dr. haleh azari aashto advanced pavement research laboratory (aaprl)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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MSR Values from iRLPD and Flow No. TestsWI(E10), WI(E3), FL, CA
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MSR Values from iRLPD and Flow No.IN, NC, TX,AL
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Ranking of Mixtures based on MSR Master curve
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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
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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
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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)
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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
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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
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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
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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
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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
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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)
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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)
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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
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•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.
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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
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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
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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)
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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?
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