• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.545-550
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• 2002

Concrete is one of the essential structural materials in the construction. But, concrete consists of many materials and is affected by many factors such as properties of materials, site environmental situations, and skill of constructor. Therefore, concrete mixes depend on experiences of experts. However, it is more and more difficult to determine concrete mixes design by empirical means because more ingredients like mineral and chemical admixtures are included. Artificial Neural Networks(ANN) are a mimic models of human brain to solve a complex nonlinear problem. They are powerful pattern recognizers and classifiers, also their computing abilities have been proven in the fields of prediction, estimation and pattern recognition. Here, among them, the back propagation network and radial basis function network are used. Compositions of high-performance concrete mixes are eight components(water, cement, fine aggregate, coarse aggregate, fly ash, silica fume, superplasticizer and air-entrainer). Compressive strength and slump are measured. The results show that neural networks are proper tools to minimize the uncertainties of the design of concrete mixtures.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.10a
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• pp.42-45
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• 1994

정밀화학, 제약산업 등에 필요한 에탄올, IPA 등과 같은 유기용매를 고순도로 농축하는 공정은 유기용매와 물과의 혼합물이 일정 농도에서 공비점을 형성하여 일반 증류로는 분리하기 힘들어 Benzene, Cycloheaxane 드의 Entrainer를 첨가하여 상대휘발도를 변화시켜 분리하는 공비증류가 이용되고 있다. 그러나 공비증류는 에너지 사용량이 많고 유독한 물질을 사용하므로 투과증발법과 같은 저에너지 소비형, 환경 친화적인 공정에 대한 관심이 높아지고 있다. 투과증발법에 의한 유기용매 농축공정은 물과의 친화성이 높은 비다공성 막을 이용하여 선택적으로 물을 투과하여 유기용매를 탈수하는 방법으로 투과를 위한 Driving force는 Feed side와 Permeate side사이의 Chemical potential gradient로 이는 물에 대한 Partial vapor pressure differnece로 다음과 같이 표시된다. $\Delta \mu_{F/P.W} = RT ln\frac{y_WP_P}{x_W\gamma_WP_{o.W}}$ 따라서 투과속도를 높이기 위해서 Permeate side를 진공상태로 하여 투과하는 물질을 기화시키고 이를 다시 응축하여 Permeate side의 압력을 낮게 유지시켜야 한다.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.04a
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• pp.38-39
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• 1995

최근 자동차 대체 연료로 가솔린에 10% 무수에탄올이 혼합된 Gasohol 사용에 관한 관심이 고조되고 있으며, 이는 Gasohol이 자동차 배기 가스중의 일산화탄소 및 탄화수소 함유량을 감소시켜 대기 오염을 줄일 수 있기 때문이다. Gasohol에 사용되는 무수에탄올의 농도는 99.5% 이상이어야 하며, 이러한 고순도의 에탄올을 제조하기 위해서는 물과 에탄올의 공비 혼합물(95.6% 에탄올)로부터 공비증류, 분자체 흡착, 투과증발과 같은 분리 조작을 이용하여 물을 제거하는 공정이 필요하다. 현재 에탄올 탈수에는 공비증류가 많이 사용되고 있으나 공비증류는 에너지 사용량이 많을 뿐더러 유독한 Entrainer를 첨가하기 때문에 투과증발과 같은 저 에너지 소비형, 환경친화적인 공정으로의 전환이 이루어지고 있다. 에탄올 탈수용 투과증발 플랜트는 전세계 20여개가 가동되고 있으며, 상업화된 플랜트의 대부분은 독일의 Deutsche Carbone사가 제조한 PVA/PAN 투과증발 복합막을 사용하고 있다. 투과증발 시스템은 물에 대한 친화도가 높은 투과증발막 및 모듈, 기타 분리 구동력을 높여주기 위한 Heater, 진공펌프, 냉각기, 열 교환기 등의 주변 설비로 구성되며, 투과증발 시스템 개발을 위해서는 우수한 막/모듈 제조와 아울러 최적 공정 설계 기술 개발이 필수적이라 하겠다.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.892-897
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• 2008

A new ethanol dehydration process utilizing a thermally coupled distillation column is proposed to reduce the energy requirement of the existing dehydration processes. An entrainer of benzene is used in the proposed system having the column profile similar to the equilibrium composition profile for the maximum distillation column efficiency, and the feed composition is arranged to close to the boundary of different distillation regions. It is found that the proposed distillation system gives some 18% of energy saving over the existing process. In addition, design guidelines are suggested for other azeotropic distillation process.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.157-168
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• 2011

Recently, the cases of freeze-thaw distress on concrete pavement in domestic have been reported periodically. Hereupon, the necessity to establish the standard of spacing factor came to the fore. The test method for analyzing spacing factor is provided in the standard of ASTM C 457. Since researchers tend to judge study results subjectively, the results should be revised throughly. Image analysis program for determining the characteristics of air-void system on hardened concrete identify air void through the difference of a color. The pixel intensity values used in this program have a significant effect on the analysis results. This study compared the automated void count by varying pixel intensity values with the manual void count in order to determine the optimum range of pixel intensity values. Also, this study analyzed the air-void characteristics on eight kinds of concrete mixtures. In this study, it was confirmed that the variation of void counted manually was around 10% from the results of round robin test, and that the optimum range of pixel intensity values is around 80~90. And it was also confirmed that air content (as a whole) was increased generally and spacing factor was decreased by increasing air-entrainer content. But some concrete mixtures showed a tendency that air content was constant and spacing factor was decreased by increasing air-entrainer content. This causes the air entrained by air-entrainer has more influence on spacing factor than air content. Also, the deviation of spacing factor by cutting position of concrete specimen was about 30~100${\mu}m$ because of the limit of 2-D image analysis. The additional study about variation of spacing factor by cutting position of concrete specimen will be performed later.

• Journal of the Korean Chemical Society
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• v.48 no.1
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• pp.28-32
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• 2004

The condensation reaction of (benzylene)triphenylphosphoranes with carbonyl compounds in supercritical carbon dioxide was examined. Reactions of (benzylene)phosphoranes (ca. 1 mmol) with several benzaldehydes in a supercritical carbon dioxide (80 $^{\circ}C$, 2,000 psi) containing THF entrainer (5%) in a 24 mL reactor proceed smoothly to yield olefination products in fairly good to excellant yields but slower, compared to reactions in a conventional THF solvent. Generally, phosphoranes that are not substituted with a nitro group show more (Z)-selective reactions with aromatic aldehydes under $scCO_2$ condition than in THF. The reaction of (benzylene)triphenylphosphoranes with 4-t-butylcyclohexanone gave the corresponding olefin compounds with a low conversion under both the supercritical carbon dioxide and the organic THF solvent. Our preliminary study showed the Wittig reaction carries out smoothly in supercritical carbon dioxide medium and also a possibile tunability of this reaction pathway by adding a entrainer. The results would be useful for devising a novel process for the environmentally friendly Wittig reaction.

• KSBB Journal
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• v.20 no.3
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• pp.205-209
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• 2005

Studies for the commercial production of sesame oil using th supercriticl carbon dioxide were made. Characteristics of sesame oil containing one of natural antioxidant 'sesamol', which only exist at sesame seed were also studied during the supercritical fluid extraction. Among the various factors influencing the sesamol contents in the sesame oil, the roasting time and temperature were checked, because sesamol can be converted from sesamol in through pyrolysis. We found that the sesamol content was increased rapidly under the condition of roasting temperature over $200^{\circ}C$ with longer roasting time. The sesamol content was increased as the temperature and pressure increased, which was caused by increase of solubility of sesamol against sesamol oil. And the sesamol content was increased also with lower speed of supercritical fluid, which increased the contact time with the raw material. The sesamol content was also increased using water increase up to $1\%$ as the entrainer. When the extraction performance with the supercritical fluid was compared to the conventional compressed extraction, the sesamol content was increased up to 11.5 times with the entrainer.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.4 s.11
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• pp.119-129
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• 2003

Concrete and steel are essential structural materials in the construction. But, concrete, different from steel, consists of many materials and is affected by many factors such as properties of materials, site environmental situations, and skill of constructors. Concrete have two kinds of properties, immediately knowing properties such as slump, air contents and time dependent one like strength. Therefore, concrete mixes depend on experiences of experts. However, at point of time using High Performance Concrete, new method is wanted because of more ingredients like mineral and chemical admixtures and lack of data. Artificial Neural Networks(ANN) are a mimic models of human brain to solve a complex nonlinear problem. They are powerful pattern recognizers and classifiers, also their computing abilities have been proven in the fields of prediction, estimation and pattern recognition. Here, among them, the back propagation network and radial basis function network ate used. Compositions of high-performance concrete mixes are eight components(water, cement, fine aggregate, coarse aggregate, fly ash, silica fume, superplasticizer and air-entrainer). Compressive strength, slump, and air contents are measured. The results show that neural networks are proper tools to minimize the uncertainties of the design of concrete mixtures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.1-8
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• 2016

This paper presents an evaluation of engineering properties in TDFA(Tire Derived Fuel Ash)- based concrete in early age. Concrete containing 0.5 of w/b(water to binder) ratio and 20% of FA(Fly Ash) replacement ratio are prepared, and FA content are replaced with TDFA from 3% to 12% for evaluating the effect of TDFA on fresh and hardened concrete properties. With higher than 6% of TDFA replacement ratio, workability is significantly worsened but it is improved with more SP(Super plasticizer) and AE(Air Entrainer) agent. Concrete with 6~12% of TDFA shows reasonable strength development and better resistance to carbonation and chloride attack in spite of early-aged condition. However concrete with 6% TDFA shows poor resistance to freezing and thawing action due to insufficient air content. If air content and workability are obtained, replacement of TDFA to 12% can be used for concrete with FA.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6A
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• pp.449-456
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• 2011

Spacing factor proposed by Power is a concept of averaging air void spacing composed of geometric models. Thus, there's a limitation on simulating actual air void characteristics in concrete. This study presents SDI(spacing distribution index) to overcome the limitation of spacing factor. SDI is also evaluated through comparing SDI with SF(spacing factor). In this study, it was confirmed that SF decreased due to increasing air-entrainer content but SDI increased. This occurs because SDI is the area of spacing distribution curve and SDI increases with increasing the frequency of spacing. SDI is evaluated to have better coverage below $300{\mu}m$ of SF so that determination of critical point of SDI above 80% of durability index can be easily obtained with more reliability. SDI is the area of spacing distribution curve and reflects actual air void characteristics in concrete. A comparative study of SDI and results of freeze-thaw test will be performed later.