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Asphalt 101:Asphalt 101:

An Introduction toAn Introduction toHot Mix AsphaltHot Mix Asphalt

MaterialsMaterials

-Part I--Part I-

Asphalt andAsphalt andModified AsphaltsModified Asphalts

Scott Shuler

CSU

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Glue:Glue:Scott ShulerScott Shuler

Sticky Glue:Sticky Glue:Marshall ShackelfordMarshall Shackelford

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Why Study Asphalt?Why Study Asphalt?

of all the ROADS IN THE U. S. A.(miles)

Concrete Earth Gravel Asphalt

100,000 400,000

1,300,000

2,200,000

95%5%

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Why Study Asphalt?Why Study Asphalt? Highway Expenditures in 2008

– $140 Billion Hot Mix Asphalt Placed Annually

– 500 Million Tons– $10.5 Billion

Employment– 300,000 directly– 600,000 additionally

Asphalt is Largely Empirical– “Old Timers” Retiring

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What Are Asphalt Pavements ?What Are Asphalt Pavements ?

Rocks Glued Together With Asphalt

About 86%

About 10%

4%

■ Rocks

■ Asphalt

■ Air

Volume

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Among the Oldest Engineering Materials– Waterproofing of Ships

Sumeria-6000 BC

– Waterproofing of Baths and Tanks “Earth Butter” Mohenjo-Daro Indus Valley-3000 BC

– Mummies Egypt-2600 BC

– Bible References Noah’s Arc Waterproofed with “Pitch” Genesis 6:14.20 Moses’ Basket Coated with “Bitumen” and “Pitch” Exodus 2:3.24

– Roman Buildings Waterproofed and Cemented Romans called the source Lacus Asphaltites

LetLet’’s Consider the Glues Consider the Glue

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So It Will Work!So It Will Work!

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Reed Boat, aka Reed Boat, aka GufaGufa

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Bitumen

Asphalts Tars

PetroleumNatural Coal

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Asphalts

PetroleumNatural

Lake

Rock

Asphaltites

Cements Liquids

Emulsions Cutbacks

Trinidad

La Brea

KY

TX

AB

UT-Gilsonite

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Crude Oil VariationsCrude Oil Variations

Gasoline 3%Kerosene 6%

Gas Oil 33%

Residuum58%

Venezuelan

Gasoline 33%

Kerosene20%

Gas Oil 46%

Residuum 1%

Nigerian Light

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Refining MethodsRefining Methods

Distillation– Atmospheric– Vacuum

Solvent Deasphalting– Propane and Butane Extraction of Lube Oils– Result is Very Hard Precipitate AC

Solvent Extraction (ROSE)– Separates AC into Asphaltenes/Resins/Oils– Result is Blended to Produce Spec AC

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Petroleum AsphaltsPetroleum Asphalts

CrudeStorage

GasolineKerosene

Cutbacks

Gas Oil

Vacu

um S

till

AsphaltCements

Emulsions

Oil Well

Atm

os S

till

Con

dens

er

H 2O

RoofingAsphalts

Air

Gas/Kero650-1050F

60-700F

60-325F

325-500F

650-850F

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Asphalt TypesAsphalt Types

Asphalt Cement Liquid Asphalts

– Emulsified Asphalts– Cutback Asphalts

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Behavior of Asphalt CementsBehavior of Asphalt Cements

Asphalt is Viscoelastic– Viscous (Flows) at High Temperatures– Elastic at Low Temperatures

Silly Putty is Viscoelastic– Pull it Slowly- It stretches – same as high temperature– Pull it Rapidly – It breaks – same as low temperature

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Asphalt Performance depends

on Environment and Traffic

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Weak BehaviorH

ot B

ehav

ior

Cold Behavior

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Temperature EffectsTemperature Effects

30°F

100°F

1 Hour

10 Hours

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Material EffectsMaterial Effects

30°F

1 Hour

Hard Asphalt Softer Asphalt

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AchievingAchievingPerformancePerformance

SUPERPAVE

To The Rescue !

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SPECIFYING PERFORMANCESPECIFYING PERFORMANCE

Based on Climate

PG 64 - 22

PerformanceGrade

Average 7-day maxpavement temperature, C

Min pavementtemperature, C

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DynamicShear

Rheometer

Tests in PG SpecificationsTests in PG Specifications

BendingBeam

Rheometer

RotationalViscometer

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Caused by Warm Weather, Traffic and Wrong Mixture

Cou

rtes

y of

FH

WA

Permanent Deformation ( )Permanent Deformation ( )

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High Temperature or,High Temperature or,Slow Loading Behavior, aka Slow Loading Behavior, aka RuttingRutting

High Pavement Temperature– Desert climates– Summer temperatures

Sustained loads– Slow moving trucks– Intersections

100°F

1 Hour

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Courtesy of FHWA

Thermal CrackingThermal Cracking

Caused by Low Temperatures, Rapid Loads, Hard Binder

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Low Temperature,Low Temperature,or Fast Loading Behavior-aka Crackingor Fast Loading Behavior-aka Cracking

Low Temperature– Cold climates– Winter

Rapid Loads– Fast moving trucks

σ

ε

CrackingFailure

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AgingAging

Asphalt reacts with oxygen– Becomes harder, more brittle– More Elastic, Less Viscous

Short term– During Mixing with Aggregates (280F-330F)

Long term– In Pavement– Air, Water, Sun

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Asphalt Plant and Construction AgingAsphalt Plant and Construction Aging

Rolling Thin Film Oven (RTFO)

Fan

RotatingBottle

Carriage

Blowing Air

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PressureAging Vessel

50 grams of Asphalt inEach Pan

Pressure Aging VesselPressure Aging Vessel

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Pressure Aging VesselPressure Aging Vessel

Courtesy of FHWA

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RV

DSR

BBR

Rutting, Hardening and Fatigue

321 cycle

TimeAA

B

C

CA

B

Fixed Lower Plate

Oscillating Upper Plate

A

Now, Measure theForce Required toRotate the Upper

Plate

And, Measure WhenMovement Occurs in

the Binder

Asphalt Glued In-Between

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Elastic Viscous

TimeAA

B

C

Strain

Strain Occurs With Stressδ = 0o

Strain Lags Stressδ = 90o

AA

B

C

AA

Stress

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Vis

cous

, G”

Elastic, G’

Complex M

odulus, G*

δ

Complex Modulus isthe vector sum of

Elastic and Viscous Components

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> Early part ofpavement life

Heavy TrucksHeavy Trucks

Controlling RuttingControlling RuttingAddressed by:

G*/sin δ on Unaged binder > 1.00 kPaG*/sin δ on Lab Aged binder > 2.20 kPa

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Caused by repeated traffic loads in wheel pathsFatigue CrackingFatigue Cracking

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Fatigue CrackingFatigue Cracking

Addressed by intermediatetemperature stiffness– G*sin δ on RTFO & PAV

aged binder < 5000 kPa

> Later part of pavement service life

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RV DSR BBR

ThermalCracking

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Bending Beam RheometerBending Beam Rheometer

Load Cell

Deflection Transducer

Fluid Bath

Computer

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BBR Measures Stiffness at LowBBR Measures Stiffness at LowTemperatures using Beam TheoryTemperatures using Beam Theory

S(t) =PL3

4 bh3 δ (t)

Creep stiffness at

t = 60 secs100 grams

Clear Span of Beam, 102 mm

Beam Width, 12.5 mm

Beam Thickness, 6.25 mm

Deflection at t = 60 secs

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Bending Beam RheometerBending Beam Rheometer Creep Stiffness Stiffness v. Time Slope

8 15 30 60 120 240

Log

Cre

ep

Stif

fnes

s, S

(t)

Log Loading Time, t (sec)

m

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Thermal CrackingThermal Cracking

Question: How Much Should the AsphaltBe Able to Stretch before Breaking?

Answer: at least 1%

How: Find the Temperature Where theAsphalt Can Stretch 1% or More

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Direct Tension TestDirect Tension Test

Δ Le

Δ L

Load

Stress = σ = P / A

Strainεf

σf

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RVDynamic

ShearRheometer

ConstructionBut Will it Flow for Mixing ?But Will it Flow for Mixing ?

BendingBeam

Rheometer

RotationalViscometer

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Rotational ViscometerRotational Viscometer(Brookfield)(Brookfield)

Inner Cylinder

Torque Motor

ThermoselEnvironmental

Chamber

Digital TemperatureController

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Spec RequirementsSpec Requirements

Make Sure It’s Not Too Thick– Keep Viscosity Below 3 Pa-sec at 275F (135C)

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Questions...