No abstract

X-ray attenuation measurements are commonly used as a non-destructive method to monitor internal concentration changes of moisture (i.e., moisture content) and other chemical compounds in porous building materials. The technique provides direct measurements of moisture content changes through analysis with a composite model consisting of a dry porous material and a thickness of water equivalent to the moisture content of the material. The current formulation of this composite model relies on certain assumptions, including a monochromatic x-ray photon beam source (i.e., x-ray photons of a single, consistent energy) and that interactions between the x-ray photons and the materials (water and porous material) are independent. However, x-ray sources typically used by researchers in this field of study produce x-ray photon beams over a spectrum of energy levels, or polychromatic x-ray photons. Implications of this inconsistency are introduced and discussed. This paper presents both an overview of fundamental descriptions of the x-ray attenuation measurement technique and results from a parametric experimental study of various porous construction materials, including calcium silicate board, aerated autoclaved concrete, clay brick, cementitious materials, and wood. Results from the parametric investigation indicate the attenuation coefficient of water is dependent on the type and thickness of the porous material.

In relation to moisture storage in porous materials, it is often assumed that the process dynamics do not affect the moisture retention. There is mounting evidence though that this notion is incorrect: various studies demonstrate that the moisture retention is influenced by the (de)saturation rates of the moisture transfer processes involved. The available evidence primarily stems from imbibition and drainage experiments on soils however, and compared to many other porous media, these tests consider rather permeable materials with relatively dominant liquid transport at comparatively large (de)saturation rates. The current knowledge may thus not be directly transferable to moisture transfer in porous media on the whole, and dedicated further research is required. This paper responds to that need, by reporting on an experimental investigation of the occurrence of dynamic effects on moisture transfer in building materials. Drying and ad-/desorption tests are executed on two building materials, in which moisture contents and moisture potentials are measured simultaneously. These are translated into dynamic retention relations and dynamic storage coefficients, which both distinctly demonstrate that moisture transfer in building materials, similar to moisture transfer in soils, is not free of dynamic effects. The findings imply that the widely accepted static theory for moisture storage in porous media is not generally valid and should be corrected for the occurrences of dynamic effects. Considering that such drying and ad-/desorption processes are dominant features in very many instances of moisture transfer in porous media, the repercussions of these findings may be large.

The achievable accuracy of hygrothermal building component simulation is significantly dependent on the applied material functions. These functions are determined by the material modelling marking the connection between the basic storage and transport parameters which are obtained from basic measurements, and the storage and transport coefficients which are defined within the balance and flow equations. It is the aim of the present study to develop a flexible and widely applicable material model which is not restricted to the current level of the transport theory. Furthermore, limits and options of this model are to be validated by means of four building materials on the basis of special transient moisture profile measurements. By the presented study, the material modelling has been decisively further developed, the set of basic measurement methods has been extended by a substantial experiment and the instantaneous profile measurement technique has been made applicable to Building Physics. Moreover, the influences of the process history and the process dynamics on the moisture transport and the resulting moisture profiles could be shown and proven. By that, not only a material model is now available which perfectly applies to the requirements of flexibility, applicability and extendibility. The obtained data provides also a powerful basis for further research and development.

Die vorliegende Studie analysiert die automatische Messung des Wasseraufnahmekoeffizienten Aw. Ein Vergleich mit dem manuellen Experiment gemäß EN ISO 15148 zeigt eine gute Übereinstimmung zwischen beiden Methoden. Beim automatischen Verfahren ist die kontinuierliche Erfassung der Wasseraufnahme von Vorteil. Auch geringe Änderungen in der Wasseraufnahme werden entsprechend ihrem zeitlichen Verlauf gemessen. Langzeitmessungen über mehrere Tage und die Bestimmung hochsaugfähiger Baustoffe sind möglich. Insbesondere klein dimensionierte Proben und dünne Beschichtungen können analysiert werden. Abweichungen von der angenommenen Linearität des Aw‐Wertes lassen Rückschlüsse über mögliche Materialveränderungen, Schichtungen oder auch Anlagerung von Wasser an Mineraloberflächen zu. Zusätzlich kann der kapillare Wassergehalt mit dem automatischen Verfahren ermittelt werden. Bei Verwendung der Geräteapparaturen, der Beprobungstechnik, des Meß‐ und Berechnungsverfahrens liefert die Methode Aw‐ und Θcap‐Wert in beliebiger zeitlicher Auflösung. Dies macht die Methode besonders interessant für die Verwendung in Simulationsprogrammen und die Verifikation von Materialparametern und ‐funktionen durch Einsatz inverser Modellierung. Die Anwendbarkeit der Methode ist durch zahlreiche Messungen belegt. Eine Stichprobe zeigt die Anwendbarkeit der Methode im Vergleich mit Resultaten nach EN ISO 15148. Die Reproduzierbarkeit und der Routineeinsatz der Technik werden exemplarisch für eine Anzahl von Materialien gezeigt.