Tag Archives: Rebar

Corrosion – Fatal Impact on Concrete Wall Flaw

A deficiency in the concrete wall construction of the basin at the Gatlinburg Wastewater Treatment Plant led to the basin wall collapsing, killing two employees in April, a report from the state issued Thursday says.

“Walls were cast in a manner that produced a cold joint between the cast wall which fell” and three interior intersecting walls, according to the report from the Tennessee Occupational Safety and Health Administration (TOSHA).

TOSHA announced in early October that it found no safety violations at the plant, and this week released a five-page report that was the basis for that finding. When TOSHA announced in early October there were no safety violations, it didn’t give a probable cause of the basin wall collapse.

The new report does. What its inspectors call a “cold smooth joint” led to leakage of acidic waste across the joint, and “as a result, corroded the rebar splice couplers over a number of years.”

The couplers were not believed to have failed at one time, but gradually over the life of the basin, the report said.

When the findings of no safety violations were announced earlier this month, Veolia spokeswoman Karole Colangelo said, “Although the findings from TOSHA reinforce our emphasis on employee safety, it does not dismiss the fact that two Veolia Water employees perished in this tragic accident, and company employees continue to mourn their deaths.”

“It was assumed the two operators were making adjustments to the effluent flow inside the equalization basin,” the report says. While the men were working, the wall collapsed and fell on the building in which they were working.

The collapse sent about 850,000 gallons of untreated wastewater into the Little Pigeon River and forced the city to pump more untreated water into the river until it could come up with a temporary solution a few days later.

According to the workers’ last journal entry at 5:30 a.m. that day, the basin contained 1.3 million gallons of water and was 85 percent full. The water level was recorded at 25.5 feet. The report says interviews with operators and plant officials show the average water level was 4-8 feet.

The plant is owned by the city but managed by Veolia Water North America Operating Services LLC. Veolia officials told the state inspectors that both Crowder Construction Co., that built the plant and Flynt Engineering Co., that designed it are out of business. The basin was finished in 1996.

TOSHA learned that after the basin was finished in 1996 the north wall had cracks and a lateral displacement/bowing of the wall and walkway. Veolia told the state that buttresses were installed that “corrected” the problems with the wall and walkway.

TOSHA noted that the flow control building where the workers were is still not accessible, but the state says “we have no probable reason to think that access to this area would reveal any additional information that would result in citation being issued to Veolia.”

The report says the contractor used “splicing couplers” instead of dowels, as required in the original drawings, noting that while that was a “deviation” from the design, it was probably not the cause of the collapse. The report did say that “formation of a cold joint resulted in accelerated corrosion of the couplers.”

TOSHA reviewed the original design of the basin and found the design of walls “adequate.”

SOURCE: http://themountainpress.com/view/full_story/16198627/article–Report–Wall-flaw-caused-accident-?instance=main_article_top_stories

Florida’s St. Augustine Beach Pier Corroding

According to St. Johns County officials, the stretch of coastline from south Georgia to Fort Lauderdale is the most corrosive in the nation.

Evidence of the corrosion can be seen on the St. Augustine Beach pier, one that’s 25 years old and nearing the end of its lifespan.

Janice Vose, who spent her time under the pier Tuesday, said she had the best seat on the beach.

“It’s shady. There’s a breeze,” Vose said.

But what she didn’t know was she could have been in danger.

A few months ago, during a routine inspection, an engineering firm found the pier has problems, most visibly the corrosion on the pilings holding it up and cracks in the concrete.

Engineers advised the county to take action, so county officials installed netting under the pier to catch any falling debris and also posted warning and danger signs to be extra safe.

“A small chance, a remote chance that some concrete could spall off of the concrete structure portion due to the rebar rusting and cause a problem, so we put up the signs as a precautionary measure,” said Mike Rubin, St. Johns County director of construction.

Most people walk right under the pier without noticing the signs, but Rubin said it would take a big storm to knock down such a sturdy structure.

“If a failure were to come, it would be when the pier would be under maximum stress during a hurricane event or a big storm or big wave action, and there’d be no one on the pier at that time anyway,” Rubin said.

The 650-foot-long pier is supported by pilings up to 36 inches in diameter.

“Those metal pilings that you’re seeing are actually filled with concrete,” Rubin said. “There’s rebar in the top 10 feet of them, and while the concrete doesn’t really provide a lot of lateral structural strength, the real strength is in the pilings themselves.”

The big question is exactly how much the pilings have decayed over time. Until that’s answered, Vose said she’s staying put.

“I’m in paradise. I feel so grateful,” she said.

The county plans to have the engineering firm take a closer look to evaluate the extent of the damage, and then the board will decide what to do. A new pier is a possibility in St. Augustine’s future, but it would probably be about five years before one could be built.

SOURCE: http://www.news4jax.com/news/28884204/detail.html

Gardiner structurally sound, experts say, after chunk smashes onto road

TORONTO: City crews will be examining sections of the Gardiner Expressway after a 4.5-kilogram chunk of concrete fell onto Lake Shore Blvd. W. earlier this week, hitting a guardrail and ricocheting into the road.

The slab, about four centimetres thick and over a meter long, was sloughed off the bottom of the elevated section, its steel reinforcing bars corroded by road salt.

No cars were hit and no one was injured. Two lanes of westbound traffic just east of Bathurst St. were temporarily closed.

The incident is the fourth in recent memory, but does not mean that drivers should steer clear of Lake Shore, city staff said.

“There really shouldn’t be any concern,” said Mike Laidlaw, Toronto’s acting manager of structures and expressways.

Aside from the dangers inherent in a chunk of concrete weighing almost as much as a bowling ball falling from the sky, the expressway itself is sound, experts say.

“The stuff on the outside, most of it could fall off without affecting the structural integrity,” said R. Doug Hooton, a civil engineering professor at the University of Toronto. “(The overpass) is not in danger of falling.”

Laidlaw said the city will be conducting extra inspections around the area. Toronto is also putting out a call for proposals from engineering firms for a complete inspection within two years.

City crews inspect the Gardiner yearly — “sounding” the concrete for unstable pieces and removing them with a hammer — and conduct visual inspections at least every six months.

“If they do see any areas of concern they’ll look after it immediately,” said Laidlaw.

In January 2007, a piece of concrete about the size of a basketball fell onto Lake Shore near York St. and narrowly missed hitting a car. A small piece fell near Spadina Ave. in February 1999 and near York St. in January 1997.

“It is a concern for anybody underneath of it,” said Laidlaw.

Hooton said the Gardiner was designed before Ontario began salting roads in the winter, so it wasn’t constructed to withstand the salt that seeps through the roadway and into the steel reinforcing bar.

The salt rusts the rebar which then expands, cracking the concrete and pushing the outer layer off. Repair work was done years ago to the road’s drainage system to prevent salt from seeping into the concrete.

“It’s not happening as much as it would have if they hadn’t done those repairs,” said Hooton.

Police said no one reported any damage to a vehicle and there were no injures.

By 3 p.m. Monday, city crews had cleared debris off the road and unblocked all westbound lanes on Lake Shore Blvd.

The incident called to mind a horrific accident in Quebec five years ago. Five people were killed when a 40-year-old Laval overpass fell onto a highway on Sept. 30, 2006, crushing several vehicles.

A year later, a commission report into the accident blamed shoddy workmanship, insufficient oversight and deficient maintenance.

SOURCE: http://www.thestar.com/news/transportation/article/1011934–gardiner-structurally-sound-experts-say-after-chunk-smashes-onto-road?bn=1