Browsing by Author "Ayuela, A."
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Item Aluminum incorporation to dreierketten silicate chains(2009-03-05) Manzano, H.; Dolado, J. S.; Ayuela, A.; Tecnalia Research & InnovationThis work explores, from a theoretical viewpoint, the aluminum incorporation into silicate chains with dreierketten conformation relevant in the cementitious calcium-silicate-hydrate (C-S-H) gel and in other minerals, such as wollastonite and hillebrandite. To this end, we have investigated by means of ab initio calculations both the stability and the formation of aluminosilicate chains. Our results show that only certain aluminosilicate chains are stable, namely, those whose tetrahedra length m obey the m ) 3n - 1 rule with n ) 1, 2, 3,..., in agreement with experiments. Moreover, our detailed analyses explain why Al ions prefer the bridging sites and introduce new insights on the growth process.Item Do cement nanotubes exist?(2012-06-26) Manzano, H.; Enyashin, A. N.; Dolado, J. S.; Ayuela, A.; Frenzel, J.; Seifert, G.; Tecnalia Research & InnovationUsing atomistic simulations, this work indicates that cement nanotubes can exist. The chemically compatible nanotubes are constructed from the two main minerals in ordinary Portland cement pastes, namely calcium hydroxide and a calcium silicate hydrate called tobermorite. These results show that such nanotubes are stable and have outstanding mechanical properties, unique characteristics that make them ideally suitable for nanoscale reinforcements of cements.Item Elastic properties of the main species present in Portland cement pastes(2009-03) Manzano, H.; Dolado, J. S.; Ayuela, A.; Tecnalia Research & InnovationThe elastic properties of the most important phases present in cement pastes have been studied by force field atomistic methods. Calculations reproduce the mechanical properties of crystalline species alite, belite and portlandite fairly well. The elastic properties of amorphous calcium-silicate-hydrate (C-S-H) gel are also explained in terms of the commonly used structural models 1.4 nm tobermorite and jennite, once the intrinsic porosity and the silicate chain length are concurrently considered through the appropriate micromechanical models. The findings conclude that bringing the atomic structure into contact with the mechanical properties of C-S-H gel may modify the actual view of the gel.Item Ettringite strengthening at high pressures induced by the densification of the hydrogen bond network(2012-08-02) Manzano, H.; Ayuela, A.; Telesca, A.; Monteiro, P. J.M.; Dolado, J. S.; Tecnalia Research & InnovationEttringite is a rare mineral with high-water content, more than half of its weight, and a relevant secondary product in Portland cement. Using density functional theory, we simulate the crystal structure and properties of ettringite under pressure. Our calculations predict a change in slope for all the lattice parameters versus pressure at about 2.5 GPa. Above such pressure, the elastic properties show a drastic increase of nearly 80% in the bulk modulus. This finding is explained in terms of a concurrent amorphization and densification of the hydrogen bond network. At low pressures, ettringite can be compressed substantially without significant repulsion in the hydrogen bond network. At high pressures, the hydrogen bonds become stiff, and their contribution to the total repulsion is then important. These changes are also supported by the evolution on the electronic density of ettringite with pressure.Item Mechanical properties of crystalline calcium-silicate-hydrates: Comparison with cementitious C-S-H gels(2007-06) Manzano, H.; Dolado, J. S.; Guerrero, A.; Ayuela, A.; Tecnalia Research & InnovationThis work explores from a theoretical viewpoint the mechanical properties of the most important hydration product present in cementitious environments, the so called C-S-H (calcium-silicate-hydrate) gel. The dependence of the bulk (K), shear (G) and Young's (E) modulus for the C-S-H crystals respect to its composition and the length of its silicate chains is analysed by lattice dynamic simulations with parameterised two-body and three-body potentials. Our simulations reveal that the mechanical properties of C-S-H crystals show a strong dependence on their composition. Nevertheless our calculated numbers systematically overestimate the experimental values for C-S-H gels. Only when the finite length of the silicate chains is taken into account this discrepancy disappears.Item Nanoscale texture development of C-S-H gel: A computational model for nucleation and growth(2013-12-02) González-Teresa, R.; Dolado, J. S.; Ayuela, A.; Gimel, Jean Christophe; Tecnalia Research & InnovationThe development of C-S-H (Calcium-Silicate-Hydrate) gels during cement hydration is often investigated by nucleation and growth models which fit reasonably well with the calorimetric measurements but predict hydration degrees which grossly exceed the experimental values. Here, a computational model is presented which explicitly considers the intrinsic nanoparticulate nature of C-S-H gel. Based on a nucleation and growth algorithm the model reproduces the experimental calorimetric and hydration degree measurements without invoking to any diffusion mechanism. The model also suggests that the peak in the calorimetric curves can be ascribed to the percolation point of the hydrates themselves within the interstitial pore volume.Item On the formation of cementitious C-S-H nanoparticles(2007-04) Manzano, H.; Ayuela, A.; Dolado, J. S.; Tecnalia Research & InnovationThis work explores from a theoretical viewpoint the underlying growth mechanisms which govern the formation of the most important hydration product present in cementitious environments, the so called C-S-H (calcium-silicate- hydrate) gel. Aiming at identifying the basic building blocks which make up the cementitious C-S-H gel, we have performed ab-initio calculations at the Hartree Fock (HF) level. Two different growth mechanisms have been identified depending on the amount of Si and Ca ions, which naturally lead to the appearance of tobermorite-like and jennite-like nano-crystals.Item Silicate chain formation in the nanostructure of cement-based materials(2007) Ayuela, A.; Dolado, J. S.; Campillo, I.; De Miguel, Y. R.; Erklzia, E.; Sánchez-Portal, D.; Rubio, A.; Porro, A.; Echenique, P. M.; Tecnalia Research & Innovation; Tecnología; ECOEFICIENCIA DE PRODUCTOS DE CONSTRUCCIÓNCement-based materials are ubiquitous in almost all built environment. In spite of this, little is known about the formation and the role played by the silicate chains always present in the cement nanostructure. By means of first principles simulations we provide compelling evidence on the pivotal role played by certain ionic species in the formation of the silicate chains inside the cementitious matrix. Moreover, we corroborate the experimental evidence which shows that the length of the most stable chains with m Si atoms follows a magic-number sequence: m=3n-1 with n=1,2,... Our results have been applied in the development of new higher performance cement-based materials by adding nanosilica.Item X-ray spectra and theoretical elastic properties of crystalline calcium silicate hydrates: Comparison with cement hydrated gels(2010) Manzano, H.; González-Teresa, R.; Dolado, J. S.; Ayuela, A.; Tecnalia Research & InnovationFor 22 crystalline Calcium Silicates Hydrates, we have calculated their structure and their elastic properties by atomistic force field methods as well as simulate their Xray diffraction patterns. From the computed Young moduli, it can be suggested that the key parameters to determine the elastic properties of crystalline Calcium Silicate Hydrates are densities and water content. We have compared these trends with those of cementitious C-S-H gel and synthetic C-S-H type I as a function of their C/S ratios and nominal water content. Our comparison show that the experimentally suggested values of density and Young moduli for C-S-H gel lie in the range of the calculated CSH crystals. However, we conclude that a detailed correspondence might require investigating structurally within CSH gels the role of water and especially of Ca and Si sites through their C/S ratio.Item Zr-metal adhesion on graphenic nanostructures(2008) Sanchez-Paisal, Y.; Sanchez-Portal, D.; Garmendia, N.; Muoz, R.; Obieta, I.; Arbiol, J.; Calvo-Barrio, L.; Ayuela, A.; Tecnalia Research & InnovationOur high resolution transmission electronic microscopy studies of multiwall carbon nanotubes show, after the growth of zirconia nanoparticles by a hydrothermal route, the presence of surface Zr, forming an atomically thin layer. Using first-principles calculations we investigate the nature of the Zr-C interaction, which is neither ionic nor covalent, and the optimal coverage for the Zr metal in a graphene flake. This preferred coverage is in agreement with that deduced from electron energy loss spectra experiments. We show also that the amount of charge transferred to the C layer saturates as the Zr coverage increases and the Zr-C bond becomes weaker.