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SuperPave Considerations

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Presentation on theme: "SuperPave Considerations"— Presentation transcript:

1 SuperPave Considerations
Roy D. McQueen, P.E. Roy D. McQueen & Associates, Ltd. For presentation at 2012 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


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 The Compactor and sample size!
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 High Temperature Adjustment to Binder Grade
Binder Grade Selection and Grade Bumping Based on Gross Aircraft Weight* Determine binder requirements from the LTTP Bind software using 98 percent reliability with no traffic or speed adjustments. Increase the high temperature grade by the number of grade equivalents indicated (1 grade is equivalent to 6 degrees C) below. Use the low temperature grade as determined from LTTP Bind. (see NOTES) Aircraft Gross Weight High Temperature Adjustment to Binder Grade All Pavement Types weight < 12,500 -- < weight < 100,000 1 weight > 100,000 2 NOTE: PG grades above a –22 on the low end (e.g. 64–16) are not recommended. Limited experience has shown an increase in block cracking with -16 or -10 grade asphalts. *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 Primary EB59A SuperPave Mix Design Criteria
< 60,000 lbs. 60 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 42 > 60,000 lbs. 85 Gyrations 4% VTM VMA: 13% - 14% VFA: 65% to 78% Dust to asphalt ratio Coarse & Fine FAA > 45 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 EB 59A SuperPave Acceptance Criteria
> 60,000 lbs. 2.5% < VTM < 85 gyrations Compaction L = 92.5% Gmm < 60,000 lbs. 2.5% < VTM < 60 gyrations Compaction L = 92.5% Gmm

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


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 19

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% % average VTM: 90% between 2% and 5% % average Limits based on actual construction data

25 Density Limit Derivation
98% Zs 90 PWL 10 PD L L = 98% (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 Primary Differences Between P-401 Marshall and 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 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 * Limits are based on construction data ** Limits not based on construction data

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


30 AAPTP 04-03 Study Approach for Ndes: Mixes:
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

31 Nequiv Results 75-blow Comparisons 50-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, psi Ndesign Less than 100 to More than Recommended Ndesign Values for Designing Airfield Mixes Tire Pressure, psi Ndesign Less than 100 to More than Indicates that EB 59A N-des may be problematic. No variability analysis.


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 & 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

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


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 performing mixes More comprehensive than other studies

41 Critical Issues N-design consistent with 75 Marshall blows
Effect of switch to SGC on 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 Mix Name Aggregate Type NMAS
Airport Aggregate Type NMAS Binder Grade* JFK/1993 JKF Gneiss 12.5 mm AC 20 JFK/1997 JFK Dolomite 19 mm PG 82-22 JFK/1996 Dolomite/granite 25 mm Atlantic City ACY Basalt PG 64-22 Lexington LEX Limestone PG 70-22 Elmira ELM Crushed gravel PG 64-28 NAPTF --- Argillite-Dolomite Charlottesville CHO Diabase * 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 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

51 Conclusions Superpave gyratory compaction level of 70 gyrations will provide similar volumetrics on average to 75 blows of a Marshall hammer. Converting an existing Marshall design to a gyratory design can be done by a slight adjustments in asphalt binder content and in some cases aggregate gradation. Mixes designed with Ndesign = 70 achieved slightly better rut resistance than 75-blow Marshall. Mixes designed using gyratory compaction with Ndesign = 70 and 75-blow Marshall compaction exhibited similar fatigue resistance.

52 FAA High Tire Pressure Study

53 Background Aircraft wheel loads and tire pressures are increasing:
L ~ 65,000 lbs. p > 240 psi Reported pavement failures in hot climates overseas

54 Study Objectives Evaluate the rutting, durability and fatigue performance of asphalt mixes at the extreme boundary of operation with respect to tire pressure, wheel load, temperature and (low) speed.

55 HTPT Study Elements Full scale tests at NAPTF heated pavements
Laboratory tests with different binders and different temperatures: Binder Sensitivity: DSR, MSCR. HMA Performance: Indirect Tensile (IDT) APA rut resistance AMPT flow number Fatigue Test Matrix: Limestone, Dolomite, Granite aggregates PG 64, , and TLA blend binders Combine with Gyratory results for updating EB59A and SuperPAVE Specification Development


57 Conclusions All Studies

58 Conclusions EB 59A N-equiv appears to be problematic
AAPTP ERDC FAA – 70 Volumetric and performance comparisons support Ndes = 70 Other Considerations Volumetrics Compaction Standard

59 Other Considerations - Volumetrics
Effect of 1% lower VMA and ½% higher air voids with EB 59A compared to P-401: 1.5% lower % AC by volume (~ 0.7% by wt.) Effect of potentially lower %AC on durability, e.g., film thickness, stripping

60 Why is VMA Important? Va & VMA Related and Va is a pay item!
Low VMA mixes are sensitive to minor variations in asphalt content Low VMA mixes can become tender Low VMA mixes may not allow for sufficient film thickness to ensure durability

61 Other Considerations - Compaction
Effect of using %MTD in lieu of % lab for compaction control: Example 1: 6% in-place air voids 4% laboratory air voids, Va 98% field compaction Example 2: 6% in-place air voids 2% laboratory air voids, Va 96% field compaction

62 What is the combined net effect of:
Raising VTM? Lowering VMA? Inconsistent (lower?) compaction

63 Ultimate Objective of All Studies
New P-401 SuperPAVE specification !

64 Questions?

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