About the author  ⁄ Gina L. Crevello

Gina Crevello is a Principal and Founder of Echem Consultants LLC. Ms. Crevello is on the Board of Directors for the Association of Preservation Technology and is active with the National Association of Corrosion Engineers and the International Concrete Repair Institute. She may be contacted at gcrevello@e2chem.com.

Repair Options and Replacement Materials

The case to replace terra cotta in-kind with the integration of a corrosion mitigation system, rather than full-scale replacement or replacement with an imitation material, provides clients with a durable, long-term repair and restoration program that retains the original building fabric. This article discusses the history of architectural terra cotta and various repair options in lieu of stripping and replacing.

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A bridge structure exposed to salt can expect corrosion of the embedded steel during its service life. Cathodic Protection (CP) has proven itself as the only permanent repair of existing corroded steel reinforced concrete. Therefore, CP must not be considered separately, but as a part of a complete rehabilitation program. (1993 Strategic Highways Research Program (SHRP) Report S-337)

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A metallized coating (a metallic alloy applied to a base metal or concrete) is intended, in most applications, to be a form of protection to an underlying metal substrate. The act of applying the coating is referred to as metallizing. Metallizing can be achieved in several ways such as hot-dipped galvanizing or thermal arc spraying, applied in situ or in a shop. Zinc, which was first used in construction in 79 AD, is the most used metal for this process. Half of the zinc produced today is used for corrosion protection of steel.

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Non-destructive Testing (NDT) plays a critical role in the understanding of existing structures. Investigative techniques available offer practical, efficient, and cost-effective solutions to obtaining information on quality, construction, and performance that may be otherwise hidden to the naked eye. The use of NDT tools vastly reduces the need for exposing embedded structure through probing, and assists in making more informed decisions when samples or probes must be performed.

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The Use of Corrosion Rates to Predict Material Performance

As concrete structures begin to age and deteriorate, the need to understand corrosion behavior is pertinent to determining where a structure is in its life cycle. One of the most successful methods of determining the corrosion rate of embedded steels is the Linear Polarization Resistance (LPR) method. The results of this test method provide measurements of corrosion current (Icorr,) or corrosion penetration rates.

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As the stock of American bridges averages an age of forty three (43) years (Figure 1), it is clearly of great value to understand their remaining service life. When you consider the theoretical design of these bridges was for fifty (50) years, it is inevitable that a high proportion of them will now be deficient. In fact, the number of deficient bridges today is 1 in 9. Within the next ten years this will become 1 in 4.

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Corrosion related damages are the root cause of numerous façade failures on masonry clad steel frame buildings (Figure 1). Corrosion of the underlying steel frame or anchorage can lead to cracking, spalling, displacement, and eventually the loss of entire masonry units or severe section loss of structural components. Corrosion is a quantifiable reaction, whereby initiation, propagation, and deterioration can be projected through comprehensive assessments and durability modelling.

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STRUCTURE magazine