Infrared Film for 35mm Camera? 2

[jheidt2543]

In the article titled "How can you be sure?" by Gerald A. Dalrymple, PE on pages 23-27 in the October 2004 issue of Structural Engineer, the author talks about ways "to ensure properly grouted reinforced masonry construction". He mentions Infrared Thermography (IRT) as one way to non-destructively inpect grouted masonry walls. His Photo #2 on page 27 shows how easily IRT photos can highlight the grouted cores in a masonry wall.

My questions:

1. Is IRT film available for standard 35 mm cameras and how available is it and how much does it cost, or does this take specialized equipment?

2. Have any of you used this technique and how practical is it for small projects?

 

[Ron]

The infrared film for 35mm cameras will not work for this application. The light response spectra are different.

What he is talking about is using infrared thermography to show the variations in surface temperature of the wall caused by the differences in mass (and thermal retention) between the filled areas and non-filled areas. I have used this technique many times to show with terrific clarity the cell filling or lack thereof. Shows well in litigation.

A good quality color infrared thermographic scanner will cost about $50,000 (US). We use it for other stuff as well so that we can get some return on the investment. Our's is digital and we can convert and save the images for reporting or presentations.

This technique is not cheap. It will cost about $1500 to $2000 per day for the field work. It takes the whole day or in some cases night to show the proper thermal differences in the wall surface. Can't just walk out there, shoot and leave.

 

[jheidt2543]

Ron,

Thanks for a very detailed response.

Would it be correct then to say that the 35 mm IR film is not sensitive or fast enough to be used in this application? Or, is it that the 35 mm film does not cover a wide enough area of the infrared spectrum?

I was hoping that the 35 mm IR film might be of some use with a longer exposure time, even if not as definitive as the scanners.

I have read of the thermographic scanners being used for heat loss inspection of buildings too.

 

[Ron]

jheidt2543....
The 35mm film does not cover the appropriate spectra for your evaluation...longer exposure time won't matter.

Thermography can be used for lots of facility applications. We use it mostly to determine the apparent moisture condition of roof insulation, though we also use if for checking wall insulation, thermal shorts or lack of sealing at windows/openings, checking for overheated breakers in electrical panels, checking for rebar/filled cells, and a variety of other applications. It is a versatile tool. I hope to develop other uses of it such as for certain types of pavement inspections as well, though as you might imagine, it is not my full time vocation to just use thermography!

 

[structuresguy]

That's pretty cool stuff you are talking about. I have seen it used for thermal and moisture related problems in walls/roofs before, mainly up north in Canada. But I have not heard of it used for checking for filled cells. Neat, if somewhat (very) expensive.

Ron, where in the world are you located? Do you have much demand for the use of the IR scanner in your area?

Just wondering how would xray or ultrasound compare economically for determining filled cells/rebar? After all, I doubt too many people have $50,000 dollar IR scanners laying around, particularly in lesser populated areas.

 

[jheidt2543]

I thought the following comments from a private exchange on this topic that I had with an aquaintance of mine might be of some interest (however,he must remain nameless):


""The 10/26/04 comment from "Ron (Structural) " definitely makes sense in the application you described. Infrared film used in "infrared photography" is sensitive to radiation in the spectral range of 700 - 1000 nm. At reasonable exposure times (a few minutes or less) it does not respond to heated objects that your dark-adapted eye can't see as a red glow (about 1000 degrees F). It requires that the object be illuminated by a "light source" that emits IR radiation in that spectral range (sunlight or an incandescent lamp, for example). Materials that exhibit unique IR reflectances will be recorded differently on IR film than they appear to the eye or to conventional film.

Thermography, on the other hand, responds to long wavelength thermal radiation emitted by objects at temperatures as low as body temperature or even less. Years ago I worked on a project for NASA using this technology to measure temperatures of critical instruments and other devices exposed to conditions of outer space. NASA was concerned that certain thermally sensitive electronic packages might overheat in direct sunlight in the absence of an atmosphere to conduct heat away. Thermography proved to be better than the traditional method of inserting hundreds of thermocouples into the packages."" Another interesting application.

structuresguy, I think both X-ray and ultrasound methods require access to both sides of the wall. The photo in the "Structural Engineering" article of the thermography of the wall is from one side at a distance where the photo can take in the entire wall, top to bottom. Just guessing I would say the photo was taken from 60' to 100' away.

 

[Ron]

Guys....I'm in Florida. Have successfully used thermography for this application many times, even in daylight.

Radiography requires access to both sides, is very expensive for the amount of data you get....for example, each film is 4"x17"...if you put 4 of them together you could shoot an area 16"x17" and your radiation source would have to be at least 2 feet from the surface of the concrete. This would produce a shot time of greater than an hour for typical strength radiation source. All people would have to be moved about 75 feet away (at least) and the film would have to be processed...you might see one filled cell and one piece of rebar. Ultrasonic and magnetic methods are similarly limited, with neither of them typically providing a record of the observations.

Using thermography, you can shoot an entire wall or large section of wall at once, it is processed immediately and digitally recorded for a permanent, visual record of significant clarity.

 

[JStephen]

The term "infrared" covers a very wide range of the spectrum. Infrared film for cameras picks up the part of the spectrum closest to visible light. What you need to detect for your application is at the other end of the IR spectrum.

I've read that IR film can detect heated objects (not quite red hot) with exposures of several minutes. But in general, it won't show where the hot spots are on anything, where the heat is leaking, where the body was, etc. That is all different equipment, as mentioned above. IR film works off reflected IR light, from the sun or light bulbs.

 

[eyec]

the key to the usefullness of IR is the ability to differentiate between temperature differences.

if the area you are inspecting is of unifrom thermal radiance then you can be sure there are no voids in the grout. if on the other hand differences are evident then you have an area of concern.

also in this (and many others) you are seeing the result of thermal transfer. if a spot shows warmer (or cooler) thermal IR then the actual offending location needs to be located, sometimes via ultrasonic testing or at worse destructively sectioning the area to pinpoint the problem.

unless you have training in IR, contract a company that has trained technicians. i have seen many pick up a thermal camera and cause more problems than providing reliable solutions.

it all boils down to cost benefit reasoning. what will the cost of a failure be if you don't do it right the first time! if there is a safety consideration then it is a no-brainer - do it!

 

[Ron]

eyec....
you wrote "if the area you are inspecting is of unifrom thermal radiance then you can be sure there are no voids in the grout. if on the other hand differences are evident then you have an area of concern."

Not necessarily true. There has to be an induced thermal difference brought about by exposure to sunlight or, in winter, the radiation of heat from the interior. Each of these affects the mass of concrete and masonry, with those areas of greater mass and density retaining the heat longer, thus showing the pattern in a transient time as the entire wall cools or heats to equilibrium.

 

[structuresguy]

Ron...thanks for the reply, I see your point on a productivity point of view. A large building would take a very long time using ultrasound of xray.

I too am in FLorida, on the spacecoast. I will have to keep you in mind if we ever need an investigation performed.

 

[Ron]

structuresguy...thanks. We're doing some work in your area now. Our IR camera is based in Orlando.

 

[structuresguy]

Hey Ron....contact me offline so I can get your contact info.

structuresguy @ yahoo . ca

 

[eyec]

structuresguy/Ron,

i was replying specifically to the grout. what you say is true if you are looking at the entire structure. i was under the impression the concern was the grout and voids or lack thereof.

even so, my comment "if on the other hand differences are evident then you have an area of concern" remains valid.

if the differences of density (of the concrete/mansonry) are drastically different (thermally) there still remains a concern. to exclude radiant difference from sunlight then shoot at night or overcast.

regardless, structuresguy has been enlightened on the benefits of IR inspections not just taking IR pictures.