セメントの偽凝結

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書誌事項

タイトル別名
  • False Setting of Cement
  • セメント ノ ニセ ギョウケツ

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説明

A complicated phenomenon of false setting by aeration of cement will be explained as the results of various factors and interactions between those in the early stage of stiffening due to hydration of plaster of Paris or aluminate.<br>With increasing of alkali carbonates, for instance, which can be formed by the aeration of cement, and act as a retarder of plaster but simultaniously as an accererater of aluminate, the false setting arises at first, because the plaster setting comes at few minutes after mixing. Later it disappears owing to a severe retardation, and finally actual rapid setting takes place by an accererated hydration of aluminates.<br>The critical amount of SO3 in the form of plaster of Paris to give false setting is in the range of ca. 0.8-1.5%, varing not only with the amount and form of alkali salts but with several factors such as the amount of co-existing dihydrate or aluminate. Then it is desirable that the amount of gypsum having a tendency to change to plaster of Paris is limited to about SO3 1%, and insoluble anhydrite is added at the same time up to the optimum SO3 content.<br>An accerelating test is considered to be available by means of the penetration of paste with addition of small amount of alkali carbonate (for example, nearly 0.1% of Na2CO3) in order to detect if a cement will show false setting after aeration.

収録刊行物

  • 窯業協會誌

    窯業協會誌 65 (740), 211-218, 1957

    公益社団法人 日本セラミックス協会

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