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“Corrosion is responsible for up to 90 percent of damage to reinforced steel structures,” Uell Angst, professor at the Institute for Building Materials, explains.

Why do people still think there is a critical chloride level in concrete that leads to corrosion? Why can’t they use the failure analysis tools that have been available since the 1960s and locate where the salt penetrates and causes corrosion? This picture is from a 2017 website that suggests LARGER samples don’t give useful information. That is true. The salt water migrates through cracks (often fatigue cracks or other mechanically-caused cracks) in the concrete and, when the free lime is used up (leaving efflorescence markings), then corrosion occurs.

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If you look at the above picture it is obvious that the corrosion is localized. Analyzing concrete (cement paste, etc.) is useless in this case. Analyze the metal surfaces and you will see that the salt water only reached the metal where corrosion occurred—probably due to cracks or voids in the concrete cover.

Here’s a couple of very old papers on this subject. I would assume newer articles have also appeared:

  • R. Heidersbach and J. Lloyd, “Corrosion of Metals in Concrete and Masonry Buildings” Paper No. 258, Corrosion/85, Boston, Massachusetts, April 1985.
  • J. Lloyd and R. Heidersbach, “The Use of the SEM to Study Cracking and Corrosion in Concrete” Concrete International, 7, no.5 (1985) 45.

Robert “Bob” Heidersbach is the author of Metallurgy and Corrosion Control in Oil and Gas Production. The book is based on Robert’s experience teaching new engineers that need to understand metallurgy and corrosion control in the oil industry. He is currently in the process of rewriting and updating the publication, and welcomes any suggestions about how to improve the book. In his spare time, Bob enjoys kayaking, biking and traveling.