Metallized coatings on reinforced concrete for cathodic protection
Metallized coatings on reinforced concrete for cathodic protection
Keywords: Power Spray, Coatings, Concrete, Corrosion prevention, Cathodic protection
Power Spray recommend the application of zinc metallized coating (ZMC)directly to the reinforced concrete surface to prevent future corrosion of the rebar. They state that the coating will function as: a distributed anode for an impressed current cathodic protection (CP) system, or a sacrificial anode for a passive CP system.
The company explains that when rebar inside concrete corrodes it expands and causes the concrete to crack. This activity left unchecked will substantially weaken the concrete structure. Zinc metallized coatings they believe will provide a conductive coating chemically compatible with concrete. ZMC sacrifices itself and corrodes in preference to the steel rebar. According to Power Spray,a ZMC 0.020" thick will last approximately 20 years. The FHWA declares that cathodic protection of reinforced concrete is the most effective means of retarding corrosion of rebar in concrete.
Zinc metallized coatings can be applied in the field during scheduled maintenance and repair cycles.
Surface preparation requires that for concrete structures with exposed rebar,abrasive blasting of the steel rebar to remove rust, scale, oil, grease, and other foreign products is necessary to achieve a SSPCoSP-10 near white metal finish. For structures without exposed rebar, lightly abrasive blasting of the concrete surface to remove all contamination and debris that could degrade the bond of the ZMC patched concrete areas should have a minimum seven day cure prior to abrasive blasting and metallizing.
Metallizing requires the setting-up and validating of the spray parameters. The concrete or rebar surface temperature should be kept at >5°F above the dew point. Operators should arc spray with a minimum of six perpendicular, overlapping passes to achieve the 0.020" ± .002" total thickness.
Suggested usages include highway bridge substructures; parking garages; waste and water treatment facilities; pulp and paper mills; petrochemical plants; and concrete structures in rivers and marine environments.
For application of the coatings, the company's spray teams utilise, when possible, its Powerarc 1500. In the company's opinion it permits superior control of process variables such as voltage, current, and air pressure. The POWERARC 1500 microprocessor is said to reduce human error and produce high quality metallized coatings which meet stringent MIL-STD-2138 (SH) and ANSI/AWS C2.18-93 requirements. These coatings are stated to be easily achieved in the shop or field.
Details available from: Power Spray, Inc., Tel: +1 800 989 3331; Fax: +1 757 363 9131; E-mail: metallize@powerspray.com;Web site: www.powerspray.com
