SuperPave Considerations

Roy D. McQueen, P.E.Roy D. McQueen & Associates, Ltd.www.rdmcqueen.com703 709-2540

For presentation at 2012 FAA Hershey Conference

Overview

Review EB 59A Background on Issues Research Results

• AAPTP Gyratory• FAA Gyratory

• ERDC• SRA

• FAA HTPT

Requirements to Complete Specification

1st Eastern Region Airports Conference - 1976

Engineering Brief 59A

ITEM P‑401 PLANT MIX BITUMINOUS PAVEMENTS (SUPERPAVE)

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

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 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!

4” Diameter Mold

6” Diameter Mold

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 GradeAll Pavement Types

 

weight < 12,500 --

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

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.

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 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.

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

Primary EB59A 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

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

Runways – same as current P-401

Taxiways Control Points Restricted Zone ?

Off Maximum Density Line – Higher VMA

EB 59A 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

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

BACKGROUND

ON ISSUES

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

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

Need to establish Ndesign for the gyratory compactor

Performance equivalent to well performing Marshall mixes

Validation testing on a variety of mixes

Stated Differently:

Make sure the new stuff works as good as the old!

Quality Issues Legal Defensibility

Average PCI at Civil Airports HMA Pavements

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

67

79

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

Density Limit Derivation

10 PD 90 PWL

L

98%

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

Zs

Air Voids Limits Derivation

L=2% U=5%

3.5%

DL= 2% + (1.28x0.65%) = 2.8% DU= 5% - (1.28x0.65%) = 4.2%

Zs Zs

2.8% 4.2%

0.7% 0.7%

Primary Differences Between P-401 Marshall and P-401 Superpave

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

* Limits are based on construction data

** Limits not based on construction data

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

SUMMARY

AAPTP STUDY

AAPTP 04-03 Study

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

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

Ndesign Values Based Upon Research

Tire Pressure, psi Ndesign

Less than 100 40 100 to 200 55 More than 200 70

Recommended Ndesign Values for Designing Airfield Mixes

Tire Pressure, psi Ndesign

Less than 100 50 100 to 200 65 More than 200 80

Indicates that EB 59A N-des may be problematic.No variability analysis.

AAPTP Ndesign

SUMMARY

ERDC STUDY

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

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 (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

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

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

SUMMARY

FAA GYRATORY STUDY

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

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

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

Mix Variables (1)

All well-performing mixes

Various mineralogy Gneiss Dolomite Granite Gravel Basalt Argillite Diabase

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 Name AirportAggregate

Type NMASBinderGrade*

JFK/1993 JKF Gneiss 12.5 mm AC 20

JFK/1997 JFK Dolomite 19 mm PG 82-22

JFK/1996 JFK Dolomite/granite 25 mm PG 82-22

Atlantic City ACY Basalt 19 mm PG 64-22

Lexington LEX Limestone 19 mm PG 70-22

Elmira ELM Crushed gravel 19 mm PG 64-28

NAPTF --- Argillite-Dolomite 12.5 mm PG 64-22

Charlottesville CHO Diabase 19 mm PG 64-22

* Phase I limited to PG 76-22

Determining N-equivalent

0

25

50

75

100

125

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Compacted Air Voids (%)

Gyr

atio

n Le

vel (

N)

Air void content from verifiedMarshall mix design = 3.5 %

N-equivalent= 49 gyrations

N-equivalent Results

Average: 62 Minimum: 34 Maximum: 99 Standard deviation: 16 Like other studies – range is large

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?

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)

0 100 200 300

JFK/19mm

JFK/25mm

ACY

LEX

ELM

NAPTF

CHO

NTU

Flow Number

Gyratory

Marshall

0.0 2.0 4.0 6.0 8.0 10.0

JFK/19mm

JFK/25mm

ACY

LEX

ELM

NAPTF

CHO

NTU

APA Rut Depth, mm

Gyratory

Marshall

AMPT Flow #

APA Rut Depth

Rut Resistance

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.

FAA

High Tire Pressure Study

Background

Aircraft wheel loads and tire pressures are increasing: L ~ 65,000 lbs. p > 240 psi

Reported pavement failures in hot climates overseas

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.

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, 70. 76, 82-22 and TLA blend binders

Combine with Gyratory results for updating EB59A and SuperPAVE Specification Development

Conclusions

All Studies

Conclusions

EB 59A N-equiv appears to be problematic• EB 59A --- 85• AAPTP ---- 55 - 65• ERDC ------ 70• FAA --------- 65 – 70

Volumetric and performance comparisons support Ndes = 70

Other Considerations• Volumetrics• Compaction Standard

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

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

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

What is the combined net effect of:

Raising VTM?

Lowering VMA?

Inconsistent (lower?) compaction

Ultimate Objective of All Studies

New P-401 SuperPAVE specification !

Questions?