Diffusive and Convective Salt Transport in Building Materials Depending on Pore Solution Concentration and Moisture Content

Abstract

For the examination of transport processes of salts in building materials there are different driving forces that are taken into consideration. One of them is the salt concentration gradient in the pore solution. This concentration gradient results into diffusive and convective salt transport. To separate between those two processes and to determine the characteristic conditions invoking them investigations are done into the dependence of those processes on different types of building materials, different moisture saturations, and different concentrations of the pore solution. Main influence on convection has the pore radius, the connectivity of the pore system, the permeability, and the concentration of the pore solution. In case of the Bucher sandstone convection already occurs at 0.5 M Na₂SO₄-solution and 30% moisture saturation. Although the decrease of moisture saturation only has a minor influence on the occurrence convection in the Bucher sandstone. The investigations demonstrate the high potential of convection occurring in overall transport processes in building materials (especially in sandstones) and in diffusion experiments.