[M-IS09] Weathering and conservation of cultural heritage and geosites

[MIS09-05] Numerical analysis of heat, moisture, and salt transfer and deformation in porous materials under atmospheric conditions

*Masaru Abuku¹, Koichi Ishii² (1.Kindai University, 2.Research Center of Computational Mechanics, Inc.)

Keywords:Poromechanics, Finite Element Method, Salt weathering, Salt crystallization, Moisture transfer

Salt weathering of porous materials such as stone, brick, etc. is a phenomenon composed of heat, moisture and salt transfer in porous materials, crystallization and phase change of salt, deformation of porous materials, and so on. Thus far, several numerical models have been developed by researchers for studying such phenomena, in addition to the efforts of measuring physical and chemical data of porous materials, ions, and salt crystals. When a numerical simulation obtained using one of these models is applied to different real-world objects, such as a building wall, stone cultural property, or masonry systems, one has to often deal with complex geometries comprising various materials and boundary conditions. To render such an application of the salt weathering prediction feasible, we have developed a generic finite element method code, namely: PMSolver. This code analyzes non-steady heat, moisture, and salt transfer in porous materials, while examining the deformation of materials from the temperature, salt solution content, and salt crystal content. Further, this code is equipped with a GUI that works on a pre- and postprocessor Femap, and incorporates the input data of geometries, material properties, and initial and boundary conditions into the solver. Furthermore, the transport, phase change, and crystallization/dissolution of a mixture, which is obtained by dissolving two different salts in water, are elucidated in this model while maintaining electrical neutrality. The code includes the data on sodium chloride and sodium sulfate. During the mechanical analysis, the pore liquid pressure, crystallization pressure, and thermal stress are considered, in addition to the stress obtained from a static mechanical analysis; this is aimed at determining the strain field at each time step. The code can also consider different types of atmospheric boundary conditions such as temporally and spatially distributed wind-driven rain with ions, sea spray, atmospheric salt deposition, and seepage water. When the seepage flow is analyzed, two iteration steps are considered.