Non-destructive determination of concrete thickness 1

[jimrcasper]

Does anyone know of a non-destrucitve means of determining the thickness of a concrete slab? So far the only means if have found is Ground Penerating Radar (GPR). Is GPR difficult to used and/or interpret? Thanks

 

[Lutfi]

I think GPR (Ground Penetrating Radar) may help. I have used it in the past to detect voids under slabs in an investigation of concrete cracks. Turns out there were a huge void under the slab.

One of the major obstacles in using GPR on concrete slabs is presence of reinforcement.

Contact any GPR lab and ask them directly.

Good luck

 

[Ron]

jimrcasper...I agree with Lutfi. Be sure that whomever does the GPR work uses the correct frequency of antenna for concrete (it is different than for soil). Determining the thickness of thin slabs is difficult, but with calibration it can be done. Keep in mind that nondestructive testing only limits the amount of destructive testing/observation that needs to be done....destructive correlation must be done to gain meaningful data.

 

[LittleWheels]

Impact echo is good at determining thin slab thickness. I find it easier to interpret than ground radar, particularly if there is a reasonable amount of reinforcing.

http://www.ndt.net/index.html

has some useful articles and links.

 

[FSS]

I would be wary of using only non-destructive methods without any on-site verification. Would really try to find somewhere inconspicuous where a small hand drill could be used. Also, once you start getting cost estimates the hand drill option starts looking better and better.

 

[sghvib]

There is another method called "impact echo". The following link is a comercially available unit. Our firm has had some success with this unit provided field conditions are right.

http://www.olsoninstruments.com/ctg/ctg.htm

Good luck
sghvib

 

[Lutfi]

Time to stand on my soapbox for a couple of things:

As I was told when I was in college by my professors, you will need to use your "Engineering Judgment". Boy, were they ever right. I think we all do that few times day.

Not that I am opposed to other methods. I think it all depends on the situation. I agree that expense is an issue. However, if you have a suspicious situation and people safety and client operations and business is on the line, do not go for the cheapest! I have problem with engineers’ who sometimes let economics, or non-qualified sources, blare their sound engineering judgment. Imagine this, you are on surgery table; do you want your surgeon using the cheapest tools and tests!

What is nice a bout GPR you can get 100% coverage of the floor area! It does not take long to scan and the scan width is limited by probe size. The one that I have seen is about 8 - 10 inches wide and the machine travel "like a lawn lower passes and the thermal paper is printed real time. The printout needs to be read and translated to useful data.

Drilling and may give a true picture for very localized.

Use your engineering judgment