@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} } @proceedings {99, title = {Modelling cement at fundamental scales: From atoms to engineering strength and durability}, journal = {Euro-C Conference}, volume = {COMPUTATIONAL MODELLING OF CONCRETE STRUCTURES, VOL 1}, year = {2014}, month = {2014}, pages = {139-148}, publisher = {CRC Press-Taylor \& Francis Group}, address = {MAR 24-27, 2014, St Anton am Alberg, AUSTRIA}, abstract = {

The mechanics and rheology of cement pastes are largely determined by the Calcium-Silicate-Hydrate (C-S-H) gel, which is normally the main binding phase. The C-S-H gel is an amorphous material with a nanoscale pore network. Here we consider a model structure of the gel, where a continuous molecular model of non-porous C-S-H is combined with a colloidal model that incorporates the porosity of the gel. Numerical simulations predict mechanical properties and microscopic processes associated with yielding under shear. The proposed model can now be used to extract further properties and to contribute to a broader effort aimed at describing and engineering the multi-scale structure and mechanical behaviour of the cement paste. We finally discuss the opportunities offered by our model with respect to the scientific and technological challenges of modelling and controlling ageing and creep over long time scales.

}, isbn = {978-1-138-02641-4; 978-1-315-76203-6}, doi = {10.1201/b16645-16}, author = {Enrico Masoero and Hamlin M. Jennings and Franz-Josef Ulm and Emanuela Del Gado and Hegoi Manzano and Roland Jean-Marc Pellenq and Sidney Yip}, editor = {Bicanic, N and Mang, H and Meschke, G and DeBorst, R} } @conference {36, title = {Water Isotherms, Shrinkage and Creep of Cement Paste: Hypotheses, Models and Experiments}, booktitle = {Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete: A Tribute to Zdenek P. Ba{\.z}ant}, year = {2013}, month = {Sep-25-2013}, publisher = {ASCE Publications}, organization = {ASCE Publications}, abstract = {

Cement paste has a complex mesoscale structure, and small changes in its pore network potentially cause large variation in measurements such as the water isotherm (also nitrogen). We deconvolute the water isotherm with the help of advanced computational techniques, hypotheses, and a re-examination of published data. The pore system is divided into four different categories, each containing water with its own physical properties. By viewing the highly interdependent roles of water in each of the pore categories as a system, new insights are gained regarding possible mechanisms that control drying, shrinkage, and creep, and experimental strategies for verification.

}, doi = {10.1061/9780784413111.015}, author = {Hamlin M. Jennings and Enrico Masoero and Pinson, Matthew B and Strekalova, Elena G and Patrick A Bonnaud and Hegoi Manzano and Qing Ji and Jeffrey J. Thomas and Roland Jean-Marc Pellenq and Franz-Josef Ulm and others} } @article {57, title = {Confined water dissociation in microporous defective silicates: Mechanism, dipole distribution, and impact on substrate properties}, journal = {Journal of the American Chemical Society}, volume = {134}, year = {2012}, month = {Feb-01-2012}, pages = {2208{\textendash}2215}, abstract = {
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Interest in microporous materials has risen in recent years, as they offer a confined environment that is optimal to enhance chemical reactions. Calcium silicate hydrate (C-S-H) gel, the main component of cement, presents a layered structure with sub-nanometer-size disordered pores filled with water and cations. The size of the pores and the hydrophilicity of the environment make C-S-H gel an excellent system to study the possibility of confined water reactions. To investigate it, we have performed molecular dynamics simulations using the ReaxFF force field. The results show that water does dissociate to form hydroxyl groups. We have analyzed the water dissociation mechanism, as well as the changes in the structure and water affinity of the C-S-H matrix and water polarization, comparing the results with the behavior of water in a defective zeolite. Finally, we establish a relationship between water dissociation in C-S-H gel and the increase of hardness due to a transformation from a two- to a three-dimensional structure.

}, doi = {10.1021/ja209152n}, author = {Hegoi Manzano and Moeini, Sina and Marinelli, Francis and Adri CT Van Duin and Franz-Josef Ulm and Roland Jean-Marc Pellenq} } @article {51, title = {Hydration of calcium oxide surface predicted by reactive force field molecular dynamics}, journal = {Langmuir}, volume = {28}, year = {2012}, month = {Mar-06-2012}, pages = {4187{\textendash}4197}, abstract = {
Abstract Image

In this work, we present the parametrization of Ca\–O/H interactions within the reactive force field ReaxFF, and its application to study the hydration of calcium oxide surface. The force field has been fitted using density functional theory calculations on gas phase calcium\–water clusters, calcium oxide bulk and surface properties, calcium hydroxide, bcc and fcc Ca, and proton transfer reactions in the presence of calcium. Then, the reactive force field has been used to study the hydration of the calcium oxide {001} surface with different water contents. Calcium oxide is used as a catalyzer in many applications such as CO2 sequestration and biodiesel production, and the degree of surface hydroxylation is a key factor in its catalytic performance. The results show that the water dissociates very fast on CaO {001} bare surfaces without any defect or vacancy. The surface structure is maintained up to a certain amount of water, after which the surface undergoes a structural rearrangement, becoming a disordered calcium hydroxyl layer. This transformation is the most probable reason for the CaO catalytic activity decrease.

}, doi = {10.1021/la204338m}, author = {Hegoi Manzano and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Markus J Buehler and Adri CT Van Duin} } @article {55, title = {Understanding and Controlling the Reactivity of the Calcium Silicate phases from First Principles}, journal = {Chemistry of Materials}, volume = {24}, year = {2012}, month = {Apr-10-2012}, pages = {1262{\textendash}1267}, abstract = {
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First principles calculations are employed to provide a fundamental understanding of the relationship between the reactivity of synthetic calcium silicate phases and their electronic structure. Our aim is to shed light on the wide range of hydration kinetics observed in different phases of calcium silicate. For example, while the dicalcium silicate (Ca2SiO4) phase slowly reacts with water, the tricalcium silicate (Ca3SiO5) shows much faster hydration kinetics. We show that the high reactivity of Ca3SiO5 is mainly related to the reactive sites around its more ionic oxygen atoms. Ca2SiO4 does not contain these types of oxygen atoms, although experiments suggest that impurities may play a role in changing the reactivity of these materials. We analyze the electronic structure of a wide range of possible substitutions in both Ca3SiO5 and Ca2SiO4 and show that while the influence of different types of impurities on structural properties is similar, their effect on reactivity is very different. Our calculations suggest that the variation of electronic structure is mainly related to the formation of new hybridized orbitals and the charge exchange between the impurity atoms and the bulk material. The charge localization upon introducing impurities is quantified to predict candidate substitutions that could increase the reactivity of Ca2SiO4, which would broaden the applicability of this lower temperature and thus less costly and energetically less demanding phase.

}, doi = {10.1021/cm203127m}, author = {Engin Durgun and Hegoi Manzano and Roland Jean-Marc Pellenq and Jeffrey C Grossman} } @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 = {
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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} }