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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
2
Glue:Glue:Scott ShulerScott Shuler
Sticky Glue:Sticky Glue:Marshall ShackelfordMarshall Shackelford
3
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%
4
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
5
What Are Asphalt Pavements ?What Are Asphalt Pavements ?
Rocks Glued Together With Asphalt
About 86%
About 10%
4%
■ Rocks
■ Asphalt
■ Air
Volume
6
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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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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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
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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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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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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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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