1

Dr. Haleh AzariAASHTO Advanced Pavement Research Laboratory (AAPRL)

Permanent Deformation Characterization Using Incremental Repeated Load Permanent Deformation Test (iRLPD) NEAUPG Steering Committee MeetingMarch 2012

RLPD Test Protocol Background•A flow number test protocol was

developed during NCHRP 9-19, which was later, refined during NCHRP 9-29 (AASHTO TP 79)

•Several parameters were left undetermined and not standardized

•FHWA ETG has created a task force to▫standardize the variables of the test

such as test temperature, stress level, confinement

▫Establish criteria that can reliably discriminate between various mixtures

Selection of Promising RLPD ProtocolsDifferent agencies have offered different approaches in

standardizing the flow number testSix promising approaches were selected by the ETG Flow

Number Task Force for further evaluationSelected methods are proposed by AAT (NCHRP 9-33),

NCAT, Van Quintus (NCHRP 9-30A), MTE, AAPRL, UNRNine different mixtures representing a wide range of

traffic and climate were provided by the state DOTs and industries for the evaluation

AAPRL is testing the nine materials according to five of the proposed methods

UNR is testing the materials according to UNR proposed method

Mix.#

Mixture Traffic Binder Grade Mixture NMAS, mm Supplier

LTPPBind High

Temperature, 50%

Reliability, °C

1 WI (E3) <3 PG 58-28 12.5 Erv Dukatz – MTE Const. 49.1

2 NC PG 64-22 9.5Todd Whittington

NC DOT58.6

3 TX PG 70-22 9.5 Dale Rand - TXDOT 62.7

4 WI (E10) <10 PG 64-28 12.5 Erv Dukatz –Mathy Const. 46.7

5 IN PG 64-22 9.5 Huber 53.3

6 FL PG 67-22 9.5 Jim Musselman - FLDOT 63.0

7 NJ >30 PG 76-22 12.5Tom Bennert

NJDOT50.2

8 AL (NCAT track sec. PG 67-22 9.5 Randy West 59.5

9 CA PG 70-10 19.0 Adam Hand 62.5

List of Materials and Suppliers

5

Description of Test Protocols• NCHRP9-30A, MTE, NCAT, NCHRP9-33 approaches

are according to conventional flow no. test:▫Test continuous until either material goes to flow,

10,000 cycles is completed, or 50,000 microstrain of total permanent deformation is reached

▫Tests are conducted on 3 replicates at one temperature and one stress level

▫MTE method is conducted on 9 replicates at 1 temperature and three stress levels (each three replicates tested at one stress level)

• AAPRL method (iRLPD) uses 3 replicates; each specimen is tested incrementally at different stress levels

Methods NCHRP 9-33 NCAT NCHRP 9-30A MTE AAPRL (iRLPD)

Confinement, kPa (psi) 0 69 (10 ) 69 (10) 69 (10) 69 (10)

Deviatoric Stress, kPa (psi) 600 (87) 482.6 (70) 482.6 (70) 400, 600, 800

(58, 87, 116)400, 600, 800

(58, 87, 116)

Mix. # Material Temperature, °C*

1 WI (E3) 49.1 43.1 29.9 49.1 49.1

2 NC 58.6 52.6 35.5 58.6 58.6

3 TX 62.7 56.7 36.0 62.7 62.7

4 WI (E10) 46.7 40.7 29.0 46.7 46.7

5 IN 53.3 47.3 33.0 53.3 53.3

6 FL 63.0 57.0 34.3 63.0 63.0

7 NJ 50.2 44.2 32.0 50.2 50.2

8 AL 59.5 53.5 35.5 59.5 59.5

9 CA 62.5 56.5 35.5 62.5 62.5

Stresses and Temperatures

*Temperatures are selected based on 50 % reliability high pavement temperature from LTPPBind at depth of 20 mm

7

Description of Incremental RLPD (iRLPD) Test• iRLPD test is conducted at one temperature (LTPPBind

High Temperature, 50% Reliability) in four increments▫1000 cycles at 100 kPa (to ensure primary stage of

deformation is completed and mixture is in the secondary stage of deformation)

▫500 cycles at 400 kPa▫500 cycles at 600 kPa▫500 cycles at 800 kPa▫Total of 2500 cycles takes 43 min.

• iRLPD method uses strain rate at the end of each increment (minimum strain rate=MSR) as the measure of resistance of a mixture to permanent deformation

RLPD Parameters

Strain rate consistent

Primary

Secondary

TertiaryFlow Number

Minimum Strain rate

• Graphs of strain and strain rate versus number of cycles• Consist of three portions : Primary, secondary, and tertiary

No. of Cycles

Output of Conventional Flow No. Test

9

Example of iRLPD Test, Increasing Temperature

0

20

40

60

80

100

120

140

160

180

200

0 200 400 600 800 1000 1200 1400

Stra

in ra

te (m

icro

stra

in p

er cy

cle)

Cycle

Permanent Strain per Cycle

T=50

T=55

T=60

T=65

T=70

10

Example of iRLPD Test, Increasing Stress

0

50

100

150

200

250

300

350

400

1 24 47 70 93 116

139

162

185 7 30 53 76 99 21 44 67 90 12 35 58 81 3 26 49 72 95 17 40 63 86 109

132

155

178

Stra

in R

ate,

Micr

ostr

ain/

cycle

Cycle

Permanent Strain Per Cycle

11

MSR vs. Temperature and Stress• For combinations of

stress and temperature the same MSR values were observed

• It was found out that effect of temperature and stress are interchangeable

• Parameter TP, which is the product of temperature and stress is then used to explain MSR

12

Create MSR Master Curve•Plot MSR as a Function of Temperature *

Pressure (TP) MSR master curve•MSR master curve defines the response of a

mixture at any temperature and stress

13

MSR Threshold ValuesCriteria for selecting stress and temperature was based on achieving MSR values in the range of 1 to 30 microstrain/cycle: A combination of temperature and stress that

results in MSR of less than 1 microstrain/cycle indicates that the mixture has the potential to stand much higher temperature and stresses

A combination of temperature and stress that results in MSR value higher than 30 microstrain/cycle indicates that the mixture is reaching its limit in resisting flow

14

MSR Threshold Values▫A combination of temperature and stress that

results in MSR of less than 1 microstrain/cycle indicates that the mixture has the potential to stand much higher temperature and stresses

▫A combination of temperature and stress that results in MSR value higher than 30 microstrain/cycle indicates that the mixture is reaching its limit in resisting flow

▫Selected the stress levels to obtain MSR values greater than 1 μstrain/cycle and smaller than 30 μstrain/cycle

MSR Curves for WI (E3), WI(E10), NC, IN

MSR Master Curves for AL,TX, FL, CA

17

MSR Values from iRLPD and Flow No. TestsWI(E10), WI(E3), FL, CA

18

MSR Values from iRLPD and Flow No.IN, NC, TX,AL

19

Ranking of Mixtures based on MSR Master curve

20

Field Applications, Estimate Rut Depth•Use traffic and pavement temperature

data to determine TP (temperature * pressure)

•Obtain MSR from the master curve for the determined TP

•Multiply MSR (strain /cycle) by traffic ESAL to obtain total strain

•Multiply strain by pavement thickness to estimate rut depth

21

Example , Estimate Rut depthMSR= a eb*TP

Material 1 Material 2 Material 3 Material 4 Material 5

a 0.0979 0.0428 0.0994 0.1965 0.2181

b 0.1169 0.1178 0.0946 0.0834 0.0584High Pavement

Temperature 46.7 58.6 62.7 53.3 63

Pressure (MPa) 0.6 0.6 0.6 0.6 0.6

Axles, millions 10 3 3 10 10

MSR, μstrain/cycle 2.6 2.7 3.5 2.8 2.0

micron/axle 0.194 0.202 0.262 0.212 0.149

Axles 1st Year 27778 8333 8333 27778 27778

Rut 1st yr, mm 5.4 1.7 2.2 5.9 4.1

Rut 20 years, mm 10.8 3.4 4.4 11.8 8.3

Thick 75Years 20

Months 4 (ratio 0.33)Hours 8 (ratio 0.33)

Wander 0.5Aging Ratio 0.5

22

Field Applications, Determine Traffic Level from MSR

▫Use traffic and temperature data to determine TP (temperature * pressure)

▫Obtain MSR from the master curve for the determined TP

▫Multiply MSR (strain /cycle) by layer thickness to obtain permanent deformation/cycle

▫Divide maximum allowable rut depth by deformation/cycle to obtain the allowable no. of passes (ESALS)

23

Example, Determine Traffic Level from MSR

Material 1 Material 2 Material 3 Material 4

MSR 35.22 10.57 3.52 2.11

Terminal Rut 12.7 12.7 12.7 12.7

micron/axle 2.64 0.79 0.26 0.16

Rut 1st yr 6.35 6.35 6.35 6.35

Axles 1st Year 2,404 8,013 24,038 40,064

With Wander 4,808 16,026 48,077 80,128

Allowable Axles, 20 yrs 865,385 2,884,615 8,653,846 14,423,077

Thick 75Years 20

Months 4 (ratio 0.33)Hours 8 (ratio 0.33)

Wander 0.5Aging Ratio 0.5

24

Field Applications,Determine Acceptable MSR Value for A Design Traffic Level

▫Divide allowable rut depth by Design ESAL to calculate allowable permanent deformation per axel

▫Divide allowable permanent deformation by design thickness to obtain strain per axel or MSR

25

Determine Acceptable MSR Values for Ranges of Design Traffic Levels

Axles 1,000,000 3,000,000 10,000,000 30,000,000 50,000,000

Terminal Rut 12.5 12.5 12.5 12.5 12.5

Rut 1st yr 6.25 6.25 6.25 6.25 6.25

Axles 5,556 16,667 55,556 166,667 277,778

Axles w/ wander 2,778 8,333 27,778 83,333 138,889

micron/axle 2.25 0.75 0.23 0.08 0.05

MSR 30.00 10.00 3.00 1.00 0.60

Thick 75Years 20

Months 4 (ratio 0.33)Hours 8 (ratio 0.33)

Wander 0.5Aging Ratio 0.5

26

Table 1-Ranges of MSR values for various Traffic levels

Axels MSR, strain/cycle

<3,000,000 >10 & <30

3,000,000 to 10,000,000 >3 & <10

10,000,000 to 30,000,000 >1 & < 3

>50,000,000 <1

27

Laboratory Application: Ranking of Mixtures

Two ways of ranking/ grading mixtures in laboratory (for a fixed stress and pavement temperature and no consideration of design ESALS):▫For a particular TP value, e.g., 36 (0.6 MPa

* 60°C), the lower the MSR, the more resistance to rutting

▫For a particular MSR value, e.g., 25, the higher the TP, the more resistance to rutting

28

Laboratory Application: Mixture Selection•If for a determined TP, MSR value of a

mixture is less than the values provided in Table 1, the mixture meets the criteria for high temperature performance

•Determine TP using:▫50 % reliability high pavement

temperature from LTPPBind at depth of 20 mm

▫Average tire pressure of 600 kPa (90 psi)

29

Selection of Mixtures, Example• High pavement temperature

for Region 1 from LTPPBind= 62.7C

• Use stress of 600 kPa (0.6 Mpa)

• TP= 62.7 * 0.6= 37.6 MPa°C

• MSR from master curve= 12.5 (> 10 & <30)

• Mixture is acceptable for design traffic of less 3 million (see Table 1)

30

Summary, Comparison of iRLPD with Conventional Flow Test •MSR values from conventional flow number

test coincided with the MSR master curve produced from iRLPD test

• iRLPD test using 3 replicates provides the same MSR values as conventional flow number test using 9 replicates

•While conventional flow number test produces one MSR value, iRLPD test produces a sweep of MSR values for creating MSR master curve

31

•Using incremental RLPD, testing time is reduced by a factor of 4

•Test takes less than 45 min for each replicate•Complete high temperature characterization of

a mixture in 2 hr. and 15 min (3 replicates)•Minimum strain rate values have much smaller

variability than flow no. or total permanent strain (average CV of 7 % vs. 13%)

•MSR values from MSR master curve are directly applied to the field without use of transfer functions

Summary, Comparison Cont.

32

Summary of Differences between Conventional Flow No. and iRLPD Tests

Test Parameters

Incremental RLPD Conventional Flow No. Test

Test property Minimum Strain Rate (MSR) Number of Cycles to Flow, minimum strain rate (MSR), total permanent strain

No. of cycles 1000, 500, 500, 500 variable

Test temperature

50 % reliability high pavement temperature from LTPPBind at depth of 20 mm

Not defined

Stress level Four stress levels: 100, 400, 600, 800 kPa (15, 58, 87, 116 psi)

Not defined

Test duration Less than 45 minutes Variable- few minutes to 3 hrs depending on temperature, stress level, and resistance of the material

Test output produces a sweep of MSR values for creating MSR master curve

produces one MSR, one flow number, one total permanent strain

Test Variability MSR has small variability Both flow no and total permanent strain are highly variable

Field application

Test results can be directly applied to the field without transfer function

Flow number has not been directly applied to the field

Laboratory application

Test results are applied for mixture selection and mixture grading

No mixture selection/mixture ranking methodology exists based on flow no. test results

33

Summary, Laboratory Application of MSR Master Curve

• Mixture selection:▫For a particular TP (pavement temperature * average

pressure) and design traffic level, a mixture with MSR values within the ranges provided in Table 1 is acceptable in terms of high temperature performance

• Ranking/grading of various mixtures:▫For a fixed TP, a mixture with lower MSR is more

resistant to permanent deformation▫For a fixed MSR, a mixture with higher TP is more

resistant to permanent deformation

34

Summary, Field Application of MSR Master Curve

•MSR (strain per cycle) from MSR master curve can be used to estimate :▫Allowable traffic ESALs ▫Total rut depth

•The design traffic ESAL can be used to calculate acceptable MSR (Table 1)

35

Recommendations: Evaluate the applicability of Incremental

RLPD for WMA, and high percentage RAP, and combination of both

Investigate Incremental RLPD test method for different confinement stresses

Thank you. Questions?