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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.

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.

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.

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.

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.

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.

Nowadays, cement manufacturers use polymers, called superplastizicers, to enhance cement pastes workability. However, cement suspensions with superplastizicers often become unstable and settle. We showed thermoassociative polymers utilization enables to avoid the settle or decrease the yield stress with temperature change. Rheological measurements have been completed with polymer adsorption data on cement particles. So, we proved that the active part of thermoassociative polymers in the thickening effect was the part of adsorbed polymer. The other part of this work consisted to use model systems (monodisperse and bidisperse silica particles, quartz) to obtain a better understanding of cement pastes behavior with or without polymer.; Actuellement, les industries cimentières utilisent des polymères, appelés superplastifiants, pour faciliter la mise en place des pâtes de ciment. Cependant, ces suspensions, en présence de superplastifiants, deviennent souvent instables et sédimentent. Nous avons montré que l'utilisation de polymères thermoassociatifs permet en changeant la température, de préparer des suspensions qui d'une part ne sédimentent pas et de l'autre ont un faible seuil d'écoulement. Les données rhéologiques ont été corrélées avec des mesures d'adsorption du polymère sur les particules de ciment. . Nous avons ainsi pu prouver que la partie du polymère thermoassociatif active dans l'épaississement était celle qui était adsorbé à la surface des particules. Une autre partie de cette thèse consistait à utiliser des systèmes modèles (particules de silices monodisperses et bidiperses, quartz) afin d'obtenir une meilleure compréhension du comportement rhéologique des pâtes de ciment sans ou en présence de polymère.

Nowadays, cement manufacturers use polymers, called superplastizicers, to enhance cement pastes workability. However, cement suspensions with superplastizicers often become unstable and settle. We showed thermoassociative polymers utilization enables to avoid the settle or decrease the yield stress with temperature change. Rheological measurements have been completed with polymer adsorption data on cement particles. So, we proved that the active part of thermoassociative polymers in the thickening effect was the part of adsorbed polymer. The other part of this work consisted to use model systems (monodisperse and bidisperse silica particles, quartz) to obtain a better understanding of cement pastes behavior with or without polymer.; Actuellement, les industries cimentières utilisent des polymères, appelés superplastifiants, pour faciliter la mise en place des pâtes de ciment. Cependant, ces suspensions, en présence de superplastifiants, deviennent souvent instables et sédimentent. Nous avons montré que l'utilisation de polymères thermoassociatifs permet en changeant la température, de préparer des suspensions qui d'une part ne sédimentent pas et de l'autre ont un faible seuil d'écoulement. Les données rhéologiques ont été corrélées avec des mesures d'adsorption du polymère sur les particules de ciment. . Nous avons ainsi pu prouver que la partie du polymère thermoassociatif active dans l'épaississement était celle qui était adsorbé à la surface des particules. Une autre partie de cette thèse consistait à utiliser des systèmes modèles (particules de silices monodisperses et bidiperses, quartz) afin d'obtenir une meilleure compréhension du comportement rhéologique des pâtes de ciment sans ou en présence de polymère.

The implementation of cement materials is improved by addition of polymer as called superplasticizer. In this study, we look for the impact of the polymer architecture on the physico-chemistry properties of cement slurries. At first, we focused on the synthesis ad characterization of sodium polymethacrylates grafted by poly(ethylene oxide) chains. Then, we observe the adsorption of these superplasticizers on different types of cement using macroscopic and microscopic techniques. Finally, we measure the setting time, the behavior at rest and the fluidity of different cement slurries with the use of new tools such as the helicoidal ribbon geometry and the ultrasound technique.; La mise en oeuvre des matériaux cimentaires est facilitée par l'ajout d'additifs polymères appelés superplastifiants. Dans notre étude, nous regardons l'impact de l'architecture macromoléculaire de ces polymères sur les propriétés physico-chimiques d'un coulis de ciment. Dans un premier temps, nous nous concentrons sur le contrôle de la synthèse et sur la caractérisation des polyméthacrylates de sodium greffés par des chaînes de poly(oxyde d'éthylène). Puis, nous observons l'adsorption de ces superplastifiants sur différents types de ciment avec l'aide de techniques macroscopiques et microscopiques. Finalement, nous mesurons le temps de prise, la structuration au repos et l'écoulement de différents coulis de ciment grâce à de nouveaux outils d'analyses comme la géométrie ruban et les ultrasons.

The implementation of cement materials is improved by addition of polymer as called superplasticizer. In this study, we look for the impact of the polymer architecture on the physico-chemistry properties of cement slurries. At first, we focused on the synthesis ad characterization of sodium polymethacrylates grafted by poly(ethylene oxide) chains. Then, we observe the adsorption of these superplasticizers on different types of cement using macroscopic and microscopic techniques. Finally, we measure the setting time, the behavior at rest and the fluidity of different cement slurries with the use of new tools such as the helicoidal ribbon geometry and the ultrasound technique.; La mise en oeuvre des matériaux cimentaires est facilitée par l'ajout d'additifs polymères appelés superplastifiants. Dans notre étude, nous regardons l'impact de l'architecture macromoléculaire de ces polymères sur les propriétés physico-chimiques d'un coulis de ciment. Dans un premier temps, nous nous concentrons sur le contrôle de la synthèse et sur la caractérisation des polyméthacrylates de sodium greffés par des chaînes de poly(oxyde d'éthylène). Puis, nous observons l'adsorption de ces superplastifiants sur différents types de ciment avec l'aide de techniques macroscopiques et microscopiques. Finalement, nous mesurons le temps de prise, la structuration au repos et l'écoulement de différents coulis de ciment grâce à de nouveaux outils d'analyses comme la géométrie ruban et les ultrasons.