• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.10
• /
• pp.1881-1891
• /
• 2000

Cenosphere particles of different fly ash formed at the pulverized coal power plant were hollow sphere or filled with small particles inside solid particles. And size was relatively larger than other fly ash particles as well as specific gravity was small to suspend in the water. In this paper, it was demonstrated to contain a variety of morphological particle type, and the physical and chemical properties related to the cenosphere and fly ash particles. Furthermore it was estimated the possibility to reuse the cenosphere particles on the base of cenosphere properties. Cenosphere formation resulted from melting of mineral inclusion in coal, and then gas generation inside the molten droplet. As the aluminosilicate particle was progressively heated, a molten surface layer developed around the solid core. Further heating leaded to cause the formation of fine particles at the core. The mass median diameter(MMD) of cenosphere particles was $123.11{\mu}m$ and the range of size distribution was $100{\sim}200{\mu}m$ with single modal. It was represented that specific density was $0.67g/cm^3$ fineness was $1135g/cm^3$. The chemical components of cenosphere were similar to other fly ash including $SiO_2$, $Al_2O_3$, but the amount of the chemical component was different respectively. In the case of fly ash, $SiO_2$ concentration was 54.75%, and $Al_2O_3$ concentration was 21.96%, so this two components was found in 76.71% of the total concentration. But in the case of cenosphere, it was represented that $SiO_2$ concentration was 59.17% and $Al_2O_3$ concentration was 30.16%, so this two components was found in 89.33% of the total concentration. Glassy component formed by the aluminosilicate was high in the cenosphere, so that it was suitable to use insulating heat material.

• Journal of the Korea Concrete Institute
• /
• v.19 no.3
• /
• pp.367-375
• /
• 2007

Critical chloride content for corrosion initiation is a crucial parameter in determining the durability and integrity of reinforced concrete structures, however, the value is still ambiguous. Most of the studies reporting critical threshold chloride content have involved the experimental measurement of the average amount of the total chloride content at arbitrary time. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on critical threshold chloride content. Furthermore, the studies have tried to define the critical chloride content within the scope of their experimental concrete mix proportion at arbitrary time. However, critical chloride content for corrosion initiation is known to be affected by a lot of factors including cement content, type of binder, chloride binding, concentration of hydroxyl ions, and so on. It is necessary to define the unified formulation to express the critical chloride content for various mix proportions of concrete. The purpose of this study is to establish an analytical formulation of the critical chloride content of concrete. In this formulation, affecting factors, such as mix proportion, environment, chemical evolution of pore solution with elapsed time, carbonation of concrete and so on are taken into account. Based on the Gouda's experimental results, critical chloride content is defined as a function of $[Cl^-]$ vs. $[OH^-]$ in pore solution. This is expressed as free chloride content with mass unit to consider time evolution of $[OH^-]$ content in pore solution using the numerical simulation programme of cementitious materials, HYMOSTRUC. The result was compared with other experimental studies and various codes. It is believed that the approach suggested in this study can provide a good solution to determine the reasonable critical chloride content with original source of chloride ions, for example, marine sand at initial time, and sea water penetration later on.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.6
• /
• pp.1299-1308
• /
• 1994

This paper is considered on the dynamic behavior and the dynamic impact coefficient on the cable-stayed bridge under the vehicle load. The method of static analysis, that is, the transfer matrix method is used to get influence values about displacements, section forces of girder and cable forces. Gotten influence values were used as basic data to analyse dynamic behavior. This paper used the transfer matrix method because it is relatively simpler than the finite element method, and calculating speed of computer is very fast and the precision of computation is high. In the process of dynamic analysis, the uncoupled equation of motion is derived from simultaneous equation of the motion of cable-stayed bridge and vehicle travelling by using mode shape, which was borne from system of undamped free vibration. The solution of the uncoupled equation of motion, that is, time history of response of deflections, velocity and acceleration on reference coordinate system, is found by Newmark-${\beta}$ method, a kind of direct integral method. After the time history of dynamic response was gotten, and it was transfered to the time history of dynamic response of cable-stayed bridge by linear transformation of coordinates. As a result of this numerical analysis, effect of dynamic behavior for cable-stayed bridge under the vehicle load has varied depending on parameter of design, that is, the ratio of span, the ratio of main span length, tower height, the flexural rigidity of longitudinal girder, the flexural rigidity of tower, and the cable stiffness, investigated. Very good agreements with the existing solution in the literature are shown for the uncracked plate as well as the cracked plate.

• Journal of Bio-Environment Control
• /
• v.14 no.3
• /
• pp.218-231
• /
• 2005

This paper reviews the engineering approach needed to support humans during their long-term missions in space. This approach includes closed plant production systems under microgravity or low pressure, mass recycling, air revitalization, water purification, waste management, elimination of trace contaminants, lighting, and nutrient delivery systems in controlled ecological life support system (CELSS). Requirements of crops f3r space use are high production, edibility, digestibility, many culinary uses, capability of automation, short stems, and high transpiration. Low pressure on Mars is considered to be a major obstacle for the design of greenhouses fer crop production. However interest in Mars inflatable greenhouse applicable to planetary surface has increased. Structure, internal pressure, material, method of lighting, and shielding are principal design parameters for the inflatable greenhouse. The inflatable greenhouse operating at low pressure can reduce the structural mass and atmosphere leakage rate. Plants growing at reduced pressure show an increasing transpiration rates and a high water loss. Vapor pressure increases as moisture is added to the air through transpiration or evaporation from leaks in the hydroponic system. Fluctuations in vapor pressure will significantly influence total pressure in a closed system. Thus hydroponic systems should be as tight as possible to reduce the quantity of water that evaporates from leaks. And the environmental control system to maintain high relative humidity at low pressure should be developed. The essence of technologies associated with CELSS can support human lift even at extremely harsh conditions such as in deserts, polar regions, and under the ocean on Earth as well as in space.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.1
• /
• pp.55-62
• /
• 2002

The upper wall-lower frame structures(mixed building structures) are usually composed of shear wall structure in the upper part of structure which is used as residential space and frame structure in the lower part of structure which is used as commercial space centering around the transfer system in the lower part of structure. These structures are characteristics of stiffness irregularity, mass irregularity, and vertical geometric irregularity. The purpose of this study is to investigate the nonlinear response characteristics and the seismic capacity of mixed building structures when the number of stories in the lower frame is varied. The conclusions of this study are following. 1) As the result of push-over analysis of structure such as roof drift(i.e. roof displacement/structural height) and base shear coefficient, when the stories of lower frame system are increased, base shear coefficient is decreased, but roof drift is increased. 2) According to an increase in stories of the lower fame, story drift and ductility ratio of upper wall system are decreased and behavior of upper wall system is closed to elastic. 3) When the stories of lower frame system are increased, the excessive story drift is concentrated on the lower frame system.

• Korean Journal of Ecology and Environment
• /
• v.49 no.4
• /
• pp.245-257
• /
• 2016

Although rivers cover only 0.5% of the total land area on the Earth, they are windows that show the integrated effects of watershed biogeochemistry. Studies on the loads and properties of riverine carbon have been conducted because they are directly linked with drinking water quality, and because regional or global net ecosystem production (NEP) can be overestimated, unless riverine carbon loads are subtracted. Globally, ${\sim}0.8-1.5Pg\;yr^{-1}$ and ${\sim}0.62-2.1Pg\;yr^{-1}$ of carbon are transported from terrestrial ecosystems to the ocean via rivers and from inland waters to the atmosphere, respectively. Concentrations, ${\delta}^{13}C$, and fluorescence spectra of riverine carbon have been investigated in South Korea to understand the spatiotemporal changes in the sources. Precipitation as well as land use/land cover can strongly influence the composition of riverine carbon, thus shifting the ratios among DIC, DOC, and POC, which could affect the concentrations, loads, and the degradability of adsorbed organic and inorganic toxic materials. A variety of analyses including $^{14}C$ and high resolution mass spectroscopy need to be employed to precisely define the sources and to quantify the degradability of riverine carbon. Long-term data on concentrations of major ions including alkalinity and daily discharge have been used to show direct evidence of ecosystem changes in the US. The current database managed by the Korean government could be improved further by integrating the data collected by individual researchers, and by adding the major components ions including DIC, DOC, and POC into the database.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.4
• /
• pp.65-73
• /
• 2002

It has been recognized that the damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the nonlinear response is required. The methods available to the design engineer today are nonlinear time history analyses, monotonic static nonlinear analyses, or equivalent static analyses with simulated nonlinear influences. Some building codes propose the capacity spectrum method based on the nonlinear static analysis(pushover analysis) to determine the earthquake-induced demand given by the structure pushover curve. These procedures are conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of structures, without iterative computations, given by the structural initial elastic period and yield strength from the pushover analysis, especially for MDF(multi degree of freedom) systems. The purpose of this paper is to investigate the accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters. The conclusions of this study are as follows; 1) NDSM is considered as practical method because the peak deformations of nonlinear system of MDF by NDSM are almost equal to the results of nonlinear time history analysis(NTHA) for various ground motions. 2) When the results of NDSM are compared with those of NTHA. mean of errors is the smallest in case of post-yielding stiffness factor 0.1, static force by MAD(modal adaptive distribution) and unloading stiffness degradation factor 0.2~0.3.

• The Journal of the Petrological Society of Korea
• /
• v.23 no.3
• /
• pp.197-208
• /
• 2014

Zircon separated from a biotite schist of the Guryong Group in Odesan area, eastern part of the Gyeonggi Massif in Korea were analysed for SHRIMP U-Pb ages. CL images display composite core-rim structures of the zircon, indicating an in-situ overgrowth of zircon through a high-grade metamorphism. The metamorphic zircon rims give a weighted mean age of $247{\pm}6Ma$. While the detrital zircon cores have zoning patterns and Th/U ratios indicative of a magmatic origin. Among 53 analyses from the cores, 46 data yield near concordant ages which are concentrated at $378{\pm}10Ma$ (n=9), $420{\pm}4Ma$ (n=6) and $1845{\pm}9Ma$ (n=18) with sporadic Neoproterozoic ($687{\pm}9Ma$) to late Archean ($2519{\pm}20Ma$) ages. The age data constraint sedimentation age of protolith of the Guryong Group, so far unknown, as late Paleozoic. The Guryong Group of this study is the first late Paleozoic strata reported from eastern Gyeonggi Massif, and its maximum depositional age (ca 378 Ma) is identical with those of the late Paleozoic strata in the southwestern Ogcheon Belt. The Triassic metamorphic age and abundant middle Paleozoic provenance (361~425 Ma) of the Guryong Group are similar with those reported from the Triassic collisional belt in central China. Thus this study indicates that the Odesan area would be an possible eastward extension of the Triassic collisional belt in central China.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.1
• /
• pp.409-418
• /
• 2019

Debris flows occur in mountainous areas due to heavy rains resulting from climate change and result in disasters in the downstream area. The purpose of this study is to estimate the impact force of a debris flow when a check dam according is installed in various locations in the channel of a highly mountainous area. A Finite Differential Element Method (FDM) model was used to simulate the erosion and deposition based on the equation for the mass conservation and momentum conservation while considering the continuity of the fluid. The peak impact force from the debris flow occurred at 0 to 5 sec and 15 to 20 sec. When the supplied water discharge was increased, greater peak impact force was generated at 16 to 19 sec. This means that when increasing the water supply, the velocity of the debris flow became faster, which results in increased energy of the consolidation between the particles of the water and the sediment made. If a number of check dams were to be set up, it would be necessary to investigate the impact force at each location of the check dam. The results of this study could provide useful information in predicting the impact force of the debris flow and in installing the check dams in appropriate locations.

• Journal of the Korean Electrochemical Society
• /
• v.24 no.4
• /
• pp.77-92
• /
• 2021

The energy density of lithium-ion batteries (LIBs) determines the mileage of electric vehicles. For increasing the energy density of LIBs, it is necessary to develop high-capacity active materials that can store more lithium ions within constrained weight. The rapid progress made in cathode technology has realized the utilization of the near-theoretical capacity of cathode materials. In contrast, commercial LIBs have still exploited graphite as active material in anodes since the 1990s. The most promising way to increase anodes' capacity is to mix high-capacity and long-cycle-life silicon oxides (SiOx) with graphite. However, the low initial Coulombic efficiency (ICE) of SiOx limits its content below 15 wt%, impeding the capacity increase in anodes. To address this issue, various prelithiation techniques have been proposed, which can improve the ICE of high-capacity anode materials. In this review paper, we introduce the principles and expected effects of prelithiation techniques reported so far. According to the reaction mechanisms, the strategies are categorized. Mainly, we focus on the recent progress of solution-based chemical prelithiation methods with commercial viability, of which lithiation reaction occurs homogeneously at liquid-solid interfaces. We believe that developing a cost-effective and mass-scalable prelithiation process holds the key to dominating the anode market for next-generation LIBs.