FEDFAA 2.0

B727 B737-800 DC10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi

10" Existing PCC R = 715 psi & SCI=50

6" P-209 Cr Ag

Overlay PCC Modulus R = 715 psi

Figure 36. Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 50 on

Conventional Subbase

2

4

6

8

10

12

14

16

18

20

22

2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




42

A thicker base slab layer will also have an effect on the overlay thickness, as shown in figures 38 and 39 for initial SCI = 50 and 75, respectively. These figures show that a thinner overlay is required for a thicker base PCC for all design methods.

2

4

6

8

10

12

14

16

18

20

2213 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17 13 15 17

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




2

4

6

8

10

12

14

16

18

20

22

14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18

Section Code

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




43

The calculated rigid overlay for the pavement structures with stabilized subbases is always thinner for FEDFAA 2.0 than the conventional method, as shown in figures 40 to 43, especially for structures with higher subgrade strengths.

2

4

6

8

10

12

14

16

18

20

22

7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911 7 911

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag


6" Stabilized Subbase


Stabilized Subbase

2

4

6

8

10

12

14

16

18

20

22

81012 81012 81012 81012 81012 81012 81012 81012 81012 81012 81012 81012 81012 81012 81012

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




Stabilized Subbase

44

2

4

6

8

10

12

14

16

18

20

22

19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23 19 21 23

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777 200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




Stabilized Subbase

2

4

6

8

10

12

14

16

18

20

22

20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24

Structure Number

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag




Stabilized Subbase

45

The average rigid overlay thickness difference between FEDFAA 2.0 and AC 150.5320-6D, Chapter 4, for single aircraft decreases with increasing number of departures, as shown in figure 44. This is true for aircraft with D and 2D gears. However, for aircraft with 3D gears, the differences vary when the departure levels increase. Figures 45 to 49 show the correlations between overlay thicknesses computed using FEDFAA 2.0 (vertical axis) and the conventional method in AC 150.5320-6D, Chapter 4 (horizontal axis). Comparisons are presented for five different single aircraft types, under varying departure levels. The correlation (R2) coefficients are between 0.51 and 0.79. The trend line for all cases falls approximately 2-2.5 inches over the equality line for D and 2D gears, and up to 6 inches for the 3D gear.

0.0

1.0

2.0

3.0

4.0

5.0

B-727 B-737 DC-10-10 B-747 B-777Single Aircraft

Thic

knes

s D

iffer

ence

s, in

ches

1,200p FEDFAA-6D6,000p FEDFAA-6D25,000p FEDFAA-6D

FEDFAA 2.0 - AC 150/5320-6D Chapter 4 = 2.0 in

Figure 44. Average PCC Overlay Comparison for Single Aircraft

46

y = 1.278x - 1.4358R2 = 0.7838

y = 1.2037x - 1.4017R2 = 0.7929

y = 1.0097x + 0.8513R2 = 0.7764

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18 20Thickness Calculated by AC 150.5320-6D, Chapter 4, inches

Thic

knes

s C

alcu

late

d by

FED

FAA

, inc

hes







Figure 45. PCC Overlay Correlation for B727 (GW 209,000 lb)

y = 1.2335x - 0.0809R2 = 0.7065

y = 1.0794x + 1.1975R2 = 0.7914

y = 0.9609x + 2.1657R2 = 0.7912

0

2

4

6

8

10

12

14

16

18

20


Thic

knes

s C

alcu

alte

d by

FED

FAA

, inc

hes








47

y = 1.2478x - 0.6685R2 = 0.6993

y = 0.9791x + 1.9929R2 = 0.7485

y = 0.8629x + 3.3003R2 = 0.7612

0

2

4

6

8

10

12

14

16

18

20


Thic

knes

s C

alcu

late

d by

FED

FAA

, inc

hes







Figure 47. PCC Overlay Correlation for DC10 (460,000 lb)

y = 1.1218x + 0.5363R2 = 0.7178

y = 0.8995x + 2.8236R2 = 0.7372

y = 0.9699x + 2.2612R2 = 0.6347

0

2

4

6

8

10

12

14

16

18

20


Thic

knes

s C

alcu

late

d by

FED

FAA

, inc

hes








48

y = 1.0121x + 4.0205R2 = 0.5135

y = 0.7928x + 6.3944R2 = 0.6321

y = 0.621x + 8.6149R2 = 0.6577

0

2

4

6

8

10

12

14

16

18

20


Thic

knes

s C

alcu

late

d by

FED

FAA

, inc

hes









The overlay thickness was calculated for the eight traffic mixes shown in table 4. Figures 50 through 57 show overlay thickness comparisons for different methods (AC 150.5320-6D, Chapter 4; FEDFAA 1.4; and FEDFAA 2.0), for two different base slab thicknesses (10 inches and 14 inches), two different initial SCI values (SCI = 50 and SCI = 75), and two different subbase materials (conventional and stabilized).

49

0

4

8

12

16

20

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

s

AC 150/5320-6D, Chapter 4FEDFAA BETA 1.4FEDFAA 2.0


10 " Base PCC, SCI=50 Modulus R = 715 psi

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

PCC Overlay Modulus R = 715 psi

i

Es =

7500

Es =

150

00Es

=25

000



0

4

8

12

16

20

23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-306 Econ.

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


Es =

7500

Es =

150

00Es

=25

000


Stabilized Subbase

50

0

4

8

12

16

20

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


Es =

7500

Es =

150

00Es

=25

000



0

4

8

12

16

20

23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-306 Econ.

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


Es =

7500

Es =

150

00Es

=25

000

Figure 53. Rigid Overlay Comparison: 10-inch Base Slab With Initial SCI = 75 on

Stabilized Subbase

51

0

4

8

12

16

20

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


Es =

7500

Es =

150

00Es

=25

000



0

4

8

12

16

20

23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-306 Econ.

6" P-209 Cr Ag

Subgrade7,500; 15,000; 25,000 psi


Es =

7500

Es =

150

00Es

=25

000


Stabilized Subbase

52

0

4

8

12

16

20

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

sAC 150/5320-6D, Chapter 4FEDFAA BETA 1.4FEDFAA 2.0



6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


i

Es =

7500

Es =

150

00Es

=25

000



0

4

8

12

16

20

23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-306 Econ.

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

PCC Overlay Modulus R = 715 psi psi

Es =

7500

Es =

150

00Es

=25

000


Stabilized Subbase

53

Figure 58 shows the difference in average overlay thickness for the eight traffic mixes as calculated by FEDFAA Beta 1.4 and AC 150.5320-6D, Chapter 4. The average thickness difference between the two methods for all mixes is 2.3 inches.

0.0

1.0

2.0

3.0

4.0

Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7 Mix 8Traffic Mix

Ave

rage

Rig

id O

verla

y D

iffer

ence

, inc

hes

Overlay Thickness Difference = tFEDFAA - tCONVENTIONAL

Average Difference Over All Traffic Mixes = 2.3 inches

Figure 58. Average Rigid Overlay Differences for All Traffic Mixes

6. FLEXIBLE-OVER-RIGID OVERLAY DESIGN RESULTS.

The pavement structures in table 3 are used to calculate the flexible overlay thickness on rigid pavement for the aircraft traffic mixes in table 4 and the single aircraft loads in table 5. The overlay thickness was calculated by the conventional method in AC 150.5320-6D, Chapter 4; FEDFAA 1.4; and FEDFAA 2.0. The minimum flexible overlay is 2 inches, as specified in AC 150.5320-6D, except for the B777 which requires a minimum flexible overlay of 4 inches. The minimum flexible overlay available in FEDFAA is 4 inches for all aircraft. For conventional structures, the FEDFAA program calculates flexible overlays for a minimum initial SCI value of 67. 6.1 SINGLE AIRCRAFT.

Figures 59 to 62 show the comparison of the overlay thickness calculated by the methods described above under a single aircraft load.

54

0

3

6

9

12

15

18

21

24

27

30

2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6 2 4 6

Section Code

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag

Flexible Over PCC

Figure 59. Flexible-Over-Rigid Overlay Comparison: 10-Inch Base Slab With Initial SCI = 75

on Conventional Subbase

0

3

6

9

12

15

18

21

24

27

30

14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18 14 16 18

Section Code

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag

Flexible Over PCC



55

0

3

6

9

12

15

18

21

24

27

30

8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12 8 10 12

Section Code

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag

Flexible Over PCC



on Stabilized Subbase

0

3

6

9

12

15

18

21

24

27

30

20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24 20 22 24

Section Code

Ove

rlay

Thic

knes

s, in

ches


B727 B737-800 DC-10-10 B747-400 B777-200


Es =

7500

Es =

150

00Es

=25

000

Subgrade 7,500; 15,000; 25,000 psi


6" P-209 Cr Ag

Flexible Over PCC




56


The overlay thickness for structures under the eight aircraft traffic mixes is compared in figures 63 to 66. The method described in AC 150.5320-6D is not suitable for calculating flexible overlay thickness for traffic mixes when an aircraft with a six-wheel gear is present in the mix. However, the calculated thickness by AC 150.5320-6D was obtained by selecting a design aircraft with two- or four-wheel gear per mix. The conversion factors for six-wheel gear aircraft used to determine the equivalent annual departures for the design aircraft correspond to those used previously by McQueen [4].

0

5

10

15

20

25

30

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

s

AC 150/5320-6D, Chapter 4FEDFAA 2.0



6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

Flexible Over PCC

Es =

7500

Es =

150

00Es

=25

000



57

0

5

10

15

20

25

30

22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36 22 29 36

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi


i

Es =

7500

Es =

150

00Es

=25

000



0

5

10

15

20

25

30

23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A 23 3337

A

Structure Number

Slab

Thi

ckne

ss, i

nche

s




6" P-306 Econ.

6" P-209 Cr Ag

Subgrade7,500; 15,000; 25,000 psi

Flexible Over PCC

Es =

7500

Es =

150

00Es

=25

000



58

0

5

10

15

20

25

30

23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A 23 33 37A

Structure Number

Slab

Thi

ckne

ss, i

nche

sAC 150/5320-6D, Chapter 4FEDFAA 2.0



6" P-306 Econ.

6" P-209 Cr Ag

Subgrade 7,500; 15,000; 25,000 psi

PCC Overlay Modulus R = 715 psi psi

Es =

7500

Es =

150

00Es

=25

000


on Stabilized Subbase 7. REFERENCES.

1. Brill, David R., Kawa, Izydor, and Hayhoe, Gordon, “Development of FAArfield Airport Pavement Design Software,” Transportation Systems 2004 Workshop, Ft. Lauderdale, Florida, 2004.

2. U.S. Department of Transportation, Federal Aviation Administration, “Airport Pavement

Design and Evaluation,” Advisory Circular 150.5320-6D, 1995. 3. Hayhoe, Gordon F., Kawa, Izydor, and Brill, David R., “New Developments in FAA

Airport Pavement Thickness Design Software,” Transportation Systems 2004 Workshop, Ft. Lauderdale, Florida, 2004.

4. McQueen, Roy D., Hayhoe, Gordon, Guo, Edward H., Rice, John, and Lee, Xiaogong

(1995), “A Sensitivity Study of Layered Elastic Theory for Airport Pavement Design,” Proceeding of 2nd International Conference on Road & Airfield Pavement Technology, pp. 586-594, 27-29 September 1995, Singapore.

5. McQueen, Roy D., Garg, Navneet, and Ricalde, Lia, “Comparative Analysis of Airport

Pavement Design Procedures,” 2004 FAA Technology Transfer Conference, Atlantic City, NJ, 2004.

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