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Keywords: foam concrete

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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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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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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