A potential C-S-H nucleation mechanism: atomistic simulations of the portlandite to C-S-H transformation
Méndez Aretxabaleta, Xabier
López Zorrilla, Jon
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Cement and Concrete Research 162 : (2022) // Article ID 106965
The nucleation of the C-S-H gel is a complex process, key to controlling the hydration kinetics and microstructure development of cement. In this paper, a mechanism for the crystallization step during the C-S-H gel non-classical nucleation is proposed and explored by atomistic simulation methods. In the proposed mechanism portlandite precursor monolayers undergo a chemically induced transformation by condensation of silicate dimmers, forming C-S-H monolayers. We studied by DFT and nudged elastic band the structural transformation from bulk portlandite to a tobermorite-like calcium hydroxide polymorph, and the silicate condensation reaction at portlandite surface. Then, both processes are studied together, investigating the topochemical transformation from a portlandite monolayer to a C-S-H monolayer at room conditions using targeted molecular dynamics and umbrella sampling methods. Comparing the free energy of the process with thermodynamic data we conclude that the proposed mechanism is a potential path for C-S-H formation.