Reducing Reflective Cracking

While construction deadlines limit mat installation, runway project should provide quantifiable comparison of sections with and without TruPave.

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Work on rehabilitating Fort Lauderdale Executive Airport's Runway 8-26 was recently completed, and time will tell whether or not sections constructed with Owens Corning's TruPave engineered mat will eliminate or reduce reflective cracking and extend the life of the new surface. The main east/west runway was last resurfaced in 1978 and is an integral part of the airport's operation, which serves 225,000 aircraft arrivals/departures annually, making it one of the busiest General Aviation airports in the nation.

The 100-foot-wide, 6,000-foot-long runway was shut down for 10 days to accommodate the milling and paving operations. Also, the entire airport was closed for a weekend to complete work on an intersection with the airport's other runway.

Weakley Asphalt Paving of Weston, FL was primary contractor on the $4+ million rehabilitation project, with Kimley-Horn and Associates providing the engineering support, and East Coast Milling handling the milling of the runway, intersections and taxiways.

Using a Roadtec RX-60C milling machine, East Coast stripped two to three inches off the runway's surface, as well as correcting the grade in the process, in preparation for a new leveling course.

Weakley then applied a 2- to 8-inch leveling course using a Caterpillar AP 900B paver and a pair of Caterpillar CB 534D vibratory rollers to compact the P 401 mix design.

Initially, 70,000 square yards of TruPave engineered mat was going to be installed over the leveling course prior to the final surface course application, but equipment problems and weather conditions limited installation to approximately 20 percent of the runway in order to maintain construction deadlines.

"We were disappointed that we were unable to install the mat on the entire runway," says David Bardt, project engineer. "Our primary interest in using this particular mat was the moisture barrier qualities it would provide and the fact that it would help reduce reflective cracking. The (mat) installer was having some equipment problems, and we had to make a decision to forego completing the installation in order to complete paving and reopen the runway on schedule. It will be interesting to see how the section where the mat was installed holds up compared to the rest of the runway."

Mat benefits

TruPave engineered paving mat delays reflective cracking and provides a superior moisture barrier. TruPave is a non-woven fiber glass/polyester hybrid interlayment designed to withstand higher hot mix asphalt temperatures (up to 495 degrees F), providing a continuous, non-deforming water-resistant barrier. The mat will not melt or shrink when it comes in contact with high-temperature asphalt mixes. The interlayment is also designed not to shrink or become brittle with age, and the mat is millable and can be recycled in mix designs that allow a certain percentage of RAP content.

The engineered mat is designed to be installed over a hot asphalt tack coat, like an AC-20, 64-22 or 60-80 penetration grade, which provides the moisture barrier properties of an interlayment installation. Higher summertime temperatures may call for a higher viscosity asphalt tack, like an AC-30, PG 67-22 or 40-60. Emulsion or cutbacks cannot be used for installation, but an emulsion can be used on top of the engineered mat for a chip seal, surface dressings, and microsurfacing or slurry seal application. American Sealing and Fabric of Palm Coast, FL installed the TruPave mat at the airport.

The fact that TruPave can be recycled seemed appropriate for the Fort Lauderdale project, considering that the milled asphalt was used to create access security roadways at the airport and the new HMA used to resurface the runway contained up to 30 percent RAP.

With the leveling course complete, Weakly applied a 2-inch surface course, laying down approximately 28,000 tons of asphalt to complete the runway project.