DeWitt Spain Airport Applies Sealcoat to Preserve New Runway Asphalt

A recent runway resurfacing project at General DeWitt Spain Airport (M01) is proving that sealcoats are not just for maintenance anymore. The general aviation airport, located minutes from downtown Memphis, TN, opted to apply a protective sealcoat over brand new asphalt to help preserve the Airport Authority’s investment and increase the life of its new pavement. 

When engineers began planning the $1.48 million rehab, no one expected it to be a leading-edge project. Brian Tenkhoff, manager of Engineering and Construction for the Memphis-Shelby County Airport Authority, explains that typical factors—aging pavement and a maxed-out surface life—prompted the need to rehab the airport’s sole runway. But a relatively new trend—applying a P608 sealcoat over the freshly laid asphalt—placed the small airport squarely on trend and is providing a valuable test case for its big sister, Memphis International.

Tenkhoff describes General DeWitt Spain as a very busy airport with a prominent flight school and about 100 based aircraft, including a few jets. Typically, the single-runway facility logs about 57,000 operations per year.  

In 2015, the Pavement Condition Index for Runway 17-35 was 68, signaling the need for more service to keep it in shape. There were no major failures, explains Tenkhoff, but the surface was nearing the end of its useful life.

The project team prescribed a relatively standard mill-and-overlay approach, taking 2 inches of asphalt off the top, and then adding 3 inches of new asphalt to create a fresh surface and address minor pavement grade issues. That’s where engineers took the process one step further and specified a protective sealcoat, a practice recently approved by the FAA and Department of Defense as a viable option to preserve all airfield pavements.

Crews sealcoated DeWitt Spain’s 3,799-foot runway in three days, and the resurfaced runway reopened for traffic in October 2020.

One Thing Leads to Another

The airport added grooves to the runway, per a recommendation from the Tennessee Department of Transportation. Grooves facilitate forced water escape when aircraft roll over the pavement surface by providing increased contact between aircraft tires and the pavement surface for better braking and directional control during rainy and icy conditions. Although a grooved runway is an unusual feature for a general aviation airport, it is especially beneficial for the King Airs and Learjet 35s that regularly use DeWitt Spain. Tenkhoff notes that receiving an attractive price for the grooving procedure helped the Airport Authority decide to include it in the work scope.

Engineers specified a P608 sealcoat to slow oxidation, aging and everyday wear and tear on the grooved pavement. Crews applied a quick-cure product from Asphalt Systems Inc. to the pavement before the final markings were applied—and before a single airplane touched down on the new surface.

“It isn’t common,” Tenkhoff remarks. “But in our designers’ past experience, they were seeing that laying a sealcoat in the early phases of the pavement was providing a significant increase in its life.”

Gregory Cline, P.E., a civil engineer and former pavements expert for the FAA and Department of Defense, completely agrees. After beginning his career studying surface treatments in the early 1980s, Cline spent nearly 40 years focusing on airfield pavement before retiring in 2019 as the FAA subject matter expert on the topic. 

“Up until 2011, surface treatments were not allowed on airfield pavements,” Cline reflects.

Naturally, DeWitt Spain had full support from all governing bodies before applying a protective sealcoat during its recent project. Thomas Henderson, P.E., engineer manager/vice president with Neel-Schaffer, notes that test patches helped the project team understand how the product would work, look and feel before applying it to the entire runway. He says it was important to monitor timing and other details during the application process to help guide future runway projects.

With the project complete, the designer and airport plan to carefully monitor how the sealcoat performs. “Ultimately, this will determine if our other airports apply this as well,” says Tenkhoff.

Gaining Traction

Joe LaRusso, technical director for Asphalt Systems Inc., estimates that 60% of the total lifespan of asphalt degrades within the first couple years, and the remaining 40% expires over the next 18 years. Cline, who concurs with LaRusso’s lifespan estimates, notes that asphalt pavement doesn’t necessarily look bad in its first two years, in fact the pavement condition index typically remains close to 100. But oxidation attacks the asphalt binder causing it to break down, and ultraviolet rays from the sun cause further breakdown of the asphalt with virtually no appearance of distress or loss of life for the first couple years. The damage that has been caused, however, cannot be reversed and results in the estimated 60% loss of life. Throughout the lifespan, 70% to 90% of asphalt airfield pavement deterioration and failure are the result of exposure to the environment and degradation of the asphalt (oxidation).

“Roads don’t have numbers like this,” Cline comments, adding that roadway pavements cannot be compared in any way to their airport counterparts, where designs of asphalt surfaces have to withstand much heavier wheel loads and non-channelized traffic resulting with a pavement surface more susceptible to environmental degradation.

Cline and LaRusso both agree that preserving pavement life up front during the original installation is a huge gain.

“The FAA and DoD realize this now, too,” says John Hunter, aviation lead with Asphalt Systems Inc. “It’s a cost savings for the airport to do this sealcoat right at construction and not wait four or five years when the environmental factors have already taken their toll on the pavement.”

Cline identifies three key turning points for sealcoats on runways:

• In 2011, Naval Facilities Engineering Command released an evaluation that provided the support to allow P608 type sealcoating on all airfield pavements
• In 2014, FAA created and published specifications for P608
• In 2018, FAA included a second product called P608-R (which, unlike the original, is not water-based) in Advisory Circular 150/5370-10H

He notes that the product has been allowed for use on new pavement since 2014, but the practice was not promoted because there wasn’t enough information to ensure that friction loss would not be a problem. The note in the 2018 advisory circular, however, prompted more engineers and airports to consider using it. 

Cline further explains that once regulators understood the preventive nature of sealcoats, funding approvals eventually followed. Previously, the product had only been considered and funded for maintenance purposes. “We did review a lot of pavements that already had this—smaller ones and a couple that had been approved locally,” he recalls. “The airports avoided the FAA for funding and were paying for the sealcoat themselves. We had a lot of data.”

By the mid-2000s, nearly 200 airports had applied sealcoats in several locations (taxiways, runways, airstrips) during self-funded projects, adds Cline. Oregon and Utah were two of five states that amassed data about how various sealcoat products helped preserve pavement.

 LaRusso notes that the information states collected has proved useful as the FAA moves toward a 40-year hot mix, in an effort to extend pavement life even longer. “They believe that it’s possible, and it is—if airports start a pavement preservation program immediately at construction,” he specifies.

Cline agrees. “We had a goal to increase pavement life (technically and for funding purposes) to 40 years through maintenance, different materials, etc. And that program continues with ongoing research by both FAA and DoD, agencies’ policy and technical changes, and product improvement and development, which is what you see with ASI’s [Asphalt System Inc.’s] P608 product.”

Memphis Moves Ahead 

As a single-runway airport, DeWitt Spain had to close briefly to facilitate its pavement rehab: eight days for mill-and-overlay work, four days for grooving, three days for sealcoating and three days for markings.

“No one ever likes to shut down their airport for nearly two weeks,” says Tenkhoff, noting that traffic was directed to Charles W. Baker Airport, a nearby general aviation airport also owned and operated by Memphis-Shelby County Airport Authority.

Because the project included a sealcoat, markings were more of a logistical issue than usual. “You have to put a percentage of paint down so you can open up the runway, then turn around, close it and sealcoat it,” he explains. “Then, you can put sealcoat around the markings or cover them up and put full markings on top of the coating.”

Crews at DeWitt Spain chose to spray the coating on most of the runway and brush it by hand around markings to avoid having to repaint them. Hunter notes that this involved some back and forth, but ultimately worked out in the end.

Cline explains that a P608 sealcoat don’t “soften” asphalt as other seals tend to do, but actually creates a hardened binding surface that provides protection from the environment and keeps the essential asphalt properties in the pavement—which is opposite of untreated asphalt. “People like me are finally backing off the old way of thinking,” he reflects. “The early use of sealcoats are okay as long as you know what you’re doing.”

Hunter credits the state of Tennessee for its forward-thinking attitude toward new pavement strategies. “This project really became about prevention, not maintenance,” he observes. “It was well-organized and thought out—the construction seal was an intentional effort to extend the service life and protect their new investment.”

And it’s much cheaper than subsequent maintenance,
stresses Cline. Nodding in agreement, Tenkhoff notes that he looks forward to monitoring the sealcoat’s performance and possibly applying lessons learned at DeWitt Spain to other pavements owned and operated by the Memphis-Shelby County Airport Authority.

“We were fortunate the project went well,” he concludes. “Over time, the top layer of asphalt dries out, and this sealcoat will protect the pavement. We are happy to be a part of this next-generation type of innovation for airports around the nation.”