Colorado NDE Firm Uses Infrared Thermography As An Investigative Tool

September 26, 2007, Boulder, Colorado - Infrared thermography has served as a nondestructive testing and forensic engineering investigative tool to locate delaminations and other defects in historic structures for some time. Now, Atkinson-Noland & Associates is researching how infrared thermography, commonly referred to as IRT, can be used to determine the presence and depth of these voids.

The process is called active thermography. Active thermography involves using a heat source, such as infrared or halogen lamps, infrared radiators, or the sun to heat the surface of the material. An infrared camera is used to observe the surface temperature. Areas containing voids or delaminations increase in temperature faster than an area void of structural defects because air or moisture in the void provide little resistance to the movement of heat. On the other hand, void-free solid material provides additional resistance.

Using active thermography allows larger areas to be tested for delaminations and voids in a manner that is more time and labor efficient than impact echo. As a result of testing more structural area, a more complete structural assessment can be provided to the owner. Active thermography also may play an important role in determining if there are life-safety issues due to pieces of material falling off structures because of naturally occurring defects in materials, such as sandstone and limestone.

The experiments conducted by Atkinson-Noland & Associates will use interfacing grout slabs to simulate the voids in natural materials such as sandstone and limestone. Various materials will be placed in the interface to determine their effect on heat transmission through the voids. A second series of tests may also be conducted to determine the effect that moisture has on the test. When working in the field, the material condition will not be the same as it was working in the laboratory. The laboratory experiment also will determine what type and size of heat source is necessary to efficiently heat the surface being studied.

Another goal of this research is to determine how dependent the method is on having an accurate estimate of the material's thermal conductivity. That thermal conductivity will affect the amount of heating time required for delaminations and voids to be located. The study's results will allow masonry consultants to use infrared thermography in a new role for performing structural assessments.

This method also will allow field work to be completed more efficiently, because larger areas can be investigated at a single time, as opposed to methods such as impact echo, where each individual object must be investigated. Active thermography can be used in areas where historic preservation and restoration are occurring to determine the conditions of the structure.