Florida Top Down Cracking Pavement Design Model
Topic Description
This presentation provides an overview of a new mechanistic-empirical top down cracking design tool for Florida.
Speaker Biography
Finished B.S.C.E. in Civil Engineering and B.S. in Mathematics from the University of North Dakota, 1986. Completed M.S. in Civil Engineering from Cornell U. and a Ph.D. in Civil Engineering from the University of Minnesota in 1996. Worked as a Civil Engineering consultant for 4+ years, joined the University of Minnesota in 1997, and the University of Florida Pavement Group in 1998. Dr. Birgisson has written over 80 papers on pavements and pavement related subjects.
Bjorn Birgisson
Session 52
University of Florida
1
2006 Design ConferenceDesigning for More Than Bridges and Roads July 31 August 2, 2006
Florida Top-Down Pavement Cracking Design Model
Bjorn Bjorn BirgissonBirgisson, , JianlinJianlin Wang, Reynaldo Wang, Reynaldo RoqueRoque
Department of Civil & Coastal Engineering University of Florida
Pavement Response and Cracking
Bottom-up cracking
Predominant in Florida
Top-down cracking
Bending effects
2
FDOT Multiyear Study
Mechanisms of Top-Down Cracking
Stiffness Gradients (Temperature differential, Aging)
Thermal Stresses
Truck tire ribs induced tension, Residual viscoelastic stresses
Cracking Models for Mixtures and Pavement
Simpler Testing and Design Calculations
Core Extracted from Field
3
A damage threshold exists (DCSE limit)
Damage = Dissipated Creep Strain Energy (DCSE)
Damage > Threshold Macro-crack(DCSE) (DCSE limit)
Macro-crack is not healable
Damage under the cracking threshold is fully healable
Florida Cracking Model Key Features
Ener
gy, E
Cycles, N
Ener
gy, E
Cycles, N
Ener
gy, E
Cycles, N
FE
DCSE
creep
xelastic elastic
Potential loading conditions in the field
Ener
gy, E
FE
DCSEDamage Healing
Day 1 Day 2
Damage Healing
x
The Threshold Concept
4
Crack Propagation (Paris Law) C
rack
Len
gth,
a
Number of Load Applications, N
dNdA
a =
Threshold
Macro-crack initiationMicro-crack Threshold
Macro-crack
Micro-crack
Crack propagation in asphalt pavements occurs in steps.
Crack Growth Model
Superpave Indirect Tensile Test:
H
V
Mixture Properties
1. Resilient modulus (Cyclic loading)
2. Creep (Constant load with time)
3. Strength (Increase load until fracture)
Dissipated energy creep rate
Energy limits
5
to calculate the amount of dissipated energy per load cycle:
HMA Fracture Model
1/ (tensile stress, D &m)DCSE cycle f=
Calculate the crack growth for a given level of applied stress.
Use Material properties m, D1 (creep rate) & DCSEf (energy limit) Structural properties AVE (modulus)
For a given mixture with known DCSEf we can predict Nffor initiation or propagation of cracking.
Multiple pairs of poor and good performing sections throughout Florida
Field Test Sections
Over 18 pairs (36 sections) to date
6
Used the HMA Fracture Model to calculate Nf for crack to propagate 2
0
2000
4000
6000
8000
10000
12000
14000
SR80
-1C
SR 16
-4C
SR 16
-6C
NW 39
-1C
TPK
2CI75
-3CI75
-1C
SR 37
5-2C
I75-1U
I75-2U
TPK
1U
NW 39
-2U
SR80
-2U
SR 37
5-1U
Section
Nf t
o Pr
opag
ate
2 in
`
Cracked Uncracked
Mixtures with Nf
7
DCSEmin is the minimum energy required to produce Nf=6000
Express the DCSEmin, D1 & m-value relation in a single function:
ADm
DCSE 12.98
min =
( ) 81.3 1046.244.33
36.6 +
=t
t
S
A
Minimum Energy
Tensile Strength
Tensile Stress
The DCSEHMA has to be greater than the DCSEmin for good cracking performance:
DCSEHMA DCSEmin
MR
Stre
ss,
Strain,
DCSE
x
DCSEHMA = AREA
Log
D(t
)
Log t1
D1
m
2.98min 1DCSE m D / A=
Energy Ratio Concept
1DCSEDCSERATIO ENERGY
min
HMA >=
8
Examined all sections Performance criteria: ER>1 ; DCSEHMA>0.75
0.00
0.50
1.00
1.50
2.00
2.50
3.00
US30
1-BS
SR80
-1C
I10-D
E
I10-D
W
SR 16
-4C
I10-M
W2
SR 16
-6C
NW 39
-1C
TPK
2CI75
-3CI75
-1C
SR 37
5-2C
US30
1-BN
I95-SJ
N
I10-M
W1
I75-1U
I75-2U
TPK
1U
SR80
-2U
NW 39
-2U
SR 37
5-1U
I95-D
N
Section
Ene
rgy
Rat
io
Cracked Uncracked
DCSEHMA2.5
Energy Ratio Results
Florida Framework for Cracking Evaluation of HMA Pavements
LABORATORY TESTSuperPave IDT
SUPERPAVE IDT FRACTURE PARAMETERS
HMA FRACTURE
MODEL
PAVEMENT RESPONSE
CRACKING MODELS
PAVEMENT DESIGN THICKNESS
&
VOLUMETRIC RELATIONOR
STRUCTUREINFORMATION
9
Accounts for structure and mixture for averaged environmental conditions
Design Premise: ensure a reasonable predicted crack depth after x number of years (Design Life)
Top-Down Cracking Design
Use Energy Ratio for M-E Top-Down Cracking Design
Level 3:
Determine thickness for ER=1 @ design life
AC ThicknessModulus, Poissons Ratio
Layered Elastic Analysis
Stress
Energy Ratio
ER 1 Design Thickness
Mixture Properties Matrix(DCSEL, FE, St, Creep Rate)
M-E Design Flowchart Level 3
no yes
Aging model w/ Design life
10
Uses a fast pavement fracture simulator to predict depth of cracking after x years (Design life), and account for the effects of:
Mixture & Structure Temperature/aging gradients Load Configuration Traffic
M-E Top Down Cracking DesignLevel 1 & 2
Level 1: Measured properties from IDT
Level 2: Estimated properties
Updated Layer Thickness
Load Configuration Load Spectra? ESALs?
Fracture Simulator
GRADIENTS: Temperature (Matrix)Aging (Matrix)
Crack Depth at Design life (CD)DL
Traffic, n
Design Thickness
DCSEL, FE, St, Creep Rate,Mr, adjusted for aging andtemperature
LEVEL 1 Layer Thickness
M-E Design Flowchart Level 2
no yes(CD)DL 2
11
New Pavement Design using Energy Ratio
Overlay Design using Energy Ratio
Design Studio
Input Menu
Structure
AC Layer Other Layers
Loads
MAAT
12
AC Layer Basic Design
Suggested gradation or input your own
Estimate an initial design thickness (will be optimized)
Input Design AV and Vb
Binder Selection
Estimate the binder viscosity at mix/laydowncondition
Predict the in-service viscosity based on the global aging model
Correction
0.76 0.78 0.8 0.82 0.84 0.860.76
0.77
0.78
0.79
0.8
0.81
0.82
0.83
0.84
0.85
0.86Viscosity of Layer A and Layer B at 60 oC
Measured log-log (cp)
Cal
cula
ted
log-
log
(c
p)
Layer A (uncorrected)Layer B (uncorrected)Layer A (corrected)Layer B (corrected)
13
Input MAAT to predict aging
MAAT Input
Mixture Properties
Layer modulus estimate from |E*| master curve
Poissons ratio estimated from EAC
IDT parameters estimated from some basic relations
-20 -15 -10 -5 0 5 10 15 202.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8Master-Curve for |E*| at 10 oC (C1 mixture)
log-frequency (Hz)
log
|E*|
(psi
)
14
Pavement Structure Other Layers
Base, sub-base and subgrade layers (elastic)
User can determine the number of layers
Default properties suggested for selected materials
User can also define the material properties
Simplified load information
Loads Input
1(1 )(1 ) 1
n
n total n
p pS Sp
+=
+
The maximum numberof ESALs/year:
totalS
n
(%)p
15
ER formula
, where
ER Calculation
0.0
0.5
1.0
1.5
2.0
2.5
0 200 400 600 800 1000 1200
Traffic (ESALs/year x1000)
Min
imum
Ene
rgy
Rat
io
Minimum ER adjusted for traffic level
According to the
traffic load input,
select the minimum
(optimum) ER
corresponding to
the traffic level
stresses at the standard
or selected location
ER value
ER Output
16
Search for the thickness that gives the minimum required ER
Thickness Optimization
1
2
1
2
t2
t1
Plot ER-thickness curves at different pavement ages
ER increases as the pavement thickness increase if the pavement is not too thin
The ER values for new and aged pavements differ significantly, especially for thick pavements
0 t1
17
Plot pavement life curves for different thicknesses
ER drops down significantly in the first couple of years
Sensitivity of ER to thickness is shown in the graph
Pavement Life Curve
h2
h1
h3
h1 < h2 < h3:
h2 = optimum thickness
h1 = h2 - 2
h3 = h2 + 2
A new M-E pavement design tool for top down cracking based on Energy Ratio
Summary
Validated on more than 30 field sections
Thickness design optimized for
traffic level
mixture type
binder type
The optimization is an automated process
18
Level 1 and 2 pavement design tool being developed
Summary (Contd)
Frame work complete
fast fracture simulator
Awarded to UF on May 1, 2006
NCHRP 1-42A: Models for top-down cracking
Questions
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