A potential C-S-H nucleation mechanism: atomistic simulations of the portlandite to C-S-H transformation

XM Aretxabaleta and J Lopez-Zorrilla and C Labbez and I Etxebarria and H Manzano, CEMENT AND CONCRETE RESEARCH, 162, 106965 (2022).

DOI: 10.1016/j.cemconres.2022.106965

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.

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