Computational modelling of coupled water and salt transport in porous materials using diffusion-advection model

The diffusion-advection model taking into account not only the influence of water flow on salt transport but also the effect of bonded salt on pore walls is used for the description of coupled moisture and chloride transport in lime plaster. Moisture and chloride concentration profiles are determined experimentally and subjected to inverse analysis making possible to identify the moisture diffusivity as a function of moisture content and salt diffusion coefficient as a function of salt concentration. The results of experimental and computational investigations show that the moisture diffusivity of lime mortar increases fast with increase in moisture content, its maximum value being about 10−6 m2/s, which indicates very fast moisture transport in that material. The chloride diffusion coefficient of lime mortar is found very high, in the range 10−6-10−5 m2/s. This can be explained by the action of additional driving forces, namely the surface diffusion and osmosis, which accelerate the chloride transport. The obtained results should find use in computational modelling of the damage of lime plasters in historical buildings caused by combined action of water and salts.