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SuperPave Considerations

SuperPave Considerations. Roy D. McQueen, P.E. Roy D. McQueen & Associates, Ltd. www.rdmcqueen.com 703 709-2540 For presentation at 2011 FAA Hershey Conference. Overview. Review EB 59A Background on Issues Research Results AAPTP Gyratory FAA Gyratory ERDC SRA FAA HTPT

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SuperPave Considerations

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  1. SuperPave Considerations Roy D. McQueen, P.E. Roy D. McQueen & Associates, Ltd. www.rdmcqueen.com 703 709-2540 For presentation at 2011 FAA Hershey Conference

  2. Overview • Review EB 59A • Background on Issues • Research Results • AAPTP Gyratory • FAA Gyratory • ERDC • SRA • FAA HTPT • Requirements to Complete Specification

  3. 1st Eastern Region Airports Conference - 1976

  4. Engineering Brief 59AITEM P‑401 PLANT MIX BITUMINOUS PAVEMENTS (SUPERPAVE)

  5. References in EB 59A • TAI Superpave Mix Design, Superpave Series No. 2 (SP‑2) • TAI Performance Graded Asphalt, Binder Specification and Testing, Superpave Series No. 1 (SP-1) • Interim Item P‑401 Plant Mix Bituminous Pavements (SUPERPAVE) EB-59A

  6. Policy: Modification to Standards • Gross aircraft weights <100,000 pounds: approval at Regional Office • Gross aircraft weights > 100,000 pounds: approval by AAS-100

  7. What’s are the Big Differences Between FAA’s SuperPave & Marshall Specs? • The Compactor and sample size! • Volumetrics measured the same • Compaction (bulk sp.g.) measured the same • Mix design & acceptance criteria are slightly different • It’s still aggregate, sand, binder and air!

  8. 4” Diameter Mold 6” Diameter Mold

  9. *Same requirement for Marshall Mix

  10. AAPTP Study 04-02 Binder Selection • The base high-temperature PG grade should be determined using LTPPBind 3.1, for a surface layer (depth of layer surface = 0 mm), using a reliability of 98 %. • The EHEs for both taxiways and runways are calculated using: EHEs = 10.4  (design tire pressure in lb/in2 / 120)2 annual departures. • The high-temperature PG grade is then determined using LTPPBind 3.1, using the calculated value for EHEs as the design traffic level.

  11. AAPTP Study 04-02 Binder Selection • For runways: LTPPBind 3.1 (“fast” traffic condition). • For taxiways without stacking, speed adjustment for “slow” traffic • For taxiways with some stacking, grade bumping: the high-temperature PG grade should be increased by 6C; for taxiways with frequent stacking, the grade should be increased by 12C. • The high-temperature PG grade may be reduced one level (6C) for lifts which are entirely 75 mm or more below the pavement surface.

  12. PG+ Criteria Polymer Modified Asphalts • Rule of “90” • “Gray” area for sum ~90, e.g., PG 70-22 • Elastic Recovery (60% to 70%) typical for this region to ensure polymerization at proper % • Criteria varies by state

  13. > 60,000 lbs. 85 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 45 < 60,000 lbs. 60 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 42 Primary EB59A SuperPave Mix Design Criteria • A coarse gradation is defined as a gradation passing below the restricted zone. • The restricted zone is defined in the Asphalt Insitute’s Manual Superpave, SP-2.

  14. Gradation Requirements • Runways – same as current P-401 • Taxiways • Control Points • Restricted Zone ?

  15. Off Maximum Density Line – Higher VMA

  16. > 60,000 lbs. 2.5% < VTM < 5.5% @ 85 gyrations Compaction L = 92.5% Gmm < 60,000 lbs. 2.5% < VTM < 5.5% @ 60 gyrations Compaction L = 92.5% Gmm EB 59ASuperPave Acceptance Criteria

  17. There are problems with EB59A mix design and acceptance criteria that need to be resolved.

  18. BACKGROUNDON ISSUES

  19. FAA Standards for production and placement of hot mix asphalt (HMA) pavements have been in place for more than 50 years. • So, why change? • Because we have to. No one is supporting Marshall. • Modifications to both Federal and State Highway standard requirements have led to the SuperPave Design process and the use of the Gyratory Compactor

  20. Major Issues Associated With Adopting SuperPave • Required number of gyrations for mix design • Volumetrics – appropriate level of VMA and VTM • Gradation Requirements • Field Compaction Standard

  21. Establishing Design Gyrations • Need to establish Ndesign for the gyratory compactor • Performance equivalent to well performing Marshall mixes • Validation testing on a variety of mixes

  22. Stated Differently: • Make sure the new stuff works as good as the old! • Quality Issues • Legal Defensibility

  23. Average PCI at Civil Airports HMA Pavements 79 67 Source: Report DOT/FAA/AR-04-46

  24. Overview of FAA P-401 • 75 blow Marshall for heavy duty • Design VTM: 2.8% - 4.2%, 3.5% typical • VMA typically 1% higher than EB 59A • TSR for moisture susceptibility (75% - 80% min) • Compaction function of lab Marshall density • PWL acceptance: • Density: 90% above 96.3% 98% average • VTM: 90% between 2% and 5% 3.5% average • Limits based on actual construction data

  25. Density Limit Derivation 98% Zs 90 PWL 10 PD L L = 98% - 1.28(1.3%) = 96.3%

  26. Air Voids Limits Derivation 2.8% 3.5% 4.2% 0.7% 0.7% Zs Zs L=2% U=5% DL= 2% + (1.28x0.65%) = 2.8% DU= 5% - (1.28x0.65%) = 4.2%

  27. P-401 Marshall* Impact Compactor 90% > 96.3% Marshall Avg.~ 98% lab density 50 or 75 blows 2.8% - 4.2% design VTM 2% to 5% acceptance 1% higher VMA Volumetric + Strength test P-401 Superpave** Gyratory Compactor 90% > 92.5% MTD Avg.~ 94.5% MTD 60 or 85 Ndes 4% design VTM 2.5% to 5.5% acceptance 1% lower VTM Strictly volumetric Primary Differences Between P-401 Marshall and P-401 Superpave * Limits are based on construction data ** Limits not based on construction data

  28. Major Issue: Ndesign • AAPTP Study • FAA Studies • ERDC • SRA • Advanced Asphalt Technologies • Soiltek • Nomenclature: • Nequivalent = equivalent N corresponding to 75 blow Marshall • Ndesign = design N for development of standard

  29. SUMMARY AAPTP STUDY

  30. Approach for Ndes: Compare In-place Density to Orig Ndes Compare with Marshall for Equivalent Performance AMPT Performance Tests Mixes: Included southwest, west Coast Mixes Not all well-performing – some poor Several military mixes Did not use P-401 volumetrics AAPTP 04-03 Study

  31. Nequiv Results • 75-blow Comparisons • Range: 32 to 59 • Avg. = 49, STD = 10 • 50-blow Comparisons • Range: 25 to 40 • Avg. = 36, STD = 11 Volumetric criteria different from P-401: VMA 1% lower & VTM 1/2% higher. This may be reflected in low Nequiv to meet EB59A volumetrics at same %AC as P-401

  32. AAPTP Ndesign Ndesign Values Based Upon Research Tire Pressure, psiNdesign Less than 100 40 100 to 200 55 More than 200 70 Recommended NdesignValues for Designing Airfield Mixes Tire Pressure, psiNdesign Less than 100 50 100 to 200 65 More than 200 80 Indicates that EB 59A N-des may be problematic. No variability analysis.

  33. SUMMARY ERDC STUDY

  34. ERDC Study • Ndes from comparative Marshalls • Mixes developed from P-401 Specification requirements, i.e., well performing mixes Not considered • 75-blow Marshall, only • P-401 volumetrics, i.e. VMA & 3.5% VTM

  35. Variables • Mineralogy: Limestone, Granite, Gravel • Aggregate Size: ½, ¾, 1 inch Max • Gradation: Coarse & Fine Sides of P-401 Band • Sand: 10% Nat’l & 100% Crushed • Binder: PG 64-22 & PG 76-22 • Nequiv Range: 25 to 125

  36. Analyses of Variability (1) • Sand: • N=75 (all crushed) vs. N=59 (10% natural) • p<0.001, significantly different • Aggregate Type: • Gravel: N=50 • Granite: N=84 • Limestone: N=69 • p<0.001, significantly different

  37. Analysis of Variability (2) • Aggregate Size: • ½ inch: N=72 • ¾ inch: N=66 • 1 inch: N=80 • p=0.051, not significantly different • Gradation: • Fine: N=80 not significantly different • Coarse: N=69 • p=0.047, not significantly different • Polymer vs. neat binders not significantly different

  38. Conclusions • Variability too cumbersome to warrant multiple compaction levels • Ndesign based on arithmetic average of 69 with a recommended value of 70 • EB 59A Nequiv criterion may be problematic • Validation study scheduled for 2011 - 2012

  39. SUMMARY FAA GYRATORY STUDY

  40. Objectives • Establish guidance for N-design • Establish specifications for designing HMA using SGC that provides performance equivalent to Marshall mixes • Verify on a range of well performingmixes • More comprehensive than other studies

  41. Critical Issues • N-design consistent with 75 Marshall blows • Effect of switch to SGCon performance • SGC could also result in subtle changes in aggregate gradation to meet volumetrics • Volumetric and compaction Issues: • VTM & VMA limits • % MTD vs. % laboratory

  42. Program to Establish Ndesign • Phase 1: • Determine Nequiv equivalent to 75-blow Marshall air voids (Gmb) • Suggest Ndesign based on volumetrics • Phase 2: • Validate Ndesign based on comparative performance tests at Ndesign and Nequiv

  43. Mix Variables (1) • All well-performing mixes • Various mineralogy • Gneiss • Dolomite • Granite • Gravel • Basalt • Argillite • Diabase

  44. Mix Variables (2) • Nominal Maximum Aggregate Size • 12.5 mm • 19.0 mm • 25.0 mm • Varying natural sand content (0%, 7.5%, 15%) • Binders • Neat asphalt • Polymers: Elastomeric (SBS) and Plastomeric (Novophalt)

  45. Mix Designs * Phase I limited to PG 76-22

  46. Determining N-equivalent

  47. N-equivalent Results • Average: 62 • Minimum: 34 • Maximum: 99 • Standard deviation: 16 • Like other studies – range is large

  48. Phase 2: Performance Evaluation • What is affect of any asphalt content and/or gradation changes needed to meet volumetric criteria @ Ndesign on rut and fatigue resistance and durability?

  49. Phase 2 Experiment Design • Test at Nequiv and Ndes • Rut resistance • AMPT E and flow number • APA rut depth • Fatigue resistance • Durability from ASTM D 4867 (modified Lottman)

  50. Rut Resistance AMPT Flow # APA Rut Depth

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