Charleston, S.C., facility finds 15-year-old epoxy still provides solid performance
The city of Charleston, S.C., experienced a drought in 1917 and 1918. The resulting water shortage, combined with the washing away of part of the Goose Creek dam in July 1916, forced the Charleston Commissioners of Public Works (CPW) to look for an immediate and long-term water source to supplement the Goose Creek Reservoir.
The decision was made to construct a 23-mile tunnel connecting the Edisto River to the Hanahan Pumping Station. The Edisto River became Charleston’s primary source of water, and it continues to provide raw water to the Hanahan Plant today.
In the mid-1940s, the Hanahan plant underwent a major expansion to keep up with the growing demand for water. The project included the addition of the Booker Filter Plant, a new pump station and, in 1963, the Stoney Filter Plant, including the 20 filter basins that are still in operation today.
After 37 years of service, the 20 filter basins at the Stoney Filter Plant had experienced degradation of the concrete surfaces. Upon inspection of the facility, it was determined that the plant showed signs of concrete degradation with exposed aggregate due to the chemicals used in water treatment. To decrease the need to build a new facility, it was decided that the current facility should be rehabilitated to save taxpayers’ money.
In 2000, the City of Charleston and the Charleston Water System put out a call for bids, and Florence, S.C.-based Dun-Right Services Inc.—a Raven Certified Applicator—won the project. This would be Dun-Right’s first application of Raven’s AquataPoxy A6 Thick. Being unfamiliar with the application procedures of A6 Thick, and with this being its first job of this size, Dun-Right requested the assistance of Raven Linings Systems’ technical department.
After the City of Charleston assessed the facility, it was determined that a 100% epoxy product, which would be NSF ANSI 61-certified, would protect and reinforce the structure from further deterioration. The technology used by Dun-Right would be a fluid-applied plural-component 100% solids epoxy at 60 mil. The cementitious underlayment at the time would be Quadex Hyperform PM with a ½-in. rebuild.
Once basins were drained and all remaining filter media was physically removed, a 5,000-psi hydro blast was performed over the entire structure with the goal of achieving a minimum concrete surface profile of a CSP 3. After completing the surface preparation, a final low-pressure water rinse was conducted to wash away the loose dust and debris. On the damp surface, ½ in. of Quadex hyperform PM was spray-applied using a standard grout/mortar pump. With the Hyperform PM cured, a secondary prep was performed using the 5,000-psi hydro blaster to remove any laitance or loose particles. With the surface dry to the touch, the AquataPoxy A6 Thick was spray applied using a Graco Hydracat set-up 1:1. Any pinholes found after holiday testing were then repaired within the recoat window. Pinholes discovered after the recoat window had expired were prepared and then repaired according to Raven recommended procedures
In 2015, it was determined that an upgrade was necessary and new troughs would be installed. Garney Construction was the general contractor awarded the task of upgrading the now-52-year-old facility. Upon inspection, the City of Charleston and Dun-Right were pleasantly surprised to discover the 15-year-old coating of the AquataPoxy was still tightly adhered with only minor structural flaws. New repairs were due to the installation of new troughs and floors. It was estimated that only approximately 32 sq ft per basin would need repair, with some basins having unexpected repairs ranging from structural movement to impact damage. It is the proper application process implemented in 2000 that resulted in very minimal repair, therefore saving the City of Charleston hundreds of thousands of dollars.
The upgrade would involve removing the existing concrete troughs and replacing them with new, upgraded fiberglass troughs. The process involved demolishing the concrete troughs and saw-cutting an opening in the existing wall for removal. Once Garney had removed the old troughs and installed the new ones, it would then re-pour the demolished wall. At that point, Dun-Right would have access to that individual basin. Once Dun-Right was granted access to the basin, it would inspect and mark all needed repairs.
“Raven is pleased to offer not only a quality product, but also a solution that continues to stand the test of time,” said D.J. Wroble, senior vice president, Raven Lining Systems. “To be able to stand here 15 years later seeing our product doing its job and protecting this city’s infrastructure is something to be proud of in this very competitive market.”
Once all repair areas had been marked and documented, Dun-Right could begin work. It would start by removing any existing A6 coating that was not tightly adhered. Since the entire surface was not being recoated, termination grooves and key ways were utilized at the edges of where the coating application ceased to assure superior adhesion existed. In instances that needed a cementitious underlayment, Raven 755 was utilized. With the Raven 755 cured, an abrasive blast was performed to all surfaces that were to be top-coated with AquataPoxy A6 Thick, with a goal of achieving a minimum concrete surface profile of CSP 3. After completing the surface preparation, a final low-pressure water rinse was conducted to wash away the loose dust and debris. Once the substrate dried, two coats of Raven 155 primer were applied to reduce moisture vapor transmission on the areas that had received the Raven 755 and new concrete. After the primer had time to properly cure, AquataPoxy application could begin. Areas that had received either new concrete repair or Raven 755 would receive a minimum topcoat of 100 mil. Areas of A6 that received a topcoat were coated with 60 mil. Any pinholes found after holiday testing were repaired within the recoat window. Pinholes discovered after the recoat window had expired were prepared and then repaired according to Raven recommended procedures.
“Once Dun-Right was granted access to the structure, they would perform adhesion tests,” said Ryan Bauman, technical service specialist, Raven Lining Systems. “This would provide the city with the peace of mind, knowing that the 15-year-old coating was performing as expected. The process involved following the ASTM D 4541 standard, including coring around the dollies. The adhesion test was perform using a Defelsko Positest AT on Filter Basin #10.”
Adhesion testing was performed on the 15-year-old AquataPoxy by gluing seven 20-mm dollies to the coating surface with a fast-setting, high-strength epoxy. After allowing the glue to set for 24 hours, the dollies were then cored using a 20-mm coring hole bit. The adhesion test was performed using a Defelsko Positest AT. All tests were perform in Filter Basin #10
- Pull 1: 619 psi (95% substrate, 5% cohesive failure in coating)
- Pull 2: 714 psi (100% substrate failure)
- Pull 3: 488 psi (100% substrate failure)
- Pull 4: 621 psi (40% substrate, 60% adhesive failure between substrate and coating)
- Pull 5: 251 psi (75% substrate, 25% adhesive failure between substrate and coating)
- Pull 6: 723 psi (100% substrate failure)
- Pull 7: 511 psi (100% substrate failure)
“It’s partnerships with applicators like Dun-Right that allow Raven to have continued success and pioneer innovative solutions in an ever-changing industry,” said Wroble.
Raven Lining Systems and AquataPoxy A-6 provided the following benefits to the Hanahan Water Treatment Plant:
- a product that was not moisture-sensitive;
- strong and durable coating for the water treatment facility;
- all-weather resistant coating; and
- peace of mind for more than 20 additional years.