(205d) A Population Balance Based Rheological Model for Fresh Cement Paste

Juan Pablo Gallo-Molina^1,2, Ingmar Nopens¹ and Karel Lesage²

¹BIOMATH, Department of Mathematical Modelling, Statistics and Bio-informatics, Ghent University, Ghent, Belgium.

²Magnel Laboratory for Concrete Research, Department of Structural Engineering, Ghent University, Ghent, Belgium.

Due to the fact that it is the largest material volume used in the world, its critical importance for infrastructure development and the environmental issues associated with the large masses involved, concrete has been attracting increasing research attention since the last decades [1]. For hardened concrete, civil engineers already possess a series of engineering tools that allow them to satisfactorily predict properties of interest (e.g. deformation, stress, etc.) as a function of material characteristics. However, when this material is encountered in a fluid state, the picture is completely different: only some empirical tests are capable of relating some material variables (e.g. concrete composition) with relevant properties (i.e. flow speed, flow spread, etc.). Although this practice is longstanding, the increasing complexity of concrete mixtures - introduced by the growing use of mineral additions, chemical admixtures and non-traditional cement chemistries - has invoked the need for developing mechanistic models with predictive capabilities.

The size range of the particles found in a typical concrete can encompass several orders of magnitude, which implies that numerous kinds of interactions and phenomena are involved. For this reason, a bottom-up modelling approach is often aimed for in the modelling of fresh concrete [2]. Consequently, adequately modelling pure cement pastes is deemed as a first step towards the mentioned goal. These pastes are, in turn, particulate systems consisting of a mixture of mineral particles suspended in an aqueous medium. As the particle size distribution and its evolution in time due to aggregation significantly impact rheological properties, Population Balance Models (PBM) are a valuable tool in the developing of models capable of predicting the rheology of fresh cement paste.

As an initial approach, in this work we present a population balance equation based rheological model [3]. This model is implemented for cement pastes under simple torsional flow and it is applied to a parallel plate rheometer geometry. In order to consider the effect of vertical position on shear rate, we introduce one spatial dimension in the model. The objective of this modelling effort is to better understand both rheological and particle size distribution measurements of these systems and to further develop the understanding of complex rheological behavior resulting from aggregate interactions. This work seeks to contribute in the developing of a suitable model capable of correlating cement properties and the rheological behavior of its paste.

References

[1] R. J. Flatt, N. Roussel, and C. R. Cheeseman, “Concrete: An eco material that needs to be improved,” J. Eur. Ceram. Soc., vol. 32, no. 11, pp. 2787–2798, 2012.

[2] N. Roussel, A. Lemaître, R. J. Flatt, and P. Coussot, “Steady state flow of cement suspensions: A micromechanical state of the art,” Cem. Concr. Res., vol. 40, no. 1, pp. 77–84, 2010.

[3] M. Mohtaschemi, A. Puisto, X. Illa, and M. J. Alava, “Rheology dynamics of aggregating colloidal suspensions,” Soft Matter, vol. 10, no. 17, p. 2971, 2014.