The following article is republished from Airport Improvement Magazine with permission. This permission is not an endorsement by Airport Improvement Magazine of the opinions expressed on this website or the content therein.
Coal Tar Free America has covered this topic before in the following articles:
- Landing on the Truth about the FAA and Coal Tar Sealers
- Another Coal Tar Sealer Extinction Factor: Fuel Resistant Alternatives
Bob Sikes Airport (CEW), in Crestview, FL, became a pavement pioneer when it used a new fuel-resistant asphalt for a $1.8 million apron project it completed last December. According to the product’s developers, P-401-FR – or the “Crestview Mix,” as it’s now known – staves off pavement degradation by providing resistance to aircraft fuels, hydraulic fluids and petroleum oils. The new asphalt mix has also demonstrated high tolerance to rutting and shoving.
In May, the American Association of Airport Executives Southeast Chapter recognized the importance of the project by naming it the 2012 General Aviation Airfield Project of the Year. In addition, airport officials predict that the project will change future airfield asphalt specifications for the FAA and Department of Defense.
Not Completely New
Okaloosa County, which owns and operates CEW, contracted AVCON to design, build and administer an apron project on the northernmost portion of the airport’s primary general aviation ramp. The rehabilitation included roughly 20,500 square yards of apron pavement – about 16,800 square yards of mill and overlay and about 3,700 square yards of new Portland cement pavement.
In addition to serving CEW on previous infrastructure and airfield improvements, AVCON was one of the first airport design firms to regularly implement the FAA’s P-401-SP Superpave specification. “It (the CEW project) was a pretty typical airport pavement project,” recalls Lee Lewis, P.E., AVCON project manager. “There really wasn’t anything unusual about it when we got started.”
Then Lewis consulted Dr. Bob Boyer, P.E., a leading authority on airport asphalt. Boyer made the game-changing suggestion of applying a fuel-resistant asphalt he’d been researching for years. The technology was developed in the Netherlands in the mid-1990s and used there on a trial basis, he explained, but had evolved in the years since. More recently, it had been tested at Boston Logan International and LaGuardia International, among other areas.
Boyer, who is also a former Asphalt Institute Regional Engineer and lead contributor to the FAA’s Superpave specification, advised Lewis that CEW’s good-size apron would be an opportune place to formalize a draft fuel-resistant specification.
“Crestview was perfect because of the variety of activities involving a wide range of airplanes,” Lewis relates. CEW’s apron serves a variety of military airframes that come to the airport for major aircraft maintenance and modifications.
Calculating the Risks
At the beginning of the project, airport officials questioned the design team about the risks associated with using a new design mix standard. “It became evident pretty quickly that the risks were minimal, if any,” Lewis recalls.
“This is not a brand-new product,” he emphasizes. “This is not an untried, unproven material. Asphalt technology has come a long way. We’re using a performance-grade asphalt binder. A better binder is going to give you a better pavement. You know what you’re getting.”
Having Boyer involved with the project further minimized the perceived risk. Okaloosa County Airports Deputy Director Tracy Stage describes him as the “grandfather of asphalt.”
“The industry relies on his experience and understanding of asphalt technology,” Lewis explains, noting that the unformalized design mix standard wouldn’t have been used without Boyer’s involvement or without Okaloosa County or the State of Florida having faith in the process.
Boyer understood the airport’s initial questions. “Any time you try new technology on a full-scale basis, rather than in a laboratory, you run a risk of things going wrong,” he relates.
That said, he had ample confidence that the P-401-FR mix was going to work, because it had already been used overseas. There, however, it had been developed for rut resistance, not fuel resistance. But when a test area was applied to an area at Boston Logan International where asphalt was being replaced every year, technicians observed rut and fuel resistance.
Boyer acknowledges there was risk for CEW, but characterizes it as minimal, because he and AVCON were putting together proven technologies from different applications to form new technology. “Many times that’s where new products come from – a different application of old technology,” he explains.
According to Lewis, the biggest challenge of the P-401-FR Crestview Mix was working with its stiffer consistency – specifically, putting it on the ground and getting the necessary compaction in the pavement before the asphalt cooled.
“We knew it would be a challenge to achieve 95 percent field densities in a stiffer mix prior to the pavement cooling less than 180 degrees,” he relates.
Heavy-duty rollers were on standby, but were never needed because the mix went down better than anticipated, he adds.
Making the Mix
Boyer describes the mix design as a system vs. a product. First, a mix is developed in the laboratory. Crestview Mix is designed for laboratory air voids of 2.5% for the plant-produced material criteria.
“We wanted it to be highly impermeable so that fuel would not get in,” Boyer explains.
In the field, the mix is compacted to a target of 4% in-place air voids, meaning it has 96% maximum theoretical density. Because P-401-FR is a highly rut-resistant mixture, further compaction under the weight of aircraft traffic isn’t expected to be an issue. According to Boyer, the pavement may densify less than 1% over the pavement’s lifetime, but most likely less than 0.5%.
The glue or asphalt binder that holds the aggregate together is highly modified performance-grade PG 82-22, so it also adds rut and fuel resistance. “We put a lot of polymer in it,” Boyer notes.
The “system,” he explains, is all of those things working together.
“You don’t just select this specification and give it to the contractor and hope it all works out well,” Lewis adds. “It takes a little bit more attention. We very carefully selected a finer gradation of aggregate. We also made sure that what’s coming out of the plant is the quality of the mix that we’re expecting, making sure the air voids are in their target range.”
The installation, or the compaction process, was also crucial. “If any one of those links in the chain is substandard, your result could be substandard,” he notes. The existing asphalt pavement was milled about 1.5 inches.
Cost Considerations
AVCON submitted two bids for the CEW apron project – a base bid with P-401-SP and an alternate using P-401-FR. Either could have been installed by the same local paving contractors and tested by the same local testing firms using the same testing processes. Although the per-ton price of installed P-401-FR was 24% higher than P-401-SP, the overall project cost increased by 8%, notes Lewis.
Because the project was wholly funded by the state of Florida, Stage coordinated with the governor’s office, the State of Florida Aviation Office and Florida’s Department of Transportation (FDOT District 3) to secure approval for the new specification, which exceeds the state standard.
“The benefits far outweigh the costs,” he explains, adding that the life expectancy for fuel-resistant asphalt is much higher than for P-401-SP.
“There’s no doubt that this is going to be a more durable, long-lasting pavement,” Lewis agrees. “The fact that it is fuel- and rut-resistant means there’s going to be less maintenance on the pavement, and the better asphalt binder increases the lifespan of the pavement.”
Lewis predicts that fuel-resistant asphalt will continue to cost 20% to 25% more per ton than standard hot mix asphalt until the production and distribution of its binder material becomes more widespread. Despite the per-ton price difference, overall project costs should remain only 8% higher, he adds. Once the binder is used more, he expects the cost to come down.
A New Standard?
“I would highly recommend the P-401-FR Crestview Mix to any other aviation-related facility that’s looking to build or rehab an apron,” says Stage. “This is cutting-edge stuff that can change how airport aprons are constructed in the future. It’s huge.”
Even before CEW won the Airfield Project of the Year award, Stage had already begun receiving requests for the design specs from other airports.
In addition, Boyer submitted the P-401-FR Crestview Mix specification for the Unified Facilities Guide Specifications, which lists Department of Defense mandates for all U.S. military services. And he anticipates its adoption later this year. Adoption by the FAA may take one to four additional years, he notes, though the FAA has announced it would adopt the Unified Facilities Guide Specifications.
“It’s a matter of the bureaucracy catching up with the paperwork,” he concludes.
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A Cloudy Future for Coal Tar
Unlike the new Crestview Mix, standard asphalt often needs extra protection from aircraft fuels and oils that soften and rapidly deteriorate airfield pavement. Coal tar sealant, the standard fix at airports, resists such fluids because it has a different origin than asphalt. It also, however, has a different coefficient of thermal expansion than asphalt, which means the two materials expand and contract at different rates. This causes the coal tar to crack, which allows fuel and oils to seep through.
In addition to its functional shortcomings, coal tar also contains polycyclic aromatic hydrocarbons, compounds identified by the Environmental Protection Agency as “probable human carcinogens” and toxic to aquatic life. As such, local and state governments have begun banning coal tar sealants and similar federal restrictions may follow.
In March, Congressman Lloyd Doggett (D-Austin) introduced the Coal Tar Sealants Reduction Act of 2012 in the House of Representatives. Doggett wants to amend the Toxic Substances Control Act to prohibit the manufacture, processing, distribution in commerce, and use of coal tar sealants.
Austin, TX, became the first municipality to ban coal tar sealants in 2006, and other local governments have since followed suit. Washington became the first state to enact similar restrictions last year.
For more information on federal legislation about coal tar sealants, visit www.govtrack.us/congress/bills/112/hr4166/text.
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