Nº 10 (2024)

The relevance of the study is due to the fact that currently monolithic construction is characterized by a high rate of construction work, since in modern market conditions this indicator determines the final cost per square meter. As it is known, the life cycle of any concrete product or structure includes the preparation of a concrete mixture, transportation, laying, sealing, hardening and further operation.Therefore, the initial stage of the life cycle – the preservation of the properties of the concrete mixture over time will determine the technological and physico-mechanical properties, respectively, of the concrete mixture and concrete. An aggravating factor in maintaining the properties of the concrete mixture in the summer is the air temperature exceeding 30^оC. The paper shows technological techniques that make it possible to level the temperature factor on the properties of the concrete mixture over time.It was found that the introduction of superplasticizers in the amount of 1% of the cement mass and the restoration of mobility at the construction site make it possible to obtain concretes with specified qualities. This study is relevant for manufacturers of concrete mixtures.

The analysis of some methods for determining the frost resistance of concrete, including computational and experimental and accelerated ones, has been performed.It is noted that direct methods for determining the frost resistance of concrete are characterized by considerable labor intensity, as well as a long test time, which for concretes of high grades in frost resistance can be several months. Indirect methods do not always make it possible to determine the grade of concrete by frost resistance with a high degree of reliability. The paper proposes an accelerated method for determining the frost resistance of concrete, based on the principles of fracture mechanics, namely the relationship between the frost resistance of concrete and changes in the stress intensity coefficient after a single freeze to a temperature of -50^оC. The proposed method allows for operational control of concrete produced monolithic and prefabricated structures. It is shown that the provisions of fracture mechanics describing the process of fatigue failure can be used to describe and analyze the mechanism of frost failure.This will make it possible to develop ways to control the process of frost destruction, slow it down and increase the frost resistance of concrete.

The results of a study of the quality of crushed stone from gravel of fr. 5–20 mm and screening of crushing of fr. 0–5 mm of the Kama field were presented and an analysis of their compliance with the requirements of regulatory documents was carried out. The characteristics of the crushing products were determined: grain composition, content of crushed grains; amount of lamellar (flaky) and needle-like shape, presence of dust-like and clay particles, crushed stone crushability during compression in a cylinder, screening fineness modulus and content of reaction silica in crushed stone and screening. Compositions of high-strength concretes of class B60–B80 were developed, in which fine quartz sand was used to enrich the crushing screening, carbonate mineral powder of MP-1 grade and microsilica (MK-85) as a filler, and polycarboxylate superplasticizer Polyplast PK as a water-reducing additive. Optimal compositions were obtained with the following cement consumption: for concrete B60 with a compression strength of 78 MPa, cement consumption was 466 kg/m³, for class B70 with a strength of 91 MPa – 483 kg/m³ and for B80 with a strength of 104 MPa – 503 kg/m³. At the same time, concrete mixtures were characterized by a cone settlement of 25–27 cm.

The problem of the life cycle of transport structures using polymer composite materials (PCM) is touched upon. It is noted that in the life cycle of transport structures, at the stage of operation, the endurance of structural materials plays a key role. The results of experimental studies of PCM depending on the magnitude of the coefficients of reinforcement with fiberglass reinforcement (SPA) are presented. The influence of the degree of prestress of the SPA on the life cycle of the structural element has been established. It is emphasized that in the study of the life cycle of structures, the coefficient of asymmetry of the external load application cycle is of no small importance. As a result of the study, it was found that with an increase in the coefficient of asymmetry of the application of an external load with a simultaneous increase in the prestress in the SPA, the coefficient of endurance, and, consequently, the life cycle of the element, increases.

The results of the application of the biomineralization process in concrete to improve concrete properties such as porosity and water absorption are presented. As a result of the research, an assessment of the activity of various bioadditives based on the Bacillus subtilis strain and isolates isolated from samples of chernozem soil of the Yelets district of the Lipetsk region was given.It was found that the immobilized bacteria slightly differ from the native form in terms of urease activity, however, when stored for more than 50 days. they maintain their activity at a high level, and native microorganisms lose their ability to function, reducing urease activity by 10 times practically to minimum values. It was also revealed that when using Portland cement of various types, there is a decrease in water absorption up to 30%, and porosity decreases up to 40%.The use of different types of fine aggregate also affects porosity, so when using the same parts of sand P1 and P2, porosity is lower than with a homogeneous fine aggregate.It was also noted that all samples had increased strength characteristics – compressive strength and bending strength by 15–25%, respectively. Thus, the use of bioadditives is optimal to achieve improved concrete characteristics.

The article substantiates the need to develop new mechanisms for the hardwood use in modern conditions of Republic of Karelia timber industry. One of the potential uses of birch wood in wooden house construction is building materials production from veneer and slab materials based on it. A large amount of associated waste from processing birch wood into veneer stands out as one of the key problems. A new slab joinery and construction material made of corrugated birch veneer is considered. The purpose of this study is to evaluate the thermophysical properties of a corrugated board made of birch wood. To achieve this goal, the tasks and methods of research are defined. An experimental device has been developed to conduct an experiment to determine the values of thermophysical characteristics. DS18B20 temperature sensors were used to measure the surface temperature, as well as to monitor device operation and the room air temperature. The sensors are connected to the Arduino microcontroller platform, which was used to record and transmit sensor readings. Additionally, the course of the experiment was monitored using a thermal imager Testo 875-1i. During the experiment, more than 1000 measurements were carried out. As a result of data processing, a diagram of the dependence of the density of the heat flux passing through the sample on time, as well as diagrams of the dependence of thermal conductivity and thermal resistance on the temperature difference on the sample surfaces, was obtained. The diagrams show the regression dependences of changes in heat flux density, thermal conductivity and thermal resistance during measurements. The values of the heat flux density, thermal conductivity coefficient and thermal resistance calculated on the basis of regression equations and the values obtained experimentally are determined. The directions of further research of the material under consideration are determined.