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The solid-liquid gel-system of hardened cement paste



Title: The solid-liquid gel-system of hardened cement paste
Author(s): Max J. Setzer, Christian Duckheim
Paper category : conference
Book title: 2nd International RILEM Symposium on Advances in Concrete through Science and Engineering
Editor(s): J. Marchand, B. Bissonnette, R. Gagné, M. Jolin and F. Paradis
Print-ISBN: 2-35158-003-6
e-ISBN: 2351580028
Publisher: RILEM Publications SARL
Publication year: 2006
Nb references: 21
Language: English


Abstract: The interaction of the solid gel with pore water is studied. Since solid gel and pore water cannot be handled separately the system is called solid-liquid gel-system. It can only be de-scribed correctly with the theory of surface thermodynamics and of disjoining pressure which are shortly outlined. Experimental data of the heat of fusion, the pure density of the solid liq-uid system for hardened cement paste specimens stored at different relative humidity, preci-sion measurement of shrinkage and swelling and of isotherms are presented for the first de-sorption and the following adsorption-desorption cycle. From results and theory it can be con-cluded that during hydration a stable stress free solid liquid system is formed with a disjoining pressure ? ˜ 0. It is established by the combination of attractive dispersion coefficients and primarily repulsive electrostatic and structural forces. The system stabilises in the secondary energetic minimum. The density of pore water with near to the bulk value 1 g/cm³ i.e. only slightly structured. In first desorption this stability is lost when the pores become empty. The only remaining part of disjoining pressure is the dispersive forces in the air filled interphase which are being attractive. The pore distances shrink below the one of secondary minimum. Macroscopic shrinkage is proportional to this i.e. the mass loss. At low humidity the loss of water is nanoscopically not generating an additional shrinkage but in contrary a constancy or a slight increase of the pure solid-liquid volume leading to a decrease of density of the solid-liquid gel-system. Macroscopically a real shrinkage is observed which can only be explained by a shrinkage of the now air filled pore volume. This shrinkage can be attributed to a change of surface energy and herewith to disjoining pressure of the air filled pores where the ad-sorbed molecular film is diminished. During adsorption this shrinkage by surface energy is reversed first. At higher humidity capillary condensation sets in and a nearly stress free sys-tem is regained however, now in the primary minimum of disjoining pressure with reduced swelling compared to the first desorption shrinkage. The pore water is now highly structured with high density and reduced heat of fusion. The article is a concise survey and conclusion of several projects [19-25].


Online publication: 2006-08-02
Classification: 3.1 Theme 1: Numerical Models: from Microstructure to Transport Properties and Durability
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2351580028.044


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