1. Dr. Haleh Azari AASHTO Advanced Pavement Research Laboratory (AAPRL)
Permanent Deformation Characterization Using Incremental Repeated Load Permanent Deformation Test (iRLPD) NEAUPG Steering Committee Meeting March 2012
Dr. Haleh Azari
AASHTO Advanced Pavement Research Laboratory (AAPRL)

2. 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

3. Selection of Promising RLPD Protocols
Different agencies have offered different approaches in standardizing the flow number test
Six promising approaches were selected by the ETG Flow Number Task Force for further evaluation
Selected methods are proposed by AAT (NCHRP 9-33), NCAT, Van Quintus (NCHRP 9-30A), MTE, AAPRL, UNR
Nine 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

4. List of Materials and Suppliers
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
9.5
Todd Whittington
NC DOT
58.6 3 TX
PG 70-22
Dale Rand - TXDOT
62.7 4
WI (E10)
<10
PG 64-28
Erv Dukatz –Mathy Const.
46.7 5 IN
Huber
53.3 6 FL
PG 67-22
Jim Musselman - FLDOT
63.0 7 NJ
>30
PG 76-22
Tom Bennert
NJDOT
50.2 8
AL (NCAT track sec.
Randy West
59.5 9 CA
PG 70-10
19.0
Adam Hand
62.5

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

6. Stresses and Temperatures
Methods
NCHRP 9-33
NCAT
NCHRP 9-30A
MTE
AAPRL (iRLPD)
Confinement, kPa (psi)
69 (10 )
69 (10)
Deviatoric Stress, kPa (psi)
600 (87)
482.6 (70)
400, 600, 800
(58, 87, 116)
Mix. #
Material
Temperature, °C* 1
WI (E3)
49.1
43.1
29.9 2 NC
58.6
52.6
35.5 3 TX
62.7
56.7
36.0 4
WI (E10)
46.7
40.7
29.0 5 IN
53.3
47.3
33.0 6 FL
63.0
57.0
34.3 7 NJ
50.2
44.2
32.0 8 AL
59.5
53.5 9 CA
62.5
56.5
*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

8. RLPD Parameters Output of Conventional Flow No. Test Primary Tertiary
Strain rate consistent
Primary
Secondary
Tertiary
Flow Number
Minimum Strain rate
No. of Cycles
Graphs of strain and strain rate versus number of cycles
Consist of three portions : Primary, secondary, and tertiary

9. Example of iRLPD Test, Increasing Temperature

10. Example of iRLPD Test, Increasing Stress

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 Values
Criteria 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

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

16. MSR Master Curves for AL,TX, FL, CA

17. MSR Values from iRLPD and Flow No. Tests WI(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 depth MSR= a eb*TP
Thick 75
Years 20
Months
4 (ratio 0.33)
Hours
8 (ratio 0.33)
Wander
0.5
Aging Ratio
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
0.0584
High Pavement Temperature
46.7
58.6
62.7
53.3 63
Pressure (MPa)
0.6
Axles, millions 10 3
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
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

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
Thick 75
Years 20
Months
4 (ratio 0.33)
Hours
8 (ratio 0.33)
Wander
0.5
Aging Ratio
Material 1
Material 2
Material 3
Material 4
MSR
35.22
10.57
3.52
2.11
Terminal Rut
12.7
micron/axle
2.64
0.79
0.26
0.16
Rut 1st yr
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

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
Thick 75
Years 20
Months
4 (ratio 0.33)
Hours
8 (ratio 0.33)
Wander
0.5
Aging Ratio
Axles
1,000,000
3,000,000
10,000,000
30,000,000
50,000,000
Terminal Rut
12.5
Rut 1st yr
6.25
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

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= C
Use stress of 600 kPa (0.6 Mpa)
TP= 62.7 * 0.6= 37.6 MPa°C
MSR from master curve= (> 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. Summary, Comparison Cont.
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

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)
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

36. Thank you. Questions?