High-Strength Concrete Binders Part B: Nonevaporable Water, Self-Dessication and Porosity of Cement Pastes With and Without Silica Fume

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Title: High-Strength Concrete Binders Part B: Nonevaporable Water, Self-Dessication and Porosity of Cement Pastes With and Without Silica Fume

Author(s): E. J. Sellevold and H. Justness

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 891-902

Keywords: binders (materials); cement pastes; nonevaporable water; porosity; hydration; self-dessication; silica fume; Materials Research

Date: 5/1/1992

Abstract:
The decrease in relative humidity during hydration and the chemical shrinkage have been measured for different cement paste compositions. The amount of nonevaporable water per degree of hydration as found by NMR, pore size distribution by mercury intrusion, and total porosity to water have also been determined. The cement pastes were made form portland cement with 0, 8, and 16 percent condensed silica fume, with w/c + s of 0.20, 0.30, and 0.40. The relative humidity (RH) was found to decrease rapidly during the first 2 weeks and reach about 78 percent RH after more than a year for the lowest w/c + s, independent of the CSF dosage. The highest ratio gave about 87 percent RH. The nonevaporable water per degree of hydration depends on the NMR-based estimate of the degree of cement hydration, but it is most consistent (i.e., independent of w/c + s and CSF dosage) when it is assumed that the CSF dosage does not consume any water. The water porosity was found to increase with increasing CSF dosage, while the mercury intrusion results showed both a finer pore structure and smaller total porosity with increasing CSF dosage. Mercury intrusion into miniconcretes (dmax = 8 mm) with the same binders gave a much coarser pore size distribution, indicating that the paste-aggregate interface region is more open than the bulk paste. No evidence was found that increased CSF dosage improved the interface pore structure. This is in contrast to other evidence in the literature, and may be caused by partial dehydration and/or microcrack formation during the drying at 105 C.