SEDL / STP / STP691-EB / STP36079S

Ice Formation in Hardened Cement Paste—II. Steam-Cured Pastes with Variable Moisture Contents

Bager, DH
Research associate and associate professor, Building Materials Laboratory, Technical University of Denmark, Teknishe Hejshole,

Sellevold, EJ
Research associate and associate professor, Building Materials Laboratory, Technical University of Denmark, Teknishe Hejshole,

Pages: 16    Published: Jan 1980

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Abstract

Ice formation in steam cured (97°C) hardened cement pastes water/cement ((W/C) from 0.35 to 0.60) with different moisture contents has been measured using the Calvet microcalorimeter. The specimen size was about 11 cm³. The major results are: (a) 60 to 80 percent of the evaporable water in saturated specimens is freezable, and most of it freezes close after nucleation (this is in sharp contrast to pastes cured at 20°C); (b) for saturated pastes the nonfrozen water content at -55°C is independent of W/C-ratio and corresponds to 3.3 equivalent BET-monolayers; (c) the nonfrozen water content decreases with decreasing initial moisture content (for a moisture content corresponding to 60 percent relative vapor pressure at 20°C the nonfrozen water content is equivalent to 2.4 monolayers; at lower moisture contents no ice forms); and (d) the differential heat capacity of the adsorbed water is equal to that of bulk water at saturation, but increases by 5 to 10 percent at monolayer coverage. The average heat capacity of the first monolayer is about 25 percent lower than that of bulk water.