Salt diffusion in brick structures Part II The effect of temperature, concentration and salt

This is our second article concerning salt diffusion measurements in porous brick materials. In the first article a method for measuring the rate of diffusion of salt in ceramic material was presented and applied to the measurement of diffusivity of NaCl in different brick materials. In this work the same method was applied to other water-soluble salts commonly found in building materials. The binary diffusion coefficients were measured for KCl, NaNO3, CaCl2, Na2SO4, MgCl2 and Na2CO3. The result for the diffusivity of 0.05 molar salts in water in new Finnish red brick varied between (0.271–0.544)*10−5 cm2/s at a temperature of 25 ± 0.05°C. The effect of temperature and concentration on the diffusivity of NaCl in new red brick was also measured. The rate of change of diffusivity as a function of temperature, concentration and the type of salt was very similar to that in free solutions. However, the values of the diffusion coefficients were lower in the porous medium than in solution. A mutual relation between the binary diffusion coefficient and the viscosity of the salt-water solution was observed in the porous brick.