Message Board Thread - "Rebar in Concrete"

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Rebar in Concrete jwstocker 8/5/2007
Greetings I am rather new to infrared tech. I currently manage a construction materials test lab in Eastern Ohio. I work with various materials such as soils, concrete, asphalt, aggregates. Many times in my line of work, when the "you know what" hits the fan with concrete construction I am required to go out and drill a core from a bridge deck, pier, roadway, tunnel, etc. Many times it is important to not drill into the rebar or post tentioning cables in the structure. My question is how deep can an infrared camera "see" rebar heat signatures into a concrete structure. Many times my glorified stud finder is wrong. I haven't needed to be dead sure "yet" but the day is coming. Any help would be appreciated.

Jace Stocker
AGGCON Testing
Re:Rebar in Concrete Intertec 8/7/2007
Your company might want to invest in GPR (Ground Penetrating Radar It is designed just for finding rebar and PT cables. GSSI and Sensors & Software both design good systems.
Re:Rebar in Concrete jvoitl 8/7/2007
I wouldn't attempt to use thermography in this application. The rebar and concrete will be the same temperatue so there will be no way for the camera to see the rebar, even if it is only just barely beneath the surface. By using an AC arc welder and coiling the leads on top of the concrete a current can be induced in the rebar creating heat that will eventually show up on the surface of the concrete. However this requires two things. One that the magnetic field from the welding leads reach deep enough into the concrete to induce a current into all the rebar, and two that the rebars are all touching other rebars near the ends to make completed electrical circuits through their entire length. These are two assumtions that are sure to get you in trouble.
Re:Rebar in Concrete EXO-Sight Infrared 8/15/2007
I agree with Intertec's post that GPR would work for this, but imagery can be fuzzy and may have false positives. I do think IR could be used in this application. Depending on the depth of the rebar you can either inductively heat the rebar or you can heat the structure up as a whole and observe the cooling process.

Contact me if you want some more information on how you would do this. (919) 302-4467

Darin Thomas
EXO-Sight Infrared
Re:Rebar in Concrete bophays 9/10/2007
For infrared to work in this application I belive a lot exact conditions must exist i.e. temp differance between materials etc. Hilti makes an instrument called a Farroscan. We have had great results using it to locate rebar and tension cables in precast concrete.
Re:Rebar in Concrete Peter T. 9/11/2007
You're better bet is to get one of the systems used for tracing buried cables, conduits, and pipes. There is usually a transmitter that injects a radio frequency signal into the metal (you have to get to the end of the rebar somewhere), and then the receiver senses the signal. I have used this type of equipment to find buried steel conduits and other metal in concrete floors in industrial facilities, so that they would not get cut or drilled into. It's not an IR answer, but it is one that could work for you. Check out the web site for a company called Radiodetection for an example.
Re:Rebar in Concrete DonW 9/12/2007
I have had good results locating rebar, waterlines, gaslines and electrical conducts that are imbedded in concrete slabs using a standard metal detector, the same type used to find buried coins.

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