Ceramics-Silikáty 44, (1) 35 - 38 (2000) |
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DETERMINATION OF MOISTURE CONTENT IN HYDRATING CEMENT PASTE USING THE CALCIUM CARBIDE METHOD |
Poděbradská Jitka 1, Maděra Jiří 1, Tydlitát Vratislav 1,
Rovnaníková Pavla 2,
Černý Robert 1 |
1 Department of Structural Mechanics, Faculty of Civil Engineering,
Czech Technical University, Thákurova 7, 16629 Prague 6
2 Institute of Chemistry, Faculty of Civil Engineering,
Technical University of Brno, Žižkova 17, 662 37 Brno
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The calcium carbide method is used for measuring the moisture content in hydrating cement paste which could be considered
as a measure of the course of the hydration process. The experimental measurements show that the readings on the acetylene
manometer used for calculating the residual moisture content in the material increase with time significantly up to
approximately six hours which is remarkably different from the measurements on the most of other materials such as bricks,
gypsum, etc., where the final constant readings are achieved already after ten minutes. Two hypotheses for the explanation of
this fact are proposed. The first consists in the assumption that calcium carbide reacts not only with free water but also with
a part of water already bonded in the cement binder. The decomposition of ettringite in the reaction bottle accompanied by
partial loss of bonded water, which becomes available for the reaction with calcium carbide should be the most probable
mechanism in this case. The second hypothesis is based on the assumption that the delay in determining the final values of
residual moisture content is caused by a slow release of water from cement gel due to the high bonding forces of water to the
porous matrix in small gel pores. In any case, the relatively long time necessary for the achievement of final readings makes
the application of calcium carbide method for monitoring the hydration process questionable because its main advantage, fast
determination of moisture content, cannot be effectively utilized. |
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