Determination of the Moisture Capacity of Porous Building Materials JAN CARMELIET*,y AND STAF ROELS

ABSTRACT: The moisture capacity, which is required to solve the isothermal moisture transport equation, is generally expressed by parametric functions covering both the hygroscopic and over-hygroscopic regime. The modality or number of analytical functions needed to describe the corresponding pore volume distribution is introduced as an important parameter for a proper description of the moisture capacity or capillary pressure curve. We used the Markov procedure to estimate the parameters. The method allows not only to evaluate the goodness of fit and the well-posedness of the parameter identification problem, but also to determine the optimal location of the experimental data in order to minimize the effect of errors on the estimated parameters. We found that the wetting capillary pressure curve, relevant for many building physics problems of hygroscopic capillary active materials, is preferentially described by bimodal functions or unimodal functions with sufficient flexibility towards the hygroscopic zone. The use of fixed values of relative humidity for determining the limit between hygroscopic and over-hygroscopic regime cannot be recommended as useful a priori information. This limiting moistur