arXiv subjects

Roland J. -M. Pellenq

Publications and source records attributed to Roland J. -M. Pellenq.

8 recordsLinked to original sources

arXiv2025

Impact of early-age exposure to power ultrasound on the micromechanical properties of hardened cement paste

Cement paste serves as the universal binder in concrete, formed by mixing water with Ordinary Portland Cement (OPC). In its fresh state, cement paste is a suspension in which the initial particle inventory continuously dissolves, while simultaneously, a growing population of colloidal calcium silica-hydrate (C-S-H) particles forms and progressively builds a percolated structure that densifies and hardens through hydration. Like most colloidal gels, cement paste is sensitive to external stimuli such as mechanical vibrations and temperature variations. Here, we show that power ultrasound (PUS) applied to OPC paste during the very early stages of hydration significantly alters the mechanical properties of the hardened material. Freshly prepared cement pastes are exposed to PUS at varying durations and intensities before curing for 28 days. Micro-indentation testing at the scale of tens of microns reveals that increasing PUS amplitude and prolonged PUS exposure degrade the micro-mechanical properties of hardened cement paste, making it more ductile. This softening behavior evolves continuously with exposure conditions and is consistent with an increase in porosity, likely caused by micro-cracks induced by PUS. This scenario is further supported by micro-scratch testing, which shows higher levels of acoustic emission in PUS-exposed samples. Finally, nano-indentation confirms that the properties of the individual phases composing the hardened paste -- low-density and high-density C-S-H -- remain largely unaffected. These findings offer valuable experimental insights into novel pathways for modifying the mechanical properties of reactive colloidal gels.

cond-mat.soft↗

arXiv2022

Ion specificity of confined ion-water structuring and nanoscale surface forces in clays

Ion specificity and related Hofmeister effects, ubiquitous in aqueous systems, can have spectacular consequences in hydrated clays, where ion-specific nanoscale surface forces can determine large scale cohesive, swelling and shrinkage behaviors of soil and sediments. We have used a semi-atomistic computational approach and examined sodium, calcium and aluminum counterions confined with water between charged surfaces representative of clay materials, to show that ion-water structuring in nanoscale confinement is at the origin of surface forces between clay particles which are intrinsically ion-specific. When charged surfaces strongly confine ions and water, the amplitude and oscillations of the net pressure naturally emerge from the interplay of electrostatics and steric effects, which can not be captured by existing theories. Increasing confinement and surface charge densities promote ion-water structures that increasingly deviate from the ions' bulk hydration shells, being strongly anisotropic and persistent, and self-organizing into optimized, nearly solid-like assemblies where hardly any free water is left. In these conditions, strongly attractive interactions can prevail between charged surfaces, due to the dramatically reduced dielectric screening of water and the highly organized water-ion structures. By unravelling the ion-specific nature of these nanoscale interactions, we provide evidence that ion-specific solvation structures determined by confinement are at the origin of ion specificity in clays and potentially a broader range of confined aqueous systems.

cond-mat.soft↗

arXiv2021

Creep in reactive colloidal gels: a nanomechanical study of cement hydrates

From soft polymeric gels to hardened cement paste, amorphous solids under constant load exhibit a pronounced time-dependent deformation called creep. The microscopic mechanism of such a phenomenon is poorly understood in amorphous materials and constitutes an even greater challenge in densely packed and chemically reactive granular systems. Both features are prominently present in hydrating cement pastes composed of calcium silicate hydrate (C-S-H) nanoparticles, whose packing density increases as a function of time, while cement hydration is taking place. Performing nano-indentation tests and porosity measurements on a large collection of samples at various stages of hydration, we show that the creep response of hydrating cement paste is mainly controlled by the inter-particle distance and results from slippage between (C-S-H) nanoparticles. Our findings provide a unique insight into the microscopic mechanism underpinning the creep response in aging granular materials, thus paving the way for the design of concrete with improved creep resistance.

cond-mat.mtrl-sci↗

arXiv2021

The physics of cement cohesion

Cement is one of the most produced materials in the world. A major player in greenhouse gas emissions, it is the main binding agent in concrete, to which it provides a cohesive strength that rapidly increases during setting. Understanding how such cohesion emerges has been a major obstacle to advances in cement science and technology. Here, we combine computational statistical mechanics and theory to demonstrate how cement cohesion results from the organization of interlocked ions and water, progressively confined in nano-slits between charged surfaces of Calcium-Silicate-Hydrates. Due to the water/ions interlocking, dielectric screening is drastically reduced and ionic correlations are proven significantly stronger than previously thought, dictating the evolution of the nano-scale interactions during cement hydration. By developing a quantitative analytical prediction of cement cohesion based on Coulombic forces, we reconcile a novel fundamental understanding of cement hydration with the fully atomistic description of the solid cement paste and open new paths for science and technologies of construction materials.

physics.app-ph↗

arXiv2020

The Effect of Confinement on Capillary Phase Transition In Granular Aggregates

Utilizing a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregates as opposed to porous structures. We show that this discrepancy can be understood in terms of the surface-surface correlation length with a connected path through the fluid domain, suggesting that this length captures the true degree of confinement. We also find that the liquid-gas phase transition in these porous materials is of second order nature near capillary critical temperature, which is shown to represent a true critical temperature, i.e. independent of the degree of disorder and the nature of solid matrix, discrete or continuous. The critical exponents estimated here from finite-size scaling analysis suggest that this transition belongs to the 3D random field Ising model universality class as hypothesized by P.G. de Gennes, with the underlying random fields induced by local disorder in fluid-solid interactions.

cond-mat.stat-mech↗

arXiv2019

Freezing point depression and freeze-thaw damage by nano-fuidic salt trapping

A remarkable variety of organisms and wet materials are able to endure temperatures far below the freezing point of bulk water. Cryo-tolerance in biology is usually attributed to "anti-freeze" proteins, and yet massive supercooling ($< -40^\circ$C) is also possible in porous media containing only simple aqueous electrolytes. For concrete pavements, the common wisdom is that freeze-thaw damage results from the expansion of water upon freezing, but this cannot explain the large pressures ($> 10$~MPa) required to damage concrete, the observed correlation between pavement damage and de-icing salts, or the damage of cement paste loaded with benzene (which contracts upon freezing). In this Letter, we propose a different mechanism -- nanofluidic salt trapping -- which can explain the observations, using simple mathematical models of dissolved ions confined to thin liquid films between growing ice and charged surfaces. Although trapped salt lowers the freezing point, ice nucleation in charged pores causes enormous disjoining pressures via the rejected ions, until their removal by precipitation or surface adsorption at a lower temperatures releases the pressure and allows complete freezing. The theory is able to predict the non-monotonic salt-concentration dependence of freeze-thaw damage in concreter and provides a general framework to understand the origins of cryo-tolerance.

cond-mat.soft↗

arXiv2019

Theory of Freezing Point Depression in Charged Porous Media

Freezing in charged porous media can induce significant pressure and cause damage to tissues and functional materials. We formulate a thermodynamically consistent theory to model freezing phenomena inside charged heterogeneous porous space. Two regimes are distinguished: free ions in open pore space lead to negligible effects of freezing point depression and pressure. On the other hand, if nano-fluidic salt trapping happens, subsequent ice formation is suppressed due to the high concentration of ions in the electrolyte. In this case, our theory predicts that freezing starts at a significantly lower temperature compared to pure water. In 1D, as the temperature goes even lower, ice continuously grows, until the salt concentration reaches saturation, all ions precipitate to form salt crystals, and freezing completes. Enormous pressure can be generated if initial salt concentration is high before salt entrapment. We show modifications to the classical nucleation theory, due to the trapped salt ions. Interestingly, although the freezing process is enormously changed by trapped salts, our analysis shows that the Gibbs-Thompson equation on confined melting point shift is not affected by the presence of the electrolyte.

cond-mat.soft↗

arXiv2018

Capillary stress and structural relaxation in moist granular materials

We propose a theoretical framework to calculate capillary stresses in complex mesoporous materials, such as moist sand, nanoporous hydrates, and drying colloidal films. Molecular simulations are mapped onto a phase-field model of the liquid-vapor mixture, whose inhomogeneous stress tensor is integrated over Voronoi polyhedra in order to calculate equal and opposite forces between each pair of neighboring grains. The method is illustrated by simulations of moisture-induced forces in small clusters and random packings of spherical grains using lattice-gas Density Functional Theory. For a nano-granular model of cement hydrates, this approach reproduces the hysteretic water sorption/desorption isotherms and predicts drying shrinkage strain isotherm in good agreement with experiments. We show that capillary stress is an effective mechanism for internal stress relaxation in colloidal random packings, which contributes to the extraordinary durability of cement paste.

cond-mat.soft↗