Safe usage of external enclosures under adverse environmental exposure

Abstract

Introduction. The study considers the issue of safety of the human vital activity environment in the field of construction and usage of buildings, which includes, along with other types of safety, thermal, biological and mechanical safety. The last ones cannot be provided if there are inorganic hygroscopic salts in construction materials of external enclosures due to influence of the salts on the thermal, mechanical and other properties of the materials. Thermal conductivity coefficient of damped saline construction materials is determined on a developed experimental facility operating according to the principle of unsteady thermal conditions. A statistical analysis of the experimental results on thermal conductivity of materials possessing various structures and densities is carried out. Significance of the influence of the “salt content” factor on the thermal conductivity of saline materials in comparison with control non-saline samples is revealed.
 Materials and methods. Construction materials for the study are selected as follows: autoclave lime-and-sand brick and burnt brick with a density of 1800 kg/m3, autoclave foamed silicate with a density of 650 kg/m3, wood concrete with a density of 616 kg/m3 and mineral wool slabs with a density of 150 kg/m3. The generally accepted methods of laboratory research and statistical processing of experimental results are used. Laboratory methods include preparation, salinization with sodium chloride, potassium sulfate and calcium chloride, and measurements of the thermal conductivity coefficient of construction material samples.
 Results. The determination of thermal conductivity of wetted saline materials under unsteady thermal conditions makes it possible to eliminate drying of the samples and migration of salts and moisture. The presence of salt crystals increases the thermal conductivity of dry materials up to 80 % (rel.). Damping the samples promotes the dissolution of the crystals and lowering the thermal conductivity of the samples to values lower than those of non-saline samples with the same moisture content.
 Conclusions. The study proves the significance of the salinization effect on the thermal and physical characteristics of construction materials that must be taken into account when thermal engineering calculating external enclosures and predicting their moisture state during usage.

The Influence of Salts’ Presence in the Materials on their Moisture and Thermal Conductivity

“…2. The building materials' thermal conductivity calculation, taking into account the salt effects for conducting the thermal engineering calculations, should be carried out in accordance with the following scheme: volume concentrations of components in the building material are determined; the thermal conductivity of the shell of the material is determined by the formula (3); the thermal conductivity of salt crystals is determined by the formulas (4, 5); the thermal conductivity of the solid phase of the material, consisting of the building material and crystalline salt shell, is determined by the formula (11); the thermal conductivity of a binary salt solution is determined by the formulas (6, 7) and multicomponent -by the formulas (6,8,9,(11)(12)(13); the thermal conductivity of the pore space is determined due to the diffusion of the vapor-air mixture above salt solutions according to the formula (15); the thermal conductivity of the inter-pore substance is determined by the formula (16); the thermal conductivity of saline building material is determined by the formulas (11,17).…”

“…The value of the calculated humidity directly affects the main indicator for thermo technical calculations -the value of the estimated thermal conductivity of the building material [4]. On the other hand, the calculated thermal conductivity is significantly influenced by the presence of some components in the material -pollutants in the form of dust and gases that come from atmospheric air [5,6] and soil, including the hygroscopic inorganic salts common in the environment used in industrial and economic human activities [7,8,9]. Getting on the building envelope, salts absorb moisture penetrate the thickness of the building material BE and in the form of solutions and are accumulated there.…”