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Note from the Joint Technical Committee on Pavements Chair
A ballot to approve the Interim AASHTO Mechanistic-Empirical Pavement Design Guide Manual of Practice has been issued to both the AASHTO Highway Subcommittee on Design and Highway Subcommittee on Materials. This ballot will be open for a period of thirty (30) days and will close on July 9th, 2007. Background information on this ballot has been provided below for voting members of the material and design subcommittees.
I very much appreciate your consideration of this very important ballot and look forward to working with both subcommittees as we move forward with MEPDG in the future.
Dan Dawood, P.E., Chair
AASHTO Joint Technical Committee on Pavements
Need for a New Design Guide
AASHTO has provided guidance to highway agencies on the design of highway pavement structures through the publication of design documents and availability of associated software. These products have served the design needs of highway agencies for many years; however, the time has arrived for a new and improved methodology to accurately design pavements for todays conditions and demands of our nations highway pavement systems. This ballot is the first step by AASHTO to adopt a new mechanistically based design methodology for highway pavements.
In 1972, AASHTO published the first pavement design guide based on the findings of the AASHO Road Test conducted in Ottawa, Illinois in the late 1950s. Subsequent updates to this original guide were published by AASHTO in 1986, 1993 and a supplement to the concrete design in 1998 to refine the process to better reflect design needs of states across the country.
The need for and benefits of an improved pavement design procedure were recognized at the time when the 1986 AASHTO Guide for Design of Pavement Structures was adopted. At this time it was recognized that a more mechanistically based design procedure was needed to better design pavements to withstand truck loadings and changing climatic conditions. To meet that need, the AASHTO Joint Task Force on Pavements (predecessor to the committee now known as the AASHTO Joint Technical Committee on Pavements (JTCoP)), in cooperation with the National Cooperative Highway Research Program (NCHRP) and the Federal Highway Administration (FHWA), sponsored the development of a Mechanistic-Empirical pavement design procedure under NCHRP Project 1-37A.
Development of the Proposed Guide
A key goal of NCHRP Project 1-37A, Phase II was the development of a Design Guide that utilized existing mechanistic-based models and data reflecting the current state-of-the-art in pavement design. The Mechanistic-Empirical Pavement Design Guide (MEPDG), as it has now become known, was completed in 2004 and released to the public for review and evaluation. A formal review of the products from NCHRP Project 1-37A was conducted by the NCHRP under Project 1-40A. This review has resulted in a number of improvements, many of which have been incorporated into the MEPDG under NCHRP Project 1-40. Project 1-40 has resulted in the following products related to the new design process:
An updated Research Report entitled Guide for Mechanistic-Empirical Design for New and Rehabilitated Pavement Structures
Version 1.0 of the MEPDG software which has been used as an tool to prove the concept of the new proposed design methodology
A guide document for highway agencies in the use of the new design approach entitled, Mechanistic-Empirical Pavement Design Guide Manual of Practice
A guide document for highway agencies to calibrate performance models entitled, Local Calibration Guidance for the Recommended Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures,(noted as MEPDG Local Calibration Guide in this document) contained within the MEPDG. This document has not yet been titled and is still under development.
It is the desire of the JTCoP to publish the Manual of Practice and the MEPDG Local Calibration Guide (Items 3 and 4 listed above) as AASHTO documents. The Research Report listed under Item 1 above will remain an NCHRP product and will not be published by AASHTO, although it will serve as a reference to the proposed AASHTO Manual of Practice. In addition, the software listed as Item 2 above will also remain an NCHRP product. Efforts are currently underway by the AASHTO Darwin Task Force to evaluate this software to determine specific requirements that would be desired in a production design software tool that could be offered to highway agencies, universities and the engineering design community through AASHTO as an AASHTOWare product. For now the software developed under NCHRP will be available free of charge until an AASHTOWare production software tool can be developed.
A two day seminar was held in Irvine, CA in April, 2007 to present an overview to the new mechanistic-empirical design approach, the use of the NCHRP software and to address any questions and comments from state highway agencies. An invitation was provided to each voting member of the AASHTO Highway Subcommittees on Design and Materials in preparation for this ballot. Forty six states participated in this seminar and each had an opportunity to ask questions and provide comments to the primary research team.
Plans to Address Gaps in Research
During the seminar the attendees were informed that the Manual of Practice currently being balloted would be considered an Interim product as there are a number of efforts underway today that will be incorporated into the design approach in the future to address gaps that exist in existing research. Some of these gaps will be addressed with the following research effort:
NCHRP Project 1-41, Models for Predicting Reflection Cracking of Hot-Mix Asphalt Overlays (Texas A&M University; Scheduled Completion: April 2008)
NCHRP Project 1-42A, Models for Predicting Top-Down Cracking of Hot-Mix Asphalt Layers (University of Florida; Scheduled Completion: April 2008)
NCHRP Project 9-29, Simple Performance Tester for Superpave Mix Design (Advanced Asphalt Technologies, LLC; Scheduled Completion: August 2008)
NCHRP Project 9-30A, Calibration of Rutting Models for HMA Structural and Mix Design (Applied Research Associates, Inc.; Scheduled Completion: November 2008)
NCHRP Project 9-38, Endurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible Pavements (National Center for Asphalt Technology; Scheduled Completion: December 2007)
NCHRP Project 9-44, Developing a Plan for Validating an Endurance Limit for HMA Pavements (Advanced Asphalt Technologies, LLC; Scheduled Completion: April 2008)
SHRP 2 Project R-21, Composite Pavement Systems (Award Anticipated in 2007)
NCHRP Project 1-46, Development of an AASHTO Pavement Handbook (Award Anticipated in 2008)
NCHRP Project 9-47, Environmental and Engineering Properties of Warm Mix Asphalt Technologies (Award Anticipated in 2008)
NCHRP Project 10-75, Evaluation of Pavement Type Selection Processes Including Alternate Design/Alternate Bidding (Award Anticipated in 2008)
Process to Ballot Guide
TheManual of Practice was balloted and approved in April, 2007 by the JTCoP and subsequently modified by the NCHRP 1-40 contractor to address comments found persuasive by the JTCoP as a result of the ballot. The resulting document entitled, AASHTO Interim Mechanistic-Empirical Pavement Design Guide Manual of Practice is now being balloted through both the Highway Subcommittee on Design and the Highway Subcommittee on Materials for consideration as an AASHTO publication.
If approved, the JTCoP will review any comments and/or negatives resulting from the concurrent subcommittee ballots to determine if they are persuasive enough to modify the proposed Manual of Practice further before it is sent on to the Standing Committee on Highways (SCOH) for approval. The proposed MEPDG Local Calibration Guide will also be balloted and reviewed in a similar process when it is completed later this year.
Links to the Manual of Practice have been provided in the ballot website as well as a Bibliography which has been provided to give you a better understanding of completed, ongoing and pending research efforts that will be used to enhance the guide in the future. The JTCoP is requesting that the ballot be open for thirty (30) days with a closing date of July 9th, 2007. This will provide the JTCoP sufficient time to review and address comments and negatives before forwarding the document to SCOH for consideration.
Contact Information
The JTCoP officers listed below can be contacted if you have any questions or need assistance in any way as you consider this ballot.
Dan Dawood (Chair) (717) 878-4246, HYPERLINK "mailto:ddawood@state.pa.us" ddawood@state.pa.us
Linda Pierce (Vice Chair) (360) 709-5470, HYPERLINK "mailto:pierceL@wsdot.wa.gov" pierceL@wsdot.wa.gov
Pete Stephanos (Secretary) (202) 366-1324, HYPERLINK "mailto:Peter.Stephanos@dot.gov" Peter.Stephanos@dot.gov
Background Information on MEPDG Ballot May 11, 2007
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