Atomistic Modelling on Cementitious Systems

Date This project started on 01 January 2009 and ended on 01 May 2013

Status This project is Finished

Ecole Polytechnique Fédérale de Lausanne, CH

Cementitious materials are complex systems with many interfacial interactions over many length scales (dissolution, nucleation, crystallization, polymer adsorption, aggregation). The significant role of the different types of interfaces, which ultimately control the properties of cements and concretes from the early stages to the final microstructures and macroscopic properties, demands a deep knowledge of the roles of the interfaces at an atomistic level.

The composition of cementitious materials is complex with several different mineral phases and the nature of the solid-liquid interfaces where dissolution of the anhydrous phase, adsorption of cement admixtures and growth of new crystalline phases take place are very difficult to access experimentally. The use of atomistic modelling has made great progress over recent years in many different fields such as properties of interfaces, crystal growth and self-assembly[1-3].

The primary objective of this project is the study of different phases of cement, namely portlandite and tobermorite as a C-S-H model structure, and their interfaces with the pore solution and possible defects. The length scale of these structures are at the limit of ab initio methods, therefore the method of choice will be mainly classical molecular dynamics which have been shown to be able to model diffusive processes in certain cases[4].

The second part of the project is to study possible growth mechanisms of the above phases and their exchange with their chemical environment. As the length scale of these processes exceeds the time limits of simple classical molecular dynamics (ns) the use of enhanced sampling algorithms, such as metadynamics, and mesoscale methods, such as kinetic Monte Carlo is envisioned for the future.

To start approaching the macroscopic behaviour of cementitious materials, the basic fundamental data from the atomistic approaches can then be supplied to other modelling groups using continuum approaches such as the finite element method (FEM) to give macroscopic property evaluation and prediction.

1 Allen J.P., Gren W., Molinari M., Arrouvel C., Maglia F., Parker S.C.
Atomistic modelling of adsorption and segregation at inorganic solid interfaces Molecular Simulation 35 584-608, (2009)
2 Spagnoli D., Banfield J.F. and Parker S.C.
Free energy change of aggregation of nanoparticles
Journal of Physical Chemistry C 78, 14731-14736, (2008)
3 Sayle, D.C., Doig, J.A., Maicaneanu S.A., Watson G.W.
Atomistic structure of oxide nanoparticles supported on an oxide substrate
Phys. Rev. B 65, 245414, (2002)
4 Aschauer U., Bowen P., Parker S.C.
Oxygen vacancy diffusion in alumina: New atomistic simulation methods applied to an old problem
Acta Materialia, 57(16), (2009), 4765-72

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