Hygric and thermal properties of materials of historical masonry
Creators: name: Cerny, Robert
name: Pavlik, Zbysek
name: Pavlikova, Milena
name: Cerny, Robert
Publisher: name: 8th Symposium on Building Physics in the Nordic Countries
Year: 2008

description: In the reconstructions and maintenance of old, historically significant buildings, such materials are required which are as close as possible to the original materials in their chemical composition and physical properties. For the materials of load bearing structures this is usually not a serious problem because the quarries where the building stones were originally taken from are usually known for a particular building and ceramic bricks similar to historical can be produced relatively easily. However, in some cases the original materials cannot be replaced in an identical way. For instance, producing lime plasters in exactly the same way as it was done centuries ago is difficult because nowadays the technology of lime production achieved a very high level resulting in very pure lime. In a comparison with lime produced in the past on imperfect devices, without sorting of the raw material and with ash matter presence, the current lime has a different quality and different bonding properties. Current lime creates the solid structure by carbonation and the final product, calcium carbonate, has lower strength than the products of hydraulic or pozzolanic hardening. In mortars and renders, this feature is eliminated by addition of Portland cement (often white cement). However, this way of modification of mechanical properties of mortars and renders is not preferred by cultural heritage authorities. Therefore, pozzolanic admixtures are used for the improvement of mechanical properties instead.

In the reconstruction works on historical buildings, considerable financial means are spent. Therefore, it is desirable to assess the durability of applied materials in the particular conditions of a specific building. This cannot be done effectively without the knowledge of their hygric and thermal properties which can be used as input parameters of computational models. In this paper, hygric and thermal properties of several types of materials which are used in reconstructions of historical buildings on Czech territory, among them ceramic brick, sandstone and lime-metakaolin plaster, are investigated in the paper. Orientation values of moisture diffusivity are determined by methods utilizing the results of water sorptivity measurements, the dependence of moisture diffusivity on moisture content and temperature is determined by measuring moisture profiles using a capacitance technique and subsequent solution of the inverse problem of moisture conduction, water vapor diffusion permeability is measured by the cup method. Sorption isotherms are determined by the common desiccator method in the range of relative humidity of 11% – 96%. Thermal conductivity and specific heat capacity are measured by an impulse technique (commercial device ISOMET 2104). Moisture diffusivity, thermal conductivity and specific heat capacity are determined in the temperature range characteristic for usual service conditions and in the moisture range from the dry state to full water saturation.