MEPDG : Where are We Now? Louisiana Transportation Engineering Conference Baton Rouge, LA February 12, 2007
Chris Wagner, P.E. FHWA – Resource Center
Auburn and LSU Common Denominator
BEAT BAMA !!!!!
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Objectives State Implementation Activities Status of MEPDG
General Overview of ME Design Benefits and Issues of Implementation Current State of the Practice
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What else happened in 1958 ? Construction finished on the AASHO Road Test
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What’s Being Used (2003 survey) Design Procedures
DOTs
1972 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
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1950s Construction Methods...
(AASHO, 1961)
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Question ? Why was the original AASHO Road Test conducted ? z
How much did it cost ?
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Objectives
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The Big Picture EICM
Climate Inputs
Material Properties
Traffic
Transfer Functions
Predicted Performance
Mechanistic Analysis
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σ Loads and Layer Stiffness E* Mr
Mr
Mechanistic Analysis Layered Elastic Analysis
Strain Calculations at Critical Locations
E = σ/ε
Predicted Performance
Empirical Portion of MEPDG
of e Lin
β
y alit u Eq
β = Empirical Shift Factor
Observed Performance
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Test Section Performance 100
Alligator Cracking (% of Total Lane Area)
90
Local Performance Data
80 70 60 50 40 30 20 10 0 -4
-3
-2
-1
0
1
2
3
Log Damage (%)
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Local Calibration Benefits Local Data Set
National Data Set
Test Section Observations
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Traffic z z
Improved traffic characterization Ability to deal with changing load types
ESAL18k
Load Spectra
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1950s Vehicle Loads... e s e d th
n o y e b s s n n o o i i t t a a l c o i ” l . p p n a r p o i a t u d “Ext a a c o l h l t i w tota d e s u e b d l shou Who drove these trucks ? Pg 7: AASHTO ‘72
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Materials z z z
Enhanced definition of material properties Relate material properties to performance Material Aging
Layer Coefficient
Modulus
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3,000,000
2,500,000
Modulus (psi)
2,000,000
1,500,000
1,000,000
500,000
0 0
6
12
18
24
30
36
42
48
54
60
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Aging Dynamic Modulus (psi)
1,400,000
AC at 1/2" Depth AC at 5" Depth AC at 10" depth
1,200,000
1,000,000
800,000
600,000
400,000
200,000
0 0
12
24
36
48
60
72
84
96
Pavement Age (month)
108
120
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1,000,000
900,000
What happened here ?? 800,000
Modulus (psi)
700,000
Granular Base
600,000
500,000
400,000
300,000
200,000
100,000
0 0
6
12
18
24
30
36
42
48
54
60
Pavement Age (month)
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100,000
90,000
80,000
70,000
Modulus (psi)
Granular Base 60,000
50,000
40,000
30,000
Input Value
20,000
10,000
Soil 0 0
6
12
18
24
30
36
42
48
54
60
Pavement Age (month)
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AASHTO Materials Characterization z
How do you Characterize your materials ?? z z z z z z
SMA Superpave HMA Hveem HMA Polymer Modified Warm Mix Asphalt RAP
Are they all ai = 0.44 ?
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Climate z
Site specific climate considerations z z
Material properties effected by climate PCC Joint openings, Curl / Warping
Extrapolated from Ottawa, IL
800 Weather Sites
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Major Advantages z z z z
Modular system that allows for incremental enhancement Produces a more reliable design No longer dependent on the extrapolation of empirical relationships Excellent for forensic analysis z
z
Answers “What if….” questions
Calibrate to Local Materials, Traffic, Climate….
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Reasons for Change z
Reduce Over-and-Under Design Costs
z
Legislative Mandate
z
Consider Alternative Designs/Unique Conditions
z
Rational Basis for Warranties, LCCA, PRS, QA/QC, Pay Factors
z
Forensic Investigations
z
Impact of Management Decisions on Pavement System
z
Tie Design to Construction
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Pavement Performance
LCCA Initial Construction First Rehab
Time
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PRS Example 60
Contractor Builds 12% Va Bottom Up Cracking (%)
50
40
$$$
8% Air Void Spec Limit 30
20
10
0 4
8
12
Air Voids (%)
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Integration Pavement Design
Materials Selection
Communication
Pavement Management
Construction
Objectives
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Implementation Team
Develop a Team and Plan z
z z z
Include In-House Experts; Pavements Materials and Traffic, PMS Consider Regional or Multi-State Effort; PFS Contract with Consultant or University Include Upper management Personnel
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Data Collection - Traffic z z
z
z z
Most States Have Inadequate Data Some are Planning Regional Weight Data by Roadway Classification (TRB Session 283) Share Collection and Storage Efforts with Other Offices Using Traffic Data Enhance WIM Quality and Magnitude Integrate with PMS
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Data Collection - Materials z z
z z
Most States Need Additional Equipment Several are Determining Mr, FWD, DCP and CBR Relationships for Catalog Testing Equipment for CTE and E* Predictive Equations for E*
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Practical Considerations z z
z
z z
You have to design before you build MEPDG is used for Design and Forensic Evaluation Don’t need to use all distress predictions for design Do not need Level 1 for all Inputs Do not throw out past experience
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Using MEPDG for Design
State specific guidance is necessary z z z
Pavement Design Manual Distress criteria and limits Design parameters to change
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Implementation Timeframe z z
Some DOT’s Already Underway Others are Awaiting Other Efforts: z z z z z z
NCHRP Projects FHWA Research Projects Copy Other State Approaches AASHTO Adoption Windfall from Gas Tax Revenues Hell Frozen
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Who will use the MEPDG? z
State DOT’s Main User z z
Pavement Designers Upper Management z
z z z
Remaining Service Life, “What if” questions
Academia Industry Consultant Designers z
Warranty, Design Build, PRS, PWL etc…..
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Other Work Lead State Implementation Plan Both
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Things to remember z
All pavement design systems need: z z z
z
Quality Materials Characterization Quality Traffic Data Calibrated to local conditions
The MEPDG is one tool for a designer z z
Focused on the structural design aspects Has limitations
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Version 1.0 Changes z z z z z z z
State DOT’s will receive 2 copies soon Batch Mode Model Recalibration Use of Volumetrics in rutting model Computer Program Stability Perpetual Pavement Concept Calculation of ESAL’s
NCHRP Draft Research Results Digest
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More Information z z
www.trb.org/mepdg www.fhwa.dot.gov/pavement/dgit z
Webcast Workshops z Traffic, Climate, Materials, Introduction
z
ARA bugtracker website
z
Local Calibration Guide and Users Manual NHI Course: Hands on Application of MEPDG
z
z Read
the book !!!
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Help Wanted z
Contact the DGIT z z z
Research Proposal Review Training Technical Assistance
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AASHTO Implementation Joint Technical Committee on Pavements
April 10-11, 2007 MEPDG Roll Out Workshop Irvine, CA Subcommittee of Design & Materials
Full AASHTO Balloting
Interim Guide – Spring 2008 ?
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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
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Perspective "We can't solve problems by using the same kind of thinking we used when we created them."
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Questions ??
BEAT BAMA !!! www.trb.org/mepdg www.fhwa.dot.gov/pavement/dgit/
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