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Ion-water restructuring under confinement is at the origin of ion-specific nanoscale forces that control cement cohesion., Cement is the most produced material in the world. A major player in greenhouse gas emissions, it is the main binding agent in concrete, providing a cohesive strength that rapidly increases during setting. Understanding how such cohesion emerges is a major obstacle to advances in cement science and technology. Here, we combine computational statistical mechanics and theory to demonstrate how cement cohesion arises from the organization of interlocked ions and water, progressively confined in nanoslits between charged surfaces of calcium-silicate-hydrates. Because of the water/ions interlocking, dielectric screening is drastically reduced and ionic correlations are proven notably stronger than previously thought, dictating the evolution of nanoscale interactions during cement hydration. By developing a quantitative analytical prediction of cement cohesion based on Coulombic forces, we reconcile a fundamental understanding of cement hydration with the fully atomistic description of the solid cement paste and open new paths for scientific design of construction materials.

Not surprisingly, with the increased awareness of environmental issues, construction with raw (crude, unbaked) earth (subsoil) is gaining renewed interest. However, it suffers from a poor image and from the difficulty to meet modern productivity standards and to pass some durability tests designed for industrial materials. The recent trend is to overcome these drawbacks by “stabilizing” the material most often with Portland cement (PC). Here we show that stabilization with PC is in general neither technically nor environmentally advisable. It brings only moderate mechanical improvement at a high environmental cost. Rather than massively transforming crude earth into a low quality concrete, it would be more appropriate to adapt the architectural practice and/or to look for milder ways to improve properties. In this respect, the recent successful attempts to improve the workability and the strength of raw earth by controlling the dispersion of its fine fraction seem to be particularly promising.

International audience; While shale gas has become a major source of energy, a more sustainable recovery requires better understanding of the gas/kerogen matrix interactions. Here we use replica exchange molecular dynamics to investigate the geological conversion of two important classes of gas-forming constituents of terrestrial organic matter: lignin and cellulose. In agreement with results from pyrolysis experiments, we show that lignin 1 produces twice as much kerogen and five times more methane than cellulose. In addition , while ex-cellulose kerogen is relatively stiff and almost non porous, ex-lignin kerogen, despite having very similar composition and bonding, is an order of magnitude more compliant due to the presence of large micropores. The obtained results can potentially improve the nanoscale brick of bottom-up models of shale gas recovery.

Concrete cannot be ignored. More concrete is produced than any other synthetic material on earth. It is the key material of our infrastructural systems, and together with mortar and other cementitious materials, it is one of the most generalizable answers to our global need for affordable and decent housing. Yet, present-day concrete is facing unprecedented challenges. In spite of an intrinsically low environmental footprint almost entirely due to its Portland cement content, it contributes an unacceptable 5–10% to our global carbon emissions, due to the enormous volumes involved. It suffers also from a poor social image, attached to its (supposedly) low technical content and its symbolic character for some of the least desirable aspects of modern societies and cities.

Reply to the discussion of the paper “Earth Concrete. Stabilization Revisited” by A.T.M. Marsh, A. Heath, P. Walker, B.V. Venkatarama Reddy, and G. Habert.

Accelerated reactive molecular dynamics simulations reveal the complex geological conversion path of organic matter into porous carbon (kerogen) and gas., The process by which organic matter decomposes deep underground to form petroleum and its underlying kerogen matrix has so far remained a no man’s land to theoreticians, largely because of the geological (Myears) timescale associated with the process. Using reactive molecular dynamics and an accelerated simulation framework, the replica exchange molecular dynamics method, we simulate the full transformation of cellulose into kerogen and its associated fluid phase under prevailing geological conditions. We observe in sequence the fragmentation of the cellulose crystal and production of water, the development of an unsaturated aliphatic macromolecular phase and its aromatization. The composition of the solid residue along the maturation pathway strictly follows what is observed for natural type III kerogen and for artificially matured samples under confined conditions. After expulsion of the fluid phase, the obtained microporous kerogen possesses the structure, texture, density, porosity and stiffness observed for mature type III kerogen and a microporous carbon obtained by saccharose pyrolysis at low temperature. As expected for this variety of precursor, the main resulting hydrocarbon is methane. The present work thus demonstrates that molecular simulations can now be used to assess, almost quantitatively, such complex chemical processes as petrogenesis in fossil reservoirs and, more generally, the possible conversion of any natural product into bio-sourced materials and/or fuel.

International audience; We measured the humidity-induced swelling of thin self-standing films of montmorillonite clay by a combination of environmental scanning electron microscopy (ESEM) and digital image correlation (DIC). The films were about 40 µm thick. They were prepared by depositing and evaporating a suspension of clay and peeling off the highly oriented deposits. The rationale for creating such original samples was to obtain mesoscopic samples that could be used to bridge experimentally the gap between the scale of the clay layer and the engineering scale of a macroscopic clay sample. Several montmorillonite samples were used: the reference clay Swy-2, the same clay homoionized with sodium or calcium ions, and a sodium-exchanged Cloisite. The edges of the clay films were observed by ESEM at various relative humidity values between 14% and 95%. The ESEM images were then analyzed by DIC to measure the swelling or the shrinkage of the films. We also measured the adsorption/desorption isotherms by weighing the film samples in a humidity-controlled environment. In order to analyze our results, we compared our swelling/shrinkage and adsorption/desorption data with previously published data on the interlayer spacing obtained by X-ray diffraction and with numerical estimates of the interlayer water obtained by molecular dynamics simulation. The swelling and the hysteresis of this swelling were found to be comparable for the overall macroscopic films and for the interlayer space. The same correspondence between film and interlayer space was observed for the amount of adsorbed water. This suggests that, in the range of relative humidities values explored, the films behave like freely swelling oriented stacks of clay layers, without any significant contribution from the mesoporosity. The relevance of this result for the behavior of clayey sedimentary rocks and the differences with the behavior of nonoriented samples (powders or compacted powders) are briefly discussed. © 2013 American Chemical Society.

Here, we focus on the hydromechanical behavior of self-standing clay films with a thickness of a few dozen microns. We measure their elastic and creep properties and how those properties depend on the interlayer cation and on the relative humidity (or water content). Those experimental results are compared with the elastic and creep behavior of nanometric clay particles, which we characterize by molecular simulations. Significant qualitative differences between the behavior of the clay films and that of the clay particles are observed, which suggests that the hydromechanical behavior of the clay films is significantly impacted by their mesostructure (i.e., by how the clay particles or tactoids are arranged in space). Upscaling the hydromechanical behavior of the clay films from that of the clay particles may be challenging.

Among the proposed pathways of sequestration and progressive transformation of organic matter (OM) during burial, the sorptive protection mechanism explains the strong relationship between total organic carbon (TOC) and mineral surface area (MSA) noted in numerous black shales around the globe. The complete mechanistic framework of preservation and evolution of OM in organo-mineral complexes remains, however, an enigma. On one hand, smectite layers composing the clay fraction are known to have a major influence on available surface area. OM maturation occurs, on the other hand, concurrently with the smectite illitization that provokes the closure of the interlayer spaces. The potential of smectite layers in the sequestration and preservation of organic molecules and the fate of these molecules with respect to the smectite illitization were therefore addressed. Here, the mineralogy of three organic-rich source rocks of various maturities was characterized in regards with the geochemistry of their OM. A thorough examination of the clay minerals present in the clay matrices provided evidences of mixed layer minerals containing smectite and illite layers with an increasing illite component with respect to maturity. The comprehensive interpretation of the X-ray diffractograms and analytical electron microscopy results suggested the presence of organic molecules in the inter-particulate and possibly the interlayer spaces of the smectite-rich components in immature source rocks. This eventuality was further supported by the presence of intercalated clay-organic nanocomposites observed by transmitted electron microscopy coupled with energy dispersive spectroscopy. Textural observations also showed that the increased illite content found in the overmature sample led to the reorganization of the OM and the clay particles into nano-scale aggregates. These results clarify the geochemical mechanism beyond the reported relationship between TOC and MSA and allow generalizing it to various organic-rich source rocks. Eventually, the understanding of the close organo-clay association raises prospects on the prediction of the evolution of the mechanical properties of economically valuable source rocks with respect to maturity.

This thematic dossier collects eight scientific papers corresponding to presentations made during two international conferences dedicated to the study of low permeability media held in Paris within six months of each other. The first conference, “The Challenge of Studying Low Permeability Materials: Laboratory, in situ (field) and numerical methods”, was organised in December 2014 by the University of Cergy-Pontoise (Geosciences and Environment Cergy Research Laboratory) under the aegis of CFMR (Rock Mechanics French Committee) and GIS Geosciences franciliennes. The second, LowPerm2015 “Low permeability media and nanoporous materials from characterisation to modeling: Can we do it better?”, was organised by IFP Energies nouvelles in June 2015 under the aegis of the French “Academie des Sciences”. An attractive and explicit title is key to the success of a conference. It sets the scene and lets possible participants know exactly what matter will be discussed. But subtitles may be as important as titles, because they may stimulate participants by confronting them with a collective challenge. Devoted to characterisation, transport properties and multiscale modeling of low to very low permeability media and nanoporous materials, LowPerm2015 was leaving very little ambiguity about the matter to be discussed. Its subtitle – Can we do better? – was a mild way of stressing that there are several areas where we should be totally unsatisfied about our present state of knowledge, and where progress is urgently needed. One of these areas is the recovery of unconventional hydrocarbon resources. There is no question that the gas and oil shale revolution has deeply changed the global energy landscape, but its long term sustainability is questionable in spite of the tremendous magnitude of the resource due to an unacceptably low rate of recovery. With close to seventy five percent of the gas and ninety five percent of the oil left in place on average, the exploitation of self-sourced organic rich shale reservoirs is one of the least efficient industrial operations. Among the main reasons for this are our poor knowledge of the complex nanoporous void space in which the hydrocarbons are trapped, and our very limited understanding of their release and transport mechanisms, particularly in multiphase conditions. Just imagine what the future would be if, thanks to improved understanding, we could switch from ninety five percent left in place to ninety five percent recovery!

A thermoresponsive copolymer solution is used to control the mechanical properties of a cement paste suspension. We use a comb copolymer consisting of a polymethacrylic acid (PMAA) backbone grafted with a polypropylene oxide (PPO) and polyethylene oxide (PEO) copolymer that possesses a low critical solution temperature (LCST). When the temperature crosses the LCST value, microphase separation occurs and the adsorption of the copolymer onto the cement particles is modified. We show that a control of the grafting ratio and of the graft chain composition allows monitoring of the transition temperature as well as the viscosity of the paste in the low and high temperature phases.

International audience; The study presented in this paper is devoted to improve the knowledge on the influence of cellulose ethers (CE) on the freshly-mixed mortars water retention. Indeed, this crucial property is the most important imparted by these polysaccharides. One of the assumptions proposed to explain this phenomenon is that CE acts as diffusion barrier to the water. To test this hypothesis, the CE effect on the self-diffusion coefficient of water in solution and on the water mobility between two fresh cement pastes was studied by Nuclear Magnetic Resonance. CE does not significantly modify the water self-diffusion coefficient in CE solution or in admixed cement pastes. Moreover the interdiffusion imaging experiments demonstrated that the water diffusion at the paste/paste interface is not affected by the presence of cellulosic admixture.

The influence of secondary phases (illite, quartz) on the geopolymerization reaction of metakaolin has been investigated by comparing two metakaolins, one prepared from a pure kaolinite and the other from illite- and quartz-containing Algerian kaolin from the Tamazert region, respectively. Geopolymerization was achieved by mixing the metakaolins with an alkaline sodium silicate solution at room temperature and curing at 50 °C. The products were characterized by X-ray diffraction and 29 Si and 27 Al MAS-NMR. The results show that the secondary phases, at the concentration used in this work, do not prevent the geopolymerization reaction.

International audience; We characterized experimentally the elastic and creep properties of thin self-standing clay films, and how their mechanical properties evolved with relative humidity and water content. The films were made of clay montmorillonite SWy-2, obtained by evaporation of a clay suspension. Three types of films were manufactured, which differed by their interlayer cation: sodium, calcium, or a mixture of sodium with calcium. The orientational order of the films was characterized by X-ray diffractometry. The films were mechanically solicited in tension, the resulting strains being measured by digital image correlation. We measured the Young’s modulus and the creep over a variety of relative humidities, on a full cycle of adsorption–desorption for what concerns the Young’s modulus. Increasing relative humidity made the films less stiff and made them creep more. Both the elastic and creep properties depended significantly on the interlayer cation. For the Young’s modulus, this dependence must originate from a scale greater than the scale of the clay layer. Also, hysteresis disappeared when plotting the Young’s modulus versus water content instead of relative humidity. Independent of interlayer cation and of relative humidity greater than 60%, after a transient period, the creep of the films was always a logarithmic function of time. The experimental data gathered on these mesoscale systems can be of value for modelers who aim at predicting the mechanical behavior of clay-based materials (e.g., shales) at the engineering macroscopic scale from the one at the atomistic scale, for them to validate the first steps of their upscaling scheme. They provide also valuable reference data for bioinspired clay-based hybrid materials.

A wide variety of fluid systems including organic liquids, mineral melts, colloidal suspensions and granular materials, undergo a dynamical arrest transition when the temperature is lowered, or the density is increased, or the applied stress is decreased. This is known as the glass transition in the first case and as the jamming transition in two latter cases. The purpose of this paper is to show that the coagulation and the setting of cement pastes share with these systems several key attributes which bring them under the same umbrella.

International audience; Swelling clays act as ion-exchange membranes owing to the presence of extra-framework ions surrounded by water molecules. A better understanding of the motion of the ions present in the pore space is required to predict the diffusion properties in these solids. Since water molecules tend to adsorb both on ions and clay surfaces, they moderate the interactions between the ions and the framework. The hydration of ions therefore has an impact on their diffusion properties. In this paper, the MX-80 montmorillonite considered for nuclear waste disposal applications has been selected and studied using an approach combining measurements of complex impedance spectroscopy and water adsorption isotherms. The number of charge carriers has been estimated, and the diffusion coefficient for interlayer cations at various hydration states was determined. The evolution of the diffusion coefficient is subsequently correlated with the effect of the opening of the interlayer space and its hydration state. The resulting picture sheds light on the reversible or irreversible character of ion exchange. Finally, our results obtained from the difference between the interlayer diffusion coefficients extracted from conductivity measurements and those obtained at the macroscopic scale is discussed in terms of the textural parameters.

A new class of bio-nanocomposites based on hybrid gelatin-perovskite hydrogels was prepared by mixing exfoliated perovskite-tetraalkylammonium species in aqueous suspensions with gelatin solutions. Colloidal nanosheets derived from the CsCa 2 Nb 3 O 10 layered perovskite re-stacked in the gelatin solutions give bio-nanocomposite materials with different content in the inorganic moiety. These films can be easily processed as homogeneous self-supported films. The partial exfoliation of the pristine mixed oxide is produced from alkylammonium exchanged phases, being the tetraalkylammonium ions (tetraethylammonium, TEA + ) an efficient intermediate to give the colloid phase constituted by well exfoliated materials useful to generate homogeneous films. The nanosheets are highly oriented in the bio-nanocomposite films in agreement with the XRD patterns and the FTIR dichroism. This orientation could be considered as a characteristic of this type of hybrid materials leading to new potential applications. In this way, we have observed that the assembling of perovskite to gelatin produces a greater increase of the dielectric permittivity than the dielectric loss in the studied samples.

Unlike other porous materials such as sandstone, brick, or porous glass, the interatomic bonding continuity of cement-based materials like concrete is far from obvious. When scrutinized at the micro- or nanoscopic level, the continuity of the ionic–covalent bonding in the solid phase is interrupted almost everywhere by water molecules or liquid water films. The same situation is found in set plaster.Yet, plaster and cementitious materials are able to withstand stresses of the same order of magnitude as rocks. Molecular simulation studies and direct-force measurements by atomic force microscopy provide strong arguments for predicting that short- and medium-range surface forces mediated by partially or totally hydrated calcium ions are the essential components of cement strength, with additional contributions from van der Waals and capillary forces. This provides a clue for understanding the nano- and mesostructure of cement-based materials and new levers for improving their properties.

This article serves to introduce the May 2004 issue of MRS Bulletin on Construction Materials: From Innovation to Conservation. By volume, building materials are by far the most widely used type of materials. The most common construction materials—concrete and wood—are paradigms of complex and hierarchical materials, with a microstructure extending quasi-continuously down to the nanoscale. In the past, most improvements have been obtained by modifying the microstructure at the largest scales, for instance, by reducing the macroporosity. Recent advances in our understanding of the interactions and microstructure development show that the major levers for improvement from now on will rely on surface and colloid science and the science of complex materials, often at the nanoscale. This can lead to remarkable properties, such as self-compaction and ultrahigh strength, and even new functionality, such as self-cleaning through photocatalysis. Construction materials face a wide range of challenges today, many of which are linked to the need for more sustainable development: reducing the consumption of raw materials, reducing the energy used in processing, and increasing service life. In many parts of the world, there is also an increasing need to repair, rehabilitate, and conserve old buildings. The articles in this issue touch on these challenges as well as the advances being made in construction materials through materials research.

Un materiau mineral mis en contact avec des molecules biologiques peut induire des reactions indesirables comme la denaturation de proteines, la coagulation du sang ou bien une reponse du systeme immunitaire. Une maniere de surmonter cet obstacle est de recouvrir le materiau avec une couche biocompatible. Les proprietes des nouveaux systemes sont alors controlees par les molecules a l'interface. Une premiere partie du texte examine l'utilisation de la Resonance Paramagnetique Electronique de marqueurs radicalaires pour obtenir des informations sur les conformations de chaines de dextrane adsorbees sur la silice. Une seconde partie decrit l'utilisation de la Resonance Magnetique Nucleaire des noyaux de 13 C et du 29 Si pour verifier le degre de couverture du mineral et minimiser les interactions non specifiques. Une troisieme partie etend ces approches a la construction de multicouches de polyelectrolytes. Des situations tres bien definies et relativement simplifiees sont etudiees pour rendre les recherches praticables et les conclusions plus claires.

This paper is a discussion of a few selected topics or trends in recent research literature which raise fundamental issues in our understanding of the way fillers improve the properties of polymers. A first topic is the now well-established experimental and theoretical evidence that the Tg and the molecular mobility in free standing or supported films are modified over a much larger thickness than was previously thought. Considering their enormous interface area this introduces a new look to the remarkable reinforcement effect obtained in delaminated clay nanocomposites. On the other hand, the reason why, in spite of their extraordinary mechanical properties and their very large surface area, carbon nanotubes, with their fibre-like morphology, are still far from giving the same reinforcement, is still an open question. A second topic to be mentionned is the development of hybrid materials and biomimetic approaches which, due to very small scale of the organic-inorganic heterogeneities which can be achieved, raises questions on the phase concept and points to the need for new theoretical approaches of the mechanical properties of these materials. Finally, a third topic is the control of the filler particles distribution in the matrix. The general theory of random diphasic media permits to define several types of good dispersions in terms of disordered distributions, according to the correlations of the particles positions in a matrix. This raises two problems, which are briefly discussed: (i) Are we able to define the type of dispersion we want? (ii) Is it relevant for modifying the properties?.

Cement pastes are used in various conditions of fluidity. This leads to the necessary introduction of polymers in order to control the rheology and to stabilize the slurry against segregation. This work describes the influence of hydrophobically modified acrylate polyelectrolytes on the rheological behavior of a tricalcium silicate paste at a constant solid volume ratio O = 0.32.

Maya blue is an ancient nanostructured pigment synthetized by assembling indigo, a natural dye, with palygorskite, a microfibrous clay mineral. The novelty of our approach is to mimic “pre-Columbian nanotechnology” and to functionalize geopolymers with a sepiolite-based hybrid organic–inorganic nanocomposite inspired from the Maya blue. It is acid- and UV-resistant, as confirmed by the stability of Maya mural paintings over time. We synthesized analogous pigments, using methylene blue (MB) and methyl red (MR) as organic dyes and sepiolite as fibrous clay mineral. We used an aqueous and a solid- state method, both leading to encapsulation of dye monomers into the clay micropores, as confirmed by UV-vis spectroscopy. This nanostructured pigment was then included into a geopolymer matrix at room temperature. The stability of the new material to UV and acid was tested. It was confirmed that it is the prior encapsulation of the dye into sepiolite that leads to the stability of the pigment in the geopolymer matrix. This first study opens the way to numerous possibilities for functionalizing inorganic binder materials with organic elements that would be otherwise sensitive to thermal treatment in conventional ceramic processing., RSC Advances, 5 (120), ISSN:2046-2069

Calcium silicate hydrate (C-S-H), the most important reaction product of Portland cement with water, is a layered lattice silicate which has much in common with smectite clays. Both materials may be synthesised (C-S-H) or found in nature (smectites) in the form of particles which are stacks of negatively charged nanometre-thick platelets separated by water molecules and charge-compensating cations. Smectite clays are well known for their ability to intercalate molecular species including polymers, to “swell” in a remarkable variety of solvents and to form nano-composites with polymers in which total delamination may eventually be obtained. In this work, we explore the possibility of intercalating cationic, anionic and neutral water-soluble polymers in C-S-H. Contrary to recent reports, no clear signs for intercalation of the macromolecules were observed. Nevertheless, the significant amount of polymer retained by the silicate suggests that the composite materials formed may be considered as meso-composites in which the individual solid units are not the individual C-S-H sheets but crystallites thereof. The localisation of electric charges and the strong Coulombic forces acting in cement hydrates are thought to be responsible for this difference.

We analyze, in the light of experiments, a few typical aspects of the rheological or mechanical behavior of pastes, defined as dense and liquid-saturated assemblies of grains, with or without physical–chemical interactions. Emphasis is placed on the consequences of jamming, which distinguishes pastes from concentrated suspensions, contact lubrication, which distinguishes pastes from dry granular media, and cohesion. The points addressed are the following: the onset of flow, the contribution of friction in the yield stress, solid–liquid segregation and compaction, adhesion (tackiness) and cohesive rupture. To cite this article: H. Van Damme et al., C. R. Physique 3 (2002) 229–238.

The current research in herbicide application aims to develop formulations that reduce leaching of the herbicide to deep layers of the soil and to concentrate its biological activity at the top layers. Adsorption of metolachlor on clay minerals, their organic derivatives or pillared forms provides the best possibility to develop slow-release formulations. Metolachlor is a selective pre-emergence herbicide widely used in irrigated crops to control annual weeds. It is adsorbed by bentonites and montmorillonites, but the amount adsorbed strongly depends on the type of bentonite and possible pretreatment reactions. Wyoming bentonites adsorbed considerable amounts of metolachlor but other bentonites did not bind this herbicide. An acid-activated pillared montmorillonite was also an effective adsorbent of metolachlor. Modification of this sample by preadsorbing different amounts of benzyl trimethylammonium ions did not influence the level of herbicide adsorption. The biological efficiency of the formulations was tested with bioassay soil columns. Slow-release formulations could be prepared with raw bentonites and the acid-activated pillared montmorillonite. A formulation, prepared by adsorbing metolachlor from aqueous solution on the acid-activated pillared montmorillonite, showed high herbicide activity at the top 10 cm, and did not diffuse significantly to greater depths. This formulation should allow a better weed control than the commercial formulations.

We show experimentally that a vertically vibrated granular packing can be densified, even when saturated by a Newtonian fluid which reduces the effective buoyancy. Densification is slower than in a dry packing, due to viscous drag, but the final density is higher, due to lubrication. The evolution of the packing density follows the global logarithmic time dependence observed with dry packings, but an additional density-dependent parameter had to be introduced.

Magnetic resonance imaging (MRI) has been used to determine quantitatively one-dimensional proton concentration profiles in clay gels prepared from water/heavy water mixtures, taking into account t...

Interactions between an acid-activated pillared clay and several organic cations including dyes (methylene blue, MB; crystal violet, CV; acriflavin, AF) and benzyl derivatives (benzyltrimethylammonium, BTMA; benzyltriethylammonium, BTEA) were studied by adsorption measurements and X-ray diffraction. When the dyes were adsorbed from low ionic strength solutions, adsorption was irreversible but saturated at levels below the cation exchange capacity (CEC) of the clay (0.6 meq/g). The difference with CEC value was largest for CV. This mode of adsorption was interpreted in terms of interlayer adsorption with steric hindrance in the pillared galleries. On the other hand, when the dyes were adsorbed from high ionic strength solutions, adsorption levels well beyond the CEC of the clay could be reached, in particular for MB and CV. This was interpreted in terms of a second adsorption mode, involving formation of molecular aggregates on the outer surface of the clay, as evidenced by X-ray diffraction. The behavior of the cationic benzyl derivatives was markedly different, with an adsorption level always below the CEC and a decrease of adsorption as the ionic strength was increased, as expected for non-complex-forming cations. Copyright 1999 Academic Press.

Six silica gels, where each gel had a characteristic calibrated pore size (40-4000 Å), have been characterized both by water vapor and nitrogen adsorption isotherms. From these results, it was concluded that two-thirds of the silica surface is hydrophobic. The selection of wide pores (300 Å) has enabled the determination of both the water and nitrogen t-curves for porous silica. It was observed that the development of the multilayer was identical in the wide pores irrespective of their size between 300 and 4000 Å. The porous silica t-curve for water coincided exactly with the t-curve of nonporous adsorbents provided that their BET C constants were similar. For nitrogen t-curves, a matching BET C constant ensured similarity only in the monolayer region, above which divergence progressively increased, becoming important close to saturation. The effect of the t-curve choice on the pore size distribution was established. A t-curve displaying reduced adsorption had a tendency to shift the pore-size distribution to lower dimensions, toward the micropore region. As a consequence, the cumulated surface area obtained from the BJH model gave increasingly higher values than the BET nitrogen surface area. However, the pore-size distribution was shifted to higher pore sizes when the selected t-curve was above the natural t-curve. Errors as much as 25% were detected for the mean pore radius and cumulated surface area for certain literature t-curves. A comparison of the water and the nitrogen t-curves indicated a crossover point when the water multilayer thickness became greater than the nitrogen thickness. Such behavior lends support to the cooperative adsorption mechanism for water vapor once a fixed number of water molecules (two layers) are present on the surface. Copyright 1998 Academic Press.

(N,V,T) Monte Carlo simulations are performed by using hyperspherical geometry in order to investigate the mechanical stability and the ionic affinity of clay particles neutralized by a mixture of counterions of different valency. In this study, clay particles are described as uniformly charged surfaces and the interactions between ions and these charged surfaces are described within the context of the 'primitive model'. The purpose of this study is to derive the maximum amount of monovalent counterions necessary to remove the stability of clay materials neutralized by divalent or trivalent counterions. From the equation of state of these charged materials we quantify the influence of ionic exchange on the interfacial free energy.

(1998). La physique des liaisons entre hydrates et les moyens d'agir au niveau moleculaire. Revue Francaise de Genie Civil: Vol. 2, No. 7, pp. 767-779.

International audience; No abstract available

The knowledge of mechanical properties of swelling clays on the scale of the clay layer is of crucial importance to build predictive hydromechanical macroscopic constitutive laws in a bottom-up approach. In this work, we computed the elastic properties of particles of a swelling clay (i.e., montmorillonite) by molecular dynamics simulations. Because of the softness of the material in the direction orthogonal to the clay layer with increasing water content, the computation of the whole stiffness tensor was not trivial: we needed to implement the elastic bath method,1 which allows us to attenuate thermal strains and compute the stiffness via strain fluctuations in isothermal–isobaric simulations. We investigated the effect of water content, temperature, and the interlayer cation on the elastic properties of swelling clays. In particular, we showed that the out-of-plane stiffness coefficients computed at 300 K differed significantly from the same coefficients computed at 0 K. The out-of-plane coefficients we...

Resume Nous montrons experimentalement que l'on peut fracturer, par injection d'un liquide ou d'un gaz, des fluides visco-elastiques possedant des proprietes elastiques extremement faibles. La vitesse de propagation des fractures peut etre tres proche de la vitesse de propagation des ondes de cisaillement et conduire a un mode de fracturation en fractures multiples et branchees. Ces experiences pourraient servir de modeles pour l'etude des instabilites de fracturation hydraulique dans les roches.

International audience; While today's galloping urbanization weighs heavily on both People and Environment, the massive instrumentation of urban spaces appears a landmark toward sustainability. Collecting massively distributed information requires the use of high-performance communication systems as well as sensors with very small ecological footprint. Because of their high sensitivity, the wide range of their observables, their energetic self-sufficiency and their low cost, micro- and nano- sensors are particularly well suited to urban metrology. A 8 years, 9 MC equipment project funded by the French 'Programme d'Investissement d'Avenir' starting in 2012, the Sense-City project will offer a suite of high-quality facilities for the design, prototyping and performance assessment of micro- and nanosensors devoted to sustainable urbanization. The scientific program of Sense-City is built around four programs, environmental monitoring, structural health monitoring, energy performances monitoring and people health and exposure monitoring. We present the activities of the consortium partners, IFSTTAR, ESIEE-Paris, CSTB, LPICM, and the prospects brought by Sense-City equipment in terms of sensor prototyping, benchmarking and operation validation. We discuss how the various sensors developed by LPICM and ESIEE (for instance conformable chemical and gas microsensors using nanomaterials at LPICM, miniaturized gas chromatographs or microfluidic lab-on-chip for particles analysis at ESIEE-Paris) can be integrated by IFSTTAR into sensors networks tested by IFSTTAR and CSTB in both lab and urban settings. The massively distributed data are interpreted using advanced physical models and inverse methods in order to monitor water, air or soil quality, infrastructure and network safety, building energy performances as well as people health and exposure. We discuss the shortcomings of evaluating the performances of sensors only in lab conditions or directly in real, urban conditions. As a solution, Sense-City will provide an environment of intermediate complexity for the testing of environmental sensors, a realistic urban test space in climatic conditions, both far more complex than clean rooms and far more controllable than actual cities.

International audience; Important structural modifications occur in swelling clays upon water adsorption. The multi-scale evolution of the swelling clay structure is usually evidenced by various experimental techniques. However, the driving force behind such phenomena is still not thoroughly understood. It appears strongly dependent on the nature of the interlayer cation. In the case of montmorillonites saturated with alkaline cations, it was inferred that the compensating cation or the layer surface could control the hydration process and thus the opening of the interlayer space, depending on the nature of the interlayer cation. In the present study, emphasis is put on the impact of divalent alkaline-earth cations compensating the layer charge in montmorillonites. Since no experimental technique offers the possibility of directly determining the hydration contributions related to interlayer cations and layer surfaces, an approach based on the combination of electrostatic calculations and immersion data is developed here, as already validated in the case of montmorillonites saturated by alkaline cations. This methodology allows to estimate the hydration energy for divalent interlayer cations and therefore to shed a new light on the driving force for hydration process occurring in montmorillonites saturated with alkaline-earth cations. Firstly, the surface energy values obtained from the electrostatic calculations based on the Electronegativity Equalization Method vary from 450 mJ m−2 for Mg-montmorillonite to 1100 mJ m−2 for Ba-montmorillonite. Secondly, considering both the hydration energy for cations and layer surfaces, the driving force for the hydration of alkaline-earth saturated montmorillonites can be attributed to the interlayer cation in the case of Mg-, Ca-, Sr-montmorillonites and to the interlayer surface in the case of Ba-montmorillonites. These results explain the differences in behaviour upon water adsorption as a function of the nature of the interlayer cation, thereby allowing the macroscopic swelling trends to be better understood. The knowledge of hydration processes occurring in homoionic montmorillonites saturated with both the alkaline and the alkaline-earth cations may be of great importance to explain the behaviour of natural clay samples where mixtures of the two types of interlayer cation are present and also provides valuable information on the cation exchange occurring in the swelling clays.

Electron paramagnetic resonance (EPR) associated with adsorption gravimetry and X-ray diffraction (XRD) has been used simultaneously to study the dehydration process in a Cu2+−hectorite. The combin...

A large scale equipment project, the Sense-City Equipex has received support from the French government in the framework of the 'Programme d’Investissement d’Avenir'. This project is led by the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) with ESIEE-Paris, the Laboratory of Physics of Interfaces and Thin Films (LPICM) and the Scientific and Technical Centre for Building (CSTB) as consortium partners. Starting in 2012, Sense-City will offer a suite of high-quality facilities for the design, prototyping and performance assessment of innovative, micro- and nanotechnology based sensors devoted to urban instrumentation. Acknowledging the shortcomings of evaluating sensors performances in laboratory conditions only or in the ever-changing environment of our cities, Sense-City will provide a realistic urban test space in climatic conditions, far more complex than clean rooms and far less complex than actual cities. Sense-city revolves around the 'mini-city' concept, a large, fully customizable climatic hall able to host full- and reduced-scale models of essential urban components. The design of the models will allow for the simulation in climatic conditions of numerous scenarios of sustainable cities. The scenarios to be implemented will correspond to different research topics related to urban sustainability: energy performances in buildings, quality of air, water and soils, quality of fluid distribution networks (gas, sewage, drink water), control of waste disposal areas, durability and safety of infrastructures.

Pousse par une urbanisation croissante et l’imperieuse necessite d’un impact minimal sur nos ressources et notre environnement, le monde de la construction est le lieu d’innovations a juste titre qualifier de nanotechnologiques. Est concerne autant l’habitat individuel que le tertiaire, le milieu urbain et nos grandes infrastructures, que celles-ci soient energetiques, environnementales ou de mobilite. L’impact des nanotechnologies sur le materiau-roi du genie civil – le beton – et sur nos grands ouvrages d’art et reseau routier, est certain. L’usage de nanomateriaux dans les câbles et haubans des ponts permettra d’en faire des composants actifs, de meme l’usage des nanotechnologies dotera la route de fonctionnalites qui la rendront adaptable, resiliente et automatisee.

International audience; The understanding of the adsorption of charged species in swelling clays is of primary importance to optimise the capture of heavy metal ions in soils. Adsorption is expected to depend on the microscopic structure of the clay, which varies strongly with the origin and history (hydration-desorption cycles, temperature ...) of the sample. Then it is necessary to evaluate the distinct interaction energies between water molecules, interlayer cations and clay surfaces, taking into account the position of the substitutions in the clay layer. Here we propose an investigation of plausible structures of some Pb-montmorillonites differing by their interlayer distances, their layer charges and the distribution of substitutions in octahedral sheet from a modelling approach, looking at the evolution of the partial charges in these structures. Using a methodology previously developed in the simpler case of alkali cations, we also estimate the surface energy in the dry state and then the details of the hydration energy for the cation and for the clay layer to interpret the capacity of ion adsorption in swelling clays to capture heavy metals. We conclude from our calculations that a cell structure with intermediate layer charge (close to 0.5 per unit cell) is probably the best candidate to allow the capture of the Pb2+ as interlayer cations considering the electrostatic effect. The hydration process of the cation appears as the most energetic part of the hydration of swelling clays compared to the interactions with the layer, but the cation mobility is limited since the hydration process is not complete. This means that the heavy metal ions, present in the interlayer space, will be unable to diffuse and will be captured in the case of a low layer charge.

This book is dedicated to Olivier Coussy, the prominent scientist and engineer who developed the fundamentals of poromechanics theory that were transformational in many application of civil environmental and petroleum engineering, bioengineering and sustainable development of materials and structures. Olivier passed away on January 15, 2010. He was the colleague and friend of all the contributors to this book. To honor the memory of Olivier Coussy , Ecole des Ponts ParisTech and IFSTTAR (French institute of science and technology for transport, development and networks) have organized a symposium held at Ecole des Ponts ParisTech from April 18 to 20, 2011. The theme of this symposium was chosen after his last monograph (Mechanics and Physics of Porous Solids, J Wiley & Sons, 2010) which embodies his most recent vision of the Poromechanics at the interface between physical chemistry and solid mechanics. Because the interface between those two fields is not often explored as he said, he aimed to bridge the gap between physical chemistry, which governs what happens at the level of the pore, and solid mechanics, which is the natural frame in which deformations, stresses and fluid transport are addressed and quantified at the macroscopic level of the porous material. In this vein the organizing committee of the symposium intended to gather academics and industrials that either develop or utilize the concepts of the mechanics and physics of porous solids as envisioned by the late Pr.Coussy.