3D Visualization of biofilms in porous media without using a contrast agent

International audienceIn this study, the challenge is to characterize biofilm growth in a natural aquifer, identified as a potential future location for storing biogas. More precisely, we want to evaluate the impact of biofilm growth on the porosity by means of high-resolution X-ray computed tomography without using artificial contrast agents as these substances could affect the phenomenon of interest

Etude du potentiel des écorces de tournesol et de maïs comme granulats végétaux dans la formulation de bétons légers

International audienceABSTRACT. Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. As one of the high-potential agricultural resources, hemp has been extensively investigated for the last 15 years. This article aims to evaluate the potential of two other vegetal aggregates as a raw material to design bio-aggregate based concrete. Being locally available, the use of sunflower and maize bark particles could reduce transport and the associated carbon dioxide emissions. This study focuses on assessing the porous structure of bio-aggregates by X-ray tomography, their hygric sorption capacities (vapour and liquid water) as well as their chemical interactions with mineral binder and their effects on setting. The results underline the high transfer and storage capacities of these materials. Hence, the findings demonstrate that sunflower and maize bark particles are high-potential plant aggregates to design bio-aggregates based concrete.L'association de particules biosourcées à un liant minéral permet de formuler des bétons végétaux légers à faible impact environnemental et aux propriétés hygrothermiques intéressantes. Ces dernières années, les travaux de recherche se sont principalement focalisés sur l'utilisation du chanvre comme granulat végétal. L'étude présentée s'intéresse au potentiel d'autres agroressources disponibles localement afin de réduire le coût environnemental lié au transport des matières premières. Les travaux menés ont visé à caractériser l'arrangement granulaire des particules (granulométrie et densité), leur structure poreuse par tomographie à rayons X, leur comportement hydrique (vis-à-vis de l'eau liquide comme de la vapeur d'eau) et les interactions chimiques entre les hydrosolubles des agroressources et une matrice minérale. L'analyse de ces résultats met en évidence des capacités de transfert et de stockage de l'humidité élevée pour les particules de tournesol et de maïs. Les travaux menés révèlent les perspectives prometteuses des écorces de maïs et de tournesol comme granulats végétaux

Characterization Study of CO2, CH4, and CO2/CH4 Hydroquinone Clathrates Formed by Gas–Solid Reaction

Hydroquinone (HQ) is known to form organic clathrates with some gaseous species such as CO2 and CH4. This work presents spectroscopic data, surface and internal morphologies, gas storage capacities, guest release temperatures, and structural transition temperatures for HQ clathrates obtained from pure CO2, pure CH4, and an equimolar CO2/CH4 mixture. All analyses are performed on clathrates formed by direct gas–solid reaction after 1 month’s reaction at ambient temperature conditions and under a pressure of 3.0 MPa. A collection of spectroscopic data (Raman, FT-IR, and 13C NMR) is presented, and the results confirm total conversion of the native HQ (α-HQ) into HQ clathrates (β-HQ) at the end of the reaction. Optical microscopy and SEM analyses reveal morphology changes after the enclathration reaction, such as the presence of surface asperities. Gas porosimetry measurements show that HQ clathrates and native HQ are neither micro- nor mesoporous materials. However, as highlighted by TEM analyses and X-ray tomography, α- and β-HQ contain unsuspected macroscopic voids and channels, which create a macroporosity inside the crystals that decreases due to the enclathration reaction. TGA and in situ Raman spectroscopy give the guest release temperatures as well as the structural transition temperatures from β-HQ to α-HQ. The gas storage capacity of the clathrates is also quantified by means of different types of gravimetric analyses (mass balance and TGA). After having been formed under pressure, the characterized clathrates exhibit exceptional metastability: the gases remain in the clathrate structure at ambient conditions over time scales of more than 1 month. Consequently, HQ gas clathrates display very interesting properties for gas storage and sequestration applications

Seismic characterization and monitoring of fresh concrete using acoustic waves

International audienceThis study focuses on the seismic characteristics and behaviour of fresh concrete (water-cement ratio >2) designed for consolidation of soils, which was not really studied in the past. The propagation of acoustic waves, which constitute a potential non-destructive imaging tool in the future, was monitored and characterized using a specifically-designed experimental device during eight hours in the laboratory, to assess the evolution of the mixed material as a function of its maturity. This study highlights the very low values of P wave velocities in such a material, as well as the corresponding S waves velocities, their associated large attenuation and dispersion in the [0.5-6 kHz] frequency range. It has been found that attenuation remains the lowest when concrete mixture is younger than 90 minutes and that no velocity dispersion was detected. The study of velocity and attenuation at early age shows that the concrete has a fluid mixture with grains in suspension, and presents an elastic behaviour which stays poorly compressible during the first eight hours

Seismic characterization and monitoring of fresh concrete using acoustic waves

International audienceThis study focuses on the seismic characteristics and behaviour of fresh concrete (water-cement ratio >2) designed for consolidation of soils, which was not really studied in the past. The propagation of acoustic waves, which constitute a potential non-destructive imaging tool in the future, was monitored and characterized using a specifically-designed experimental device during eight hours in the laboratory, to assess the evolution of the mixed material as a function of its maturity. This study highlights the very low values of P wave velocities in such a material, as well as the corresponding S waves velocities, their associated large attenuation and dispersion in the [0.5-6 kHz] frequency range. It has been found that attenuation remains the lowest when concrete mixture is younger than 90 minutes and that no velocity dispersion was detected. The study of velocity and attenuation at early age shows that the concrete has a fluid mixture with grains in suspension, and presents an elastic behaviour which stays poorly compressible during the first eight hours

Current Issues in reading Comprehension

International audienc

Reading comprehension development: Presentation of the special issue

International audienceThe papers presented in this special issue highlight three theoretical topics central to the reading comprehension research. The first relates to the component skills of reading comprehension performance. Among the multiple linguistic and cognitive skills involved, vocabulary retained much of the researchers' attention. Three papers described the influence of vocabulary on various aspects of comprehension. The second topic is tied to the assessment of reading comprehension and the analysis of individual differences. Despite the multidimensional nature of the reading comprehension process, most assessment tools provide a single measure of performance. Four papers focused on analyzing the specific dimensions of comprehension being assessed by existing and novel tests. The third topic is relevant to the teaching of comprehension and the prevention of reading comprehension difficulties. A final paper presented the findings of an intervention study designed to enhance oral language in kindergarten

Etude du potentiel des écorces de tournesol et de maïs comme granulats végétaux dans la formulation de bétons légers

International audienceABSTRACT. Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. As one of the high-potential agricultural resources, hemp has been extensively investigated for the last 15 years. This article aims to evaluate the potential of two other vegetal aggregates as a raw material to design bio-aggregate based concrete. Being locally available, the use of sunflower and maize bark particles could reduce transport and the associated carbon dioxide emissions. This study focuses on assessing the porous structure of bio-aggregates by X-ray tomography, their hygric sorption capacities (vapour and liquid water) as well as their chemical interactions with mineral binder and their effects on setting. The results underline the high transfer and storage capacities of these materials. Hence, the findings demonstrate that sunflower and maize bark particles are high-potential plant aggregates to design bio-aggregates based concrete.L'association de particules biosourcées à un liant minéral permet de formuler des bétons végétaux légers à faible impact environnemental et aux propriétés hygrothermiques intéressantes. Ces dernières années, les travaux de recherche se sont principalement focalisés sur l'utilisation du chanvre comme granulat végétal. L'étude présentée s'intéresse au potentiel d'autres agroressources disponibles localement afin de réduire le coût environnemental lié au transport des matières premières. Les travaux menés ont visé à caractériser l'arrangement granulaire des particules (granulométrie et densité), leur structure poreuse par tomographie à rayons X, leur comportement hydrique (vis-à-vis de l'eau liquide comme de la vapeur d'eau) et les interactions chimiques entre les hydrosolubles des agroressources et une matrice minérale. L'analyse de ces résultats met en évidence des capacités de transfert et de stockage de l'humidité élevée pour les particules de tournesol et de maïs. Les travaux menés révèlent les perspectives prometteuses des écorces de maïs et de tournesol comme granulats végétaux

Influence of types of binder and plant aggregates on hygrothermal and mechanical properties of vegetal concretes

International audienceBio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. In this paper, different formulations of bio-aggregate concrete are proposed and analysed. We focus on two types of locally available bio-aggregates, namely maize and sunflower bark chips, and two types of binder matrices, based on respectively metakaolin and lime. The study specifically focuses on the pore structure of the composite material, as this quantity has a decisive impact on the insulating properties (thermal conductivity), the hygric behaviour (sorption isotherms, water vapour permeability and moisture buffer value) as well as on the mechanical performance (compressive strength). The results underline the impact of the constituents' porosity on the complex porous structure of the bio-concrete and the influence of porosity on its performance. The findings demonstrate that metakaolin and sunflower are high-potential raw materials for the design of a bio-aggregate based concrete

Caractérisation haute résolution des propriétés physiques de la subsurface (Apport du radar géologique)

PAU-BU Sciences (644452103) / SudocSudocFranceF