Image

Credit: National Asphalt Pavement Association

Warm-mix asphalt design may soon be added to national paving standards.

WHO: National Cooperative Highway Research Program (NCHRP)
PROJECT: Mix Design Practices for Warm-Mix Asphalt (Project 9-43)
TIMELINE: March 2007 – January 2011
NEXT STEP: Adoption into the American Association of State Highway and Transportation Officials (AASHTO) “Superpave” standard

THE LATEST: After nearly four years, NCHRP's Mix Design Practices for Warm-Mix Asphalt project is complete.

Dr. Ramon Bonaquist, chief operating officer of Advanced Asphalt Technologies in Sterlig, Va., developed the recommended practices based on AASHTO's Superpave (Superior Performing Asphalt Pavements) mix design methods. They include design procedures for warm-mix technologies used to lower mixing an and compaction temperatures. The final document, NCHRP Report 691, will be published in June. It will be the basis of a new chapter in the program's 2012 edition of the Mix Design Manual for Hot-Mix Asphalt.

The chapter will be available at the Transportation Research Board's Web site (www.trb.org) this summer. The National Highway Institute will also offer an online training course on warm-mix design in August.

“The culmination of this project will be to ultimately see it as part of the national paving standards,” says Bonaquist. His research has been submitted as a recommended appendix to AASHTO's R35 Standard Practice for Superpave Volumetric Design for Hot-Mix Asphalt.

The document is being reviewed by the AASHTO Subcommittee on Materials' Technical Section for Proportioning Asphalt Mixtures. Chairman Rick Harvey, state materials engineer for Wyoming DOT, expects they will recommend the appendix for final subcommittee vote in the fall. If approved, warm-mix design practices will be added to AASHTO's 2012 Standard Specifications for Transportation Materials and Methods of Sampling and Testing next summer.

Putting mix on the ground

“The evaluation process should have little effect on the progress of implementing the technology,” says Frank Fee, chairman of the Federal Highway Administration's (FHWA) Expert Task Group on Mixture and Construction and technical support manager at NuStar Asphalt Refining in Media, Pa. “Most state agencies have been evaluating warm-mix for several years.”

Fee's group is part of a task force — including state agencies, contractors, academic experts, and researchers — that's testing the proposed design methods. Led by Matthew Corrigan, asphalt pavement engineer for FHWA's Office of Pavement Technology, they will test the recommended practices with aggregates and binders not included in the original research, to simulate warm mixes across the country. Corrigan will conduct some testing through the FHWA's Mobile Asphalt Lab. Based on its results, the task force may recommend further changes to AASHTO.

In the meantime, the practice is gaining momentum. “In some states, warm-mix paving is a normal practice and they have their own specifications,” says Harvey. “The national standard will simply provide a template for best practices going forward.”

To read the original article that appeared in the April 2008 issue, click here.