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Where are the SuperpaveBinder Specifications
headed.
John D’Angelo
Federal Highway AdministrationPresented at the 1st International Symposium
On Binder Rheology and Pavement Performance
August 14, 2000
Pre-Superpave Shortcomings
• Viscosity! viscous effects only
• Penetration! empirical measure of viscous and elastic effects
• No Low Temperature Properties Measured• Problems with Modified Asphalt
Characterization• Specification Proliferation• Long Term Aging not Considered
2525 6060 135135-15-15
ConsistencyConsistency(pen or(pen or vis vis))
hardhard
softsoft
penpenvisvis
visvis
AABB
CC
Temperature, CTemperature, C
Superpave Binder Specifications
• Performance Related Binder Spec for thepurchase of asphalt binders used in hot mixasphalt.
• Measure of the rheological properties of thebinders over a wide range of temperaturesand loading conditions.
• Developed as part of the Strategic HighwayResearch Program.
FatigueFatigueCrackingCrackingRuttingRutting
PAV - agingPAV - aging
RTFO - aging RTFO - aging No agingNo aging
Pavement AgePavement Age
ConstructionConstruction
[RV][RV][DSR][DSR]
Low TempLow TempCrackingCracking
[BBR][BBR]
[DTT][DTT]
Temperature Control
• Current Specs. require +/- 0.1 oC control.! 0.1 oC can represent 2% error in the DSR.
• Most equipment does not meet this spec.! ISO 10012 requires precision of 0.03 for 0.1
control.
Temperature Control
• Current specs will need to be changed.! The temperature shall be calibrated by a NIST
traceable device with measurement uncertaintyless then 1/3 of the required tolerance of themeasurement per (ISO 10012-1, par. 4.3). Fortemperature control of +/- 0.1Ε C thecalibration device uncertainty shall be +/-0.033Ε C
! This will require separate calibration.
Superpave Binder Specifications
• Test Variability! PAV DSR.
• AMRL Jan 1995 Samples had CV 44%
• AMRL Jan. 2000 Samples had CV 22%.
! This is a dramatic improvement, but still needsgreater reduction.
• Experiment to evaluate using larger plates to reducevariability may lead to improved repeatability.
Superpave Binder Specifications
• PAV DSR.
! DSR testing with 8mm plate and 2 mm gap has2DS CV of 44%
! Preliminary testing with 12 mm plates and1mm gap has 2DS CV of 20%. This is mostlyfrom improved procedures. New procedures tobe sent to AASHTO.
Superpave Binder Specifications
• Silicone molds effect test results: time totest and the silicone cause variability.
Direct Tension Test
• Coefficient of Variation reported at over 30%or 2Ds 83%
• New Equipment and procedure trainingresults CV 10% or 2Ds of 27%.
Test Repeatability
• Through training and improved procedurestesting variability will continue to go down.
Revisions to Screening Tests
• Laboratory Asphalt Stability Test (LAST)! Measure storage stability with and without
agitation
• Modify RTFO! Better evaluates modified binders.
Laboratory Asphalt Stability Test
• AASHTO procedure is being developed forETG review.
165.0
Electric Motor25-27 RPM
TemperatureController
(Brookfield)
TemperatureProbe
Heater
Propeller(4 Blades)
Gas Purging
Sampling
Baffle
Modification of the RTFO• Modified binders do
not age in the RTFO
• Some modifiedsystems creep out ofthe bottle
• A uniform thin film isneeded to age bindersproperly
Modification of the RTFO
• NCHRP study! Rods do not effect neat asphalt binders! Modified systems age 3 to 4 times the unaged
binders with rods.
• FHWA evaluation of procedure! Verification of research results.! Time to scrape bottles.! Effect of air during scraping time.
Mississippi SPS – 9 Project
• I 55, 3 binders same mix design, 2years and 2.4 million ESAL’s!58-22 exhibited 7 mm of rutting.
!64-22 exhibited 3 mm of rutting.
!76-22 exhibited no rutting.
Pennsylvania I80 Clearfield Co.
S Crack80-1927.8Gilsonite
80-2715.1SB
77-2516.4SBS
M Crack77-2120EVA
M Crack76-2023.2PE
M Crack67-2619.7AC-20
distressPG gradeG*sin∗ temp
AC Binder
Low Temperature Performance
• Lamont test sections.
SX ID # 1 3 4 5 6 7
CGSBGrading
80/100B 300/400A 80/100C 80/100A 150/200A 200/300A
Air blown Yes No No Yes No No
Field No Crack
-30.2 -35.9 -23.6 -26.1 -33 -35.9
Field Crack -33 -26.1 -35.9 -35.9
Current Spec -34.0 -38.8 -27.8 -37.5 -34.8 -40.0
Superpave Binder Specifications
• What is in the Future?! Not all binders of the same grade perform the
same.
! Not all modifiers are the same.
! The Superpave binder spec. has to be madeblind to modifiers.
Superpave Binder Specifications
• The BBR works well in determining unmodifiedbinders critical cracking temperature.! This has been verified on Canadian and US test sections
• Modified systems and some neat asphalts neednew tools to evaluated critical crackingtemperatures.
Superpave Binder Specification
• New Low temperature specificationcombines the DT and the BBR.! Thermal stress is calculated from BBR data.
! Strength is determined from the DT.
! If the strength of the material is greater than the stressfrom the temperature drop the binder will not crack.
Specification Comparison
-40
-34
-28
-22
-16
-40 -34 -28 -22 -16
Current Spec
Pro
pos
ed S
pec
AAA-1 AAB-1 AAD-1 AAF-1 AAM-1
Lamont #1 Lamont #3 Lamont #6 Lamont #7
Proposed MP1a Spec.
Binder Tcr Current Spec Tcr Proposed Spec
70-22 Air Blown -24.5 -22.570-22 Conventional -25.1 -22.570-22 SBS Modified -26.0 -30.5Chemically Modified 64-28 A -29.0 -28.0Chemically Modified 64-28 B -27.5 -27.0Chemically Modified 64-28 K1 -29.5 -27.5Chemically Modified 58-28 M1 -27.3 -27.0Elvaloy Modified 64-34 DP -34.7 -36.0
Binder High Temp Properties
• I 80 Nevada Study same mix differentbinders.PG 64-22 mod. no rutting PG 64-22 unmod. 15mm rutting
Binder High Temp Properties
• New test procedure to evaluate binders.
0.0
0.2
0.4
0.6
0.8
1.0
0 2.5 5 7.5 10
time, s
No
rma
lize
d S
tra
in
BM (PMA)
HSK(Conventional)
εacc HSK
εacc BM
Binder High Temp Properties
Testing 3 different PG 82's
02468
101214
0 200 400 600 800 1000 1200
Time
Acc
umul
ated
Str
ain
SBRPEOxd
Superpave Binder Specification
• The Superpave Binder Specifications willcontinue to evolve.
• As findings from various studies becomeavailable the ETG will review these andmake recommendation for changes to theSpec.
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