Relationships between Composition and Density of Tobermorite, Jennite, and Nanoscale CaO−SiO2−H2O
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- 作者：Jeffrey J. Thomas ; Hamlin M. Jennings ; Andrew J. Allen
- 刊名：Journal of Physical Chemistry C
- 出版年：2010
- 出版时间：May 6, 2010
- 年：2010
- 卷：114
- 期：17
- 页码：7594-7601
- 全文大小：186K
- 年卷期：v.114,no.17(May 6, 2010)
- ISSN：1932-7455
文摘
Relationships between composition, mass density, and atomic packing density for CaO−SiO2−H2O (C−S−H), the main hydration product of cement, and its mineral analogues tobermorite and jennite, are examined. A graphical approach, similar to a phase diagram, is used to display the variation in density as a function of water content. In order to provide insight into atomic packing density differences between these phases, hypothetical phase transitions are performed by adding the stoichiometrically correct amount of CaO and H2O to convert one phase into another, and then the molar volumes before and after the transformation are compared. These calculations indicate that C−S−H formed from cement hydrated under normal conditions has a considerably higher atomic packing density than both tobermorite and jennite. This is attributed to both the atomic structure of C−S−H and to its nanoparticulate morphology. The solid density values for C−S−H are used to predict the amount of chemical shrinkage that should occur in a pure tricalcium silicate or dicalcium silicate paste, and these calculations are in good qualitative agreement with published experimental measurements for cement paste. New experimental measurements for the composition and mass density of C−S−H in cement paste cured at elevated temperatures, dried and resaturated, and hydrated with silica fume are presented and interpreted using the same approach. An important finding is that curing at 80 °C leads to a C−S−H phase with a lower atomic packing density, a finding in agreement with experimental observations of less chemical shrinkage at elevated temperatures.