Fine Quartz Sand Research Articles

Optimization of UHPC based on reactive powder concrete: Box-Behnken Design, analysis of variance, components interaction effects and sensitivity analysis

The primary factors in reactive powder concrete mix design include the water-to-cement ratio, sand-to-cement ratio, and the substitution of silica sand with proper materials. Addressing the inherent behavioral sensitivity of reactive powder concrete to variations in these factors is critical. Accordingly, this research utilized the Box-Behnken Design to meticulously plan and execute experiments, aiming to explore the combined effects and interactions of these main factors on its properties. Results show that the sensitivity of reactive powder concrete to changes in the sand-to-cement ratio and silica sand substitution generally has a more pronounced impact on both compressive and flexural strengths compared to the water-to-cement ratio. Especially in specimens containing fine calcium carbonate, the substitution ratio notably influenced the flexural behavior, whereas, in specimens with fine quartz sand, the water-to-cement ratio’s impact on flexural strength surpassed that of the substitution after the sand-to-cement ratio. The more critical interactions occurred between the sand-to-cement ratio and the silica sand substitution ratio than the substitution ratio and water-to-cement, which were influenced by the choice of substitute materials. Also, scrutiny studies on the microstructure of specimens further demonstrated that while the use of fine calcium carbonate enhances the formation of CH within the microstructure, potentially weakening this concrete, it considerably benefits the flexural strength. Conversely, using fine quartz sand fosters a more significant formation of C-S-H gel, which beneficially influences the compressive and tensile strengths of the concrete.

Class B60-B80 cement concretes using crushed gravel from the Kama field

The results of a study of the quality of crushed stone from gravel of fr. 5–20 mm and screening of crushing of fr. 0–5 mm of the Kama field were presented and an analysis of their compliance with the requirements of regulatory documents was carried out. The characteristics of the crushing products were determined: grain composition, content of crushed grains; amount of lamellar (flaky) and needle-like shape, presence of dust-like and clay particles, crushed stone crushability during compression in a cylinder, screening fineness modulus and content of reaction silica in crushed stone and screening. Compositions of high-strength concretes of class B60–B80 were developed, in which fine quartz sand was used to enrich the crushing screening, carbonate mineral powder of MP-1 grade and microsilica (MK-85) as a filler, and polycarboxylate superplasticizer Polyplast PK as a water-reducing additive. Optimal compositions were obtained with the following cement consumption: for concrete B60 with a compression strength of 78 MPa, cement consumption was 466 kg/m3, for class B70 with a strength of 91 MPa – 483 kg/m3 and for B80 with a strength of 104 MPa – 503 kg/m3. At the same time, concrete mixtures were characterized by a cone settlement of 25–27 cm.

Геохимическая характеристика озера Чваниха, памятника природы Кировской области

The article presents characteristics of the abiotic components (water and bottom sediments) of the karst Lake Chvanikha. The lake is located in the Nolinsky district of the Kirov region and has the status of the hydrological natural monument of regional significance. The results are based on precision analytic data (obtained by ICP-MS, X-ray fluorescence analysis, chemical methods, photometry, etc.) and on thermodynamic calculations (Visual-MINTEQ. ver. 3.1). The composition of the waters indirectly indicates to the development of carbonate karst (mainly the dissolution of dolomite) in the upper rock strata at the base of the lake basin and to the presence of minor gypsum interlayers at depth. The concentrations of dissolved forms of trace elements do not exceed the MPCs of harmful substances in the waters of fishery basins and generally corresponds to the average contents in the rivers of the world. The base forms of trace elements in water are their free ions (for Sr, Ba, Fe, Mn, Zn, Ni, Co, Cd) and carbonate complexes (for Pb and Cu). The bottom sediments are represented of fine quartz sands, which overlap the karst rocks. In the absence of a significant technogenic impact, the poor grade of sand’s ferruginization determines low contents of potential pollutants (Cu, Zn, Pb, Cd, As, Mo, Ni, Cr, V), typical for quartz sands.

Crack development and fracture performance of Recycled Powder Engineered Cementitious Composites (ECC): Experimental investigation

In this paper, recycled concrete powder (RCP) and recycled brick powder (RBP), with particle sizes ranging from 10 to 130 μm, are used to completely replace the fine aggregate quartz sand at a ratio of 1:1. On this basis, recycled glass powder (RGP), with a discussed particle sizes range of 38–300 μm, is used to partially substitute the cementitious materials. Polyethylene (PE) fibers are used as the reinforcement in the Engineered Cementitious Composites (ECC). Using the particle size range and substitution rate of RGP as variables, the crack development, crack mouth opening displacement (CMOD), fracture toughness and fracture energy of Recycled glass powder ECC (RGP-ECC) were discussed through a three-point bending experiment on a single-edge notch beam. A relatively comprehensive evaluation was made on the fracture performance and behavior of recycled ECC, and a suitable mix ratio of recycled powder ECC was given. The results show that the addition of various recycled powders will not affect the multi-slit cracking behavior of ECC, and the cracks can still spread densely, giving the specimen greater deformation capacity and CMOD. The total substitution of fine aggregate by RCP and RBP has a positive impact on the fracture toughness KICini, KICun and fracture energy (GF), but the addition of RGP has some minor negative effects. Among the particle size range and substitution rate of RGP, the influence of substitution rate is more obvious, and the fracture performance will show a downward trend after growth as the substitution rate increases. Choosing the appropriate RGP substitution rate and particle size range can maximize the recycling of construction waste while ensuring fracture performance.

Development of low-cost engineered cementitious composites using Yellow River silt and unoiled PVA fiber

One of the main problems for restricting the extensive practical application of Engineered Cementitious Composite (ECC) is its expensive price due to the incorporation of high-price fine quartz sand and polyvinyl alcohol (PVA) fibers. To address this defect, the replacement with solid waste fine aggregate and locally produced PVA fiber has been proved to be a good choice. This work aims to develop low-cost green ECC using Yellow River silt as fine aggregate and locally produced unoiled PVA fiber. The effects of water-binder ratio, sand-binder ratio, and PVA fiber content on the mechanical characteristics of as-prepared ECC were evaluated by a comparative experiment. It has been indicated that the mechanical characteristics of as-prepared low-cost ECC are significantly affected by water-binder ratio, sand-binder ratio, and PVA fiber content. As the water-binder ratio rises, the tensile ductility of as-prepared low-cost ECC gradually increases, but the tensile strength, compressive strength, and flexural strength all decrease. The compressive strength and flexural strength exhibit a positive correlation with the sand-binder ratio, albeit with a minimal impact. Too low or high sand-binder ratio leads to a decrease in strain-hardening ability. Moreover, the as-prepared ECC exhibits a comparatively reduced tensile strain capacity when using locally produced unoiled PVA fiber as opposed to imported oiled PVA fiber. Finally, the environmental impact and economic benefits of the as-prepared low-cost ECC and Typical ECC are compared. The as-prepared low-cost ECC has good strain-hardening ability and low cost, indicating a potential application in real engineering.

Performance enhancement of engineered cementitious composite through tailoring recycled iron sand

Engineered cementitious composite (ECC) possesses predominant tensile properties while a relatively low modulus of elasticity (MOE) due to the low sand-to-binder ratio and fine quartz sand (QS, QS-ECC). Further, the excessive consumption of QS in concrete industry has imposed a serious challenge to natural resource preservation. Iron sand (IS), a by-product of the iron industry with high particle modulus, could be a potential alternative in developing ECC (IS-ECC). This research focused on recycling IS as fine aggregate to develop a sustainable ECC with high mechanical performance, especially high MOE. The influences of water-to-binder ratio, sand-to-binder ratio, and IS particle size were systematically investigated. The results indicated that all the IS-ECC demonstrated robust tensile performance with the tensile strength and strain capacity over 5 MPa and 5%, respectively. Compared with the QS-ECC, a comparable or even superior compressive strength was achieved by all the IS-ECC. Impressively, the MOE of IS-ECC with 20–40 and 40–80 mesh of IS particles exhibited 68% and 60% higher than that of QS-ECC, respectively. SEM observations well reflected the macroscopic tensile performances. The cost and environmental effect analysis revealed the sustainability of IS-ECC. This research provides the groundwork for promoting the utilization of IS in developing high performance ECC material.

Reinforcement of Different Sands by Low-pH Bio-Mineralization.

Different sands have significant influences on MICP reinforcement effects. Using calcium carbonate production and bioflocculation lag period as evaluation criteria, this study investigates the optimal theoretical pH values of bacterial solutions with different concentrations. We reinforced four different sands using MICP at the optimal theoretical pH, and based on permeability, moisture retention, raindrop erosion, wind erosion, penetration, and SEM tests, the influence of sand properties on low-pH MICP reinforcement was analyzed and the low-pH MICP mechanism was revealed. The results indicate the following: (1) The optimal theoretical pH values for bacterial solutions with concentrations of 0.67 × 108 cells/mL, 3 × 108 cells/mL, and 10 × 108 cells/mL are 4.5, 3, and 4, respectively. (2) With 0.67 × 108, 3 × 108, and 10 × 108 cells/mL bacterial solutions, the strength of tailings sand containing calcium salt was 21.15%, 44.42%, and 13.61% higher than that of quartz sand, respectively. The effective reinforcement depth of alkaline reclaimed sand was 10, 8, and 6 mm lower than that of neutral calcareous sand, respectively. The strength of fine tailings sand was 70.41%, 58.04%, and 22.6% higher than that of coarse reclaimed sand. The effective reinforcement depth of fine quartz sand was 6, 4, and 4 mm lower than that of coarse calcareous sand. (3) Low pH temporarily suppresses urease activity, delaying calcium carbonate flocculation and enhancing reinforcement uniformity. To achieve optimal reinforcement effects, adjusting the actual optimal pH values of bacterial solution based on sand properties is essential in engineering applications.

Impact of prolonged heating on the color and crystallinity of bone

Duration of an anthropogenic fire event is one aspect of fire use and maintenance that is linked to combustion feature function but has low archaeological visibility. In this study, we describe the transformations to fresh, modern cortical bone with prolonged exposure to heat in order to evaluate the utility of archaeological bone for the recognition of long duration thermal alteration. Cores of bovid cortical bone were heated exposed to air at 300, 550, and 750 °C in a sequence of experimental trials in a Nabertherm muffle furnace for periods of 10 minutes, 9 hours, and 48 hours, plus an extensive cooling period on heat retaining sediments (gravel or gravel compacted with fine quartz sand) to mirror the smoldering and extinguishing of actualistic fires. After heating, bone cores were analyzed with a color tool, Fourier-transform infrared spectroscopy, and X-ray diffraction to evaluate changes in structure, composition, and crystallinity of bioapatite as a function of different temperature thresholds and time. Results indicate that prolonged heating in air induces specific structural and chemical changes in bone compared to shorter duration burned counterparts. Coloration changes also demonstrate that white coloration, a primary characteristic utilized by zooarchaeologists to record information about burning intensity, is not an exclusive indicator of calcination at moderate to high temperatures but may also result from long duration exposures at low temperatures.

ОСОБЕННОСТИ СТРУКТУРООБРАЗОВАНИЯ КОМПОЗИЦИОННЫХ ГИПСОВЫХ ВЯЖУЩИХ С КОМПЛЕКСОМ МИНЕРАЛЬНЫХ И ОРГАНИЧЕСКИХ ДОБАВОК

For the dynamically developing low-rise construction industry, there is a growing need to expand the range of building materials, including fast-hardening types of binders. Composite gypsum binders are effective, including a carefully selected mixture of gypsum binder, Portland cement and active mineral additives. Materials based on them harden quickly and gain the required strength. An increase in the performance characteristics of this type of binders is achieved when mineral and chemical additives are used in a complex. This helps to regulate the processes of their structure formation and hardening, depending on the activity of the components, changes in water demand, as well as the peptizing, adsorption and air-entrapping effects of chemical additives. The article presents the results of a study of the effect of chemical additives – superplasticizers MARF SU 84, MELFLUX 5581 F and the retarder of the setting time of PlastRetard PE – on the physico-mechanical properties of a hardened composite gypsum binder, including gypsum binder, Portland cement and a complex of mineral components (fine quartz sand, metacaolin VMK-45, limestone dust). The issues of management of its structuring processes are considered. It has been established that finely dispersed mineral additives from quartz sand, VMK-45 metacaolin and limestone dust are effective components for the production of composite gypsum binders. The developed complex chemical additives MARFSU 84 (0.1%)+PlastRetard PE (0.08%) and MELFLUX 5581 F (0.1%)+ PlastRetard PE (0.08%) can significantly slow down the beginning and end of setting of gypsum cement mixtures up to 45...48 min and increase the compressive strength of the hardened KGV after 28 days by 1.5 ...1.6 times (up to 18.3...20.4 MPa), respectively.

ВЛИЯНИЕ ГРАНУЛОМЕТРИЧЕСКОГО СОСТАВА КОМПОЗИЦИОННОГО ГИПСОВОГО ВЯЖУЩЕГО НА ЕГО СВОЙСТВА

The primary task of technologists-designers is to optimize the structure and properties of building composite materials. Its achievement allows simultaneously increasing their efficiency, reliability and durability. The article presents the results of determining the granulometric composition of a composite gypsum binder (CGB) by computational and experimental modeling using the known equations of "ideal" curves. Due to the fact that when designing the binder composition, one of the main tasks is to optimize its structure at the micro level with finding the best ratios sizes and quantitative content of particles in the hardening system to create a dense packing, in the work a comparison is made of the granulometric compositions of 3, 4 and 5-component KGV. It has been established that the developed 5-component composition of KGV, including (% by weight): 68 % gypsum binder (G5B-II - 70% and GVVS-16 – 30 %), 10 % Portland cement, 20% fine quartz sand, 0.5 % metakaolin VMK-45 and 1.5% limestone dust, in terms of the ratio of components and their granulometric composition, deviates from that calculated using a computer program using the equations of the "optimal" Funk-Dinger curve by 15.3 %, which causes a denser packing of its particles with an increase in average density, strength indicators and softening coefficient even with a decrease in the content of gypsum binder

Development of high-volume recycled glass ultra-high-performance concrete with high C3A cement

Ultra-high-performance concrete (UHPC) is a special cementitious composite material with outstanding qualities like compressive strength greater than 120 MPa, and outstanding durability in comparison to other types of concrete. However, its production implies a large carbon footprint and significant consumption of natural resources such as quartz powder and fine quartz sand, both classified as carcinogenic to humans by the International Agency for Research on Cancer. This study produced a UHPC paste created with greener pozzolans and aggregates compared to current UHPC mixture proportions. In this regard, quartz powder and fine quartz sand were replaced by two different sizes of recycled glass powder. Furthermore, reducing the cement dosage was a goal in optimizing the UHPC mixture. This total replacement of the aggregate and reduction of the cement reduces the carbon footprint and the costs of the final material in two different ways: firstly, by decreasing the use of natural resources to produce quartz powder and sand, and secondly, by using waste material that otherwise would occupy landfill space. To reproduce the findings of this paper in developing countries with limited-quality cement, high C3A locally available cement is used in this research. The latter represents a significant challenge in the production of UHPC. Statistical methodologies such as center composite design and multiobjective optimization were undertaken to develop an efficient, healthy, safe, and environmentally friendly mixture design that meets the ASTM strength criteria for UHPC while maintaining the lowest cement content and the highest waste material dosage. The results showed that the fact that all the ground recycled glass particles have a size of less than 1 mm is not a sufficient condition to avoid the harmful alkali-silica reaction. In addition, it was observed that the high C3A content of the locally available cement had a slight positive effect on the 1-day compressive strength but a significant negative effect on the 28-day compressive strength of the UHPC. Finally, the present investigation demonstrated the feasibility of producing a UHPC that, using a local cement with almost 10% C3A, met the threshold criteria with a large volume use of recycled glass powder representing more than fifty percent by weight of total concrete.

Use of tactile sensors for horizontal stress measurements on a large calibration chamber

Large flexible calibration chambers (CCs) to evaluate and develop interpretation methods for cone penetration tests (CPTs) in cohesionless soils have been used since the late 1960s. Nevertheless, only average boundary stress values are known in almost all tests already performed. Tactile pressure sensors (TPS) represent a useful tool to assess the stress distribution in an area under loading and have been applied in some geotechnical studies. This study presents the results of CPTs carried out on a large flexible CC in a very loose and a medium-dense fine quartz sand. TPS were placed on the walls of the CC, allowing the measurement of horizontal stresses and their spatial distribution in all test phases: sample formation, lateral and cavity cell filling, piston filling, sample stressing and CPT. In particular, TPS were able to measure the horizontal stresses before the cavity and lateral cell filling – that is, when no information is available about the horizontal stresses in regular tests. The measurements contribute to the discussion on the influence of the CC boundaries on the test results. The results encourage the use of TPS on a more routine basis in large flexible CC testing.

An Investigation of the Ground Walnut Shells’ Addition Effect on the Properties of the Fly Ash-Based Geopolymer

The development of geopolymers is in line with the requirements of sustainable development. Creating a new type of material from various industrial and bio-based wastes and by-products can lead to reduced energy consumption, reduced waste generation, reduced global CO2 emissions, as well as reduced resource extraction of natural resources. In this study, geopolymer composites based on class F fly ash with the addition of fine quartz sand and ground walnut shells used as a substitute for sand were examined. The study focused on investigating the effects of different weight percentages of ground walnut shells and quartz sand on the density and strength properties, including compressive and flexural strength, thermal conductivity, efflorescence formation, and water absorption of the fly ash-based geopolymer composites. The microstructure of the studied geopolymers was also analyzed using a scanning electron microscope (SEM). It was observed that the addition of ground walnut shells contributes to the decrease in density and mechanical properties, increase in absorption properties, and decrease in porosity of fly ash-based geopolymers. Furthermore, the addition of ground walnut shells allows for a significant reduction in efflorescence on the surface of the tested geopolymer composites. Moreover, partial or complete replacement of sand by ground walnut shells in geopolymer composites based on fly ash allows for a significant reduction in their thermal conductivity, which makes it possible to use these composites as insulation materials.

Using a simplified technology to make an alkaline binder from silica additives

Introduction. The global expertise in the industry-scale application of alkaline composites in construction and their unique properties have proven strong prospects for and the relevance of a clinker-free technology and its development. The elaboration of alkaline-activated formulas for binders, containing fine powders of the aluminosilicate origin, allows making new efficient high quality products. New composite construction materials contain alkaline solutions of sodium silicate, although the large-scale application of this technology will require an alternative sealant.
 Materials and methods. The paper presents a method for the accelerated preparation of an alkaline-silicate sodium binder composed of a 40 % solution of caustic soda, having density of 1,430 kg/m3 and ultrafine powders featuring high silica content extracted from quartz glass sands and volcanic tuff. The resulting liquid-glass binder was studied using a special method to determine the concentration of SiO2 that reacted with NaOH and the SiO2/Na2O silicate module. Scanning electron microscopy is employed to study the synthesized alkaline solutions, or the filtrate and the suspension.
 Results. The results have proven the effectiveness of the “wet” method for preparing the alkaline-silicate sodium binder using the simulated compositions. Ultrafine microparticles are quite active and capable of rearranging in the suspension. As a result, hydrated nepheline compounds and hydro-alumino-silicate metastable phases of variable compositions are generated. The binder system has a sufficient amount of structureless silica that converts into a solution in the process of leaching; it is also capable of synthesizing new compositions corresponding to sodium hydrosilicate Na2[Si4O10]∙4H2O.
 Conclusions. The prospects for and availability of fine off-grade glass quartz sands are beyond doubt; the proposed “wet” method of making less energy- and resource-intensive liquid glass binders will expand the clicker-free technology of alkali-activated binders, thereby reducing the environmental load and promoting an alternative to expensive and energy-intensive Portland cement.

Effect of Waste Fines and Fibers on the Strength and Durability Performance of Silica Fume Based Reactive Powder Concrete

The demand and consumption of conventional concrete materials is increasing day by day, which in turn leads to the extinction of natural resources. Certain researchers tend to draw a circle to solve this global problem by finding alternative materials satisfying all aspects, mainly efficiency, eco-friendly and economical. The present research work aimed to study the combined use of coal bottom ash (CBA) and waste concrete powder (WCP) in silica fume based reactive powder concrete (SF-RPC) subjected to thermal curing. The replacement of cement by silica fume was limited to 20% and the fine aggregate quartz sand replaced by CBA and WCP varied from 5% to 25% each. The material composition of SF-RPC involves the exclusion of coarse aggregates and the inclusion of finer materials with micro-steel fibers. The steel fibers played a significant role in order to obtain a ductile and stable product of SF-RPC. The experimental investigation on SF-RPC comprised of the determination of fresh concrete properties such as slump flow and the compaction factor, as well as mechanical properties like compressive strength, flexural strength and split-tensile strength. The study was also extended to investigate durability properties such as water absorption, sorptivity and resistance to acid attack. The results showed that silica fume proves to be a feasible alternative to partially replace cement and also that optimum incorporation of pre-treated and processed CBA and WCP attains better mechanical and durability performance without compromising the necessary qualities.

Experimental investigation in the permeability of methane hydrate-bearing fine quartz sands

The permeability is one of the intrinsic parameters that determines the fluid flow in the porous media. The permeability in hydrate-bearing sediments affects the gas recovery and production of hydrate reservoirs significantly. The irregular permeability characteristics are challenging for fine-grained hydrate-bearing sediments. In this study, a series of experiments was conducted using an one-dimensional pressure vessel to investigate the hydrate formation characteristics and the permeability in hydrate-bearing fine quartz sands (volume weighted mean diameter was 36.695 μm). Hydrate saturations (0–26% in volume) were controlled and calculated precisely based on the amount of injected water and gas, the system pressure and temperature. The results indicated that the hydrate nucleation induction period was completed during gas injection, and the average time of hydrate formation was within 500 min. The permeability of methane hydrate-bearing fine quartz sands was investigated by steady gas volume flow. For hydrate saturation lower than 13.94%, the hydrate mostly formed in grain-coating, the permeability reduction exponent calculated by Parallel Capillary, Kozeny Grain Coats and Simple Cubic Filling models were 2.00, 2.10 and 1.74 respectively, and Simple Cubic Filling model was in accordance with the experimental data best. However, for hydrate saturation ranged from 13.94% to 25.91%, the permeability increased due to the flocculation structure formation of fine quartz sands and hydrate, which caused the increase of effective porosity. A new relationship among hydrate saturations, effective porosity, the ratio of permeability in the presence and the absence of hydrate was developed. This study developed the mathematical models for predicting the permeability with hydrate saturation in fine quartz sands, which could be valuable for understanding the characteristics of hydrate-bearing fine-grained sediments.

Viséan transgression and reworking at Boudouda (NW Benahmed, western Moroccan Meseta)

At Boudouda NW of Benahmed, upper Frasnian goniatite shales are in unconformable contact with massive, partly dolomitized conglomerate boulders of the new Oued Ayada Formation. They represent debris flow deposits of localized channels and contain reworked supposed Emsian reefal organisms and Frasnian to lower/?middle Famennian conodonts. Rare foraminifers prove upper Visean (Upper Asbian) sedimentation. Laterally, a ca. 35 m thick sequence of bioclastic limestones with crinoids, mostly fragmented brachiopods or gastropod-rich forms a second member. Thin-sections show a dominance of variably sorted wacke-, pack- and grainstones with abundant coated grains (initial ooids) and subangular fine quartz sand. Biota include calcareous green algae, foraminifers, and various Algospongia (Aoujgaliidae and Palaeobereselliidae). Throughout the succession, there are reworked Frasnian to middle Tournaisian deeper-water conodonts, which shows that a probably small-sized pelagic platform existed once in the region, which had been uplifted during the Eovariscan 2 tectonic phase. A single, juvenile, originally pyritic goniatite gives limited evidence for an upper Tournaisian/lower Visean goniatite shale, which has no equivalents elsewhere in the Meseta. Based on a rich record of foraminifers (more than 70 taxa) and stratigraphically meaningful other calcareous microfossils, polyphase erosion and re-deposition by storms occurred on a shallow-water, photic zone carbonate ramp in the upper Visean. The Oued Ayada Formation correlates with the transgressive limestones of the basal Melilla Formation in the southern Mdakra Basin and the Bled Mekrach Formation in the NE Rehamna.

The application of automotive glass waste in the production of epoxy polymer concrete

In this paper, the production of aggregate from car windshield cullet and the use of this aggregate, in various compositions with fine quartz sand, as the reinforcing phase of the epoxy matrix polymer concrete were used and the obtained samples were tested. The bending and compressive strength, Charpy’s impact resistance tests were performed on the obtained composites. The porosity, water absorption, and density were also determined. The tests performed have shown that the application of car windshield cullet in polymer concrete, seems to be a good way to recycle this waste. The highest compressive strength, equal to 101 MPa, was obtained by composites containing 20 vol% of milled glass. It is nearly 7 times higher than the value of traditional concrete tested simultaneously, which has about 15 MPa. The highest flexural strength was noted for the composite containing 35 vol% of the glass. Polymer concrete samples did not show high impact resistance, which was in the range of 5.85 - 10.13 kJ/m2 . However, it increases with increasing glass content and the highest value was obtained for the composite containing 50% of the glass volume. Among the polymer concrete samples, the best properties were obtained for the mixture of 35% sand, 35% ground glass and 30% epoxy resin. Open porosity of traditional concrete is 15.9%, and for polymer concrete it was lower than 0.38%. The large difference in open porosity and water absorption for traditional concrete and polymer concrete, allow us to conclude that the latter will have higher frost resistance. The test results clearly show the significantly better mechanical properties of polymer concrete than of traditional concrete.

Influence of fine quartz sand faction on the properties of composite material

Expanding the production base of raw materials for concrete mix allows rationally and purposefully reducing the cost of production of building materials based on Portland cement. The purpose of the research is to obtain high-strength vibropress products based on fine quartz and ground sands by regulating the rheological properties of the mixture, as well as the waste from the enrichment plant for the production of dolomite flour in Vladikavkaz. The developed technology allows for the consumption of Portland cement 200–230 kg/m3 to obtain concrete with a strength of up to 40 MPa. Together, fine quartz sand with ground allow you to get a rheologically active matrix of concrete mixture.

Coupling effect of porosity and hydrate saturation on the permeability of methane hydrate-bearing sediments

The water effective permeability (kw) of the methane hydrate-bearing sediments is a key parameter in the investigation of natural gas exploitation, and it is closely related to hydrate saturation (SH) and the initial porosity of sediments. In this work, the effect of SH on the kw were systematically investigated in different initial porosities of fine quartz sands. The results show that the initial porosity of sediments has significant influence on the kw of the sediments with and without methane hydrates, and the hindrance of methane hydrates was more pronounced in the sediments with higher initial porosity. The stability and decomposition process of hydrates in this study could be clearly measured by the differential pressure of the sediments, and the stability of hydrates during the permeability measurement was more than 3 h, which was new record in permeability measurement. Finally, a new reduction empirical model on the basis of simple cubic model and oblique cubic model was integrated, and the effect of initial porosity of sediments on water relative permeability could be eliminated. This model could provide a more accurate prediction of the permeability of hydrate reservoirs with the porosity variation of the sediment.