Historic Terminal A at Ronald Reagan National Airport Electrochemically Treated with Norcure® Re-alkalization and Norcure® Chloride Extraction
February, 2005

In 1941, the historic Terminal A at Ronald Reagan National Airport was constructed to service the metropolitan Washington, DC area. Over the years, exposure to atmospheric carbon dioxide had caused the concrete cover to carbonate resulting in a loss of alkalinity in the concrete pore water solution to a level that is insufficient to keep the embedded reinforcing steel in a passive, non-corroding state. Carbonation-induced corrosion combined with low concrete cover led to spalling of the concrete facade. Testing indicated average carbonation depths of 25 mm with some areas exhibiting carbonation as deep as 50 mm from the concrete surface.

In addition to widespread carbonation, testing revealed that isolated sections were also chloride-contaminated. It was determined that chlorides were cast-in during the original construction. Some believe a chloride-based set accelerating admixture was used to speed construction of the facility as the US prepared to enter World War II.

As part of a major renovation project to restore the Terminal to its original design and architecture, the concrete facade on the air side was to be rehabilitated. The selection of all materials and procedures were based on providing a long service life with minimum impact on the historic features.

In 2004, Norcure Electrochemical Re-alkalization and Chloride Extraction (ECE), generically referred to as Electrochemical Treatments, were utilized to passivate the active corrosion while respecting the historic nature of the facility. Electrochemical treatments achieve long-term corrosion protection by addressing the underlying cause of corrosion. For many projects, electrochemical treatments are a cost-effective strategy for providing corrosion protection over large areas.

ECE is an electrochemical treatment whereby an electric field is temporarily applied between the reinforcement in the concrete and an externally mounted mesh. The mesh is embedded in a conductive media, generally a sprayed-on mixture of potable water and cellulose fiber.

During treatment the concrete is kept saturated to lower the resistivity of the concrete and allow salts to go into solution. The negatively charged chloride ions (Cl-) are repelled from the negatively charged rebar and attracted toward the positively charged external electrode mesh as a result of the applied electric field. This action significantly lowers the amount of chloride adjacent to the steel. A substantial portion of the chloride is transported out of the concrete, where it is trapped and removed in the conductive media. An ECE treatment generally takes 4 to 6 weeks to complete.

For structures with carbonation-induced corrosion, a variation of the ECE process can be utilized to re-alkalize (increase the pH) the concrete cover. The installation for Re-alkalization is essentially the same as for ECE except the conductive media is saturated with an alkaline solution such as sodium or potassium carbonate. The sodium (Na+) or potassium (K+) ions in the alkaline solution are transported into the concrete by the application of the electric field. A Re-alkalization treatment generally takes 4 to 7 days to complete and will not re-carbonate.

In total, approximately 1,300 m2 of carbonated concrete facade was successfully re-alkalized at Reagan National airport. Additionally, 120 m2 of concrete surface received the electrochemical chloride extraction treatment.

For additional information on Norcure Electrochemical Treatment of concrete structures and other products and services for corrosion mitigation of concrete and masonry structures, please contact Vector Corrosion Technologies.

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