performance grading of bitumen - asfaltblij€¦ · performance grading of bitumen. outline •...
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H. BahiaThe University of Wisconsin-Madison
Performance Grading of Bitumen
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
Transport Network
How much is spent on Roads ?
Common Targets forBitumen Specifications
• Constructability
• Performance
• Durability
RuttingFatigue Cracking
Thermal Cracking
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
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
Asphalt Behavior
Hard
Soft
Elastic Viscous
Lower TempShorter loading time(High Traffic Speed)
Higher TempLonger loading timeSlower Traffic Speed
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
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
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.
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
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)
Important ConsiderationsTraffic and Pavement Structure
• Effect of traffic Volume & Speed
4ESALS !, Speed limits!
• Pavement Damage
8Weak vs. Strong base!
ThermalCracking
FatigueCracking
PermanentDeformation
(mixing & compact)
Pavement Temperature, C- 20 20 60 135
RTFOPAV
RuttingFatigue CrackingThermal Cracking Production
Performance Grading – PG system
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)
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
What are our problems? 1.Rutting in Asphalt Layer
originaloriginalprofileprofile
weak asphalt layerweak asphalt layershear planeshear plane
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
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
““alligatoralligator””crackingcracking
2. Fatigue of Pavements
6 6 -- 30 m30 m
3. Low TemperatureCracking
Bending Beam Rheometer
• Evaluates– low temperature stiffness properties
• Output–creep stiffness–m-value
TimeTime
DeflectionDeflection
TimeTime
LoadLoad
deflectiondeflection
Load
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
Direct Tension Tester
• Evaluates– low temperature ability to stretch
• Output– tensile strain at failure lengthlength
before testbefore test
LoadLoad
LoadLoad
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
stressstress
strainstrain
brittlebrittle
brittlebrittle--ductileductile
ductileductile
Failure Properties Strength and Strain Tolerance
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
163 Cempty bottleempty bottlebeforebefore
coated bottlecoated bottleafterafter
controlscontrols fanfan
bottle carriagebottle carriageair jetair jet
Rolling Thin Film Oven Short Term aging
asphaltasphalt
sample pansample pansample racksample rackpressure vesselpressure vessel
airairpressurepressure temperaturetemperature
probeprobe
The Pressure Aging Vessel
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
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
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 %
Grading System
PG 64PG 64--2222
PerformancePerformanceGradeGrade
Average 7Average 7--daydaymax pavementmax pavement
design tempdesign temp
Min pavementMin pavementdesign tempdesign temp
Binder PG Grades (AASHTO) PG HT- LT LTHT
-10 -16 -22 -28 -34 -40 -46
82767064585246
Modified Bitumen
Unmodified Bitumen
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
Methods of Selection
• Select base grade based upon:–Geographic Area–Air Temperature –Pavement Temperature
• Adjust base grade based upon:–Traffic Speed –Traffic Volume
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
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
Thank You for your attention
Questions !