• Geomechanics and Engineering
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• 제14권2호
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• pp.151-159
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• 2018

Annually, the global production of construction aggregates reaches over 40 billion tons, making aggregates the largest mining sector by volume and value. Currently, the aggregate industry is shifting from sand to hard rock as a result of legislation limiting the extraction of natural sands and gravels. A major implication of this change in the aggregate industry is the need for understanding rock fragmentation and energy absorption to produce more cost-effective aggregates. In this paper, we focused on incorporating dynamic rock and soil mechanics to understand the effects of loading rate and water saturation on the rock fragmentation and energy absorption of three different sandstones (Red, Berea and Buff) with different pore sizes. Rock core samples were prepared in accordance to the ASTM standards for compressive strength testing. Saturated and dry samples were subsequently prepared and fragmented via fast and dynamic compressive strength tests. The particle size distributions of the resulting fragments were subsequently analyzed using mechanical gradation tests. Our results indicate that the rock fragment size generally decreased with increasing loading rate and water content. In addition, the fragment sizes in the larger pore size sample (Buff sandstone) were relatively smaller those in the smaller pore size sample (Red sandstone). Notably, energy absorption decreased with increased loading rate, water content and rock pore size. These results support the conclusion that rock fragment size is positively correlated with the energy absorption of rocks. In addition, the rock fragment size increases as the energy absorption increases. Thus, our data provide insightful information for improving cost-effective aggregate production methods.

• 한국건축시공학회지
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• 제8권1호
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• pp.57-62
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• 2008

Twelve mortars were mixed and tested to explore the effect of gypsum on the compressive strength development and shrinkage strain of alkali-activated mortars. Powder typed sodium silicate and ground granulated blast-furnace slag were employed as alkaline activator and source material, respectively, to produce cementless mortar. The main variables investigated were alkali quality coefficient combining the concentration of activator and main compositions in source material, and the adding amount of gypsum ranged between 1 and 5% with respect to the weight of binder. Initial flow, compressive strength development, modulus of rupture, and shrinkage strain behavior of mortar specimens were measured. In addition, the hydration production of alkali-activated pastes with gypsum was traced using X-ray diffraction and energy-dispersive X-ray analysis combined with scanning electron microscope image. Test results showed that the initial flow of slag-based alkali-activated mortar was little influenced by the adding amount of gypsum. On the other hand, the effect of gypsum on the compressive strength of mortar specimens was dependent on the alkali quality coefficient, indicating that the compressive strength increased with the increase of the adding amount of gypsum until a certain limit, beyond which the strength decreased slowly. Shrinkage strain of mortar tested was little influenced by the adding amount of gypsum because no ettringite as hydration product was generated. However, the adding of gypsum had a beneficial effect on reducing the microcrack in the alkali-activated mortar.

• 한국식품과학회지
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• 제21권5호
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• pp.601-605
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• 1989

쌀보리(새쌀보리)의 주된 입자(7과 10mesh 크기)를 무게비로 5%씩 30%까지 정맥하고 $20-50^{\circ}C$에 침지시키면서 수분흡수속도를 분석하였다. 침지온도 $40^{\circ}C$에서 평형수분함량에 도달하는 시간은 정맥율이 5-15%인 쌀보리의 경우에는 37% 정도 감소하였으며 정맥율이 20-30%인 경우에는 50%가 감소되었다. 정맥수율 95%인 쌀보리의 $40^{\circ}C$에서의 수분흡수속도와 확산계수는 정맥하지 않은 시료보다 각각 1.5배와 2.8배 정도 빨랐다. 수분흡수의 활성화 에너지 값은 정맥수율이 5%씩 감소됨에 따라 약 0.4kcal/mole 정도씩 감소되었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.586-591
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• 2001

This research investigated the feasibility of the accelerated carbonation of cement waste forms with carbon dioxide in a supercritical state. Hydraulic cement has been used as a main solidification matrix for the immobilization of radioactive and/or hazardous wastes. As a result of the hydration reaction for major compounds of portland cement, portlandite (Ca(OH)$_2$) is present in the hydrated cement waste form. The chemical durability of a cement form is expected to increase by converting portlandite to the less soluble calcite (CaCO$_3$). For a faster reaction of portlandite with carbon dioxide, SCCD (supercritical carbon dioxide) rather than gaseous $CO_2$, in ambient pressure is used. The cement forms fabricated with an addition of slated lime or Na-bentonite were cured under ambient conditions for 28days and then treated with SCCD in an autoclave maintained at 34$^{\circ}C$ and 80atm. After SCCD treatment, the physicochemical properties of cement matrices were analyzed to evaluate the effectiveness of accelerated carbonation reaction. Conversion of parts of portlandite to calcite by the carbonation reaction with SCCD was verified by XRD (X-ray diffraction) analysis and the composition of portlandite and calcite was estimated using thermogravimetric (TG) data. After SCCD treatment, tile cement density slightly increased by about 1.5% regardless of the SCCD treatment time. The leaching behavior of cement, tested in accordance with an ISO leach test method at 7$0^{\circ}C$ for over 300 days, showed a proportional relationship to the square root of the leaching time, so the major leaching mechanism of cement matrix was diffusion controlled. The cumulative fraction leached (CFL) of calcium decreased by more than 50% after SCCD treatment. It might be concluded that the enhancement of the characteristics of a cement matrix by an accelerated carbonation reaction with SCCD is possible to some extent.

• 한국지반신소재학회논문집
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• 제20권4호
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• pp.1-7
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• 2021

본 연구에서는 건설공사시 시멘트 사용에 따른 탄소배출 저감과 천연모래 고갈에 따른 대응방안으로 산화그래핀 및 다공성 장석을 적용하였다. 산화그래핀은 부착특성을 증가시키기 위해 (3-aminopropyl)trimethoxysilane으로 기능화 시켰으며, 이를 적용하여 표준배합 모르타르 대비 시멘트 함량을 5% 감소시킨 배합조건으로 공시체를 제작하여 압축강도를 평가하였다. 다공성 장석과 기능화된 산화그래핀이 적용된 시편과 표준배합시편의 압축강도는 각각 26MPa, 28MPa로 큰 편차를 보이지 않았으며, 지반구조물에서 요구하는 시멘트 모르타르의 압축강도를 만족하는 것으로 평가되었다. 시멘트 함량감소에도 적정강도를 유지할 수 있는 원인으로는 다공성 장석에 대표적 포졸란 성분인 SiO₂와 Al₂O₃가 다량으로 함유되어 수화과정에서 Ca(OH)₂와의 반응을 증가시켰고, 나노크기의 그래핀 표면이 수화생성물이 활발히 반응할 수 있는 반응면으로 작용하였으며, Carboxyl 작용그룹의 강력한 공유결합 특성이 수화물의 결합강도를 증가시켰기 때문에 시멘트 함량을 감소시켰음에도 적정한 압축강도가 유지되었던 것으로 판단된다.

• 한국건축시공학회지
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• 제23권6호
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• pp.703-714
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• 2023

본 연구에서는 효율적인 콘크리트용 당류계 초지연제를 개발하기 위해 현재 시판되고 있는 당 성분의 물질들을 대상으로 이들의 종류 및 혼입률 변화에 따른 시멘트 페이스트의 응결지연 특성, 압축강도 발현 특성 및 미시구조 특성을 분석하고자 하였다. 당류계 초지연성 혼화제 중 백설탕, 슈가파우더 및 스테비오사이드를 사용할 경우 응결지연에 효율적인 것으로 나타났다. 슈가파우더 및 스테비오사이드를 제외한 여타 배합의 경우 Plain 대비 동등한 수준의 압축강도를 발휘하는 것으로 나타났다. 특히, 백설탕의 경우 0.2% 혼입시 재령 1일에서 강도가 발휘되지 않다가 재령 28일에서는 Plain과 비교하여 동등 이상의 강도를 발휘하는 것으로 나타났다. XRD, SEM 및 EDS 분석 결과, XRD를 통해 백설탕에 의한 C₃S의 수화지연(응결 지연)을 확인하였으며, EDS의 정량 분석을 통해 추가적으로 확인할 수 있었다. 수화물의 유무는 SEM를 이용하여 존재를 확인하였다. 본 연구 범위에 한하여 콘크리트용 당류계 초지연성 혼화제로써 백설탕을 사용할 경우 응결지연 성능 및 압축강도 발현 성능에 효과적일 것으로 판단된다.

• 펄프종이기술
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• 제47권4호
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• pp.160-167
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• 2015

The reduction of energy consumption in papermaking process has been considered as one of the major issue in the paper technology. The energy efficiency of paper mill becomes more significant for the mill which manufacture the board grade products such as linerboard with recycled paper such as OCC. The application of lignocellulose spacer to the board grade paper stock would be the feasible solution by increasing the paper bulk and the drying efficiency. The major defects originated from the application of the lignocellulose spacer could be the loss of strength properties. In this study, the ways for improving the strength properties of the spacer-added linerboard were suggested and evaluated. The effects of the addition of various types polyelectrolytes were tested and the different methods of polyelectrolytes were applied for finding the efficient way. The pretreatments of lignocellulose spacer with the polyelectrolytes during wood spacer hydration resulted in the higher strength properties than the typical application method such as the addition to the mixed stock. Multilayer treatments of the spacer with polyelectrolytes were also evaluated and leaded to the higher strength properties with the similar bulk improvement.

• Korean Membrane Journal
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• 제10권1호
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• pp.46-52
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• 2008

Optimization of ionomer solution was conducted in order to improve the performance of MEAs in PEMPC. The interface between membrane and electrodes in MEAs is crucial region determining fuel cell performance as well as ORR reaction at cathode. Through the modification of Nafion ionomer content at the interface between membrane and electrodes, an optimal content was obtained with Nafion 115 membranes. Two times higher current density was obtained with the outer Nafion sprayed MEA compared with the non-sprayed one. In addition, the symmetrical impedance spectroscopy mode (SM) exhibited that the resistances of membrane area, proton hydration, and charge transfer decreased as the outer Nafion is sprayed. From the polarization curves and SM, the highest current density and the lowest resistance was obtained at the outer ionomer content of $0.15\;mg\;cm^{-2}$.

• 한국건축시공학회지
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• 제2권4호
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• pp.177-182
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• 2002

The purpose of this study is to develope the strength prediction model by Maturity Method. A maturity function is a mathematical expression to account for the combined effects of time and temperature on the strength development of a cementious mixture. The method of equivalent ages is to use Arrhenius equation which indicates the influence of curing temperature on the initial hydration ratio of cement. For the experimental factors of this study, we selected the concrete mixing of W/C ratio 45, 50, 55 and 60% and curing temperature 5, 10, 20 and $30^{\circ}C$. And we compare and evaluate with logistic model that is existing strength prediction model, because we have to verify adaption possibility of new strength prediction model which is proposed by maturity method. As the results, it is found that investigation of the activation energy that are used to calculate equivalent age is necessary, and new strength prediction model was proved to be more accurate in the strength prediction than logistic model in the early age. Moreover, the use of new model was more reasonable because it has low SSE and high decisive factor.

• 태양에너지
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• 제14권2호
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• pp.91-101
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• 1994

[ $Ca(OH)_2/CaO$ ]계 가역반응 싸이클을 이용하는 화학축열에서 열전도도가 낮은 고체입자 충전층의 전열성능을 개선하여 축열장치의 효율을 높이고자 한다. 본 연구에서는 반응기내의 CaO 입자 충전층의 전열성능 향상을 도모하기 위해 반응기 속에 구리판으로 된 전열핀을 설치하고 수화발열 반응시의 방열특성을 조사 하였다. 이 때 반응조건의 변화에 따른 반응층내의 온도 분포를 조사하고 전열촉진 효과에 대해 검토하였다. 그 결과 구리판 전열핀의 방열촉진 효과로 인하여 수화발열반응의 방열시간이 전열핀을 사용하지 않은 때보다 1/2 이상 단축되었으며, 방열시간은 전열핀의 매수에 가장 많은 영향을 받았다.