Current methods test sealants statically, by placing them outdoors for long periods of time, to measure their resistance to the elements. The problem, says White, is that under normal conditions, sealants are also affected by constant movement: the temperature-induced expansion and contraction of the different kinds of materials they seal together—such as glass, in a window, and steel, in the window and building frame.
"When you put sealant on a building, it is because the glass window and steel frame expand and contract at different rates with changes in temperature," he explains. "The sealant needs to be able to seal this gap, as it changes." This creates fatigue in the sealant, eventually causing it to crack and fail.
Using simple materials that can largely be purchased from a hardware store—including PVC pipe, wood, steel supporting frames, and toilet flanges—White and his colleagues have developed the first instruments to test sealants under real-world conditions, while monitoring their displacement and load with sensors and tracking environmental conditions with a weather station. "This new device—which is very inexpensive—induces movement that is very similar to what a sealant would see in the actual application, in a building," he says.
The designs of the two devices—one that puts sealants in tension and one that puts them in compression when cold—have been passed along to an industrial consortium of sealant manufacturers working with NIST. "Two companies have actually built and are using them for sealant testing," says White.
The paper, "Design, Fabrication and Implementation of Thermally Driven Devices for Building Joint Sealants," by Christopher White, Kar Tean Tan, Emmet O'Brien, Don Huntson, and Joannie Chin, appears in the Review of Scientific Instruments. See: URL
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Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques. Its contents include original and review articles on instruments in physics, chemistry, and the life sciences; and sections on new instruments and new materials. One volume is published annually. Conference proceedings are occasionally published and supplied in addition to the Journal's scheduled monthly issues. RSI publishes information on instruments, apparatus, techniques of experimental measurement, and related mathematical analysis. Since the use of instruments is not confined to the physical sciences, the journal welcomes contributions from any of the physical and biological sciences and from related cross-disciplinary areas of science and technology. See: http://rsi.aip.org/
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