Quartz Aggregates Research Articles

A NEW APPROACH TO THE ACCELERATED METHOD FOR ASSESSING THE ALKALI REACTIVITY OF DOMESTIC AGGREGATES

In Poland, the prevailing protocols for examining the alkali reactivity of aggregates are based on indirect methodologies such as petrographic appraisal, in addition to direct methodologies including the measurement of expansion in mortar and concrete specimens containing the aggregate under investigation. The available research methods exhibit certain deficiencies, which have been mitigated under the experimental conditions delineated in the novel accelerated approach for ascertaining the reactivity of aggregates, otherwise known as the MCPT – Miniature Concrete Prism Test. The methodology of MCPT has the potential to become an alternative for the existing procedures of quality assessment for both fine and coarse aggregates. This work presents the assessment results of the alkaline reactivity of indigenous fine quartz aggregate, examined in accordance with the protocols established by the Polish General Directorate for National Roads and Motorways along together the novel, expedited MCPT methodology.

Interrogating an along-strike variation in the evolution and rheology of a large continental strike-slip fault zone

Along-strike variations in lithology, temperature, fluid activity, etc. can induce rheological changes in strike-slip faults that may be recorded by different fault rocks and fabrics. This article interrogates localized formation of granite-derived mylonite in a large strike-slip fault zone in which ultramylonite is the principle granite-derived fault rock to better understand this rock record of faulting. Microtextures show that rate-limiting deformation mechanisms in mylonite were dislocation creep in quartz and diffusion creep in very-fine-grained feldspar aggregates. Microtextures also show that mylonite formation is fully compatible with continuous viscous deformation whereas coeval ultramylonite along strike formed after whole-rock cataclasis at the brittle-viscous transition. Differential stresses determined from quartz aggregates in ultramylonites are 40–150% greater than stresses in mylonites. Hence, mylonites represent a local weak sector within this otherwise relatively strong fault zone. Mylonite formation is correlated with syndeformational chemical alteration as well as quartz microstructures and mineral assemblages indicating elevated deformation temperatures. Not all mylonite samples record significant chemical alteration. Therefore, mylonite formation likely records locally elevated temperatures. These results illustrate how a local shift in deformation conditions can affect the evolution and rheology of a large strike-slip fault zone, and how fault rocks record these processes.

Study on thermal crack characteristics of granite in Shandong Province, China under different temperatures and heating/cooling treatments

The qualitative and quantitative analysis of crack initiation characteristics, extended procedure, and crack network morphology of rock under different temperatures and heating/cooling paths was conducted in order to delve deeper into the mechanism of thermal cracking, and the analytical perspectives mainly include microstructure, thermodynamics, and mineral crystal properties. Research results indicate that 200–300 °C and 600 °C are two obvious mutation points of water-cooled samples, while air-cooled samples show mutation points around 600 °C. The initiation positions of thermal cracking under all temperature paths are relatively similar, with intergranular crack located between particles at the edge of the sample or intercrystalline cracks in the middle of feldspar or quartz aggregates. Slow heating and rapid cooling contribute to the complexity of the thermal crack network, and rapid heating can form larger sized thermal cracks. The process of thermal cracking can be divided into three stages: initiation of small cracks, joint development of main cracks and small cracks, and interconnection of cracks to form a network structure. The thermal cracking mechanism is attributed to differences in expansion and thermal conductivity among various crystals.

Evaluation of the effect of E-waste on the permeability properties of polymer concrete composites and their behavior in aggressive environments

The rapid increase in the number of electronic products worldwide, in terms of both variety and advanced technology, together with the decrease in costs, has led to the generation of a large amount of electronic waste (e-waste), which has significantly increased environmental pollution. This study was conducted to investigate the hypothesis that the adhesion of polymer binders and plastic origin e-waste will be more effective and stronger, and therefore have a positive effect on the permeability properties of polymer concrete and its behavior against aggressive solutions. For this purpose, quartz aggregates and gravel used as an aggregate in polymer concrete were replaced with 0%, 3%, 6%, 9%, 12% and 15% e-waste. In the study where unsaturated polyester resin was used as a binder, the changes in the permeability properties (capillary water absorption, rapid chloride permeability) of the e-waste polymer concrete and its behavior against aggressive solutions (acid and sulfate attacks) were evaluated after 7, 28 and 90 days. In addition, mechanical experiments were conducted and comparisons were made. After the control concrete, the highest compressive strengths were obtained from the polymer concrete specimens using 3% e-waste, measured as 59.05 MPa, 64.5 MPa and 73.05 MPa after 7, 28 and 90 days, respectively. The research showed that polymer concretes with capillary water absorption coefficient values close to zero after 90 days can be produced with using up to 9% e-waste. The use of e-waste as an aggregate in polymer concrete at 3%, 6% and 9% e-waste, in particular, produced concrete with a high resistance to acid and sulfate attacks. The hypothesis of the study was confirmed after extensive experiments.Graphical

Importance of grain boundary processes for plasticity in the quartz-dominated crust: Implications for flow laws

When H2O is present along grain boundaries, the deformation processes responsible for plasticity in silicate mineral aggregates can deviate from what may be conventionally expected. Although a necessary component of understanding crustal deformation processes, there is no theoretical framework that incorporates grain boundary processes into polycrystalline quartz rheology. To address this issue, we carried out high-pressure and high-temperature deformation experiments on fine-grained quartz aggregates. Our study illustrates that grain boundary migration (GBM) through dissolution-precipitation (in the presence of an aqueous fluid) and grain boundary sliding (GBS) may act as accommodation mechanisms to prevent hardening from dislocation glide. GBM and GBS can relax incompatibilities resulting from an inadequate number of independent slip systems, plastic anisotropy between neighbouring grains, and non-planar grain boundaries together with grain boundary junctions. As demonstrated earlier in the literature, GBM may act as a recrystallization mechanism counteracting hardening, but also is a potential mechanism that allow H2O to enter in the quartz crystal (hydrolization) at the experimental time-scale. The above serial processes occur over a range of more than two orders of magnitude in grain size (∼3 to 200 μm) and explain a grain-size-insensitive stress exponent (n = 2) and low activation energy (Q = 110 kJ/mol). In the absence of a switch to grain size sensitive deformation mechanisms induced by grain size reduction, our results imply that only a modest weakening (∼5 times the strength of the protolith) is needed (or possible) to localize shear zones in the Earth's crust.

Microtextural evidence for the recrystallization of opal-A to quartz in epithermal veins: A case study from the McLaughlin deposit, California

High-grade ores in low-sulfidation epithermal deposits commonly consist of banded veins containing quartz as the most abundant gangue mineral. Previous studies suggested that at least some of the quartz has formed as a product of recrystallization from a noncrystalline silica precursor. Detailed petrographic studies confirm that high-grade veins from the <2.2 Ma McLaughlin deposit in California were originally entirely composed of opal-AG. The noncrystalline silica is isotropic in crossed-polarized light and consists of compacted microspheres that are up to several micrometers in size. In many bands of the high-grade veins, the thermodynamically unstable opal-AG has matured to quartz. The recrystallization of the noncrystalline silica resulted in the development of quartz and ore textures that mask the original conditions of vein formation. Incipient recrystallization of the opal-AG caused the formation of lepispheres consisting of opal-CT as well as the development of concentrically banded silica spheres. Continued maturation led to the growth of elongated quartz crystals or complexly shaped quartz aggregates in the cores of the concentrically banded silica spheres. Amalgamation of quartz crystals caused the development of mosaic quartz or flamboyant quartz. Ripening produced large prismatic quartz crystals, which are characterized by zones of feathery appearance. Fluid inclusions within the quartz formed through recrystallization are typically highly irregular in shape and show inconsistent liquid-to-vapor volumetric proportions, but assemblages with consistent ratios are also present. Bands rich in fluid inclusions occurring along former recrystallization fronts in prismatic quartz crystals resemble growth zones in zonal quartz. Recrystallization of the silica matrix resulted in grain coarsening of the ore minerals and encapsulation of ore minerals by quartz. In areas where recrystallization of the noncrystalline silica proceeded to completeness, the quartz textures could be easily misinterpreted to indicate that quartz growth occurred in open space with the ore minerals infilling vug spaces. Correct recognition of recrystallization textures has significant implications for paragenetic investigations on vein material from epithermal deposits as well as the design of fluid inclusion studies.

К вопросу о возрасте джежимской свиты Южного Тимана

We have described jasper pebbles from gravelites of the Dzhezhim formation on the Zhezhimparma uplift in the Southern Timan. The chip has a zonal structure. The central part is composed of devitrified volcanic glass and is surrounded by the rocks with an oolitic and crustified structure, composed of hematite-pigmented microgranular hexagonal quartz aggregates. We made a conclusion that one of the sources of the detrital material was rocks of timanide (preuralide) orogen, which final collision stage was Late Vendian by the age.

Dating mortars and bricks of Santalla de Bóveda Monument (Lugo, NW Spain)

Santalla de Bóveda Monument (Lugo, NW Spain) is a small semi-buried building, under the Bóveda parish church, built in the 18th century, with an apsidal quadrangular floor plan, which was divided into three naves, a small vaulted apse and a rectangular floor plan vaulted, where paintings depicting birds and plant elements have been well preserved. The monument has aroused great interest since its discovery, but its chronology and functionality has always been the subject of controversy. Several hypotheses have suggested that the monument was built in the Roman period and some others around the 5h, 8th or 9th century AD. However, any direct evidence or absolute age has been provided until today. The stratigraphic analysis of the building suggests five constructive phases. Bricks and mortars of all phases were sampling to perform absolute dating techniques and to get a precise and accurate chronology. Radiocarbon dating of mortars and Optically Stimulated Luminescence (OSL) dating of bricks and mortars have been used to this purpose. A total of 34 samples were taken, being 20 used for luminescence (mortars and quartz aggregates) and 15 used for 14C ages (charcoal fragments of lime mortars). 5 brick samples were also dated by Thermoluminescence (TL). The obtained ages have allowed, for the first time, stablishing an accurate and precise chronology being the first phase assigned to the 4th Century AD. Alterations of the building and the vault paintings were performed in the early 7th century, while the construction of the second floor and occasional repairs were performed during the 10th-12th centuries.

The effect of photooxidation aging on the cohesion and interfacial adhesion behavior of epoxy asphalt with a composite acidic curing system based on molecular simulation

AbstractThis paper investigated the cross‐linking network structure of epoxy asphalt (EA) with the different ratio of composite curing agents, and further determined the effect of photooxidation aging on the tensile and interfacial adhesion behavior of EA with different cross‐linking network structures through molecular simulation. Based on the molecular models of EA and the interface model between EA and aggregate, the crosslinking network structural characteristics and tensile mechanical behavior were determined. The interfacial adhesion behavior and the mechanization were further studied. The results indicate that 20‐EA and 6‐EA have an epoxy resin cross‐linked network with uniform pore structure and phase distribution. 2‐EA showed a denser cross‐linking network and uneven aggregation phenomenon. Photooxidative aging alleviated the aggregation phenomenon. A dense cross‐linking network improved the tensile strength and the ability of tensile performance to resist photooxidation aging. The interface of EA‐quartz exhibited higher adhesion strength than EA‐calcite due to the closer distance and stronger nonbonding interactions between EA and quartz. The low anhydride content and photooxidation aging made EA approach to the aggregate interface, increasing nonbonding interaction and interfacial adhesion strength. In addition, quartz aggregates were more suitable for application in EA mixtures due to the higher interfacial adhesion strength and lower water sensitivity.

Origin of quartz and its implications for different phase fluids in lacustrine shales from the Qingshankou Formation, southern Songliao Basin, China

Quartz, an important mineral that occurs in lacustrine shales, can be of different types and origins. Yet, only few studies have investigated how quartz from different sources contribute to phase fluids, such as adsorbed and free fluids present within shale matrix pores. This study integrates various experimental techniques, including X-ray diffraction analysis, geochemical analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and high-frequency two-dimensional nuclear magnetic resonance analysis to quantitatively characterize the different phase fluids associated with various types of quartz occurring in the Qingshankou Formation shale. The characterization results indicated four distinct quartz types: silt-sized quartz, microcrystalline quartz linked with clay minerals, organism-skeletal quartz, and quartz aggregates comprising multiple crystals. The Fe–Al–Mn ternary diagram and SiO2 versus Zr scatter plot indicate that terrigenous clastic material is the primary source of SiO2 in shale quartz. Smectite-to-illite transition plays a pivotal role in authigenic quartz formation. Based on quartz concentration data obtained using major element analysis, we estimated the ranges of terrigenous clastic quartz, diagenetic quartz formed by the smectite-to-illite transition, and biogenic quartz concentrations to be from 55.49% to 92.03% (average 84.70%), 6.67%–20.30% (average 13.12%), and 0%–24.21% (average 2.17%), respectively. The solid organic matter in shale is affected by both terrigenous detrital quartz and authigenic quartz transformed from the clay in the basin. Authigenic quartz, formed by the smectite-to-illite transition, considerably enhances the development of solid organic matter in the Qingshankou Formation. By contrast, an abundance of terrigenous detrital quartz can lead to a dilution of the solid organic matter. Thus, this study provides the first direct evidence that along with a high value of bio-organic matter yield factor, the source of quartz plays a significant role in controlling organic matter abundance.

Fracturing and widening of grain boundary networks in quartz, plagioclase and olivine crystal aggregates during exhumation at low P-T conditions

Grain boundary networks of quartz, plagioclase and olivine crystal aggregates in metamorphic rocks have been investigated from the nanometer to the millimeter scale by polarized-light microscopy, SEM, and TEM. The studied materials show different grain sizes and experienced different retrograde P-T histories. The aggregates of quartz and plagioclase are traversed by networks of ∼90% continuously open boundaries with μm-sized cavities along the boundaries or at triple junctions. The boundaries are up to ∼500 nm wide open with typically parallel opposing grain faces. Olivine boundaries are filled with serpentine that does not replace olivine but fills the initially open space homogeneously and mostly with random orientation. For quartz there is no correlation between the crystallographic orientation of grain boundaries and their widths. Amongst all samples analyzed, a weak positive correlation exists between grain size and width of open grain boundaries. The application of measured volume changes and elasticity data from the literature to the cooling-decompression paths of the analyzed materials suggests that fracturing with subsequent widening of the grain boundaries starts at temperatures recognizably below the transition from crystal-plastic to brittle behavior of quartz, plagioclase and olivine but not only under surface conditions. The high amount of open boundaries causes an extensive permeability.

Evolution of H2O content in deforming quartz aggregates: An experimental study

Deformation experiments were carried out on pure quartzite samples (>99% quartz) with a grain size of ∼200 μm from Tana, Northern Norway. Deformation conditions were 900 °C, 0.1 wt% H2O added, strain rate ∼1 × 10−6 s−1 at variable confining pressures from 600 to 2000 MPa. Detailed FTIR measurements of H2O indicate that the H2O content in the grain boundary region is higher than that inside quartz grains. Hydrostatic treatment and deformation at the chosen temperature and pressure conditions lead to further H2O loss from grain interiors and H2O increase in the grain boundary region. Varying the confining pressure does not have an observable effect on the H2O transfer from grains to the grain boundary region. The 3585 cm−1 absorption band increases systematically with increasing confining pressure. As this band is associated with OH in dislocations, the increase may indicate an increased dislocation density with increasing pressure. The triplet of 3317, 3375 and 3438 cm−1 associated with Al-content in quartz increases in the grain boundary region indicating an exchange of H+ together with Al3+ for Si4+. The Al and H exchange suggest dissolution-precipitation processes in the grain boundary region facilitating the movement of the quartz grain boundaries (grain boundary migration). The H2O in the grain boundary region will be important for enhancing grain boundary migration and thus recrystallization processes during deformation.

Evidence of fluid-induced myrmekite formation after alkali-feldspar megacrysts: an example from a meta-porphyritic granitoid in Makrohar, Madhya Pradesh, India

Abstract A meta-porphyritic granitoid in the Makrohar Granulite Belt, Central India contains extensive myrmekite. This work evaluates the controls of fluid in relation to deformation and the formation of myrmekite all along the periphery of an alkali-feldspar megacryst. Two different myrmekite morphologies are present: (1) vermicular intergrowth of plagioclase (An38–39) and quartz (Myr1); and (2) polygonal aggregates of coarse plagioclase (An45–46) and quartz (Myr2). Petrographic features suggest that myrmekite Myr1 nucleates on alkali-feldspar and plagioclase porphyroclasts and the myrmekite front moved into the alkali feldspar by replacing it; and that myrmekite Myr2 and the secondary biotite which replaces plagioclase porphyroclasts and garnet form together. Deformation had a decisive role in forming the polygonal aggregates of Myr2, however field and microtextural features do not support any significant control of deformation during the formation of Myr1. Reaction modelling and a mass-balance calculation suggest that Ca and Na are added to, and K is removed from, the alkali feldspar during the myrmekite formation at nearly constant Si and Al. However, the secondary biotite-forming reaction, consumes K and releases Ca. Interpretation of the reaction textures in different isothermal–isobaric sections of μK2O–μCaO in the KCFASH system suggest that CaO and K2O moved in opposite directions for myrmekitisation and along their respective chemical potential gradients created between the sites of formation of myrmekite and secondary biotite. The feedback mechanism which operated between the two reaction sites was controlled by infiltration of brine-rich fluid in the meta-granitoid during a regional hydration event (550–600oC and 5–6 kbar). Volume reduction of ~10% during the formation Myr1 and Myr2 drew the brine-rich fluid towards the alkali feldspar and thus facilitated the process of myrmekite formation. Variation in the morphology of quartz in the myrmekite is attributed to the cooling of the complex.

Transient Creep of Quartz and Granulite at High Temperature Under Wet Conditions

AbstractTransient creep of crustal rocks is important to explain time‐dependent geological processes such as postseismic deformation following a large continental earthquake. While the steady‐state creep flow law parameters of quartz and feldspar, major minerals in the upper and lower crust, are well known, the physical mechanism behind transient creep and the corresponding flow law parameters are poorly understood. We quantify the flow law parameters for both quartz and granulite (mixture of plagioclase and pyroxene) under wet conditions with a nonlinear Burgers model using a Markov chain Monte Carlo (MCMC) method. Modeling results yield an activation energy of 70 ± 20 kJ/mol and a stress exponent of 2.0 ± 0.1 for transient creep of quartz aggregates. For granulite/feldspar, we find activation energies of 280 ± 30 and 220 ± 20 kJ/mol and stress exponents of 1.0 ± 0.2 and 0.9 ± 0.1 under mid (1050–1100°C) and high (1125–1150°C), temperature conditions, respectively. The stress exponents and activation energies of transient creep are consistently smaller than those of steady‐state creep for both quartz and granulite/feldspar. Combined with results for transient creep of olivine that were previously obtained (Masuti &amp; Barbot, 2021, https://doi.org/10.1186/s40623-021-01543-9), we suggest that the activation energies and stress exponents of transient creep are smaller than those of steady‐state creep for volumetrically important silicate minerals of the crust and upper mantle. Extrapolation of the estimated flow law parameters of granulite/feldspar to natural conditions suggests that transient creep may dominate during the postseismic period and lasts longer than previously thought.

Potential improvement of clinker sand in the mechanical high temperature and transport properties with GGBS-based prepacked geopolymer composite

In this study, a new generation prepacked geopolymer composite (PGC) material that can meet different needs was obtained by combining geopolymer concrete (GPC) and prepacked aggregate concrete (PAC) technology. In the production of PGC, 5-8 mm quartz aggregates were placed in molds and, geopolymer mortar was injected between these aggregates. Aluminosilicate based blast furnace slag (GBFS) was used as binding in geopolymer mortars; sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as alkali activator. In addition, clinker aggregate in different proportions was used as fine aggregate (0–4 mm) in the production of mortar. Within the scope of the study, the physical, mechanical, permeability and high temperature resistance properties of PGC were investigated. The produced samples were cured at 30 and 60 °C for 6 and 8 hours. Hardened unit weights of PGC vary between 2342 and 2539 kg/m3, and sorptivity values vary between 0 and 0.04 kg/m2.min0.5. While the increase in curing temperature and curing time increases the hardened unit weight values, it decreased permeability values. While the increase of clinker aggregate in the mortar phase does not change the hardened unit weight, it significantly reduced permeability. When the PGC samples are cured at 30 °C, the compressive strengths are 20.38–39.03 MPa; when curing at 60 °C, the compressive strengths are 35.21–57.04 MPa. Flexural strengths, 2.35–6.96 MPa with 30 °C cure, achieved 4.27–9.93 MPa results with 60 °C curing. Increasing the curing time and curing temperature significantly increased the compressive and flexural strengths. The increase in the amount of clinker aggregate added to the mortar phase decreased the strength values. While the compressive strength values of PGC mixtures do not fall below 15 MPa after being exposed to 300 °C high temperature; after the application of 600 °C high temperature, it lost up to 70% of its strength. Increasing the curing time and curing temperature, increased the high temperature resistance. The increase in the amount of clinker aggregate in the mixtures, decreased the strength loss rate.

Contamination and dissolution-crystallisation textures of granite relics in xenolith-rich composite Coral Island Dike of the Paraná-Etendeka Magmatic Province

The Coral Island Xenolithic Dike (CIXD) is a composite intrusion with mafic borders and apophyses (Pulse 1) and a felsic centre with a high amount of granitic xenoliths and xenocrysts (Pulse 2). The xenoliths, most abundant in the dike core, are granitic and vary from millimetres up to 1.5 m in size. The xenolithic composite dike is low-TiO2 Gramado-type. The xenoliths are concentrated in the dacitic core, partially molten and accompanied by relict feldspar and partly resorbed quartz xenocrysts. Field, petrographic and geochemical data attest to contamination by assimilation processes in the central part. Flowage differentiation (Bagnold Effect) has concentrated the large xenoliths in the dacitic core. Evidence of xenolith partial melting comprises spherulitic K-feldspar/albite intergrowths and polycrystalline quartz aggregates. Coronas around the pyroxenes in the dacite and the absence of mesostasis in the dike magmas attest to supercooling of the system at shallow-level conditions. The ascent of the central part of the dike (dacite + xenoliths + relict xenocrysts) was only possible due to the proximity of the magma reservoir to the emplacement site and chamber recharging with hot basic magma input (Pulse 1) that prevents the system from cooling and crystallising.

Siliceous Origin of the Cambrian Qiongzhusi Formation Shale in the Middle Part of the Upper Yangtze Platform: Significance of Organic Matter Enrichment.

The early Cambrian Qiongzhusi Formation shale is rich in organic matter and is a high-quality marine Source rock. However, the origin of Qiongzhusi Formation siliceous rocks is unknown, and the role of siliceous rocks in the process of organic matter enrichment or preservation is also lacking. This study combines thin section, scanning electron microscopy, SEM/EDS, major and trace element analysis, and N2 adsorption experiments to analyze and evaluate the shale of the Qiongzhusi Formation in the central region of the Sichuan Basin. The quartz types in the shale of the Qiongzhusi Formation are divided into four types, namely, bioclastic siliceous rocks, terrestrial detrital quartz, siliceous microcrystalline quartz particles, and microcrystalline quartz aggregates; at the same time, according to petrographic and geochemical parameters, the content of authigenic quartz in Qiongzhusi Formation shale decreases from top to bottom, and terrigenous detrital quartz tends to increase, and biogenic silicon accounts for the majority of authigenic quartz components; autogenous quartz has a positive impact on the pore structure of shale, providing sufficient pore space for the development of organic pores and protecting the internal pore network by forming intergranular pores as rigid frameworks. At the same time, it plays a crucial role in the enrichment and preservation of organic matter.

Age influence on compressive strength for concrete made with different types of aggregates after exposed to high temperatures

This study investigates the influence of concrete age and the type of coarse aggregate on compressive strength after exposure to high temperatures. Three coarse aggregates were used: crushed clay bricks as recycled aggregates, expanded glass as lightweight aggregates, and normal quartz aggregates. Specimens were initially cured in water for seven days, and then kept in laboratory conditions for different durations (28 days, 120 days, and 240 days). On the age of 120 and 240 days, specimens were exposed to high temperatures ranging from 200 °C to 1000 °C, and their residual compressive strength was determined.Results indicate that the compressive strength tests for the unheated specimens revealed an increase in strength with age, which can be attributed to the hydration of cement and the formation of a denser microstructure. The results of the residual compressive strength tests for concrete with quartz aggregates (M1-QZ) at 120 and 240 days showed a decline with increasing temperature and age. At 120 days, the strength ranged from 74.3% to 16.9%, and at 240 days, it ranged from 83.5% to 23.8%. Similarly, concrete with expanded glass aggregates (M2-EG) demonstrated decreased compressive strength with increasing temperature and age. The strength ranged from 94.3% to 8.6%, and 88.9% to 10.3% at 120 and 240 days, respectively. In contrast, concrete with crushed clay bricks (M3-CB) exhibited more favourable resistance to high temperatures, with a lower compressive strength reduction. The values ranged from 97.9% to 23.1% at 120 days and from 98.7% to 22.2% at 240 days. The reduced compressive strength after exposure to high temperatures can be attributed to the differences in thermal expansion and aggregates and the moisture loss.These findings demonstrate that the coarse aggregate type significantly influences the concrete's residual compressive strength after exposure to high temperatures.

Study of technological properties of the sample ethiopian iron ore of the arabian-nubian shield. Part 2. Microscopic analysis of ore samples with a thickness of +40.0+5.0 mm

As a result of the research, the mineral composition of the mineralogical and petrological varieties of material of the 10-20 mm and 20-40 mm size classes of the studied ore sample was specified. Transparent and polished sections of the above-mentioned granulometric samples were prepared. Microscopic examination was carried out using a transmitted and reflected light microscope «Carl Zeiss Jena NU-2 Microscope». A description of the discovered minerals was completed. It was found that the main ore minerals of the studied ore are dispersed hematite and hydrohematite, and their amount is about 54.0% of the total volume. Microscopic analysis also revealed hydrohematite spherulites, including in the intergranular space in quartz aggregates. It is shown that secondary ore minerals in the studied raw materials are goethite and hydrogoethite. Microscopic analysis showed their content at the level of 4.0 %. The color of goethite and hydrogethite, which are represented by iron hydroxides of yellow, brown, brown and black color and their form in the form of nodular aggregates, spherulites of crusts, and nest-like aggregates, is also determined. It was found that the main non-metallic mineral in the studied raw material is quartz, the content of which is on average 30 %. This mineral in the sample of the studied ore is characterized by a variety of morphological features and a wide range of grain sizes – from several micrometers to several centimeters. Microscopic examination of quartz showed that it is represented by xenomorphic grains with a complex nature of fusions with other minerals, rounded and acute-angled grains, chalcedony (agat) grains and thin-prismatic crystals. The presence of a secondary non-ore mineral, which has clay properties and is represented by kaolinite, is also shown. An additional study was carried out, in which chalcopyrite – an additional component of iron ore raw materials – was analyzed. The conducted microscopic studies made it possible to draw a conclusion about the mineral and petrological characteristics of the raw material. It is shown that the type of iron ore of the Arabian-Nubian shield is similar to ores of volcanic-sedimentary origin and brown iron ores

Morphology and Composition Changes in Fluid Inclusions from Quartz under Progressive Deformation: Case Study of a Vein System in the Western Kelyan-Irokinda Fold Zone (Western Transbaikalia)

Abstract —The behavior of fluids during plastic deformation is studied from the morphology and distribution of fluid inclusions in quartz grains of different microstructure types from a vein system controlled by thrusting and strike-slip faulting in the eastern Sayan–Baikal fold area. The analytical work includes electron backscatter diffraction (EBSD) for quartz microstructure and crystallography, as well as Linkam heating-and-freezing analysis and Raman spectroscopy for the composition of fluid inclusions. The studied fluid inclusions are of seven types that differ in morphology and position in the deformed quartz structure. A model is suggested to describe successive structural changes of quartz aggregates during dislocation sliding and subsequent creep-related recrystallization associated with redistribution of fluid. Fluid inclusions undergo qualitative and quantitative changes due to water leakage at all stages of plastic deformation. The changes occur by two main mechanisms: (i) mass transfer during dislocation sliding at medium temperatures and strain rates and (ii) diffusion creep at low strain rates and high temperatures. The contribution of creep increases gradually with temperature, which maintains the interaction of inclusions with migrating grain boundaries.