Einfluss von Rissen in hydrophobiertem Beton auf den kapillaren Wassertransport

In practice, hydrophobing impregnation has been established as an effective surface protection system against water and de-icing salt attack. Cracks in concrete, whether impregnated by a hydrophobing treatment or not, are unavoidable and can therefore lead to damage. In absorption tests on laboratory samples, the significant influences of cracks on the penetration behaviour of capillary water have been determined and quantified. The experimental results show that the water uptake depends on the craclc width and the penetration depth of the hydrophobing agent. There exists a 'critical' crack width depending on the penetration depth of the hydrophobing agent which can maintain the hydrophobing behaviour. Finally practical conclusions of the present work are draw

Einfluss des Feuchtigkeitsgehaltes auf das kapillare Saugen

Some surface treatments such as hydrophobing and realcalisation rely on capillary suction as the driving force. In this context, the critical admissible moisture content must be known. The porous structure of a series of different building materials has been characterized. The porosity and pore size distribution has been determined on 3 different types of autoclaved aerated concrete (AAC), on samples made of hardened cement paste with 3 different water-cement ratios, on natural sandstone and on burned brick. The sorption isotherm and at each equilibrium moisture content the remaining capillary suction has been measured on identical specimens. It can be shown that capillary suction of materials with a coarse porous structure such as sandstone or burnt brick depends slightly only on the moisture content Capillary suction of hardened cement paste with a fine porous system, in contrast, is drastically diminished with increasing moisture content and reaches negligible values near 100 % RH. Results presented in this contribution allow us to fix a critical admissible moisture content for different building materials. At the same time, building materials can be identified for which the moisture content has to be carefully controlled before surface treatment is to be applied It must be mentioned, however, that in critical cases the moisture profile must be determined up to the intended depth of the treatment instead of the surface moisture conten

Untersuchung von Feuchtetransport mittels numerischer Modellierung und Neutronentransmissionsanalyse

Moisture transport in porous building materials is described by a transport model that expresses the action of the several transport mechanisms of liquid water and water vapor in the porous system by a single material specific transfer coefficient. This parameter has to be determined by experimental measurement of moisture distributions inside samples exposed to known initial and boundary conditions. Neutron radiography is employed as experimental method because of its high sensitivity and good spatial resolution. The moisture distribution is determined from the raw data obtained in the measurement by a calculation procedure based on a signal transfer model of the neutron transmission. This approach is illustrated by two examples: the drying of a plain brick sample and the drying of a composite sample consisting of two brick elements separated by a layer of morta

Rechnerische Bestimmung der lonenbeweglichkeit in Ziegelstein unter Zuhilfenahme von Ergebnissen aus nichtstationären Diffusionsversuchen

Ion concentration profiles in sandwich-brick specimens have been determined experimentally at different degrees of water saturation. Based on the experimental data, ion diffusion coefficients were determined by inverse analysis. The diffusion equation served as a basis for an optimization technique. It has been shown that the ion diffusivity in bricks decreases markedly as the moisture content decreases. The interface between two adjacent bricks slows down the ion migration at low water content in particular. It is planed to investigate the interface between mortar and bricks in further experimental and numerical studie