@article {575, title = {Le Ch{\^a}telier{\textquoteright}s conjecture: Measurement of colloidal eigenstresses in chemically reactive materials}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {112}, year = {2018}, month = {Mar-2018}, pages = {334 - 344}, abstract = {

Volume changes in chemically reactive materials, such as hydrating cement, play a critical role in many engineering applications that require precise estimates of stress and pressure developments. But a means to determine bulk volume changes in the absence of other deformation mechanisms related to thermal, pressure and load variations, is still missing. Herein, we present such a measuring devise, and a hybrid experimental-theoretical technique that permits the determination of colloidal eigenstresses. Applied to cementitious materials, it is found that bulk volume changes in saturated cement pastes at constant pressure and temperature conditions result from a competition of repulsive and attractive phenomena that originate from the relative distance of the solid particles- much as Henry Louis Le Chatelier, the father of modern cement science, had conjectured in the late 19th century. Precipitation of hydration products in confined spaces entails a repulsion, whereas the concurrent reduction in interparticle distance entails activation of attractive forces in charged colloidal particles. This cross-over from repulsion to attraction can be viewed as a phase transition between a liquid state (below the solid percolation) and the limit packing of hard spheres, separated by an energy barrier that defines the temperature-dependent eigenstress magnitude. (C) 2017 Elsevier Ltd. All rights reserved.

Fig. 1. Pressure vessel measurement device for volume changes under constant pressure{\textellipsis}

Fig. 2. Bulk Volume Change measurement results under drained and fluid saturated{\textellipsis}

Fig. 3. Eigenstress Scaling: (a) Normalized eigenstress (|σ*|/max|σ*|) vs

Fig. 4. Eigenstress interpretation: (a) volume fractions vs

}, keywords = {Poromechanics; Colloidal stresses; Cement-based materials; Expansion; Shrinkage}, issn = {00225096}, doi = {10.1016/j.jmps.2017.12.012}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0022509617309985}, author = {Muhannad Abuhaikal and Katerina Ioannidou and Petersen, Thomas and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {532, title = {Phase separation of stable colloidal clusters}, journal = {Physical Review Materials}, volume = {2}, year = {2018}, month = {Sep-25-2018}, abstract = {

This article presents a nonequilibrium thermodynamic theory for the mean-field precipitation, aggregation, and pattern formation of colloidal clusters. A variable gradient energy coefficient and the arrest of particle diffusion upon \“jamming\” of cluster aggregates in the spinodal region predicts observable gel patterns that, at high intercluster attraction, form system-spanning, out-of-equilibrium networks with glasslike, quasistatic structural relaxation. For reactive systems, we incorporate the free energy landscape of stable prenucleation clusters into the Allen-Cahn reaction equation. We show that pattern formation is dominantly controlled by the Damk\öhler number and the stability of the clusters, which modifies the autocatalytic rate of precipitation. As clusters individually become more stable, bulk phase separation is suppressed.

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}, doi = {10.1103/PhysRevMaterials.2.095602}, url = {https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.095602}, author = {Petersen, Thomas and Bazant, Martin Z. and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {525, title = {A reaction model for cement solidification: Evolving the C{\textendash}S{\textendash}H packing density at the micrometer-scale}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {118}, year = {2018}, month = {Sep-2018}, pages = {58 - 73}, abstract = {

Cement paste is a multiphase material of complex chemistry, of which 60\% by volume is typically composed of calcium\–silicate\–hydrates (C\–S\–H), the phase that lends the material its strength and stiffness. Moreover, it has been shown that the C\–S\–H phase is a dispersion of nanometer-sized particles that are characterized by an attractive\–repulsive potential and densify in course of the hydration reaction. Herein, we model the nucleation and growth of the nanoparticles as a continuous density field subject to a reaction equation. Using this phase-field approach, we aim to reduce the parameter space present in similar hydration models and create a vehicle to upscale mechanical information from the nanometer-scale to the micrometer-scale. Despite the apparent simplification of the physics at play, we readily reproduce the cement paste reaction kinetics and microtexture\—functions of temperature, coarseness of the calcium\–silicate source particles, and initial water-to-cement ratio\—, and vet them against experimental observations. Presenting results for two-dimensional simulations, we achieve excellent agreement with measurements of hydration heat curves, pore-chord-length and solid-chord-length density functions, distributions of low- and high-density C\–S\–H products, and elasticity.

Illustration of the dissolution and nucleation and growth processes driving{\textellipsis}

A comparison between the mean coordination number ⟨z⟩ of the particles modeled{\textellipsis}

Gibb{\textquoteright}s free energy that interpolates between the source phase ψ=1 and open pore{\textellipsis}

Gibb{\textquoteright}s energy of reaction and (b) reaction rate for nanoparticle{\textellipsis}

Evolution of the mean packing fraction of C{\textendash}S{\textendash}H (〈ϕ〉V'; opaque) and the{\textellipsis}

Diagram of the volume fractions of hydrating cement paste

}, issn = {00225096}, doi = {10.1016/j.jmps.2018.05.010}, url = {https://www-sciencedirect-com.libproxy.mit.edu/science/article/pii/S0022509617308876}, author = {Petersen, Thomas and Valdenaire, Pierre-Louis and Roland Jean-Marc Pellenq and Franz-Josef Ulm} }