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Keywords: thermal conductivity

Experimental determination of heat losses through cracks in building walls

https://doi.org/10.58224/2618-7183-2026-9-5-5
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Abstract
This study investigates how a repaired crack affects heat losses through a building envelope. An experimental setup was designed and assembled to test wall specimens containing a crack repaired by injection grout. A calculation procedure was developed to determine the specific heat loss through the repaired crack under the conditions of the proposed experimental apparatus. The experimental data were statistically processed using the Shapiro-Wilk test to assess normality. Differences in the specific heat loss before and after crack formation were evaluated with the paired Student's t-test. Statistical significance was accepted at p < 0.05. All statistical analyses were carried out in IBM SPSS Statistics. Tests were carried out on foam-concrete, clay brick, and reinforced concrete specimens. Ten speci-mens were prepared for each material under investigation. During the first stage, intact specimens without cracks were tested. Afterwards, an artificial crack was introduced into each specimen, repaired by injection grouting, and the specimens were tested again under identical conditions. The measured results showed a statistically significant increase in heat loss after crack repair. On average, the specific heat loss increased by 12.1%. The experimental findings were compared with numerical simulations. The temperature field around the repaired crack was calculated by solving the two-dimensional steady-state heat conduction equation. Robin (third-kind) boundary conditions were assigned to the external surfaces exposed to air, Neumann (second-kind) boundary conditions were specified at the truncated boundaries of the computational domain, and fourth-kind boundary conditions were applied at material interfaces. Numerical simulations were performed in ANSYS Workbench 2024. The difference between the numerical predictions and the experimental measurements did not exceed 2.1% for foam concrete, 3.8% for clay brick, and 2.4% for reinforced concrete. The results demonstrate that even after repair, wall cracks noticeably affect the thermal performance of building envelopes. The proposed mathematical model can therefore be used for numerical assessment of heat transfer in walls containing cracks repaired with injection grout.
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Patterns of formation of the pore matrix structure and thermophysical properties of calcareous-ash mortars modified with opoka and recycled basalt fiber

https://doi.org/10.58224/2618-7183-2026-9-4-2
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Abstract
The study investigates patterns in the formation of the structure and properties of calcareous-ash mortars modified with silica rock opoka and recycled basalt fiber. The research goal was to establish the relationship between the composition, pore structure, and thermophysical and physico-mechanical characteristics of the material.
The raw components used included lime, fly ash, granulated blast furnace slag, opoka, quartz sand, and recycled basalt fiber obtained from spent mineral wool substrate after heat treatment. The conducted studies involved the determination of density, compressive and bending strength, thermal conductivity, shrinkage strain, and microstructure.
The introduction of opoka was found to contribute to the formation of a microporous structure, providing a 20-35% reduction in average density and a decrease in thermal conductivity to 40-55%. Recycled basalt fiber reduced shrinkage strain and improved crack resistance by stabilizing the pore matrix structure. The study showed that synergetic interaction of components leads to the formation of a hierarchical structure providing the optimal combination of strength and thermophysical characteristics.
The optimal density range achieving the best balance of properties has been determined (1,400–1,600 kg/m³).
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Mathematical modeling of heat transfer through building envelopes with cracks

https://doi.org/10.58224/2618-7183-2026-9-4-4
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Abstract
Cracks formed in building walls are frequently restored by injecting specially formulated repair grouts into the damaged areas. This study examines the effect of such repaired cracks on the thermal performance of building envelopes. Heat transfer within cracked wall sections was modeled by solving the two-dimensional steady-state heat conduction equation. Convective boundary conditions of the third kind were specified on the exterior surfaces to account for heat exchange between the wall and the surrounding environment. The truncated edges of the computational domain were assigned insulated (second-kind) boundary conditions, corresponding to zero normal heat flux. At the interfaces between adjacent materials, continuity of both temperature and heat flux was enforced through fourth-kind boundary conditions. The numerical analysis was carried out using the finite element method implemented in ANSYS Workbench 2024. Based on the obtained numerical results, a procedure was developed for constructing nomograms that characterize the specific heat losses associated with wall cracks repaired by injection grouting. The temperature fields of aerated concrete, clay brick, and reinforced concrete wall assemblies were investigated. The results indicate that injecting a repair grout into a crack increases the heat flux through the examined section in brick and aerated concrete walls, whereas the opposite effect is observed for reinforced concrete walls, where the heat flux decreases after crack injection. The simulations demonstrated that replacing the air-filled crack with injection grout increases the heat flux across the repaired region of the wall. Graphical nomograms were therefore established to estimate the heat flow through repaired cracks directly from two governing parameters – the crack depth and the crack opening width – without the need for a complete numerical solution of the temperature field. In addition, the paper presents a practical algorithm describing the application of these nomograms in engineering calculations. The developed graphical tools can be employed to evaluate the overall thermal resistance of building envelopes during reconstruction, rehabilitation, and major renovation of existing buildings.
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Controlling the density and thermal conductivity of silicate bricks by adjusting the dispersity of glass powder from glass waste

https://doi.org/10.58224/2618-7183-2026-9-3-6
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Abstract
Under tightening requirements for the energy efficiency of buildings, the development of building materials with reduced thermal conductivity and with the use of secondary resources is gaining particular relevance. A promising area is the use of cullet in the production technology of silicate bricks as a wall building material. The aim of the study was to investigate the influence of dispersity and the content of glass powder obtained from sheet glass waste on the physicomechanical and thermophysical properties of autoclaved silicate bricks. Glass powder was examined as an active silica-containing additive and a source of alkaline Na⁺ ions that affect hydrothermal phase formation. The samples were molded by semi-dry pressing at a pressure of 20 MPa and 10–12% humidity of the mixture, after which the bricks were autoclaved according to the industrial regime of the silicate brick factory of West Kazakhstan Corporation of Building Materials, JSC (174–175°C, 0.8 MPa). The introduction of 5–15% fine glass powder was found to decrease the average density and thermal conductivity coefficient of the product while maintaining strength at the level of grades M150–M200. Microstructural and phase analysis showed a predominance of an amorphous and semi-crystalline C–S–H phase with the suppression of tobermorite formation due to the alkaline effect of glass powder. The study determined that the modification of silicate bricks with glass powder allows obtaining more energy-efficient wall materials without changing the industrial production technology. The findings testify to the prospects of recycling cullet in the silicate brick production technology with the aims of increasing the energy efficiency of the enclosing structures.
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Eco-Friendly Foam Concrete with Improved Physical and Mechanical Properties, Modified with Fly Ash and Reinforced with Coconut Fibers

https://doi.org/10.58224/2618-7183-2025-8-1-1
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Abstract
The development of new types of environmentally friendly and cost-effective building materials is currently a relevant topic and is actively developing throughout the world. In modern construction materials science, the most popular direction is the development of new concrete compositions using waste of various origins. The objective of this study is to develop new compositions of foam concrete using local waste from the fuel and energy complex and plant natural fibers. To determine the optimal amount of the modifying additive fly ash (FA), 7 experimental concrete compositions with different percentages of cement replacement by FA were made. The content was established as optimal. Foam concrete with 15% FA has the lowest density of 1075 kg/m3 and a minimum thermal conductivity coefficient of 0.248 W/m × °C, as well as increases in compressive and bending strength of 23.3% and 21.7%, respectively. The effect of coconut fiber (CF) was assessed on the composition of foam concrete modified with the optimal amount of FA 15%. The optimal dosage of CF was 0.6%. As a result of FA modification and CF dispersed reinforcement, a complex effect was obtained. The increase in compressive and bending strength was 30.14% and 72.83%, respectively, compared to conventional foam concrete. The density and thermal conductivity coefficient decreased by 9.8% and 8.34%, respectively. The results obtained during the experimental studies prove the effectiveness of the proposed formulation solutions and allow obtaining an energy-efficient foam concrete composite with improved characteristics.
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Analysis of thermal efficiency of external fencing made of innovative ceramic blocks

https://doi.org/10.58224/2618-7183-2024-7-3-1
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Abstract
The paper presents a comprehensive theoretical study of the external fencing structure made of innovative Porortherm 38 ceramic blocks in comparison with traditional structures made of solid ceramic brick, hollow ceramic brick and gas block. The study was conducted in the climatic conditions of Shymkent city, South Kazakhstan. The middle temperature values of the frostiest 5 days with a provision of 0,92 were adopted as the external temperature. The results of the study of the actual resistance (Rf) of the structures under study showed that all adopted structures meet the condition Rf˃Rreq, while the actual resistance of the new structure is 1.3 times more efficient than traditional ones. The analysis of temperature fields showed that the new structure is 2% more efficient than traditional ones. Moreover, no additional insulation costs are required. The obtained results were also confirmed by computer modeling in the ELCUT software package. The results of calculating the humidity regime showed that a condensation area appears in almost all the structures under consideration. The results of calculating the amount of moisture evaporated from the multicoat structure of the external fencing during the torrefaction period showed that all the accumulated moisture will evaporate during the specified period, the calculation of the condition of inadmissibility of moisture accumulation in the structures of external fencings for an annual period and for the period of moisture accumulation showed that all the considered structures meet the requirement . The results of calculating the air regime of multicoat structures of external fencings also showed that all structures including the new one meet the condition . The result of calculating the value of thermal inertia (D) in the proposed structure is up to three times more efficient than traditional structures, which applies to structures with high inertia (7˂D). The obtained results of the study indicate that the new proposal of a structure made of ceramics is cost-effective, innovative blocks can be proposed as a supplement to the register of materials of existing standards.
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Analysis of the effect of porosity on thermal conductivity with consideration of the internal structure of arbolite

https://doi.org/10.58224/2618-7183-2024-7-3-4
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Abstract
A theoretical study of the effect of porosity and internal structure of the exterior envelope in the ANSYS and BLENDER software systems has been carried out in the paper. As an example of exterior enclosure structure, an arbolite block with porosity up to 20% and fiber structure in the direction along and across the heat flux, as well as randomly and at an angle of 45° was studied. As a result of the study, it was found that the significant effect of the heat flux dependence on the porosity of the material is the porosity of the block over 10%, which reached up to 5.92%, and with porosity up to 5% showed a difference of 1.3%. At the same time, the fiber structure also showed a significant difference from 8.16% to 15.33% depending on the fiber direction. At the same time, the analysis of the effect of porosity on the thermal conductive value also showed a difference of up to 15.33% for the same value of heat flux. At the same time, the influence of fiber structure shows an additional difference of up to 5.9%. The results of the study showed that the most thermally conductive arbolite blocks are, those in which the direction of fibers are located along (along the X axis) and at 45 ° relative to the structure of fibers across (along the Y axis) and random, the difference of which was up to 1.6%. The obtained results of this study, further excluding the costly experiments to determine the coefficient of thermal conductivity can be used to accurately estimate the coefficient of thermal conductivity of external envelopes made of arbolite blocks, considering porosity and fiber structure in the design of residential buildings.
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