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Concrete Dec 2018

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34 CONCRETE COVERED DECEMBER 2018 COATINGSPROMAG.COM R einforced concrete columns and piles are at risk of corrosion in marine environment due to long-term exposure to chlorides, oxygen, and water. Both conventionally reinforced and prestressed concrete piles in seawater are at risk of chloride-induced corrosion and concrete deterioration. A practical and cost-effective solution to this problem can be provided by galvanic cathodic protection (CP) jackets, accord- ing to David Whitmore of Vector Corrosion Technologies Ltd. ey can extend the service life of corroding piles and columns even in cases where structures have suffered significant concrete damage or require structural strengthening. CP jackets are especially beneficial when repairing load-bearing members, such as bridge columns or marine piles, where excavation around and behind the horizontal ties, and the vertical reinforcing, could result in the instability or failure of the structure unless shoring is installed. When CP jackets are used, only the damaged concrete needs to be removed. e remaining chloride contam- inated concrete can be left in situ, and the reinforcing steel can be protected from corrosion by incorporating a galvanic or impressed-current CP system into the jacket. Corroding concrete piles have sometimes been jacketed with an overbuilt layer of reinforced concrete or a concrete- filled, stay-in-place, fiber-reinforced polymer (FRP) form installed without CP. In the 1990s, it was documented that FRP jacketing without CP was ineffective for chloride-contaminated concrete piles as it allowed corro- sion to continue, and the jacketing concealed pile damage from detection by visual inspection. 1 In 1998, research conducted for the Florida Department of Transportation led to the imple- mentation of a policy that required all jacketing to include CP. 2 CP jackets can employ impressed current cathodic protection (ICCP) or galvanic anodes. ICCP is effective but requires a permanent power supply and commitment to system monitoring. By contrast, galvanic jackets are an effec- tive, low-maintenance option for the bridge preservation engineer. ey use sacrificial zinc anodes that are directly connected to the steel or are connected to the steel via an exterior electrical junction box. Galvanic jackets can include additional reinforcing steel if corrosion has reduced the cross section of the existing reinforcement or if there is a need to strengthen the pile. Reinforced concrete piles in seawater are exposed to four distinct zones (see Figure 1). e unique environmental condition within each zone results in differences in moisture content, oxygen availability, chloride content, and resistivity. Due to these differences, it is essential that an appropriate system is selected and installed. Submerged Zone Underwater sections of marine piles are continuously exposed to salt water and will become contaminated with chlorides. Despite this, submerged sections of reinforced piles are gener- ally less affected by corrosion due to limited oxygen availabil- ity. e submerged section of marine piles can be protected using zinc or aluminum bulk anodes without the need for a CP jacket unless the concrete section needs to be rebuilt or enlarged. Bare zinc or aluminum bulk anodes corrode readily in seawater, and protective current can be passed many feet through conductive salt water. If the submerged section is Corrosion Protection of Reinforced Concrete Columns and Piles in a Marine Environment By David Whitmore, Vector Corrosion Technologies Ltd. Photos Courtesy of the author High Tide Low Tide Concrete Column Airborne Atmospheric Periodic Splash Regular Tidal Wet Submerged Zone 4 Zone 3 Zone 2 Zone 1 Less Moisture More Moisture More Oxygen Less Oxygen Figure 1: Corrosion zones in a marine environment. Concrete Covered

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