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
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!
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.
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
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
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
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
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
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
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.
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
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