Gregor Scheffler

On the Hysteresis in Moisture Storage and Conductivity Measured by the Instantaneous Profile Method

The relative humidity (or the capillary pressure) and volumetric water content can be determined at specific locations inside a porous medium by means of the proposed instantaneous profile method (IPM). The measurements are carried out with temperature and relative humidity (RH) sensors as well as with time domain reflectometry probes during the whole duration of the experiment. Thus, the IPM allows a transient measurement of the moisture retention characteristic. In addition, from the spatial and temporal distributions of moisture content and RH one may calculate the moisture conductivity as a function of moisture content and RH as well. The adsorption and successive desorption experiments presented in this article have been performed on calcium silicate (a capillary active material). The results show a hysteretic behavior that appears to depend on the nature of the process. The moisture conductivity as function of RH shows a significant hystereses; however, the moisture conductivity in relation to the moisture content appears to be non-hysteretic.

Evaluation of Functional Approaches to Describe the Moisture Diffusivity of Building Materials

With a set of material parameters and a material model called engineering model of hygrothermal material characteristics, both proposed in (Scheffler, 2004), the material functions used for input to hygrothermal building component simulation programs can be adjusted. Using inverse identification of functional parameters by simulation of laboratory experiments, the model is calibrated to reproduce measured water uptake and drying curves. The developed material functions contain an approach to describe the liquid water conductivity of building materials. In addition, moisture storage data approximated by a GAUSSian functional approach, showing sufficient flexibility in the whole moisture range, is available. There with the derivative of the moisture retention curve is known at high precision and the liquid water diffusivity can be derived, too. There exists a wide interest in applicable material functions based on literature data. But literature reviews of hygrothermal material parameters often yield incomplete datasets and experimentally determined curves are lacking or are available at lower accuracy only. Different authors introduced several diffusivity approaches requiring less input parameters for description of liquid water transport in building materials. These models are evaluated by means of diffusivity data derived from the calibrated liquid water conductivity function of the engineering model. A selection of four accurately measured materials is used for this investigation. The investigation is based on controlled laboratory data of high resolution. With the knowledge gained from this study, the uncertainties in interpretation of incomplete datasets frequently encountered in literature reviews shall be reduced.