Balanced HMAC Designs

Dale Rand, P.E.

TxDOT Construction Division

Flexible Pavements Branch

IHEEP

Conference

San Antonio, Tx.

September 29, 2009

BackgroundStability and durability are arguably the two most important factors related to HMA performanceThe goal is to have a mix that is both resistant to rutting (stability) and resistant to cracking (durability)Over the past 10 years, rutting has diminished significantly due to the use of polymers and the Hamburg Wheel Test (HWT) Reflective cracking is arguably the most common distress associated with flexible pavements in Texas No state’s currently evaluate HMA mixtures for cracking resistance at the mixture design stageGenerally speaking “we test for rutting resistance with the HWT and hope for cracking resistance”

Background (continued)

The Overlay Tester appears to be a good predictor of reflective crackingThe overlay tester has revealed that most TxDOT mixes are relatively susceptible to crackingThere is a lot of potential for using the Overlay Tester to improve the way we design our mixesTxDOT is currently working with TTI on project 0-5123 to develop HMA mixes that are both stable (rut resistant) and durable (crack resistant)

Project 0-5123:Advanced overlay design system incorporating both rutting and

reflection cracking requirements

Feb. 27, 2006, Austin, TexasFujie Zhou, Tom Scullion, and Sheng Hu

Texas Transportation Institute

Lab testing:performance evaluation

Hamburg Wheel Tracking Device Overlay Tester

Loading Configuration

Sample - 6’’ length, 3’’ width, 1.5’’ height

Loading - Continuously triangular displacement, 5 sec loading & 5 sec unloading

Standard Test ConditionsOpening displacement - 0.025 in.Room temperature - 77 ± 3 F

Definition of failure93% Load Reduction Visible crack on surface

Fixed plate

0.08 in

Aluminum plates

150 mm (6 in)

Test Sample

Movable Plate

Ram direction

1.5 in

Displacement (in)

Time (sec)10 20

0.025

Statewide Evaluation of Good/Bad reflection cracking projects

Crack Stops

Latex Modified Asphalt Binder

US 84 Abilene (6 mo old)

Inplace RecyclingUS 175 Dallas

10 year old section

Field Validation Studies

1) Does the test rank materials correctly ?

2) What are acceptable criteria ?

Overlay Tester Results

0

200

400

600

800

HIPR C76-22 DAC5 + L D64-22 L CM64-22CR

reps

- fa

ilure

300

700

252

520

IH-10 Type C (PG76-22L), 4.4%AC

Hamburg Test@50C

00.5

11.5

22.5

33.5

0 5000 10000 15000 20000 25000

No. of Passes

Rut

Dep

th (m

m)

I-10

Properties Result Target

Cracking(overlay tester cycles to failure)

2 >200

Rutting(APA rutting after 8000 cycles)

2.6 mm <6mm

RuttingHamburg(Hamburg cycles to 0.5 inch rut)

>20K >20K

Rut resistance mix (4 in thick) placed on IH 10 in 2002 heavy traffic

Reflection cracking in 2004

Current Completion Dates

• Rutting testing Jan. 2004• Fatigue testing (100-mm) Mar. 2006• Fatigue testing (150-mm) Dec. 2007

Two FHWA ALFs with 12 Pavement Lanes Constructed in

the Summer and Fall of 2002

As-Built Pavement Lanes

CR-AZ----70-22

1

PG70-22Control

2

AirBlown

3

SBSLG

4

CR-TB

5

TP

6

PG70-22

+Fibers

7

PG70-22

8

SBS64-40

9

AirBlown

10

SBSLG

11

TP

12

Lane 1

CR-AZ

300,000

Lane 2

Control

100,000

Lane 3

Air Blown

100,000

Lane 4

SBS LG

300,000

Lane 5

CR-TB

100,000

Lane 6

TP

200,000

Percentage of Area Cracked vs. ALF Wheel Load Passes

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 50000 100000 150000 200000 250000 300000 350000

Number of ALF Passes

Perc

enta

ge o

f Are

a C

rack

ed, %

L2S3 (Control)L3S3 (Air Blown)L5S3 (CR-TB)L6S3 (Terpolymer)L4S3 (SBS LG)L1S2 (CR-AZ)

L4S3L6S3

L5S3

L2S3

L1S2

L3S3

OT vs. FHWA-ALF Fatigue Test Results

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 50000 100000 150000 200000 250000 300000 350000

Number of ALF Passes

Perc

enta

ge o

f Are

a C

rack

ed, %

L2S3 (Control)L3S3 (Air Blown)L5S3 (CR-TB)L6S3 (Terpolymer)L4S3 (SBS LG)L1S2 (CR-AZ)

18901120

890

60

Did not crack

80

Influence of Mix Type

0

200

400

600

800

1000

1200

1400

Num

ber o

f Cyc

les

Median 47 317 374 1200Count 417 76 39 58Minimum 1 3 24 83Maximum 1200 1200 1200 1200Average 172 507 548 978

Dense Graded Performance Designed

Stone-Matrix Asphalt RBL/CAM

Frequency DistributionDense-Graded Hot Mix Asphalt

0

30

60

90

120

150

180

210

0 40 80 120

160

200

240

280

320

360

400

440

480

520

560

600

640

680

720

760

800

840

880

920

960

1000

1040

1080

1120

1160

1200

Number of Cycles

Freq

uenc

y

Influence of Mix TypeDense-Graded Hot Mix Asphalt

0

100

200

300

400

500

600

700

Num

ber o

f Cyc

les

Median 13 10 61 78 438Count 15 108 119 162 13Minimum 2 1 2 2 43Maximum 98 1200 752 1200 1200Average 28 97 127 232 621

Type A Type B Type C Type D Type F

Frequency DistributionDense-Graded Type C

0

5

10

15

20

25

30

35

40

45

50

0 40 80 120

160

200

240

280

320

360

400

440

480

520

560

600

640

680

720

760

800

840

880

920

960

1000

1040

1080

1120

1160

1200

Number of Cycles

Freq

uenc

y

Lab testing: Performance evaluation-SMA Mixtures

Houston: SMA-C (¾”)---AC=6%HWTT: 4.9 mm @20,000 passesOT: 450 cycles

Dallas (IH635): SMA-D (½”)---AC=6%HWTT: 4.2 mm @20,000 passesOT: 410 cycles

Beaumont (US96): SMA-D (½”)---AC=6.3%HWTT: 7.2 mm @20,000 passesOT: >1500 cycles

Influence of Aggregate TypeAll mixtures

0

200

400

600

800

1000

1200

1400

Num

ber o

f Cyc

les

Median 53 90 262 271 344 1200Count 147 62 80 15 25 14Minimum 2 2 2 80 10 457Maximum 1200 1200 1200 1200 1200 1200Average 204 232 512 378 555 1030

Limestone Gravel Granite Rhyolite Sandstone Quartzite

Influence of Asphalt

0

100

200

300

400

500

600

Num

ber o

f Cyc

les

Median 84 96 55 80 344Count 119 156 69 172 21Minimum 2 1 2 2 14Maximum 1200 1200 1200 1200 1200Average 199 297 306 336 555

64-22 70-22 70-28 76-22 CRM

All mixtures

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Rutting check:

Hamburg wheel tracking test

Balanced HMA Mixture Design-1

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Performance check

Hamburg TestOverlay Tester

Design asphalt content

Current HMA Mixture Design

Design asphalt content

Rut resistance mixture

pass

fail

Balanced HMA mixture

pass

fail

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Rutting check:

Hamburg wheel tracking test

Balanced HMA Mixture Design-2

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Hamburg Test Overlay Test

“Design asphalt content (DAC)”

Current HMA Mixture Design

Design asphalt content Vary asphalt contents:

DAC, DAC+0.5%, DAC+1%

Rut resistance mixture

pass

fail

Performance Evaluation

Balanced HMA mixture

pass

fail

Methodology for Balancing Rutting and Cracking Requirements

Balancing Rutting and Cracking

0

2

4

6

8

10

12

14

16

4 4.5 5 5.5 6 6.5 Asphalt Content (%)

Rut

Dep

th (m

m)

0

100

200

300

400

500

600

700

800

Cra

ckin

g Li

fe (c

ycle

s)

RutCrack

Acceptable Rutting &Cracking

Acceptable Rutting Acceptable Cracking

Criteria

•Rutting: 12.5 mm

•Cracking: 300* cyclesCurrently used in Houston, originally based on field experience.

Lab testing: performance evaluation

Hamburg wheel tracking test: 12.5 mmPG64-22: Rut depth @10000 passesPG70-22: Rut depth @15000 passesPG76-22: Rut depth @20000 passes

Overlay tester: 300 cyclesCracking life: 93% load reduction of max. load at first cycle

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Rutting check:

Hamburg wheel tracking test

Balanced HMA Mixture Design-1

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Performance check

Hamburg TestOverlay Tester

Design asphalt content

Current HMA Mixture Design

Design asphalt content

Rut resistance mixture

pass

fail

Balanced HMA mixture

pass

fail

Lab testing: balanced HMA mixture design-1

Mixture type Aggregate Asphaltbinder

DesignAC (%)

VMA(%)

HWTT(mm)

OT(cycles)

AsphaltAbsorption(%)

TXI-limestone PG64-22 4.8 15.2 3.0 189 0.07

TXI-limestone PG76-22 4.7 15.2 5.0 200 0.14

TCS-limestone PG64-22 5.5 16.3 13.4 25 0.93

Type D

Sandstone PG76-22 5.4 16.0 4.6 580 0.16

Sandstone PG64-22 5.0 15.1 5.9 112 1.07

Sandstone PG70-22 5.1 15.3 2.4 35 1.37

Gravel PG76-22 5.5 16.4 3.0 105 0.30

Superpave-CNdesign=100

Quartzite PG76-22 5.4 16.3 3.0 230 0.63

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Rutting check:

Hamburg wheel tracking test

Balanced HMA Mixture Design-2

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Hamburg Test Overlay Test

“Design asphalt content (DAC)”

Current HMA Mixture Design

Design asphalt content Vary asphalt contents:

DAC, DAC+0.5%, DAC+1%

Rut resistance mixture

pass

fail

Performance Evaluation

Balanced HMA mixture

pass

fail

TXI-PG76-22

0

1

2

3

4

5

6

7

8

9

10

4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9

Asphalt Content (%)

Rut

Dep

th (m

m)

0

100

200

300

400

500

600

700

800

900

1000

Cra

ckin

g Li

fe (N

o. o

f Cyc

les)

HWTT

OT

Lab testing: Performance evaluation-Type D Mixtures

Balanced AC=5.3%

Lab testing: Performance evaluation-Type D Mixtures

TXI-PG64-22

0

5

10

15

20

25

4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9

Asphalt Content (%)

Rut D

epth

(mm

)

0

300

600

900

1200

1500

Crac

king

Life

(No.

of C

ycle

s)

HWTTOT

Balanced AC=5.1%

Sandstone PG76-22

0

2

4

6

8

10

5 5.5 6 6.5

Asphalt Content (%)

Rut D

epth

(mm

)

0

300

600

900

1200

1500

1800

2100

Crac

king

Life

(No.

of C

ycle

s)

HWTTOT

Lab testing: Performance evaluation-Type D Mixtures

Balanced AC=5.9%

Sandstone_L- PG64-22

0

2

4

6

8

10

12

14

4.8 5 5.2 5.4 5.6 5.8 6 6.2

Asphalt Content (%)

Rut D

epth

(mm

)

0

50

100

150

200

250

300

350

400

450

Crac

king

Life

(No.

of C

ycle

s)

HWTTOT

Lab testing: Performance evaluation-Superpave C Mixtures

Balanced AC=5.8%

Lab testing: Performance evaluation-Superpave C Mixtures

Sandstone_NL- PG70-22

0

0.5

1

1.5

2

2.5

3

3.5

4

5 5.2 5.4 5.6 5.8 6 6.2

Asphalt Content (%)

Rut

Dep

th (m

m)

0

50

100

150

200

250

300

350

400

450

Crac

king

Life

(No.

of C

ycle

s)

HWTTOT

No balance: either redesign or increase asphalt content again.

Quartzite MD L-PG64-22

0

1

2

3

4

5

6

5.2 5.4 5.6 5.8 6 6.2 6.4 6.6

Asphalt Content (%)

Rut D

epth

(mm

)

0

150

300

450

600

750

Crac

king

Life

(No.

of C

ycle

s)

HWTTOT

Lab testing: Performance evaluation-Superpave C Mixtures

Balanced AC=6.0%

Balanced HMA Mixture Design

Asphalt Aggregate

Gradation, Ndesign

Volumetric design

Hamburg Test Overlay Test

“Design asphalt content (DAC)”

Vary asphalt contents:DAC, DAC+0.5%, DAC+1%

Performance Evaluation

Balanced HMA mixture

pass

fail

Summary & ConclusionsMixes such as SMA and CAM balance stability & durability very wellFor dense graded mixes, the current design procedure results in mixes that are stable but not very durableA “balanced” mix design procedure can be used to improve dense graded mixes This approach shows promise but is not ready for full implementation yet