Supercritical drying of cementitious materials
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Date
2017-09
Publication Type
Journal Article, Journal Article
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no
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Abstract
Techniques to characterize the microstructure of hydrated cement require dried materials. However, the microstructure of hydrated products is significantly altered by high capillary forces during drying when using the conventional drying methods. To avoid drying stresses when preparing samples, we have employed supercritical drying (SCD) which has been used for decades to prepare aerogels that undergo no shrinkage during drying, but has rarely been used for cementitious materials. The pore solution is first replaced with isopropanol, and then with trifluoromethane (R23). The temperature and pressure are raised above the critical point, where no menisci or capillary pressure can exist; therefore, the dried samples are free of artifacts created by stresses. Images from scanning electron microscope show less compact morphology for supercritically dried samples than that dried by conventional methods, while BET surface areas of SCD samples are very close to samples dried by the isopropanol replacement method. This can be explained by the fact that isopropanol and supercritical fluid enter the micropores and block them. The nature of the chemical interactions of isopropanol and R23 with cement pastes are still not clear, but no reaction products were identified in the present study.
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Publication status
published
Editor
Book title
Journal / series
Volume
99
Pages / Article No.
137 - 154
Publisher
Elsevier
Event
Edition / version
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Geographic location
Date collected
Date created
Subject
Supercritical drying (E); Microstructure (C); Trifluoromethane (C); Isopropanol exchange (A); Scanning electron microscopy (B); Nitrogen adsorption (A)
Organisational unit
09593 - Angst, Ueli / Angst, Ueli
02606 - Institut für Baustoffe (IfB) / Institute for Building Materials