• Geomechanics and Engineering
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• v.24 no.6
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• pp.519-529
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• 2021

In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause dynamic disasters, posing a major challenge for the safety of coal mine production. To improve the understanding of the dynamic disaster mechanism of gas outburst and rock burst coupling, triaxial devices are applied to axial pressure cyclic loading-unloading tests under different axial stress peaks and different pore pressures. The existing empirical formula is use to perform a non-linear regression fitting on the relationship between stress and permeability, and the damage rate of permeability is introduced to analyze the change in permeability. The results show that the permeability curve obtained had "memory", and the peak stress was lower than the conventional loading path. The permeability curve and the volume strain curve show a clear symmetrical relationship, being the former in the form of a negative power function. Owing to the influence of irreversible deformation, the permeability difference and the damage of permeability mainly occur in the initial stage of loading-unloading, and both decrease as the number of cycles of loading-unloading increase. At the end of the first cycle and the second cycle, the permeability decreased in the range of 5.777 - 8.421 % and 4.311-8.713 %, respectively. The permeability decreases with an increase in the axial stress peak, and the damage rate shows the opposite trend. Under the same conditions, the permeability of methane is always lower than that of helium, and it shows a V-shape change trend with increasing methane pressures, and the permeability of the specimen was 3 MPa > 1 MPa > 2 MPa.

• The Journal of Engineering Geology
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• v.32 no.3
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• pp.339-350
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• 2022

There are a variety of types in tafoni formed in Miocene tuff from Golgulsa, Gyeongju. Tuff bearing tafoni was quite weathered, composed of quartz, feldspars, micas, vermiculite, chlorite, smectite, and analcite. In the early stage of the tafoni development, tafoni preferentially formed from cavities where volcanic breccias were removed or from microcavities where microcrystals were chemically altered. Small tafoni grew into large one by merging each other. The orientation of tafoni is inversely arranged to slopes, with slight inclination toward the inner cavity. Height, width, and depth of tafoni are closely interrelated: the correlation coefficients are 0.839 (width-height), 0.900 (width-depth), and 0.856 (height-depth), respectively. Removal of walls between tafoni resulted in lenticular or crescent forms, and small tafoni laterally combined to large tafoni. Large tafoni is weak because of high porosity and low strength compared to normal slope. Therefore, systematic monitoring for slope strength, pore proportion and volume, and growth of cavity needs to secure the slope stability where tafoni in Golgulsa is widespread.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3631-3640
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• 2022

Uranium mill tailing ponds (UMTPs) are risk source of debris flow and a critical source of environmental U and Rn pollution. The technology of microbial induced calcium carbonate precipitation (MICP) has been extensively studied on reinforcement of UMTs, while little attention has been paid to the effects of MICP on U & Rn release, especially when incorporation of metakaolin and bacillus subtilis (MBS). In this study, the reinforcement and U & Rn immobilization role of MBS -MICP solidification in different grouting cycle for uranium mill tailings (UMTs) was comprehensively investigated. The results showed that under the action of about 166.7 g/L metakaolin and ~50% bacillus subtilis, the solidification cycle of MICP was shortened by 50%, the solidified bodies became brittle, and the axial stress increased by up to 7.9%, and U immobilization rates and Rn exhalation rates decrease by 12.6% and 0.8%, respectively. Therefore, the incorporation of MBS can enhance the triaxial compressive strength and improve the immobilization capacity of U and Rn of the UMTs bodies solidified during MICP, due to the reduction of pore volume and surface area, the formation of more crystals general gypsum and gismondine, as well as the enhancing of coprecipitation and encapsulation capacity.

• Advances in concrete construction
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• v.12 no.6
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• pp.479-490
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• 2021

Present research is mainly focused on, microstructural and durability analysis of Graphene Oxide (GO) in Wollastonite (WO) induced cement mortar with silica fume. The study was conducted by evaluating the mechanical properties (compressive and flexural strength), durability properties (water absorption, sorptivity and sulphate resistance) and microstructural analysis by SEM. Cement mortar mix prepared by replacing 10% ordinary portland cement with SF was considered as the control mix. Wollastonite replacement level varied from 0 to 20% by weight of cement. The optimum replacement of wollastonite was found to be 15% and this was followed by four sets of mortar specimens with varying substitution levels of cementitious material with GO at dosage rates of 0.1%, 0.2%, 0.3% and 0.4% by weight. The results indicated that the addition of up to 15%WO and 0.3% GO improves the hydration process and increase the compressive strength and flexural strength of the mortar due to the pore volume reduction, thereby strengthening the mortar mix. The resistance to water penetration and sulphate attack of mortar mixes were generally improved with the dosage of GO in presence of 15% Wollastonite and 10% silica fume content in the mortar mix. Furthermore, FE-SEM test results showed that the WO influences the lattice framework of the cement hydration products increasing the bonding between silica fume particles and cement. The optimum mix containing 0.3% GO with 15% WO replacement exhibited extensive C-S-H formation along with a uniform densified structure indicating that calcium meta-silicate has filled the pores.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.125-131
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• 2022

Effect of sulfation processes on the physicochemical properties of ZrO₂ and TiO₂ nanoparticles were thoroughly investigated. SO₄/ZrO₂ and SO₄/TiO₂ catalysts were synthesized to identify the acidity character of each. The wet impregnation method of ZrO₂ and TiO₂ nanoparticles was employed using H2SO₄ with various concentrations of 0.5, 0.75, and 1 M, followed by calcination at 400, 500, and 600 ℃ to obtain optimum conditions of the catalyst synthesis process. The highest total acidity was found when using 1 M SO₄/ZrO₂-500 and 1 M SO₄/TiO₂-500 catalysts, with total acidity values of 2.642 and 6.920 mmol/g, respectively. Sulfation increases titania particles via agglomeration. In contrast, sulfation did not practically change the size of zirconia particles. The sulfation process causes color of both catalyst particles to brighten due to the presence of sulfate. There was a decrease in surface area and pore volume of catalysts after sulfation; the materials' mesoporous structural properties were confirmed. The 1 M SO₄/ZrO₂ and 1 M SO₄/TiO₂ catalysts calcined at 500 ℃ are the best candidate heterogeneous acid catalysts synthesized in thus work.

• Journal of the Korea Institute of Building Construction
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• v.23 no.4
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• pp.381-392
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• 2023

This research scrutinizes the mechanical characteristics of ultra-high strength concrete using oxide graphene nanoplatelet(GO) and hollow glass powder(HGP). The investigation covered various mechanical attributes, including workability, compression strength, tensile strength, water resistance, and the internal microstructure of standard concrete. Our findings reveal that workability experiences a significant improvement with the incorporation of a minimal amount of HGP, and an increase was also observed in tensile strength and water resistance. It was confirmed that cGO(C company GO) and HGP demonstrated commendable dispersion and the pore volume exhibited a reduction of more than 20%. The potential of cGO and HGP to substitute silica fume(SF) was also explored. Consequently, it was found that both workability and mechanical properties were enhanced in the absence of SF when cGO and HGP were used. This finding implies that the utilization of these novel materials could potentially modify conventional methods of concrete manufacturing.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.287-294
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• 2009

Suction Drain Method is a relatively new technique to improve soft ground using vacuum pressure which can be directly applied to the soft ground through drains that the pore water pressure around them are decreased without changing total stress. This can accelerate volume changes and increase strength of the ground. This paper shows the results of field test of the suction drain method applied at dredged and reclaimed clay. To evaluate the improvement effects of soft ground by the suction drain method, this paper analyzed real-time field measurements to the results of the laboratory tests and numerical analysis. The comparisons of the settlement and shear strength between suction drain method and surcharge preloading method show possibilities for replacement of the preloading methods. The settlements by suction drain method were 2.3 times larger and undrained shear strength were 300%~400% higher than surcharge method. Moreover, the water content is decreased about 30% and the preconsolidation pressure is increased about $0.52kgf/cm^2$.

• New & Renewable Energy
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• v.20 no.1
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• pp.135-144
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• 2024

The present study investigated waste medium from a domestic shiitake mushroom farm, which was pyrolyzed to produce biochar. The yield rate of the biochar was compared after exposure to various pyrolysis temperature conditions, and the characteristics of the produced biochar were analyzed. The present study focused on the carbon dioxide (CO₂) adsorption capacity of the resulting biochar. The CO₂ adsorption capacity exhibited a correlation with the pyrolysis temperature of the biochar, with increasing temperatures resulting in higher CO₂ adsorption capacities. Brunauer-Emmett-Teller (BET) analysis showed that the CO₂ adsorption capacity was related to the surface area and pore volume of the biochar. Calcium is added to the process of producing mushroom medium. Experiments were performed to investigate the CO₂ adsorption capacity of the biochar from the waste medium with the addition of calcium. In addition, CO₂ adsorption experiments were conducted after the pyrolysis of kenaf biochar with the addition of calcium. The results of these experiments show that calcium affected the CO₂ adsorption capacity.

• Steel and Composite Structures
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• v.51 no.2
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• pp.185-202
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• 2024

In this research paper, and for the first time, wave propagations in sigmoidal imperfect functionally graded material plates are investigated using a simplified quasi-three-dimensionally higher shear deformation theory (Quasi-3D HSDTs). By employing an indeterminate integral for the transverse displacement in the shear components, the number of unknowns and governing equations in the current theory is reduced, thereby simplifying its application. Consequently, the present theories exhibit five fewer unknown variables compared to other Quasi-3D theories documented in the literature, eliminating the need for any correction coefficients as seen in the first shear deformation theory. The material properties of the functionally graded plates smoothly vary across the cross-section according to a sigmoid power law. The plates are considered imperfect, indicating a pore distribution throughout their thickness. The distribution of porosities is categorized into two types: even or uneven, with linear (L)-Type, exponential (E)-Type, logarithmic (Log)-Type, and Sinus (S)-Type distributions. The current quasi-3D shear deformation theories are applied to formulate governing equations for determining wave frequencies, and phase velocities are derived using Hamilton's principle. Dispersion relations are assumed as an analytical solution, and they are applied to obtain wave frequencies and phase velocities. A comprehensive parametric study is conducted to elucidate the influences of wavenumber, volume fraction, thickness ratio, and types of porosity distributions on wave propagation and phase velocities of the S-FGM plate. The findings of this investigation hold potential utility for studying and designing techniques for ultrasonic inspection and structural health monitoring.

• Applied Chemistry for Engineering
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• v.35 no.4
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• pp.352-359
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• 2024

Environmental pollution from heavy metal ions (HMIs) is a global concern. Recently, biosorption methods using cellulose sorbents have gained popularity. The objective of this study was to assess the removal efficiency of Cu(II), Pb(II), and Hg(II) ions at low concentration levels (100-700 ppb) from aqueous solutions using three different cellulose fiber-based filter media. Sample A was pure cellulose fiber, Sample B was 10% activated carbon-cellulose fiber, and Sample C was cellulose fiber-glass fiber-30% activated carbon-20% amorphous titanium silicate (ATS). The samples were characterized by several physicochemical techniques. The porosity measurements using N₂ sorption isotherms revealed that Samples A and B are nonporous or macroporous materials, whereas the addition of 50% filler materials into the cellulose resulted in a microporous material. The Brunauer-Emmett-Teller (BET) surface area and pore volume of Sample C were found to be 320.34 m²/g and 0.162 cm³/g, respectively. The single ion batch adsorption experiments reveal that at 700 ppb initial metal ion concentration, Sample A had removal efficiencies of 7.5, 11.5, and 13.7% for Cu(II), Pb(II), and Hg(II) ions, respectively. Sample B effectively eliminated 99.6% of Cu(II) ions compared to Pb(II) (14.2%) and Hg(II) (31.9%) ions. Cu(II) (99.37%) and Pb(II) (96.3%) ions are more efficiently removed by Sample C than Hg(II) (68.2%) ions. The X-ray photoelectron spectroscopy (XPS) wild survey spectrum revealed the presence of Cu(II), Pb(II), and Hg(II) ions in HMI-adsorbed filter media. The high-resolution C1s spectra of Samples A and B reveal the presence of -C-OH and -COOH groups on their surface, which are essential for HMIs adsorption via complexation reactions. Additionally, the ATS in Sample C facilitates the adsorption of Pb(II) and Hg(II) ions through ion exchange.