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Improving HMA Performance Improving HMA Performance with Superpave®with Superpave®

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SHT

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I N D U S T R YSUPERPAVE 2005

Federal Highway AdministrationFederal Highway Administration

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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.

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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

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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

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FHWA

Business as usual will not work !Business as usual will not work !

Business as Usual Will not Work !

Pavement Performance

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Distress Modes in AsphaltDistress Modes in Asphalt

Primary three are:Primary three are:RuttingRuttingFatigue crackingFatigue crackingLowLow--temperature crackingtemperature cracking

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Rutting

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Fatigue Cracking

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Low Temperature CrackingLow Temperature Cracking

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Binder SpecificationsBinder Specifications

The pavement see many temperatures The pavement see many temperatures and loads.and loads.

Heavy TrucksHeavy Trucks

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Binder Grade is a function of

environment and traffic level

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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

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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

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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

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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

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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

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ConsistencyConsistency(pen or(pen or visvis))

2525 6060 135135--1515

penpenvisvis

visvis

AABB

CC

hardhard

softsoft

Temperature, CTemperature, C

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Superpave Binder Superpave Binder MeasurementsMeasurements

Temperature RelationshipsTemperature Relationships

Pavement Age RelationshipsPavement Age Relationships

FHWAPavement Temperature, CPavement Temperature, C

-- 2020 2020 6060 135135

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Asphalt Mixture BehaviorAsphalt Mixture Behavior

Permanent DeformationPermanent DeformationFatigue CrackingFatigue CrackingLow Temperature CrackingLow Temperature Cracking

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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

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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

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Fatigue CrackingFatigue CrackingDistress in Wheel pathDistress in Wheel pathProgressive DamageProgressive Damage

longitudinal crackinglongitudinal crackingalligator crackingalligator crackingpotholespotholes

Affected byAffected byasphalt binderasphalt binderaggregatesaggregatespavement structurepavement structure

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HMAHMA tensile stressestensile stresses

HMA must beHMA must bestrong & resilientstrong & resilient

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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

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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

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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

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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

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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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Final PayoffFinal Payoff

Better asphalt pavementsBetter asphalt pavementsExtended service lifeExtended service life