Journal
CEMENT AND CONCRETE RESEARCH
Volume 162, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cemconres.2022.106965
Keywords
Calcium Silicate Hydrate; Portlandite; Atomistic simulation; Nucleation; Free energy of reaction
Funding
- Departamento de Educacion, Politica Lingueistica y Cultura del Gobierno Vasco'' [IT1458-22]
- Ministerio de Ciencia e Innovacion [PID2019-106644GB-I00]
- University of the Basque Country
- UPV/EHU [PIF17/118]
- Basque Country Government [PRE_2019_1_0025]
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This paper proposes and explores a mechanism for the crystallization step during C-S-H gel non-classical nucleation through atomistic simulation methods. The study suggests that the condensation reaction between silicate dimmers and portlandite precursor monolayers is a potential path for C-S-H formation. By comparing the free energy of the process with thermodynamic data, the proposed mechanism is found to be a key process for C-S-H gel formation.
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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