CONCRETE LEAKING PROBLEM AT NEW WWTP SOLVED WITH 100% PURE POLYUREA SOLVES
The Sherwin-Williams Company
Concrete is an important building material commonly used in the construction of waste water treatment plants. Concrete surfaces are porous and permeable and may crack and leak even when skill is used in placement. If not specifi ed originally, as was the case for this project, polyurea protective coatings may be used for rehabilitation of cracked, leaking concrete surfaces.
During the testing of concrete circular grit chambers
in a wastewater treatment plant under construction, serious leaking problems were discovered prior to project completion. In-person and telephone conversations took place with the Owner, Design and Construction engineering firms, painting contractor, and coatings manufacturer to determine a course of action. 80 mils of 100% pure polyurea was specifi ed to be applied to these concrete surfaces to stop the leaking and prepare the grit chambers for operation.
Note: this project was presented at the Paint and Coatings Expo (PACE) earlier this year.
Background This project was an upgrade of an existing treatment plant so that output could be increased to 60MGD and beyond. It as existing concrete walls “in common” with newly placed concrete walls in at least two important areas – an electricalcontrol room and an administrative area.
Prior to start-up, while still under construction, tests were done at this wastewater treatment plant (WWTP)and several leaks were found. A sodium silicate slurry coat was applied to concrete surfaces in the grit chamber areasbut it did not prevent leaking. Both epoxy and urethanecompounds were injected into cracks but they, too, did not prevent leaking. After several conference calls, fact-fi nding and research activities, and face-to-face meetings, the Owner felt convinced that the information and assurances provided by the Design and Construction engineers, the material supplier,and a certifi ed applicator would merit their acceptance of the polyurea coating in these troubled areas. Th e work was to begin immediately and, since it was winter and the site
was near of Lake Michigan, weather was a concern.
Repair & Remediation At first, ice and water was removed from the work site. Heat and air movement were provided next. Th e environment was maintained at approximately 50° to 65°F, with a relative humidity at 20 – 40% and a surfacetemperature of up to 55°F.
Abrasive blasting, to achieve an ICRI CSP 3 to CSP 6, took place to remove the sodium silicate slurry coat and roughen the existing surfaces for the application of primer, filler, and topcoat.
A polymer-modified, cementitious patching material was applied to prepared areas to fill bugholes and voids. Afterwards, a clear, low temperature, 100% solids epoxy primer was applied at approximately 6.0 to 8.0 mils DFT. A moisture cured urethane sealant was then used to smooth edges where metals met concrete surfaces, where transitions on concrete surfaces required “rounding”, and otherappropriate interface areas. Metal surfaces, such as aluminum gates were protected prior to the application of the polyurea.
A test area of polyurea was sprayed onto polyfi lm to verify proper equipmen ratio (no discoloration) and confi rm the system would be pinhole-free. Finally, approximately 80 mils DFT of polyurea were applied to all interior surfaces in the grit chambers. Drying and curing followed the manufacturer’s recommendation.
Conclusion This wastewater treatment plant is now in full operation and the grit chambers are not leaking. Crack-bridging, fl exing, and leak-deterring properties are features of pure polyurea elastomers and this is one of the many successful and suitable uses for these types of coatings.
