No 1 (2024)

Доктор технических наук, доцент, профессор кафедры «Проектирование, строительство и технологии», руководитель проектов Инженерно-технического института Северо-Восточного федерального университета имени М. К. Аммосова, один из ведущих специалистов республики в области строительства.

Introduction. Self-compacting concrete has become increasingly popular in contemporary monolithic construction in recent years. By using self-compacting concrete, construction projects can be completed faster, with better surface quality and lower labour and energy costs involved in laying concrete mixtures. Self-compacting concrete mixtures, however, are more expensive, require more cement, and have unique design specifications for concrete mixes in comparison with other types of concrete mixtures. Finding the optimal component ratio that ensures the lowest amount of cement consumption while maintaining the necessary performance, mechanical, and physical properties of concrete is one of the primary tasks of developing rational compositions of concrete mixtures. In order to achieve the appropriate grain expansion and lower friction between the aggregate grains, it is crucial to consider that the amount of cement mixture exceeds the volume of voids between the grains in order to generate highly mobile self-compacting concrete mixtures.

The aim of the research was to determine the most effective ratio of fine and coarse aggregates in self-compacting concrete mixture composition in order to minimise aggregate intergranular porosity, optimise mixture workability, and maximise concrete strength.

Materials and methods. Natural quartz sand with a particle size modulus of 1.9 was used as fine aggregate. Crushed rock with a fraction of 5-20 mm was used as a coarse aggregate. The compositions of self-compacting concrete mixtures were selected from the condition of obtaining mixtures with workability grade RK2 (spread of a standard cone 66...75 cm) based on the requirements of GOST R 59714-2021.

Research results reveal that the lowest intergranular porosity of aggregates, the best workability of concrete mixtures, and the highest strength of concrete are all attained with a sand to aggregate ratio of r = 0.45. Reduced sand content deteriorates the structure, causes self-compacting concrete mixtures to segregate and bleed, reduces the strength of the concrete, and increases its capillary porosity.

Increasing the proportion of sand makes it possible to enhance stability and the viscosity of self-compacting concrete mixtures while reducing their workability, which leads to a decrease in the capillary porosity of concrete and as a result weakens the mixture strength.

Conclusion. It has been determined how the ratio of sand to aggregate affects the characteristics of self-compacting concrete mixtures and concretes. It was discovered that the ratio r = 0.45 represents the most efficient combination of fine and coarse particles in self-compacting concrete mixtures.

Introduction. The territory of the Republic of Sakha (Yakutia) is characterised by extreme climatic conditions with outdoor temperatures below -40 °C lasingg 50-60 days and the presence of permafrost soils. In these conditions, a multilayer wall structure with thermal insulation constructed from mineral wool slabs and a vented facade are used to provide thermal protection for buildings with load-bearing walls built from MHM-panels. The surface of the enclosing buildings is typically the only factor taken into consideration by thermal engineers when making design decisions for exterior walls, basements, attics, and floor-to-floor ceilings in projects. However, the practice of building operation shows that the greatest heat losses occur through the junctions of the basement floor with the outer and inner walls, as well as through the corner joints of the outer walls.

The aim of the research is to evaluate the thermal engineering properties of typical structural solutions for the junction of external and internal walls to the basement floor in the standard projects of houses with load-bearing walls made from MHM-panels.

Materials and methods. In order to achieve this goal, an analysis of typical structural solutions of nodal joints used in real projects of buildings with load-bearing walls made of MHM-panels was carried out by conducting thermal engineering calculations of 3D models of structural elements using the certified HEAT 3D software package and comparing with the results of a full-scale thermal imaging survey of existing buildings made of MHM-panels.

Research results. The thermal analysis showed that the greatest number of violations of thermal protection in real operating conditions at an outdoor temperature of 45 °C and below is observed in house basements. Significant heat losses through the enclosing structures of low-rise buildings made of MHM-panels are observed at the junctions of the basement floor with external and internal walls, as well as at the sites of angular joints of external walls. Calculations have shown that the temperature on the inner surface of the enclosing structures in the corner sections of the interface of the outer walls with the basement floor is significantly lower than the dew point temperature.

Conclusion. Conventional methods for connecting nodes in basement floors of buildings with load-bearing walls made from MHM panels do not account for temperature variations. As a result, energy-efficient node solutions must be developed and updated in order to be used in the harsh climate of northern Russia.

Introduction. In industrial buildings and constructions, structural steel is widely used due to its exceptional seismic qualities, low self-weight, and high strength. Frame buildings and bridges, for example, frequently use continuous steel beams with two or more spans. Not only does their design ensure strength, but it also reduces weight and material expenses. However, due to environmental influences, steel structures are subject to corrosion. As a result of corrosion damage accumulation steel structures lose some of their bearing capacity and operational safety. Ensuring the durability and reliability of steel structures during their operation is the main challenge for the construction industry. Managing the operational life of buildings and other structures in actual surroundings, as well as selecting the best structural and technological innovations while strengthening the existing framework, are the main approaches to deal with this issue.

The aim of research is to consider the features of the reliability assessment in damaged steel structures.

Methods. The following methods were used in research: mathematical modelling, forecasting, systematisation, experimental research, generalisation.

Research results. It seems appropriate to consider the steel structure's background operation and use a combination of the Monte Carlo method (MC) and the finite element method (FEM) to assess the corrosion losses of the cross section of a steel beam. This will allow for the assessment of a steel structure's reliability based on its service life, the effects of an aggressive external environment, and the ageing of the metal itself. The loading history of accumulated fatigue is determined using left-sided truncated normal Gaussian distribution of a random resistance value. Atmospheric corrosion of metals is a complex process that depends on a large number of interacting environmental factors. In order to assess corrosion losses and the depth of corrosion, it is proposed to use a model that takes into account the influence of sulphur dioxide through its concentration and the rate of chloride deposition. The Monte Carlo method based on the use of pseudorandom sampling and the strong law of large numbers to assess the reliability of any system is chosen as a simulation. The article presents an algorithm for determining the probability of unreliability of steel structural systems by adapting the MC approach.

Conclusion. The methodology that combines the finite element method with the Monte Carlo method is proposed to evaluate the reliability of a continuous steel beam based on its service life and the atmospheric environment's corrosive effects.

Introduction. The presence of both organic and inorganic contaminants makes the purification of wastewater from the leather industry a challenging operation.

The aim of the research is to assess the effectiveness of a technology that combines physical-chemical methods (adsorption) with a biological approach (in an aerotank) for wastewater treatment, considering its potential to reduce the concentration of pollutants in the wastewater from leather factories, thus maintaining water quality and ensuring sustainability of natural resource management. The following research objectives were established in order to achieve the goal: to identify the ideal parameters for the physical-chemical and biological treatment processes; to investigate the potential technology of treating wastewater from tanneries.

Materials and methods. The technology was investigated using real wastewater from a leather factory. Experiments were conducted under laboratory conditions at Astrakhan State Technical University. The process of chromium ion adsorption was carried out using vegetable waste (potato peel) with an initial chromium concentration in the wastewater of 37.5 mg/L. The adsorption process was studied under the following conditions: pH = 2.5; contact time between water and the adsorbent was 1 hour, and the stirrer rotation speed was 300 revolutions per minute.

Research results. As the adsorbent dose increases, the removal rate of chromium ions increases to a certain threshold value. The removal efficiency of chromium ions increases from 44 to 99.93% when the adsorbent dose changes from 0.5 g to 8 g. In the aeration tank, wastewater undergoing physical and chemical treatment was then exposed to biological treatment. The efficiency of biological treatment was monitored by a number of indicators: concentration of contaminants in the initial and treated water by BOD₅, air flow rate, activated sludge concentration, dissolved oxygen concentration. The results showed that the maximum oxidation rate is 87.53 (mg of substrate per 1 g of sludge per hour). The most optimal process parameters were 3.5 g/L of sludge, 6 hours of aeration, and 4 mg/L of oxygen.

Conclusion. As a result of the conducted research on the development of effective technology for wastewater treatment in tanneries, it was found that the application of this technology will allow to achieve deep purification to the requirements corresponding to the standards of discharges. Optimal parameters of the process of physical and chemical purification are duration of stirring 1 hour, speed of rotation of the stirrer 300 r/min, adsorbent dose 5 g. Optimal parameters of the biological purification process are as follows: aeration duration 6 hours; activated sludge dose 3.5 g/l; dissolved oxygen concentration 4 mg/l. Efficiency of chromium ion removal by physical-chemical process (adsorption) is 99.93%; effective oxidation rate of chromium ions is 99.93%. This wastewater treatment method helps preserve the environment from the negative impact of leather manufacturing industry.