1

4.75 mm Superpave MixRefinement Study

Southeast Asphalt User Producer GroupNashville, TN

December 13, 2005

Participating States

Baseline Mixes

4.75 mm Pooled Fund Study

Objectives

• Validate or refine AASHTO mix design criteria.

• Provide guidelines for applications. • Provide guidelines for production and

construction.

AASHTO Specifications for 4.75 mm Mixes

Background• Survey of Usage• Current Criteria• Supporting Research• Issues to Evaluate

Survey on the Use of 4.75mm HMA Mixtures

Survey of states21 State DOT responded

Alaska, Arizona, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Kansas, Missouri, Montana, Nevada, New Jersey, North Dakota, North Carolina, South Carolina, South Dakota, Tennessee, Vermont, Washington, and West Virginia

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Respondents w/ 4.75mm designation

Respondents w/ fine mix designation

Respondents w/ no fine mix designation

Response Summary• Typically three aggregate components in these

mixtures:– Rock or chip 0-30%– Screenings (manufactured sand) 0-50%– Natural sand 0-30%

• Most common asphalt grade – PG 64-22 5-9%

• Additives– Lime, cement, and anti-strip 0-1%

Response Summary• Spread rates:

– Average ≈ 80lb/sqy– Range 35-125 lb/sq.yd.

• Mix design methods:– Marshall – Superpave gyratory, Ndes = 50

• In-place density requirements– Most states responded no in-place density requirement– Four states responded yes, Range 85-94% of Gmm

• Advantages– initial cost is less than competing products– better appearance– better performance

Response Summary• What are the primary uses of this type of mixture?

– surface mix for low volume roads – leveling or scratch course– thin overlay for pavement maintenance

• Disadvantages– adds no strength to the pavement structure – susceptible to rutting

• Average production– The average annual production ≈ 420,000 tons/year per state.– Range (1.7million – 15,000) tons/year

• Is production quantity expected to change over the next two years?

– Most states believe this quantity will remain steady or increase.

12.5 mm Nominal Sieve Size

19.0

12.59.5

4.75

2.36

1.18

0.60

0.30

0.15

0.07

5

0

20

40

60

80

100

120

Sieve Size (mm)

Perc

ent P

assi

ng

S-III

S-I

9.5 Norcross

Typical HMA composition for Low-Volume Roads

• Marshall mix design• fine-graded blend • higher asphalt content• Natural Sand contents 10 to 30%• RAP contents 15 to 30%• unmodified grade of asphalt

Non DOT mixtures• City and County Overlays, New Commercial

& Residential Developments.• We have a good level of comfort with these

mixtures.

3

Superpave Criteria for Mixtures Used on Roads

with < 300,000 ESALs/20 years

• %Gmm @ N6 <= 91.5• %Gmm @ N50 = 96.0• %Gmm @ N75 <= 98.0• VFA: 70-80%, DP 0.6 to 1.2• Min. 55% one crushed face, 40% SE• No requirement on FAA or F&E• Are these criteria appropriate?

Evaluation of the Superpave Gyratory Compactor for

Low Volume Roads

• Kansas study of field produced mix and roadway cores

• Lowest Superpave Traffic Category SGC compactive effort is greater than 50 blow Marshall

• The major problem meeting the Superpave mix requirements is meeting the minimum VMA

Cross & Lee, Report No. KS-00-2, June 2000

Example Marshall Mixes Used on Low Volume Roads

Missouri 1/2” surface 43Georgia Type G 38Florida S-III 27Kansas 37 to 49

Number of Equivalent Gyrations

Superpave Gyratory Compactive Effort

Majority of Interstate system…

Many two-lane, multilane, & partially or completely controlled access roadways. Medium to heavy traffic city streets, state routes, US highways, and some rural Interstates

Collector roads, medium trafficked city streets & county roads

Local roads with very light traffic volumes

Typical Applications

205

160

115

75

Nmax

125

100

75

50

Ndes

9

8

7

6

Nini

>30

3 to 30*

0.3 to <3

<0.3

Design ESALs(millions)

AASHTO Specification (M 323)Gradation

12

60-

100100

Max.

6

30-

9095

100

Min.

0.075

1.182.364.759.5

12.5

Sieve

4.75 mm Nominal Sieve Size

9.50

12.5

0

4.75

2.36

1.180.60

0.30

0.15

0.07

5

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Perc

ent P

assi

ng

AASHTO Specification (M 323) Fine Aggregate Angularity andSand Equivalent

Depth from Surface

504545100>3045

45

40

40

Sand Equivalent

404040-

≥ 100 mm

454540-

≤ 100 mm

100757550

Ndes

10 to 303 to <100.3 to <3

<0.3

Design ESALs(millions)

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AASHTO Specifications (M323)4.75 mm Volumetric Requirements• Air Voids: 4.0%• VMA: 16.0% min.• VFA:

<0.3 M ESALs: 70-80%0.3 to 3.0 M ESALs: 68-78%>3.0 M ESALs 75-78%

• Dust Proportion: 0.9 – 2.0• %Gmm @ Nini: same as other NMAS

4.75 mm Mix SpecificationsSupporting Research at NCAT• 2 aggregate types: granite & limestone

– Fine Agg. Angularity• granite: 49• limestone: 46

• 3 blends: coarse, med., fine• 3 dust contents: 6, 9, 12%• 1 binder: PG 67-22• 2 design air void contents: 4 & 6%• 1 compactive effort: 75 gyrations

4.75 mm Mix SpecificationsSupporting Research - Findings• All study mixes had % Gmm @ Nini ≤ 88.9%

(passed strictest criteria)• Only 1 of 18 mixes designed at 6% air voids had

VFA > 68% (i.e. only one met VFA)• Designing to 6% air voids typically reduced

asphalt contents by about 0.7%

4.75 mm Superpave MixRefinement Study

Current Research Plan

Possible Criteria for Evaluation

• Gradation Control Points• Design Air Void Content• Minimum VMA• VFA Range• Dust Proportion

Volumetric CriteriaRationale for Limits• Target Air Voids of 4.0% is the same as specified for all

other Superpave mixtures.• Minimum VMA of 16.0% for 4.75 mm mixes follows the

progression of 1.0% higher VMA for every NMAS decrease.

• Minimum VMA is considered a criteria to ensure good durability. For a fixed air void content, minimum VMA is the same as requiring a minimum effective asphalt volume percentage.

• The minimum VMA of 16.0% is somewhat supported by correlation with dust/asphalt ratio (DP). A maximum DP of 2.2 corresponded to a minimum VMA of 16.0%.

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Volumetric CriteriaRationale for Limits• For 4.0% air voids and 16% minimum

VMA…• the minimum VFA calculates to be 75%. So any VFA

limit below 75% is pointless.• Maximum VFA of 78% is the same as a maximum VMA

of 18.1%;• maximum VFA of 80% is the same as a maximum VMA

of 20%.

Generalized Optimum Asphalt Contentfor a Given Aggregate & Gradation

Film Thickness

Rutti

ng

Cracking

Asphalt Content

Generalized Optimum Asphalt Contentfor a Given Aggregate & Gradation

Asphalt Volume

Cost

Cracking

Asphalt Content

Phase 1Design Mixes

13 Aggregate Blends4 & 6% Air Voids50 & 75 Gyrations

Fractional Experimental Design

Obtain Field ProducedBaseline Mixes

Rutting Testusing MVT

Permeability TestASTM PS 129

Stripping TestAASHTO T283

Ageing Testusing FE Ratio

Start

Draft Phase 1 Report

Analysis

Refine Criteria for 4.75 mm Mixtures

Performance Testing

33Baseline Mix 4

32Baseline Mix 3 (MD)

31Baseline Mix 2 (GA)

30Baseline Mix 1 (MS)

2928Blend Adjustment 4

2726Blend Adjustment 3

2524Blend Adjustment 2

2322Blend Adjustment 1

212019New Hampshire

1817Connecticut

1615Tennessee

1413Alabama

121110Minnesota

98Missouri

76Virginia

54Wisconsin

321Florida

Aggregate Blend

6464Air Voids

7550Ndesign Gyrations Maryland 4.75 mm Superpave 75 gyrations, 3.5% voids, PG64-22

1.62.00.9DP

13.2Vbe

16.316.0VMA

6.5Pb

8.1

19

31436196

JMF

12

-

-60

-100

Max

6

-

-30

-90

Min

0.075

0.30

0.601.182.364.75

Sieve

4.75 mm Nominal Sieve Size

9.50

12.5

0

4.75

2.36

1.180.60

0.30

0.15

0.07

5

0

1020

3040

50

6070

8090

100

Sieve Size (mm)

Perc

ent P

assi

ng

MD

154045

Percent

Sand89’s10’sMaterial

6

Georgia 4.75 mm Superpave 50 gyrations, 6.6% voids, PG67-22

1.52.00.9DP

12.8Vbe

16.716.0VMA

6.0Pb

8.7

22

-455879

QC

12

-

-60

-100

Max

6

-

-30

-90

Min

0.075

0.30

0.601.182.364.75

Sieve

4.75 mm Nominal Sieve Size

9.50

12.5

0

4.75

2.36

1.18

0.60

0.30

0.15

0.07

50102030405060708090

100

Sieve Size (mm)

Per

cent

Pas

sing

GA

0.98

2566

Percent

Hydrated LimeGranite W10’sRAPGranite 810’sMaterial

Mississippi 4.75 mm Superpave 50 gyrations, 4.0% voids, PG76-22

11.7Vbe

1.6 2.00.9DP

17.716.0VMA

6.0Va

6.0Pb

11.3

22

35507598

QC

12

-

-60

-100

Max

6

-

-30

-90

Min

0.075

0.30

0.601.182.364.75

Sieve

4.75 mm Nominal Sieve Size

0.07

50.

15

0.30

0.60

1.18

2.36

4.75

12.5

0

9.50

010

2030

4050

6070

8090

100

Sieve Size (mm)

Per

cent

Pas

sing

1111969

Percent

Hydrated LimeNatural SandCrushed GravelLimestoneMaterial

Performance TestingMix Verification Tester• Smaller version

of the Asphalt Pavement Analyzer

• Ndes samples• 100 lbs.• 100 psi• 64oC• 8000 cycles

Performance TestingPermeability Testing• ASTM PS 129• Lab specimens

compacted in SGC to 1 inch height, 9±0.5% air voids.

Performance TestingMoisture Susceptibility Testing• AASHTO T 283

– 9±0.5% air voids.

• No antistrip additive used

Performance TestingFracture Energy Ratio

• Indirect Tensile Strength– 20 C– Measure horizontal and

vertical strain– Calculate fracture energy

as area beneath the stress-strain plot

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4.75mm

0.60

1.18

2.36

4.75 9.50

12.5

0

0.07

50.

15

0.30

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Perc

ent P

assi

ng

Florida

Minnesota

New Hampshire

Tennessee

Virginia

4.75mm

0.30

0.15

0.07

5

12.5

0

9.50

4.75

2.36

1.180.60

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Perc

ent P

assi

ng

Alabama

Connecticut

Missouri

Asphalt Content

0

2

4

6

8

10

12

14

AL 4.0%Va

AL 6.0% V

a

TN 50G4.0

%Va

TN 75G4.0

%Va

MO 4.0%Va

MO 6.0%Va

VA 50G4.0

%Va

VA 75G4.0

%Va

FL 50G

4%Va

FL 75G

4%Va

FL 75G

6%Va

CT 50G 4%

Va

CT 50G 6%

Va

MN 50G 4%

Va

MN 75G 4%

Va

MN 75G 6%

Va

NH 50G 4%

Va

NH 75G 4%

Va

NH 75G 6%

Va

%A

C

Film Thickness

0

2

4

6

8

10

12

14

AL 4.0%Va

AL 6.0% V

a

TN 50G4.0

%Va

TN 75G4.0

%Va

MO 4.0%Va

MO 6.0%Va

VA 50G4.0

%Va

VA 75G4.0

%Va

FL 50G

4%Va

FL 75G

4%Va

FL 75G

6%Va

CT 50G 4%

Va

CT 50G 6%

Va

MN 50G 4%

Va

MN 75G 4%

Va

MN 75G 6%

Va

NH 50G 4%

Va

NH 75G 4%

Va

NH 75G 6%

Va

Film

Thi

ckne

ss (M

icro

ns)

VMA

0

5

10

15

20

25

30

AL 4.0%Va

AL 6.0% V

a

TN 50G4.0

%Va

TN 75G4.0

%Va

MO 4.0%Va

MO 6.0%Va

VA 50G4.0

%Va

VA 75G4.0

%Va

FL 50G

4%Va

FL 75G

4%Va

FL 75G

6%Va

CT 50G 4%

Va

CT 50G 6%

Va

MN 50G 4%

Va

MN 75G 4%

Va

MN 75G 6%

Va

NH 50G 4%

Va

NH 75G 4%

Va

NH 75G 6%

Va

% V

MA

VFA

55

60

65

70

75

80

85

90

AL 4.0%

Va

AL 6.0%

Va

TN 50G4.0

%Va

TN 75G4.0

%Va

MO 4.0%

Va

MO 6.0%

Va

VA 50G4.0

%Va

VA 75G4.0

%Va

FL 50G

4%Va

FL 75G

4%Va

FL 75G

6%Va

CT 50G 4%

Va

CT 50G 6%

Va

MN 50G 4%

Va

MN 75G 4%

Va

MN 75G 6%

Va

NH 50G 4%

Va

NH 75G 4%

Va

NH 75G 6%

Va

%VF

A

VFA Range for < 0.3 Million ESALs

8

4.75mm

0.60

1.18

2.36

4.75 9.50

12.5

0

0.07

50.

15

0.30

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Perc

ent P

assi

ng

Florida

Minnesota

New Hampshire

Tennessee

Virginia

Change in %AC and VMA for 4%Va (50 -75 Gyrations)

∆%AC ∆%AC

∆%AC

∆%AC

∆%AC

∆ VMA

∆ VMA

∆ VMA

∆ VMA

∆ VMA

0.0

0.5

1.0

1.5

2.0

TN VA FL MN NH

% C

hang

e

4.75mm

0.30

0.15

0.07

5

12.5

0

9.50

4.75

2.36

1.180.60

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Perc

ent P

assi

ng

Alabama

Connecticut

Missouri

Change in Opt. Pb and VMA, 4% to 6% Air Voids

-0.5

0

0.5

1

1.5

2

AL MO FL CT MN NH

Cha

nge

(%)

Opt. PbVMA

%AC vrs VMA

y = 1.3471x + 8.5531R2 = 0.567

10

12

14

16

18

20

22

24

26

5 6 7 8 9 10 11 12 13

% AC in Mix

VMA 50G4%Va

50G6%Va75G4%Va75G6%Va

P 200 vrs Optimum %AC

y = -0.4652x + 12.741R2 = 0.4074

4

5

6

7

8

9

10

11

12

13

5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

% Passing # 200

optim

um %

AC

50G4%Va

50G6%Va

75G4%Va

75G6%Va

NH

FL

CT VA

MO

AL

Mn

TN

9

VMA vrs P 200

y = -1.0008x + 29.207R2 = 0.5892

10

12

14

16

18

20

22

24

26

5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

Percent Passing #200

VMA

50G4%Va

50G6%Va

75G4%Va

75G6%Va

NH FL

CT

VA

MOAL

MN

TN

MVT Rut Depths

0.0

5.0

10.0

15.0

20.0

25.0

30.0

AL 4

.0%

VaAL

6.0

% V

aTN

50G

4.0%

VaTN

75G

4.0%

VaM

O 4

.0%

VaM

O 6

.0%

VaVA

50G

4.0%

VaVA

75G

4.0%

VaFL

50G

4%

VaFL

75G

4%

VaFL

75G

6%

VaCT

50G

4%

VaCT

50G

6%

VaM

N 50

G 4

%Va

MN

75G

4%

VaNH

50G

4%

VaNH

75G

6%

VaM

issi

ssip

piM

aryl

and

Geo

rgia

MV

T R

ut D

epth

(mm

)

Did not complete 8000 cycles

٭

+

+ Modified Binder

+

Optimum AC% vrs Rut depth

y = 0.8818x + 8.1424R2 = 0.2823

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

% AC

MVT

Rut

Dep

th (m

m)

50G4%Va

50G6%Va

75G4%Va

75G6%Va

Permeability

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

180.00

AL 4.0%Va

AL 6.0% Va

TN 50G4.0%Va

TN 75G4.0%Va

MO 4.0%Va

MO 6.0%Va

VA 50G4.0%Va

VA 75G4.0%Va

FL 50G 4%

Va

FL 75G 4%

Va

FL 75G 6%

Va

Mississ

ippi

Marylan

d

Georgia

k *1

0-5

Film Thickness vrs TSR

y = 0.0645x + 0.1626R2 = 0.424

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

4 5 6 7 8 9 10 11 12 13

Film Thickness (Microns)

TSR

Phase 2Four Field Projects

Design Mixes as Needed

Rutting Testusing MVT

Permeability TestASTM PS 129

In-PlaceDensity

Start

Draft Final Report

Analysis

Validate Criteria for 4.75 mm Mixtures

Mobile Laboratory on Site• Document Production & Construction•Test AC Content, Gradation, Gmb, Gmm, Field Permeability, Dynamic Friction, CT Meter• Obtain Cores

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Thank You