1
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)
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 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
List of Materials and Suppliers
Mix.
Mixture
Traffic
Binder Grade
Mixture NMAS, mm
1
WI (E3)
<3
PG 58-28
12.5
2
NC
PG 64-22
9.5
3
TX
PG 70-22
9.5
Dale Rand - TXDOT
62.7
4
WI (E10)
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
7
NJ
PG 76-22
12.5
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
#
<10
>30
Supplier
LTPPBind
High
Temperature,
50%
Reliability, °C
Erv Dukatz – MTE
Const.
Todd Whittington
NC DOT
Jim Musselman FLDOT
Tom Bennert
NJDOT
49.1
58.6
63.0
50.2
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
Stresses and Temperatures
Methods
NCHRP 9-33
NCAT
NCHRP 9-30A
MTE
AAPRL (iRLPD)
Confinement, kPa
(psi)
0
69 (10 )
69 (10)
69 (10)
69 (10)
600 (87)
482.6 (70)
482.6 (70)
400, 600, 800
(58, 87, 116)
400, 600, 800
(58, 87, 116)
Deviatoric Stress, kPa
(psi)
Temperature, °C*
Mix. #
Material
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
*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
Output of Conventional Flow No. Test
RLPD Parameters
Primary
Tertiary
Flow
Number
Minimum
Strain rate
Secondary
Strain rate
consistent
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
Permanent Strain per Cycle
200
180
Strain rate (micro strain per cycle)
160
140
120
T=50
100
T=55
80
T=60
T=65
60
T=70
40
20
0
0
200
400
600
800
Cycle
1000
1200
1400
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
Strain Rate, Microstrain/cycle
10
Example of iRLPD Test, Increasing Stress
Permanent Strain Per Cycle
400
350
300
250
200
150
100
50
0
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 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
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. 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
Years
Months
Hours
Wander
Aging Ratio
75
20
4 (ratio 0.33)
8 (ratio 0.33)
0.5
0.5
Material 1
Material 2
Material 3
Material 4
Material 5
a
0.0979
0.0428
0.0994
0.1965
0.2181
b
High Pavement
Temperature
0.1169
0.1178
0.0946
0.0834
0.0584
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
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
Years
Months
Hours
Wander
Aging Ratio
75
20
4 (ratio 0.33)
8 (ratio 0.33)
0.5
0.5
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
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
Years
Months
Hours
Wander
Aging Ratio
75
20
4 (ratio 0.33)
8 (ratio 0.33)
0.5
0.5
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
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
>50,000,000
>1 & < 3
<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
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
Not defined
Test duration
Less than 45 minutes
Test output
produces a sweep of MSR values for creating MSR master curve
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
(15, 58, 87, 116 psi)
Variable- few minutes to 3 hrs depending on
temperature, stress level, and resistance of the
material
produces one MSR, one flow number, one total
permanent strain
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?