For development of the potential of nanosilica application in Portland cement concrete the effect in compressive strength Rcom increase was studied in the age from 1 to 360 d. Sol of hydrothermal nanosilica (HNS) solution produced by technology developed was used with SiO2 particles Brunauer-Emmett-Teller surface area of 500 m2/g. Concretes compositions were tested with liquid/binder ratio 0.5 and SiO2 doses of cement replacement 0.5, 1, 2, and 3 wt. com 1,7 /R com 28 and R com 28 /R com 360 are higher in modified concrete. The obtained results can be used to model the hardening and predict the strength of modified concrete at the age of 2, 4, and 10 y. Results of the thermogravimetry, X-ray diffraction, scanning electron microscopy and water absorption methods provided explanations of pozzolanic reaction effects on compressive strength, water impermeability, abrasion and frost resistance, impact viscosity and durability were discussed. The dependence of kec coefficient on SiO2 dose and concrete’s age was analyzed. Using the coefficient kec for different doses of SiO2 at the age of 28 d, the corresponding clinker’s savings coefficient (23.4

Hydrothermal nanosilica sol with specific surface area of SiO2 particles SBET 500 m2/g produced by technology developed in our previous researches was used in the testing of concrete compressive strength (kec, Delta Rcom = 14.8%-86.4%) with liquid/binder ratios (L/B) =0.50--0.52, nanosilica doses [SiO2] = 0.5-3.0 wt.%, curing ages 1-360 days and compressive (kec, Delta Rcom = 2%-108.8%) and tensile bending (kectb, Delta Rtb = 10-211%) strength of mortar with liquid-binder ratio L/B = 0.40, [SiO2] = 0.01-6.0 wt.%, ages 1-90 days. The efficiency coefficients kec and kectb based on the relative increase in mechanical strength and the dose of replacement of Portland cement with pozzolanic additive were introduced and compared with the coefficients based on the Bolomey's and Feret's models. The coefficients kec and kectb for concrete and mortar monotonically decreased with increasing of nanosilica dose. These dependencies can be approximated by power functions (kec, kectb) =A/[SiO2]n, A = 19-86, n = 0.4-0.76. The coefficients kec and kectb showed the tendency to decrease with increasing of curing time. The level of kec values for nanosilica (8-1-33) significantly exceeds the values for pozzolanic additives (0.1-0.5-1-2-4): condensed silica fume, metakaolin, fly ash, slag, volcanic glass and tuff. The correlation of kec coefficient with SBET in the wide range of values 0.6-560 m2/g for different nanosilica and pozzolanic additives and on L/B were analyzed.

We present the first magnetotelluric sounding (MTS) data acquired in the southern part of the Lena River delta which is a junction zone of the Siberian Craton and the Verkhoyansk fold-and-thrust belt, in the transition zone from the Eurasian Continent to the shelf of the Laptev Sea. The MTS data were used to construct a vertical section of the bulk electrical resistivity (ER) structure of the Earth’s crust down to a depth of 8 km. The upper high-resistivity layer (320–1000 Ohm m) corresponds to the permafrost rocks ranging in thickness from 1 km to 400 m under the channels of the Lena River. The underlying deformed Mesoproterozoic–Lower Triassic rocks can vary in composition, but they are poorly differentiated in ER values (110–240 Ohm m). We detected three low-resistivity anomalies (10–60 Ohm m) related to the fluid-saturated core and damage zones of active faults. A deep-lying high-resistivity anomaly (320–350 Ohm m) identified at the northeastern part of the section can correspond to the Lower Proterozoic or Archean metamorphic rocks.

—The Salair fold-thrust orogenic belt (Salair orogen, Salair) is located in the northwestern Altai–Sayan fold area within the Central Asian Orogenic Belt. The Salair orogen is an allochthon overriding the Kuznetsk Basin on a system of imbricate thrusts. The southern flank of the Salair thrust system is tectonically juxtaposed against the Gornaya Shoria terrane which differs markedly from Salair in its geological setting. The Salair and Gornaya Shoria terranes are separated by the Nenya-Chumysh Basin, a deep Mesozoic trough. The Salair orogen is composed of Cambrian–Early Ordovician island arc volcanic and sedimentary rocks, widespread garnet amphibolites and gneisses of the Angurep complex in its southern flank, and the Shalap subduction-related melange in the Alambai ophiolite suture. The southern Salair orogen and its junction with Gornaya Shoria have been imaged down to the lower crust by magnetotelluric (MT) soundings, which is an efficient tool for investigating the deep structure and tectonic history of orogenic areas. The MT surveys were performed at 25 stations on a 120 km long profile. MT data revealed an up to 70 km wide low-resistivity zone (a conductor) traceable till a depth of 20 km between the Salair and Gornaya Shoria terranes. The low-resistivity zone has a complex structure with its outer and interior boundaries dipping almost vertically. The conductor lies under several major geological structures: the Shalap melange, the Nenya-Chumysh Basin, and the NE trending Altai–Salair right-lateral strike-slip fault. The Altai–Salair fault, along which the Salair allochthon was displaced relative to Gorny Altai and Gornaya Shoria, joins the Salair system of imbricate thrusts. The Nenya-Chumysh Basin at the Salair–Gornaya Shoria junction is a deep trough having an asymmetric transversal profile with a steep western side and a shallower-dipping stepped eastern side. The southeastern flank of the basin is a wide area of thin sediments over the Paleozoic basement dipping gently in the northwestern direction. The revealed deep structure of the Nenya-Chumysh trough is consistent with its tectonic model implying an Early Cretaceous basin superposed over an early Jurassic pull-apart basin. Early Mesozoic motions on major faults is a regional-scale phenomenon known from many areas of southern West Siberia.

Received December 27,, 2022; revised August 10, 2023; accepted October 2, 2023Geophysical observations of the structure of glacial-permafrost rock formations (hereinafter referred to as GPRF), common in the Central Altai in the valleys of the Chuya, Dzhelo, Elangash and Akkol rivers, were carried out by way of electrical resistivity tomography using the multi-electrode electro-prospecting station “Skala-48”. The main objective of the research was to identify the features of the internal structure of GPRF basing on the data of electrical sounding and aerial photography. The application of the geophysical method made it possible to localize rock-ice cores within the GPRF. Analysis of the geoelectrical cross-sections allowed finding that the rock-ice cores were characterized by high values of specific electrical resistance (SER) – from 10 to 100 kOhm ⋅ m and more. The depths of occurrence of rock-ice material on the geoelectrical sections varied from 2 to 10 m, on the average. Using the data of the aerial photography carried out above the studied areas, three-dimensional geoelectric models and maps of the distribution of SER were built for different depths. When analyzing the three-dimensional model of the GPRF, it is clearly noticeable that the features of the nature of the SER distribution reflects the inhomogeneous distribution of ice within the rock-ice core of the GPRF. As a result of our studies performed by the method of electrical tomography and interpretation of a three-dimensional geoelectric model, it was estimated that thicknesses of the rock-ice material varied from 7 to 32 m, thawing niches were revealed and localized, and the potential volume of the rock-ice core was determined. Thus, the above mentioned geophysical and geomorphological studies in that the features of the internal structure of GPRF in key areas have been established. For each GPRF, the thicknesses, resistivity, and depth of occurrence of rock-ice cores were determined, and the dependence of the morphological structure of the GPRF surface on internal structure of them was analyzed. A preliminary assessment of water reserves in individual GPRF had also been made.

Studies have been carried out aimed at improving the corrosion resistance of concrete and its other characteristics for operation in harsh environmental conditions. The influence of a complex additive containing multilayer carbon nanotubes and hydrothermal SiO 2 nanoparticles on the durability of concrete has been determined. Experiments were carried out to study water tightness, frost resistance, water absorption, and power parameters of concrete (stress intensity factors). It has been established that the introduction of nanoparticles into concrete improves the microstructure of its cement matrix, which leads to a decrease in the penetration of chloride ions into concrete and to an increase in its water permeability.

The x-ray phase analysis method has been used to study the effects of small doses of hydrothermal SiO 2 nanoparticles and nanoparticles of multiwalled carbon nanotubes (MCNTs) on the structure of a Portland cement composite separately and in a combination at the age from 4 h to 28 days. It has been established that clinker minerals and Portlandite components do not differ significantly in nanomodified specimens compared to control specimens, which agrees with the thermogravimetrical data for the ages of 1 and 28 days. In the region of the angles 2θ = 5–12 degrees, structural differences were identified for the CSH gel in the nanomodified specimens: at the age of 1 day (24 h), there were CSH peaks (I) in the diffraction patterns of the modified specimens with Basel distances of 12.44–12.54 Å between the layers. At the age of 28 days, relatively higher peaks of a tobermorite-like structure were identified with a Basel distance reaching a maximum value of 14.54 Å in a specimen modified by a combination of SiO 2 and MCNT nanoparticles. The increase in the Basel distances corresponds to a reduction in the values of the Ca/Si ratio and an improvement in the ordering of the CSH-gel structure and agrees with the IR-spectroscopy data having shown the higher degree of polymerization of silicon–oxygen tetrahedrons in nanomodified specimens.

Результаты измерений методом магнитотеллурических зондирований (МТЗ) на Салаирском кряже вдоль профиля г.Тогучин -п.Маслянино 1 Федеральное государственное бюджетное учреждение науки Институт нефтегазовой геологии и геофизики им.А. А. Трофимука Сибирского отделения Российской академии наук, г.Новосибирск, Российская Федерация

—We consider the possibility of using circular polarizations, which make the field vector in a wave rotate clockwise or counterclockwise, as independent polarizations of the primary wave during magnetotelluric sounding (MTS). This approach has been proposed for the first time to search for possible manifestations of the Hall effect under natural conditions during MTS; in this case, if the effect is small, waves with circular polarization become normal modes in a horizontally layered medium located in the constant magnetic field of the Earth. Standard impedance relations are replaced by the corresponding apparent resistance impedances and curves for waves with circular polarization (mode). In the search for manifestations of the Hall effect during MTS, it becomes necessary to determine differences in the mode apparent resistivity curves due to the presence of lateral inhomogeneities of the medium. This study deals with the specific features of MTS in the case of representing the primary source field by circular polarization waves. Results of the theoretical analysis of mode impedances are demonstrated. Numerical simulation is used to investigate the differences in the mode impedances and curves depending on the nature of the distribution of lateral inhomogeneities in the medium. Mode apparent resistivity curves obtained by processing the experimental data of the MTS in Gorny Altai are presented. It is shown that, in comparison with standard curves, mode curves are subject to less distortion by lateral inhomogeneities of the medium owing to the specific features of distributions of the charges and currents excited by circular polarization waves in them.

Portland cement composites modified with hydrothermal SiO2 nanoparticles (0.01-3.0 wt.%) and basalt microfiber (1.5 wt.%) with W/C=0.4 were developed. At different doses of SiO2 nanoparticles aged 1-28 days in combination with the microfiber, the compressive strength F-com (up to 51.1 MPa, 1.5 times higher than the specimen without nanoparticles and microfiber) and flexural strength F-flex (up to 13.2 MPa, 3.4 times) after 28 days of aging were determined. In addition, the impact viscosity, the number of blows before the first fracture N-ff and before ultimate failure N-cd,N- impact coefficient N-iv=N-cd/N-ff (up to 30; 2.72 times), and specific energy of impact destruction (up to 199.4 kJ/m(2), 22.2 times) were calculated. Synergetic effects of the combined action of different scale modifiers on F-flex(28) (1.29 times) and on Ncd and E-im/S-c (1.95 times) were revealed. Statistical correlations with high R-2 values were obtained between the characteristics, (N-cd,N-ff)-(F-com(28),F-flex(28)) and (F-flex(1,7,28), Fcom1,7,28), (N-ff, N-cd, N-iv) and dose of SiO2 nanoparticles, which can used for the design of concrete structures and reduction of cement consumption. The mechanism of the strong synergetic effect of this combination can be explained by the increased volume fraction of the high density (HD) phase of the calcium silicate hydrates (CSH) gel with more packed nanogranules in a basic volume of cement matrix and interfacial transition zone (ITZ) and the increase in the shear stress of the CSH gel relative to the lateral microfiber surfaces inside the HD phase volume. (C) 2022 American Society of Civil Engineers.

Cement concretes modified with hydrothermal nanosilica and basalt microfiber were developed. The compressive strength F-com, flexural strength Fflex, and characteristics of impact viscosity were determined: the number of blows before the first fracture N-ff and before ultimate failure N-cd, the coefficient N-iv = N-cd/N-ff, and the specific energy of impact destruction E-im/S-c. The strong effect of SiO2 action and synergistic effect of the combined action of nanoparticles and microfiber on N-cd and E-im/S-c was revealed. Statistical correlations with high R-2 values were obtained between the characteristics of mechanical strength and impact viscosity at different doses of SiO2 nanoparticles. Correlations obtained can be used for reduction of the cross section of concrete structures and cement consumption. The mechanism of the strong synergistic effect of the combination is explained by the enlargement of the volume fraction of the high-density (HD) phase of calcium-silicate-hydrate (C-S-H) gel with more packed nanogranules and an increase in the shear stress of C-S-H gel relative to the lateral microfiber surfaces inside the HD-phase volume. The reduction of the coefficient of water filtration K-f and an increase in the frost resistance were achieved.

—The magnetotelluric sounding (MTS) method implemented on drifting ice floes in the Arctic is suitable for detection of 3D inhomogeneities in crustal conductivity while recording the transverse magnetic (TM) mode potential of the electromagnetic field. Highconductivity layers of seawater and sediments shield the underlying 3D inhomogeneity. Their presence virtually does not affect changes in the standard responses of the medium used in MTS but is quite noticeable in the characteristics of the TM mode. To register them, one can use a circular electric dipole (CED) located at the surface of an ice floe. During the drift, the electric field can be measured on the ice floe using electrodes in seawater. We propose to lower the magnetic sensors beneath the ice, in seawater, because ice deformations interfere with the magnetic-field component measurements. The coordinates of the observation station during MT soundings on the ice floe in the Arctic (similarly to earlier observations at the North Pole stations) can change significantly. To take into account the effect of horizontal movements of the drifting station, we propose to complement all the recorded time series with the coordinates of measurement points. We have developed a technique for processing such data to take into account nonplane-wave effects, which can occur in the Arctic because of the proximity of ionospheric current jets. We carry out the synchronization of all observations in the investigated area, using a model of spatial and temporal field variations and data accumulation. To test our approach, we use the synthetic experimental data for the model that considers the existence of seawater, sediment, resistive crust, crustal object, and underlying mantle. We determine the crustal 3D object parameters with account of the TM-mode potential distributions at the seawater surface restored from the synthetic experimental data obtained at the drifting station during the drift. We use the Nelder–Mead method for optimization of the object characteristics. The parameters of the object become highly similar to their test values if the trajectory of the drifting station passes through an object, covering it most fully.

The use of a combined additive containing low doses of SiO2 nanoparticles (NPs) and multilayer carbon nanotubes (MWNTs) made it possible to improve the technology of Portland cement concrete. To substantiate the mechanism of action of nanoparticles, various hypotheses were put forward, which, taken together, were confirmed by a set of methods.

The approach of numerical simulation of orthosilicic acid OSA polymerization and SiO2 nanoparticle formation in hydrothermal solution have been developed based on the model of the homogeneous stage of nucleation and the subsequent growth of particles. The influence of surface tension on the interface of SiO2–water, the rate of molecular deposition, and Zeldovich factor Z were evaluated. Temperature dependence on time, pH, initial OSA concentration, and ionic strength are the main parameters that determine the kinetics of colloid phase formation, the final average size of SiO2 nanoparticles, and the particle size distribution and its polydispersity index. The results of the numerical simulation were verified with experimental data on OSA polymerization and measurement of nanoparticles sizes using the method of dynamic light scattering in a wide range of temperatures of 20–180 °C, pH = 3–9, SiO2 content Ct of 300–1400 mg/kg, and ionic strength Is of 0.0001–0.42 mol/kg. The results obtained can be used in the technology of hydrothermal synthesis of sols, gels, and nanopowders to regulate the kinetics of OSA polymerization and SiO2 nanoparticle growth, particle size distribution, morphology, and structure of products.

Tests were carried out on various nanoconcrete matrices and with different dispersed reinforcement fabric: carbon nanotubes, basalt fiber (polymer, 3 types of steel, and their combinations). It has been established that the value of the stress intensity factor KIIC in the case of normal separation increases most with steel fiber (up to 400%). Polymer fiber exerted the least effect on crack resistance - up to 40%. The influence of dispersed reinforcement on the stress intensity factor in the case of normal separation depends on the type of concrete matrix, on the material of fiber fabric, and on the quantity of the latter. As a result of the tests, the values of KIIC have been obtained for various dispersed-reinforced nanoconcretes, differing in the compressive strengths of the nanoconcrete matrix and in polyreinforcement with dispersed fabric at different structural levels. It has been established that dispersed reinforcement has a significant effect on increasing the crack resistance of the material. Increasing the value of KIIC relative to nonreinforced nanoconcrete was from 74 to 150% with steel wire fiber, from 29 to 129% with steel fiber from sheet, from 14 to 131% with polymer fiber, and from 22 to 124% with polyreinforced material.

The influence of hydrothermal small doses of SiO 2 nanoparticles (NPs) and multiwalled carbon nanotubes (MCNTs) separately and combined with adding a polycarboxylate superplasticizer (SP) at the water–cement ratio W/C = 0.21 has been studied by the IR-spectroscopy method. From the shift of the frequency of absorption of silicon–oxygen tetrahedrons SiO 4 to the region of reciprocal electromagnetic-radiation (EMR) wavelengths 900–1100 cm –1 , it has been established that the nanoparticles added increase their kinetics and the degree of their polycondensation. The influence on the degree of polycondensation of silicon–oxygen tetrahedrons was more significant than on the rate of hydration of clinker minerals and the gross amounts of hydration products of cement. The effect of influence on the kinetics and the degree of polycondensation of silicon–oxygen tetrahedrons depended on the chemical composition of the added nanoparticles (SiO 2 , MCNTs, and SiO + MCNTs) and on the age of hardening of the cement composite: it was more pronounced at the age of 28 days than at the age of 1 day for the combination of nanoparticles (SiO 2 + MCNTs) and was absent at the age of 4 h. Increase in the dehree of polycondensation of silicon–oxygen tetrahedrons corresponds to the rise in the crystallinity of a CSH gel and to the increase in the volume density of packing of nanogranules of the gel, and also determines the increment in the mechanical characteristics of the cement composite.