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 !