Impact of the drying rate on the moisture retention curve of porous building materials

Abstract

The storage of moisture in porous building materials is described via the moisture retention curve, which is often assumed a one-to-one function linking the local moisture potential to the local moisture content, independent of the moisture transfer process and the (de) saturation rate. Prior studies have however called this assumption into question, by showing that the moisture retention curve might indeed vary, depending on whether it has been determined at steady-state or transient conditions.This work aims at extending the current knowledge on the above topic by investigating the desorption process of capillary active building materials (calcium silicate, ceramic brick and aerated concrete) via drying experiments. The moisture retention curve is thus determined by employing a lumped parameter approach based on the measurement of the drying rate and surface temperature of the samples during time. The tests are repeated for different boundary conditions, and the results are compared with those obtained via a steady-state technique (i.e. the pressure plate method). The impact of the drying rate on the desorption curve is quantified via a material specific dynamic storage coefficient, which is described as an empirical function of the moisture content.