Abstract

The purpose of this work is to achieve a better understanding of the relationship between damage, failure and the transport properties of cementitious materials. Many authors have looked for predictive models of porous media permeability. Usually, analyses are restricted to intrinsic permeability of the material and the evolution of the apparent permeability, with respect to the pressure gradient and to the nature of the fluid considered are left aside. This paper aims at presenting a new model capable to provide estimates of the apparent permeability directly from the pore size distribution (PSD) and from the properties of the fluid to be considered. The intrinsic permeability and the evolution of the apparent permeability with mean pressure are provided by combining Darcy’s law which represents the flow in the porous media at the macroscale and a combination of Poiseuille’s and Knudsen’s laws which represent respectively viscous flow and the diffusion flow at the microscale. In order to achieve a porous network in the material, which is consistent with a mercury intrusion technique, random generation of pores is implemented. The technique yields a hierarchical porous network, which mimics the porous space measured experimentally, without the need for entering neither the tortuosity nor the exact topological information about the pore shapes. Comparisons with experimental data acquired on mortar specimens show that the model is able to reproduce the intrinsic permeability and its evolution when the material is subjected to mechanical damage, provided the pore size distributions are available. For a given pore size distribution, the evolution of the apparent permeability is also provided and test data with several types of gases compare quite well with the model.

1. INTRODUCTION

The purpose of this work is to achieve a better understanding of the relationship between damage, failure and the transport properties of cementitious materials. This is typically of utmost importance in the long-term assessment of tightness of vessels and containment facilities.

Many authors have looked for predictive models of porous media permeability. Pioneering work by Kozeny [1] related the permeability to the porosity, the tortuosity and an average pore size and later on Katz & Thompson [2] predicted the permeability from the electrical conductivity of the porous material through a critical pores radius. There are also several studies in which the pore size distribution (PSD) was modeled, e.g. with a bimodal [3] or multimodal distribution [4], and then entered into some capillary bundle model. Recently, models for the calculation of the intrinsic permeability derived directly from the experimental PSD, without any idealization have been also discussed [5].

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