Superpave-PG BinderGrading.pdf

Performance Graded Asphalt Binders Bob Horan, P.E. Consulting Engineer Mechanicsville, VA

October 30, 2003

T3S - Superpave for Low Volume Roads - R. Horan

1

What is Asphalt?

October 30, 2003


2

The 3 A’s of Hot Mix Asphalt

Aggregates,

Asphalt, and Air

HMA = Asphalt + Aggregates + Air October 30, 2003


3

Asphalt Overview • • • • • • •

Terminology History Uses Background Asphalt Behavior Classification (Grading) of Asphalt Asphalt Modification

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4

What is Asphalt? • Called different things – Bitumen – Asphalt – Liquid Asphalt – Asphalt Cement – Asphalt Binder – Binder … But mean basically the same thing! October 30, 2003


5

Background • Asphalt

• Tar

– Soluble in petroleum products – Generally a byproduct of petroleum distillation process – Can be naturally occurring October 30, 2003

– Resistant to petroleum products – Generally byproduct of coke (from coal) production


6

Asphalt - Definition: “A dark brown to black cementitious material in which the predominating constituents are bitumens which occur in nature or are obtained in petroleum processing.” (ASTM D8)

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Brief History • 3200 - 540 B. C. Extensive use in Mesapotamia and Indus Valley as cement for masonry and street construction and as waterproofing agent • 300 B.C. Used for mummification in Egypt • 1870 First asphalt pavement laid in Newark, New Jersey • 1876 First sheet asphalt pavement laid in Washington, DC with imported lake asphalt • 1902 Approx. 20,000 tons of asphalt refined from petroleum in United States Over 30,000,000 tons produced in U.S. • Now October 30, 2003


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Asphalt Sources • Refining produces asphalt with specific characteristics for varied uses – Paving asphalt – Roofing asphalt – Other special uses • Waterproofing • Sealing October 30, 2003


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Sources of Asphalt

• Natural asphalt deposits • Petroleum asphalts

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Asphalt Types • Natural asphalt deposits – Natural evaporation of volatile portions of petroleum leaving the asphalt fractions – Lake asphalt • Trinidad • Bermudez

– Rock asphalt • Natural asphalt deposits in porous rock October 30, 2003


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Trinidad Lake Asphalt

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Background • Each lake asphalt source very consistent – Used solubility test to determine source • Insolubles differed substantially between sources

• Demand for paved roads exceeded the supply of lake asphalts in late 1800’s – Led to use of petroleum asphalts October 30, 2003


16

Petroleum Asphalt

Asphalt is one of the products of the petroleum industry October 30, 2003


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Petroleum-Based Asphalts • Asphalt is waste product from refinery processing of crude oil – Sometimes called the “bottom of the barrel”

• Properties depend on:

Barrel of Crude Oil

– Refinery operations – Composition crude which are source-dependent

Gasoline Kerosene Lt. Gas Oil Diesel Motor Oils Burner Fuel Asphalt

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Refinery Operation LIGHT DISTILLATE PUMPING STATION

FIELD STORAGE

MEDIUM DISTILLATE HEAVY DISTILLATE

TOWER DISTILLATION REFINERY

RESIDUUM

STORAGE GAS

TUBE HEATER

OR

CONDENSERS AND COOLERS

ASPHALT CEMENTS AIR BLOWN ASPHALT

PETROLEUM SAND AND WATER

PROCESS UNIT

AIR

FOR PROCESSING INTO EMULSIFIED AND CUTBACK ASPHALTS

STILL

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Asphalt Binder Behavior –

Temperature

–

Time of Loading

–

Aging is also important

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Asphalt Binder Behavior Consistency Semi-Solid Asphalt is a thermoplastic material that softens as it is heated and hardens when cooled.

Liquid Temperature October 30, 2003


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Asphalt Binder Behavior Stiffness (Response to Load) Asphalt has Viscoelastic Properties

elastic

? elastic solid

viscous -30

October 30, 2003

viscous fluid

25 60 Temperature, °C

135


23

Asphalt Binder Behavior Time versus Temperature 60 C

1 hour

(MS-22, Fig. 2.03)

Flow

1 hour

10 hours

25 C

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Binder Behavior - Aging • Asphalt Reacts with Oxygen – Long and Short Term –

“oxidative” or “age” hardening

• During Construction - Short Term – –

hot mixing placing/compaction

• In Service - Long Term – –

hot climate worse than cool climate summer worse than winter

• Volatilization- Short Term – volatile components evaporate during construction October 30, 2003


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Early Specifications • Lake Asphalts – Appearance – Solubility in carbon disulfide

• Petroleum asphalts (early 1900’s) – Consistency • Chewing • Penetration machine – Measure consistency October 30, 2003


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Penetration Grading Viscosity

0 sec 100 g

penetration

5 sec 100 g

Typical Pen Grades 85-100 • 120-150 October 30, 2003


28

Viscosity Grading Viscosity vacuum

Typical Vis Grades AC - 20 • AC - 10 October 30, 2003


29

“Stiffness” of three different asphalts pen

Penetration Test

hard

A B soft

C -15

October 30, 2003

25 60 135 Temperature, C T3S - Superpave for Low Volume Roads - R. Horan

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“Stiffness” of three different asphalts pen hard

vis

Penetration and Viscosity Test

A B soft

vis -15

25

60

C 135

Temperature, C October 30, 2003


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Problems with Current System • Viscosity –viscous effects only at 60 C

• Penetration –empirical consistency only at 25 C

• No Low Temperature Properties Measured

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Problems with Current System • Problems with Modified Asphalt Characterization • Specification Proliferation • Long Term Aging not Considered

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Why Modify Asphalt? • Change effects of temperature and loading on physical properties of asphalt • Provides a “stiffer” binder at high temperatures (higher PG binder grade) • Reduce effects of aging/oxidation on asphalt properties • Improve adhesion to aggregates

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Modified PG Binders • Many different types of modified binders – elastomers (Stylink, Citgoflex, others) -SBS,SBR – plastomers (Novophalt, Vestoplast, others) – gelled (Multigrade) – blown, oxidized

• Little performance history with some modifiers • Use of modified binder grades will increase cost (materials cost $2 - $5/ton of mix) • Is it worth the extra cost? October 30, 2003


36

When should a modified binder be specified? • In extreme climatic conditions (very hot or very cold) • In very heavy traffic conditions, especially when loading is slow or stopped • In problem situations where rutting, shoving, instability is occurring • Where improved elastic properties are needed (i.e. resistance of reflective cracking) • To provide for thicker binder film thickness in open graded and gap graded mixes October 30, 2003


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What is Asphalt? • • • • •

Black, glue-like, waterproof material A product of the petroleum refining operation Used extensively in the paving, roofing industries Is a thermoplastic material Must be in liquid form for roadway applications (heat, dilution in solvent, emulsification) • Can be used in pavements effectively in the full range of climate and loading conditions • Can be polymer modified to improve properties for better performance when necessary October 30, 2003


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Performance Graded Binders • History • Testing • Specification • Grade Selection

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HMA BindersPerformance Graded (PG) System • Product of Strategic Highway Research Program (SHRP) • New tests and specification • Provides a temperature range through which the asphalt must meet certain physical properties to resist rutting and cracking • Includes conditioning procedures to simulate changes in asphalt properties due to aging in the field October 30, 2003


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Illustration of PG Binder Tests Low Temp. Cracking

- 20

Fatigue Cracking

20

Rutting

Handling

60

135

Pavement Temperature, C October 30, 2003


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Low Temperature Cracking

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Alligator Cracking (Fatigue)

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Rutting in Subgrade or Base

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Rutting in Asphalt Surface Layer

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Rutting at a Roundabout

In what layer is rutting occurring? October 30, 2003


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Superpave Asphalt Binder Specification • Grading System Based on Climate

PG 58 - 22 Performance Average 7-day Min pavement Grade max pavement design temp design temp October 30, 2003


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Performance Graded Binder Specifications • Superior to viscosity and penetration grading systems • Have resulted in higher quality binders • Allow appropriate grade of binder for specific location based upon: – air and pavement temperature – loading conditions – traffic speed October 30, 2003


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Construction

Rutting

Low Temp Cracking

Fatigue Cracking

[DTT] [RV]

[DSR]

Pavement Age No aging October 30, 2003

[BBR]

RTFO - aging PAV - aging


49

Rolling Thin Film Oven controls

fan

163 C

air jet bottle carriage October 30, 2003


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air pressure

Pressure Aging Vessel temperature probe

asphalt pressure vessel sample rack sample pan October 30, 2003


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Rotational Viscometer applied torque from motor spindle asphalt sample sample chamber

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DSR Test Equipment

Binder Sample

Oscillating Plate Fixed Base Plate

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Deflection Transducer Air Bearing Control and Data Acquisition

Load Cell

Fluid Bath

Asphalt Beam

Temperature Probe October 30, 2003

Loading Frame Supports T3S - Superpave for Low Volume Roads - R. Horan

54

Direct Tension Tester L Le Load ∆L Failure

L+

L

change in length (∆ L) failure strain (εf) = effective gauge length Le October 30, 2003


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Performance Grades CEC

Avg 7-day Max, oC

1-day Min, oC

PG 46

PG 52

PG 58

PG 64

PG 70

PG-76

PG 82

-34 -40 -46 -10 -16 -22 -28 -34 -40-46 -16 -22 -28 -34 -40 -10 -16 -22-28 -34 -40 -10 -16 -22 -28 -34 -40 -10 -16 -22 -28 -34 -10 -16 -22 -28-34

ORIGINAL > 230 oC

(Flash Point)

< 3 Pa.s @ 135 oC

RV

(Rotational Viscosity)

> 1.00 kPa 46

(Dynamic Shear Rheometer)

DSR G*/sin

52

64

58

52

58

64

(PRESSURE AGING VESSEL) 20 Hours, 2.07 MPa

90

90

10 7

4

76

( Bending Beam Rheometer)

100 (110)

100 (110)

(Bending Beam Rheometer)

> 1.00 %

(Direct Tension) -2 -30 -36 0

October 30, 2003

110 (110)

DSR G* sin BBR “S” Stiffness BBR

31 28 25 40 37 34 312 8

& “m”- value

-24 -30 -36 0 -6 12 -18 -24 30 -36 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0

Report Value

82

PAV

25 22 19 16 13 10 7 25 22 19 16 13 31 28 25 22 19 16 34 31 8 25 22 19 37 34

m > 0.300

82

Mass Loss < 1.00 %

70

100

(Dynamic Shear Rheometer)

< 5000 kPa S < 300 MPa

100

76

DSR G*/sin

(Dynamic Shear Rheometer) 46

70

RTFO

(ROLLING THIN FILM OVEN) > 2.20 kPa

FP

-6 -12 -18 -24 0 -6 -12 -18 -24

Physical Hardening

DT

-6 -12 -18 -24 -30 -36 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 -30 0 -6 -12 -18 -24 0 -6 -12 -18 -24


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Which PG grades should I use at my facility??? • Many factor to consider – Suggested grades from Superpave Weather Database – Amount and type of traffic loadings – Desired reliability – Reclaimed Asphalt Pavement (RAP) usage – Current available grades – Capabilities of binder suppliers – Typical types of distress in pavements

– Binder costs

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Developed from Air Temperatures A > 20 years

SHR -648 P A

• Superpave Weather Database – 6500 stations in U.S. and Canada

• Annual air temperatures – hottest seven-day temp (avg. and std dev) – coldest temp (avg. and std dev)

• Calculated pavement temperatures used in PG selection October 30, 2003


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Effect of Loading Rate on Binder Selection

90 kph

• Dilemma – specified DSR loading rate is 10 rad/sec – what about longer loading times ?

• Use binder with more stiffness at higher temps – slow - - increase one high temp grade – stationary - - increase two high temp grades – no effect on low temp grade October 30, 2003


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Effect of Loading Rate on Binder Selection • Example with heavy loading – for toll road PG 64-22 – for toll booth PG 70-22 – for weigh stations PG 76-22 October 30, 2003

90 kph Slow

Stopping


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Effect of Traffic Amount on Binder Selection 80 kN ESALs • 10 - 30 x 106 ESAL – Consider increasing -- one high temp grade

• 30 x 106 + ESAL – Recommend increasing -- two high temp grades > Equivalent Single Axle Loads October 30, 2003


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Superpave Asphalt Binder Specification • Grading System Based on Climate

PG 58 - 22 Performance Average 7-day Min pavement Grade max pavement design temp design temp October 30, 2003


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Which PG asphalt should perform best in resisting thermal cracking? • PG 64-22 • PG 76-22 • PG 64-28 • PG 58-34 October 30, 2003


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Which PG asphalt should perform best in resisting thermal cracking? • PG 64-22 • PG 76-22 • PG 64-28 • PG 58-34 October 30, 2003


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Which of the following PG binders should perform best in resisting rutting? • PG 82-22 • PG 76-28 • PG 70-28 • PG 76-22 October 30, 2003


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Which of the following PG binders should perform best in resisting rutting? • PG 82-22 • PG 76-28 • PG 70-28 • PG 76-22 October 30, 2003


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Superpave Binder Implementation 1999 Lead State Survey

2003 2004 Undetermined October 30, 2003


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PG Binders in South Carolina • Adopted in 2000 for all work • Two grades selected: – PG 64-22 • Low volume secondary, primary and interstate pavements

– PG 76-22 • Heavy loaded interstate and specealty locations (intersections) October 30, 2003


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Performance Graded Binder Testing, Specification and Grade Selection

Questions? October 30, 2003


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Superpave-PG BinderGrading.pdf

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