Proportion Of Mesopores Research Articles

Activation of solid residues from batch pyrolysis of waste tires

The paper deals with a two-stage process of thermal treatment of waste tires in order to obtain a carbonaceous adsorbent. A fraction of 0.4 ‒ 0.8 mm of the ground material was involved in the experiments. In the first stage, pyrolysis took place in a retort apparatus, which provided about 43 % of solid residues, 41 % of condensates and 16 % of gas at temperatures of 600 and 800 ° C. The mass balance was confirmed by the TGA method independently of the retort apparatus. N-alkanes, mono- to trialkylated benzenes, cycloalkenes, higher alcohols, ethers, acetates and aliphatic and aromatic thiols were identified in the liquid product by GC-MS. The main components of the condensates were: 50% n-al-kanes and more than 25 % alkylated benzenes. According to GC-TCD-FID, the separated pyrolysis gases contained nine main components with a volume fraction >1 %. Of these majority compounds, methane with volume fractions approaching 30 % was the most represented. Other important compounds were in descending order: hydrogen (20.2 and 20.8 %), carbon dioxide (8.9 %), ethane (8.5 %) and ethene (7.0 %). Due to the upper calorific value of 44 ‒ 45 MJ m‒3, the gas can be advantageously used energetically, but the high sulfur content must be considered anyway. The solid residues were subjected to steam activation in a separate apparatus. The activation apparatus operated with a batch reactor of similar design as the pyrolysis retort. By activation, the specific surface area of the pyrolysis residues was increased from a very small initial value <59 m2 g‒1 to a maximum of 337 m2 g‒1. However, this result, in contrast to the reference sample prepared from hardwood, required aggressive conditions, namely 900 °C combined with a steam exposure time of 60 min. The combination of the lower of the selected pyrolysis temperatures and the higher activation temperature led to better results than the opposite setting. Both the crude pyrolysis residues and the obtained activated products were significantly mesoporous and pores with a diameter of 20 ‒ 80 nm predominated in their structure. Prior to activation, the pyrolysis residues always had a pore content of at least 60 %, while the activation further increased their proportion to 81 %. Such a significant proportion of mesopores 20 - 80 nm suggests that the material could be suitable for the next modification/improving step in the form of wet impregnation.

In Ukrainian

The paper considers an approach to the processing of waste of agro-industrial raw materials due to chemical activation. To obtain a sorption material, waste was used, which is the shell of Juglansregia walnuts. The aim of the work was to develop adsorbents from walnut shells with a large proportion of mesopores, to determine the parameters of the porous structure and to study their adsorption capability to absorb egg albumin as a marker of medium molecular toxins of a protein nature. Activated carbon samples with a high mesopore content (550 m2/g) were obtained by combined activation of the feedstock. The sorption of one of the obtained samples and, for comparison, the medical product SORBEX was studied by the spectrophotometric method, and its effectiveness was proved in the absorption of egg albumin from aqueous solutions. The significant capability of the obtained sample to sorb protein (35–38 mg/g) was shown, it has been assumed that in the process of sorption, macromolecules are concentrated near the inlets into the pores of the adsorbent. It can be stated that the adsorption of albumin increases in proportion to the increase in the specific surface area of the mesopore. Using the obtained sorption isotherms, the parameters of adsorption processes were calculated. Adsorption isotherms were calculated using the Langmuir and Freundlich equations. It is shown that the maximum adsorption values calculated using the Langmuir equation are in good agreement with the experimental data.

Research on mechanical and electromagnetic shielding properties of cement paste with different contents of fly ash and slag

This paper studied the mechanical properties and electromagnetic shielding effectiveness of cement paste (CP) mixed with fly ash and slag. With pure CP as the control group, 10%, 20%, and 30% cement contents were replaced by fly ash and slag. Then the compressive and flexural strength of the samples were tested. Wet resistance and dry resistance of samples were tested by the four-probe technique. The electromagnetic shielding effectiveness of the sample in the 3.94 GHz–5.99 GHz band was tested. Finally, based on the mercury intrusion porosimetry (MIP) test and backscattered electron and energy-dispersive X-ray spectroscopy (BSE-EDS) test, the impact mechanism of fly ash and slag on the electromagnetic properties of CP was expounded from the pore structure and element distribution. The results show that with the increase of fly ash or slag, the strength of the sample decreased. Mineral admixtures had little effect on wet resistance, while dry resistance showed an increasing trend with the increase of mineral admixture content. The reflection loss had the greatest impact on electromagnetic shielding effectiveness. With the increase of mineral admixture content, the reflection loss and multiple reflection loss of the sample increased, but the absorption loss decreased. The reason for the effect of compounding different proportions of fly ash and slag on the electromagnetic shielding effectiveness of CP is mainly due to the change in the proportion of mesopores with an aperture less than 100 nm and the content of metallic elements (e. g. Fe) in the specimens.

Main controlling factors of marine shale compressive strength: A case study on the cambrian Niutitang Formation in Dabashan Mountain

Lower Paleozoic shale is an important hydrocarbon source rock and natural gas reservoir in the Upper Yangtze Plate. In this study, compressive strength + acoustic emission (AE), low-pressure nitrogen adsorption and desorption (LP-N2A), low-field nuclear magnetic resonance (NMR), total organic carbon (TOC), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM) and other experiments were carried out on the marine shale of the Cambrian Niutitang Formation in Fucheng Town, Dabashan Mountain. The results showed that: 1) The compressive strength of shale with an average of 58.38 MPa, and its rupture process can be divided into four stages; 2) The high proportion of mesopores in shale is significantly negatively correlated with compressive strength; 3) TOC in shale averaging 2.37 wt% was positively correlated with compressive strength; 4) The main element was SiO2 averaging 68.47 wt%, which is positively correlated with compressive strength. Meanwhile, Al2O3, Fe2O3 and CaO + MgO content were negatively correlated with compressive strength. To sum up, the organic and quartz content in shale jointly increase the compressive strength of shale, while the mesopores proportion has a constraining effect on the compressive strength. This study provides geological information and a theoretical basis for shale fracture development.

Study on the Improvement of Waterproof Performance of Historical Silt Sites with Silicone Waterproofing Agent

Silt has the characteristics of obvious capillary water effect and strong water sensitivity. The flooding of the Yellow River caused the water level in Kaifeng to be high, and the damage of capillary water to the silt site of Kaifeng Zhouqiao site is increasing day by day. In order to improve the waterproof performance of the site soil, three kinds of silicone waterproof materials were selected, and the site soil was improved by internal mixing. The improvement effects of different materials were compared through the capillary water rise test, and the contact angle of the modified soil with the optimal ratio was measured. Microscopic tests were conducted to evaluate its wetting properties and reveal the mechanism of action of the modified materials. The results show that the three kinds of silicone waterproofing agents can improve the waterproofing effect of soil, among which 0.5% sodium methylsilicate modified soil has the most significant waterproofing effect; its capillary water absorption inhibition effect can reach 98.34%, and the contact angle is 137.06. The surface of the modified soil is hydrophobic after the addition of sodium methylsilicate. An evenly distributed waterproof film is thus formed on the surface of the soil particles, which changes the contact mode between the soil particles and strengthens the connection between the soil particles, so that the proportion of large pores decreased. The proportion of mesopores and small pores increased, which made the soil sample more compact. These results explain the improvement of the waterproof performance of the soil sample.

Facile synthesis of N, S co-doped hierarchical porous carbon/MnO2 composites for supercapacitor electrodes via sodium alginate crosslinking

Porous carbon materials have been widely used as electrode materials for supercapacitors. However, low specific capacitance severely hinders the practical application. To further improve the capacitance, this work reports a facile approach to prepare N, S co-doped hierarchical porous carbon/MnO2 composites (NSPC/MnO2). Acidified thiourea, acting as N and S source, is used to crosslink sodium alginate (SA) to give SA-based composite gels which are pyrolyzed to produce NSPC/MnO2. X-ray diffraction and X-ray photoelectron spectra proved that manganese exists in the porous carbon in the form of MnO2. The obtained NSPC/MnO2 exhibit hierarchical porous structure, remarkable mesoporous feature (the proportion of mesopores and macropores reached 32.69%), and high specific surface area of 1701 m2 g−1. Meanwhile, NSPC/MnO2 show abundant heteroatom doping, i.e. Mn (2.05 at%), N (6.76 at%), and S (2.16 at%), which provided plenty of pseudocapacitance. The electrochemical tests show that NSPC/MnO2 as electrode material can reach a high specific capacity of 281.1 F g−1 at 1 A g−1 (which is almost 1.85 times higher than the comparative sample), with good cycling stability (86.02% after 5000 cycles at 10 A g−1).

Use of biochar co-mediated chitosan mesopores to encapsulate alkane and improve thermal properties

Phase-change materials (PCMs) plays a significant role in energy conservation and thermal management systems. However, excessive seepage and insufficient thermal conductivity of pristine PCMs are restricting its real-world applications. Herein, “anisotropic-like” biochar with favorable pore characteristics is designed by combining it with chitosan for dodecane encapsulation. The use of biochar could overcome high manufacturing costs and associated environmental issues of PCM supporting materials. Biochar co-mediated chitosan enrich the mesopore proportion (96.5%) and provide interactive synergistic architecture. The prepared composite PCM exhibited outstanding latent heat retention of 95.9% after repeated cycling, high loading ratio, enhanced thermal conductivity (0.373 W/(m·K)), leakage-free, and repeatable utilization properties above the melting point of pristine dodecane. A figure of merit of 33.94 × 106 W2 S/(m4oC) was achieved, far surpassing that measure among reported biochar-based composite PCMs. This study provides insights into next-generation sustainable energy storage development for a key global sustainability goal.

Rational design of carbon network structure in microporous layer toward enhanced mass transport of proton exchange membrane fuel cell

Microporous layer (MPL) is commonly applied to gas diffusion layer to improve water management performance of a proton exchange membrane fuel cell (PEMFC). In this work, we introduce a new type of MPL comprising whisker-like carbon nanotubes (WCNTs) and Ketjen Blacks (KBs) onto the macroporous substrate to optimize the pore structures. Scanning electron microscopy images show that KBs populate overlapping networks formed by WCNTs, leading to an increased proportion of mesopores (about 34.87%) of crack-free MPL. This optimal structure of MPL with a superhydrophobic surface ensures the maximum power density up to 2.046 W cm−2 at 100% relative humidity. The electrochemical impedance spectroscopy verifies that the mass transfer resistance is significantly lower, which means rapid drain of excess water and supply of reactant gas, and it is further confirmed by theoretical analysis of pore characteristics. A mechanism of gas-water transport balance promoted by the network structures of MPL constructed by WCNTs/KBs is proposed, which allows enhancing PEMFC performance at high humidity conditions.

Contribution of Na/K Doping to the Activity and Mechanism of Low-Temperature COS Hydrolysis over TiO2-Al2O3 Based Catalyst in Blast Furnace Gas

As an organic sulfur pollutant generated in blast furnace gas, carbonyl sulfide (COS) has attracted more attention due to its negative effects on the environment and economy. The TiO2-Al2O3 composite metal oxide (Ti0.5Al) with uniformly dispersed particles was prepared by the co-precipitation method. And on this basis, a series of Na/K-doped catalysts were prepared separately. The activity evaluation results showed that the introduction of Na/K significantly improved the low-temperature COS hydrolysis activity, which exhibited a COS conversion of 98% and H2S yield of 95% at 75 °C with 24,000 h–1. And K showed a better promoting effect than Na. Brunauer–Emmett–Teller (BET) results revealed the increased mesopore proportion of Na/K-modified catalysts. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that Na and K formed prismatic and nanorod-like structures, respectively. More weakly basic sites with enhanced intensity and decreased Oads/Olat content contributed to the excellent catalytic activity, as certified by the results of CO2 temperature-programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). It was also proposed that the decrease of weakly basic sites ultimately deactivated catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the introduction of Na/K enhanced the dissociation of H2O, and the generated abundant hydroxyl groups promoted the adsorption of COS and formed surface transition species, such as HSCO2– and HCO3–.

Effect of adding solid waste silica fume as a cement paste replacement on the properties of fresh and hardened concrete

Due to the large-scale infrastructure construction and environmental protection pressure in China, the demanded cement is in short supply and the price is rising, and the overcapacity of silica fume has caused its price to fall, thus replacing cement paste by silica fume could achieve better economic and environmental benefits. In this study, silica fume (SF) with SiO2 content of 86.3% and high purity silica fume (HSF) with SiO2 content of 96% were used to replace cement paste in different proportions. The effects of adding SF or HSF on the workability of fresh concrete, the mechanical properties and microstructure of hardened concrete were investigated. The microstructures (i.e., porosity, pore size distribution and micromorphological characteristics) were analyzed by using low field nuclear magnetic resonance (LF NMR) and field emission scanning electron microscopy (FE-SEM). The results showed that the slump and air content of the concrete gradually decreased as the amount of SF or HSF increased. When the replacement amount of SF was increased from 0% to 10%, the cubic compressive strength and splitting-tensile strength of concrete were increased by 26.7% and 40.7%, while the cost per cubic meter of concrete was only increased by 1.9%. When the replacement amount of HSF was increased from 0% to 10%, the cubic compressive strength and splitting-tensile strength of concrete were increased by 44.7% and 57.4% respectively, while the cost per cubic meter of concrete was only increased by 5.3%. The total porosity of concrete gradually decreased as the amount of SF or HSF increased, with the proportion of macropores (>1000 nm) decreasing, and the proportion of mesopores (100–1000 nm) and capillary pores (0–100 nm) increasing, significantly refining the pore structure and densifying the microstructure of concrete.

High Rank Coal Pore Fracture Structure and its Impact on Reservoir Characteristics in the Southern Qinshui Basin

Although the southern Qinshui Basin is the most successful area for coalbed methane (CBM) development in China, the production of CBM wells in different blocks in the area is significantly different. One of the key reasons is the difference in pore structure in various-ranked coal. In this study, No. 3 coal seam of Sihe and Zhaozhuang blocks in southern Qinshui Basin was selected as the research object to investigate the high rank coal pore fracture structure and its impact on reservoir characteristics. Mercury intrusion porosimetry (MIP), low-temperature liquid nitrogen adsorption (LTN2A), scanning electron microscopy (SEM), and isothermal adsorption tests were conducted. The results show that the Sihe No.3 coal seam was mainly composed of open cylindrical and flat pores with a high proportion of transition pores (10–100 nm), large specific surface area, good connectivity, strong adsorption capacity, high gas content, and reservoir energy. Zhaozhuang No.3 coal had high proportion of mesopores (100–1,000 nm), small specific surface area, poor pores connectivity, weak adsorption capacity, poor gas content, low reservoir energy, and critical desorption pressure. The proportion of cylindrical pores, parallel plate pores, and wedge-shaped pores closed at one end was high. The anomalies in pore morphology and pore structure characteristics of coal reservoir were the main factors that caused variation in gas production of No.3 coal seam in Sihe and Zhaozhuang blocks.

Waste-converted nitrogen and fluorine co-doped porous carbon nanosheets for high performance supercapacitor with ionic liquid electrolyte

In this work, nitrogen and fluorine co-doped porous carbon nanosheets (NFPCNS) were fabricated from pharmaceutical drug residues derived from the fermentation synthesis of lincomycin hydrochloride via high-temperature pyrolysis and subsequent KOH activation without adding any nitrogen and fluorine reagents. The obtained NFPCNS exhibits an optimized integration of three dimensional interconnected nanosheet structure, large specific surface area of 2912 m2 g−1, hierarchical porous structure with large mesopore proportion (Smeso/Smicro = 151.5%, Vmeso/Vmicro = 248.2%) and high level heteroatom content (13.2 at.% O, 4.3 at.% N and 1.0 at.% F). Therefore, NFPCNS based supercapacitors using 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte exhibit an excellent gravimetric capacitance of 296F g−1 at 1 A g−1, good rate capability of 65% at 20 A g−1 and high energy density of 125 Wh kg−1. Furthermore, an ultra-high energy density of 173 Wh kg−1 and a long cycling life with 93% capacitance retention after 2000 cycles has been achieved by NFPCNS based supercapacitors with 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide electrolyte. NFPCNS should be a green and efficient electrode materials for next-generation high-energy supercapacitors.

Unlocking Zinc-Ion Energy Storage Performance of Onion-Like Carbon by Promoting Heteroatom Doping Strategy.

Onion-like carbon (OLC) is one kind of a quasi-nanosphere with a concentric graphite shell structure and abundant mesopores, which is appropriate for a high rate of charging/discharging and long-lifespan cycling. However, the moderate specific surface area seriously impeded its capacitance performance in comparison with activated carbon and porous carbon. Herein, we have unlocked the Zn ion storage performance of OLC material through introducing N and P dopants. Benefitting from the fabricated N,P-OLC with a fully accessible external surface area for ion adsorption, high proportion of mesopores for fast ion migration, and synergistic effect of N and P co-doping in a carbon matrix favoring chemical adsorption of Zn2+ ions, when applied as a cathode electrode for Zn ion hybrid supercapacitors (ZHSCs), such a device can deliver a high specific capacitance of 420.3 F g-1 (184.5 mA h g-1) at 0.5 A g-1, an outstanding capacitance retention capability of 262.7 F g-1 even at 20 A g-1 (∼63% capacitance retention), a high energy density of 149.5 W h kg-1, and a high power density of 26.7 kW kg-1. Furthermore, this N,P-OLC material can in situ tightly integrate with a carbon cloth (CC) or carbon fiber to construct a freestanding and flexible electrode. The fabricated Zn//N,P-OLC@CC device achieved a high energy density of 85.3 mW h cm-2, a high power density of 24.3 W cm-2, and a long-term cycling lifespan (77.8% after 50 000 cycles). At last, the assembled quasi-solid-state fiber-shaped ZHSCs also present excellent flexibility and practicality. Our study exhibits that OLC can act as a promising carbon electrode for ZHSCs.

Modified Approach Using Mentha arvensis in the Synthesis of ZnO Nanoparticles—Textural, Structural, and Photocatalytic Properties

Zinc oxide arouses considerable interest since it has many applications—in microelectronics, environmental decontaminations, biomedicine, photocatalysis, corrosion, etc. The present investigation describes the green synthesis of nanosized ZnO particles using a low-cost, ecologically friendly approach compared to the classical methods, which are aimed at limiting their harmful effects on the environment. In this study, ZnO nanoparticles were prepared using an extract of Mentha arvensis (MA) leaves as a stabilizing/reducing agent, followed by hydrothermal treatment at 180 °C. The resulting powder samples were characterized by X-ray diffraction (XRD) phase analysis, infrared spectroscopy (IRS), scanning electron microscopy (SEM), and electron paramagnetic resonance (EPR). The specific surface area and pore size distribution were measured by the Brunauer–Emmett–Taylor (BET) method. Electronic paramagnetic resonance spectra were recorded at room temperature and at 123 K by a JEOL JES-FA 100 EPR spectrometer. The intensity of the bands within the range of 400–1700 cm−1 for biosynthesized ZnO (BS-Zn) powders decreased with the increase in the Mentha arvensis extract concentration. Upon increasing the plant extract concentration, the relative proportion of mesopores in the BS-Zn samples also increased. It was established that the photocatalytic performance of the biosynthesized powders was dependent on the MA concentration in the precursor solution. According to EPR and PL analyses, it was proved that there was a presence of singly ionized oxygen vacancies (V0+) and zinc interstitials (Zni). The use of the plant extract led to changes in the morphology, phase composition, and structure of the ZnO particles, which were responsible for the increased photocatalytic rate of discoloration of Malachite Green dye.

Influence of the Addition of Blast Furnace Slag to Alkali-Activated Mixtures Based on Natural Zeolites

This study focuses on a comparison of alkali-activated materials based on natural zeolites without and with the addition of blast furnace slag and their subsequent modification by acid leaching. The addition of slag to alkali-activated mixtures is generally used to increase the strength. The subsequent modification of its chemical, textural and mechanical properties by acid leaching makes this material usable in other industries, especially in the chemical industry. This study aimed to examine the influence of the addition of blast furnace slag to alkali-activated mixtures based on natural zeolites and observe the effect of subsequent acid leaching on the chemical, textural and mechanical properties and CO2 adsorption capacity of these materials. The modification of alkali-activated materials was carried out by acid leaching using 0.1 M HCl and then using 3 M HCl. The properties of these materials were determined using N2 physisorption, Hg porosimetry, XRF, XRD, DRIFT, TGA and strength measurements. The results showed that the addition of blast furnace slag significantly increased the cutting-edge strength of the obtained materials and affected the textural properties, especially in leached samples. The presence of blast furnace slag generated a higher proportion of mesopores, which are attributed to the presence of the calcium silicate hydrate (C–S–H) phase and are easily removed by leaching, as shown by the XRF results. The obtained data showed an improvement in properties and extension of the potential applicability of these materials in the chemical industry, especially for catalytic and adsorption applications.

Experimental Study on Mechanical Properties and Pore Structure Deterioration of Concrete under Freeze-Thaw Cycles.

Understanding the evolution of mechanical properties and microscopic pore structure of concrete after freeze–thaw cycles is essential to assess the durability and safety of concrete structures. In this work, the degradation law of mechanical properties and damage characteristic of micro-structure of concrete with two water-cement ratios (w/c = 0.45 and 0.55) is investigated under the condition of freezing–thawing cycles. The influence of loading strain rate on dynamic compressive strength is studied. The microscopic pore structure after frost damage is measured by low-field nuclear magnetic resonance (LF-NMR) technique. Then, a damage model based on the porosity variation is established to quantitatively describe the degradation law of macroscopic mechanical properties. The test results show that the relative dynamic modulus of elasticity (RDME), dynamic compressive strength, flexural strength, and splitting tensile strength of concrete decrease with the increase of freeze–thaw cycles. Empirical relations of concrete dynamic increase factor (DIF) under the action of freeze–thaw cycles are proposed. Moreover, the experimental results of NMR indicate that the porosity as well as the proportion of meso-pores and macro-pores of concrete gradually increased with the increasing of freeze–thaw cycles. The research results can provide reference and experimental support for the anti-frost design theory and durability life prediction of hydraulic concrete structures in cold regions.

Reservoir Characteristics and Controlling Factors of Oil Content in Hybrid Sedimentary Rocks of the Lucaogou Formation, Western Jimusar Sag, Junggar Basin

Hybrid sedimentary rocks (HSR) are a major reservoir type in unconventional oil exploration. The reservoir characteristics and controlling factors of the oil content of HSR are not clear, restricting the understanding of the storage mechanism and sweet spots within HSR. The Lucaogou Formation in the western Jimusar Sag is taken as a case study. Starting with the classification of the lithofacies system, differences in the microscopic pore structure, oil content and controlling factors of HSR reservoirs are revealed. The results show that seven lithofacies are recognized based on mineral composition, sedimentary structure, and organic matter characteristics, exhibiting rapid vertical and horizontal changes affected by the sedimentary environment. Layered mudstone lithofacies of the shallow lake mud and massive dolomitic mudstone lithofacies of dolomitic mud flats have the worst physical properties and oil content properties. However, they do have high organic matter contents and are the main source rocks of the Lucaogou Formation. The massive argillaceous siltstone and massive argillaceous dolomite lithofacies interbed frequently. Although their physical properties are moderate, “source-reservoir integrated” unconventional oil reservoirs can be formed, due to the adjacent to the source rock. Massive dolomitic siltstone, massive siltstone, and massive silty dolomite lithofacies are developed in the middle of the Lucaogou Formation, with the highest proportion of mesopores and macropores, which is indicative of good storage properties. When these lithofacies are filled with crude oil generated from source rocks at the top and bottom of the formation, “source storage adjacent” unconventional oil reservoirs be formed. The oil content is also controlled by the pore structure and specific surface area. The proportion of macropores and mesopores is positively correlated with oil content. The oil content of the samples is very low, when the specific surface area exceeds 2 m2/g. This manuscript provides a geological basis for evaluating and establishing reasonable interpretation models of HSR sweet spots.

Macro-meso properties and constitutive behavior of concrete affected by early-age loading

To explore the influence of early-age loading on the mechanical properties and internal structures of concrete, loads equivalent to 10%, 25%, and 40% of the concrete current compressive strength were applied to 1 day and 3 days specimens. The results of mechanical properties and mesoscopic scanning tests show that the development of uniaxial compression damage of concrete affected by early-age loading is divided into three stages. With an increase in early-age loading, the elastic modulus decreased and the Poisson's ratio first increased and then decreased. When the loading was 10% of current compressive strength of specimens, the number of macropores and cracks would decrease, and the subsequent mechanical properties of concrete would not be affected considerably. A continuous increase in early-age loading, the proportion of mesopores and cracks increased considerably, the cementitious structure loosened, and the mechanical properties of concrete deteriorated in the subsequent stage. By analyzing the relationship between the total deformation and the deformation of primary flaws and skeleton, the concept of void strain ratio was proposed. Accordingly, a constitutive behavior that reflects the nonlinear characteristic of primary flaws compaction stage during uniaxial compression process was established, the theoretical calculation is in good agreement with the experimental results.

In Ukrainian

As an alternative to means for lowering total cholesterol and low-density lipoprotein (LDL) cholesterol, the paper considers the possibility of using carbon adsorbents. From a medical point of view, the removal of cholesterol with enterosorbents is extremely effective. By binding cholesterol, sorbents reduce the risk of cardiovascular disease. The paper searches for new raw material sources and attempts to create enterosorbents with a high capability to adsorb cholesterol. The aim of the work was to develop adsorbents from spent coffee residue with a large proportion of mesopores, to determine the parameters of the porous structure and to study their adsorption capacity against cholesterol. Samples of activated carbon with a large proportion of mesopores (399 and 465 m2/g) were obtained by the traditional method of carbonization-activation of spent coffee grounds and pre-treated hexane to remove fatty acids. The sorption of cholesterol from alcohol solutions has been studied by spectrophotometric method and its effectiveness for the prevention and treatment of atherosclerosis was proved. It has been shown that a sample of activated carbon from spent coffee residue pre-treated with hexane (maximum value reaches 7.5 mg/g) has the best sorption capacity. The intermediate position is occupied by the sample obtained without pre-treatment with solvent (maximum value reaches 6.3 mg/g). Natural Brand carbon has the weakest sorption characteristics (maximum capacity reaches 5.3 mg/g). It can be stated that the adsorption of cholesterol increases with the growth of the specific surface area of mesopores. The parameters of adsorption processes were calculated using the obtained sorption isotherms. Adsorption isotherms were calculated using the Langmuir and Freundlich equations. It is shown that the values of the maximum adsorption calculated by the Langmuir equation have a good agreement with the experimental data.

Effect of early age loading on the subsequent mechanical and permeability properties of concrete and its mechanism analysis

Modern construction methods often result in concrete structures bearing loads at an early age, which is different from the stress condition under the standard curing in the laboratory. This study experimentally examined effects of different ages and external loads on subsequent mechanical and permeability properties of concrete, and investigated the mechanism of effect from the perspective of internal structure changes. The results show when the early age loading reaches 40% of the current concrete strength, the original internal structure of specimens will be severely damaged, reflecting significant increase in the proportion of mesopores and macropores and obvious connectivity cracks, thus making the mechanical and permeability properties deteriorate, and the earlier the applied load, the greater of this deterioration. However, when loading at 10%, the original internal structure cannot be changed greatly due to the low load level, and some parts of the original pores are even compacted rather than expanded which has little effect on subsequent mechanical and permeability properties of concrete.