@article {578, title = {Doping as a Way To Protect Silicate Chains in Calcium Silicate Hydrates}, journal = {ACS Sustainable Chemistry \& Engineering}, volume = {6}, year = {2018}, month = {Sep-09-2018}, pages = {15015 - 15021}, abstract = {

A critical challenge in reducing anthropogenic impacts on the environment is to decrease the carbon footprint of the cement industry. A key concern in the search for more sustainable cement designs is the understanding and control of the depolymerization process that eventually determines the integrity of their silicate chains under mechanical, chemical, or thermal stresses. Herein, we use metadynamics to show that the depolymerization of cement silicate skeletons consists of hydroxylation followed by bond-breaking. We then clarify the local effects of doping the silicate chains: a stable pentacoordinate state following hydroxylation is promoted by aluminum atoms but restrained by phosphorus additions, the presence of two dopants being related to energy landscapes less favorable to bond-breaking. The role of these dopants is explained in cement-based materials and is key to the quest for low-cost opportunities to preserve the strength of cement for high temperatures or even over time.

Abstract Image

}, keywords = {Bond-breaking; Calcium silicate hydrate; Doping; Green cement; Silicate chains}, issn = {2168-0485}, doi = {10.1021/acssuschemeng.8b03488}, url = {http://pubs.acs.org/doi/10.1021/acssuschemeng.8b03488}, author = {Dupuis, Romain and Dolado, Jorge S. and Surga, Jose and Ayuela Andr{\'e}s} } @article {239, title = {Disorder-induced stiffness degradation of highly disordered porous materials}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {106}, year = {2017}, month = {Sep-2017}, chapter = {207-228}, abstract = {

The effective mechanical behavior of multiphase solid materials is generally modeled by means of homogenization techniques that account for phase volume fractions and elastic moduli without considering the spatial distribution of the different phases. By means of extensive numerical simulations of randomly generated porous materials using the lattice element method, the role of local textural properties on the effective elastic properties of disordered porous materials is investigated and compared with different continuum micromechanics-based models. It is found that the pronounced disorder-induced stiffness degradation originates from stress concentrations around pore clusters in highly disordered porous materials. We identify a single disorder parameter, \φsa, which combines a measure of the spatial disorder of pores (the clustering index, sa) with the pore volume fraction (the porosity, \φ) to scale the disorder-induced stiffness degradation. Thus, we conclude that the classical continuum micromechanics models with one spherical pore phase, due to their underlying homogeneity assumption fall short of addressing the clustering effect, unless additional texture information is introduced, e.g. in form of the shift of the percolation threshold with disorder, or other functional relations between volume fractions and spatial disorder; as illustrated herein for a differential scheme model representative of a two-phase (solid\–pore) composite model material.

Fig. 1. Two-dimensional porous media: (a) ordered system, (b) type 1 disorder (pores{\textellipsis}

Fig. 2. Two-point probability functions and associated microstructures of four systems{\textellipsis}

Fig. 3. Probability Density Function (PDF) of the local porosity (φa) and associated{\textellipsis}

Fig. 4. (a) Degrees of freedom of a link element between points i and j, (b) D3Q18 unit{\textellipsis}

Fig. 5. Dimensionless effective Young{\textquoteright}s modulus: Eeff(φ)/Es as function of the porosity{\textellipsis}

Fig. 6. Dimensionless effective Young{\textquoteright}s modulus: Eeff(φ)/Es as function of the porosity

Fig. 7. Ordered system under uniaxial strain, (a) schematic stress map, the darker the{\textellipsis}

Fig. 8. Dimensionless effective Young{\textquoteright}s modulus: Eeff(φ)/Es as function of the porosity

Fig. 9. Probability Density Function (PDF) of the normalized stress (σxx/〈σxx〉) in the{\textellipsis}

Fig. 10. Dimensionless disordered Young{\textquoteright}s modulus: F(φsa)=Eeff(φ,sa)/Eordered(φ) as{\textellipsis}

Fig. 11. Two-phase periodic porous solid

Fig. 12. Dimensionless disordered Young{\textquoteright}s modulus: FMT(φsa)=Eeff(φ,sa)/EMT(φ) as{\textellipsis}

Fig. 13. Integration path for the lower bound differential scheme

Fig. 14. Dimensionless effective Young{\textquoteright}s modulus: Eeff(φ)/Es as function of porosity the

Fig. 15. Dimensionless disordered Young{\textquoteright}s modulus: FMT(φsa)=Eeff(φ,sa)/EMT(φ) as{\textellipsis}

Fig. B.16. (a) Porosity as a function of the number of pores

Fig. D.17. High porosity limit geometry

Fig. E.18. Calculation of the local porosity in a square observation window

}, doi = {10.1016/j.jmps.2017.05.008}, author = {Hadrien Laubie and Monfared, Siavash and Farhang Radja{\"\i} and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {252, title = {Data analytics for simplifying thermal efficiency planning in cities}, journal = {Journal of The Royal Society Interface}, volume = {13}, year = {2016}, month = {Apr-2016}, pages = {Article Number: 20150971}, abstract = {

More than 44\% of building energy consumption in the USA is used for space heating and cooling, and this accounts for 20\% of national CO2emissions. This prompts the need to identify among the 130 million households in the USA those with the greatest energy-saving potential and the associated costs of the path to reach that goal. Whereas current solutions address this problem by analysing each building in detail, we herein reduce the dimensionality of the problem by simplifying the calculations of energy losses in buildings. We present a novel inference method that can be used via a ranking algorithm that allows us to estimate the potential energy saving for heating purposes. To that end, we only need consumption from records of gas bills integrated with a building\&$\#$39;s footprint. The method entails a statistical screening of the intricate interplay between weather, infrastructural and residents\&$\#$39; choice variables to determine building gas consumption and potential savings at a city scale. We derive a general statistical pattern of consumption in an urban settlement, reducing it to a set of the most influential buildings\&$\#$39; parameters that operate locally. By way of example, the implications are explored using records of a set of (N= 6200) buildings in Cambridge, MA, USA, which indicate that retrofitting only 16\% of buildings entails a 40\% reduction in gas consumption of the whole building stock. We find that the inferred heat loss rate of buildings exhibits a power-law data distribution akin to Zipf\&$\#$39;s law, which provides a means to map an optimum path for gas savings per retrofit at a city scale. These findings have implications for improving the thermal efficiency of cities\&$\#$39; building stock, as outlined by current policy efforts seeking to reduce home heating and cooling energy consumption and lower associated greenhouse gas emissions.

}, issn = {1742-5689}, doi = {10.1098/rsif.2015.0971}, author = {Mohammad Javad Abdolhosseini Qomi and Noshadravan, Arash and Sobstyl, Jake M. and Toole, Jameson and Ferreira, Joseph and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Gonzalez, Marta C.} } @article {163, title = {Diffusion of Interlayer Cations in Swelling Clays as a Function of Water Content: Case of Montmorillonites Saturated with Alkali Cations}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, month = {May-14-2015}, pages = {10370 - 10378}, abstract = {
Abstract Image

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.

}, issn = {1932-7447}, doi = {10.1021/jp512986d}, author = {Salles, Fabrice and Douillard, Jean-Marc and Bildstein, Olivier and El Ghazi, Samira and Prelot, B{\'e}n{\'e}dicte and Zajac, Jerzy and Henri Van Damme} } @article {651, title = {Density functional approach for the magnetism of}, journal = {Physical Review B}, volume = {89}, year = {2014}, month = {Mar-01-2014}, abstract = {

Density functional calculations have been carried out to investigate the microscopic origin of the magnetic properties of \β-TeVO4. Two different approaches, based either on a perturbative treatment of the multiorbital Hubbard model in the strongly correlated limit or on the calculation of supercell total energy differences, have been employed to evaluate magnetic couplings in this compound. The picture provided by these two approaches is that of weakly coupled frustrated chains with ferromagnetic nearest-neighbor and antiferromagnetic second-nearest-neighbor couplings. These results, differing substantially from previous reports, should motivate further experimental investigations of the magnetic properties of this compound.

}, issn = {1098-0121}, doi = {10.1103/PhysRevB.89.104414}, url = {https://link.aps.org/doi/10.1103/PhysRevB.89.104414}, author = {Andres Sa{\`u}l and Guillaume Radtke} } @article {62, title = {A density functional approach of the magnetism of b-TeVO4}, journal = {Phys. Rev. B.}, volume = {89}, year = {2014}, month = {Mar-2014}, chapter = {104414}, abstract = {

Density functional calculations have been carried out to investigate the microscopic origin of the magnetic properties of
\β-TeVO4. Two different approaches, based either on a perturbative treatment of the multiorbital Hubbard model in the strongly correlated limit or on the calculation of supercell total energy differences, have been employed to evaluate magnetic couplings in this compound. The picture provided by these two approaches is that of weakly coupled frustrated chains with ferromagnetic nearest-neighbor and antiferromagnetic second-nearest-neighbor couplings. These results, differing substantially from previous reports, should motivate further experimental investigations of the magnetic properties of this compound.

Figure

Figure

Figure

Figure

}, doi = {10.1103/PhysRevB.89.104414}, author = {Andres Sa{\`u}l and Guillaume Radtke} } @article {306, title = {Discussion: Strength-to-fracture scaling in scratching}, journal = {Engineering Fracture Mechanics}, volume = {119}, year = {2014}, month = {Mar-2014}, pages = {21 - 28}, abstract = {

In their paper, Lin and Zhou (2013) add a new dimension to the scratch test analysis, challenging the applicability of Linear Elastic Fracture Mechanics to scratch tests. The question raised is how to integrate the three-dimensionality of scratch tests into the energetic Size Effect Law (SEL) formulated by Ba{\v z}ant for quasi-brittle materials. We show that Lin and Zhou\’s analysis, although relevant is incomplete, as it neglects the blade width, which is critical for the fracture property assessment. In return, if the blade width is properly taken into account, the SEL here proposed is a formidable means to ascertain the fracture toughness from scratching.

Fig. 1. Description of macroscopic scratch tests

Fig. 2. Influence of cutter width w on the intrinsic specific energy ε and the{\textellipsis}

Fig. 3. Strength scaling of scratch tests for different geometries (straight vs

Fig. 4. (a) Presence of a horizontal propagating crack during scratch testing{\textellipsis}

Fig. 5. Application of Ba{\v z}ant{\textquoteright}s Size Effect Law to scratch tests for different{\textellipsis}

}, issn = {00137944}, doi = {10.1016/j.engfracmech.2014.02.025}, author = {Ange-Therese Akono and Franz-Josef Ulm and Zden{\v e}k P Ba{\v z}ant} } @article {37, title = {Docking 90 Sr radionuclide in cement: An atomistic modeling study}, journal = {Physics and Chemistry of the Earth, Parts A/B/C}, volume = {70{\textendash}71}, year = {2014}, month = {2014}, pages = {39{\textendash}44}, abstract = {

Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium\–silicate\–hydrate (C\–S\–H) and its crystalline analog, the 9\ \Å-tobermorite. C\–S\–H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C\–S\–H and 9\ \Å-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium.

Image for unlabelled figure

}, doi = {10.1016/j.pce.2013.11.007}, author = {Youssef, Mostafa and Roland Jean-Marc Pellenq and Bilge Yildiz} } @article {97, title = {Docking Sr-90 radionuclide in cement: An atomistic modeling study}, journal = {Physics and Chemistry of the Earth}, volume = {70-71}, year = {2014}, month = {2014}, pages = {39-44}, type = {Article}, abstract = {

Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium silicate hydrate (C-S-H) and its crystalline analog, the 9 angstrom-tobermorite. C-S-H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C-S-H and 9 angstrom-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium. (C) 2013 Elsevier Ltd. All rights reserved.

}, keywords = {Cement, mechanical properties, Molecular simulation, Nuclear waste storage}, issn = {1474-7065}, doi = {10.1016/j.pce.2013.11.007}, author = {Youssef, Mostafa and Roland Jean-Marc Pellenq and Bilge Yildiz} }