A Simplified model for salt diffusion and crystallization in historic masonry

To conserve historic masonry structures there is an increasing need to understand the deterioration processes in a unified framework, which involve not only mechanical but also environmental causes. Among these salt rising and crystallization are recognized as among the major factors of degradation of porous materials like masonry. The mechanical behaviour of the masonry, in terms of the more meaningful phenomena, i.e. damage and friction toughness, has been extensively studied in literature (see for example [1]). On the other hand, studies have been devoted also to the chemical processes of masonry degradation due to salt crystallization at microscale (see for example [2],[3]). There the two perspectives are rarely combined in the literature. A study of the deterioration of masonry in a unified framework which takes into account for both the mechanical and the chemical aspects of the problem and their coupling requires a look at the chemical deterioration process on the same scale (macroscale) as the mechanical process. There are few contributions in this direction specifically for masonry structures [4],[5]. The aim of this work is to present a simple macroscale model able to describe the diffusion and the crystallization of salt inside a masonry. The governing equations of the model are: a diffusive equation for the humidity, a diffusive equation for the salt and an equation which takes the salt crystallization into account. The equations are fully coupled, non linear and time dependent. Some numerical tests are performed to show the effectiveness of the proposed model.