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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

100

100 90

72

65

48

36

22

15

9

4

100

99 89

72

65

48

36

22

15

9

4



100

0.075 .3 2.36 4.75 9.5 12.5 19.0

Percent Passing

control point

restr icted zone

max density line

max

size

nom

max

size

Sieve Size (mm) Raised to 0.45 Power



Superpave Aggregate Gradation

100

0

.075 .3 2.36 12.5 19.0

Percent Passing

Design Aggregate Structure

Sieve Size (mm) Raised to 0.45 Power



Superpave Mix Size

DesignationsSuperpave Nom Max Size Max Size

Designation (mm) (mm)

37.5 mm 37.5 50

25 mm 25 37.5

19 mm 19 25

12.5 mm 12.5 19

9.5 mm 9.5 12.5



Gradat ions

* 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 MoreCrushed 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/--85/80

95/90

100/100

100/100

--/--

--/--

50/--60/--

80/75

95/90

100/100

First number denotes % with one or more fractured faces

Second 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-productof 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

Penetration 40 - 50 200 - 300

Flash Point, C 450+ 350+

Ductility, cm 100+ 100+

Solubility, % 99.0+ 99.0+

Retained Pen., % 55+ 37+

Ductility, cm NA 100+



Viscosity Graded Specifications



Types of Viscosity Tubes

Asphalt Institute TubeZietfuchs Cross-Arm

Tube



Table 1 Example

AC 2.5 AC 40

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

Visc, 135C 80+ 300+

Penetration 200+ 20+

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

Ductility 100+ 10+



40

50

60

7085

100

120

150

200300

Penetration Grades

AC 40

AC 20

AC 10

AC 5

AC 2.5

100

50

10

5

V i s c o s i t y ,

6 0 C ( 1

4 0 F )



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 L iquid



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

s = t E

Hooke’s Law

h i



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

Concentr ic Cyl inder Rheometers

t Rq =Mi

p Ri2 L

g = W R

Ro - Ri



Dynamic Shear Rheometer (DSR)

• Parallel PlateShear flow varies with

gap height and radius

Non-homogeneous flow

gR =

R Q

h

tR = 2 M

p R3

Sh t T Bi d A i



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

D Le

D L

Load

Stress = s = P / A

Strainef

sf

S



Summary

FatigueCrackingRutting

RTFOShort Term AgingNo aging

Construction

[RV][DSR]

Low Temp

Cracking

[BBR]

[DTT]

PAV

Long Term Aging



Superpave BinderPurchase 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

Performance Grades



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) RTFO Mass Loss < 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) PAV

ORIGINAL

> 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

Performance Grades

(Dynamic Shear Rheometer) DSR G*/sin


< 3 Pa.s @ 135 oC

> 230 oC

CEC

How the PG Spec Works



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) RTFO Mass Loss < 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) PAV

ORIGINAL

< 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 Works



< 3 Pa.s @ 135 oC

> 230 oC

CEC

58 64

Test Temperature

Changes

Spec Requirement

Remains Constant

> 1.00 kPa



PG 58-22

PG 52-28

PG 64-10PG 58-16

> Many agencies haveestablished 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 testtemperatures

•Determine asphalt cement propertiesand compare to specification limits



Asphalt Concrete MixDesign

History

H Mi A h l C



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

MIXDESIGN



Marshall Mix Design

• Developed by Bruce Marshall for theMississippi Highway Department in the late30’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 andloads



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 andaggregates

– Compact specimen (100 mm diameter)



Marshall Design Criteria

Light 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

DesignSuperpave

Superpave Volumetric Mix



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

C i



reaction

frame

rotating

base

loadingram

control and data

acquisition panel

mold

height

measurement

tilt bar

Key Components of Gyratory Compactor

Compaction

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 beevaluated

1.25o

Ram pressure

600 kPa



% Gmm

Log Gyrations

10 100 1000

Nini

Ndes

Nmax

Three Poin ts 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 airtemp

– traffic level

• Log Nmax = 1.10 Log Ndes

• Log Nini

= 0.45 Log Ndes

% Gmm

Log Gyrations10 100 1000

Nini

Ndes

Nmax

S T i



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

S i i



Superpave Mix Design

• Determine mix properties at NDesign and compare tocriteria

– 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

S Mi D i



Superpave Mix Design

Gyratory Compaction Criteria

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