Panarin I.I.

Head of Department, Far Eastern Federal University, Department of Management of the Chief of Engineering Troops, Russia

Injection mortars based on composite cements for soil fixation

https://doi.org/10.58224/2618-7183-2023-6-4-15-29
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
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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