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Gypsum concrete is a building material used as a floor underlayment used in wood-frame and concrete construction for fire ratings, sound reduction, radiant heating, and floor leveling. It is a mixture of gypsum plaster, Portland cement, and sand.〔 The brand name Gyp-Crete, a Maxxon Corporation trademark, has come into general use as a term for gypsum concrete by construction professionals and architects.〔http://forums.jlconline.com/forums/showthread.php?31934-Concrete-or-Gypcrete〕 == Composition == US patent 4,444,925 lists the components of Gyp-Crete® as atmospheric calcined gypsum, sand, water, and small amounts of various additives. Additives listed include polyvinyl alcohol, an extender such as sodium citrate or fly ash, a surfactant such as Colloid defoamer 1513 DD made by Colloids, Inc., and a fluidizer based on sodium or potassium derivatives of naphthalene sulfonate formaldehyde condensate. One example mix is shown below.〔Feldman, J. G. (1984) ''(U.S. Patent No. 4,444,925 )''. Washington, DC: U.S. Patent and Trademark Office.〕 The purpose of the polyvinyl alcohol is to prevent the surface of the concrete from becoming dusty. While the exact mechanism is not known, it is thought that as the concrete sets, water migrates to the surface, bringing with it fine, dusty particles. When the water evaporates, the dusty particles are deposited on the surface. It is thought that the polyvinyl alcohol prevents the dusty particles from migrating upwards with the water.〔 The mix is prepared on site using a specialized truck. The truck contains a tank for water, a mixing tank, a holding tank, a pump, and a conveyor for the sand and calcined gypsum. A hopper for the sand and gypsum is mounted externally on the vehicle.〔Jorgenson, C. R., et al. (1978) ''(U.S. Patent No. 4,075,374 )''. Washington, DC: U.S. Patent and Trademark Office.〕 To prepare the mix, the sand and calcined gypsum are added to the hopper and mixed. Most of the required water is added to the mixing tank, then the sand and calcined gypsum are mixed in. Once all the sand and calcined gypsum have been mixed in, the rest of the water is added until the proper consistency is attained. Finally, the additives are mixed in and the whole batch of concrete is moved to the holding tank to be pumped out into the required area via long hoses. A small sample is taken from the batch and set aside so that the set-up time can be observed and adjustments can be made to the amount of additives so that the timing is correct. Once the mix has been poured, little leveling, if any, is needed. The mix should be smoothed gently with a flat board, such as a 40” 1x4. This helps to concentrate the calcined gypsum at the surface.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gypsum concrete」の詳細全文を読む スポンサード リンク
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