RDU replacing main runway’s crumbling concrete at night and with a sense of urgency

Raleigh-Durham International Airport hopes to build a new main runway in the coming decade, one long enough to accommodate flights to Asia. But in the meantime it needs to make sure the existing runway lasts that long.

The 10,000-foot runway, known as 5L/23R, was built in 1986 and would be nearing the end of its useful life in the next few years anyway. But some of the concrete has already begun to crack and chip off because of a condition known as ASR, or alkali-silica reaction, related to the makeup of the stone used to make it, according to Bill Sandifer, the airport’s chief operating officer.

It’s the same kind of problem that prompted the N.C. Department of Transportation to dig up and replace 11.5 miles of Interstate 40 across the south side of Raleigh a few years ago, Sandifer said. But while a wayward piece of crumbling concrete might ding a car, it could be disastrous for a jet airliner.

“When you start having large fragments of concrete pop up on a runway, they could get ingested into an engine,” Sandifer said. “On takeoff that could be really, really hazardous. So we make sure that doesn’t happen.”

RDU can’t close its main runway for even 24 hours without causing problems for overseas flights and those carrying cargo. The big planes that fly those routes need the 10,000-foot runway; the other runway used by commercial jets at RDU is only 7,500 feet long.

So RDU has identified the sections of concrete that need to be replaced most urgently and hired contractors to do it a bit at a time. Each night that conditions are right, the airport closes 5L/23R, and workers go out about 10 p.m. to break up and remove a 25-by-25-foot slab. They then pour fresh concrete, which must dry and cure in time for the big planes to land on it the following afternoon.

The runway is 40 inches thick, starting with a layer of crushed stone on the bottom, topped by 7 inches of asphalt and 16 inches of concrete on top. Only the 16 inches of concrete is being replaced. Sandifer describes it as a “military-type operation,” done with a sense of urgency.

“They get out there in force with equipment, removing slabs in very big chunks and immediately re-pouring fresh concrete,” he said.

While the main runway is closed, all of RDU’s commercial flights use the 7,500-foot runway, closest to the terminal occupied by Southwest Airlines. That can require more time to taxi to and from Terminal 2 where all nine other airlines operate.

RDU began the slab replacement in April and will knock off June 30, during the hottest time of the year, then resume Sept. 1 and work through Nov. 30. It plans to do the work on the same schedule next year.

RDU has determined that 120 slabs of concrete need replacing soon; that’s about 5 percent of the 2,500 slabs that make up the runway, Sandifer said. Between now and the end of next year, RDU will almost definitely identify more slabs that need to be replaced, he said, and the work will likely continue, perhaps for as long as the runway is in use.

“We’re doing everything we can do to extend the life of the runway for 10 years,” Sandifer said.

RDU expects to spend $12.56 million to preserve the runway. The new runway will cost an estimated $350 million and will be 1,500 feet longer than the existing one, to ensure that a fully-loaded and fueled plane bound for Asia could safely take off. The amount RDU expects to spend patching the current runway was not available.

Sandifer said he doesn’t expect the Federal Aviation Administration will complete the environmental studies and give its blessing for the runway project until 2022. Construction is expected to take another three years, meaning the earliest planes will begin using the new runway will be 2025, he said.

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Richard Stradling covers transportation for The News & Observer. Planes, trains and automobiles, plus ferries, bicycles, scooters and just plain walking. Also, #census2020. He’s been a reporter or editor for 32 years, including the last 20 at The N&O. 919-829-4739, rstradling@newsobserver.com.