PT-1: Long-Life Pavement

Greenroads
Jun 15th, 2011

To Fares Abdo and Wayne Adaska: Got your comments and will take these under consideration for the next version of Greenroads. We agree that there are MANY things to consider for long-life pavement. Our goal with this credit is not to specify all of these but we will make a concerted effort to cover them in the "research" section in the next version as they are quite important. Some items are addressed in other credits (e.g., construction quality is addressed in PR-4 and CA-1) but certainly not all. As with all the credits here, blindly pursuing a credit for points without understanding the greater system is not a wise idea.

FaresA
May 21st, 2011

The following are comments posted by Fares Abdo and Wayne Adaska of the Portland Cement Association and Lionel Lemay of the National Ready Mixed Concerete Association

Steve,
We understand your wish to provide local agencies with simplified method to earn the credit. Keeping in mind the ultimate goal – building more sustainable pavements, our concerns are as follows:
1. The PCC design curve is overly conservative and encourages waste or non-sustainable designs, especially for 1,000,000 EASLs or less. It would be counterproductive to require agencies in charge of local streets and roads to design rigid pavements with a minimum of 7 inches of concrete over 6 inches of base on high-quality subgrade. That is the opposite of being sustainable.
2. Government agencies and the paving industry recognize that sustainable pavements cannot be designed based on thickness solely. Many additional factors have much higher effects on pavement service life including optimized mix design, proper details, and construction and maintenance methods.
As Lionel commented earlier, easy to use thickness design methods (ACI 325.12R and StreetPave computer program to name a couple) are available and commonly used to determine the required thickness of local streets and roads. The availability of these simple thickness design tools should ease concerns with respect to local municipalities being able to earn the points based on this credit. Therefore, we recommend the following:
1.The pavement thickness should meet the requirements as set in the recently issued FHWA Sustainable Highways Self Evaluation Tool, Pilot Test version, Long-Life Pavement credit PD-22, and
2.The guidelines* listed below should be met.

2.1 Materials/Mix Design
2.1.1 For PCC
• High-quality durable aggregates.
• Optimized cementitious materials content and water-cementitious materials ratio to meet appropriate strength and durability requirements approved by the owner in consultation with the designer, contractor and concrete supplier.
• Effective air-void system in freeze-thaw areas.
2.1.2 For HMA
• Minimize potential for aggregate segregation during production.
• Fatigue resistant lower layer.
• Fatigue and rut resistant intermediate layer.
• Rut resistant surface layer.

2.2 Other Design Details
2.2.1 For PCC
• Appropriate subbase (if required).
• Appropriate joint spacing to control crack location (as required).
• High quality joint sealant (if used).
• Corrosion resistant dowel bars (if used).
2.2.2 For HMA
• Strong pavement foundation.
• Need for subsequent overlays during the design period to maintain functional serviceability.

2.3 Construction Practices
2.3.1 For PCC
• Uniform production, delivery,
placement, and consolidation.
• Effective placement of embedded steel.
• Effective finishing, texturing, and curing.
• Minimal handwork.
•Timely and adequate curing.
•Timely joint sawing (when used).
2.3.2 For HMA
• Maintaining quality control during mixture production and placement.
• Obtain adequate bond between HMA lifts.
• Obtain adequate density in all HMA layers.
• Minimize potential of temperature differential during mix transport and placement.

2.4 Maintenance
2.4.1 For PCC
• Provide timely maintenance – joint sealing (when used), surface texturing (when used), and localized repairs.
2.4.2 For HMA
• Provide timely maintenance – Renewal of surface layer, crack sealing, and localized repairs.

*Based on excerpts from an independent consultant’s report prepared for the Portland Cement Association

LionelL
May 19th, 2011

To SteveM: After further review of Figure PT-1.1, and the FHWA Sustainable Highways Self-Evaluation tool that recently removed any reference to a simple graph for thickness design, I would like to modify my comment to PT-1 submitted on April 28, 2011. At one point you indicated to me that you wanted a simple graph because some jurisdictions don’t conduct pavement designs but in fact only rely on typical details or standard designs they’ve used in the past. This concerns me, especially for streets and local roads. Since they don’t do rational designs, they might in fact use Figure PT-1 for thickness design of concrete pavements.
I am convinced using Figure PT-1.1 for concrete thickness design would result in significantly over-designed concrete sections. It’s hard to imagine a low volume street with a 7 inch concrete section. That is simply not sustainable.
However, I do think there are simple rational design methods that could be used by smaller jurisdictions that would not cause hardship. This credit should reward those jurisdictions for undergoing some form of rational design for their pavements. Therefore, I would like to amend my proposed wording for this credit as follows:
Goal

Minimize life cycle costs by promoting design of long-lasting pavement structures.
Design the pavement using MEPDG design procedures, AASHTO 93 design procedures or other rational design method* to demonstrate a minimum 40-year service life for highway pavements and 30-year service life for streets and local roads under the predicted traffic loading. Do not include shoulders, medians, sidewalks and other paved areas.
* Other rational design methods are those that calculate service life of a pavement based on sound mechanistic design principals taking into account traffic loading and material properties (pavement and base materials). Examples include:
1. Guide for Design of Jointed Concrete Pavements for Streets and Local Roads (ACI 325.12R-02), American Concrete Institute.
1. StreetPave, American Concrete Pavement Association.

OTHER NOTES:
Steve:
There are significantly more influences on pavement service life than pavement thickness that should also be addressed in this section. For example, mix design characteristics, construction methods, and maintenance all have a role in pavement life and there should be some reference to these items. I intend to provide more input on this soon.

Greenroads
May 10th, 2011

To LionelL: We tend to think the "before resurfacing" portion of your #2 is overly restrictive. We would just say "40-year design life."

Greenroads
May 10th, 2011

To FaresA and LionelL: We wrote the pilot version for the FHWA version and you can expect Version 2.0 of Greenroads to have the OR statement about using an approved design method. The figure to which you refer is likely to remain in Greenroads. This is because we see a substantial level of interest from local owner agencies (i.e., Cities and Counties) that are not likely to own or have the expertise to use something like the MEPDG or even the AASHTO method. Many pavements at this level come from standard plans or are chosen based on a table or other non-technical design method. While the origins of such tables/plans may come from widely accepted design procedures the time/expertise needed to carry out a full-fledged design is not likely at this level. So, if we eliminated the graph we feel we would be effectively barring these organizations from considering long-life pavement as a viable sustainability best practice. That would be unfortunate since this is one of the most impactful things a project can do.

FaresA
May 5th, 2011

The following comments are submitted by Wayne Adaska and Fares Abdo of the Portland Cement Association.

The Pilot Version of the Federal Highway Administration (FHWA) Sustainable Highways Self Evaluation Tool was recently released and is available for viewing on the website www.sustainabilityhighways.org. This Tool was primarily developed by the same developers of the Greenroads manual with many of the same categories included. This Pilot Version of the FHWA Tool represents a significant revision to the FHWA Beta Tool released in the Fall of 2010. One major modification was the simplification of credits and scoring. We believe this is a very positive change and commend FHWA for taking this approach. Our comment has to do with a particular Project Requirement in the FHWA Tool that relates to the Greenroads manual under PT-1 Long-Life Pavement. The FHWA Tool has eliminated the earlier version requirement that included a figure for determining minimum thicknesses for asphalt and concrete pavements based on the number of lifetime ESALs. They also expanded the requirement for pavement design to include the 1993 AASHTO Design of Pavement Structures manual or the AASHTO MEPDG – 1 Mechanistic – Empirical Pavement Design Guide. Both these changes are a vast improvement and we would recommend they be incorporated into the Greenroads manual under PT-1 Long-Life Pavement. Greenroads has received several comments in the past regarding technical issues and the prescriptive method associated with Figure PT-1.1 as well as the need to consider using the MEPDG design methodology. In addition to the technical concerns with Figure PT-1.1, there is a real danger this figure will be misused in practice. Our question is, are you planning to update PT-1 to reflect the requirements listed under PD-22 of FHWA Tool, Pilot Test version? Doing so would require deleting the requirement based on Figure PT-1.1 and all the details, examples and documentation pertaining to this figure.

LionelL
Apr 28th, 2011

a. This seems too prescriptive in my opinion. I suggest including an option for a performance path. Use MEPDG software to predict service life of the proposed design. Provide points for service life prediction of 30 years without the need for resurfacing. This is a progressive approach which is consistent with the Greenroads rating system. MEPDG is the design methodology of the future, it would be a shame to exclude it from the standard as an option at least.

I suggest you modify the language as follows:

Goal

Minimize life cycle costs by promoting design of long-lasting pavement structures.

Requirements - Meet one of the following:

1. Design at least 75% of the total new or reconstructed pavement surface area for regularly trafficked lanes of pavement to meet long-life pavement design criteria as described in Figure PT-1.1 (see credit PDF). Compute the total surface area of all trafficked lanes and show that 75% minimum of that area is designed for long-life. Do not include shoulders, medians, sidewalks and other paved areas in the computation.

2. Design the pavement using MEPDG design procedures to demonstrate a minimum 30-year service life before resurfacing. Do not include shoulders, medians, sidewalks and other paved areas in the computation.