Abstract
Reinforced concrete structures can be designed and maintained to achieve long service lives, even in aggressive chloride environments. Unfortunately, many structures, such as bridges, piers, and wharves, show signs of active corrosion (e.g. rust staining, concrete spalling, etc.) in as little as 5 to 10 years. Left unchecked, chloride induced corrosion can lead to major structural problems. Many severely corroded structures have been replaced at great expense and with significant disruption to the public. As an alternative to demolition and replacement, a viable option is to repair and protect severely deteriorated structures utilizing a galvanic encasement that both structurally upgrades and catholically protects the structure. This approach can provide an effective, low maintenance galvanic cathodic protection solution for deteriorated concrete structures. Galvanic encasements consist of distributed galvanic anodes embedded in a concrete overlay or concrete jacket. The galvanic encasement may include additional reinforcing steel to create a one-step structural repair and protection system. This paper presents case studies on the use of galvanic encasements to repair and protect reinforced concrete structures. Long term monitoring of field projects over more than 10 years indicates that effective cathodic protection can be provided for 20 to 40+ years.
Highlights
Chloride induced corrosion of reinforcing steel in concrete is a major problem worldwide
Work completed by the US Bureau of Reclamation under ACI 2020 has shown the use of galvanic anodes to be a very effective repair strategy compared to other common repair methods (Figure 5)
Impressed current was required to supply sufficient current to the reinforcing steel to achieve cathodic protection. This is no longer the case as properly designed galvanic encasements using high output, alkali-activated, long-life distributed galvanic anodes do not introduce any corrosive constituents into the concrete and can be designed to provide sufficient current density to polarize the reinforcing steel and meet all NACE / EN cathodic protection criteria
Summary
Chloride induced corrosion of reinforcing steel in concrete is a major problem worldwide. Chlorides can be introduced into the concrete via exposure to seawater, de-icing chemicals, or in certain cases as contaminants or additives in the initial concrete mix This leads to localized breakdown of the normally passive reinforcing steel and results in pitting corrosion (Figure 1). Similar galvanic anodes have been used in either a grid configuration or as elongated chains to mitigate low level steel corrosion in undamaged reinforced concrete elements which were at risk of corrosion. This application is known as corrosion control where corrosion cannot initiate at new locations and locations where corrosion is already occurring is gradually reduced.
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