• 한국전산유체공학회지
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• 제20권4호
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• pp.81-92
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• 2015

Construction waste mainly consists of concrete aggregates of various size. Improper handling of concrete waste would be a major environmental problem whereas its recycling would be both economically useful and environmentally friendly. Bigger concrete aggregates are crushed and converted to medium and fine particles to make them recyclable. An apparatus to separate the concrete aggregates by their size is thus needed for their effective recycling. In this work, segregation of concrete particles in air flows from a newly designed rotary separator having three stages of blades is simulated using a commercial software, ANSYS-CFX. Both 2-D and 3-D models with 360, 240 and 180 blades in each stage are considered. Fundamental mechanism of separation of particles(pase) and the effect of design parameters such as particle size, rotor speed, air flow rate etc. on the performance of the separator are investigated. Critical size of particles that can be separated by the developed separator is also presented in this work. Simulation results are overall in good agreement with data predicted from the theoretical model previously reported in the companion paper.

• 콘크리트학회논문집
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• 제17권5호
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• pp.821-828
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• 2005

To investigate the role of RH and temperature on the transport of chloride in the concrete, two groups of specimens were configured. For both groups, mix design was based on w/c=0.45, $400kg/m^3$ cement, $794kg/m^3$ fine aggregate and $858kg/m^3$ coarse aggregate. After specimen fabrication these were exposed to four different RH (35, 55, 75 and $95\%$ RH) and temperature (0, 20, 30 and $40^{\circ}C$) conditions. After 3 and 6 months $15\%$ NaCl exposure 5mm cores were taken. These cores were sliced and individual cores were ground to powder. In addition, to evaluate the effect of temperature on the chloride binding some powder samples were leached in the each of four temperature chambers. Chloride titration fur these was performed using FDOT acid titration method. Based upon the resultant data conclusions were reached regarding that 1) effective diffusion coefficient, $D_e$, increased with increasing exposure RH, suggesting that the size and number of water paths increased with elevated moisture content in the specimens, 2) $D_e$ increased with increasing temperature in the range of 0 to $40^{\circ}C$ possibly by elevated thermal activation of chloride ions and reduced chloride binding at higher temperature, 3) water soluble chloride concentration, $[Cl^-]_s$, increased with increasing temperature, and 4) chloride concentration profile for initially dry concrete specimens was higher than for the initially wet ones indicating pronounced capillary suction (sorption) occurred for the dry concrete specimens.

• 한국분말재료학회지
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• 제26권6호
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• pp.493-501
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• 2019

In this work, ultra-fine calcium oxide (CaO) powder derived from eggshells is used as the starting material to synthesize mineral trioxide aggregate (MTA). The prepared CaO powder is confirmed to have an average particle size of 500 nm. MTAs are synthesized with three types of fine CaO-based powders, namely, tricalcium silicate (C3S), dicalcium silicate (C2S), and tricalcium aluminate (C3A). The synthesis behavior of C3S, C2S and C3A with ultra-fine CaO powder and the effects of C₃A content and curing time on the properties of MTA are investigated. The characteristics of the synthesized MTA powders are examined by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), and a universal testing machine (UTM). The microstructure and compressive strength characteristics of the synthesized MTA powders are strongly dependent on the C3A wt.% and curing time. Furthermore, MTA with 5 wt.% C3A is found to increase the compressive strength and shorten the curing time.

• Journal of Korea Trade
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• 제24권3호
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• pp.1-19
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• 2020

Purpose - This study empirically analyzes the effects of provisional anti-dumping duties levied on imports by Korea following anti-dumping investigations. An anti-dumping duty is a legal tool that countries use to impose duties on imports to offset injurious dumping. This study verifies how effective the imposition of a provisional anti-dumping duty is and whether such duties have trade chilling effects on aggregate imports. Specifically, this study examines import trade diversion from named to unnamed countries caused by the imposition of provisional anti-dumping duties. Design/methodology - This empirical analysis employs an econometric model of provisional anti-dumping measures for cases in which Korea imposed final affirmative anti-dumping measures. We construct a monthly panel dataset for each stage of anti-dumping investigation undertaken by Korea for all manufacturing industries during 1995-2013. We illustrate a stage-by-stage analysis of anti-dumping investigations from initiation, preliminary decision, imposition of provisional duty, final affirmative decision, and imposition of final affirmative duty on a monthly basis at the six-digit harmonized system code-level. Findings - For cases in which provisional duties are imposed, the reduction in imports from named countries outweighs the increase in imports from unnamed countries. The substantial reduction in imports from named countries is large enough to offset the import diversion to unnamed countries, suggesting that import diversion in investigations is limited during the investigation period. Therefore, the use of provisional anti-dumping duties in Korea is effective, providing evidence of a chilling effect on aggregate imports. Originality/value - Few studies examine the size of the effects on import trade diversion of the imposition of provisional anti-dumping duties. We contribute to the literature by disentangling separate trade effects for each phase of the anti-dumping investigation process and imposition of provisional duty.

• 자원리싸이클링
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• 제31권6호
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• pp.36-43
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• 2022

순환골재 입도 분리를 위해 사용되는 일반적인 스크린은 막힘 현상으로 인해 함수 시료 처리가 제한적이다. 따라서 본 연구에서는 기존 스크린의 분리 효율을 개선하기 위하여, DEM(Discrete Element Method) 기반의 모사 실험을 통해 스프링 기반의 추가 보조 진동 장치의 우수성을 판단하였다. 스프링 디자인에 따른 변위, 진폭 및 변형 각 분석을 통해 운동 특성을 확인하였으며, 이를 스크린에 적용하여 입자의 거동을 모사하였다. 입자 모사 결과, 스프링이 적용된 스크린의 물질 흐름 및 분리 효율은 각각 9.2 kg/s, 97 %로 나타났으며, 기존 스크린과의 비교를 통해 막힘 방지 스프링의 적용은 기존 스크린을 개선할 수 있음을 확인하였다.

• 한국토양비료학회지
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• 제8권1호
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• pp.19-23
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• 1975

답토양(畓土壤)에 유기물(有機物)을 연용(連用)함으로써 토양(土壤)의 이화학적성질(理化學的性質)에 미치는 영향(影響)을 구명(究明)하기 위(爲)하여 20년간(年間) 퇴비(堆肥)를 시용(施用)한 조립질토양(粗粒質土壤)의 시료(試料)를 채취(採取) 분석(分析)한 결과(結果)는 다음과 같다. 1. 립경조성(粒徑組成)은 퇴비연용구(堆肥連用區)와 무퇴비구간(無堆肥區間)에 차이(差異)가 없었으나 수리전도도(水理傳導度), 수중침정용적(水中沈定容積)은 퇴비연용구(堆肥連用區)에서 높았다. 2. 가비중(假比重), 토양경도(土壤硬度)는 퇴비연용구(堆肥連用區)에서 낮았으며 공극률(孔隙率)은 높았다. 3. Atterberg 상수(常數)(액성한계(液性限界), 소성한계(塑性限界) 및 소성지수(塑性指數))가 퇴비연용구(堆肥連用區)에서 높았다. 4. 립국분포(粒國分布)는 퇴비연용구(堆肥連用區)에서 뚜렷하게 증가(增加)되지 않았다. 5. pH, 유기물함량(有機物含量), 염기치환용량(鹽基置換用量), 치환성염류(置換性鹽類) 등(等)은 퇴비연용구(堆肥連用區)에서 근소(槿少)하게 높았다.

• 한국응용과학기술학회지
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• 제34권2호
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• pp.357-366
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• 2017

천연색소는 색을 발현할 수 있는 물질로서 식품, 화장품, 의약품 등에 사용된다. 천연색소는 동 식물에서 추출하여 만들기 때문에 크기가 균일하지 않으며 특히 적색색소의 경우, 다른 색의 색소에 비해 친유성이 강해 수용액 상태에서 쉽게 응집이 되는 경향이 있다. 또한 응집에 의한 크기변화로 인해 색의 재현이 어려운 문제점이 있다. 적색색소로 기존에 사용했던 동물성 색소인 코치닐 추출 색소는 알레르기를 유발하고 식용으로서의 거부감이 있는 등의 문제점으로 인하여 사용이 기피되는 추세이다. 본 연구에서는 적색의 식물성 색소인 라이코펜 추출물과 치자황색소를 사용하였고 Ball-milling을 이용하여 색소의 크기를 균일하게 만든 후 Asymmetrical flow field-flow fractionation(AsFlFFF), Dynamic light scattering(DLS)를 이용하여 크기를 분석하고 색차계를 이용하여 색을 확인하는 연구를 진행하였다. 실험결과 milling 전에는 색소 입자의 크기가 크고 크기분포가 넓었으나, milling 후에는 크기가 감소하고 크기분포가 좁아짐을 확인하였다. 색차계 측정 결과, milling 시간이 증가함에 따라 밝기, 적색도, 황색도가 높아져서 밝은 적색을 나타내었다.

• 한국결정성장학회지
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• 제5권4호
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• pp.414-422
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• 1995

석탄회를 요업원료로 재활용하기 위하여 하소 및 수비에 의하여 선별화 하였으며, 선별화의 영향을 고찰하기 위하여 비처리 석탄회와 하소 및 수비 처리한 석탄회의 결정상, morphology, 화학성분, 입도분포, 강열감량을 측정하였다. 또한, 기존의 점토 수비 실험식이 석탄회의 수비에도 적용될 수 있는지 여부를 조사하였다. 점토에 대한 수비 실험식을 석탄회의 수비에 적용한 결과 Rittinger의 실험식과 비교적 잘 일치하였다. 처리조건에 관계없이, 석탄회는 mullite와 quartz가 주결정을 이루고, 비처리 및 수비 처리한 석탄회에서는 calcite 결정이 관찰되었으나 하소한 경우 calcite의 결정 peak가 나타나지 않았다. 입자의 형태는 비처리 석탄회의 경우 cenosphere, coke type, silicate type, whisker type, aggregate type 입자로 이루어져 있고 하소한 경우에는 coke type 입자가 제거되고 상대적으로 aggregated type 입자가 많이 관찰되었다. 특히 수비 4단계의 경우에는 비교적 구형의 cenosphere가 많이 얻어졌다. 하소에 의해 입도분포가 좁아졌으며, 특히 수비에 의해서 매우 좁은 입도분포를 얻었다.

• Carbon letters
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• 제4권1호
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• pp.1-9
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• 2003

Recently, the control of pore-characteristics of nano-porous materials has been studied extensively because of their unique applications, which includes size-selective separation, gas adsorption/storage, heterogeneous catalysis, etc. The most widely adopted techniques for controlling pore characteristics include the utilization of pillar effect by metal oxide and of templates such as zeolites. More recently, coordination polymers constructed by transition metal ions and bridging organic ligands have afforded new types of nano-porous materials, porous metal-organic framework(porous MOF), with high degree and uniformity of porosity. The pore characteristics of these porous MOFs can be designed by controlling the coordination number and geometry of selected metal, e.g transition metal and rare-earth metal, and the size, rigidity, and coordination site of ligand. The synthesis of porous MOF by the assembly of metal ions with di-, tri-, and poly-topic N-bound organic linkers such as 4,4'-bipyridine(BPY) or multidentate linkers such as carboxylates, which allow for the formation of more rigid frameworks due to their ability to aggregate metal ions into M-O-C cluster, have been reported. Other porous MOF from co-ligand system or the ligand with both C-O and C-N type linkage can afford to control the shape and size of pores. Furthermore, for the rigidity and thermal stability of porous MOF, ring-type ligand such as porphyrin derivatives and ligands with ability of secondary bonding such as hydrogen and ionic bonding have been studied.

• Journal of Forest and Environmental Science
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• 제37권2호
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• pp.116-127
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• 2021

Predicting carbon distribution of soil aggregates is difficult due to complexity in organo-mineral formation. This limits global warming mitigation through soil carbon sequestration. Therefore, knowledge of land use effect on carbon stabilization requires quantification of soil mineral cations. The study was conducted to quantify carbon and base cations on soil mineral fractions in Natural Forest, Plantation Forest and Farm Land. Five 0.09 ha were demarcated alternately along 500 m long transect with an interval of 50 m in Natural Forest (NF), Plantation Forest (PF) and Farm Land (FL). Soil samples were collected with soil cores at 0-15, 15-30 and 30-45 cm depths in each plot. Soil core samples were oven-dried at 105℃ and soil bulk densities were computed. Sample (100 g) of each soil core was separated into >2.0, 2.0-1.0, 1.0-0.5, 0.5-0.05 and <0.05 mm aggregates using dry sieve procedure and proportion determined. Carbon concentration of soil aggregates was determined using Loss-on-ignition method. Mineral fractions of soil depths were obtained using dispersion, sequential extraction and sedimentation methods of composite soil samples and sieved into <0.05 and >0.05 mm fractions. Cation exchange capacity of two mineral fractions was measured using spectrophotometry method. Data collected were analysed using descriptive and ANOVA at α_0.05. Silt and sand particle size decreased while clay increased with increase in soil depth in NF and PF. Subsoil depth contained highest carbon stock in the PF. Carbon concentration increased with decrease in aggregate size in soil depths of NF and FL. Micro- (1-0.5, 0.5-0.05 and <0.05 mm) and macro-aggregates (>2.0 and 2-1.0 mm) were saturated with soil carbon in NF and FL, respectively. Cation exchange capacity of <0.05 mm was higher than >0.05 mm in soil depths of PF and FL. Fine silt (<0.05 mm) determine the cation exchange capacity in soil depths. Land use and mineral size influence the carbon and cation exchange capacity of Gambari Forest Reserve.