@article {572, title = {Potential-of-Mean-Force Approach for Molecular Dynamics{\textendash}Based Resilience Assessment of Structures}, journal = {Journal of Engineering Mechanics}, volume = {144}, year = {2018}, month = {Aug-2018}, pages = {04018066}, abstract = {

A molecular dynamics (MD)-based structural mechanics approach is proposed for the assessment of resilience of buildings. At the core of the approach, potentials of mean force (PMFs) suitable for structural members for both two-body (stretch) and three-body (bending) interactions are derived to define the energy states between mass points discretizing structural members. An original potential parameter calibration procedure is proposed: for close-to-equilibrium potential parameters, the procedure is based on matching measured frequency of a structure with the frequency of the molecular model. In turn, for bond-rupture parameters, it is shown that classical interatomic potential expressions, such as Morse potential, can be used to calibrate the energy content of many structural members and connections. By way of example, the MD-based structural mechanics approach is applied to a large-scale structure. Compared with classical continuum-based approaches, the added value of the method thus proposed is a rational means of determining the progressive structural collapse load of structures based on thermodynamic integration. By redefining structural mechanics within the context of statistical physics, molecular simulations, and potentials of mean force, the approach provides a powerful means of determining fragility curves required for the assessment of resilience of buildings.

}, keywords = {Molecular dynamics; Structural mechanics; Potential of mean force; Morse potential; Progressive structural collapse; Fragility curves}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0001491}, url = {http://ascelibrary.org/doi/10.1061/\%28ASCE\%29EM.1943-7889.0001491}, author = {Keremides, Konstantinos and Abdolhosseini Qomi, Mohammad Javad and Roland Jean-Marc Pellenq and Franz-Josef Ulm} } @article {574, title = {Role of City Texture in Urban Heat Islands at Nighttime}, journal = {Physical Review Letters}, volume = {120}, year = {2018}, month = {Mar-09-2018}, pages = {Article Number: 108701 }, abstract = {

An urban heat island (UHI) is a climate phenomenon that results in an increased air temperature in cities when compared to their rural surroundings. In this Letter, the dependence of an UHI on urban geometry is studied. Multiyear urban-rural temperature differences and building footprints data combined with a heat radiation scaling model are used to demonstrate for more than 50 cities worldwide that city texture-measured by a building distribution function and the sky view factor-explains city-to-city variations in nocturnal UHIs. Our results show a strong correlation between nocturnal UHIs and the city texture.

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}, keywords = {IDEAL CONDITIONS; CLIMATE-CHANGE; CITIES; SIMULATION; GEOMETRY; ENERGY; HEALTH; IMPACT; MODEL}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.108701}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.108701}, author = {Sobstyl, Jake M. and Emig, Thorsten and Qomi, M. J. Abdolhosseini and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {587, title = {Methodology for Estimation of Nanoscale Hardness via Atomistic Simulations}, journal = {Journal of Nanomechanics and Micromechanics}, volume = {7}, year = {2017}, month = {Dec-2017}, pages = { Article Number: UNSP 04017011 }, abstract = {

Statistical mechanics has provided powerful techniques to measure mechanical properties of materials at the nanoscale and paved the way for bottom-up computational materials design. The introduction of such techniques in civil engineering applications, namely construction and geotechnical materials, remains limited to the elastic and fracture properties. This paper presents an atomistic approach to calculate the nanoscale cohesion, friction angle, and hardness. This method is based on the application of biaxial external deformation, or stress, in the weakest crystallographic direction in the material. The onset of the failure is characterized by investigating the unloading paths from several points on the stress-strain curve. Such calculations of the failure stress along different deformation paths provide multiple failure Mohr circles in the normal-shear stress space, which is found to provide a failure envelope akin to the Mohr-Coulomb failure criterion that is widely used for the plastic analysis of granular geomaterials. The failure envelope characterizes the nanoscale cohesion and friction angle, which in conjunction with continuum mechanics can be utilized to estimate the nanoscale hardness of layered materials. Application of this method to tobermorite and Na-montmorillonite crystals yields values that are close to the experimental measurements obtained using nanoindentation and atomic force microscopy techniques. (C) 2017 American Society of Civil Engineers.

}, keywords = {Atomistic simulation; Friction; Cohesion; Hardness; Tobermorite; Montmorillonite}, issn = {2153-5434}, doi = {10.1061/(ASCE)NM.2153-5477.0000127}, url = {http://ascelibrary.org/doi/10.1061/\%28ASCE\%29NM.2153-5477.0000127}, author = {Qomi, M. J. Abdolhosseini and Ebrahimi, Davoud and Mathieu Bauchy 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 {248, title = {Fracture toughness anomalies: Viewpoint of topological constraint theory}, journal = {Acta Materialia}, volume = {121}, year = {2016}, month = {Dec-2016}, pages = {234 - 239}, abstract = {

The relationship between composition, structure, and resistance to fracture remains poorly understood. Here, based on molecular dynamics simulations, we report that sodium silicate glasses and calcium\–silicate\–hydrates feature an anomalous maximum in fracture toughness. In the framework of topological constraint theory, this anomaly is correlated to a flexible-to-rigid transition, driven by pressure or composition for sodium silicate and calcium\–silicate\–hydrates, respectively. This topological transition, observed for an isostatic network, is also shown to correspond to a ductile-to-brittle transition. At this state, the network is rigid but free of eigen-stress and features stress relaxation through crack blunting, resulting in optimal resistance to fracture. Our topological approach could therefore enable the computational design of tough inorganic solids, which has long been a \“holy grail\” within the non-metallic materials chemistry community.

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}, issn = {13596454}, doi = {10.1016/j.actamat.2016.09.004}, author = {Mathieu Bauchy and Wang, Bu and Wang, Mengyi and Yu, Yingtian and Mohammad Javad Abdolhosseini Qomi and Smedskjaer, Morten M. and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @proceedings {98, title = {Is cement a glassy material?}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1}, year = {2015}, month = {Jun-22-2015}, pages = {169-176}, publisher = {CRC PRESS-TAYLOR \& FRANCIS GROUP}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

The nature of Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains a controversial question. In particular, contrary to the former crystalline model, it was recently proposed that its nanoscale structure was actually amorphous. To elucidate this issue, we analyzed the structure of a realistic simulation of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue to cement, and to an artificial ideal glass. Results clearly support that C-S-H is amorphous. However, its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that its amorphous state mainly arises from its hydration.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-19}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Roland Jean-Marc Pellenq and Franz-Josef Ulm}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @proceedings {331, title = {C-S-H across Length Scales: From Nano to Micron}, journal = {10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete StructuresCONCREEP 10}, volume = {CONCREEP 10: MECHANICS AND PHYSICS OF CREEP, SHRINKAGE, AND DURABILITY OF CONCRETE AND CONCRETE STRUCTURES }, year = {2015}, month = {Sep-17-2015}, pages = {39-48}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Despite their impact on longevity, serviceability, and environmental footprint of our built infrastructure, the chemo-physical origins of nanoscale properties of cementitious materials, and their link to macroscale properties still remain rather obscure. Here, we discuss a multi-scale approach that describes different aspects of physical properties of C-S-H at the nano- and meso-scales. These include dynamics of water, thermal properties and mechanical behavior of C-S-H and its effect on properties of cement paste at different scales.

}, doi = {10.1061/978078447934610.1061/9780784479346.006}, url = {http://ascelibrary.org/doi/book/10.1061/9780784479346http://ascelibrary.org/doi/pdf/10.1061/9780784479346http://ascelibrary.org/doi/10.1061/9780784479346.006http://ascelibrary.org/doi/pdf/10.1061/9780784479346.006}, author = {Mohammad Javad Abdolhosseini Qomi and Enrico Masoero and Mathieu Bauchy and Franz-Josef Ulm and Emanuela Del Gado and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @article {137, title = {Fracture toughness of calcium{\textendash}silicate{\textendash}hydrate from molecular dynamics simulations}, journal = {Journal of Non-Crystalline Solids}, volume = {419}, year = {2015}, month = {Jul-01-2015}, pages = {58 - 64}, abstract = {

Concrete is the most widely manufactured material in the world. Its binding phase, calcium\–silicate\–hydrate (C\–S\–H), is responsible for its mechanical properties and has an atomic structure fairly similar to that of usual calcium silicate glasses, which makes it appealing to study this material with tools and theories traditionally used for non-crystalline solids. Here, following this idea, we use molecular dynamics simulations to evaluate the fracture toughness of C\–S\–H, inaccessible experimentally. This allows us to discuss the brittleness of the material at the atomic scale. We show that, at this scale, C\–S\–H breaks in a ductile way, which prevents one from using methods based on linear elastic fracture mechanics. Knowledge of the fracture properties of C\–S\–H at the atomic scale opens the way for an upscaling approach to the design of tougher cement paste, which would allow for the design of slender environment-friendly infrastructures, requiring less material.

}, issn = {00223093}, doi = {10.1016/j.jnoncrysol.2015.03.031}, author = {Mathieu Bauchy and Hadrien Laubie and Mohammad Javad Abdolhosseini Qomi and Christian G. Hoover and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {646, title = {Les mat{\'e}riaux poreux : un domaine scientifique et technologique pluridisciplinaire au futur radieux}, journal = {Mat{\'e}riaux \& Techniques}, volume = {103}, year = {2015}, month = {2015}, pages = {701}, abstract = {

Porous materials cover a broad multidisciplinary scientific and technological domain. They are used in numerous existing and emerging devices and processes related to key societal issues both in environmental protection and for the benefit of the economy. Our choice was to illustrate advances in porous materials through three specific examples: porous materials engineering in the case of organic mesoporous materials prepared from block polymers, modeling and numerical simulation of adsorption of molecular species at the nanoscale and, finally technological applications as thermal insulators.

}, issn = {0032-6895}, doi = {10.1051/mattech/2015050}, url = {http://www.mattech-journal.org/10.1051/mattech/2015050}, author = {Ayral, Andre and Calas-Etienne, Sylvie and Benoit A. Coasne and Deratani, Andr{\'e} and Grande, Daniel and Quemener, Damien and Rossignol, Sylvie} } @article {138, title = {Physical Origins of Thermal Properties of Cement Paste}, journal = {Physical Review Applied}, volume = {3}, year = {2015}, month = {Jun-17-2015}, pages = {Article Number: 064010}, abstract = {

Despite the ever-increasing interest in multiscale porous materials, the chemophysical origin of their thermal properties at the nanoscale and its connection to the macroscale properties still remain rather obscure. In this paper, we link the atomic- and macroscopic-level thermal properties by combining tools of statistical physics and mean-field homogenization theory. We begin with analyzing the vibrational density of states of several calcium-silicate materials in the cement paste. Unlike crystalline phases, we indicate that calcium silicate hydrates (CSH) exhibit extra vibrational states at low frequencies (\<2\ \ THz) compared to the vibrational states predicted by the Debye model. This anomaly is commonly referred to as the boson peak in glass physics. In addition, the specific-heat capacity of CSH in both dry and saturated states scales linearly with the calcium-to-silicon ratio. We show that the nanoscale-confining environment of CSH decreases the apparent heat capacity of water by a factor of 4. Furthermore, full thermal conductivity tensors for all phases are calculated via the Green-Kubo formalism. We estimate the mean free path of phonons in calcium silicates to be on the order of interatomic bonds. This satisfies the scale separability condition and justifies the use of mean-field homogenization theories for upscaling purposes. Upscaling schemes yield a good estimate of the macroscopic specific-heat capacity and thermal conductivity of cement paste during the hydration process, independent of fitting parameters.

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}, doi = {10.1103/PhysRevApplied.3.064010}, author = {Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {131, title = {Rigidity transition in materials: hardness is driven by weak atomic constraints.}, journal = {Phys Rev Lett}, volume = {114}, year = {2015}, month = {Mar-23-2015}, pages = {Article Number: 125502}, abstract = {

Understanding the composition dependence of the hardness in materials is of primary importance for infrastructures and handled devices. Stimulated by the need for stronger protective screens, topological constraint theory has recently been used to predict the hardness in glasses. Herein, we report that the concept of rigidity transition can be extended to a broader range of materials than just glass. We show that hardness depends linearly on the number of angular constraints, which, compared to radial interactions, constitute the weaker ones acting between the atoms. This leads to a predictive model for hardness, generally applicable to any crystalline or glassy material.

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}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.114.125502}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {102, title = {Anomalous composition-dependent dynamics of nanoconfined water in the interlayer of disordered calcium-silicates}, journal = {Journal of Chemical Physics}, volume = {140}, year = {2014}, month = {Feb-07-2014}, pages = {Article Number: 054515}, type = {Article}, abstract = {

With shear interest in nanoporous materials, the ultraconfining interlayer spacing of calcium-silicate-hydrate (C-S-H) provides an excellent medium to study reactivity, structure, and dynamic properties of water. In this paper, we present how substrate composition affects chemo-physical properties of water in ultraconfined hydrophilic media. This is achieved by performing molecular dynamics simulation on a set of 150 realistic models with different compositions of calcium and silicon contents. It is demonstrated that the substrate chemistry directly affects the structural properties of water molecules. The motion of confined water shows a multi-stage dynamics which is characteristic of supercooled liquids and glassy phases. Inhomogeneity in that dynamics is used to differentiate between mobile and immobile water molecules. Furthermore, it is shown that the mobility of water molecules is composition-dependent. Similar to the pressure-driven self-diffusivity anomaly observed in bulk water, we report the first study on composition-driven diffusion anomaly, the self diffusivity increases with increasing confined water density in C-S-H. Such anomalous behavior is explained by the decrease in the typical activation energy required for a water molecule to escape its dynamical cage. (C) 2014 AIP Publishing LLC.

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}, issn = {0021-9606}, doi = {10.1063/1.4864118}, author = {Mohammad Javad Abdolhosseini Qomi and Mathieu Bauchy and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {72, title = {Combinatorial molecular optimization of cement hydrates}, journal = {Nat Commun}, volume = {5}, year = {2014}, month = {Sep-24-2014}, pages = {Article Number: 4960}, abstract = {

Despite its ubiquitous presence in the built environment, concrete\â\€$(1s (Bmolecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete\â\€$(1s (Benvironmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

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}, doi = {10.1038/ncomms5960}, author = {Mohammad Javad Abdolhosseini Qomi and Konrad J. Krakowiak and Mathieu Bauchy and Stewart, K.L. and Rouzbeh Shahsavari and Jagannathan, D. and Brommer, D.B. and Alain Baronnet and Markus J Buehler and Sidney Yip and Franz-Josef Ulm and Krystyn J. Van Vliet and Roland Jean-Marc Pellenq} } @article {70, title = {Multiphase equation of state for carbon addressing high pressures and temperatures}, journal = {Phys Rev. B}, volume = {89}, year = {2014}, month = {Jun-2014}, chapter = {224109}, abstract = {

We present a 5-phase equation of state for elemental carbon which addresses a wide range of density and temperature conditions: 3g/cc\<\ρ\<20g/cc,0K\<T\<\∞. The phases considered are diamond, BC8, simple cubic, simple hexagonal, and the liquid/plasma state. The solid phase free energies are constrained by density functional theory (DFT) calculations. Vibrational contributions to the free energy of each solid phase are treated within the quasiharmonic framework. The liquid free energy model is constrained by fitting to a combination of DFT molecular dynamics performed over the range 10000K\<T\<100000K, and path integral quantum Monte Carlo calculations for T\>100000K (both for \ρ between 3 and 12 g/cc, with select higher- \ρ DFT calculations as well). The liquid free energy model includes an atom-in-jellium approach to account for the effects of ionization due to temperature and pressure in the plasma state, and an ion-thermal model which includes the approach to the ideal gas limit. The precise manner in which the ideal gas limit is reached is greatly constrained by both the highest-temperature DFT data and the path integral data, forcing us to discard an ion-thermal model we had used previously in favor of a new one. Predictions are made for the principal Hugoniot and the room-temperature isotherm, and comparisons are made to recent experimental results.

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}, doi = {10.1103/PhysRevB.89.224109}, author = {L. X. Benedict and K. P. Driver and S. Hamel and B. Militzer and T. Qi and Alfredo A. Correa and Andres Sa{\`u}l and E. Schwegler} } @article {115, title = {Nanoscale Structure of Cement: Viewpoint of Rigidity Theory}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {Jun-12-2014}, pages = {12485-12493}, type = {Article}, abstract = {
Abstract Image

Rigidity theory is a powerful tool to predict the properties of glasses with respect to composition. By reducing such molecular networks to simple mechanical trusses, topological constraint theory filters out all the unnecessary details that ultimately do not affect macroscopic properties. However, the usual constraint enumeration is restricted to networks that are amorphous, homogeneous, and fully connected. On the contrary, calcium\–silicate\–hydrate (C\–S\–H), the binding phase of cement, is partially crystalline and heterogeneous and shows some isolated water molecules. Here, we report how rigidity theory can be used to describe the nanoscale structure of this material by relying on molecular dynamics simulations. The distinction between intact and broken constraints is clearly defined at the atomic scale, thus allowing a precise enumeration of the topological constraints. We show that the rigidity of the C\–S\–H network can be increased by decreasing the Ca/Si molar ratio, which, as predicted by rigidity theory, allows improvement of the hardness of the material. This study suggests that rigidity theory could be applied with great rewards to a broader range of materials than glasses.

}, issn = {1932-7447}, doi = {10.1021/jp502550z}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Christophe Bichara and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {262, title = {Order and disorder in calcium{\textendash}silicate{\textendash}hydrate}, journal = {The Journal of Chemical Physics}, volume = {140}, year = {2014}, month = {Jun-07-2014}, pages = {Article Number: 214503}, abstract = {

Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium\–Silicate\–Hydrate (C\–S\–H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C\–S\–H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C\–S\–H, and compared the latter to crystalline tobermorite, a natural analogue of C\–S\–H, and to an artificial ideal glass. The results clearly indicate that C\–S\–H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C\–S\–H retains some signatures of a tobermorite-like layered structure, hydrated species are completely amorphous.

}, issn = {0021-9606}, doi = {10.1063/1.4878656}, author = {Mathieu Bauchy and Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {278, title = {Penetration test in coarse granular material using Contact Dynamics Method}, journal = {Computers and Geotechnics}, volume = {55}, year = {2014}, month = {Jan-2014}, pages = {248 - 253}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. Indeed, the data are considerably more sensitive in this case to various parameters such as fabric structure, particle shapes or the applied impact energy. In order to achieve a better understanding of the penetration process into a coarse granular material, a numerical study was performed by means of contact dynamics simulations. The penetration of a moving tip in a sample composed of irregular grain shapes was studied and the influence of the driving velocity and input energy on the penetration strength was analyzed. The results show that the latter grows with both the penetration rate and energy, despite the strong fluctuations occur due to a jamming\–unjamming process in which the contact network connectivity evolves intermittently in correlation with the penetration strength. This analysis suggests that the time-averaged data provided by a penetrometer is reliable information from which the bulk strength properties of coarse granular materials can be evaluated.

}, issn = {0266352X}, doi = {10.1016/j.compgeo.2013.09.006}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @article {274, title = {Predicting the settlement of coarse granular materials under vertical loading}, journal = {Scientific Reports}, volume = {4}, year = {2014}, month = {Jul-16-2014}, pages = {Article Number: 5707}, abstract = {

Granular materials are widely used in industrial processes despite their complex and poorly understood mechanical behaviour both in static and dynamic regimes. A prototypical example is the settlement and compaction of a granular bed under vibrational loading. The elementary mechanisms of this process are still unclear and there is presently no established theory or methodology to predict the settlement and its statistical variability. By means of a parametric study, carried out on a full-scale track, and a critical analysis of density relaxation laws, we introduce a novel settlement model in coarse granular materials under cyclic loading. Our extensive experimental data indicate that the settlement process is governed by three independent parameters strongly correlated with the vibration intensity and initial packing fraction. We show that the mean settlement is well predicted by the model with its parameter values extracted from experimental data.

Granular materials are both pressure-dependent and density-dependent materials and exhibit a broad range of intricate behaviours due to their discrete nature, dissipative interactions and generic structural disorder1. The packing fraction may vary as a result of particle rearrangements induced by shearing or vibrations and it leads to dramatic changes in the structure and mechanical response of a granular material2,3,4,5,6,7,8. A long-time logarithmic relaxation law of the packing fraction is systematically observed in experiments9,10. In simple compaction models, this behaviour is attributed to the exponentially increasing time for the particles to reach a new configuration of lower packing fraction. The case of settlement under cyclic loading has, however, been much less investigated. The settlement of granular bed occurs due to both compaction and side-wise spreading. An important industrial example is the railway ballast, which undergoes gradual settlement under the static and dynamic overloads induced by train traffics11,12,13,14. The readjustment of differential settlements requires costly operations on fast-train railways. For this reason, an improved understanding of the parameters governing the settlement process is a critical technological challenge for new developments in this field.

In this paper, we show that the total settlement N under vertical cyclic loading is governed by a logarithmic relaxation law as a function of the number N of cycles:

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where the three fitting parameters \∞, B and N0 can be evaluated from the loading parameters, namely the frequency (related to the train speed for ballast) and initial packing fraction of the material. Our experimental correlations between model and loading parameters show consistently that \∞ and B depend on the dimensionless loading intensity \Γ = (A\ω2)/(pd2/m + g), where A is the vibration amplitude, p is the confining pressure (under the sleeper for ballast), d is the average particle diameter, m is the average particle mass and g is gravitational acceleration. We also find that the parameter N0 is linked to the initial packing fraction of the material. In fact, this parameter controls the initial settlement rate, and it was systematically determined by means of a light penetrometer in our experiments on ballast material.

}, doi = {10.1038/srep05707}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}} } @proceedings {360, title = {Penetration strength of coarse granular materials from DEM simulations}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013 }, year = {2013}, month = {Jun-18-2013}, pages = { 241-244}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer test is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. In fact, the data are considerably more sensitive to various parameters such as fabric structure, particles shape or the applied impact energy. In order to achieve a better understanding of the underlying phenomena, we performed a numerical study by means contact dynamics DEM simulations. We consider the penetration of a moving tip into a sample composed of irregular grain shapes and we analyze the influence of the driving velocity and applied energy on the penetration strength. We find that the latter grows with both the penetration rate and energy. Force fluctuations on the tip involve a jamming-unjamming process. The typology of contact network and inter-granular friction play a major role in the fluctuations and measured values of the cone penetration strength.

}, doi = {10.1063/1.4811912}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {219, title = {Reactive elastomeric composites: When rubber meets cement}, journal = {Composites Science and Technology}, volume = {75}, year = {2013}, month = {Feb-11-2013}, pages = {77 - 83}, abstract = {

This paper describes a novel reactive composite material comprised of hydrogenated nitrile butadiene rubber (HNBR) compounded with slag cement. The composite initially looks and behaves like rubber, but when exposed to water it simultaneously swells and stiffens due to hydration of the cement component. The material eventually reaches a stiffness that is intermediate between that of HNBR and hydrated cement, while maintaining a relatively large ductility that is more characteristic of rubber. This behavior, which is ideal for sealing applications, differentiates this material from conventional swellable materials that become less stiff upon swelling. The development of this new type of material was motivated by the requirements of oilfield zonal isolation, where alternatives to cement are needed for some challenging sealing applications. A mechanism for the swelling and stiffening of the reactive composite is proposed: water diffuses into the HNBR matrix and is converted to bound water through hydration reactions with the cement, causing the effective solid filler content of the composite to increase. A model is proposed that treats the composite as a cellular solid with a continuous filler phase (hydrated cement). This model is able to reproduce the observed increase in the elastic modulus with time during exposure to water.

Elastic modulus ratio (current/initial) as a function of swelling, for HNBR ...

Kinetics of swelling of all three materials during approximately 1month of ...

Evolution of the elastic modulus of all three materials during approximately ...

Tensile stress{\textendash}strain curves for HNBR-cement (61{\textendash}39\% by volume, pre-exposure) ...

Schematic of the hydration process occurring inside the HNBR-cement material, ...

SEM images of HNBR-cement material before (left) and after (right) hydration. It ...

}, issn = {02663538}, doi = {10.1016/j.compscitech.2012.11.012}, author = {Robisson, Agathe and Sudeep Maheshwar and Musso, Simone and Jeffrey J. Thomas and Auzerais, Francois M. and Han, Dingzhi and Qu, Meng and Franz-Josef Ulm} } @proceedings {361, title = {Settlement statistics of a granular layer composed of polyhedral particles}, journal = {7th International Conference on Micromechanics of Granular Media (Powders and Grains)}, volume = {Book Series: AIP Conference Proceedings POWDERS AND GRAINS 2013}, year = {2013}, month = {Jun-18-2013}, pages = {333-336}, publisher = {AIP}, address = {JUL 08-12 2013 Sydney, AUSTRALIA}, abstract = {

We use 3D contact dynamics simulations to investigate the mechanical equilibrium and settlement of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction force at the top and bottom boundaries, the transient deformation induced by a constant vertical load increment is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation.

}, doi = {10.1063/1.4811935}, author = {Quezada, Juan Carlos and Saussine, Gilles and Breul, Pierre and Farhang Radja{\"\i}}, editor = {Yu, A and Dong, K and Yang, R} } @article {54, title = {Evidence on the Dual Nature of Aluminum in the Calcium-Silicate-Hydrates Based on Atomistic Simulations}, journal = {Journal of the American Ceramic Society}, volume = {95}, year = {2012}, month = {Jan-23-2012}, pages = {1128{\textendash}1137}, abstract = {

Hydration of tri-calcium silicate (C3S) and di-calcium silicate (C2S) precipitates calcium-silicate-hydrate (CSH) which is the bonding phase responsible for the strength of cementitious materials. Substitution of part of C3S and C2S with aluminum-containing additives alters the chemical composition of hydration products by precipitating calcium-aluminate-silicate-hydrate (CASH). Incorporation of aluminum in the molecular building blocks of CSH entails structural and chemo-mechanical consequences. These alterations can be measured through solid state nuclear magnetic resonance (NMR) experiments. By conducting a wide spectrum of atomistic simulation methods on thousands of aluminum-containing molecular CASH structures, an overall molecular approach for determination of CASH nanostructure is presented. Through detailed analysis of different order parameters, it is found that aluminum can exhibit a tetra-/penta-/octahedral behavior which is fully consistent with the recent NMR observations. This corresponds to the formation of a class of complex three-dimensional alumino-silicate skeletons with partial healing effect in the CASH nanostructure potentially increasing durability and strength of hydration products. We explored the variation of mechanical observables by increasing aluminum content in CASH structures of varying calcium to silicon ratio. Finally, deformation of CSHs and CASHs of different chemical formula in a multi-scale fashion unravels the effect of chemical composition on the strength and kinematics of deformation in this particular type of composites.

}, doi = {10.1111/j.1551-2916.2011.05058.x}, author = {Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {297, title = {Stability, deformation, and variability of granular fills composed of polyhedral particles}, journal = {Physical Review E}, volume = {86}, year = {2012}, month = {Sep-28-2012}, pages = {Article Number: 031308 Part: 1}, abstract = {

By means of extensive contact dynamics simulations, we investigate the mechanical equilibrium and deformation of a granular material composed of irregular polyhedral particles confined between two horizontal frictional planes. We show that, as a consequence of mobilized wall-particle friction forces at the top and bottom boundaries, the transient deformation induced by a constant vertical load is controlled by the aspect ratio (thickness over width) of the packing as well as the stress ratio. The transient deformation declines considerably for increasingly smaller aspect ratios and grows with the stress ratio. From the simulation data for a large number of independent configurations, we find that sample-to-sample fluctuations of the deformation have a broad distribution and they scale with the average deformation. We also analyze the evolution of particle connectivity during settlement and with the applied force. The face-face and edge-face contacts between polyhedral particles concentrate strong force chains with a growing proportion as a function of the applied force.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.86.031308}, author = {Quezada, Juan Carlos and Breul, Pierre and Saussine, Gilles and Farhang Radja{\"\i}} } @proceedings {349, title = {Creep behaviour of confined layers of polyhedral grains}, journal = {2nd International Conference on Particle-Based Methods - Fundamentals and Applications (Particles)}, volume = {PARTICLE-BASED METHODS II: FUNDAMENTALS AND APPLICATIONS }, year = {2011}, month = {Oct-2011}, pages = {574-583}, address = {OCT 26-28 2011 Barcelona, SPAIN}, abstract = {

By means of contact dynamics simulations, we investigate the creep deformation of a thin granular layer composed of irregular polyhedral particles under the action of a constant vertical overload applied on a horizontal wall on top of the layer. We show that the total deformation induced by the overload increases with the ratio between the vertical and confining horizontal stresses and the aspect ratio of the sample. The effect of the aspect ratio is a consequence of the mobilized wall-grain friction forces at the top and bottom boundaries, that lead to enhanced strength by stabilizing strong force chains at the center of the sample. We also evidence the influence of loading history due to strain-induced fabric change or inertial effects resulting from the instant application of the overload. The topology of the contact network evolves in close correlation with creep. In particular, the face/face contacts between polyhedral particles concentrate largest force chains and their number is an increasing function of creep. A crucial feature of a confined granular system is the statistical variability of the mechanical response that we analyzed for creep deformations by performing a large number of simulations for independent initial configurations. Our data indicate that the distribution of fluctuations with respect to the mean creep falls off exponentially.

}, url = {https://hal.archives-ouvertes.fr/hal-00761094}, author = {Quezada, Juan Carlos and Farhang Radja{\"\i} and Breul, Pierre and Saussine, Gilles}, editor = {Onate, E and Owen, DRJ} } @article {291, title = {Impact of Chemical Impurities on the Crystalline Cement Clinker Phases Determined by Atomistic Simulations}, journal = {Crystal Growth \& Design}, volume = {11}, year = {2011}, month = {Jul-2011}, pages = {2964 - 2972}, abstract = {
Abstract Image

The presence of chemical substitutions is believed to play a crucial role in the hydration reactions, structure, and elastic properties of cement clinker phases. Hence, substitutions are of great technological interest, as more efficient production of cement clinkers would result in a reduction of CO2 emissions, as well as possible economic benefits. Here we use a combination of classical and quantum mechanical simulation methods to study the detailed physicochemical changes of the clinker phases alite (Ca3SiO5) and belite (Ca2SiO4) when Mg2+, Al3+ and Fe3+ guest ions are incorporated into their structure. Using classical force field methods, we considered random substitutions among possible sites and different compositions in order to identify the preferential substitution sites on the crystalline structures. Then, the resulting structural changes that take place to accommodate the guest ions are investigated and discussed in detail. Using quantum mechanical density functional theory calculations the electronic structure of representative configurations has been computed to determine the potential impact of impurities on the reactivity.

}, issn = {1528-7483}, doi = {10.1021/cg200212c}, author = {Hegoi Manzano and Engin Durgun and Mohammad Javad Abdolhosseini Qomi and Franz-Josef Ulm and Roland Jean-Marc Pellenq and Jeffrey C Grossman} }