Materials Performance

OCT 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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13 NACE INTERNATIONAL: VOL. 55, NO. 10 MATERIALS PERFORMANCE OCTOBER 2016 Visual inspections of the concrete were a key part of the repair process. Photo courtesy of Stephen Foster. Continued on page 14 waterline, as well as beam and slab soff its, widespread areas of delaminated concrete were present. The HCP measurements within the splash zone and above showed rates of active corrosion. On all cores, chloride con- centrations were up to 1.25 in (32 mm) into the concrete—above the threshold to initi- ate corrosion. The next step was the prioritization of assets. Unlike other primary structures at the plant, the owner found no operational redundancy for the sump, since all of the other operations were dependent upon this one sump. Accordingly, it was the top priority for repair. Adding to the chal- lenge, any repairs needed to be completed quick ly enough to take place during a routine outage. Four repair strategies were considered by the owner, including an impressed cur- rent cathodic protection (ICCP) system with embedded titanium anode ribbons, a thermally sprayed metal coating system, a single-layer coating system, and a con- crete liner system. An ICCP system does not require a coating, could address both the walls and soff its, could easily be installed in the sump, and has an expected service life of 25 or more years. However, the need for periodic monitoring, a complex design and installation process, and the mainte- nance required for the mechanical sys- tems and instrumentation could be drawbacks. In a thermally sprayed zinc system, a thick zinc or aluminum-zinc-indium blended coating is applied to the exposed concrete surface. The zinc is melted by applying opposing electrical charges to zinc wires and the molten wire is sprayed onto the substrate by a stream of com- pressed air. The resulting coating is porous with excellent adhesion to con- crete. The reaction between the anode and the reinforcement results in con- sumption of the zinc and gives rise to the formation of zinc oxides. Advantages include ease of installation and the poten- tial application to both the walls and sof- f it. Since zinc can be applied to damp concrete surfaces, it is ideal for marine infrastructure. On the other hand, the thermally sprayed system requires multiple applica- tions over the life of the system, as well as a moderately dry surface. Since the exact consumption rate for the zinc is un - known, the standard service life when using that system is only 10 to 12 years. To achieve a service life similar to an ICCP system, one to two additional appli- cations of metalizing would likely be required. A single-layer coating system uses either a paint coating or a metalized coat- ing, depending on the area on the struc- ture, to protect the parent concrete from further distress. The ty pical service life is 20 or more years. To achieve a complete bond of most high-performance coatings, the surface preparation is relatively dry and abrasive blasting is used to achieve a roughened surface prof ile. Positives include ease of quick application, a Information on corrosion control and prevention

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