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Cause of collapse revealed Investigators say chloride corrosion in beams at fault
Posted: Thursday May 25, 2000 07:51 PM
CONCORD, N.C. (AP) -- A pedestrian walkway that collapsed at Lowe's Motor Speedway was built with material contaminated with calcium chloride, which corroded the steel beams, investigators said Thursday. The testing lab hired by the speedway to investigate Saturday's collapse found high levels of calcium chloride in the concrete slabs on the 320-foot-long bridge, said Charles Manning of Accident Reconstruction Analysts in Raleigh. Saturday night, an 80-foot section collapsed, spilling fans leaving the raceway onto U.S. 29 seventeen feet below. A total of 107 people were injured; three remained in critical condition on Thursday. The calcium chloride was somehow mixed into grout that a Spartanburg, S.C., company used when it connected the four bridge sections. The grout plugged gaps around steel rods that ran horizontally through the slabs, Manning said. It's unclear how the calcium chloride got in the grout. Industry standards discourage the use of chlorides in prestressed concrete structures because the substance permits rust to form more easily when moisture is present. Chlorides occur when the element chlorine is combined with another element, such as sodium to make sodium chloride, or table salt. "The mix that was used and poured into the plugs obviously carried chloride, and I don't know how it got in there," said Manning. "Somehow it was mixed into the grout. I can't say if the company got some bad bags [of grout], or maybe a supplier gave them a mislabeled bag. I just don't know." Tindall Corp., a family-owned company that supplied the grout used in the bridge, acknowledged the contamination occurred at its Spartanburg facility, but chief executive William Lowndes IV did not know how it occurred. He refused to answer questions after reading a brief statement. "We are diligently investigating how this compound was introduced into the grout material," he said. In the construction trade, calcium chloride is sometimes used as a concrete additive, because it shortens the time it takes for concrete to set up, but it also is known to retain moisture. Manning said it could be difficult to pinpoint exactly how the grout was contaminated because the footbridge was built in 1995. But he said it was unlikely that the chloride was intentionally mixed in. Lowndes said his company is looking into other structures for which it provided concrete and grout, but believed the contamination was limited to the walkway at the speedway. Tests show that a second, four-year-old walkway at the track, also made by Tindall, is not contaminated and can be reopened, Manning said. Track president H.A. "Humpy" Wheeler said he didn't know if the track would use the bridge for Sunday's Coca-Cola 600, which is expected to draw more than 180,000 fans. Fans used the footbridges to cross U.S. 29 from the parking lots to the track. Wheeler said speedway officials would discuss reopening the second walkway with the state Department of Transportation. Now, race fans must use crosswalks to get across U.S. 29. "We just don't know, because the psychological aspect also enters into it," Wheeler said. "But I walked across that bridge yesterday, and it didn't come down." Since both bridges are privately owned, they are not subject to the two-year inspections that state- and federal-owned bridges must undergo. But the state DOT earlier this week ordered all nine remaining privately owned walkways over North Carolina highways to undergo inspections at the soonest opportunity. Manning said a visual inspection could not have detected a possible problem and it's unlikely that anyone could have suspected the corrosion eating away at the inside of the bridge. "I would have bet my life that I never would have found something like this when i inspected the outside of the bridge," Manning said. "Never would it have gotten into my head, and I am a corrosion specialist." Wheeler, who said track engineers checked the foot bridges every year, said the speedway has routinely used Tindall for construction projects at the track and would continue to do so in the future. "We will use Tindall again, and we will use them to rebuild the bridge if we get the right price," Wheeler said.
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