Originally Posted By: jbowman This post was automatically imported from our archived forum.
How many of us have inspected a house or seen a house that has been refurbished or remodeled after an extensive fire. Here is a possible write up that you may consider when reviewing or commenting on the foundation.
CONCRETE TIP: Concrete or foundation has been subjected to past fire(s) and possible damage.
Fire - When a fire occurs servere concrete damage may occur because of a method known as "heat shocking". In layman's terms concrete expands as it's heated. In the extreme heat of a fire, the outer shell or layer will expand much more quickly than the inner portion, causing the outer layer to fracture and break away. This process is known as "differential expansion". It can also occur in reverse when the fire is doused by fire hoses or sprinkler systems. In this case, hot concrete is cooled suddenly causing the outer layer to shrink and break away.
Place your disclaimer here requesting review by an expert.
Originally Posted By: mkober This post was automatically imported from our archived forum.
Over the last 30 years or so, I’ve seen probably a dozen examples of heat-damaged concrete–most were bridge structures impacted by tanker trucks, although one was a house totally destroyed by fire and then rebuilt over the original poured concrete foundation. The contractor took the “high road” and extensively sand-blasted all of the suspect concrete off, then reformed the front faces and poured a reinforced wall “overlay.” A good testing lab will do a petrographic analysis on core samples to determine the extent of fire damage, although most heat-damaged concrete is easy to detect with a Schmidt hammer (compressive strengths of 1000 psi or less) or even a sounding hammer and scratch awl–it will lack the normal “ring” of undamaged concrete, and will scratch easily and have a somewhat “chalky” consistency. Of course, surface spalling will be obvious to all. Just don’t mistake common carbonation for heat damage–they both exhibit similar symptoms. Most H.I.'s would probably do best by deferring to a specialist (if available) to avoid operating out of their area of expertise.
Originally Posted By: ccoombs This post was automatically imported from our archived forum.
Another concern is with post-tension foundations. The concern is the melting of the plastic sheathing on the tendons and heat damage to the steel. Most of the inspection requests I get are for insurance reasons. I typically won’t sign off on fire damaged slab. I defer to a more qualified expert.
Originally Posted By: roconnor This post was automatically imported from our archived forum.
mkober wrote:
Most H.I.'s would probably do best by deferring to a specialist (if available) to avoid operating out of their area of expertise.
I agree there, although deferring to an engineer on evaluation of fire damaged concrete is mandatory in my book.
I have done some structural fire damage investigations, and it gets very involved. Well beyond a home inspection. But I still think it's good for an HI to know a little about the topic, like how different colors generally mean different levels of fire exposure (and potential for real damage). It can help visually identify a real concern. I will see if I can find a link to post for the members, unless ya have one handy.
And when are ya gonna trade in that Schmidt Hammer for some good Impact Echo equipment ...  ... I threw out the compressive strength chart that comes with it the day I got it (for good reason). Although I must admit I still use a mineral hammer for sounding myself, no matter what the equipment readouts are. Old habits, and having a "feel" for things as an engineer also, never die ...
-- Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong
Originally Posted By: mkober This post was automatically imported from our archived forum.
Robert,
Don't know of any links for fire-damaged concrete assessment. And I'll have you know my trusty Schmidt hammer is, like, part of the family. I mean, would you trade in the little woman just cuz she's getting a little gray around the temples? Haven't had the hammer calibrated in years, but it's still a valuable tool for determining RELATIVE compressive strengths when compared to a known standard. The key is in how well one preps the surface with the rubbing block--over time, the block has to be traded in for a newer, more abrasive model. I doubt I'll ever spring for some fancy gadget whose cost I could never justify. Besides, I just like getting my money's worth out of something--put 383,000+ miles on one motorcycle before I got tired of having to carry a ton of spare parts on every long trip!
Originally Posted By: roconnor This post was automatically imported from our archived forum.
mkober wrote:
... my trusty Schmidt hammer ... still a valuable tool for determining RELATIVE compressive strengths
Very true, it is a pretty handy tool for engineers. I was mostly just yanking your chain a bit ... as long as ya threw out the F'c chart ... 
I guess I will dig a bit and see if I can find a good link with some info on visual inspection of fire damaged concrete. Most of the stuff I have is too technical or relates to evaluations.
-- Robert O'Connor, PE
Eagle Engineering ?
Eagle Eye Inspections ?
NACHI Education Committee
I am absolutely amazed sometimes by how much thought goes into doing things wrong