مدل سازی تشکیل یخ در جامدات متخلخل با توجه به شرح آسیب یخ

The freezing and thawing of liquid in porous media in connection with the question concerning the frost durability of solid materials is an important subject for discussion in civil engineering. Each construction or body which is in contact with liquid and frozen water is criticized by its resistance to the environment. The durability concerning frost attacks of a building material is affected by its porosity and the pore size distribution. The ice formation is a phenomenon of coupled heat and mass transport in freezing porous media, and is primarily caused by the expansion of ice in connection with hydraulic pressure. The volume increases due to the freezing front inside the porous solid. Taking into account the aforementioned effects in porous materials, a simplified macroscopic model within the framework of the Theory of Porous Media (TPM) for the numerical simulation of initial and boundary value problems of freezing and thawing processes of super saturated porous solids will be presented. The phase change between the ice and the liquid phase is modeled by different real densities of the phases.

Transport phenomena with and without phase transition in porous media are encountered, e.g., in civil engineering. Examples include the drying of porous solids, the freezing of soils, the geothermal application, etc. One of the main issues in material science is the frost resistance of solid materials. Each construction is criticized by its resistance to the environment. Therefore, frost attack is divided into two main types: (i) internal frost attack caused by the freezing of a liquid phase inside the material; (ii) surface scaling, normally caused by the freezing of weak salt solutions at the surface of the solid matrix. The two types of attack depend on the same basic mechanism, namely, that too much liquid is present in the pores. It has been shown that after a high number of freeze-thaw cycles frost damage is not a fatigue mechanism, see [13]. In the present paper a coupled heat and moisture flux in a porous solid matrix will be simulated by using the Theory of Porous Media (TPM). Therefore, a representative unit cell of the solid matrix will be considered. The “representative unit cell” is a material volume that is big enough to represent the material in bulk, but not much bigger than that, i.e., it shall be big enough to contain the same porosity and the same pore size distribution as the material in bulk. The exchange between the ice and liquid phase is modeled by the different real densities of the phases. During the phase change a mass transport from liquid to ice and vice versa takes place.

In this article, a ternary macroscopic model has been presented with respect to the simulation of freeze-thaw cycles in saturated porous media. Within the framework of this model the thermal dilatation of the solid matrix, the expansion of ice during freezing and the hydraulic pressure on the surrounding surfaces can be described.In view of semi-saturated porous media, further studies would be made to extend the approach by a significant microstructure.A semi-saturated matrix is macroscopically filled by gas and liquid.Fur thermore, viscous flow from the microstructure to the ice lenses might take place, i.e., frost-shrinkage can be observed in real structures.