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MEPDG : Where are We Now?
Louisiana Transportation Engineering Conference
Baton Rouge, LAFebruary 12, 2007
Chris Wagner, P.E.FHWA – Resource Center
Objectives
State Implementation Activities Status of MEPDG
Current State of the Practice
General Overview of ME DesignBenefits and Issues of Implementation
What’s Being Used (2003 survey)
Design Procedures DOTs1972 AASHTO Guide 3
1986 AASHTO Guide 2
1993 AASHTO Guide 26
Agency’s own pavement design guide or combination of AASHTO/Agency design procedures
17
The Big Picture
Climate Inputs
EICM
Material Properties
Transfer Functions
Predicted Performance Mechanistic Analysis
Traffic
Loads and Layer Stiffness
Mechanistic AnalysisLayered Elastic Analysis
E*
Mr
Mr
σ
Strain Calculations at Critical Locations
E = σ/ε
Empirical Portion of MEPDGP
redi
cted
Per
form
ance
Observed Performance
Line of Equality
β = Empirical Shift Factorβ
Test Section Performance
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) Local Performance Data
Local Calibration Benefits
Test Section Observations
National Data Set
Local Data Set
Traffic
Improved traffic characterizationAbility to deal with changing load types
ESAL18k Load Spectra
1950s Vehicle Loads...1950s Vehicle Loads...
Who drove these trucks ?
“Extrapolations beyond these
total load applications
should be used with caution.”
Pg 7: AASHTO ‘72
MaterialsEnhanced definition of material propertiesRelate material properties to performanceMaterial Aging
LayerCoefficient Modulus
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
0 6 12 18 24 30 36 42 48 54 60
Pavement Age (month)
Mod
ulus
(psi
)
Aging
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1,400,000
0 12 24 36 48 60 72 84 96 108 120
Pavement Age (month)
AC at 1/2" DepthAC at 5" DepthAC at 10" depth
Dyn
amic
Mod
ulus
(psi
)
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
800,000
900,000
1,000,000
0 6 12 18 24 30 36 42 48 54 60
Pavement Age (month)
Mod
ulus
(psi
)
What happened here ??
Granular Base
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
0 6 12 18 24 30 36 42 48 54 60
Pavement Age (month)
Mod
ulus
(psi
)
Granular Base
Soil
Input Value
AASHTO Materials Characterization
How do you Characterize your materials ??SMASuperpave HMAHveem HMAPolymer ModifiedWarm Mix AsphaltRAP
Are they all ai = 0.44 ?
ClimateSite specific climate considerations
Material properties effected by climatePCC Joint openings, Curl / Warping
Extrapolated fromOttawa, IL 800 Weather Sites
Major Advantages
Modular system that allows for incremental enhancement Produces a more reliable designNo longer dependent on the extrapolation of empirical relationshipsExcellent for forensic analysis
Answers “What if….” questionsCalibrate to Local Materials, Traffic, Climate….
Reasons for ChangeReduce Over-and-Under Design Costs Legislative MandateConsider Alternative Designs/Unique ConditionsRational Basis for Warranties, LCCA, PRS, QA/QC, Pay FactorsForensic InvestigationsImpact of Management Decisions on Pavement SystemTie Design to Construction
PRS Example
0
10
20
30
40
50
60
4 8 12
Air Voids (%)
Bot
tom
Up
Cra
ckin
g (%
)
8% Air Void Spec Limit
Contractor Builds 12% Va
$$$
Pavement Design
Pavement Management Construction
Materials Selection
Communication
Integration
Implementation Team
Include In-House Experts; Pavements Materials and Traffic, PMSConsider Regional or Multi-State Effort; PFSContract with Consultant or UniversityInclude Upper management Personnel
Develop a Team and Plan
Data Collection - Traffic
Most States Have Inadequate DataSome are Planning Regional Weight Data by Roadway Classification (TRB Session 283)Share Collection and Storage Efforts with Other Offices Using Traffic DataEnhance WIM Quality and MagnitudeIntegrate with PMS
Data Collection - Materials
Most States Need Additional EquipmentSeveral are Determining Mr, FWD, DCP and CBR Relationships for CatalogTesting Equipment for CTE and E*Predictive Equations for E*
Practical Considerations
You have to design before you buildMEPDG is used for Design and Forensic EvaluationDon’t need to use all distress predictions for designDo not need Level 1 for all InputsDo not throw out past experience
Using MEPDG for Design
State specific guidance is necessaryPavement Design Manual Distress criteria and limitsDesign parameters to change
Implementation Timeframe
Some DOT’s Already UnderwayOthers are Awaiting Other Efforts:
NCHRP ProjectsFHWA Research ProjectsCopy Other State ApproachesAASHTO AdoptionWindfall from Gas Tax RevenuesHell Frozen
Who will use the MEPDG?
State DOT’s Main UserPavement DesignersUpper Management
Remaining Service Life, “What if” questions
AcademiaIndustryConsultant Designers
Warranty, Design Build, PRS, PWL etc…..
Things to remember
All pavement design systems need:Quality Materials CharacterizationQuality Traffic DataCalibrated to local conditions
The MEPDG is one tool for a designerFocused on the structural design aspectsHas limitations
Version 1.0 Changes
State DOT’s will receive 2 copies soonBatch ModeModel RecalibrationUse of Volumetrics in rutting modelComputer Program StabilityPerpetual Pavement Concept Calculation of ESAL’s
NCHRP Draft Research Results Digest
More Informationwww.trb.org/mepdg www.fhwa.dot.gov/pavement/dgit
Webcast WorkshopsTraffic, Climate, Materials, Introduction
ARA bugtracker website
Local Calibration Guide and Users ManualNHI Course: Hands on Application of MEPDG
Read the book !!!
AASHTO ImplementationJoint Technical Committee on Pavements
Subcommittee of Design &
Materials
Full AASHTO Balloting
Interim Guide – Spring 2008 ?
April 10-11, 2007MEPDG Roll Out Workshop
Irvine, CA
Perspective•1960 – Completion of Road Test Experiment
•1961-62 AASHO Interim Guide for the Design of Rigid and Flexible Pavements
•1972 AASHTO Interim Guide for the Design of Pavements
•1981 Revised Chapter III on Portland Cement Concrete Pavement Design
•1986 Guide for the Design of Pavement Structures
•1993 Revised Overlay Design Procedures
•1998 Supplement to Concrete Design Procedures
"We can't solve problems by using the same kind of thinking we used when we created them."
PerspectivePerspective
