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, said Peter Champe, a preservation specialist.
The process is called active thermography, Champe said. 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, Champe said. 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, Champe said.
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, Champe said. Various materials will be placed in the interface to determine their effect on heat transmission through the voids.
A second series of tests also may be conducted to determine the effect that moisture has on the test. When working in the field, the material s condition will not be the same as it was working in the laboratory, Champe said. 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, Champe said.
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.
About Atkinson-Noland Atkinson-Noland & Associates has provided structural engineering services including nondestructive testing and nondestructive evaluation (NDE) for federal, state and private organizations since its founding in 1975. NDE employs various techniques such as ground penetrating radar (GPR) and metal detection to provide information about building materials and building components. The company provides a variety of professional engineering services for building assessment, repair and evaluation. It specializes in nondestructive and in-place testing of masonry structures. With expertise in masonry, nondestructive evaluation and historic preservation, their services can be customized to meet clients needs.
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