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Atkins-led rehabilitation of St. Lucie County International Airport taxiways benefits from the use of cold in-place recycled asphalt - August 1, 2012

Tampa, FL — All airport runways and taxiways eventually need resurfacing and rehabilitation. And in today’s age of resource cutbacks, time and budget constraints, and environmental sensitivity, American airport managers are looking for sustainable, affordable, and efficient ways to keep airport pavement in good condition. That’s why Atkins is pleased to report that its client, St. Lucie County International Airport of Fort Pierce, Florida has gained noteworthy benefits from an innovative solution for rehabilitating several of its key taxiways: the process known as cold in-place recycling (CIR).

Traditional methods for rehabilitating asphalt pavement are limited to either milling and overlaying, or full-depth reconstruction. The mill-and-overlay approach typically involves removing and replacing existing asphalt with new bituminous material hauled in from another location. While the mill-and-overlay process is effective—and cheaper than full-depth pavement reconstruction—recent industry developments have yielded more cost-effective and environmentally friendly solutions; such as CIR, a process that efficiently recycles and reuses existing bituminous paving material.

The CIR process starts with variable-depth milling of existing asphalt, which is then blended with a new binder and/or additional virgin aggregate. The new pavement is then laid down and compacted to the desired grade, slope, and profile; and the entire process is accomplished with a single-pass equipment train.

CIR’s range of benefits includes reduced environmental impact, improved time savings, increased public acceptance, and significant cost savings. SLCIA gained many of these benefits from the recent Atkins-directed rehabilitation of its Taxiways A and B—one of the first uses of CIR on airfield pavement in Florida.

The taxiway rehabilitation project kicked off in October 2011 and wrapped up in June 2012.

“Compared to conventional hot-mixed asphalt, CIR is a significantly more environmentally friendly pavement rehabilitation process,” said Atkins group manager Craig Sucich, PE. “For example, no heat is applied to the asphalt during the CIR process—and there’s much less transportation of milled and new asphalt material. So only minimal amounts of noxious fumes and greenhouse gasses are produced.”

Sucich pointed out that the CIR process reduces material-hauling requirements.

For the SLCIA project, Sucich said he and his team were tasked with engineering the rehabilitation of about 60,000 square yards of asphalt taxiway pavement. Conventional mill-and-overlay techniques would have required 300 to 350 truckloads of milled material to be hauled offsite, and about the same amount of new asphalt to be brought to the site.

“But with CIR,” Sucich noted, “we rehabilitated and re-used more than 90 percent of the pre-existing taxiway asphalt as a 3-inch asphalt base course; only a small quantity of material had to be hauled in or hauled away. And because we recycled most of the existing material, landfill impact was negligible.”

According to Sucich, CIR also saves time.

For the 60,000 square yards of pavement that had to be rehabilitated at SLCIA, at the typical milling rate of 8,000 square yards per day it would have taken about 8 days to mill the designated pavement area. The milled area would then have been overlaid with approximately 10,000 tons of asphalt. At a typical rate of 700 tons per day, it would have taken about 15 days to place new asphalt—which means it would have taken about 23 days to mill and overlay the taxiways using conventional methods.

“CIR, however, yields an average daily construction rate of about 4,500 square yards,” Sucich said. “At SLCIA, the total repavement operation lasted 14 days—a time savings on the construction schedule of 9 days—nearly 40 percent—compared to conventional processes.”

Another aspect of time savings from CIR is the reduced operational impact on a client’s facilities. Because CIR minimizes the time for which a segment of pavement must be closed during construction, some pavement segments can be re-opened the same day the rehabilitation is performed.

Other CIR benefits include:

• Reduced cracking. CIR eliminates or retards reflective cracking by pulverizing the existing asphalt pavement surface, which destroys the crack pattern in the layer being recycled.
• Increased reusability. When it is time to rehabilitate pavement again, CIR can be readily recycled and re-used.
• Broad industry support. Because CIR is environmentally friendly, it is widely supported by local governments and communities.

But for cash-strapped agencies, boards, and commissions, perhaps the greatest benefit of CIR is cost savings.

To rehabilitate Taxiways A and B at SLCIA using conventional methods, it would have cost about $1.1 million to mill 4 inches of asphalt and overlay 3 inches of new hot-mix asphalt. But Sucich said the use of CIR cut that cost in half.

“For SLCIA,” noted Sucich, “the CIR portion of the taxiway rehabilitation project consisted of recycling and emulsifying 4 inches of existing pavement, and re-laying that material as a 3-inch base course—and it was done for only $550,000. In addition, the excess CIR material was re-used on other portions of the taxiways that were being widened, thus resulting in minimal waste.”

Sucich also pointed out that because CIR uses a much smaller quantity of new asphalt than traditional methods, paving projects can often eliminate the high cost of operating a hot-mix asphalt plant.

Upon project completion, Todd A. Cox, C.M., Airport Manager at SLCIA, expressed satisfaction with the benefits the Airport gained from the CIR process.

“The reality is that project design and implementation have changed significantly in the past few years,” Cox stated. “And it makes no difference the size of the airport. Many airports today are looking for ways to replace aging infrastructure through economically and environmentally sound methods. This project has given us an opportunity to work with regulatory agencies and local partners to showcase how sustainable development can provide a technically feasible, cost-effective, and environmentally sound solution that benefits all stakeholders.”

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