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2014SumShotcreteEMag

Using Galvanic Anodes in Shotcrete Repairs By David W. Whitmore and J. Chris Ball Iincrease. Corrosion of reinforced concrete Because the corrosion by-product, iron oxide,ural protection afforded to the steel in alkalineconcrete breaks down and corrosion is initiated.n recent years, the use of embedded galvanicanodes in concrete repair has continued to structures such as bridges and marine piers is occupies a greater volume than the steel, internal typically caused by penetration of chlorides into concrete tensile forces from expansion of the the concrete. When sufficient chloride reaches reinforcing steel cause concrete cracking, delam- the reinforcing steel, typically 0.03% by weight inations, and spalling. of concrete in noncarbonated concrete, the nat- Patch-Accelerated Corrosion When these structures are repaired, chlo- ride-contaminated but sound concrete remains in place. An electrochemical incompatibility can occur between the new chloride-free repair and the remaining chloride-contaminated con- crete. These new corrosion sites can eventually cause new concrete damage adjacent to the previous repairs. Embedded Galvanic Anodes The purpose of using embedded galvanic anodes is to mitigate this patch-accelerated cor- rosion activity. Embedded anodes can be used around the perimeter of the repair or on a grid pattern throughout the repair area. When the anode is connected to the reinforcing steel, a protective current is provided to the steel, which will prevent or control corrosion in the area around the anode. A good reference for those specifying and Fig. 1: Corrosion damage on concrete bridge pier applying embedded galvanic anodes is “Repair Fig. 2: Patch-accelerated corrosion in parent Fig. 3: Galvanic anode for concrete repair concrete around previous repair 16 Shotcrete • Summer 2014


2014SumShotcreteEMag
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