Materials Performance

MAR 2018

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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28 MARCH 2018 W W W.MATERIALSPERFORMANCE.COM T FEATURE ARTICLE Protecting Concrete Wharves with Cathodic Protection By Kathy Riggs Larsen The Port of Brisbane (Brisbane, Queensland, Austra- lia), Queensland's largest seaport, is located near the city of Brisbane at the mouth of the Brisbane River on Queensland's southeast coast. With 29 operating berths and more than 7,700 m of quay line, this port is one of Australia's fastest growing multi-cargo ports. Every year, the Port of Brisbane handles ~AUD$50 billion in international trade, which includes around 95% of Queensland's containers, more than 90% of its motor vehicles, and about half of its agricultural exports. 1 In 1999, an impressed current cathodic protection (ICCP) system was installed and commissioned on several steel-reinforced concrete structures that sup- port the Port of Brisbane's Wharves 4 and 5. Atef Cheaitani, managing director of Remedial Technology Pty., Ltd. (Gladesville, New South Wales, Australia), designed the ICCP system that was installed there more than 18 years ago. About three years ago, after the ICCP system had been in service for 15 years, the port's management company commissioned a com- prehensive audit of the Wharves 4 and 5 to assess the status of the concrete structures and ICCP system, and to determine if any renovation work was needed to sustain the ICCP system and extend the service life of the wharves for another 30 years. The Original Cathodic Protection System Cheaitani notes the total combined length of Wharves 4 and 5 is 600 m and the approximate area protected by the ICCP system is 8,000 m 2 . When the initial ICCP system was installed, he says, the area being cathodically protected—the wharves' substruc- ture—was in an advanced state of deterioration. Major concrete repair work was being done on the wharves' abutment, front and rear crane beams, relieving slab, and the fenders, an area that totaled ~5,000 m 2 . Although chlorides had permeated the con- crete to a depth beyond the steel reinforcing bar (rebar), the repair methodology included concrete removal only to the level of the rebar, which left the steel exposed to chloride-contaminated concrete. Approximately 2,000 metric tons of dry sprayed gunite were used to replace the contaminated concrete. For corrosion protection of the reinforcing steel, CP was determined to be the most effective long-term solution. The ICCP system was divided into 13 sections; 12 sections were ~48-m long and one section was 24-m long. Each section was divided into 14 separate electrical zones that incorporated tidal areas (abut- ment wall and slab, relieving slab, and fender wall) and atmospheric areas (relieving slab, landward crane beam, and seaward crane beam). Issues such as varia- tions in concrete resistivity, corroding conditions of the elements to be protected, tidal variations, and structural geometry were considered when zoning the system, Cheaitani says. Two installation methods were used to install ~30 km of mixed metal oxide titanium ribbon anode (10-mm wide by 0.9-mm thick with a current capacity of 5.28 mA/linear meter). In the first method, 10-mm wide by 30-mm deep slots were cut into existing con- crete, and the ribbon anode was placed in the slot and backfilled with grout material. Where the contami- nated concrete had been removed, the second method, the ribbon anode was placed between two layers of gunite that was compatible with the existing concrete. The ICCP system included a total of 365 embedded titanium and silver/silver chloride (Ag/AgCl)

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