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FHWA Team Educates in Mechanistic-Empirical Pavement Design

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Mechanistic-Empirical Pavement Design
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Centered on Service is a quarterly publication dedicated to sharing success stories and updates on FHWA Resource Center projects and ongoing news about services provided by the Technical Service Teams to the FHWA Division Offices, Headquarters Offices, and State Partners.

FHWA Team Educates Field Offices, State Highway Agencies, and Industry in Mechanistic-Empirical Pavement Design

In June 2004, the National Cooperative Highway Research Program (NCHRP) released the Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures. The Federal Highway Administration (FHWA) organized a Design Guide Implementation Team (DGIT) to immediately begin the process of informing, educating, and assisting the FHWA's field offices, State highway agencies, industry, and others about the new design guide. The FHWA considers implementation of the Mechanistic-Empirical Design Guide (M-E PDG) a critical element in improving the National Highway System.

The M-E PDG defines uniform guidelines for designing common features of flexible, rigid, and composite pavements. Pavement and materials engineers can use mechanistic-empirical design to analyze and predict pavement distress including fatigue in asphalt pavements, and cracking and faulting in concrete pavements. The guide also presents recommendations for evaluating existing pavements, along with references for rehabilitation treatments, drainage, and foundation improvements.

DGIT Team Deploys M-E PDG Around the Globe
The DGIT Team has put forth a strategic plan of action to deploy this new technology and has executed an extensive outreach campaign, educating to date more than 1,200 engineers across the Nation in 21 States and around the globe in Canada, Europe, China, India, and Central and South America. Mechanistic-Empirical Pavement Design can contribute to longer life cycles for pavements and cost savings to users. State highway agencies are not required to adopt the principles designated in the M-E PDG. However, the design guide represents the most comprehensive and current manual on pavement design. The FHWA encourages States to evaluate the utility that the M-E PDG offers and to carefully implement the guidelines and recommendations.

NCHRP 1-37A: Mechanistic-Empirical Pavement Design
The M-E PDG is a product resulting from the efforts initiated by the American Association of State and Highway Transportation Officials (AASHTO) Joint Task Force on Pavements and the NCHRP to enhance and improve existing pavement design procedures. Two components comprise this technology: 1) the Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures, along with the 2) Design Guide Structural Analysis Software. Understanding the guidance and applying the software will allow States to use the M-E PDG to its full potential.

What's New with the M-E PDG Software?
The NCHRP recently released an upgrade to the M-E PDG software program to address some of the known "bugs" in the program. The original version of the software (version 0.700) was released in April 2004. Summarized below are some of the minor and major changes that have been made in version 0.800 of the software.

• Many minor items were fixed to reduce crashes and increase accuracy of computation. A few examples:
  • Correction of error found in the calculation of degree of saturation of soils.
  • Improved defaults for continually reinforced concrete pavements base friction.

• Major items include:
  • Hot mix asphalt (HMA) thermal cracking model.
  • Improved accuracy of the HMA overlay design strain calculations.
  • Increased quantity of hourly weather data (9 years).
    
    
• Updated design examples are included for several analysis types.
  
  
• New bug-tracking software web site is now available.

The upgraded software is available online at the Transportation Research Board web site. A limited number of the CD-ROM version of the upgraded software is available for the FHWA, if a copy is needed for an office. The online and CD-ROM versions of the software are the same. Due to the software's security feature, the CD-ROM must remain in the CD drive or the computer must be connected to the Internet for the software to operate.

Another upgrade, version 0.900, is scheduled for March 2006. This version will include the following:

• Updated version of the Asphalt Layered Elastic Analysis Program.
• Incorporation of improved calibration coefficients.
• Improvement to treatment of unbound layers.
• Correction of known software errors.

DGIT Team: Objectives
Deployment of the M-E PDG will take an estimated 5 to 8 years. Deployment strategies consist of 1) education, 2) enhancement, 3) and implementation. The DGIT Team's objectives include the following:

• Support AASHTO and NCHRP activities.
• Increase understanding of mechanistic-empirical pavement design and direct resources for guide modifications.
• Establish support approach for implementation (e.g., pooled-fund, Lead States, etc.).
• Provide a forum in which to discuss issues related to successfully utilizing and adopting new mechanistic-empirical pavement design concepts.
• Raise awareness of what benefits result from using M-E Pavement Design.

The DGIT Team achieves these objectives through a series of activities: workshops, briefings, web seminars, a DGIT web site, a Community of Practice, and a Lead States initiative.

DGIT Team: Education
The DIGIT Team has initiated a series of training opportunities, beginning with an Introduction to Mechanistic-Empirical Design, in 2004. These resources and services are free of cost to the State DOTs and industry engineers. The educational activities include the following workshops:

FY 2004

• Introduction to Mechanistic-Empirical Design Workshop
  • 1-day workshop
  • On-line version also available on the Connecticut DOT web site

FY 2005

• Traffic in Mechanistic-Empirical Design Workshop
  • 2-day workshop
    
• Materials Characterization of Inputs to Mechanistic- Empirical Pavement Design
  • 2-day workshop
  • On-line version also available on the Connecticut DOT web site
    
• Web Seminar on Traffic Monitoring Enhancements Needed for New Mechanistic-Empirical Pavement Design Guide

FY 2006

• Climatic Inputs for Mechanistic-Empirical Pavement Design
  • Under development
  • Pilot: February 2006
  • Purpose: Educate pavement designers on the effects of climate on materials and pavement performance.

FY 2007

• Local Calibration
  • Under development
  • Planned for Winter 2007
  • Purpose: Discuss sensitivity of inputs and local calibration procedures; educate pavement designers and pavement managers.

In addition, the DGIT Team is collaborating with the National Highway Institute to develop and deliver the following courses:

• NHI #131064: Introduction to Mechanistic Design (Available)
  
• NHI #131109: Analysis of New and Rehabilitated Pavement Performance with Mechanistic-Empirical Pavement Design Software
  • Under development
  • Pilot: May 2006
  • Hands-on format with computers loaded with software
  • Focus on user, not theory
  • Objective: For audience to be capable of performing flexible, rigid, rehab designs
    
• NHI #132040: Geotechnical Aspects of Pavements (Available)
• NHI #151018: Application of the FHWA Traffic Monitoring Guide (Available)

DGIT Team: Enhancement
The concepts of Mechanistic-Empirical Pavement Design are generally applicable and modular such that a full range of future enhancements are possible, incorporating improvements continuously over time. The DGIT team currently has the following projects in progress:

• Evaluation of the Rigid Pavement Design Procedure. This FHWA-sponsored research will evaluate the rigid pavement performance prediction models in the Mechanistic-Empirical Pavement Design Guide.
  
• National Center for Asphalt Technology (NCAT) Structural Section Studies. The FHWA has sponsored the construction and analysis of two full-scale pavement test sections at the NCAT Test Track to provide fundamental research associated with pavement response to traffic loading and to aid in further validation of the M-E PDG.
  
• TrafLoad Conversion Utility. The DGIT team has developed a software program that will aid pavement designers by allowing the direct integration of the Trafload Program files with the M-E PDG. This process will be integrated into newer versions of the M-E PDG.
  
• Anytime Weather and LTPP Bind Software. The development of the Anytime Weather software program from previous efforts associated with LTTP Bind allows pavement designers to look more closely at climatic information for their local areas.

The DGIT team continues to work closely with NCHRP, serving on review panels and contributing to associated projects:

• NCHRP 1-40: Independent Review (The object of this research is to facilitate the implementation and adoption of the recommended M-E PDG.)
  
• NCHRP 1-42: Top-Down Fatigue Cracking (Active)
  
• NCHRP 1-41: Reflection Cracking of Hot-Mix Asphalt Overlays (Active)
  
• NCHRP 9-30a: Calibration of Rutting Models (Pending)
  
• NCHRP 9-38: Endurance Limit of HMA (Active)

DGIT Team: Implementation
The DGIT team promotes mechanistic-empirical pavement design, assisting to implement this new methodology through the following activities:

• Asphalt/Concrete Trailer Materials Testing. The Asphalt and Concrete Trailers are fully capable of doing many of the materials tests associated with the M-E PDG. The trailers can be requested by contacting DGIT Team Leader Gary Crawford.
  
• CTE Testing and Equipment Development. The development and testing of the design equipment used for determining the coefficient of thermal expansion (CTE) in concrete pavements is currently underway. This FHWA initiative will result in a suggested test procedure and commercially available CTE Testing equipment.
  
• Sensitivity Analysis. The DGIT team continues to evaluate the M-E PDG through sensitivity analyses and other methods. The results of this evaluation are used and presented in the DGIT-sponsored workshops and associated materials.

In addition, to encourage communication and knowledge sharing among State highway agencies, the DGIT team has established a Lead States Group. The mission of the Lead States Group is to "help promote and facilitate the refinement, implementation, and evolution of Mechanistic-Empirical Pavement Design procedures in conjunction with AASHTO, NCHRP, and FHWA activities." Currently, 17 States are participating. (See story on Lead States.)

NCHRP 1-40: User Comments Online Discussion
The FHWA is working with the AASHTO Joint Technical Committee on Pavements to collect comments on and experiences with the NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide. As a part of NCHRP 1-40, the 1-37A guide will be reviewed and recommendations for changes may be made. Users of the new M-E PDG are encouraged to submit product issues, concerns, or comments through the FHWA DGIT Community of Practice.

For more information on M-E PDG, or to schedule training, contact:

The FHWA Design Guide Implementation Team
E-mail: DGIT@fhwa.dot.gov


Gary Crawford
Team Leader, DGIT
Office of Pavement Technology, Concrete Team
FHWA Headquarters
(202) 366-1286
gary.crawford@fhwa.dot.gov


Chris Wagner
Pavements and Materials Engineer
Pavement and Materials Technical Service Team
FHWA Resource Center
(404) 562-3693
chris.wagner@fhwa.dot.gov

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