x-raying to detect necked down rebar due to corrosion

[ajk1]

Can x-raying be used to detect corrosion severed #6 rebar that has necked down to threadlike proportions and severed (as found in sme locations in chipped out inspection pits?

Has anyone done that successfully?

GPR has been tried and does not work because of the separation planes.

It is 2" mastic asphalt, then 1" concrete topping (mostly debonded), 1/8 asphaltic membrane, 7½" thick 2-way reinforced slab, then 2½" thick drop panel. Total thickness = 13.125" approx. 2-way slab. Top bars specified cover ¾".

 

[Ron]

ajk1....somewhat difficult to do. Not impossible, but difficult.

If you are looking at the bottom bars in the slab you have a much better chance of a good image as the object to film distance is lower, resulting in a more distinct image. For top bars, they will look "fuzzier" as an image.

A few difficulties.....

First, the thickness of the slab will dictate a very long time shot (upwards of 60 minutes or more) using Iridium 192. If you can find a lab that has a Cobalt 60 radioisotope, the shooting time would be less, but there's probably only a handful of labs that have Cobalt 60 in North America.

Secondly, because of the long shot time, there will have to be a large safe perimeter established in every direction as these are live radioactive isotopes (an x-ray machine is not powerful enough to shoot through concrete, effectively) using gamma rays and they are dangerous and highly regulated.

Third, the image size is going to be limited to what you can get onto a 4"x17" film or multiples of the 4" width, keeping in mind that the wider the film shot, there is a higher likelihood that the source to film distance will need to be increased, thus increasing the shot time even more.

......and, it's expensive!!

But to go back to your original question, yes....you can show what you described.

 

[ajk1]

Hi Ron - sounds like you are very knowledgeable on this. Thanks for the information. Could the source not be placed on the slab soffit and the film on the top, to increase clarity of the top bars?

 

[Ron]

ajk1...yes, it can be done from either side, but you have two layers of topping on the top side, plus the cover, so that puts the image to film distance at over 3". Will make the image less distinct.

 

[ajk1]

Ron - ok, good point. Thanks again.

 

[ImminentCollapse]

One other caveat, not certain what your application is, but Cobalt 60 comes in a rather large lead sarcophagus. On our applications that stayed on the truck. They cranked the source out say 30' or so, but I'm sure there is a limitation on that distance. So if you have difficult or tight access, you may not even be able to physically get Cobalt there.

As Ron mentions, Iridium is easier to deal with but may not have the pop you need, and I second the cost comment.

IC

 

[ajk1]

To ImminentCollapse - ok, I take your point. I think that I have given up on x-raying. Thanks for your help. You guys must be either in the x-ray business or doing a lot of it!

 

[Ron]

ajk1....I am a former ASNT Level III radiographer. I did that for over 10 years, but have not done so in quite some time. In my consulting, I'm still peripherally involved so I try to stay up with the technology and capability.

 

[ajk1]

To Ron: I see. Well that is good to know. You have been very helpful. Thanks again. Much appreciated.