Evaluation of Concrete for Fire Damage
Just read a well-written article in Structure magazine about evaluating fire damage to concrete foundations, entitled Engineering Evaluation of Fire Damage to Concrete Foundations, by Peter Marxhausen, M.S., P.E. Mr. Marxhausen writes about his approach to evaluating numerous concrete foundations after the Waldo Canyon fire in June 2012 and the Black Forest fire in June 2013.
The most interesting part of the article to me was his observation regarding the development of his method of evaluating fire damage. He noted that a decade ago he would typically obtain concrete core samples and submit them to a testing lab for chemical, strength, and microscopic evaluation, which often would take four to six weeks at a cost of $3,500 to $6,000. But since that time he has learned, in the words of one of my former employers Russell Fling, P.E., “To work smarter, not harder.”
Mr. Marxhauser proceeds to describe the method he has developed to perform a relatively quick and economical evaluation to categorize the concrete foundations “as positively undamaged, positively damaged, or questionable requiring a further detailed analysis.” His procedure consists of a visual assessment for surface damage, cracking, color changes, spalls, etc.; an audible assessment where he uses a framing hammer to sound the concrete listening for a high pitched ring or a dull thud; a fracture assessment where he strikes the concrete with a hammer to see if the concrete material has been weakened by internal cracking from exposure to the excessive heat; and a relative strength assessment where he compares the strength of concrete exposed to the fire with that not exposed to the fire using a Schmidt hammer or a Swiss hammer.
His article was encouraging to us because we have developed a similar simplified method based on our university education regarding concrete; our continued education through consideration of articles, publications, and studies regarding the evaluation of fire damaged concrete; and our observations and hand-on experience evaluating fire-damaged structures.
This article was even a bit humorous to me because we have sometimes been questioned, doubted, or even ridiculed by contractors, home owners, even clients, etc. while using our simplified methods. Many who observe us doing a visual, audible, or fracture assessment think these are too simple to reveal any helpful information and are expecting us to remove samples and test them in a laboratory or as one person asked “are you going to perform carbon dating?”
Although laboratory tests may be beneficial in some cases, they are not necessary in most cases and the simplified method brings about a quicker resolution, with accuracy and with less expense to the client. Furthermore, when testing of the material is necessary, it can always be performed after the simplified method has been completed. Then the testing may be limited to those areas of the foundation where the simplified method was insufficient to render a professional opinion within a reasonable degree of engineering certainty.