Analytical model for the moisture absorption in capillary active building materials

- An analytical model describing the moisture absorption in a capillary building material is proposed.
- A closed form equation relating the water uptake coefficient to the diffusivity is derived.
- A good agreement with the measured data and with a numerical solution is found.
- A novel method for the inverse determination of the diffusivity is proposed.

Isothermal absorption of moisture in a semi-infinite porous body is described with a diffusion law as a free boundary problem in which the porous domain is divided into a nearly saturated and a nearly dry region. This problem is solved via an analytical approach by assuming the diffusivity as a step function of the volumetric water content. The analytical solution is then applied to modeling the behavior of two real building materials during a water uptake test. It is shown that the model is able to explain the absorption process adequately, and that a good agreement with the measured data is obtained. Finally, a novel method for the inverse determination of the diffusivity via water uptake tests is proposed.