Did Caltrans misinform its corrosion reviewer?

Published: Saturday, May. 18, 2013 - 10:05 pm
Last Modified: Saturday, Apr. 12, 2014 - 7:26 pm

Caltrans hired a single independent corrosion expert, professor Alberto Sagues of the University of South Florida, to review the adequacy of the agency's study of skyway tendons. A Bee comparison of that study against the construction record shows that Caltrans did not give Sagues a complete and accurate accounting. Other corrosion experts said the discrepancies cast doubt on Sagues' conclusions.

Q: How many tendons were available to test and how many were tested?

What Caltrans reported*: 2,076 tendons were accessible in ungrouted ducts, nearly all in the westbound span. Caltrans examined 1,635 visually and a few samples in the lab. Federal experts also conducted limited lab tests.

What Sagues concluded: The vast majority of accessible tendons were examined.

What the Caltrans report did not reveal: About 1,000 tendons on the eastbound span, accessible when testing began, were not examined.

Q: What did tests show?

What Caltrans reported*: About 40 percent of tendons showed mild corrosion, deemed unimportant. About 4.5 percent showed moderate corrosion or had exposures suggesting moderate corrosion. Lab samples showed acceptable strength in all but one case.

What Sagues concluded: "(T)he pre-grouting mechanical consequences of that corrosion were generally minor..."

What the Caltrans report did not reveal: Testing showed conditions of the tendons at the time of testing, but experts said that subsequent grouting delays might have worsened corrosion. According to UC Berkeley metallurgist Thomas Devine, an expert in stress corrosion cracking of metals, methodological and other flaws in the Caltrans study rendered its findings "essentially useless." He called the study "woefully inadequate" and "meaningless" for detecting "environmentally assisted cracking," a key concern the Caltrans report addressed.

Q: Did tendons in the untested eastbound span and the tested westbound span experience the same corrosion risk?

What Caltrans reported*: "(G)iven the similarities between exposure conditions ... it is reasonable to assume that both structures experienced similar levels of corrosion."

What Sagues concluded: "Uncertainty remains as direct inspection was not possible in most tendons in the Eastbound bridge, so condition there is inferred from evidence of the Westbound bridge and assumption that environmental and service conditions were comparable..."

What the Caltrans report did not reveal: On average, eastbound tendons were exposed 73 days longer than westbound tendons. Nearly 90 percent of the most extreme exposures were in the eastbound span. More than twice as many sections of the eastbound span had extreme warning signs for corrosion.

Q: Were ducts grouted one at a time, the standard practice to help ensure reliable grouting?

What Caltrans reported*: Not noted

What Sagues concluded: Not noted

What the Caltrans report did not reveal: About 1,100 tendon ducts were grouted together in groups of up to 21 - an unorthodox practice that experts said suggests a higher likelihood of voids within ducts that could cause further corrosion.

Q: What was recommended and done to apply corrosion-inhibiting powder?

What Caltrans reported*: "(C)orrosion inhibiting powder should be recharged into the ducts to prevent further corrosion deterioration."

What Sagues concluded: "(R)eported information is not sufficient to prove that the ... corrosion inhibitor played an effective role" or might actually have promoted localized corrosion.

What the Caltrans report did not reveal: Anti-corrosion powder was applied in only about 25 percent of ducts, and nearly always in a manner out of compliance with requirements for effective use.

Q: What was recommended and done after the corrosion study to protect against further corrosion caused by water in the ducts?

What Caltrans reported*: "All grout tubes should be adequately sealed at the deck surface to minimize water intrusion into the tendon ducts." "Remove all water from tendon ducts by forced dry air." "Where possible, tendon ducts should be grouted within a 30-day time period."

What Sagues concluded: (G)routing or service deficiencies including but not limited to improper flushing of accumulated water prior to grouting, bleed water formation and voids ... could result in serious damage to the tendon, even if the strand had suffered no pre-grouting corrosion ... Prior corrosion ... could seriously aggravate the effect of those deficiencies."

What the Caltrans report did not reveal: Many grout tubes were left unsealed for many months after the problem was discovered. Water was not evacuated from many ducts prior to grouting, which often took place months after Caltrans examinations.

*Reflects statements in the report and excludes supplementary information, if any, conveyed verbally to Sagues

Source: Caltrans reports and construction records, Bee reporting by Charles Piller

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