improving hma performance with superpave® improving hma performance with superpave® a a s h t o f...
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FHWA
Improving HMA Performance Improving HMA Performance with Superpave®with Superpave®
AA
SHT
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I N D U S T R YSUPERPAVE 2005
Federal Highway AdministrationFederal Highway Administration
FHWA
Highway Pavements R&THighway Pavements R&T
Critical issuesCritical issues
Pavements are Pavements are the backbone of transportation.the backbone of transportation.
Growing expectations of the highway user for Growing expectations of the highway user for smoother ride and reduced delay and disruption.smoother ride and reduced delay and disruption.
FHWA
Long Life Pavements for the Long Life Pavements for the 2121stst CenturyCentury
Critical issuesCritical issues“Just in time” delivery has increased from “Just in time” delivery has increased from 10% in 1990 to over 60% in 2000.10% in 1990 to over 60% in 2000.
Of every dollar invested in highways more Of every dollar invested in highways more than 50 than 50 cents goes to pavements.cents goes to pavements.
4 million miles of roadways in US 4 million miles of roadways in US
FHWA
Why Superpave?Why Superpave?
Pavement performance for the US highways Pavement performance for the US highways was not improving.was not improving.
Demands on the system were increasing.Demands on the system were increasing.
New materials coming on the market were New materials coming on the market were difficult to evaluate.difficult to evaluate.
FHWA
ChangesChanges
Increased traffic and loadingsIncreased traffic and loadingsSupply sourcesSupply sourcesUse of baghousesUse of baghousesUse of recycled materials (RAP)Use of recycled materials (RAP)Drum plants vs. batch plantsDrum plants vs. batch plantsPersonnel experiencePersonnel experienceStaff reductionsStaff reductions
FHWA
Evolution of TrafficEvolution of Traffic
Interstate highways Interstate highways -- 19561956AASHTO Road Test AASHTO Road Test -- 19581958--6262
still widely used for pavement designstill widely used for pavement designlegal truck load legal truck load -- 73,280 lbs73,280 lbs
Factors for higher stressesFactors for higher stresses75% increase in truck miles (1973 75% increase in truck miles (1973 --1993)1993)Legal truck load limit increase in 1982 Legal truck load limit increase in 1982 (73,280 to 80,000 pounds)(73,280 to 80,000 pounds)Advent of radial tires
StrStressess
Advent of radial tires
FHWA
Business as usual will not work !Business as usual will not work !
Business as Usual Will not Work !
Pavement Performance
FHWA
Distress Modes in AsphaltDistress Modes in Asphalt
Primary three are:Primary three are:RuttingRuttingFatigue crackingFatigue crackingLowLow--temperature crackingtemperature cracking
FHWA
Binder SpecificationsBinder Specifications
The pavement see many temperatures The pavement see many temperatures and loads.and loads.
Heavy TrucksHeavy Trucks
FHWA
HMA BehaviorHMA BehaviorAsphalt Binder BehaviorAsphalt Binder Behavior
TemperatureTemperatureTime of LoadingTime of LoadingAge also importantAge also important
Aggregate BehaviorAggregate BehaviorSurface CharacteristicsSurface CharacteristicsParticle ShapeParticle ShapeGradationGradation
Asphalt Mixture BehaviorAsphalt Mixture BehaviorAsphalt BehaviorAsphalt BehaviorAggregate BehaviorAggregate BehaviorCharacteristics of combinationCharacteristics of combination
FHWA
Time vs. TemperatureTime vs. Temperature
60 C60 C 1 hour1 hour
25 C25 C1 hour1 hour 10 hours10 hours
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Temperature, °CTemperature, °C
Stiffness (Response to Load)Stiffness (Response to Load)
--3030 2525 6060 135135
elasticelastic
viscousviscous
elasticelasticsolidsolid
viscousviscousfluidfluid
FHWA
Binder Behavior Binder Behavior -- AgingAgingAsphalt Reacts with OxygenAsphalt Reacts with Oxygen
“oxidative” or “age” hardening“oxidative” or “age” hardening
During Construction During Construction -- Short TermShort Termhot mixinghot mixingplacing/compactionplacing/compaction
In Service In Service -- Long TermLong Termhot climate worse than cool climatehot climate worse than cool climatesummer worse than wintersummer worse than winter
Volatilization Volatilization -- Short TermShort Termvolatile components evaporate during constructionvolatile components evaporate during construction
FHWA
PrePre--Superpave Asphalt Superpave Asphalt Property MeasurementsProperty Measurements
PenetrationPenetration(1900s)
ViscosityViscosity(1950s)(1900s)
100 g100 g
0 sec0 sec
100 g100 g
5 sec5 secpenetrationpenetration
(1950s)
vacuumvacuum
CANNON
CANNON
100100A9A9
FHWA
PrePre--Superpave ShortcomingsSuperpave ShortcomingsViscosityViscosity
viscous effects onlyviscous effects only
PenetrationPenetrationempirical measure of viscous and elastic effectsempirical measure of viscous and elastic effects
No Low Temperature Properties MeasuredNo Low Temperature Properties MeasuredProblems with Modified Asphalt Problems with Modified Asphalt CharacterizationCharacterizationSpecification ProliferationSpecification ProliferationLong Term Aging not Considered Long Term Aging not Considered
FHWA
ConsistencyConsistency(pen or(pen or visvis))
2525 6060 135135--1515
penpenvisvis
visvis
AABB
CC
hardhard
softsoft
Temperature, CTemperature, C
FHWA
Superpave Binder Superpave Binder MeasurementsMeasurements
Temperature RelationshipsTemperature Relationships
Pavement Age RelationshipsPavement Age Relationships
FHWA
Asphalt Mixture BehaviorAsphalt Mixture Behavior
Permanent DeformationPermanent DeformationFatigue CrackingFatigue CrackingLow Temperature CrackingLow Temperature Cracking
FHWA
Rutting in Asphalt LayerRutting in Asphalt Layer
originaloriginalprofileprofile
weak asphalt layerweak asphalt layer
shear planeshear plane
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Repeated Shear DeformationRepeated Shear Deformation
deformationdeformation
number of loadsnumber of loads
(permanent)(permanent)plasticplastic
elasticelastic
FHWA
Mixture Resistance to RuttingMixture Resistance to Rutting
Asphalt BinderAsphalt Binderstiff and elastic at high temperaturesstiff and elastic at high temperatures
AggregateAggregatehigh interhigh inter--particle frictionparticle frictiongradation acts like gradation acts like one large elastic stoneone large elastic stone
FHWA
Fatigue CrackingFatigue CrackingDistress in Wheel pathDistress in Wheel pathProgressive DamageProgressive Damage
longitudinal crackinglongitudinal crackingalligator crackingalligator crackingpotholespotholes
Affected byAffected byasphalt binderasphalt binderaggregatesaggregatespavement structurepavement structure
FHWA
HMAHMA tensile stressestensile stresses
HMA must beHMA must bestrong & resilientstrong & resilient
FHWA
HMA Fatigue BehaviorHMA Fatigue Behavior
Longer Fatigue LifeLonger Fatigue Lifeflexible materialsflexible materialslow stress/strain levellow stress/strain level
Shorter Fatigue LifeShorter Fatigue Lifestiff materialsstiff materialshigh stress/strain levelhigh stress/strain level
ExceptionExceptionthick pavementsthick pavementsnonnon--deflecting support layers
Heavy TrucksHeavy Trucks
deflecting support layers
FHWA
Low Temperature CrackingLow Temperature Cracking
Environmental DistressEnvironmental DistressStresses/Strains Induced by Temperature Stresses/Strains Induced by Temperature ChangeChangeTransverse CracksTransverse CracksOne CycleOne Cycle vsvs Many CyclesMany CyclesAffected Primarily by Asphalt Binder Affected Primarily by Asphalt Binder
6 6 -- 30 m30 m
FHWA
Cures for Low Cures for Low Temperature CrackingTemperature Cracking
Use Less Stiff Asphalt BinderUse Less Stiff Asphalt Binderlower stiffness at low tempslower stiffness at low tempsrelaxation of stressesrelaxation of stresses
Use Asphalt Binder Less Prone to AgingUse Asphalt Binder Less Prone to AgingConstruct HMA with Proper Air VoidsConstruct HMA with Proper Air Voids
FHWA
The Superpave SystemThe Superpave System
What is SuperpaveWhat is SuperpaveA performanceA performance--related binder specificationrelated binder specificationA performanceA performance--related mix specificationrelated mix specificationMixture analysis toolsMixture analysis tools
FHWA
Superpave Performance TestingSuperpave Performance TestingWhat Are We Doing?What Are We Doing?
Rut DepthRut Depth
ESALsESALsPerformancePerformance
TestTest
PerformancePerformancePredictionPredictionStill under developmentStill under development
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