Panhandle Engineers Develop New Asphalt Technology
Paving the Way
To most people, asphalt is something they drive on. To engineers and others involved in the material’s design and application, however, asphalt is living matter — complete with its own DNA and characteristics, and subject to modification and improvement. Which explains the excitement of a group of Panhandle engineers who have developed a new asphalt technology that promises to revolutionize the airport pavement industry.
“My wife rolls her eyes when I talk about asphalt … but the airport pavement world is about to change based on what we did in Northwest Florida,” asserts Virgil C. “Lee” Lewis of AVCON Inc., the Niceville engineering/planning firm that in partnership with Dr. Bob Boyer, a former Asphalt Institute engineer and nationally acclaimed asphalt expert, developed the cutting-edge technology.
Commonly called “the Crestview Mix” (CM) because it was first installed at the Bob Sikes Airport in Crestview, Okaloosa County, in 2011, the new asphalt boasts greater strength, durability and rut resistance. But its singular and innovative distinction is its fuel resistance, a quality that resolves a longstanding airport pavement maintenance problem.
As Lewis explains it, asphalt pavements are generally subject to deterioration through exposure to environmental factors such as oxygen, sunlight, temperature and rain — elements that over time cause the binder, or black glue, to degrade. Airport pavements additionally experience the wear and tear of heavy aircraft loads, which cause rutting, pushing/shoving and other damage. Add also frequent spills of jet fuel and sundry oil-based fluids, whose chemical compatibility with the petroleum-based asphalt cause the latter to soften and weaken, furthering the degradation.
Historically, airports have protected against jet fuels and oil-based fluids by applying coal tar sealants to the pavement surface. The problem with coal tar sealants, however, is that they are basically short lived and potentially carcinogenic. Enter CM, a viable and long-lasting alternative.
“Game changer,” “fascinating new development” and “environmentally safe” are phrases variously used to describe the new technology, which — like most innovations — had a long gestation period, this one in Dr. Boyer’s mind. Bringing the idea to fruition required not only his expertise, but also the collaboration and calculated risk-taking of AVCON, what is now the Florida Department of Economic Opportunity (FDEO) and the airport leadership. Not to mention certain evolutions in the overall asphalt industry that figuratively paved the way for the new technology, most notably the development of higher-grade asphalt binders.
Per Lewis and Boyer, fuel-resistant asphalt was first developed in the Netherlands in the 1990s and variously applied at airports overseas and in this country, including LaGuardia and Boston-Logan. These projects, however — in layman’s terms — utilized “souped-up” mixes that were more or less custom made and didn’t necessarily employ standard ingredients, making their duplication difficult and their specifications proprietary. Also, the intended and primary function of these applications was mostly for rut-resistance.
Boyer’s ingenuity lies in taking the existing technology and tweaking it, so that he developed a standardized system that is highly duplicable, uses off-the-shelf ingredients and is non-proprietary and fuel-resistance specific.
“Everything is within current specifications; it’s just the method that’s been changed,” Boyer says.
Consider asphalt’s three components: the binder, aggregate (rocks and sand) and air voids, or air suspended in the mix. Boyer’s achievement was to take the highest grade of polymer-modified binder on the market, currently PG82-22 (meaning it performs well at 82 to minus 22 degrees Celsius) and designing a mix of smaller-sized aggregate — and equally significant — lower air voids. (The less air in the mix, the more impermeable and fuel resistant the material.)
He also specified higher field compaction to increase the asphalt’s density and impermeability.
Altogether, the highly-modified polymer, smaller aggregate and reduced air voids, in combination with the higher density, give CM its fuel resistance.
“First is the highly-modified binder material,” Boyer enumerates the key components. “Second, you design it at 2.5 percent air voids rather than at 4 percent. And third, you construct it to 4 percent air voids in the field instead of 6 percent. All three things together give you a system that’s fuel resistant. If all three aren’t there, it breaks the link in the chain.”
The latter is a point Boyer and Lewis can’t emphasize enough: CM “is a system, not a product.” If any step is missed or mishandled, the result is compromised.
When Bob Sikes Airport decided to rehab its north apron and AVCON proposed using the new technology, it represented a risk, as its performance was unproven and the specification unformalized. The Federal Aviation Agency (FAA), Florida Department of Transportation and other state/federal agencies won’t fund projects employing unformalized specifications, or those not formally proven viable and adopted by them.
Fortunately, the Florida Department of Economic Opportunity didn’t have such a requirement and was willing to fund the project, based on Lewis and Boyer’s representations, as AVCON and the airport leadership were willing to trust CM’s performance based on Boyer’s reputation and expertise.
The concern then was whether the desired field compaction could be achieved before the hot-mixed asphalt cooled, as CM is stiffer and less workable.
“It’s possible, if you roll across it too many times, you break down the aggregate and start losing density,” explains John Collins, another AVCON engineer. “Finding that fine line of how many times to roll across this material to get the optimum density was a challenge.”
Amazingly, the desired density was achieved relatively easily, Collins says.
CM has since been installed at Jacksonville’s Herlong Airport, earned recognition from the American Association of Airport Executives Southeast Chapter and drawn interest from airports across the Southeast. Moreover, the FAA, Department of Defense and other funding agencies are considering adoption of the specification.
Tracy Stage, deputy director of Okaloosa County airports, says CM’s performance at Bob Sikes Airport has exceeded expectations. He considers CM an engineering advancement that will change how airport aprons are rehabilitated and constructed.
“As the industry takes notice and interest builds, I believe that sooner rather than later, CM will be a funding agency preferred method,” Stage says.