Drying experiments are performed one various types of material, e.g., fired-clay brick, mortar, sand-lime brick, concrete and gypsum. In the inset of figure 1 the experimental set-up is given. Using a control unit an air-flow can be generated from 0 to 100 l/min and a relative humidity from 0 to 98 % over the samples. Drying experiments last in general from 12 hours to 4 days.
In figure 1 and 2 as an example the resulting moisture profiles for fired-clay brick and sand-lime brick are plotted as measured during drying with air of a relative humidity of 45 %. Each drying experiment was performed for a period of 40 hours or longer. Inspection of the profiles shows variations, which are substantially larger than the experimental noise, and reproduce from profile to profile, e.g., for fired-clay brick at a position of 5 mm. These variations reflect the inhomogeneities of the sample. In both cases a receding drying front is observed after some time. The evolution of the moisture profiles, however, is quite different for these two materials. For fired-clay brick a drying front is observed after approximaately 7 hours, whereas it takes more than 20 hours for a drying front to develop in sand-lime brick. After the drying front has entered the material, a residual moisture content is observed for sand-lime brick. These moisture profiles can be used to determine the moisture diffusivity as a function of moisture content (see articles).