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3 results on '"Aleksandr Karabtsov"'

1. Structural forming of soil composites using as a pavement subgrade strengthening

Author

Pavel Pankov, Dmitry Bespolitov, Nikolay Shavanov, Nataliya Konovalova, Maria Ushkova, Aleksandr Karabtsov, Irina Tarasenko, Valery Petukhov, Igor Panarin, Mikhail Zayakhanov, and Aleksandr Bituev

Subjects
Composite materials, Organic-inorganic materials, Technogenic soil, Stabilizing additive, Structure formation, Cryogenic treatment, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

The article substantiates the possibility of obtaining composite materials with improved functional properties to strengthen the subgrade, containing technogenic soil stabilized by an additive based on a gelling polymer. The introduction of technogenic soils into composites will not only reduce the consumption of expensive materials, but also solve a complex of acute environmental problems. Composite materials can be used in the construction of structural layers of road pavements, foundations of buildings and structures, sites for various purposes, for the prevention and elimination of defects in the foundations of engineering structures during their construction, reconstruction and repair, including in permafrost areas. Stabilized technogenic soils are more durable, frost-resistant and waterproof, which makes them applicable for creating impervious curtains in hydraulic structures and sealing storage facilities for hazardous substances. The cryogenic effect on a composite material allows one to vary its properties within a wide range and modify its macroporous structure. Studying the process of structure formation of the resulting organic-inorganic materials, consisting of macromolecules of high-molecular substances and inorganic inclusions that have undergone cryogenic treatment, will make it possible to specifically regulate their performance characteristics. The best values of strength characteristics were obtained for samples with a stabilizing additive concentration of 100 g/l. The resulting composite materials are hydrophobic, frost-resistant, characterized by a compressive strength of 2.3–6.5 MPa and a thermal conductivity of 0.19–0.20 W/(m·K). Data from differential scanning calorimetry and thermogravimetry and IR spectroscopy revealed that the binding of mineral particles by a stabilizing additive occurs due to the formation of organomineral complexes with the participation of clay minerals and the restructuring of hydration shells. SEM data indicate that crystallinity zones formed due to hydrogen bonds of hydroxyl groups of neighboring polymer chains can participate in the formation of the composite structure. An increase in the number of cryogenic treatment cycles promotes additional structuring and strengthening of the polymer phase due to the formation of additional nodes of the supramolecular network, ordering of crystallinity zones and the appearance of compacted areas in the structure. Computed X-ray tomography revealed an increase in the density of the composite upon drying, which helps to increase its strength characteristics. The structure of the sample is characterized by heterogeneity of the pore space, which is characterized by the presence of both fine-porous and large-porous regions, which determines its thermophysical properties.

Published
2024
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2. Sulfide inclusions in alkali basalt-associated garnet megacrysts shed light on the mysterious megacryst nature

Author

Anna Aseeva, Aleksandr Ignatyev, Aleksandr Karabtsov, Aleksey Ruslan, Anton Sinev, Tatyana Velivetskaya, Sergey Vysotskiy, and Maria Ushkova

Abstract

We have carefully studied an unusual sulfide-bearing garnet megacryst from the ever-surprising Cenozoic Shavaryn-Tsaram basaltic cone (Tariat Platou, Mongolia). Similar sulfide inclusions in minerals constituting mantle xenoliths and clinopyroxene megacrysts related to alkali basalts were already known (Peterson and Francis, 1977, Chaussidon et al, 1989, Ionov et al, 1992) but they have never been found in garnet megacrysts. Since these garnets are believed to be mantle-derived material, their sulfide inclusions provide information on the deep sulfur cycle.The sulfide-rich garnet megacryst from Shavaryn Tsaram pyroclastic strata is a chip of a large (up to 3 cm) cracked and partly quenched glassy crystal (fig. 1A, fig.1B) with melt pockets (Aseeva et al, 2021) inside (fig. 1C). Sulfide inclusions are primary, isometric, elongated, and orientated towards crystal growth with a distinctive arrangement (3D X-ray images, Skyscane, fig. 2A). Swarms of inclusions contour the growth planes typical for the deltoidal icositetrahedron (fig. 2B).Sulfide inclusions mainly consist of Ni-bearing pyrrhotite (1.66-2), scarce chalcopyrite (fig.3A and B), and rarely of pentlandite. Incompletely crystallized droplets of MSS (monosulfide solid solution) occur periodically as thin crystal pyrrhotite and pentlandite intergrowths (fig. 3C). These MSS inclusions are thought to be a product of the sulfide melt exsolution caused by undercooling (Chaudison et all, 1989).The multi-isotope sulfur composition of these sulfide inclusions has been studied to define whether the sulfur source is crustal or mantle-derived. Thus, their δ34S values account for 0.2-0.4‰, δ33S for 0.1-0.2‰, and Δ33S for 0.00-0.03‰, which is characteristic of mantle, meteoric, MORB, and volcanic settings. As for the host garnet, its oxygen isotope composition (Δ18О 5.4 to 5.8‰) also suggests the volcanic origin of these sulfides.Submicron surface analysis (Bruker Dimension Icon and Solver NT-MDT) reveals the linear-globular structure of garnet (fig. 4A). Being probable nuclei, nearly 1 μm globules compose layers of garnet. We assume that garnet crystal formed via epitaxial growth from the gas phase. Garnet megacryst linear structures consisting of globules differ significantly from the metamorphic garnet crystal lattice (fig. 4B). Sulfur redundancy causes sulfide droplets, immiscible with silicate material (fig. 4C), to gather and form bulbs on top of a growing crystal due to surface tension (fig. 4C). The following conclusions may be drawn: 1. Sulfide inclusions in alkali basalt-associated garnet megacrysts are primary. 2. Sulfides hosted in garnet are mantle-derived according to isotopic data. 3. Garnet megacryst formation was caused by epitaxial growth.

Published
2022
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