Investigation of water to ice phase change in porous media by ultrasonic and dielectric measurements

International audienceThe main objective of this paper is to study the evolution of the ice content of porous media submitted to sub-zero temperatures by dielectric and ultrasonic measurements. Dielectric measurements are made by a capacitive sensor-based apparatus. The amount of ice formed within the tested sample is estimated from the global dielectric constants of the sample and of all the phases that form the tested composite material. On the other hand, ultrasonic measurements are based on the evolution of the ultrasonic wave velocity through the tested sample during a freezing-thawing cycle. These two methods lead to very close results and appear to be cheaper alternatives to low temperature calorimetry. The ice content curves are analyzed with the help of thermoporometry concepts in order to characterize the pore size distribution. Results appear to be complementary to mercury intrusion porosimetry ones. Moreover the commonly observed hysteresis of the ice content during a freezing-thawing cycle is investigated with respect to material microstructure

Comportement au gel-dégel d'une structure en ciment

Ce travail vise à l'étude du comportement au gel-dégel des matériaux cimentaires. Le model poromécanique développé dans cette optique permet d'étudier l'influence sur la mécanique du couplage entre le changement de phase eau/glace, les transports en milieu poreux, la conduction thermique et le comportement de chacune des phases en présence. Nous pouvons ainsi prédire une pression de pore maximale au voisinage de la surface soumise au gel-dégel pouvant induire un endommagement localisé superficiel. Par la suite, l'influence relative des différents phénomènes physiques responsables de l'endommagement au gel-dégel est étudiée, permettant d'identifier les pressions hydrauliques de Powers comme prépondérantes

INVERSION OF THE MARANGONI CONVECTION WITH INCREASING TEMPERATURE Aqueous Fatty Alcohol Solution‐Air Interface

SCOPUS: ar.kFLWNAinfo:eu-repo/semantics/publishe

Application du froid artificiel au traitement des boues et des sols pollués par des métaux lourds (théorie et expériences à petite échelle sur des milieux modèles)

MARNE-LA-VALLEE-ENPC-BIBL. (774682303) / SudocSudocFranceF

Experimental evidence for the minimum of surface tension with temperature at aqueous alcohol solution/air interfaces

The equilibrium surface tension of an aqueous solution of fatty alcohol/air goes through a minimum when the temperature is raised. As a consequence, the surface tension gradient originated by a given temperature difference between two regions of a free surface has to be reversed when the temperature increases. Simple devices are built-up to visualize this effect. A defined local region of the free surface is heated by a metallic plate near the interface. Talc particles on the surface show surface motion using a profile projector. The expected inversion of the direction of the talc particles with increasing temperature is often observed. © 1984 Academic Press, Inc. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Surface-tension-driven flows in a thin layer of a water-n-heptanol solution

A model for Marangoni flows that we observed on plane free surfaces of thin layers of aqueous fatty alcohol solutions is developed by considering evaporation-condensation of alcohol. The velocities of surface-tension-driven flows caused by gradients in temperature and in concentration are evaluated for water-n-heptanol solutions, which have a minimum of the equilibrium surface tension near 40°C. Theoretical results are discussed on the basis of experimental observations. © 2001 Academic Press.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A micromechanics model for partial freezing in porous media

International audienceBased on the local physical characterization of partial freezing in porous media, the role of the unfrozen water film, located between the in-pore ice crystal and pore wall, is paid special attention to in this study. The disjoining pressure within unfrozen water film, the membrane stress induced by surface tension effect, the thermal stress and the initial stress are fully accounted for in the proposed micromechanics model. The micromechanics model improves the physical understanding of the macroscopic mechanical behaviors of the partially frozen porous media. The micromechanics model is applied to simulate the free swelling of a undrained cement paste (denoted by CP) and an air-entrained mortar (denoted by AM). The model results are comparable with the experimental results on cement paste. The reasons for the discrepancies between the model results and experimental results on cement paste may lie in the overestimation of the ice content, which here is estimated by the pore size distribution by mercury intrusion porosimetry (MIP) and Gibbs–Thomson equation. However, the model results agree well with the experimental results of the air-entrained mortar, the ice content of which is determined by the differential scanning calorimeter (DSC). The disjoining pressure within partially frozen porous media will become more and more significant with decreasing temperature