Décontamination électrocinétique des milieux poreux. Etude expérimentale et modélisation appliquées au césium dans les matériaux cimentaires

LIMOGES-ENSCI (870852305) / SudocTOULOUSE-INSA (315552106) / SudocSudocFranceF

Effect of composition and aging on the porous structure of metakaolin-based geopolymers

International audienceA combination of intrusive and small-angle scattering techniques is used to characterize the porous structure of metakaolin-based geopolymers. The influence of the geopolymer paste composition and the aging time in a 100percent relative humidity environment at 20DC are studied. The effect of the alkali activator, the water amount and the silica amount were investigated. The results show a strong "ink-bottle" effect indicating a two-level pore structure: a meso-and macroporous network. Both alkali activator and water amount have a significant impact on porosity and microstructure in the studied formulation range. After a period of one month, the pore structure is stable over a period of one year except for a small closure of porosity, revealed by nitrogen sorption and small-angle neutron scattering (SANS). These results highlight the geopolymer stability in the curing conditions. For the first time, SANS combined with the contrast matching technique was used to determine a fraction of closed porosity in geopolymer pastes. It was found that the geopolymer porosity is mainly open, the closed porosity representing less than 5percent of the pore volume after six months of aging

Cement-Based Materials for Nuclear Waste Storage

XVIII, 266 p.online resource

Experimental investigation of gas diffusion through monomodal materials. Application to geopolymers and Vycor (R) glasses

WOS:000328594500005International audienceThis paper documents the influence of the water saturation level and the pore size distribution of porous materials on the diffusion of hydrogen. The materials are two monomodal materials: geopolymers and Vycor glasses. First, the pore size repartition is measured by means of mercury intrusion porosimetry and nitrogen adsorption porosimetry. Next, the materials are characterized through their water sorption isotherms. Finally, the diffusion coefficients measured as a function of the water saturation degree allows to quantify the impact of water on the gas diffusion through the materials. The results highlight the existence of a threshold value of saturation degree which leads to a decrease of two orders of magnitude in the hydrogen diffusion coefficient. (C) 2013 Elsevier Inc. All rights reserved

Influence of the pore network on hydrogen diffusion through blended cement pastes

WOS:000317699700004International audienceThis article presents a study on the influence of the pore size distribution on gas diffusion through CEM V cement pastes, for different water saturation degrees. The numerical results are compared to the experimental hydrogen diffusion coefficients obtained with water saturation levels ranging from 20% to 95%. The model developed in our research group accounts for the various types of transfer through the pore network: Knudsen diffusion or molecular diffusion depending on the pore size, together with hydrogen diffusion through water. The virtual pore network is created from mercury porosimetry data as a result of the combination of different sizes pore families. By testing different combinations, we could propose pore arrangements leading to diffusion coefficients corresponding to the experimental ones, and show how the combinations of the biggest pore family contribute to control the gas diffusion process. (C) 2012 Elsevier Ltd. All rights reserved

Altération d’un verre nucléaire borosilicaté en eau cimentaire : effets antagonistes du calcium

Dans le contexte du stockage des déchets radioactifs en couche géologique profonde, les colis de déchets vitrifiés de moyenne activité à vie longue (MA-VL) pourraient être placés dans un environnement saturé à long terme par des solutions correspondantes à différents stades de dégradation du ciment. L’objectif de ce travail est de comprendre quels sont les mécanismes et cinétiques d’altération du verre dans un tel environnement. Les résultats obtenus mettent en évidence des interactions spécifiques silicium-calcium et suggèrent l’existence de deux mécanismes antagonistes à pH basique qui contrôleraient la durabilité du verre selon le progrès de la réaction et la concentration en calcium

Influence of alkali activator on the rheological behavior during geopolymerization

International audienc

Cement-Based Materials for Nuclear Waste Storage

As the re-emergence of nuclear power as an acceptable energy source on an international basis continues, the need for safe and reliable ways to dispose of radioactive waste becomes ever more critical. The ultimate goal for designing a predisposal waste-management system depends on producing waste containers suitable for storage, transportation and permanent disposal. Cement-Based Materials for Nuclear-Waste Storage provides a roadmap for the use of cementation as an applied technique for the treatment of low- and intermediate-level radioactive wastes.Coverage includes, but is not limited to, a comparison of cementation with other solidification techniques, advantages of calcium-silicate cements over other materials and a discussion of the long-term suitability and safety of waste packages as well as cement barriers. This book also: Discusses the formulation and production of cement waste forms for storing radioactive material Assesses the potential of emerging binders to improve the conditioning of problematic  wastes Covers sophisticated monitoring techniques that can be used to identify leakage of radioactive waste from cement waste packages and barriers Cement-Based Materials for Nuclear-Waste Storage is an ideal book for researchers and nuclear engineers studying and working on the challenges in radioactive waste disposal and storage

XRD Analysis of the Role of Cesium in Sodium-Based Geopolymer

International audienc

Geopolymer assembly by emulsion templating: Emulsion stability and hardening mechanisms

International audienceThis work investigates emulsion templating to synthesize hexadecane oil/geopolymer composites. In a system with hexadecane as the internal (dispersed) phase and an alkali activated continuous phase without added surfactant, adding aluminosilicate clay particles does not increase resistance against creaming or coalescence, while adding a surfactant (L35 or CTAB) stabilizes the solid-liquid interface. Infrared studies and rheological studies of the associated geopolymerization determined that the presence of the organic phase or surfactant has no significant effect on the geopolymerization kinetics, as determined by the change in time of the Si-O-T IR stretching frequency and the rheological moduli involved during the process. The stabilization of the organic template is reminiscent of Pickering emulsion even though we employ a much greater amount of inorganic material for geopolymer formation. Although the addition of surfactant has a significant effect on the behavior of the paste, the percolation of the network remains unmodified, highlighting the fact that the phenomenon is not dependent on viscosity. Finally, rheological measurements were used to obtain the mass fractal dimension of the as-made gel network, which is able to differentiate the interfacial effect between surfactant molecules with a slightly denser interphase when a cationic surfactant is used