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Friday, May 26, 2000
Chloride in grout caused walkway to collapse
Police say bridge was built with material contaminated with substance that corroded steel beams
By Jenna Fryer
Associated Press
CONCORD, N.C. - A pedestrian walkway that collapsed at a race track, injuring more than 100 fans, was built with material contaminated by an ingredient found in salt that corroded the steel beams, investigators said Thursday.
The testing lab hired by Lowe's Motor Speedway to investigate the collapse found high levels of calcium chloride in the concrete slabs of the 320-foot-long bridge.
An 80-foot section of the bridge collapsed May 21, spilling fans onto an empty highway 17 feet below. Three of those injured remained in critical condition Thursday.
The chloride was mixed into grout that a company used when it connected the four bridge sections.
The grout plugged gaps around steel rods that ran horizontally through the slabs, said Charles Manning of Accident Reconstruction Analysts in Raleigh.
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.
"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," Manning said.
Tindall Corp., a family-owned company that supplied the grout, acknowledged that the support beams were made at its Spartanburg facility but it didn't know how the contamination occurred.
"We are diligently investigating how this compound was introduced into the grout material," chief executive William Lowndes IV said. He refused to comment further.
Calcium chloride is sometimes used as a concrete additive because it shortens the time it takes for concrete to set, but it also is known to retain moisture.
Industry standards discourage its use in pre-stressed concrete structures because the substance permits rust to form more easily when moisture is present.
Tests also showed that a second, four-year-old walkway at the track, also made by Tindall, is not contaminated and can be reopened, Manning said.
Since both bridges are privately owned, they are not subject to regular inspections.
The state Department of Transportation earlier this week ordered that all nine remaining privately owned walkways over North Carolina highways be inspected.
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.
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