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| Rust, corrosion, 2/10/14 |
"Caltrans tests indicate that salt water from the bay may be seeping into the foundation of the new Bay Bridge eastern span’s tower, an ominous prospect that raises questions about the long-term viability of hundreds of massive steel rods that anchor the landmark structure..
The state agency has known since late 2014 that many of the 424 rods, each of them 25 feet long and made of hardened steel, were steeping for years in rainwater, the apparent result of a botched grouting and sealing job by bridge contractors. Crews drained the water from the rods’ sleeves, but the contractor complained to Caltrans last month that water was regularly reappearing — even when there was no apparent source.
Preliminary tests that Caltrans did last week found that in some of the sleeves, chloride levels were far higher than is typically found in rainwater. Two independent experts say the likely culprit is bay water that is permeating the base of the structure, possibly through gaps or cracks in the concrete.
Caltrans spokeswoman Leah Robinson-Leach said in a statement Tuesday that the chloride levels in a “few locations” were “half ... of what would be expected in salt water.” However, even that is about 50 times higher than the chloride content of rainwater removed from the flooded rod sleeves last year.
“Reaching a conclusion about the reason for chloride at this point would be clearly speculative,” Robinson-Leach said. “We are currently monitoring to thoroughly evaluate the situation. But in the end, what matters is drying the foundation and keeping it dry, which is exactly what we intend to do.”
Signs of damage
Caltrans has already removed two rods that were exposed to freshwater to check for signs of damage, and reported last month that there were rust and tiny cracks — both indications of corrosion. An invasion by salt water would be significantly worse, both because it could accelerate corrosion and because a logical source would be the bay — something an improved grouting job can’t fix.
“It’s bad news,” said Yun Chung, a retired Bechtel engineer who has been critical of Caltrans’ use of high-strength steel for the rods, which is more prone to corrosion than regular steel. “We just don’t know how bad because we don’t have the data to show how susceptible they are.”
Chung said saltwater is clearly permeating gaps in the concrete base, posing a continuing threat to the already problematic rods. “Based on what we know, the rods are questionable,” he said. “It’s a big question mark.”
On Monday, after an emergency meeting, the bridge project’s oversight committee voted to test water from 100 flooded rod sleeves at a cost of $400,000.
Earthquake safety
One of the rods’ most important functions is to keep the 525-foot-tall tower from heaving up and down in an earthquake. If the rods are steeping in salt water, it could shorten their life span.
Caltrans will have no easy solution if the rods are damaged. They were installed before the bridge tower was put in place in 2011, and there is no longer room to remove a rod without destroying it or to maneuver a replacement into position.
If bay water is seeping into the rod sleeves, one source could be cracks that appeared in the foundation during construction. Officials say crews filled in the cracks, which developed as the concrete set, but it’s possible that some cracks escaped detection.
Dispute with contractor
Until recently, Caltrans blamed the flooding in the steel sleeves on the bridge’s main contractor, a joint venture called American Bridge/Fluor Enterprises, for failing to properly grout and seal them.
In a letter to Caltrans last month, American Bridge/Fluor pointed out that water was continuing to flood the base of the rods even after the sleeves had been drained. The contractor blamed voids in the concrete foundation, which was built by another contractor, Kiewit.
American Bridge/Fluor identified 21 sleeves that filled up on a daily basis with at least 6 inches of water. Removing all the standing water “cannot be achieved,” the contractor told Caltrans.
“What is seemingly obvious,” wrote the contractor’s project director, Brian Petersen, “is there are apparent voids within the T-1 tower foundation that exist which appear to prove a constant and consistent flow of water back into the tower anchor bolt sleeves.”
The sleeves, Petersen said, were not sealed against water at the bottom — making them vulnerable to repeated flooding that he said was not the fault of American Bridge/Fluor.
Reflooded sleeves
In its reply, Caltrans blamed American Bridge/Fluor for the renewed presence of water, saying the contractor chose for unexplained reasons to reflood the drained rod sleeves on March 4. Caltrans said “unexpected and unauthorized” water was simply trickling down to the base of the sleeves over time. The discovery of apparent salt water suggests that the contractor may be right, and that bay water is invading via gaps or cracks in the concrete structure.
“Chlorides are like the icing on the cake,” said Lisa Fulton, a corrosion expert in Berkeley who has studied the project and who did testing that confirmed corrosion on vital components.
“There is no magic number, but the basic thing is the higher the chloride level, the more accelerated the corrosion,” Fulton said, adding that the most likely source is bay water infiltrating the base.
“Once the chlorides come into contact with the steel rods, they stay put and become concentrated,” Fulton said. “They initiate corrosion and accelerate the corrosion rate by orders of magnitude.”
Charles McMahon, a materials science professor emeritus at the University of Pennsylvania, said chloride interferes with “the development of a protective oxide film” that would otherwise guard the steel. The fact that the water has half as much chloride as sea water is not much consolation, he said, given that the high-strength steel being used is already overly susceptible to corrosion.
“Chloride ions are bad news,” he said. “It’s really sad — maybe when this is all said and done, engineers will decide they’d better consult somebody about the materials they are going to use.”" via Lucianne
Image caption: "Rust and corrosion from a puddle of water are seen next to bolts in one of the hollow steel box girders that make up the roadway of the Eastern span of the Bay Bridge in Oakland, CA Monday, February 10, 2014." Special to the Chronicle, Michael Short
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