The analysis of the existing dependences describing the capillary absorption of liquid in porous materials is carried out on the basis of an ideal model and data of mercury porosimetry. It is shown that when passing from the hydraulic radius of an ideal model to the hydraulic radius of a capillary-porous material, it is necessary to take into account the tortuosity of capillaries and the effect of their narrowing (expansion), the effect of temperature increase associated with the sorption of water vapor, the effect of changing the viscosity of water depending on the hydraulic radius of the capillary. A quantitative assessment of these effects was carried out using experimental data. On this basis, a formula has been proposed for determining the hydraulic radius of the porous structure of ceramic materials for building products
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