Numerical Simulation of Porosity in Cements
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Numerical Simulation of Porosity in Cements Q. H. Do · S. Bishnoi · K. L. Scrivener
Received: 28 June 2012 / Accepted: 13 May 2013 / Published online: 24 May 2013 © Springer Science+Business Media Dordrecht 2013
Abstract The pores in cementitious materials, their sizes and connectivity have an important influence on the durability of concrete. Several microstructural models have been developed to simulate the three-dimensional pore network in cement pastes. In this article, microstructures with the µic model are compared with experimental results. It is seen that despite having a resolution for the capillary pores very close to reality, the experimentally observed breakthrough diameter from mercury intrusion is much lower than the values obtained by applying an algorithm of mercury intrusion to the simulated microstructure. The effect of some of the most important input parameters on the pore sizes in the simulated microstructure explored. The phenomenon which seems best able to explain this discrepancy is that C–S–H is not in fact a phase with a smooth surface as represented in microstructural models, but a phase which grows as needles into the pore space, leading to very small water-filled capillary pores from quite young ages. The results demonstrate it will be extremely challenging to represent the porosity of real microstructures in microstructural models on the scale of hundreds of microns necessary to study macroscopic transport. Keywords Modelling · Microstructure · Pore sizes · Mercury intrusion porosimetry · Cement hydration
1 Introduction The transport of fluids through the capillary pore network is known to control the durability of concrete. This network is formed during the hydration of cement, when unhydrated phases react with water to form hydrates which increase the solid volume, filling the originally Q. H. Do (B) · K. L. Scrivener Laboratoire des Matériaux de Construction, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland e-mail: [email protected] S. Bishnoi Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India
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water-filled space between the cement particles. This leads to a refinement in the capillary porosity and hence a reduction in the permeability of the material. Two main approaches have been developed to model the transport properties of hydrating cement pastes. In the first approach, transport is calculated by homogenising the microstructure using experimentally measured or calculated global values (e.g. Marchand et al. 2002). In the other approach, microstructural models are used to recreate the complex capillary pore network in cement pastes (Garboczi and Bentz 1991; Navi and Pignat 1996; Munch and Holzer 2008; Zhou et al. 2010). This article examines the ability of such microstructural models to accurately reproduce the capillary pore network of cementitious materials. Microstructural models numerically simulate microstructural development and generate three-dimensional images of the microstructure a
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