Study of the dependence of equilibrium sorption humidity of heat-insulating products on temperature

The desiccator method for products like mineral wool has a low accuracy, which is due to the small mass of the samples and the uneven content of the binder between the samples. The standard method does not involve testing materials at different temperatures. However, the value of sorption moisture depends not only on the nature and structure of the material, but also on the temperature conditions. At the moment, the regularities of changes in the sorption moisture content of materials depending on the air temperature have been studied only in separate scientific works and do not cover the entire spectrum of modern building materials. The paper presents the results of a study of the sorption moisture content of modern mineral wool products at various temperatures above 0 ºС. The results show an increase in sorption humidity with decreasing temperature from 22 ºС to 0 ºС. The greatest increase in humidity occurs at values of relative air humidity in the range of 90–97 %. It is shown that the standard desiccator method for studying sorption moisture requires scientific development and increased control of test conditions with decreasing temperature.

Physical parameters of insulation with a structure-forming material from flax noils

The results of studies to evaluate the effective operation of the obtained thermal insulation slabs made of flax fibers or noils were carried out. The sorption moisture content of insulants based on flax fibers or noils with modified liquid glass was determined at a relative humidity of 40–97%. The influence of humidity on the thermal conductivity of the test materials was studied. The coefficient of vapor permeability of insulation made of flax fibers or noils was established. The results of field tests of experimental thermal insulation materials on the attic flooring of a residential building during the cold season were considered. The graphs of the temperature distribution over the structure of the attic flooring and heat flow indicators were obtained. The values of the heat transfer resistance of the attic flooring were calculated at an air temperature of -20 °C to -2 °C. The moisture content of insulation at the end of the cold period was determined and the dependence of the distribution of moisture over the thickness of the thermal insulation layer was plotted. The results of the tests carried out indicate the highest efficiency of thermal insulation slabs made of flax fiber noils in comparison with insulants based on flax fibers.

Technology and Physico-Mechanical Properties of Claydite Foam Concrete for Monolithic and Prefabricated Construction

Theoretical and experimental investigations have resulted in obtaining an effective insulating and structural material (claydite foam concrete) that is not subjected to slump and shrinkage in the range of main grades used in construction in terms of average density D300–D700, characterized by 5–31 % greater strength and 8–27 % elasticity modulus, as well as a higher (£30.7 %) level of vapor permeability and moisture return (by 17.4–46.7 %) with lower values (by 10.0–83.2 %) of water absorption, sorption moisture and thermal conductivity in comparison with aerated concrete of autoclave hardening and foam concrete of equal density. A three-stage technology has been developed for preparing claydite foam concrete. At the first stage cement dough is prepared and if it is necessary an optimum amount of hardening accelerator (1 % CaCl2 from cement mass) and additives condensing cement stone structure (1 % Al2SO4 from cement mass ) are introduced into it, they prevent slump of a binder (foam concrete) during the subsequent hardening, and in combination with 0.5 % from cement mass “Hydroxypropylmethylcellulose УСК-200 TT” – and shrinkage of foam and claydite foam concrete during the subsequent drying. At the second stage, the binder is aerated while introducing protein-based foam agent (Laston) into the cement dough in an optimal amount (depending on the given density) 0.5–1.3 % from the cement mass; and at the third stage, expanded clay gravel is introduced into prepared foam concrete mixture (in rational amount of approximately 0.7–0.8 m3 per 1 m3 of claydite foam concrete) with continuous mixing for 60–90 seconds. Methodologies for calculation of foamand claydite foam concrete compositions have been developed; molding modes of expanded clay foam concrete with high degree of homogeneity (variation coefficient of density and strength uk £ 6.2 % in the process of manufacturing molding with layer height up to 1500 mm) have been justified that confirms efficiency of the proposed technology.

Modeling of capillary-sorption process steam condensation in the system of microcapillaries of grain shells

The aim of this study is to simulate the capillary-sorption process of steam condensation in the system of microcapillaries of grain shells [1]. Modeling of the processes of intensive moisture transfer during drying of a number of materials was considered in [2,3]. In order to significantly reduce the time of moistening, moisture transfer by effusion is considered in the form of steam produced at low pressure (vacuum) with its further guaranteed condensation in micro-cavities (microcapillaries) of a porous shell of grain [4]. Study of intensity of moisture transport in accordance with the changes in concentrations of vapour along the length of the capillary in a vacuum proved the possibility of intensifying the process of moistening the grain before grinding. The obtained mathematical model will allow to calculate the values of the theoretical weight gain of moisture in microcapillaries depending on the parameters and the time of vacuum-sorption moisture.

Determination of Poroelastic Parameters of Porous Building Materials

Variations of sorption moisture in the capillary porous materials result in strong fluid-skeleton interactions due to molecular and surface forces, which produce moisture-induced deformation. The effect of moisture sorption on the non-linear elastic behavior of hygroscopic porous building materials has been experimentally investigated showing strong influence of moisture especially in the lower moisture content range. In the framework poroelasticity moisture influence on elastic behavior is described by two poroelastic coefficients, which present the fluid-skeleton coupling. This paper presents an application of the procedure for the determination of the coupling coefficients for medieval brick.

EVALUATION OF SORPTION MOISTENING IN RESEARCH OF MOISTURE-CAUSED DEFORMATIONS OF BUILDING MATERIALS

Investigation methods described in literature and standards do not evaluate the influence of sorption moisture upon moisture-caused deformations of building materials. Therefore, the usual deformations measuring methods had to be amended by measuring moisture deformations in various models and by setting sorption moisture. The improved methods was applied for solving the tasks of durability of articles. The basic point of the developed methods intended for investigating the moisture-caused deformations is investigation of the groups of specimens by measuring deformations in the environment of fixed sorption moisture using four models. According to the methods described in this article, the dependence of deformations (eu) of various construction materials (concrete, porous concrete, sand-lime and ceramic bricks, cement-lime plasters) upon moisture and changes therein was investigated: eu = f(u). Analysing the materials with different capillary structures enables us to provide—in a very concise form—some References concerning value and nature of deformations. Linear moisture-caused deformations of basic construction materials (concrete, sand-lime and ceramic bricks, cement-lime plasters, porous concrete) vary within the limits of 0,33—0,77 mm/m. In case of articles containing organic fillings they can reach up to 6 mm/m. When the material is of a fine capillary structure the highest relative moisture elongation K of a material is observed in the environment of vapour area. Relative moisture elongation of the tested materials with the outset of intense capillary condensation varies from 0,05 mm/(mx%) to 0,51 mm/(mx%).