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Root Causes of Deck Deterioration
Early details of pre-stressed systems had certain
characteristics that caused the tendons and anchors to collect,
or be exposed to, moisture, leading to subsequent corrosion. The
protection of pre-stressing tendons was not officially addressed
until 1985, and continued investigation into the causes and effects
of corrosion on post-tensioned concrete has been carried out by
the American Concrete Institute (ACI). In January 1995, ACI Committee
423 filed a draft report entitled, "Corrosion of Unbonded Post-Tensioning
Tendons" which was used in the investigation of the Ocean Vista
Deck were virtually unprotected, active corrosion was ongoing.
Alkali-Silica Reaction (ASR) is a tremendous
concern in certain regions of the United States because of the uncontrollable
deterioration of concrete manufactured using aggregates that are
now known to be reactive. Areas near the coast are particularly
vulnerable because of the high chloride content of the moisture
which is allowed to penetrate the concrete. The Saticoy region of
Ventura County, source of the aggregate used, is one of the regions
known to quarry reactive fine aggregates.
In 1983, samples of the deck concrete were analyzed
in the laboratory and shoed the presence of reactive fine aggregates;
however, no specific conclusions on ASR were documented. A load
test was performed to assess excessive deflection under service
loads; but no noticeable deflection was measured.
In 1985, it was suggested that the live load
capacity, or service load, of the deck be reduced from 300 psf (1465
kilograms/sq. m) to 1250 psf (732 kilograms/sq. m) This was due
to the corrosion which had been observed and the questions which
remained as to the integrity of the deck. It was also recommended
that a protective coating be applied to prevent further moisture
penetration. This coating has probably been the greatest contributor
in reducing the amount of distress to this deck since its application
in 1985.
In 1991, concrete repairs were performed to localized
spalls in the underside of the deck. When it was observed that these
spalls were the result of corroded and broken pre-stressing tendons,
concerns as to a possible safety hazard due to the loss of pre-stressing
led to the development of a plan to restore the loss of strength
to the deck.
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