Einfluss des Feuchtigkeitsgehaltes auf das kapillare Saugen / Influence of Moisture Content on Capillary Suction

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 content.