Alwayslearningelec
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So I guess this scenario only takes place in an existing building when core will be needed.???
XRAY Concrete slabs
- Thread starter Alwayslearningelec
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So I guess this scenario only takes place in an existing building when core will be needed.???
macmikeman
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Yea, I have never used in in new construction, I sleeve slabs if needed when new. I used to do a lot, lot of drilling at the local airport. It was more cost effective to purchase a core drill and bits. (and find a good bit repair shop as well). But for occasional work, no way- I call Concrete Coring Company in.
Alwayslearningelec
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Thanks fo that info.
We always sub this work out to a company that only does scanning but they are expensive. We've recently found a company that does ground penetrating radar and have only used them once but they are about half the price and just as good. Although I still haven't figured out if the X-ray is in fact more expensive or if we were just getting ripped off 
Alwayslearningelec
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- NJ
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Ok, dso if I doing a renovations of an existing 4 story building How do I figure where xraying will be needed. Wherever coring is going to take place?
macmikeman
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And not to mention the potential for drilling thru encased conduits with live conductors. My core drill has a little "dometer" on it that shows the pressure the bit is encountering. With practice you can mostly tell when you are about to drill thru metal like rebar or emt, (not tension wire, thats actually really easy to cut thru). Years ago one of my guys wasn't paying attention to that on a Friday afternoon and managed to drill into an encased outside feeder conduit that was for unattached building that was a freezer for meat headed to the outer islands at Aloha Air. Big Problem.. Big problem because my crew preferred going to the local Holiday Inn bar after work every Friday, not fix broken conduit and re-pull new feeders. However, some stayed with me and about 3 or 4 hours later, we had it dug up, fixed, and re-pulled, and working again. The slab was outside the building and the core was so we could put in a traffic bollard in front of new gear mounted to the building. That is why you want to make sure to x-ray.
Subsurface Imaging Inc
Member
- Location
- Southern California
Hi guys, new to the forum. Came across this thread while searching for something else online.
I don't want to come across as spam, so I will do my best to cover questions without trying to sell my services.
There are basically two types of inspection for concrete coring. One, as you guys have discussed is concrete x-ray.
The other is ground penetrating radar.
Like most tools, each has advantages and disadvantages.
Radar has the ability to scan the concrete from only one side, as a scanning devise, it is recommended that each core has a 2'x2' area around it clear for movement of the antenna. There are no harmful energies present with radar, so most jobs can be completed during the day while other trades are present. Also, since only one side of the concrete needs to be scanned, slab on grade is not a problem. Actually radar is about the only imaging method available for slab on grade.
The disadvantage to radar is that it is almost impossible to differentiate between rebar and post-tension cable. I know, I know, so and so company said they can, the manufacture of the radar said you can etc. It is possible under certain circumstances, but that is the exception. Also, plastic conduit is very difficult to see with radar. The reason is simple, radar works by somewhat measuring the dialectric constant of the medium that it is going through. As far as radar is concerned plastic (PVC) conduit has the same dialectric constant as concrete. Again, there are exceptions, but as a rule we say "best effort"
Concrete x-ray needs access to both sides of the concrete at each location to be drilled, as a rule of thumb, we need as much room as the core driller needs top and bottom. Typically, you mark where you want to drill, and the x-ray crew will locate the bottom side. Depending on concrete thickness, you will need to clear a 50' radius around each location of all non-xray personnel. Barrier tape will be posted to keep the area clear. Many times it is more productive to xray after hours.
The advantage of xray is we can see basically everything in the deck. Rebar (including size), conduit, with or with out wires, number of wires etc. and post-tension cable.
It is our belief that you need to have both, and use them accordingly.
One extra thought to keep in mind, our radioactive materials license from the state of California is very expensive (yearly), the paperwork involved with our radiation safety program is very time consuming, and the amount of support equipment involved with xray is very expensive. I.e. Fullsize trucks with mobile darkrooms, two men on the clock for every xray job ect.
Radar has virtually no support equipment, can be dispatched out of basically any car, needs only one person on the clock, etc. Our margins are much better with radar, why do we still do xray? Because it is necessary at times.
Sorry if it was long winded, let me know if you have any questions..
I don't want to come across as spam, so I will do my best to cover questions without trying to sell my services.
There are basically two types of inspection for concrete coring. One, as you guys have discussed is concrete x-ray.
The other is ground penetrating radar.
Like most tools, each has advantages and disadvantages.
Radar has the ability to scan the concrete from only one side, as a scanning devise, it is recommended that each core has a 2'x2' area around it clear for movement of the antenna. There are no harmful energies present with radar, so most jobs can be completed during the day while other trades are present. Also, since only one side of the concrete needs to be scanned, slab on grade is not a problem. Actually radar is about the only imaging method available for slab on grade.
The disadvantage to radar is that it is almost impossible to differentiate between rebar and post-tension cable. I know, I know, so and so company said they can, the manufacture of the radar said you can etc. It is possible under certain circumstances, but that is the exception. Also, plastic conduit is very difficult to see with radar. The reason is simple, radar works by somewhat measuring the dialectric constant of the medium that it is going through. As far as radar is concerned plastic (PVC) conduit has the same dialectric constant as concrete. Again, there are exceptions, but as a rule we say "best effort"
Concrete x-ray needs access to both sides of the concrete at each location to be drilled, as a rule of thumb, we need as much room as the core driller needs top and bottom. Typically, you mark where you want to drill, and the x-ray crew will locate the bottom side. Depending on concrete thickness, you will need to clear a 50' radius around each location of all non-xray personnel. Barrier tape will be posted to keep the area clear. Many times it is more productive to xray after hours.
The advantage of xray is we can see basically everything in the deck. Rebar (including size), conduit, with or with out wires, number of wires etc. and post-tension cable.
It is our belief that you need to have both, and use them accordingly.
One extra thought to keep in mind, our radioactive materials license from the state of California is very expensive (yearly), the paperwork involved with our radiation safety program is very time consuming, and the amount of support equipment involved with xray is very expensive. I.e. Fullsize trucks with mobile darkrooms, two men on the clock for every xray job ect.
Radar has virtually no support equipment, can be dispatched out of basically any car, needs only one person on the clock, etc. Our margins are much better with radar, why do we still do xray? Because it is necessary at times.
Sorry if it was long winded, let me know if you have any questions..
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
We appreciate your understanding, since forum rules do not allow any time of selling. But your post was very informative and helpful, and I thank you for the contribution.
Subsurface Imaging Inc
Member
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- Southern California
Usually an Obgyn..:grin:
Ultrasound is not practical for this type of work. It has been tried before, but it picks up every grain of sand and concrete is too porous.
dduffee260
Senior Member
- Location
- Texas
What about a ferrous scan. Have you checked on it?
X-Raying something requires a source.
Radiographing power pipe is an X-Ray. The source used is a "pill" of highly radioactive cobalt or othe nasty stuff. Mostly it's done off shift because people can't take the zoomies.
To x-ray something you need a source ( x-ray generator, radio active element etc) on one side and a detector (film or _____) on the other.
Installing anchor bolts in a nuke plant was always a problem. Hit rebar and you had to move or redesign the hanger. Detecting anything deeper than the top layer of rebar was dreaming.
Rebar detectors are good but not perfect.
Core -drilling was not allowed near any embedded conduit.
Your first indication you didn't locate everything might be the water is disappearing next is the "bang" and then the blue smoke comming out of the whole.
I recommend you find a way to let the GC run the "locate" program.
The best plan was accurate "As-builts" and photographs.
Radiographing power pipe is an X-Ray. The source used is a "pill" of highly radioactive cobalt or othe nasty stuff. Mostly it's done off shift because people can't take the zoomies.
To x-ray something you need a source ( x-ray generator, radio active element etc) on one side and a detector (film or _____) on the other.
Installing anchor bolts in a nuke plant was always a problem. Hit rebar and you had to move or redesign the hanger. Detecting anything deeper than the top layer of rebar was dreaming.
Rebar detectors are good but not perfect.
Core -drilling was not allowed near any embedded conduit.
Your first indication you didn't locate everything might be the water is disappearing next is the "bang" and then the blue smoke comming out of the whole.
I recommend you find a way to let the GC run the "locate" program.
The best plan was accurate "As-builts" and photographs.
Subsurface Imaging Inc
Member
- Location
- Southern California
Ferrous scanners are pretty much useless unless you have a single mat, somewhat close to the surface, and atleast 5" or so spacing on the rebar.
Will not tell the difference between rebar, P.T. cable, and I'm not sure it will pick up conduit.
Basically, there are two tools to be considered for pre-core/saw-cutting inspection. Ground penetrating radar, and concrete x-ray.
There are other tools that are available, but, in our experience aren't worth considering.
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