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THE CHALLENGE: A high altitude, massive concrete buttress type dam suffered from leakage through the structure and 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 is almost impossible to properly coat surfaces on the negative side of hydrostatic pressure and flowing leaks it was necessary to identify suitable coatings capable of being applied to the positive side of the water flow under the cold and wet conditions often prevailing at the dam.
A further requirement was that the coating must be environmentally benign in order that there would be no possibility of damage to local wildlife and ultimate down-stream users of the damsí water.
THE SOLUTION: TFT Epoxies (UK) modified three of its standard underwater/wet surface epoxy coatings to tailor-make a product for the application. Bearing in mind the low application temperatures expected on this job the products were modified to have lower application viscosity while still retaining excellent non-sag characteristics and to have a more rapid curing reaction than normal. All three formulations were variations of a product that had received complete and unreserved approval as a coating for potable water applications.
In view of the size of the dam and its pristine location the only feasible method of surface preparation was by high-pressure water jetting. At a pressure of 4,000 psi this was effective in removing the heavy algal growth to expose firm, granular concrete.
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Roller applications of 10 sq.ft. each were carried out immediately after water jetting at ambient temperature of 45°F while the surface was still running wet, to compound the wetness it was raining heavily during the application and subsequent curing period.
THE RESULT: After nine months of weathering and one winter the test results were assessed. All three products were seen to be in perfect condition with adhesion to the concrete so great that it was impossible to remove coating without removing the underlying concrete.
BIO-GARD 257 was chosen as the best candidate for further trialling because of its excellent adhesion and exposure results and its overall greatest ease of application by brush or roller under adverse conditions.
For more information regarding this project contact:
Paddy Atkinson Director
TFT Epoxies (UK) Limited
13 Ryecroft Lane, Belmont Village
Bolton, Lancashire BL7 8AH
Phone: Telephone: +44 (0) 7973 553 447
FAX: +44 (0) 1204 811 212
E-mail: info@TFT-epoxies.co.uk
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