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MP "Material Matters" department. Contact MP Editor .larsen@nace.org. 14 OCTOBER 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 10 MATERIAL MATTERS Prior to installing the new coating system, localized, partial-depth repairs were made to corrosion-induced spalls. Photo courtesy of Stephen Foster. Quality assurance and quality control testing was conducted on the prepared surfaces to ensure a durable repair. Photo courtesy of Stephen Foster. Continued f rom page 13 reduction of excess water, the ability to repair or reapply the coating, and the availability of a manufacturer's warranty. Because of the simpler installation pro- cess, the need for a specialized contractor is minimized. However, coatings are v ulnerable to damage, and some form of mainte- nance—such as reapplication—is required multiple times throughout the life of the system. In addition, certain sur- faces, like the overhead concrete surfaces around the pumps or soff its, cannot be coated with a paint coating. The mem- brane could poten- tially block moisture migration from the top surface, which can lead to coating delam- inations and blisters or deterioration of the concrete. As a result, the paint coating would need to be used in tandem with ther- mally sprayed zinc at the soff it areas, since the zinc can be applied to damp sur- faces. Even away from the soff its, developing a dry surface to apply the paint coating is also diff icult. Finally, a concrete liner system with embedded zinc strip anodes offers a passive CP system without the need for monitoring, and a projected ser- vice life of 25 or more years. One to two rows of continuous sacrif i- cial galvanic strip anodes are adhered to the concrete surface or attached to supple- mental reinforcing steel at or above the high waterline, and cast concrete or shot- crete encases the anodes, thereby pro- viding a protective current. A good sur- face bond of the supplemental concrete or shotcrete is supported by mechanical anchors, reinforcing steel, and proper surface preparation. A liner system, how- ever, can be expensive, complicated, and lengthy to install, and the surface prepa- ration needs for this project were com- plex. Additionally, the liner system would reduce the overall sump capacity. After considering the options, the owner selected the coating system in tan- dem with thermally sprayed zinc on the soff its. Prior to coating, localized repairs were achieved by removing 3 to 5 in (76 to 127 mm) of concrete to a depth of 1 in (25 mm) behind the reinforcing steel, clean- ing and coating the reinforcing bar sur- faces with a corrosion-inhibiting coating, and replacing the concrete with an alka- line repair material. Discrete galvanic anodes were installed at the perimeter of repairs not located in areas that would receive the thermally sprayed metalizing. Once repairs were completed, the coatings contractor abrasive blasted and cleaned the concrete surfaces in prepara- tion for coating application. Quality assurance and quality control testing of the prepared surfaces, as well as pull-off testing of the applied coatings, were per- formed to ensure a durable repair. In the end, the work was completed successfully and the assessment and prioritization plan helped the operator to reduce corro- sion and extend the lifecycle of its water treatment facility without signif icant downtime. Reference 1 S. Foster, C. Larosche, J. Kurth, "Assess and Prioritize: The Key to Managing Aging Con- crete Infrastructure," NACE Corrosion Risk Management Conference, paper no. RISK16- 8735 (Houston , TX: NACE International , 2016). —Ben DuBose Material Matters continued on page 17