A 3D model for salt diffusion and crystallization in masonry structures

Damp rising and salt crystallization are important factors affecting degradation of porous materials like masonry. As the water evaporates, the salt concentration of pore solution increases until salt precipitates leading to efflorescence or sub fluorescence with possible severe damage. Here, a simple 3D model for salt diffusion and crystallization in masonry structures is proposed. The independent variables chosen to describe all the process are: the pore humidity, the concentration of dissolved salt and the temperature. These independent variables are supplemented by two internal variables: the water content and the concentration of crystallized salt. The governing equations of the model are: the moisture balance equation expressed in function of the humidity, the conservation equation for the total stored energy, the balance equation for the dissolved salt and a kinetic expression for the salt crystallization law. The model parameters have been calibrated through an extended experimental campaign conducted within the SMooHs EU project. After the calibration, the model has been employed for the long term simulation of some laboratory tests involving masonry panels subjected to various environmental conditions. A good agreement between the model predictions and the experimental evidences has been obtained, so validating the good predictive capabilities of the proposed model.