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Keywords: reliability

Injection mortars based on composite cements for soil fixation

https://doi.org/10.58224/2618-7183-2023-6-4-15-29
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 15-29 p.
Abstract
The fixation of subsidence soils is an important practical scientific and technical task, which makes it possible to carry out construction and repair work on weak (subsidence) base soils. Composite cements (CC) have been developed, including aluminosilicates (AS), obtained by enrichment of ash and slag mixture (up to 65 wt.%), Portland cement clinker and gypsum. Based on the developed CC, a wide range of injection solutions with water-binding ratios from 1.0 to 2.0, including screening of crushed granite from 0.7 fineness modules, has been created. The developed injection mortars are capable of effectively fixing the soils of the foundations of underground structures, providing the strength of the soil-concrete mass up to 25.6 MPa with a deformation modulus of 10.1 GPa. According to the sedimentation analysis of solutions, it can be seen that these materials have a percentage of water separation from 22.5% at W/B=1 to 36.5% at W/B=2. At the same time, the viscosity indicators of these materials indicate a high penetrating ability, since the time of the expiration of mortars through a Marsh viscometer for mortars IR5 and IR6 is 39 and 40 seconds at W / B = 1.5 and W/ B = 2, respec-tively. The effect of increasing the density of injection mortars on composite cement at the age of 28 days was maximum at an AS dosage of 45% by weight, then it decreased with an increase in the con-tent of the aluminosilicate component. There are high ratios of the values of strength properties on the second day to similar indicators in the 28-days age: for compressive strength 0.24 (0.20-0.22 for addi-tive-free clinker compositions), for flexural strength 0.16 (0.15 for additive-free clinker compositions; while increasing the AS content above 45%, this ratio decreases to 0.14). High early strength makes it possible to effectively use injection mortars for urgent fixing of soils during the repair of underground structures.
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Reinforcement of construction of underground structures with shotcrete

https://doi.org/10.58224/2618-7183-2022-5-6-5-18
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 5-18 p.
Abstract
An urgent scientific task, which is of great practical importance for increasing the defense capability of the state and preserving the population, is the improvement of constructive methods for the complex repair of underground structures. Reinforced shotcrete concretes have been developed and their research has been carried out to strengthen underground structures. Achieving the uniform workability of shotcrete (slump 19 cm) was carried out by varying the dosage of the superplasticizer, which has a high water-reducing ability (40%). Some reduction in slump flow (47 cm) was observed at a dosage of ACC in the amount of 35 wt. %. An increase in the density of the mixed mixture with an increase in the content of the aluminosilicate component in the polymineral binder was established. The introduction of the alumino-silicate component in small quantities (up to 25 wt.%) slightly increases the 28-day density of the cement paste (0.3-0.4%). With an increase in the dosage of ACC (up to 35 percent by weight), an increase in the density of 28-day-old samples was noted, which linearly raised with an increase in the amount of introduced aluminosilicates. The effect of increasing the compressive strength of shotcrete concretes on a polymineral binder increased with an increase in the dosage of ACC up to 35% by weight, and the maximum effect is noted for early strength values, in particular, at the age of 1 day, an increase in compressive strength by compared with the composition without additives was 56%, and with bending 62%. This is also confirmed by the high ratios of the values of strength properties in the first day to similar indicators in the grade age: for compressive strength 0.27 (0.23 for clinker compositions without additives), for bending strength 0.30 (0.26 for additive-free clinker compositions). Theoretically and practically proved the effectiveness of the use of the developed shotcrete for strengthening the supporting structures of underground structures with an increase in strength of more than 2 times, which is explained both by the high strength of the obtained repair composition and the monolithic contact zone between the old and new layers of concrete. The developed shotcrete is able to provide the necessary degree of strengthening of the supporting structures of underground structures, while the thickness of the repair layer of 6 cm (with proper soil fixation) allows the use of underground structures as dual-use facilities.
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Technological Solutions Ensuring Reliable Operation of Steel Vertical Reservoirs in Seismic Areas

https://doi.org/10.58224/2618-7183-2022-5-5-5-16
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 5-16 p.
Abstract
The article discusses the relevance of reliable operation of vertical steel reservoirs (RVS) in earthquake-prone areas. Based on the analysis of a number of scientific publications, it has been estab-lished that for the safe functioning of large–sized RVS, it is necessary to install anchor devices, the main purpose of which is the transmission of vertical forces arising from an earthquake in the wall to the base. To do this, they must be securely fixed to the wall and the base in order to evenly distribute efforts across the office of the RVS. In some cases, poor-quality connection of the anchor with the RVS leads to significant stresses in the anchors and there is a possibility of both rupture of the housing itself and rupture of the connection of the housing with the bottom of the tank. It is known that large-sized tanks require a massive base and the installation of anchors with a large number of bolts is a very expensive undertaking.
The article discusses the most common variants of anchors that are used in practice, lists some of their disadvantages and suggests an improved version based on the analysis of scientific publications. The authors present their own development – a modified version of the anchor device, the corresponding design solutions are given and the technology of the device is described. In addition, it was noted the need to increase the bearing capacity of the soils of the RVS foundation, constructed in earthquake-prone areas using geocomposite materials. It is emphasized that the required number and length of an-chor devices, as well as the choice of geocomposite material for soil hardening should be justified by appropriate calculations. It is concluded that in order to ensure reliable operational characteristics of RVS located in seismically hazardous areas, the installation of anchors, despite attracting additional financial resources, is a prerequisite, since in the event of a spill of petroleum products, the restoration of biogeocenosis requires more than one decade and involves enormous material costs.
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THE RELIABILITY COEFFICIENT FOR FIBRE CONCRETE MATERIAL

https://doi.org/10.58224/2618-7183-2022-5-2-51-58
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 51-58 p.
Abstract
One of the main parameters of the method for calculating building structures made of concrete and fibre concrete by limiting states is the reliability coefficient for the material, which characterizes the heterogeneity of the physical and mechanical properties of the material. In national and foreign standards, it takes a constant value of 1.3 (obtained on the basis of direct tests), or 1.5 (obtained on the basis of indirect tests and the use of graduated dependencies). The concrete matrix for the formation of the structure of fibre concrete is most often fine-grained concrete with special additives, which has greater uniformity in comparison with heavy concrete, which cannot but affect the reliability of the composite material in question as a whole: the stock coefficients for fibre concrete should be lower than for normal concrete, which has not been reflected in modern standards for design yet. Starting from interval estimates of the average strength value, a new approach to determining the reliability coefficient for the material, differentiated by the 1st and 2nd groups of limit states, is proposed. The results of calculations according to the proposed formulas for previously conducted tests of steel- and glass-fiber concrete images allowed us to conclude: the introduction of fiber into the concrete matrix of the proposed effective composite composition increases the uniformity of the strength properties of the material, which leads to an increase in the reliability of its use in building structures, a decrease in the value of the reliability coefficient (margin) for the material to 1.164...1.235 for central axial compression and up to 1.172...1.272 – for central axial stretching. The obtained actual coefficients in strength calculations will allow to reveal the supplemented reserves of the bearing capacity of structures made of this material up to 22.4%.
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