Post on 17-Feb-2018
transcript
Structural Overlay Design
Using NDT Methods
Zhong Wu, Ph.D., P.E.
Louisiana Transportation Research Center
2007 Transportation Engineering Conference
Baton Rouge, February 11-14, 2007
Outline
Background
Objective
Overview of Overlay Design Methods
Research Projects
Summary
Recommendations
Background
Asphalt overlay has been considered as
simplest and fastest means of restoring the distressed surfaces of rigid and flexible pavements
A quality overlay design
improve the roadway’s rideability
restore the pavement structural stability.
Structural overlay thickness design requests
Existing subgrade condition
Existing pavement strength
Engineering judgment
Background (cont…) Current DOTD overlay thickness design
the 1993 AASHTO Pavement design guide software (DARWin)
One required design input, subgrade resilient modulus value, Mr, the pre-assigned parish-map values
not base on in-situ soil properties
Uses component analysis (layer co-efficients) method to determine the existing pavement’s structure number
SNeff = ∑aihi
Such method can lead to design errors (over- or under-estimated overlay thickness) since design values do not represent actual field conditions
Overlay Design Example
-30 -20 -10 0 10 20 30 40 50 60 70 80Change in Mr (MPa)
-150
-100
-50
0
50
100
150
Dif
fere
nce
in o
ver
lay t
hic
kn
ess
(mm
)
-4000 -2000 0 2000 4000 6000 8000 10000Change in Mr (psi)
Hot mix asphaltD1=102 mm, a1=0.0165/mm
Base courseD2=241 mm, a2=0.0063/mm
SubbaseD3=457 mm, a3=0.0040/mm
Subgrade soil
Typical pavement section
W18=5,000,000 ESALs
R=95 %
PSI=1.9S0=0.35
Design Mr=34.5 MPa
Design SN=5
∆Mr = 2,000 psi
=> Underestimated AC
thickness of 1.5 in
∆Mr = -2,000 psi
=> Overestimated AC
thickness of 2.0 in
Objective
to establish a methodology for mechanistic
pavement overlay design, based on
in-situ pavement conditions, and
utilizing non destructive test (NDT) methods,
specifically the FWD and/or Dynaflect.
Dynatest 8002 model Falling Weight Deflectometer Dynaflect
Overview of Overlay Design Methods
Effective Thickness (ET) Approach
1993 AASHTO Pavement Design Guide
Asphalt Institute (AI) ET Method (MS-17)
Deflection-based Approach
AI Benkelman Beam Deflection Method (MS-17)
Caltran Flexible Pavement Rehabilitation
Mechanistic-Empirical (M-E) Approach
EVERPAVE (WsDOT)
New M-E Pavement Design Guide
Effective Thickness (ET) Approach
- Asphalt Institute (MS-17)
Thickness of Overlay = Tn - Te
Tn, new pavement thickness, determined from AI
Design Chart for Full-depth Asphalt Concrete, using
ESALd and Mr
Te, effective thickness of existing pavement
structure
Te=∑ Cihi
where, hi=thickness of the ith layer of the existing
pavement;
Ci=conversion factor associated with the ith existing layer
Effective Thickness (ET) Approach
-1993 AASHTO Pavement Design Guide
Overlay Thickness Equation
SNf from AASHTO pavement design equation
where Mr is a required input, which can be determined from
Laboratory Testing
Backcalculation from NDT measurements
Approximate relationships (used by DOTD)
The effective structure number of existing pavement, SNeff
NDT method
Component analysis method (used by DOTD)
Remaining life method
OL
efff
OL
OLOL
a
SNSN
a
SNh
Deflection-Based Approach
- Asphalt Institute Benkelman Beam (MS-17)
Pavement is modeled as a two-layer system
Layer 1: AC Overlay
Layer 2: Existing pavement
Overlay thickness is determined as following steps:
Determine Representative Rebound Deflection (RRD)
Layer 2’s elastic modulus is determined from RRD.
Compute Design Rebound Deflection (DRD) based on the allowable ESAL: DRD=1.0363 (ESAL)-0.2438
Other Deflections (e.g. FWD, Dynaflect) can be converted into Benkelman beam deflections, such as
Benkelman Beam = 1.61 * FWD
Benkelman Beam = 20.63 * Dynaflect
Mechanistic-Empirical (M-E) Approach
Modeled pavement as multi-layered elastic
or visco-elastic structure
Pavement materials described by their
stiffness and strengths at different times of
the year
Determine the critical stress, strain, or
deflection by mechanistic methods
Predict resulting damages by empirical
failure criteria, e.g. fatigue cracking, rutting.
Mechanistic-Empirical (M-E) Approach
-EVERPAVE
Developed by Washington DOT
Steps:
Backcalculate layer moduli using FWD data
Analyze and determine the two failure criteria parameters.
Fatigue cracking
Rutting
Compute allowable repetitions to failure at each season
Compute damage at each season and sum the seasonal
damage ratio.
Determine the overlay thickness based on the sum of the
damage ratio is less than or equal to one.
)log(854.0)log(291.382.14log actf EN
4843.418 )(10077.1log VfN
New M-E Pavement Design Guide
Developed under
NCHRP 1-37A
New Traffic input
Enhanced Integrated
Climatic Model
(EICM)
Season variations
New Distress Models
Need Calibration
Dr. Matthew W. Witczak (2003)
NDT Overlay Design SurveyState Method Software
Arkansas Equivalent Thickness ROADHOG
Mississippi Equivalent Thickness ELMOD5
Alabama 1993 AASHTO Spreadsheet program
Maryland 1993 AASHTO Spreadsheet program
(VDOT)
Virginia 1993 AASHTO Spreadsheet program
California Deflection-based Design Manual
North Carolina AI Deflection-based Spreadsheet program
South Carolina Deflection-based Spreadsheet program
Idaho M-E WinFlex
Minnesota M-E MNPAVE
Oregon M-E /
Texas M-E FPS-19W
Washington M-E EVERPAVE
Project Selection
Four in-service pavements
I-12 (ESALd=24,400,000, life=15yrs)
LA28 (ESALd=1,513,000, life=10yrs)
LA74 (ESALd=700,590, life=10yrs)
LA44 (ESALd=353,256, life=10yrs)
Each project about 3 to 5 miles long
Design Plan
Based on current DOTD overlay design
method (Mr-parish map, SNeff-estimated)
I-12 4.5” AC overlay + 2” cold planning
LA28 4.5” AC Overlay + 2” cold planning
LA44 3.5” AC overlay + 2” cold planning
LA74 3.5” AC overlay + 2” cold planning
NDT Tests
FWD and Dynaflect tests were performed on
each project site
at 0.1 mile interval
on both traffic directions
8” 4” 6” 6” 12” 12” 12” 12”
d1 d2 d3 d4 d5 d6 d7 d8 d9
FWD Load
Dynaflect Deflection Analysis
Kinchen and Temple
(1980) developed a
“Pavement Evaluation
Chart” for Louisiana
SN of existing pavements
Subgrade Modulus
Routinely use in
pavement research
projects
Pavement Evaluation Chart
FWD Analysis (D0 & D9)
LA 44
0
5
10
15
20
25
1.0
1.2
1.4
1.6
1.8
2.0
3.1
3.3
3.5
3.7
3.9
6.0
6.2
6.4
6.6
6.8
7.0
Station (miles)
FW
D D
efl
ec
tio
n (
mils
)D0 (NB)
D0 (SB)
D9 (NB)
D9 (SB)
LA 74
0
10
20
30
40
50
0.1
0.3
0.5
0.7
0.9
1.1
1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
Station (miles)
FW
D D
efl
ec
tio
n (
mil
s)
D1 (EB)
D0 (W B)
D9 (EB)
D9 (W B)
Overlay Thickness Deflection-Based Approach (AI Method)
3.5"3.5"
4.5"4.5"
2"
4"4.5"
3"
2"
3"
2"
3"
0
2
4
6
8
I-12 LA28 LA74 LA44
Project
Ov
erla
y T
hic
kn
ess
(in
)
Current Plan
AI (NB/EB)
AI (SB/WB)
Equivalent Thickness Method
(Arkansas ROADHOG)
3.5"3.5"
4.5"4.5"
2.8"2.7"
4.2"
2"2.6"
2.2"2.9"
2"
0
2
4
6
8
I-12 LA28 LA74 LA44
Project
Ov
erla
y T
hic
kn
ess
(in
)
Current Plan
ROADHOG(NB/EB)
ROADHOG(SB/WB)
Based on M-E Design Approach
Only 0 or 1” overlay thickness required for all
four projects.
Possible explanations:
Backcalculated modulus too high
Default values used in distress models (no
Calibrated)
Not fully understand how to choose a
representative design value
Summary (Deflection-based method)
Simple to use (e.g. AI method)
Needs to verify and calibrate the relationship
between FWD (or Dynaflect) measured
deflections and BB rebound deflections
Relationship between allowable rebound
deflection and ESALd also needs to be
verified and calibrated
Summary (Equivalent Thickness
method)
Simple to use (e.g. AASHTO and ROADHOG)
1993 AASHTO NDT-based method generally
underestimate the overlay thickness, due to over-
estimate the existing pavement SN.
ROADHOG uses its own relationship in estimation
of SNeff.
Such relationships between SNeff and delta(D) may or
may not be applicable to Louisiana condition
Summary (M-E design method)
Complicate to use.
M-E-based overlay design method needs
sophisticate inputs, which usually are not
available directly from in-situ NDT tests
The fatigue and rutting models used in any M-
E base design software must be verified and
calibrated before any locally implementation.
Proposed NDT-based Overlay Design
Procedure for Louisiana Use Effective Thickness approach
The future Structure Number (SNfuture) determined from 1993 AASHTO design equation
Mr determined from in-situ tests (DCP, FWD or Dynaflect)
SNeff determined from FWD or Dynaflect test
If FWD used, SNeff (FWD) needs to be scaled down to SNeff (Dynaflect) for Louisiana Condition
Overlay thickness = (SNfuture-SNeff)/aAC