Corrosion threat on Ohio bridge deck discovered

Grout packed into bundles of steel cables that compress the Veterans’ Glass City Skyway’s concrete deck sections together may contain elevated levels of salts that would cause those cables to corrode prematurely, the grout’s manufacturer has warned the Ohio Department of Transportation.

The I-280 bridge over the Maumee River, which opened five years ago, is one of several dozen projects across the United States that used grout made at a Marion, Ohio, plant owned by Sika Corp. U.S. in which excessive chloride compounds, traced to cement the plant bought from an unnamed supplier, have been discovered.

Also potentially affected is the Perry Street bridge in Napoleon, which carries State Rt. 108 over the Maumee and was replaced in 2005, the U.S. 33 bridge over the Ohio River between Pomeroy, Ohio, and Mason, W.Va., and as many as eight other smaller bridges in Ohio. Mike Gramza, the planning and engineering administrator at the transportation department’s district office in Bowling Green, said about 30 projects were affected overall.

Mr. Gramza and a Sika spokesman both said last week they are not yet sure that the particular batches of grout used in the Toledo or Napoleon project contained the elevated chlorides. A company alert identified all grout produced in Marion during an unspecified time that ended in March, 2010, when production there stopped.

In the worst case, they said, chloride presence would not create an imminent — or even short-term — safety hazard on the $273 million bridge built between 2002 and 2007.

But there is the possibility, they said, that as the bridge ages, chloride in the grout could cause the cables — known formally as “post-tensioning tendons” — to corrode and fail sooner than they otherwise would.

Samples will be taken within a few months from the Skyway, Mr. Gramza said, for testing “to see if there is a problem or not.” “It’s not an immediate issue,” he said, “But it could impact the life of the structure.”

More than 3 million pounds of grout from five sources was used on the I-280 bridge to seal ducts through which the post-tensioning strands pass. Those cables, which are distinct from the stay cables that support the bridge deck vertically, compress the bridge’s precast concrete segments against each other and also maintain transverse tension to reinforce the structure.

Grout is a mixture of water, cement, and sand that hardens once mixed. Its purpose in post-tensioning tendons is to protect the steel cables from moisture, road salt, and anything else that would cause them to rust.

Mr. Gramza said the transportation department’s specifications for project materials included an 0.08 percent limit on chlorides in the grout, a normal industry standard. But the suspect grout from Marion, he said, had chloride concentrations as high as 0.5 percent.

Chlorides — the most common of which is sodium chloride, otherwise known as table salt — accelerate the corrosive action of water and oxygen on metals such as steel.

So as long as the grout keeps air or water from reaching the post-tensioning tendons, chlorides’ presence in the grout causes no damage.

But over time, it is likely that tiny cracks will develop in the grout. Any air or water that seeps into it through the post-tensioning tendons’ outer ductwork might eventually reach the cables themselves, delivering the grout’s chlorides — plus any salt already in the water from ice control on the bridge — to the cables and initiating the corrosive chemical reaction that creates rust.

Mr. Gramza said that although grout delivered to the project was tested for strength, it was not tested for chemical composition. The transportation department learned of the problem in “late October or early November,” when it was notified by Sika, he said.

Diana Pisciotta, the Sika Corp. spokesman, agreed that grout is not routinely tested for chloride concentration.

She would not elaborate on how the problem came to Sika’s attention, disclose the source of the cement used at the Marion plant, nor comment on any theories Sika may have about how that cement came to be high in chlorides. But she said the company had been forthright in notifying the grout’s users once it identified where material made in Marion had gone before production halted in 2010.

“We at Sika are not happy that this has happened. We have tried to be proactive in reaching out to people. This really is a situation where you want to be aware,” Ms. Pisciotta said. An advisory describing the matter on a Sika company Web site, dated Dec. 6, said the company had, “over the past several months,” been “working aggressively to address reports” of excessive chlorides in SikaGrout 300 PT product made in Marion.

“There is a concern that, depending on the level of elevated chlorides in the grout in installed locations, the risk of corrosion in the tendon strands could increase,” the advisory said. “While this issue could affect the long-term service life of certain infrastructure projects [roads, bridges, etc.] where the impacted grout was used, Sika is unaware of any damage to structures to date arising from this elevated chloride issue.”

In November, 2010, Sika began “an enhanced quality-control testing regime” that includes chloride analysis for SikaGrout 300 PT made at other plants.

With one exception, listed by the company, all of the Marion-produced grout had lot numbers ending with the letter “M” on bags of the material.

Mr. Gramza said detailed records were kept showing the sources of grout used on various areas of the I-280 bridge, so sampling will be limited to areas where Sika’s Marion-made grout was used. Samples will be tested at a transportation department laboratory, a Sika lab, and a third-party location, he said.

“If there is a problem, we will have to investigate it, and evaluate the potential impact on traffic,” he said. The transportation department will consider Sika liable for the cost of any corrective measures, Mr. Gramza said.

Asked Sika’s position on its liability exposure, Ms. Pisciotta responded: “Our intention is to collaborate with them [ODOT] as they review this issue. We will continue the conversation with them as to what the appropriate next steps are.”

The grout problem is at least the fourth significant materials problem with the Skyway.

In 2004, about 184 cubic yards of concrete was removed from the bridge’s central pylon after sample testing determined a particular batch was weaker than required. Later in the project, officials discovered cracks in the plastic coatings on the bridge’s stay cables and ordered them replaced at the supplier’s expense.

And in 2008, a year after the bridge opened to traffic, inspectors discovered that epoxy glue holding the stay cables’ stainless-steel sheaths together was not holding up and the sheaths were slipping. The sheaths were welded together to remedy that problem.

The bridge also has had sporadic problems with ice forming on its pylon and stays during winter storms, then falling off in sheets onto the roadway when the weather warms, but so far this winter, such ice has not been an issue.

SOURCE: http://www.toledoblade.com/local/2012/02/06/Corrosion-threat-on-Skyway-bridge-deck-discovered.html

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