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The Geosynthetic Materials Association (GMA) recently made progress regarding the use of asphalt interlayers on airfield pavement projects funded by the Federal Aviation Administration (FAA). The use of interlayers has been severely restricted for these projects for approximately seven years, based on policy guidance issued by the FAA Airport Engineering Division.
With the assistance of Whitmer & Worrall, on September 29, 2022, GMA met with Bradley Mims, deputy administrator of the FAA. The meeting’s objectives were to present the benefits of geosynthetics related to the sustainability and resilience goals of the Bipartisan Infrastructure Law (BIL) and to discuss issues that have arisen in the past regarding the use of asphalt interlayers on FAA-funded projects. We were successful in both cases, and we received a commitment from Mims to assist with the Airport Engineering Division on the interlayer issues.
With Mims’ help, we secured a meeting on November 15 with Alberto Cruz, Jeffrey Crislip, and Dr. Navneet Garg of the FAA. Cruz is the head of the Airport Engineering Division, Crislip is one of two pavement engineers in the division, and Dr. Garg oversees research at the National Airport Pavement & Materials Research Center, FAA-Airport Technology Research and Development (ATRD) center in Atlantic City, N.J. Crislip addressed the interlayers issue and informed us that the advisory circular covering pavement design has been updated.
The updated advisory circular, version, 5320-6g, allows interlayers to be used at the discretion of the designer. The designer must present and support the expected benefits through a Modification of Standard (MOS) proposal. The current advisory circular can be found at this link: https://www.faa.gov/documentLibrary/media/Advisory_Circular/
150-5320-6G-Pavement-Design.pdf
The MOS is required because asphalt interlayers are not yet included in the FAA standard specification, found in advisory circular 5370-10h. This document can be found at this link: https://www.faa.gov/documentLibrary/media/Advisory_Circular/150-5370-10H.pdf
The need for a MOS will be triggered by the funding program to be used for the project. Projects that do not rely on federal funding may use interlayers (and have in the past) without proposing a MOS. The designer of the project should be aware of the funding programs to be used and proceed accordingly.
Crislip said there is currently a project proposing to use interlayers at South Arkansas Regional Airport in El Dorado, Ark. It was also suggested that the probability for success of an interlayer could be improved by having the designer include provisions in the specifications that support and detail proper installation. These might include the installation of a test strip by the contractor under the supervision of the manufacturer, or some sort of certification program for the installer. GMA’s Interlayer Task Force is currently looking at options for a certified installer program.