5 References in EB 59ATAI 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 OfficeGross 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 sameCompaction (bulk sp.g.) measured the sameMix design & acceptance criteria are slightly differentIt’s still aggregate, sand, binder and air!
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 WeightHigh Temperature Adjustment to Binder GradeAll Pavement Typesweight < 12,500--< weight < 100,0001weight > 100,0002NOTE: 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” trafficFor taxiways with some stacking, grade bumping: the high-temperature PG grade should be increased by 6C; for taxiways with frequent stacking, the grade should be increased by 12C.The high-temperature PG grade may be reduced one level (6C) 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 70-22Elastic 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 Gyrations4% VTMVMA: 13% - 14%VFA: 65% to 78%Dust to asphalt ratioCoarse & FineFAA > 42> 60,000 lbs.85 Gyrations4% VTMVMA: 13% - 14%VFA: 65% to 78%Dust to asphalt ratioCoarse & FineFAA > 45A 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-401TaxiwaysControl PointsRestricted Zone ?
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 Compactor19
20 Major Issues Associated With Adopting SuperPave Required number of gyrations for mix designVolumetrics – appropriate level of VMA and VTMGradation RequirementsField Compaction Standard
21 Establishing Design Gyrations Need to establish Ndesign for the gyratory compactorPerformance equivalent to well performing Marshall mixesValidation testing on a variety of mixes
22 Stated Differently: Make sure the new stuff works as good as the old! Quality IssuesLegal Defensibility
23 Average PCI at Civil Airports HMA Pavements 7967Source: 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% typicalVMA typically 1% higher than EB 59ATSR for moisture susceptibility (75% - 80% min)Compaction function of lab Marshall densityPWL acceptance:Density: 90% above 96.3% % averageVTM: 90% between 2% and 5% % averageLimits based on actual construction data
27 Primary Differences Between P-401 Marshall and P-401 Superpave Gyratory Compactor90% > 92.5% MTDAvg.~ 94.5% MTD60 or 85 Ndes4% design VTM2.5% to 5.5% acceptance1% lower VTMStrictly volumetricP-401 Marshall*Impact Compactor90% > 96.3% MarshallAvg.~ 98% lab density50 or 75 blows2.8% - 4.2% design VTM2% to 5% acceptance1% higher VMAVolumetric + 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 TechnologiesSoiltekNomenclature:Nequivalent = equivalent N corresponding to 75 blow MarshallNdesign = design N for development of standard
30 AAPTP 04-03 Study Approach for Ndes: Mixes: Compare In-place Density to Orig NdesCompare with Marshall for Equivalent PerformanceAMPT Performance TestsMixes:Included southwest, west Coast MixesNot all well-performing – some poorSeveral military mixesDid not use P-401 volumetrics
31 Nequiv Results 75-blow Comparisons 50-blow Comparisons Range: 32 to 59 Avg. = 49, STD = 1050-blow ComparisonsRange: 25 to 40Avg. = 36, STD = 11Volumetric 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 NdesignLess than100 toMore thanRecommended Ndesign Values for Designing Airfield MixesTire Pressure, psi NdesignLess than100 toMore thanIndicates 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 considered75-blow Marshall, onlyP-401 volumetrics, i.e. VMA & 3.5% VTM
35 Variables Mineralogy: Limestone, Granite, Gravel Aggregate Size: ½, ¾, 1 inch MaxGradation: Coarse & Fine Sides of P-401 BandSand: 10% Nat’l & 100% CrushedBinder: PG & PG 76-22Nequiv Range: 25 to 125
36 Analyses of Variability (1) Sand:N=75 (all crushed) vs. N=59 (10% natural)p<0.001, significantly differentAggregate Type:Gravel: N=50Granite: N=84Limestone: N=69
37 Analysis of Variability (2) Aggregate Size:½ inch: N=72¾ inch: N=661 inch: N=80p=0.051, not significantly differentGradation:Fine: N=80 not significantly differentCoarse: N=69p=0.047, not significantly differentPolymer vs. neat binders not significantly different
38 ConclusionsVariability too cumbersome to warrant multiple compaction levelsNdesign based on arithmetic average of 69 with a recommended value of 70EB 59A Nequiv criterion may be problematicValidation study scheduled for
40 Objectives Establish guidance for N-design Establish specifications for designing HMA using SGC that provides performance equivalent to Marshall mixesVerify on a range of well performing mixesMore comprehensive than other studies
41 Critical Issues N-design consistent with 75 Marshall blows Effect of switch to SGC on performanceSGC could also result in subtle changes in aggregate gradation to meet volumetricsVolumetric 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 volumetricsPhase 2:Validate Ndesign based on comparative performance tests at Ndesign and Nequiv
43 Mix Variables (1) All well-performing mixes Various mineralogy Gneiss DolomiteGraniteGravelBasaltArgilliteDiabase
51 ConclusionsSuperpave 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.
53 Background Aircraft wheel loads and tire pressures are increasing: L ~ 65,000 lbs.p > 240 psiReported pavement failures in hot climates overseas
54 Study ObjectivesEvaluate 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 resistanceAMPT flow numberFatigueTest Matrix:Limestone, Dolomite, Granite aggregatesPG 64, , and TLA blend bindersCombine with Gyratory results for updating EB59A and SuperPAVE Specification Development
58 Conclusions EB 59A N-equiv appears to be problematic AAPTPERDCFAA – 70Volumetric and performance comparisons support Ndes = 70Other ConsiderationsVolumetricsCompaction 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 contentLow VMA mixes can become tenderLow 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 voids4% laboratory air voids, Va98% field compactionExample 2: 6% in-place air voids2% laboratory air voids, Va96% 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 !