Abstract
The time-dependent liquid water distribution in cement mortar mixtures during water absorption was determined using a proton nuclear magnetic resonance imaging (NMRI) technique. The variation of the material water diffusion coefficient with the water content was established on the basis of these results. Eight different mortar mixtures were prepared and tested. Test variables included water/binder ratio (0.60, 0.40 and 0.25), type of cement (an ASTM Type 1 cement and a commercial white cement) and the use of silica fume. In addition, the effect of drying treatments on the water transport properties was also investigated. The absorption of water in dry mortars is found to be well described by a non-linear diffusion equation based on the extended Darcy's law of continuum mechanics. Results also confirm that the macroscopic water diffusion coefficient (D(□)) of mortar is strongly dependent on the material water content. The relationship between the two parameters can be modeled by two exponential equations. Test results finally show that a reduction of the mortar water/binder ratio and the use of silica fume tend to significantly decrease the absorption of water. This phenomenon is well described by the water penetration coefficient λmax.
Résumé
L'évolution de la distribution de la teneur en eau dans divers mélanges de mortier de ciment durant un essai d'absorption capillaire a été étudiée à l'aide d'une technique d'imagerie par résonance magnétique nucléaire du proton. Les résultats ainsi obtenus ont par la suite permis d'évaluer la variation du coefficient de transport de l'humidité en fonction de la teneur en eau de ces différents matériaux. Huit différents mélanges de mortier ont été testés. Les variables étudiées concernaient le rapport eau/liant (0.60, 0.40 et 0.25), le type de ciment (un ciment portland ordinaire de type I selon l'ASTM et un ciment blanc), l'ajout de fumée de silice et le conditionnement des éprouvettes avant l'essai (type de séchage). Les résultats démontrent que le transport de l'eau lors d'un essai d'absorption capillaire peut être décrit par une équation de diffusion non-linéaire. La variation du coefficient de transport de l'humidité peut être modélisée ⦏ l'aide d'une combinaison de deux équations exponentielles. Les données expérimentales indiquent également que la réduction du rapport eau/liant et l'ajout de fumée de silice contribuent à ralentir le transport de l'eau par absorption. Ces phénomènes sont correctement décrits par le coefficient de pénétration de l'eau λmax.
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Editorial Note Loval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attacle’.
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Hazrati, K., Pel, L., Marchand, J. et al. Determination of isothermal unsaturated capillary flow in high performance cement mortars by NMR imaging. Mat. Struct. 35, 614–622 (2002). https://doi.org/10.1007/BF02480354
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DOI: https://doi.org/10.1007/BF02480354