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

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.

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