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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. Overview. Review EB 59A Background on Issues Research Results AAPTP ERDC FAA Requirements to Complete Specification.

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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 2010 FAA Hershey Conference

overview
Overview
  • Review EB 59A
  • Background on Issues
  • Research Results
    • AAPTP
    • ERDC
    • FAA
  • Requirements to Complete Specification
references in eb 59a
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)
policy modification to standards
Policy: Modification to Standards
  • Gross aircraft weights <100,000 pounds: approval at Regional Office
  • Gross aircraft weights > 100,000 pounds: approval by AAS-100
what s the big differences between faa s superpave marshall
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!
aaptp study 04 02 binder selection
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.
pg criteria for polymer modified asphalts
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
primary superpave mix design criteria
> 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.
gradation requirements
Gradation Requirements
  • Runways – same as current P-401
  • Taxiways
    • Control Points
    • Restricted Zone ?
primary superpave acceptance criteria
> 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
slide16

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
major issues associated with adopting superpave
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
establishing design gyrations
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
stated differently
Stated Differently:
  • Make sure the new stuff works as good as the old!
average pci at civil airports
Average PCI at Civil Airports

79

67

Source: Report DOT/FAA/AR-04-46

overview of faa p 401
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
density limit derivation
Density Limit Derivation

98%

Zs

90 PWL

10 PD

L

L = 98% - 1.28(1.3%) = 96.3%

air voids
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%

primary differences between p 401 marshall and p 401 superpave
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

major issue n design
Major Issue: Ndesign
  • AAPTP Study
  • ERDC Study
  • FAA Study
aaptp 04 03 study
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
slide28

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.

n equiv results
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

slide30

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

erdc study
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
variables
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
analyses of variability
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
anova type analyses 2
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
conclusions
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
objectives
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
critical issues
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
research program to establish n equiv
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
phase 1 subtasks completed
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
mix variables 1
Mix Variables (1)
  • All well-performing mixes
  • Various mineralogy
    • Gneiss
    • Dolomite
    • Granite
    • Gravel
    • Basalt
    • Argillite
    • Diabase
mix variables 2
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)
mix designs
Mix Designs

* Phase I limited to PG 76-22

n equivalent results
N-equivalent Results
  • Average: 62
  • Minimum: 34
  • Maximum: 99
  • Standard deviation: 16
  • Like other studies – range is large
phase 2 performance evaluation
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?
experiment design
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
background
Background
  • Aircraft wheel loads and tire pressures are increasing:
    • L ~ 65,000 lbs.
    • P > 240 psi
  • Reported pavement failures in hot climates overseas
  • Have we reached “the end” with HMA?
study objectives
Study Objectives

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

study elements
Study Elements
  • Full scale testing at NAPTF heated pavements
  • Laboratory tests with different binders and different temperatures:
    • Binder: DSR, viscosity, other.
    • HMA: MSCR, Indirect Tensile (IDT), Dartmouth accelerated pavement tester, NCHRP protocols, other.
    • Under development
  • Combine with SuperPave to improve HMA performance and Ndes = f (p)
slide56
EB 59A N-equiv appears to be problematic

EB 59A --- 85

AAPTP ---- 55 - 65

ERDC ------ 70

FAA --------- 65 - 70

How to handle variations in N-equiv?

% natural Sand

Aggregate Type: Mineralogy or Angularity?

Other Considerations

Volumetrics

Compaction Standard

other considerations volumetrics
Other Considerations - Volumetrics
  • Effect of 1% lower VMA and ½% higher air voids with Superpave:
    • 1.5% lower % AC by volume (~ 0.7% by wt.)
    • Effect of potentially lower %AC on durability
why is vma important
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
other considerations compaction
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
lessons
LESSONS
  • Need to carefully establish Ndesign to provide equivalent performance
  • Be careful with changing volumetric criteria
    • Dry mix – low durability
    • Under-compacted – prone to rutting
    • Combination = Disaster
ultimate objective of all studies
Ultimate Objective of All Studies

New P-401 specification

(while Carl Steinhauer and I are still alive)

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