flexible pavement performance models in mepdg
TRANSCRIPT
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Flexible Pavement Performance Flexible Pavement Performance Models in MEPDGModels in MEPDG
Lev KhazanovichLev Khazanovich University of MinnesotaUniversity of Minnesota
Seminar on Pavement Design Systems and Pavement Performance Models
March 22 –
23, 2007 Reykjavik, Iceland
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AcknowledgementsAcknowledgementsGuide for Design of New and Rehabilitated Pavements Structures (NCHRP 1-37A and 1-40D).• Arizona State University (Prof. Matt Witczak, Mohamed El-Basyouny, & many others) • University of Maryland (Prof. C. Schwartz)• University of Illinois (Prof. W. Butler)• Several consultants around the world
Many slides in this presentation were developed under the above projects
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OutlineOutline
• Overview of the MEPDG• Load Related Cracking• Rutting Models• Thermal Cracking• Roughness models • Conclusions
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Design ProcessDesign ProcessFoundation
AnalysisClimate Materials
PropertiesTraffic Analysis
Trial Design
Pavement Response Model
Calibrated Damage-Distress/IRI Models
MeetPerformance
Criteria?
ModifyDesign
Inputs
AnalysisNo
Yes
Damage AccumulationOver time
OutputsIRIRutAlligator Ck
Long CkTemp Ck
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Damage Accumulation Damage Accumulation -- Incremental Incremental Damage ConceptDamage Concept
• Design life is divided into time increments of:– 1 month for rigid pavements– 15 days for flexible pavements
Design life
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Incremental Changes Over Pavement Life Incremental Changes Over Pavement Life
Time, years
CTB Modulus
Each load application
Granular Base Modulus
2 8640
Subgrade Modulus
Traffic
AC Modulus
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SubSub--Layering for Structural AnalysisLayering for Structural Analysis
Asphalt
Asphalt
Unbound
Unbound Compacted Natural
Bedrock
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• Cracking: εt at surface + bottom of all bound layers
• Rutting: εc at midthickness of all layers+ top of subgrade
Critical Response ValuesCritical Response Values
εtεc
εtεc
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Critical Response LocationsCritical Response Locations
x
y
8 in 8 in 8 inSx
Sy
CL
A1 A2 A3 A4 A5 A6 A7 A8 A9 A10
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10
4 in4 in
70 Evaluated Points in X-Y Plane
Top of the AC layer
Mid-dept
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ProblemProblem
•
In 2002 DG, layered elastic analysis is required for each month of the pavement design life. (260 design increments for 20 years design
life) •
Up to 20 layers in each model
•
70 evaluated points in each layer, up to 1400 points for each time increment
Single design iteration takes between Single design iteration takes between 30 to 60 min on a typical PC30 to 60 min on a typical PC
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MNLAYER vs. JULEA and BISARMNLAYER vs. JULEA and BISAR
0
5
10
15
20
25
30
80 160 240 320 400
No. of Evaluated Points
Tim
e (S
econ
d)
MNLAYERJULEABISAR
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Flexible Pavement PerformanceFlexible Pavement Performance
Fatigue Cracking
Thermal Cracking
Longitudinal Cracking
IRI
Rut Depth
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HMA Fatigue Modeling HMA Fatigue Modeling
•Bottom – Up Crack Propagation:
•Top – Down Crack Propagation
(Classical Fatigue Mechanism)
Temperature &Speed of Loading
E* Varies w/HMA Layers
High Shear Stress Contact Pressure
Aging @ Surface High E @ Surface
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Fatigue Damage Accumulates Over TimeFatigue Damage Accumulates Over Time
TIME
FATIGUECRACKING
DesignPeriod
Criteria
( )∑∑= = ⎥
⎥⎦
⎤
⎢⎢⎣
⎡=Δ
m
k
j
i ki
i
tN
nDI1 1 ε
SeasonLoadTop DownBottom Up
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Allowable Number of Load ApplicationsAllowable Number of Load Applications
( )( ) ( ) ( ) 332211
ffff kHMA
ktfHff ECCkN ββεβ=
Nf = Allowable number of axle load applications εt = Tensile strain at critical locations EHMA= Dynamic modulus of the HMA, psi kf1, kf2, kf3= Global field calibration parameters βf1, βf2, βf3= Local calibration constants; =1.0 by default
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Allowable Number of Load Applications (cont.)Allowable Number of Load Applications (cont.)
( )( ) ( ) ( ) 332211
ffff kHMA
ktfHff ECCkN ββεβ=
MC 10= ⎟⎟⎠
⎞⎜⎜⎝
⎛−
+= 69.084.4
bea
be
VVV
M
( )HMAH
H
e
C
49.302.111003602.0000398.0
1
−++
=
( )HMAH
H
e
C
8186.2676.15100.1201.0
1
−++
=
Bottom-up cracking
Top-down cracking
Vb e= Effective asphalt content by volume, percent Va = Percent air voids in the HMA mixture CH = Thickness correction term
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BottomBottom--Up Cracking Up Cracking
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛+
= + 601*
e16000
100))*log10(D**C'C*C'(C 2211bottomFCwhere:
FCbottom
= bottom-up fatigue cracking, percent lane area
D
= bottom-up fatigue damageC1
= 1.0'2
'1 2CC −= 12 =C
856.22 )1(*748.3940874.2' −+−−= hacC
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TopTop--Down CrackingDown Cracking
where:FCtop
= top-down fatigue cracking, ft/mileD
= top-down fatigue damage
( )( ) ⎟⎠⎞
⎜⎝⎛+
= − TopDILogCCTop eC
FC211
56.10 4
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Factors Affecting Fatigue Cracking in Factors Affecting Fatigue Cracking in Flexible Pavements Flexible Pavements
• HMA layer thickness.• HMA layer dynamic modulus.• Binder grade in the HMA
mixture.• Air voids in the asphalt layers.• Effective binder content in the
asphalt layers.
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Factors Affecting Fatigue Cracking in Factors Affecting Fatigue Cracking in Flexible Pavements Flexible Pavements
• Base thickness.• Subgrade modulus.• Traffic load configuration.• Traffic load, contact area and
tire pressure.• Traffic load repetitions.• Temperature and environmental
conditions.
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BottomBottom--Up Fatigue (Alligator) Up Fatigue (Alligator) Cracking CalibrationCracking Calibration
0
10
20
30
40
50
60
70
80
90
100
-4 -3 -2 -1 0 1 2 3
Log Damage (%)
Alli
gato
r Cra
ckin
g (%
of T
otal
Lan
e A
rea)
Se = 5.01%Se/Sy = 0.815N = 405R2 = 0.275
Log Damage (%)Alli
gato
r Cra
ckin
g (%
of
Tota
l Lan
e A
rea)
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TopTop--Down Fatigue (Longitudinal) Down Fatigue (Longitudinal) Cracking CalibrationCracking Calibration
0
1000
2000
3000
4000
5000
6000
7000
0 1000 2000 3000 4000 5000 6000 7000
Measured Cracking (ft / mile)
Pre
dict
ed C
rack
ing
(ft /
mile
)
R2 = 0.544Se = 582.8 ft /mileSe/Sy = 0.688N = 312
Measured Cracking (ft/mile)
Pred
icte
d C
rack
ing
(ft/m
ile)
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Effect of AC Thickness on CrackingEffect of AC Thickness on CrackingBottom Up Cracking - Alligator
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 36 72 108 144 180 216
Pavement Age (month)
Alli
gato
r Cra
ckin
g (%
)
50 mm
75 mm
100 mm
150 mm
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Permanent Deformation Accumulates Over TimePermanent Deformation Accumulates Over Time
TIME
RUTDEPTH
DesignPeriod
Criteria
( )( )[ ]∑∑∑= = =
=Δm
k
j
i
l
dikddP hRD
1 1 1,
εLoad Month Depth
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Accumulation of RuttingAccumulation of Rutting
∑=
×ε=N sub-layers
1i
iip hPD
Load, P
AC Layer
Base Layer
Subgrade
See Fig. A.
Fig. A
εp from pred. Eq.
Sub-layer
Similar for unbound layers
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Permanent Deformation in AC LayerPermanent Deformation in AC Layer
iβ
where:εp =Accumulated plastic strain at N repetitions of load (in/in)εr = Resilient strain of the asphalt material as a function of mix
properties, temperature and time rate of loading (in/in)N = Number of load repetitionsT = Temperature (deg F)ai
= Non-linear regression coefficients= field calibration factors
rrTNkh HMArzrHMAHMAp
HMAp 32 *5606.1*4791.035412.3)(1
)(
)( 10 ββεβε
−==Δ
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Permanent Deformation in Unbound Permanent Deformation in Unbound Layer (Layer (Tseng and Tseng and LyttonLytton
Model)Model)
Δp(Soil) = Permanent or plastic deformation for the layer/sublayer N = Number of axle load applications εo, β, and ρ = material properties obtained for the resilient strain εr εv = Average vertical resilient or elastic strain in the layer/sublayer hSoil = Thickness of the unbound layer/sublayer, inches ks1 = Global calibration coefficients; =1.673 for granular materials =1.35 for fine-grained materials βs1 = Local calibration constant
βρ
εε
εβ⎟⎠⎞
⎜⎝⎛−
⎟⎟⎠
⎞⎜⎜⎝
⎛=Δ N
r
osoilvsssoilp ehk 11)(
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Total Pavement Total Pavement -- RuttingRutting
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1 1.2
Average Measured Total Rutting (in)
Pre
dict
ed T
otal
Rut
ting
(in)
Predicted vs Measured Total Rutting Equality Line
R2 = 0.577N = 334Se = 0.107Se/Sy = 0.818
Average Measured Rutting
Ave
rage
Pre
dict
ed R
uttin
g
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Effect of AC Thickness of RuttingEffect of AC Thickness of RuttingPermanent Deformation: Rutting
0
2
4
6
8
10
12
14
16
0 36 72 108 144 180 216
Pavement Age (month)
Rut
ting
Dep
th (m
m)
Hac=50 mmHac=75 mmHac=100 mmHac=150 mm
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Thermal CrackingThermal Cracking
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HMAHMA--Thermal FractureThermal Fracture
• Uses SHRP Thermal Fracture Model– Recalibrated Using Approximately 30 Sections in
NCHRP Project 9-19
• Thermal Fatigue (cyclic) – Propagation of Cracks Through the Asphalt Layer
• Thermal Stresses– Very Low Temperature– Mixture Properties– Friction
• Mixture Fracture Properties
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Materials Characterization (IDT)Materials Characterization (IDT)
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Schematic of Crack Depth Fracture Schematic of Crack Depth Fracture Model Model
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Amount of Crack Propagation in aAmount of Crack Propagation in a Cooling CycleCooling Cycle
nKAC Δ=Δ
ΔC=
Change in the crack depth due to a cooling cycle.ΔK=
Change in the stress intensity factor
A, n = Fracture parameters for the asphalt mixture
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Stress Intensity Factor ApproximationStress Intensity Factor Approximation
)C1.99 + (0.45 = K 0.56oσ
K
= stress intensity factorσ= far-field stress from pavement response
model at depth of crack tipCo
= current crack length
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SchaperySchapery--MolenaarMolenaar--LyttonLytton
Model Model
⎟⎠⎞
⎜⎝⎛ +=
mn 118.0
( )n)**(E*2.52 - 4.389*m10 = A σβ log(
where:E=Mixture stiffness.σm =
Undamaged mixture tensile strength.
β=Calibration parameter.
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Effect of AC Thickness on Thermal Effect of AC Thickness on Thermal CrackingCracking
Thermal Cracking: Total Length Vs Time
0
50
100
150
200
250
300
0 36 72 108 144 180 216
Pavement Age (month)
Tota
l Len
gth
(m/k
m) Hac=50 mm
Hac=75 mmHac=100 mmHac=150 mm
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Pavement Smoothness Pavement Smoothness –– IRIIRI
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IRI = IRIi + ΔIRID + Δ
IRISF
IRIi = Initial IRI at construction
ΔIRID = Change in IRI due to distress
ΔIRISF = Change in IRI due to site factors
(age, subgrade properties, non- load distress)
Generalized Smoothness ModelGeneralized Smoothness Model
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Site FactorSite Factor
( ) ( ) ( )( )100064.01Pr008.0102.0 +++++= FIecipPIAgeSF
Age
= Pavement age, yearsPI
= Percent plasticity index of the soil
FI
= Average annual freezing index, degree F daysPrecip= Average annual precipitation or rainfall, inches
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Generalized Smoothness ModelGeneralized Smoothness Model
( ) ( )( ) ( )RDTC
FCSFIRIIRI Totalo
0.400080.0400.00150.0
++++=
IRIo = Initial IRI after construction, in./mi. SF = Site factor FCTotal = Area of fatigue cracking ft2/mi TC = Length of transverse cracking ft./mi. RD = Average rut depth, inches
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IRI Model CalibrationIRI Model Calibration
0
50
100
150
200
0 50 100 150 200Measured IRI, in/mi
Pred
cite
d IR
I, in
/mi
N = 1926R2 = 56 percentSEE = 18.9 in/mi
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Flexible Flexible ──
Effect of Fatigue Cracking Effect of Fatigue Cracking (Wheelpath: Longitudinal & Alligator) (Wheelpath: Longitudinal & Alligator)
Initial IRI = 63 in/mi, cracking accumulated linearly over 25 years0
40
80
120
160
200
0 10 20 30 40 50 60 70
Fatigure Cracking, percent area
IRI,
in/m
i
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ConclusionsConclusions• The MEPDG incorporated the following
performance prediction models– Load Related Cracking– Rutting Models– Thermal Cracking– Roughness
• The models are calibrated based on the performance data from the LTPP sections located throughout the US and Canada.
• Local calibration of the models is recommended
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More InformationMore Information
www.trb.org/mepdg
• Guide Documentation • Software• Climatic database