Salt transport and crystallization in non-isothermal, partially saturated porous materials considering ions interaction model

Crystallizing salt changes the inner pore structure of materials. MIP tests of cement mortar and brick saturated with NaCl, CaCl2, Na2SO4 solutions were performed. The changes of porosity, pore size distribution and pore shape (ink-bottle type pores) were investigated by performing two intrusion–extrusion cycles. The crystallization pressure bursts the mezopores. During salt crystallization the additional heat is released, which must be considered in energy conservation equation of multiphase domain. The model of coupled heat, moisture and salt transport considering the salt crystallization is presented. The key factor while modeling the salt crystallization is the kinetics of salt phase change, which is approximated in the presented research by means of Freundlich non-equilibrium isotherms. In order to calculate the solution supersaturation ratio the short and long range ions interaction was taken into account applying the Pitzer model. The mathematical model was solved using FEM and FDM and some practical examples were calculated and discussed. It was proved that the higher rate order appears in the kinetic law the higher crystallization pressure might be generated. The approximation procedures were tested numerically.