Pingos are hills where the Arctic landscape heaves upward because of the freezing of ground water as it seeps upward. While pingos are benign, the same forces that create them cause major headaches in another part of the wintry neighborhood. Lifting and cracking of buildings and paved surfaces, such as airport runways, pose a special challenge for facilities in cold climates. To help combat the problem, researchers at the National Institute of Standards and Technology are studying the behavior of supercooled salt solutions as models of the cold ground water involved in frost-heaving. NIST has developed the first precise measurements of the thermodynamic properties of supercooled salt solutions and has improved upon measurements for pure water.
Supercooled water is an unfrozen liquid at temperatures below zero.
Damage to buildings and other infrastructure can occur when water rising from the soil underneath freezes. For NIST, the lead designer and manufacturer of the new case, it was a case of deja vu. Nearly 50 years before, NIST's predecessor, the National Bureau of Standards, had designed and built the current encasements. In February 2000, Archives staff sealed the first prototype case with the transmittal page of the U.S. Constitution safely inside, the first test of the technology involving one of the Charters documents. Prototype two, an encasement with slight modifications from the original, rolled off the NIST production floor in July.