• Journal of The Geomorphological Association of Korea
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• v.20 no.3
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• pp.1-14
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• 2013

This study aims to investigate the formation and sedimentary environment including formative period, grain composition and climate change from loess-paleosol sequence deposited on a gravel bed of river terrace in the Jincheon Basin, Chungbuk Province. The Jincheon section consists downward of a surface layer, loess-paleosol sequence, transitional layer I, transitional layer II and gravel bed. It can be suggested from the OSL age dating that the sequence was deposited during MIS 6 to 4. The sequence can be divided into four horizons based on the variation in the magnetic susceptibility values. Grain size analysis reveals that the sequence indicates similar properties of grain size to loess deposits in Korea and especially, the Y values in the sequence are lower than those in the loess and paleosol horizons in the Chinese Loess Plateau and similar to those in the Red Clay in the Chinese Loess Plateau and Xiashu loess in the lower reaches of the Yangtze River. These Y values in the sequence can be attributed to the remote source and/or experience of intensive weathering process after deposition in the Korean Peninsula.

• Korean Chemical Engineering Research
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• v.44 no.3
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• pp.289-293
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• 2006

In the CMSMPR (continuous mixed suspension mixed product removal)system, the effect of temperature and RPM on the CSD (crystal size distribution) in the calcium carbonate process was investigated. In the steady state operation, the change of solution pH was small. At the low temperature and below 300 RPM, volume mean size change of calcium carbonate was stable and CSD was narrow. In the SEM view, calcite and aragonite was obtained.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.714-719
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• 2017

The controlled synthesis of inorganic materials with a specific size and morphology is an important factor in the development of new materials in many fields, such as nanoparticles, medicine, electronics, semiconductors, pharmaceutical sand cosmetics. Solution crystallization is one of the most widely used separation processes in the chemical and pharmaceutical industries. Calcium carbonate has attracted a great deal of attention in industry because of its numerous applications. The mean crystal size, crystal size distribution and morphology are important factors in the continuous crystallization process. In this study, the continuous crystallization of calcium carbonate by the calcium chloride process was investigated. The mean crystal size and crystal size distribution data were obtained by a particle size analyzer. The morphological imaging of the crystalswasper formed by SEM. Under steady state operation, the mean crystal size change was small, but increasing the input concentration and mixing rate increased the crystal size. In this operation, some aragonite was found, but the main crystal phase was calcite.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.55-61
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• 2017

This paper is to investigate experimentally the effect of substitution of recycled coarse aggregate(RCA) under 13mm on the engineering properties of the concrete using gap graded coarse aggregates. Concretes with 0.4 of water to cement ratio(W/C) were fabricated to achieve 30MPa of design strength with coarse aggregate over 13mm in size with the maximum size of 25mm. RCA was substituted for coarse aggregate over 13mm from 10% to 50% and crushed coarse aggregate under 13mm was also substituted for coarse aggregate over 13mm from 20% to 40%, respectively. Test results indicated that the replacement of RCA up to 20% resulted in an increase of fluidity and strength. It also caused a decrease in the drying shrinkage due to dense packing effect by achieving continuous grading of mixed aggregates. For practical application of RCA, when properly substituted, the use of RCA enabled the concrete to reduce water contents and sand to aggregate ratio in mixing design stage of the concrete. And, it can also enhance the compressive strength of the concrete.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.246-246
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• 2019

점착성 유사는 비점착성 유사보다 작은 입자 크기를 가지며 전자기적 점착력에 의해 연속적인 응집과 파괴의 과정인 응집현상을 겪는다. 응집현상에 의해 생긴 유사 덩어리를 플럭(Floc)이라고 하며 유사의 응집현상은 점착성 유사가 가지는 입자 크기, 침강속도, 밀도를 변화시킨다. 유사의 이동은 크기, 침강속도, 밀도에 영향을 받는다. 따라서 점착성 유사의 여러 특성에 관여하는 입자의 크기에 대한 충분한 이해는 점착성 유사의 이동을 파악하는 데에 필수적이다. 본 연구에서는 점착성 유사의 여러 특성 중, 입자 크기 분포에 대한 특성을 분석하는 것을 수행하였다. 일반적으로 점착성 유사의 연구에서 입도 분포는 Log-normal 분포로 가정하여 사용되고 있다. 그러나 그 적합성에 대해서는 검증된 바가 없다. 따라서 과거 연구에서 조사된 점착성 유사의 입도 분포 자료를 현장에서 측정된 자료와 실험실에서 측정된 자료로 나누어 수집한 후, 표본에 통계학적인 방법인 적합도 검정을 사용하여 실제 어떠한 분포를 모사하는지 살펴보았다. 적합도 검정은 Kolmogorov- Smirnov (K-S)검정을 이용하였으며 K-S 검정의 결과가 유의수준 5%를 통과하는 경우 가정된 분포가 실제 표본을 잘 모사하는 것으로 판단하였다. 적합도 검정 결과, 점착성 유사의 입도 분포는 현장 실험과 실험실 실험에서 다른 특징을 나타내었다. 현장 실험의 경우 입도 분포의 형태가 지수 분포의 형태를 나타내는 경우가 많았으며 Gamma 분포가 우수하게 모사하였다. 실험실 실험의 입도 분포는 일반적인 양의 왜곡도를 가지는 분포를 그렸으며 GEV 분포와 Gamma 분포가 우수하게 모사하였다. 두 경우 모두 Log-normal 분포가 적합하다고 판단되는 경우는 많지 않았다. 그러나 Log-normal 분포에 위치 매개변수를 추가하여 3 매개변수의 분포로 모사한 경우 유의수준 5%를 통과하는 경우가 크게 증가하였다. 향후에는 점착성 유사의 입도 분포를 모사하고 사용함에 있어 Log-normal 분포를 무조건적으로 이용하는 것은 지양해야할 것으로 판단된다. 2 매개변수의 분포를 점착성 유사의 입도분포로 사용할 경우, Gamma 분포를 추천하며, 기존에 사용되던 Log-normal 분포를 사용할 경우 위치 매개변수를 추가하여 3 매개변수의 Log-normal 분포를 이용할 것을 추천한다. 또한 점착성 유사의 입도를 모사하는 분포를 개발하여 사용한다면 점착성 유사의 이동과 특성을 연구할 때 가장 중요한 크기 특성에 대한 많은 정보를 제공할 수 있다고 판단된다.

• Journal of Korea Water Resources Association
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• v.44 no.1
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• pp.65-72
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• 2011

Natural streams meander, forming pools at the outer part of bend and riffles at the crossing. Pools are deep at a lower flow velocity, and riffles are shallow at a higher flow velocity. Attentions are being paid to pool-riffle sequences in meandering streams because pool-riffle sequences tend to increase biodiversity of the stream ecosystem. This study investigates the characteristics of distribution of bed sediment particles in the upstream reach of the Gap Stream, which is a tributary of the Geum River in Korea. The upstream part of the Gap Stream, the study reach, is a gravel-bed stream, showing a pool and three riffles due to meandering. The reach also includes pools at the upstream and downstream parts of the weir. The characteristics of bed sediment particles sampled at the wetland and in the side channel are studied, revealing that the median particle diameter in the riffle is about four times larger than that in the pool. In addition, flow simulations are carried out for ordinary discharge and design flood, and such parameters important to sediment transport as velocity, shear stress, dimensionless shear stress (or Shields number), and dimensionless shear velocity are provided to see the mobility of sediment particles in the pool-riffle sequence.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.43-49
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• 2015

The objective of this paper is to investigate experimentally the effect of the substitution of recycled aggregates under 13mm on the properties of the concrete using coarse aggregate with size of 13~25mm. Recycled aggregate under 13mm were substituted to the concrete ranged from 10% to 100%. To compare the properties with the case of recycled aggregate, crushed stone with smaller than 13mm was also substituted to the concrete by 20% and 40%. Test results showed that increase of recycled aggregate under 13mm resulted in the increase of slump and compressive strength compared with plain mixture, which was made with only aggregate with 13~25mm size. This is due to the dense gradation of aggregate in association with addition of relatively small particle. It is thought that the use of recycled aggregate under 13mm along with 30% contributes to the quality improvement of the concrete made with only 13~25mm aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.873-876
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• 2008

Although Permeable concrete is resently used as a pavement at a parking lot, a public squre and a bicycle road, we use without enough examining. most the maintenance of quality for Permeable concrete is only dealt with strength and color tone. also, there is not yet enough fundamental data about dynamical properties for strength, rate of void and water permeability. even when it is applied to at the scene, it is been a matter.

• Journal of Adhesion and Interface
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• v.3 no.2
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• pp.9-16
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• 2002

In the synthesis of water-based polyurethane using self-emulsification process, after being neutralized, polyurethane pre-polymers containing ionic pendant groups are dispersed by simple convective mixing. Preparation of dispersion is followed by chain extension reaction, which is considered as important step for growth of the molecular weight of polyurethane. In this work, pH variations in the aqueous phase were monitored during the chain extension process in the presence of water-soluble diamines. The optimum degree of chain extension and the average particle size in the polyurethane dispersions were examined with varying ionic pendent group contents, type of chain extenders, and feed rate of chain extenders, The initial pH value in the aqueous phase linearly increased and the optimum chain extension point could be obtained from the intersection of two linear lines having different slopes, All average particle sizes before chain extension reaction were almost same, however, the final average particle size increased as feed rates of chain extenders increased, In addition, as the ionic pendant group contents increased, the particle size decreased since the hydrophilicity and hydrodynamic volume increased. As carbon numbers of the chain extenders increased, the final particle size increased significantly. From the results, it was concluded that the chain extension reaction took place among the particles not only in a particle.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.138-139
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• 2014

In this study, conventional aggregate obtained from a ready mixed concrete factory and the aggregate with a modified grading produced in lab. condition were prepared. Results showed that a good grading of aggregate the ratio of 5~13 mm and 13~25 mm is 20~40 % produced in the lab. condition significantly improved the slump and the compressive strength of the concrete.