A realistic molecular model of cement hydrates

By R. Pellenq, A. Kushima, R. Shahsavari, K. V. Van Vliet, Markus J. Buehler, Sidney Yip, Franz-Josef Ulm. Proceedings of the National Academy of Sciences of the United States of America, 2009

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Despite decades of studies of calcium-silicate-hydrate (C-S-H), the structurally complex binder phase of concrete, the interplay between chemical composition and density remains essentially unexplored. Together these characteristics of C-S-H define and modulate the physical and mechanical properties of this “liquid stone” gel phase. With the recent determination of the calcium/silicon (C/S = 1.7) ratio and the density of the C-S-H particle (2.6 g/cm3) by neutron scattering measurements, there is new urgency to the challenge of explaining these essential properties. Here we propose a molecular model of C-S-H based on a bottom-up atomistic simulation approach that considers only the chemical specificity of the system as the overriding constraint. By allowing for short silica chains distributed as monomers, dimers, and pentamers, this C-S-H archetype of a molecular description of interacting CaO, SiO2, and H2O units provides not only realistic values of the C/S ratio and the density computed by grand canonical Monte Carlo simulation of water adsorption at 300 K. The model, with a chemical composition of (CaO)1.65(SiO2)(H2O)1.75, also predicts other essential structural features and fundamental physical properties amenable to experimental validation, which suggest that the C-S-H gel structure includes both glass-like short-range order and crystalline features of the mineral tobermorite. Additionally, we probe the mechanical stiffness, strength, and hydrolytic shear response of our molecular model, as compared to experimentally measured properties of C-S-H. The latter results illustrate the prospect of treating cement on equal footing with metals and ceramics in the current application of mechanism-based models and multiscale simulations to study inelastic deformation and cracking.

Subfields: Civil and Structural Engineering, Environmental Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/49522d27cd21215e25a20eebd5640cbeb0cf615f

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Citations in the corpus

Fracture toughness of calcium-silicate-hydrate from molecular dynamics simulations (2014, background): “Despite the prevalence of concrete in the built environment, the molecular structure of C–S–H has just recently been proposed [7–10,4], which makes it possible to investigate its mechanical properties at the atomic scale.”
Nanogranular packing of C–S–H at substochiometric conditions (2010, neutral): “In the backanalysis we fixed the value ofms=65 GPa, on the basis of atomistic simulation results [47,48].”
Nano-chemo-mechanical signature of conventional oil-well cement systems: Effects of elevated temperature and curing time (2015, background): “It is interesting to note that both of the crystalline phasesmentioned above have higher average stiffness values than C–S– H gel≈ 63 GPa [77,78], namely,≈81 GPa for α-C2SH and≈71 GPa for hillebrandite [79].”
cemff: A force field database for cementitious materials including validations, applications and opportunities (2017, methodology): “The rigorous validation of CSH-FF has been achieved for two cases (the 11 Å tobermorite, and the 14 Å tobermorite) where the 11 Å to bermorite has been used for the development of CSH-FF parameters, but the 14 Å tobermorite has not [52].”
Nano-engineering of construction materials using molecular dynamics simulations: Prospects and challenges (2018, background): “Based on those pilot works in modeling different constituents within C-S-H, the breakthrough of a full atomistic model for CS-H has been reported [36].”