@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 {243, title = {Topological Control on the Structural Relaxation of Atomic Networks under Stress}, journal = {Physical Review Letters}, volume = {119}, year = {2017}, month = {Jul-21-2017}, pages = {Article Number: 035502}, abstract = {

Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C-S-H), the binding phase of concrete. Under constant shear stress, C-S-H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.

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}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.035502}, author = {Mathieu Bauchy and Wang, Mengyi and Yu, Yingtian and Wang, Bu and Krishnan, M. Anoop and Enrico Masoero and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @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.

Image 1

}, 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} } @article {196, title = {Mesoscale texture of cement hydrates}, journal = {Proceedings of the National Academy of Sciences}, volume = {113}, year = {2016}, month = {Feb-23-2016}, pages = {2029 - 2034}, abstract = {

Strength and other mechanical properties of cement and concrete rely upon the formation of calcium\–silicate\–hydrates (C\–S\–H) during cement hydration. Controlling structure and properties of the C\–S\–H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C\–S\–H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C\–S\–H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C\–S\–H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C\–S\–H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.

Fig. 1.

}, issn = {0027-8424}, doi = {10.1073/pnas.1520487113}, author = {Katerina Ioannidou and Konrad J. Krakowiak and Mathieu Bauchy and Christian G. Hoover and Enrico Masoero and Sidney Yip and Franz-Josef Ulm and Pierre E. Levitz and Roland Jean-Marc Pellenq and Emanuela Del Gado} } @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 {332, title = {Creep of Bulk C-S-H: Insights from Molecular Dynamics Simulations}, 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 = {511-516}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

Understanding the physical origin of creep in calcium\–silicate\–hydrate (C\–S\–H) is of primary importance, both for fundamental and practical interest. Here, we present a new method, based on molecular dynamics simulation, allowing us to simulate the long-term visco-elastic deformations of C\–S\–H. Under a given shear stress, C\–S\–H features a gradually increasing shear strain, which follows a logarithmic law. The computed creep modulus is found to be independent of the shear stress applied and is in excellent agreement with nanoindentation measurements, as extrapolated to zero porosity.

}, doi = {10.1061/978078447934610.1061/9780784479346.061}, author = {Mathieu Bauchy and Enrico Masoero and Franz-Josef Ulm and Roland Jean-Marc Pellenq}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @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} } @proceedings {334, title = {Kinetic Simulations of Cement Creep: Mechanisms from Shear Deformations of Glasses}, 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 = {555-564}, publisher = {American Society of Civil Engineers}, address = {September 21{\textendash}23, 2015, Vienna, AustriaReston, VA}, abstract = {

The logarithmic deviatoric creep of cement paste is a technical and scientific challenge. Transition State Theory (TST) indicates that some nanoscale mechanisms of shear deformation, associated with a specific kind of strain hardening, can explain the type of deviatoric creep observed experimentally in mature cement pastes. To test this possible explanation, we simulate the shear deformations of a colloidal model of cement hydrates at the nanoscale. Results from quasi-static simulations indicate a strain hardening analogous to that postulated by the TST approach. Additional results from oscillatory shear (fatigue) simulations show an increase of deformation with number of loading cycles that is consistent with the observed creep. These findings indicate that nanoscale simulations can improve our current understanding of the mechanisms underlying creep, with potential to go beyond the logarithmic creep and explore the onset of failure during tertiary creep.

}, doi = {10.1061/978078447934610.1061/9780784479346.068}, author = {Enrico Masoero and Mathieu Bauchy and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Sidney Yip}, editor = {Hellmich, Christian and Pichler, Bernhard and Kollegger, Johann} } @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.

Image of FIG. 1.
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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.

Figure 1

}, 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 {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} }