performance grading of bitumen - asfaltblij€¦ · performance grading of bitumen. outline •...
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H. BahiaThe University of Wisconsin-Madison
Performance Grading of Bitumen
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Outline• Background on Transport• Targets of Bitumen Specifications• Traditional Specifications• Performance grade Specifications
– Why we need to learn about them – Test methods necessary– The Superpave Bitumen grading system
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Transport Network
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How much is spent on Roads ?
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Common Targets forBitumen Specifications
• Constructability
• Performance
• Durability
RuttingFatigue Cracking
Thermal Cracking
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ConsistencyConsistency(pen or (pen or visvis))
2525 6060 135135--1515
hardhard
softsoft
penpen visvis
visvis
AABBCC
Temperature, CTemperature, C
A, B, C are same grade!
Historical Specifications 100 g100 g
100 g100 gpenetrationpenetration
0 sec0 sec5 sec5 sec
vacuumvacuum
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4050
6070
85100
120150
200300
Penetration GradesAC 40
AC 20
AC 10
AC 5
AC 2.5
100
50
10
5
Visc
osity
, 60C
(140
F)
AR 16000
AR 8000
AR 4000
AR 2000
AR 1000
Conventional Bitumen Grades
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Asphalt Behavior
Hard
Soft
Elastic Viscous
Lower TempShorter loading time(High Traffic Speed)
Higher TempLonger loading timeSlower Traffic Speed
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60 C
25 C
1 hour1 hour
1 hour1 hour 10 hours10 hours
Effects of Time and Temperature
Flows rapidly at High temperatures
Flows slowly with time at lower temperatures
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Elastic Viscous
BeforeBeforeLoadLoad
DuringDuringLoadLoad
AfterAfterLoadLoad
Tire Tire LoadLoad Recoverable Recoverable
DeformationDeformation
BeforeBeforeLoadLoad
DuringDuringLoadLoad
AfterAfterLoadLoad
Tire Tire LoadLoad NonNon--Recoverable Recoverable
DeformationDeformation
Effects of Visco-Elasticity
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Performance GradingShould:
• Include measures describing stress-strain relationships under field loading.
• Consider the pavement conditions– Temperature, traffic speed, traffic
volume, and pavement structure. • Include acceptance limits derived from
experience and factual field performance.
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Variables that affects Binder Selection
• Geographic Area:– Air Temperature, solar radiation– Pavement Temperature: Max & Min
• Traffic volume: High, Medium, Low
• Traffic speed: Fast, Slow
• Pavement Structure: Strong, Weak– Stress and strain
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Selection of Grades by Pavement Temperature
63 C
57 C
Maximum: @ 20-mm below surface(approximately 18 C higher)
Minimum: @ surface (approximately 8 C higher)
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Important ConsiderationsTraffic and Pavement Structure
• Effect of traffic Volume & Speed
4ESALS !, Speed limits!
• Pavement Damage
8Weak vs. Strong base!
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ThermalCracking
FatigueCracking
PermanentDeformation
(mixing & compact)
Pavement Temperature, C- 20 20 60 135
RTFOPAV
RuttingFatigue CrackingThermal Cracking Production
Performance Grading – PG system
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Performance Grading of Asphalt Binder- The Superpave System
• Workability at Construction Temperatures• Rotational Viscometer (RV) – η at 135 C - unaged
• Rutting at High Pavement Temperature• Dynamic Shear Rheometer (DSR) - G*/sin δ (unaged & RTFO)
• Fatigue at Average Pavement Temperature • (DSR) - G*.sin δ (PAV aged)
• Thermal cracking at Low Pavement Temperature • Bending Beam Rheometer (BBR) - S(60), m(60) (PAV aged)• Direct Tension Tester (DTT) - Strain at failure
• Durability Properties - short term and long term • rolling thin film oven (RTFO), pressure aging vessel (PAV)
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Rotational Viscometer• Evaluates
– handling and pumping properties
• ASTM D 4402• Other Names: Brookfield
viscometer, rotational coaxial cylinder viscometer
• Output– viscosity at 135 C– viscosity temperature chart for
mix design
motor andcontroller
temperaturecontroller
thermo -container
sample chamber
spindleasphalt sample
appliedtorque
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What are our problems? 1.Rutting in Asphalt Layer
originaloriginalprofileprofile
weak asphalt layerweak asphalt layershear planeshear plane
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Dynamic Shear Rheometer• Evaluates
– elastic and viscous properties– time and temperature effects
• Other Names– oscillatory shear rheometers– dynamic rheometers
• Output– complex shear modulus (G*)– phase angle (δ)
Applied StressApplied Stressor Strainor Strain
Fixed PlateFixed Plate
OscillatingOscillatingPlatePlate
BB CCAA
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AsphaltAsphalt
Applied StressApplied Stressor Strainor Strain
Fixed PlateFixed Plate
OscillatingOscillatingPlatePlate
BB CCAA
Test at Pavement Temperature
ResultingResultingShearShearStrainStrain
ττmaxmax
AppliedAppliedShearShearStressStress
γγmaxmaxδδ
G* = G* = γγmaxmax
ττmaxmax
δδ = time lag/w= time lag/w
timetime
timetime Measures elasticity
Measures hardness
Dynamic Shear Rheometer
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““alligatoralligator””crackingcracking
2. Fatigue of Pavements
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6 6 -- 30 m30 m
3. Low TemperatureCracking
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Bending Beam Rheometer
• Evaluates– low temperature stiffness properties
• Output–creep stiffness–m-value
TimeTime
DeflectionDeflection
TimeTime
LoadLoad
deflectiondeflection
Load
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Log CreepLog CreepStiffness, SStiffness, S
Log Loading TimeLog Loading Time
slope = mslope = m--valuevalue
60 sec60 sec88 1515 3030 120120 240240
S(60)m(60)
Results of the Bending Beam Rheometer
ThermalStress build up
ThermalStress relaxation
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Direct Tension Tester
• Evaluates– low temperature ability to stretch
• Output– tensile strain at failure lengthlength
before testbefore test
LoadLoad
LoadLoad
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elongationelongation
length before testlength before test
lengthlengthat failure at failure
elongationelongationat failureat failure
lengthlengthbefore testbefore test
LoadLoad
LoadLoadfailure strain = failure strain =
Direct Tension Testing
failure stress = Load at break /areafailure stress = Load at break /area
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stressstress
strainstrain
brittlebrittle
brittlebrittle--ductileductile
ductileductile
Failure Properties Strength and Strain Tolerance
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Asphalt Aging Behavior• Asphalt Reacts with Oxygen and
hardens• During Construction - Short Term
–hot mixing, placing, and compaction• In Service - Long Term
–hot climate worse than cool climate–So What?–Pavement layer is brittle >> cracking
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163 Cempty bottleempty bottlebeforebefore
coated bottlecoated bottleafterafter
controlscontrols fanfan
bottle carriagebottle carriageair jetair jet
Rolling Thin Film Oven Short Term aging
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asphaltasphalt
sample pansample pansample racksample rackpressure vesselpressure vessel
airairpressurepressure temperaturetemperature
probeprobe
The Pressure Aging Vessel
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Superpave Binder Specifications
Mod
ulus
S=300MPam>0.3 G*sinδ=5 MPa
G*/sinδ=.001,.0022 MPaTemperature
Tmin Tavg Tmax
RTFO
PAV-aged
η= 3.0 pa-s
Unaged
135 C
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Asphalt Binder Selection
• Performance Based–permanent deformation– fatigue cracking– low temperature cracking
• Physical Properties–criteria remain the same–temperature at which criteria achieved
varies–measured on aged binder
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Grade is First Selected from Pavement Temperatures
Max Pave Temperature (HT)
PG 58 -
Min Pav Temperature (LT)
-16 -22 -28 -34 -40
Viscosity at 135 C @ 135 C < 3.0 Pa-s G*/sin d (ungaed) @ HT > 1.0 Kpa G*/sin d (RTFO-aged) G*.sin d (RTfO+PAV-aged)S( 60) (RTfO+PAV-aged) M(60) (RTfO+PAV-aged) Strain @ failure (RTFO+PAV)
@ HT >2.2 Kpa @ IT <5000 Kpa @ LT <300,000 Kpa @ LT >0.300 @ LT >1.0 %
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Grading System
PG 64PG 64--2222
PerformancePerformanceGradeGrade
Average 7Average 7--daydaymax pavementmax pavement
design tempdesign temp
Min pavementMin pavementdesign tempdesign temp
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Binder PG Grades (AASHTO) PG HT- LT LTHT
-10 -16 -22 -28 -34 -40 -46
82767064585246
Modified Bitumen
Unmodified Bitumen
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PG HT-LT
40
46
52
58
64
70
76
82
88
-52 -46 -40 -34 -28 -22 -16 -10 -4Low-Temp Grade (LT
High
-Tem
p G
rade
(HT)
StandardCrude
ModifiedBitumen
Best Crude
Map for Production of PG Grades
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Methods of Selection
• Select base grade based upon:–Geographic Area–Air Temperature –Pavement Temperature
• Adjust base grade based upon:–Traffic Speed –Traffic Volume
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Considering traffic volume and speed - adjustment to PG Grade
Traffic Volume ESALs
Traffic Speed
Standing Slow Standard <0.3 (~ +1) - -
0.3 to < 3 +2 +1 - 3 to <10 +2 +1 -
10 to < 30 +2 +1 (~ +1) > 30 +2 +1 +1
+1 : Increase PG grade by 6 degrees; e.g. PG 64-22 to PG 70-22
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Effect of Traffic Speed and Volume on Binder Selection• Examples• Base Grade PG 58 -22
– for toll road – (high Volume) PG 64-22
– for toll booth – ( high volume and slow traffic) PG 70-22
– for rest area– (high volume and standing traffic) PG 76-22
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Thank You for your attention
Questions !