@article {97, title = {Docking Sr-90 radionuclide in cement: An atomistic modeling study}, journal = {Physics and Chemistry of the Earth}, volume = {70-71}, year = {2014}, month = {2014}, pages = {39-44}, type = {Article}, abstract = {

Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium silicate hydrate (C-S-H) and its crystalline analog, the 9 angstrom-tobermorite. C-S-H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C-S-H and 9 angstrom-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium. (C) 2013 Elsevier Ltd. All rights reserved.

}, keywords = {Cement, mechanical properties, Molecular simulation, Nuclear waste storage}, issn = {1474-7065}, doi = {10.1016/j.pce.2013.11.007}, author = {Youssef, Mostafa and Roland Jean-Marc Pellenq and Bilge Yildiz} } @article {94, title = {Comparison of computational water models for simulation of calcium-silicate-hydrate}, journal = {Computational Materials Science}, volume = {53}, year = {2012}, month = {Feb-2012}, pages = {234-240}, type = {Article}, abstract = {

Calcium silicate hydrate, or C-S-H, is the chief hydration product of Portland cement. The structure of the C-S-H phase within cement has been proposed and developed via molecular simulations. In such simulations, empirical interatomic potentials for water molecules within C-S-H are adopted to govern the position and relative motion of this key constituent. Initial simulations and force fields of C-S-H have assumed the simplest molecular model of H2O termed {\textquoteleft}{\textquoteleft}single point charge{\&$\#$39;\&$\#$39;} or SPC, but this choice has not been validated by comparison with other computational models of water that confer additional bond flexibility or charge distribution. To enable efficiently computational modeling of C-S-H and to explore the role that H2O plays in maintaining C-S-H structure and properties, the choice of an efficient and accurate water model is critical. Here, we consider five distinct, classical atomistic water models (SPC, TIP3P, TIP4P, TIP4P05, and TIP5P) to determine the effects of these computational simplifications on C-S-H properties. Quantitative comparison of all five water models shows that the appropriate water model depends on the C-S-H characteristics of interest. Among these models, both SPC and TIP5P models successfully predict key properties of the structure and elastic constants of C-S-H, as well as the dynamics of water molecules within C-S-H. (C) 2011 Elsevier B. V. All rights reserved.

Schematics of (a) five water models and (b) calcium{\textendash}silicate{\textendash}hydrate (C{\textendash}S{\textendash}H) ...

Comparison of C{\textendash}S{\textendash}H structural characteristics. (a) Unit cell dimensions, where ...

Comparison of C{\textendash}S{\textendash}H dynamic characteristics. (a) Infrared absorption spectrum ...

Comparison of C{\textendash}S{\textendash}H elastic properties. (a) Elastic constants and the relative ...

}, keywords = {C-S-H, Cement, Simulation, Water model}, issn = {0927-0256}, doi = {10.1016/j.commatsci.2011.08.024}, author = {Qing Ji and Roland Jean-Marc Pellenq and Krystyn J. Van Vliet} }