SuperPave Considerations

1. SuperPave Considerations Roy D. McQueen, P.E. Roy D. McQueen & Associates, Ltd. www.rdmcqueen.com 703 709-2540 For presentation at 2010 FAA Hershey Conference

2. Overview • Review EB 59A • Background on Issues • Research Results • AAPTP • ERDC • FAA • 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)

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 the Big Differences Between FAA’s SuperPave & Marshall? • The Compactor! • 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. *Same requirement for Marshall Mix Also AAPTP 04-02

9. 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. • For runways:LTPPBind 3.1 (“fast” traffic condition). • For taxiways without stacking, speed adjustment for “slow” traffic • For taxiways with some stacking, 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. No additional grade reductions should be made.

10. PG+ Criteria for Polymer Modified Asphalts • Rule of “90” • “Gray” for sum ~90, e.g., PG 70-22 • Elastic Recovery (60% to 75%) typical for this region to ensure polymers at proper % • Criteria varies by state

11. > 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 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.

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

13. Off Maximum Density Line – Higher VMA

14. > 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 Primary SuperPave Acceptance Criteria

15. BACKGROUND ON ISSUES

16. 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 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

17. 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

18. 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

19. Stated Differently: • Make sure the new stuff works as good as the old!

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

21. 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 • Air voids: 90% between 2% and 5% • Limits based on actual construction data

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

23. Air Voids 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%

24. P-401 Marshall* 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** 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

25. Major Issue: Ndesign • AAPTP Study • ERDC Study • FAA Study

26. SUMMARY of AAPTP STUDY

27. AAPTP 04-03 Study • Approach for Ndes: • Compare In-place Density to Orig Ndes • Compare with Marshall for Equivalent Performance • Performance Tests • Mixes: • Included Southwest, West Coast Mixes • Not all well-performing – some poor • Several Military mixes • Performance Test: Flow # • Did not use P-401 volumetrics

28. Estimated Ndesign Values Based upon Performance Testing Airfield Gross Wt. Tire (lbs) p (psi) Ndesign Jacqueline Cochran Regional Airport 20,000 10,000 75 50 Mineral County Memorial Airport 12,500 6,250 90 50 Oxford-Henderson Airport 30,000 15,000 75 35 Little Rock Air Force Base 155,000 38,750 105 50 Naval Air Station Oceana* 66,000 33,000 240 75 Volk Field 42,500 21,250 215 75 Jackson International Airport 890,000 55,625 200 35 Newark Liberty International Airport 873,000 54,563 200 35 Palm Springs International Airport 800,000 52,500 200 N/A Spokane International Airport 400,000 100,000 200 N/A N/A – Insufficient Data to Estimate Appropriate Ndesign Value * Evaluated mix rutted in the field. Performance tests inconclusive for civil airport mixes.

29. 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

30. 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 No robust “Phase 2” type validation study EB 59A N-des may be problematic To what extent did volumetrics influence results No variability analysis

31. SUMMARY of ERDC STUDY

32. ERDC Study • Approach Similar to FAA Study, i.e. 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

33. 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

34. Analyses of Variability • 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

35. ANOVA Type Analyses (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 • Coarse: N=69 • p=0.047, significantly (?) different • Polymer vs. neat binders not significantly different

36. Conclusions • Variability too cumbersome to warrant multiple compaction levels • Ndesign based on arithmetic average of 69 with a recommended value of 70 • + 10 gyrations ----- + 0.5% VTM • EB 59A Nequiv criterion may be problematic • Validation study scheduled for 2010 - 2012

37. SUMMARY of FAA STUDY

38. 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 mixes • More comprehensive than other studies

39. Critical Issues • Primary issue will be N-design levels consistent with 75 Marshall blows • Effect on stability & flow • SGC could also result in subtle changes in aggregate gradation to meet volumetrics • Volumetric and compaction Issues for spec development

40. Research Program to Establish N-equiv • Phase 1: • Determine N-equiv • Equivalent to 75-blow Marshall • Phase 2: • Validate N-equiv • Performance Tests for N-equiv

41. Phase 1 Subtasks - completed • Identify Mixtures and Binders • Verify Mix Designs • Perform 1st and 2nd Replicates of Gyratory Compaction & Volumetrics – 2 labs • Perform Mixture Variation Experiment • Compile, Analyze and Summarize Data

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

43. 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)

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

45. Determining N-equivalent

46. Plot of Results with +/- 2s error bars

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 asphalt content and/or gradation changes on rut resistance? • What is affect on compactibility? • What is affect on durability?

49. Experiment Design • Test at Nequiv and Ndes • Rut resistance • AMPT / flow number • APA • Compactibiltiy from compaction curve • Durability from ASTM D 4867 (modified Lottman) • Results due June 2010

50. FAA High Tire Pressure Study