DISSIPATED ENERGY STUDY
OF FATIGUE IN AIRPORT
PAVEMENTS
PHD Candidate: Shihui Shen
Advisor: Prof. S. H. Carpenter
FAA Project Review
Nov. 9, 2005
INTRODUCTION
Dissipated Energy (RDEC)– Unifying Concept
Load Modes, Gear Configurations, Load Pulse
Duration, Load Levels
Fatigue Endurance Limit
Thick airport pavements
Thickness below which no damage occurs
Healing is the Recovery from Damage
Impacts total loads to failure
Damage Concept is Amenable to a Thickness
Design Procedure
DISSIPATED ENERGY CONCEPT REVIEW
STRESS
Initial Load Cycle
Second Load Cycle
STRAIN
Different Dissipated Energy
Between First And Second Load Cycle
Ratio of Dissipated Energy Change (RDEC)
Dissipated Envergy Vs. Loading cycles
IDOT Mix 6-7-1A 1000 Microstrain
0.016
0.014
0.012
DER
Ratio of Dissipated Energy Change, Log
RDEC REVIEW
I
0.01
0.008
0.006
Plateau Value
0.004
50% Stiffness
0.002
0
10
510
II
1,010
1,510
2,010
2,510
Number of Load Cycles
Plateau Value
Load Repetitions, Log
III
3,010
3,510
4,010
DE
PV CALCULATION
IDOT03 mix 3N704B
DE vs. Loading cycles 800microstrain
1.4
1.2
1
0.8
Slope f = - 0.1638
0.6
y = 3.4255x-0.1638
0.4
R2 = 0.9512
0.2
Nf50
0
0
1000
2000
3000
4000
5000
Loading cycles
UNIQUE PV-Nf RELATIONSHIP
plateau value (PV), log
1.E-02
1.E-03
y = 0.4428x -1.1102
R2 = 0.996
Normal strain/damage
1.E-04
1.E-05
1.E-06
1.E-07
Data Points: 546
Mixture types: 98
1.E-08
Loading modes: 2
Frequency: 0.5-10 Hz
1.E-09
sec.
1.E+02Rest period:
1.E+03 0- 0.4
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
loading cycles @ 50% stiffness reduction (Nf50), log
UNIQUE PV-Nf RELATIONSHIP
Unique energy level at which no fatigue damage exists
Plateau Value, log
1.E+04
1.E-01
Normal PV
Low PV
Fatigue Endurance Limit
1.E-06
1.E-11
PVL=6.74E-9
1.E-16
1.E-21
1.E-26
1.E-31
1.E-36
1.E+00
Nf=1.10E+7
1.E+04
1.E+08
1.E+12
1.E+16
1.E+20
1.E+24
1.E+28
1.E+32
loading cycles @ 50% stiffness reduction, log
APPLY RDEC IN HEALING STUDY
Researchers suggest healing can be better
understood by carefully considering energy
behavior and viscoelastic properties of an HMA
PV, energy based, can provide a unique
indication of the impact of a load pulse followed
by a rest period
Research hypothesis:
Rest periods promote healing effect and make it
quantifiable through lab test
Healing reduces the damage
Reduced damage produces a lower PV, which
translates into a longer fatigue life
FATIGUE-HEALING TEST
Four Point Bending Beam (SHRP T321-03)
Mode of Loading: Constant Strain @ 500 microstrain
Wave Shape: Haversine
Load Pulse Width: 100ms (10 Hz)
Rest Period: 0~9 second
Temperature: 20℃
FATIGUE-HEALING TEST
ε
A short rest
period after each
load pulse ~ to
simulate rest
between loads;
Haversine Load Pulse Sequence
No rest period, 0.1 second
load pulse
1 second
3 second
9
second
Loading time, second
An intermediate
strain level, 500
microstrain, is
used ~ relatively
high damage
level and shorter
tests.
The whole nature of energy change during a test is
still continuous, thus the dissipated energy and the PV
can be obtained for each test to perform the
RDEC analysis,
PV, log
PV-Nf FOR HEALING TEST
With 9 second rest period, the
Unique
relationship
fatigue PV-Nf
life is extended
5 times
neat binder
forforhealing
test mix and 10
times for polymer binder mix
1.E-04
21010(RP=0 sec.)-neat
1.E-05
33070 (RP=0 sec.)-polymer
y = 0.4429x-1.1102
1.E-06
114700
neat
polymer
1.E-07
1.E+04
neat binder mix
395950
1.E+05
polymer binder mix
1.E+06
Nf 5 0 , log
HEALING TEST
~ PV vs. (RP+1) FOR NEAT BINDER
HEALING TEST
~ PV vs. (RP+1) FOR POLYMER BINDER
PV, log
1.E-04
1000 microstrain
1.E-05
800 microstrain
500
mic
ro
s tra
in
1.E-06
1.E-07
500microstrain
y = 4.302E-06x-1.347
R2 = 0.7957
300 microstrain
1.E-08 200 microstrain
PVL
1.E-09
1
6
10
121
399 540
100
1000
(RP+1), (second), log
HEALING AND FEL
Healing study using RDEC approach helps to
understand the existence of FEL
PV-IDE AT NORMAL STRAIN (DAMAGE)
Plateau Value, log
At normal strain/damage condition and continuous loading, the
PV is found has good correlation with Initial Dissipated Energy
(IDE).
Under normal condition, load effect is
dominant, while healing is negligible
1.E-02
1.E-03
1.E-04
1.E-05
IDE, initial energy capacity
1.E-06
PV, total effect of fatigue
behavior
2.416E+00
y = fatigue
1.137E-05x
(material
resistance and load
2
effect)
R = 7.934E-01
1.E-07
1.E-08
1.E-09
0
0.5
1
1.5
2
2.5
3
Initial Dissipated Energy
PV-IDE FOR WHOLE LOADING RANGE
IDE, log
PV,
combined
effect,
no longer be
At1.E+01
low
damagehealing
level
when
PVcan
reaches
With
decreased
damage
level,
the
roleIDE,
of healing
represented
by
initial
loading
status,
threshold
PV
,
the
PV-IDE
curve
start
to
Low
Damage
L significant: healing startsflatten,
becomes
more
starting
from
the endurance
limit, PVL to
leading
to
extended
fatigue
life
dominate the performance comparing to damage
PVL
1.E+00
Normal Damage
1.E-01
y = 38.221x 0.3288
R2 = 0.7947
1.E-02
1.E-03
1.E-41
1.E-36
1.E-31
1.E-26
High
Normal damage
1.E-21
1.E-16
Nf
low damage
1.E-11
1.E-06
1.E-01 1.E+04
PV, log
Low
PAVEMENT DESIGN
Requires Relation to Standard Parameters
Load Level
Speed
Repetition Interval
Mix Variables
Asphalt Grade
PRELIMINARY
PV PREDICTION MODEL
Based on 19 IDOT mix
Including neat binder and polymer binder mix; various gradations;
2 air voids levels;
Rich bottom binder mixes are included
5
PV  4.598  10 ε
5.329
S
3.750
AV
2.676
 2.681
(
) C
AV  Vb
Where:
ε: controlled tensile strain
S : the flexural stiffness of HMA mix, MPa
AV : the air voids of mixture
Vb : the asphalt content by volume
C : the aggregate gradation parameter, C=(PNMS-PPCS)/P#200
PNMS : the percent of agg. passing nominal maximum size sieve
PPCS : the percent of agg. passing primary control sieve (PCS = NMS * 0.22)
P#200 : the percent of agg. passing #200 sieve
PV PREDICTION
PV predicted
1.E-02
1.E-03
R2 = 0.902
1.E-04
1.E-05
Line of equality
1.E-06
1.E-07
1.E-08
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
PV tested
BINDER FATIGUE TEST - DSR
Gemini 200 Dynamic Shear Rheometer
DSR Testing Geometry Schematic
G*
DE
TYPICAL BINDER DE-Nf CURVE
2.00E+04
1.E+08
G*
8.E+07
I
II
50% complex
modulus
reduction
6.E+07
1.60E+04
DE
1.20E+04
8.00E+03
4.E+07
III
2.E+07
4.00E+03
0.E+00
0.00E+00
0
50000
100000
150000
200000
250000
Loading Cycles
50 Pen Bitumen with 65% limestone, 1% Controlled strain
TYPICAL BINDER RDCE CURVE
0.0006
0.0005
RDEC
0.0004
0.0003
Failure Point
Plateau
Plateau Stage
Stage, II
0.0002
III
0.0001
0
0
50000
100000
150000
200000
250000
300000
loading cycles
50Pen Pure Bitumen, 15% Controlled Strain
COMPARE PV-Nf CURVES FOR
BINDER AND MIXTURE
1.E-03
Plateau Value (PV)
Binder (Mastic):
y = 1.7663x-0.9598
1.E-04
2
R = 0.9819
1.E-05
1.E-06
Mix: y = 0.5787x-1.101
R2 = 0.988
1.E-07
1000
10000
100000
1000000
10000000
Nf @ 50% stiffness reduction
Binder: con-strain
Binder: con-stress
Mixture
CONCLUSIONS
RDEC provides a successful way to study HMA,
fatigue, healing, and its role on fatigue
endurance limit
Healing does exist and its effect on fatigue
behavior can be observed through lab
accelerated fatigue-healing test:
CONCLUSIONS (cont.)
The occurrence of healing is highly related to
the level of damage; healing effect can be
dominant under low load damage condition.
Healing under the low damage condition is a
key to understand the existence of a fatigue
endurance limit (FEL).
Healing potential exceeds damage potential for any
one load cycle.
RECOMMENDATIONS
PV can be predicted based on material properties,
which can be integrated into pavement structural
design.
Combine this with PVL, the energy based FEL established
before, provides a simple way to estimate the strain level
that can reach “unlimited” fatigue life.
The fatigue-healing test can be extended to different
temperature, load levels, and more diversity of mix
types.
Asphalt binders’ energy recovery rates and healing
capacity can be studied using the RDEC approach. It
should provide an insight of the healing kinetics
derived from the existing fatigue-healing study for
mixture.
THANK YOU !!
QUESTIONS ?