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CONCORD — Concrete grout at the center of a pedestrian bridge that collapsed at Lowe’s Motor Speedway contained high levels of calcium chloride.
Combined with air and water, the chloride rusted the cables in the 80-foot section to the point that they couldn’t support the bridge anymore. The 11 steel cables snapped Saturday night, dumping concrete and more than a hundred people into a pile of rubble on U.S. 29.
Thirty-seven people remain in area hospitals, three in critical condition.
H.A. “Humpy” Wheeler, president of the racetrack’s parent company, Speedway Motorsports, reassured a room of reporters Thursday afternoon that another pedestrian bridge nearby is safe.
“This has obviously been a trying few days for us at Lowe’s Motor Speedway,” Wheeler said.
Speedway Motorsports hired engineering firm Accident Reconstruction Analysis this week to study how part of the pedestrian bridge fell.
The grout — used to fill holes during the bridge’s construction — contained as much as 46 percent chloride. That’s far more than ocean water, said Charles Manning, head of the investigative team. Other areas of the same bridge contained grout with just .02-.04 percent chloride. Chlorides are the most common reason for corrosion of steel in concrete, Manning said.
“When they get eaten up like that, they won’t carry any load,” he said, “and we found they were all eaten up.”
But Manning and others could not explain why chloride was mixed with the concrete grout used to fill holes in parts of the bridge. Tindall Corp of Spartanburg, S.C., installed the concrete slabs in the $1 million bridge.
Sometimes chloride has been used to allow concrete to set quicker in cold weather. But the bridge was built in August 1995.
“This obviously is an isolated instance,” Manning said. “Obviously, I think (Tindall) got some bad material there. It could not possibly occur naturally at that level.”
“This appears to be an isolated incident,” added Tindall CEO William Lowndes III, speaking only briefly before leaving a meeting Thursday at the speedway.
Manning said speedway officials could not have prevented the accident.
“In my opinion, there wasn’t anything the speedway did that could have caused this,” Manning said. “I know everybody tries to blame the speedway for everything.”
Manning said he’s never seen such an unusual amount of corrosion without visible signs during his career of almost 50 years. No signs of corrosion were visible; the cables were entirely encased in concrete.
“I would have put my life (on the line) that I could never find something like this on the inside (and) not have found it on the outside,” Manning said.
The bridge design and the cables themselves were good when the bridge was built, he said.
Emphasizing the racetrack’s safety efforts, Wheeler said that racetrack staff could have done X-rays or chipped out the grout and inspected the cables. But “nobody does those things,” he added.
Wheeler said the second pedestrian bridge is “absolutely, perfectly safe,” but he wasn’t yet sure whether fans could use it Sunday during the Coca-Cola 600.
Wheeler said other areas of the racetrack have Tindall concrete, and the track will rely on the company again.
“We are constantly, constantly, checking everything here in the speedway,” Wheeler said. “There’s some things that don’t look good. After all, this place was built in the 1960s. But it’s safe.”
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