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THE CHALLENGE:
A high altitude, pumped storage, concrete buttress-type dam
suffered from leakage through the structure and from consequent freeze/thaw
damage on both the downstream and pressure-side walls during frequent periods of
heavy frost. Although the dam was in no danger of structural failure, continual
freeze/thaw damage was causing significant wear on the pressure side and heavy
spalling damage on the downstream face.
Since it was
nearly impossible to properly coat surfaces on the negative side of hydrostatic
pressure and flowing leaks, it was therefore necessary to seal by coating the
positive or pressure side. As the dams water level changes as much as 80 feet
daily, the selected coating had to be completely tolerant to wet surfaces
as well as environmentally benign so there would be no possibility of damage to
local wildlife or ultimate down-stream users of the dams water.
THE SOLUTION:
TFT tested an accelerated version of BIO-GARD 257 designed to accommodate
the harsh application conditions experienced on site. (See Case Histories 43
& 44). These test applications, made under the severe practical
circumstances, remained in perfect condition after two years exposure.
Consequently, the dam operators decided to undertake a much broader coating
operation aimed at sealing the dry pour joints that were leaking during the
summer of 2004.
The BIO-GARD 257 was applied by roller
in two coats over the actual dry pour joints extending about 26 feet (8 meters)
on either side to a depth of 80 feet (24 meters). The first coat of
mauve-tinted coating was easily applied onto the running wet concrete
surface immediately after preparation by hydro blasting. A second coat of
gray-tinted material was applied after 4 24 hours.
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Applications were made from
a hanging scaffold that followed the water level as it fell throughout the day.
Water blasters, operating at about 5,000 psi, were effective in removing algae
and other surface contamination resulting in a wet, but otherwise clean
surface. BIO-GARD 257 coating with a pot life in excess of 45 minutes,
was applied with no problem directly to the surface using rollers, and it cured
to a firm condition in about 5 hours.
THE RESULT:
The application by roller
directly onto running wet concrete was completely without problems. The BIO-GARD
257 cured well overnight, even when underwater, and has formed a tough,
tightly adherent coating which will give many years of protection to the
irreplaceable dam structure.
For more information regarding this project contact:
Jeff Longmore, Technical Director
Thin Film Technology, Inc.
P.O. Box 580669
Houston TX 77258-0669
(713) 910-6200
FAX: (713) 910-6210
E-mail: jeff@thinfilmtech.net
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