Existing CMU - Determining Reinforcing

A magnetic rebar locator will work..as will radiography and infrared thermography if you can heat the rebar (such as attaching a welder to it at relatively low amperage).

Thanks Ron. Is the magnetic rebar locator something common enough that a contractor would (or should) already have?

If you have a contact at Hilti, they carry a ferroscan tool. I have demo'd it, but did not purchase.

It rolls over the surface of the wall, and will produce rebar size (i think to within 1/8" diameter) as well as depth in the wall.

You may be able to rent them.

there's some instruments at i'd suggest getting a higher end instrument otherwise you'll say "yep, it shows rebar there and nope i don't know anything else". at least a higher end instrument might give indication of the size. there's still questions about lap, rebar type, grout strengths, groutspace cleanliness, etc etc etc

In my opinion and experience (and now for the "con" side to pacometers)...

One possible drawback to a magnetic scanner, pacometer, whatever you wish to call it, on a masonry wall could be that while you may be able to pick up the reinforcing, you may very well pick up on the wire reinforcing placed between the CMU blocks embedded in the mortar, which may give you a false reading.

Also, reinforcing at door locations and wall joints are usually doubled up, but the scanner will only accurately pick up that reinforcing is there, not how much reinforcing...if it doesn't pick up on the door jamb.

Short of mini-drilled holes spaced at a certain preset on center (32" or 48", usually), other methods could be considered a best-guess scenario.

There are newer tools out there for locating rebar. Hilti has two new rebar locators (PS-30 and PS-35 rebar locators). Much cheaper than the PS200, Ferro-scanner. That said, there are many rebar locators out there now (all have limitations). I've seen scanners find a lot of junk in masonry walls...

Clarke Engineering Services, PC
Construction Consulting & Anchor Testing

Thanks. It turns out that the wall is completely hollow - no grout, no reinforcing.... nothing.

This brings up another question which is unrelated - I am having them reinforce and grout all the areas where I am involved in new work. I have recommended to the arch. that they grout/reinf cells for the remainder of the wall but I don't think this will happen. There is no way this wall "works" as is but it obviously is working... what is my responsibility beyond suggesting they do further work beyond what I am involved in?

You've touched on the million dollar question! You are responsible to design per the latest codes but the structure was built per the latest code...at that time.
I used to inspect bridges in NYC. There were holes in walls (not meant to be there) that I could walk through. I was young and couldn't understand how it was still standing. yet there it was! We are so trained to think that concrete and masonry will not stand without steel... but Rome did pretty well for a while )
There are variences allowed for rehabiliting old structures where you can design under the older codes. Give the DoB a buzz or check their website which is pretty good..

Clarke Engineering Services, PC
Construction Consulting & Anchor Testing

If you are in the US and working under the 2006 IBC, then your responsibilty could end up being much greater than you think, want or expect.

If you are working under the above code, I suggest you read chapter 34 very carefully. It can be interpretted that you own the entire structure if you make even a small modification to a seismic force resisting element.

bookowski:

When ispecting CMU structures, a rebar scanner is something you should have in your hip pocket. I picked up mine at ACE hardware 15 years or so ago, and it works just fine. Saved my a** a once or twice too.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

Chapter 34 was removed from the NYC Building code.

Clarke Engineering Services, PC
Construction Consulting & Anchor Testing

I say the Hilti PS35 on ebay for US$499. I also heard good things about the Zircon stud finder. It should be able to locate reinforcement but that is about all it can tell.

As for your structure, if you believe it is a safety issue for the occupants then it is your responsibility to notify the owner of the conditions and/or defects. (I do not work in seismic country so I am not that concerned with seismic force resisting elements).