S52_Research Update Testing and Analysis of LWT and SCB Properties of Asphaltic Concrete Mixtures_LTC2013

7/29/2019 S52_Research Update Testing and Analysis of LWT and SCB Properties of Asphaltic Concrete Mixtures_LTC2013

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Testing and Analysis of LWT and SCB

Properties of Asphaltic Concrete MixturesSamuel Cooper III

Louisiana Transportation ConferenceFebruary 18 - 20, 2013

Baton Rouge, Louisiana


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Acknowledgements

LTRC Asphalt Research GroupJeremy Icenogle, Patrick Frazier, Willie Gueho, Md.Kabir, Bill King


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Introduction

LADOTDs current QA/QC practice relies upon: Gradation

AC Content

VFA, VMA, % Air Voids

Moisture Susceptibility Test (Modified Lottman), and

Roadway Parameters: Density, Smoothness

But these volumetric properties are not adequate to

reflect the pavement performance in the field.Must develop methods to evaluate pavementperformance indicators


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Introduction

New laboratory tests are required to evaluate the as-built pavementqualities.The test will screen materials prone to rutting, cracking andalternative moisture damage indicators.

Create a Balanced Mixture Design


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Introduction

What is a balanced mixture design?Process to ensure adequate resistance to rutting and cracking distress

Two laboratory tests are proposed:Rutting: Loaded Wheel Tracking (LWT) TestCracking: Semi-Circular Bend (SCB) Test

VolumetricParameters

CrackingPerformance

HighTemperaturePerformance

00.20.40.60.8

11.21.41.6

0 5 10 15 20

C r a c

k i n g

R e s

i s t a n c e

Rutting Resistance


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Research Objective

To implement the Loaded Wheel Tracking (LWT) test as ameasure of mixture rutting resistance.To evaluate a simplified Semi-Circular Bend (SCB) testsas an end result parameter for intermediate temperaturecracking resistance.

Rutting

Cracking


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Laboratory Experiment: LWT Test

Performance IndicatorResistance to Rutting and MoistureSensitivityTest ProtocolAASHTO T324

Temperature50CLoading

Wheel Diameter: 203.5 mm (8 inch)Wheel Width: 47mm (1.85 inch)

Fixed Load: 703 N (158 lbs)Rolling Speed: 1.1 km/hr

Passing Rate: 52 passes/min


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Laboratory Experiment: LWT Test

Performance IndicatorsResistance to Rutting andMoisture SensitivityRutting Indicator:

Plot Rut Depth vs Number of PassesReport Rut Depth at

1000, 5000, 7500, 10000, 15000, and 20000 PassesMoisture Sensitivity Indicator

Determine Stripping Inflection PointThe point where slope of the line begins to steepen


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Laboratory Experiment: SCB Test

Performance IndicatorResistance to Crack PropagationTest ProtocolMohammad et al. [2004]Temperature

25CLoading0.5 mm/min vertical deformation

The Critical Value of FractureResistance,

da

dU

b J c )

1(

b = sample thickness,a = notch depth,U = strain energy to failure

a

2s

P

notch

P

2

P

2


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SCB Sample Preparation

150mm x 57mm


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Laboratory Experiment: Conventional SCB Test

Servo Hydraulic Test SystemEnvironmental ChamberExpensiveComplicated

Load

Deformation


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Laboratory Experiment: Modified SCB Test

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.5 1 1.5 2 2.5

F o r c e

( K n

)

Length(mm)

Original DataMax of Data set

Fitted Curve

Peak of Curve

da

dU

b J

c )1

(

Load

Deformation


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.5 1 1.5 2 2.5

F o r c e

( K n

)

Length(mm)

Original Data

Max of Data set

Fitted Curve

Peak of Curve

da

dU

b J

c )

1

(

*Temperature is controlledusing an externalenvironmental chamber


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Analysis: Loaded Wheel Tester


CrackiPerforma


Level 1

Level 2

90%!


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Preliminary Analysis: Semi-Circular Bend


CrackiPerforma


42% 58% 72% 0%


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Preliminary Analysis: Balanced Design


CrackiPerforma


Level 1Level 250%


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Preliminary Analysis: Balanced Design


CrackiPerforma


Level 150%


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How do we get there?

A system to conduct mechanical property test to determine theanticipated performance of asphalt mixtures is neededLTRC has been using LWT and SCB test as forensics investigative toolsand performance indicators.Incorporate tests into state specification compliance evaluation.

Develop a simplified SCB test procedure.Adapt SCB test to a commonly used load frames

Must control TEMPERATURE!


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How do we get there?Nominal Max., Size Agg. 0.5 inch(12.5 mm)

0.75 inch(19 mm)

1.0 inch(25 mm)

1.5 inch(37.5mm)

S

Type of Mix IncidentalPaving Wearing Course Wearing

Course Binder Course Binder Course BaseCourse ATB

BaseCourse We

Level A 1 2 2 1 2 1 2 1 1 1

Asphalt Binder Table 502-2, (3% minimum for Asphalt Treated base (ATB), 6% min for SMA)

Friction Rating Table 502-3

RAP, Max. % of Mix 20 15 15 15 20 20 20 20 30 30 30

Compacted Mix Volumetrics 4

VMA, Min. % 13.0 13.0 13.0 12.0 12.0 12.0 11.0 11.0 11.0 n/a 10.5 1Air Voids, % (2.5-4.5);; (no limit for ATB)

VFA, % (69-80); no limit for ATB

Ninitial 90% max. (Gyrations) 7 7 7 7 7 7 7 7 7 n/a 7

Ndesign 96.51 % (Gyrations) 65 65 75 75 65 75 65 75 65 30 65

Nmax 98 % max. (Gyrations) 100 100 115 115 100 115 100 115 100 n/a 100 1LWT, max. rut-design, mm

@ # passes,@ 50 C 10 @

10,00010 @

20,0006 @

20,0006 @

20,00010 @

20,0006 @

20,00010 @

20,0006 @

20,00012 @

20,00010

@10,00012 @

20,0006

20

Dust/Effective AsphaltRatio, % 0.6 1.6

Lift Thickness, inch (mm) 2.0-(50-)

1.52.0(38-50)

1.52.0(38-50)

2.03.0(50-75)

2.54.0(65-100)

2.5+(65+)

3.0+(75+)

4.0+(100+)

1.5(38

H d g t th ?


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How do we get there?Nominal Max., Size Agg. 0.5 inch(12.5 mm)

0.75 inch(19 mm)

1.0 inch(25 mm)

1.5 inch(37.5mm)

S

Type of Mix IncidentalPaving Wearing Course Wearing

Course Binder Course Binder Course BaseCourse ATB

BaseCourse We

Level A 1 2 2 1 2 1 2 1 1 1

Asphalt Binder Table 502-2, (3% minimum for Asphalt Treated base (ATB), 6% min for SMA)

Friction Rating Table 502-3

RAP, Max. % of Mix 20 15 15 15 20 20 20 20 30 30 30

Compacted Mix Volumetrics 4

VMA, Min. % 13.0 13.0 13.0 12.0 12.0 12.0 11.0 11.0 11.0 n/a 10.5 1Air Voids, % (2.5-4.5);; (no limit for ATB)

VFA, % (69-80); no limit for ATB

Ninitial 90% max. (Gyrations) 7 7 7 7 7 7 7 7 7 n/a 7

Ndesign 96.51 % (Gyrations) 65 65 75 75 65 75 65 75 65 30 65

Nmax 98 % max. (Gyrations) 100 100 115 115 100 115 100 115 100 n/a 100 1LWT, max. rut-design, mm@ # passes,@ 50 C

10 @10,000

10 @20,000

6 @20,000

6 @20,000

10 @20,000

6 @20,000

10 @20,000

6 @20,000

12 @20,000

10@10,000

12 @20,000

620

Dust/Effective AsphaltRatio, % 0.6 1.6

Lift Thickness, inch (mm) 2.0-(50-) 1.52.0(38-50)

1.52.0(38-50)

2.03.0(50-75)

2.54.0(65-100)

2.5+(65+)

3.0+(75+)

4.0+(100+)

1.5(38


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Whats Next?

Continued evaluation of the SCB testValidate Jc criteria for mixture design

Communicate with other on-going research projects: 10-4B


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Whats Next?


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Thank You!

Documents

S52_Research Update Testing and Analysis of LWT and SCB Properties of Asphaltic Concrete Mixtures_LTC2013