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Concrete In Australia : September 2008
Figure 7: Continuity trench exposing prestressed strands. Figure 8: Application of activated arc sprayed zinc. all prestressing strands. Each prestressing strand was checked for continuity, and then zinc was sprayed across the exposed strands in the trench and onto the deck surface. The purpose of this procedure was to provide negative connections from the zinc anode coating to the reinforcing in the deck unit. (ii) A delamination survey was conducted over the entire deck unit, and all deteriorated concrete was repaired. (iii) The surface of the concrete was prepared by light abrasive blasting in order to clean the concrete and to provide an anchor profi le for the zinc spray. Figure 9: Installed activated arc sprayed zinc on portions of the prestressed deck units. covers were fastened to the terminal boxes. System energising The energising stage of installation involved measuring the: • continuity between negative connections (re-verifi ed in mV) • anode to steel potential (mV) • off or static potential of the steel (mV) • instant on potential of the steel (mV) • 24-hour polarised potentials of the steel (mV) • energising current (mA). Activated arc sprayed zinc for protection of precast deck units The precast concrete deck units were protected using activated arc sprayed zinc applied to the deck soffi t. After installation of the metalised high purity zinc coating, humectant activator solution was applied to the surface of the zinc to achieve a higher level of current output and protection. Installation procedure (i) A 5cm-wide continuity trench was excavated along the entire underside of each deck unit, exposing the surface of (iv) The zinc spray was applied in multiple passes of approximately 120 microns per pass with each layer overlapping the last in a crosshatch pattern. Uniform gun movement was used to ensure an even thickness. Sufficient zinc was applied to achieve a nominal thickness of 500 microns. The continuity trench received a total of 1000 microns of zinc coating. The performance of all jackets was measured and recorded as part of the system energisation procedure. (v) Continuity of all the prestressing strands was reverified. (vi) The continuity trench was coated with two layers of epoxy to protect and maintain the connections during the life of the system. The trench was then fi lled with patching mortar and re-sprayed with zinc for aesthetic purposes. (vii) Humectant activator was then sprayed over the entire surface of the zinc. (viii) Inorganic, zinc rich paint was then applied over the humectant activated zinc anode to help prevent self corrosion of the zinc and extend the service life of the galvanic protection. Concrete in Australia Vol 34 No 3 47