FHWA Condensed Superpave

Asphalt Specifications

Lecture Series

SUPERPAVE

Aggregates

Usually refers to a soil that has in some way been processed or sorted.

Aggregate Size Definitions

• Nominal Maximum Aggregate Size– one size larger than the first sieve to retain

more than 10%

• Maximum Aggregate Size– one size larger than nominal maximum

size

10010010010090907272656548483636222215159944

100100999989897272656548483636222215159944

100100

00 .075.075 .3.3 2.36 2.36 4.75 4.75 9.59.5 12.5 19.012.5 19.0

Percent PassingPercent Passing

control pointcontrol point

restricted zonerestricted zone

max density linemax density line

maxmaxsizesize

nomnommaxmaxsizesize

Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power

Superpave Aggregate Gradation

100100

00 .075.075.3.3 2.36 2.36 12.5 12.5 19.019.0

Percent PassingPercent Passing

Design Aggregate StructureDesign Aggregate Structure

Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power

Superpave Mix Size Designations

SuperpaveSuperpave Nom Max SizeNom Max Size Max SizeMax SizeDesignationDesignation (mm) (mm) (mm) (mm)

37.5 mm37.5 mm 37.5 37.5 50 50 25 mm25 mm 25 25 37.5 37.5 19 mm19 mm 19 19 25 25 12.5 mm12.5 mm 12.5 12.5 19 19 9.5 mm9.5 mm 9.5 9.5 12.5 12.5

Gradations* Considerations:

- Max. size < 1/2 AC lift thickness

- Larger max size

+ Increases strength

+ Improves skid resistance

+ Increases volume and surface area of agg which decreases required AC content

+ Improves rut resistance+ Increases problem with segregation of particles

- Smaller max size

+ Reduces segregation + Reduces road noise + Decreases tire wear

Percent Crushed Fragments in Gravels

• Quarried materials always 100% crushed

• Minimum values depended upon traffic level and layer (lift)

• Defined as % mass with one or more fractured faces

Percent Crushed Fragments in Gravels

0% Crushed 100% with 2 or More Crushed Faces

Coarse Aggregate Angularity Criteria

Traffic Depth from SurfaceMillions of ESALs < 100 mm > 100 mm

< 0.3< 1< 3< 10< 30< 100 100

55/--65/--75/--85/8095/90

100/100100/100

--/----/--50/--60/--80/7595/90

100/100

First number denotes % with one or more fractured facesSecond number denotes % with two or more fractured faces

Asphalt Cements

Background

History of Specifications

Background• Asphalt

– Soluble in petroleum products

– Generally a by-product of petroleum distillation process

– Can be naturally occurring

• Tar– Resistant to

petroleum products– Generally by-product

of coke (from coal) production

Penetration Testing• Sewing machine needle

• Specified load, time, temperature

100 g

Initial

Penetration in 0.1 mm

After 5 seconds

Penetration Specification

• Five Grades• 40 - 50• 60 - 70• 85 - 100• 120 - 150• 200 - 300

Ductility

Typical Penetration Specifications

PenetrationPenetration 40 - 50 40 - 50 200 - 300200 - 300

Flash Point, CFlash Point, C 450+ 450+ 350+ 350+

Ductility, cmDuctility, cm 100+ 100+ 100+ 100+

Solubility, %Solubility, % 99.0+ 99.0+ 99.0+ 99.0+

Retained Pen., % 55+Retained Pen., % 55+ 37+ 37+

Ductility, cmDuctility, cm NA NA 100+ 100+

Viscosity Graded Specifications

Types of Viscosity Tubes

Asphalt Institute TubeZietfuchs Cross-Arm

Tube

Table 1 Example AC 2.5AC 2.5 AC 40AC 40

Visc, 60CVisc, 60C 250 250 ++ 50 4,000 50 4,000 ++ 800 800

Visc, 135CVisc, 135C 80+ 80+ 300+ 300+

PenetrationPenetration 200+ 200+ 20+ 20+

Visc, 60CVisc, 60C <1,250<1,250 <20,000 <20,000

DuctilityDuctility 100+ 100+ 10+ 10+

4050

6070

85100

120150

200300

Penetration Grades

AC 40

AC 20

AC 10

AC 5

AC 2.5

100

50

10

5

Vis

cosi

ty,

60C

(14

0F)

Asphalt Cements

New Superpave Performance Graded Specification

PG Specifications

• Fundamental properties related to pavement performance

• Environmental factors

• In-service & construction temperatures

• Short and long term aging

High Temperature Behavior

• High in-service temperature– Desert climates– Summer temperatures

• Sustained loads– Slow moving trucks– Intersections

Viscous Liquid

Pavement Behavior(Warm Temperatures)

• Permanent deformation (rutting)

• Mixture is plastic

• Depends on asphalt source, additives, and aggregate properties

Permanent Deformation

Function of warm weather and traffic

Courtesy of FHWA

Low Temperature Behavior

• Low Temperature– Cold climates– Winter

• Rapid Loads– Fast moving trucks

Elastic Solid

E

Hooke’s Law

Pavement Behavior(Low Temperatures)

• Thermal cracks– Stress generated by contraction due to drop in

temperature– Crack forms when thermal stresses exceed

ability of material to relieve stress through deformation

• Material is brittle

• Depends on source of asphalt and aggregate properties

Thermal Cracking

Courtesy of FHWA

Superpave Asphalt Binder Specification

The grading system is based on Climate

PG 64 - 22

Performance Grade

Average 7-day max pavement temperature

Min pavement temperature

Pavement Temperatures are Calculated

• Calculated by Superpave software

• High temperature – 20 mm below the surface of mixture

• Low temperature– at surface of mixture

Pave temp = f (air temp, depth, latitude)

Concentric Cylinder

Concentric Cylinder Rheometers

RMi

Ri2 L

R

Ro - Ri

Dynamic Shear Rheometer (DSR)

• Parallel Plate Shear flow varies with gap height and radius

Non-homogeneous flow

R = R

h

R = 2 M

R3

Short Term Binder Aging

• Rolling Thin Film Oven– Simulates aging from hot mixing and construction

Pressure Aging Vessel(Long Term Aging)

• Simulates aging of an asphalt binder for 7 to 10 years

• 50 gram sample is aged for 20 hours

• Pressure of 2,070 kPa (300 psi)

• At 90, 100 or 110 C

Bending Beam Rheometer

Air Bearing

Load Cell

Deflection Transducer

Fluid Bath

Computer

Direct Tension Test

Le

L

Load

Stress = = P / A

Strainf

f

Summary

FatigueCrackingRutting

RTFOShort Term AgingNo aging

Construction

[RV] [DSR]

Low TempCracking

[BBR]

[DTT][DTT]

PAVLong Term Aging

Superpave Binder Purchase Specification

Superpave Asphalt Binder Specification

The grading system is based on Climate

PG 64 - 22

Performance Grade

Average 7-day max pavement temperature

Min pavement temperature

PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82

(Rotational Viscosity) RV

90 90 100 100 100 (110) 100 (110) 110 (110)

(Flash Point) FP

46 52 58 64 70 76 82

46 52 58 64 70 76 82

(ROLLING THIN FILM OVEN) (ROLLING THIN FILM OVEN) RTFO RTFO Mass Loss Mass Loss << 1.00 % 1.00 %

(Direct Tension) DT

(Bending Beam Rheometer) BBR Physical Hardening

28

-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

Avg 7-day Max, oC

1-day Min, oC

(PRESSURE AGING VESSEL) (PRESSURE AGING VESSEL) PAVPAV

ORIGINALORIGINAL

> 1.00 kPa

< 5000 kPa

> 2.20 kPa

S < 300 MPa m > 0.300

Report Value

> 1.00 %

20 Hours, 2.07 MPa

10 7 4 25 22 19 16 13 10 7 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 31

(Dynamic Shear Rheometer) DSR G* sin

( Bending Beam Rheometer) BBR “S” Stiffness & “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 -6 -12 -18 -24 0 -6 -12 -18 -24

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

PPerformance erformance GGradesrades

(Dynamic Shear Rheometer) DSR G*/sin

(Dynamic Shear Rheometer) DSR G*/sin

< 3 Pa.s @ 135 oC

> 230 oC

CEC

PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82

(Rotational Viscosity) RV

90 90 100 100 100 (110) 100 (110) 110 (110)

(Flash Point) FP

46 52 58 64 70 76 82

46 52 58 64 70 76 82

(ROLLING THIN FILM OVEN) (ROLLING THIN FILM OVEN) RTFO RTFO Mass Loss Mass Loss << 1.00 % 1.00 %

(Direct Tension) DT

(Bending Beam Rheometer) BBR Physical Hardening

28

-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

Avg 7-day Max, oC

1-day Min, oC

(PRESSURE AGING VESSEL) (PRESSURE AGING VESSEL) PAVPAV

ORIGINALORIGINAL

< 5000 kPa

> 2.20 kPa

S < 300 MPa m > 0.300

Report Value

> 1.00 %

20 Hours, 2.07 MPa

10 7 4 25 22 19 16 13 10 7 25 22 19 16 13 31 28 25 22 19 16 34 31 28 25 22 19 37 34 31 28 25 40 37 34 31

(Dynamic Shear Rheometer) DSR G* sin

( Bending Beam Rheometer) BBR “S” Stiffness & “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 -6 -12 -18 -24 0 -6 -12 -18 -24

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

How the PG Spec WorksHow the PG Spec Works

(Dynamic Shear Rheometer) DSR G*/sin

(Dynamic Shear Rheometer) DSR G*/sin

< 3 Pa.s @ 135 oC

> 230 oC

CEC

58 64

Test TemperatureTest TemperatureChangesChanges

Spec RequirementSpec RequirementRemains ConstantRemains Constant

> 1.00 kPa

PG 58-22PG 58-22

PG 52-28

PG 64-10PG 64-10PG 58-16PG 58-16

> Many agencies have established zones

PG Binder Selection

Summary of How to Use PG Specification

• Determine – 7-day max pavement temperatures– 1-day minimum pavement temperature

• Use specification tables to select test temperatures

• Determine asphalt cement properties and compare to specification limits

Asphalt Concrete Mix Design

History

Hot Mix Asphalt Concrete (HMA)

Mix Designs• Objective:

– Develop an economical blend of aggregates and asphalt that meet design requirements

• Historical mix design methods– Marshall – Hveem

• New – Superpave gyratory

Requirements in Common

• Sufficient asphalt to ensure a durable pavement

• Sufficient stability under traffic loads

• Sufficient air voids– Upper limit to prevent excessive environmental

damage– Lower limit to allow room for initial densification due

to traffic

• Sufficient workability

MARSHALL MIX

DESIGN

Marshall Mix Design• Developed by Bruce Marshall for the

Mississippi Highway Department in the late 30’s

• WES began to study it in 1943 for WWII– Evaluated compaction effort

• No. of blows, foot design, etc.• Decided on 10 lb.. Hammer, 50 blows/side• 4% voids after traffic

• Initial criteria were established and upgraded for increased tire pressures and loads

Marshall Mix Design

• Select and test aggregate• Select and test asphalt cement

– Establish mixing and compaction temperatures

• Develop trial blends– Heat and mix asphalt cement and

aggregates– Compact specimen (100 mm diameter)

Marshall Design CriteriaLight Traffic Medium Traffic Heavy Traffic ESAL < 104 10 4 < ESAL< 10 ESAL > 106

Compaction 35 50 75

Stability N (lb.) 3336 (750) 5338 (1200) 8006 (1800)

Flow, 0.25 mm (0.1 in) 8 to 18 8 to 16 8 to 14

Air Voids, % 3 to 5 3 to 5 3 to 5

Voids in Mineral Agg. (VMA) Varies with aggregate size

Asphalt Concrete Mix Design

Superpave

Superpave Volumetric Mix Design

• Goals– Compaction method which simulates field – Accommodates large size aggregates– Measure of compactibility– Able to use in field labs– Address durability issues

• Film thickness• Environmental

reactionframe

rotatingbase

loadingram

control and dataacquisition panel

mold

heightmeasurement

tilt bar

Key Components of Gyratory Compactor

Compaction

Compaction• Gyratory compactor

– Axial and shearing action– 150 mm diameter molds

• Aggregate size up to 37.5 mm• Height measurement during compaction

– Allows densification during compaction to be evaluated

1.25o

Ram pressure600 kPa

% G% Gmmmm

Log GyrationsLog Gyrations

1010 100100 10001000

NNiniini

NNdesdes

NNmaxmax

Three Points on SGC Curve

SGC Critical Point Comparison%Gmm= Gmb / Gmm

Gmb = Bulk Mix Specific Gravity from compaction at N cycles

Gmm = Max. Theoretical Specific Gravity

Compare to allowable values at:

NINI : %Gmm < 89%

NDES: %Gmm < 96%

NMAX: %Gmm < 98%

Design Compaction

• Ndes based on– average design high air

temp– traffic level

• Log Nmax = 1.10 Log Ndes • Log Nini = 0.45 Log Ndes

% Gmm

Log Gyrations10 100 1000

Nini

Ndes

Nmax

Superpave Testing

• Specimen heights• Mixture volumetrics

– Air voids– Voids in mineral aggregate (VMA)– Voids filled with asphalt (VFA)– Mixture density characteristics

• Dust proportion• Moisture sensitivity

Superpave Mix Design

• Determine mix properties at NDesign and compare to criteria

– Air voids 4% (or 96% Gmm)

– VMA See table

– VFA See table

– %Gmm at Nini < 89%

– %Gmmat Nmax < 98%

– Dust proportion 0.6 to 1.2

• VMA requirements:– Nominal max agg size Min. VMA

» 9.5 mm 15

» 12.5 mm 14

» 19 mm 13

» 35 mm 12

» 37.5 mm 11

Superpave Mix Design

• VFA requirements:– Traffic (millions of ESALs) Range of VFA

Superpave Mix Design

< 0.3 70 to 801 to 3 65 to 78> 3.0 65 to 75