• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.253-260
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• 2017

As global warming became a worldwide issue, a significant effort has been made on the development of technology related to $CO_2$ capture and storage. Geologic sequestration of $CO_2$ is one of those technologies for safe disposal of $CO_2$. Geologic sequestration stores $CO_2$ in the form of supercritical fluid into the underground site surrounded by solid rock, and concrete is used for prevention of $CO_2$ leakage into the atmosphere. In such case, concrete may experience severe damage by attack of supercritical $CO_2$, and especially in contact with underground water, very aggressive form of carbonation can occur. In this work, to prevent such deterioration in concrete, calcium phosphates were added to the portland cement to produce hydroxyapatite, one of the most stable mineral in the world. Temperature rise, viscosity, set and stiffening, and strength development of cement paste incorporating three different types of calcium phosphates were investigated. According to the results, it was found that the addition of calcium phosphate increased apparent viscosity, but decreased maximum temperature rise and 28 day compressive strength. It was found that monocalcium phosphate was found to be inappropriate for portland cement based material. Applicability of dicalcium and tricalcium phosphates for portland cement needs to be evaluated with further investigation, including the long term compressive strength development.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.9
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• pp.1467-1474
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• 2013

To develop a starter culture system for the fermentation of mukeunji, we introduced lactic acid bacteria and yeast isolated from mukeunji into kimchi fermentation as a single or a mixed culture. On evaluating mukeunji flavor, we found that the mixed starter kimchi prepared with two strains, ML17 and MY7, gave the best sensory score. These strains were identified as Lactobacillus (Lb.) curvatus ML17 and Saccharomyces (S.) servazzii MY7 by molecular identification method. The fermentative characteristics of starter kimchi were investigated by measuring changes in the physicochemical and microfloral characteristics during the fermentation. The decrease in pH and increase in acidity in the starter kimchi were faster compared to respective values of control kimchi. There was a gradual decrease in hardness of starter kimchi, which was still slow compared to hardness decrease in control kimchi. Microbial analysis of starter kimchi revealed that Lb. curvatus ML17 and S. servazzii MY7 were the dominant organisms during the entire fermentation period. The lactic acid and citric acid contents of starter kimchi were higher than those of the control kimchi after 90 days of fermentation. By sensory evaluation, the starter kimchi scored higher in appearance, mukeunji flavor, sourness, carbonated flavor, savory taste, texture, and overall acceptability, but lower in off-flavor than the control kimchi.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.871-877
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• 2002

Alumina slurriers, having various amount of alumina and ratio of organic additives, were prepared for tape casting. The relative viscosities were compared to investigate influence of composition on stability of the slurry and plotted as a function of powder fraction. They raised with increasing powder fraction of slurries, revealing a exponential function curve, which means that stability of slurry was not affected by amount and composition of organic additives. Cast green tapes were tested under tensile condition at room temperature. The increase in alumina ratio and binder ratio was found to decrease strain to failure of green tapes from 363% to 45% and from 68% to 25%, respectively. Tensile strength of green tapes increased abruptly with increasing alumina ratio, which showed its maximum at 1 MPa. On other hand, Tensile strength increased continuously from 0.5 MPa to 4 MPa with increasing binder ratio. Mechanical properties of them were affected seriously and lost their properties by elevating temperature from 20$^{\circ}C$ to 80$^{\circ}C$.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.233-242
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• 2018

To overcome the low mechanical strength and corrosion behavior of a carbon steel canister at high temperature condition of a deep borehole, SiC ceramics were studied as an alternative material for the disposal canister. In this paper, a design concept for a SiC canister, along with an outer stainless steel container, was proposed, and its manufacturing feasibility was tested by fabricating several 1/3 scale canisters. The proposed canister can contain one PWR assembly. The outer container was also prepared for the string formation of SiC canisters. Thermal conductivity was measured for the SiC canister. The canister had a good thermal conductivity of above $70W{\cdot}m^{-1}{\cdot}K^{-1}$ at $100^{\circ}C$. The structural stability was checked under KURT environment, and it was found that the SiC ceramics did not exhibit any change for the 3 year corrosion test at $70^{\circ}C$. Therefore, it was concluded that SiC ceramics could be a good alternative to carbon steel in application to deep borehole disposal canisters.

• Tunnel and Underground Space
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• v.15 no.2 s.55
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• pp.111-118
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• 2005

The area of investigation belongs to Okchon metamorphic zone and the fault fractured zone runs parallel to the tunnel direction. It causes the independent decline of tunnel face and the slackness of the tunnel surrounding base so, after all, the severe displacement has occurred within the tunnel. Accordingly, the TSP(Tunnel Seismic Prediction) survey has been performed to investigate the extent of fault fractured zone and to analize its characteristics. Also, we have analized the behavior causes by performing the tunnel face mapping and drilling investigation, and confirmed the position and scale of geological anomaly area and front fractured zone which influences tunnel excavation and supporting. Collected data analyzed ground layer condition through 3 dimensional modeling. Several variables included in the modeling were analyzed by geostastistics. The analysis of the modeling data shows that the belt of weathering by fault fractured zone is developing on the basis of the right side of tunnel and that is decreasing to the left side. The fault fractured zone was confirmed that it has strike, $N0\~5^{\circ}E$ dip NW, and it is consisted of large-scale fractured zone including several anomalies. The severe displacement in tunnel is probably caused by asymmetrical load that n generated by the crossing of discontinuity and the rock strength imbalance of tunnel's both side by fault fractured zone, and judge that need tunnel reinforcement method of grouting etc.

• Journal of the Korean Wood Science and Technology
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• v.33 no.1 s.129
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• pp.29-37
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• 2005

The main objective of this research was conducted to evaluate the impacts on the thermoplastic polymer which is a matrix polymer and the rice husk flour (RHF) which is a reinforcing filler relative to the manufacturing temperature and time when bio-composites were manufactured. In order to evaluate the impacts on the rice husk flour relative to the manufacturing temperature, the rice husk flour was persevered for 10 minutes to 2 hours period at $220^{\circ}C$ temperature which was then added with the polypropylene (PP) and low-density polyethylene (LDPE) to complete the manufacturing process of the bio-composites and measure the corresponding mechanical properties. As preserving time increased at $220^{\circ}C$, the tensile and impact strength were decreased due to the thermal degradation of the main components within the rice husk flour. The thermogravimetric analysis (TGA) was used to measure weight loss caused by the actual manufacturing temperature and the result was that the thermoplastic polymer had not scarcely occurred weight change, but there had been increasing rate of weight loss relative to time for the rice husk flour and the bio-composites under the consistent temperature of $220^{\circ}C$ for 2 hour time period. Therefore, the proper manufacturing temperature and time settings are significantly important features in order to prevent the reduction of mechanical properties which were induced throughout the manufacturing process under the high manufacturing temperature.

• Restorative Dentistry and Endodontics
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• v.25 no.2
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• pp.272-288
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• 2000

Calcium hydroxide is used as a root canal medicament with its several pharmacological effects. However, it has been known that the usage of calcium hydroxide in the root canal system before canal filling with gutta-percha and zinc oxide eugenol-based cement induced change in the properties of root canal cement which might adversely affect sealing ability of the canal filling. The purpose of this study was to identify the reactivity of calcium hydroxide-eugenol compound made from chemical interaction of between calcium hydroxide and zinc oxide eugenol. Chemical properties of calcium hydroxide, eugenol, zinc oxide eugenol, calcium hydroxide-eugenol and calcium hydroxide-zinc oxide eugenol compound were analyzed using XRD. FT-IR Spectrophotometer and FT-NMR Spectrometer. The results were as follows: 1. The compound made from interaction between calcium hydroxide and zinc oxide eugenol was as follows : 2. Calcium hydroxide was shown to make chemical bond (ionic bond) with eugenol. 3. Since bonding between $Ca^{2+}$ and eugenol is simple ionic nature, under water existence, calcium hydroxide-eugenol compound may be ionized easily and its physical property be deteriorated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.224-234
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• 2019

Waterproof layers are installed in civil engineering structures and bridge construction is commonly finished by applying a layer of regular or asphalt concrete above the waterproof layer. However, asphalt materials are susceptible to melting at high temperature due to its superior temperature sensitivity, and this causes the waterproofing material to melt due to the high temperature of the asphalt concrete, thereby increasing the defect occurrence rate due to the thickness reduction. In this study, tensile strength and elongation of hard and soft type of MMA(Methyl Methacrylate) applied to bridges were compared in accordance to standard performance criteria based on different mixture ratios. Results of comparative testing showed that hard MMA resin can display a satisfactory tensile strength, and soft MMA resin displays satisfactory elongation properties, but as the two resin types are separately used, neither types are able to satisfy the standard requirements outlined in KS F 4932. When the amount of the powder exceeds 56.25% of the total amount, voids are generated on the surface after curing and self leveling was impossible and a heterogeneous surface is formed. Furthermore, when the hard resin: soft resin: powder mixture ratio was set to 15g: 85g: 150g. the tensile strength was $1.5N/mm^2$ and the elongation percentage was 133% which satisfy the tensile performance of KS F 4932.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.22-22
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• 1999

교란에 대한 고체 추진제의 연소율의 반등에 대한 이해는 고성능 추진제를 설계하는데 매우 중요한 요소이다. 그 동안의 연구는 고체 추진제의 표면에서 발생하는 교란이 매우 작은 크기로 발생한다는 선형적인 가정을 사용하여 이론적인 응답 함수를 구하였다. 특히 실험실에서 행해지는 교란에 대한 추진제의 응답 함수를 구하기 위하여 이용한 비집촉식 교란 방법을 사용하였다. 이 경우 추진제 표면으로 전달되는 복사열 전달의 크기는 레이저에 의한 복사 일전달과 기체 영의 화염에 의한 열전달을 동시에 고려하여야 한다. 그러나 언급하였던 것처럼 대부분의 이론적 연구는 추진제 표면의 온도 구매가 단열인 것으로 가정하여 진행하였다. 이러한 가정을 기체 영역으로부터 추진제로 전달되는 열전달 량이 작은 점소화초기 등에서 타당한 가정이나, 기체 영역에서 연소가 활발하게 진행되는 경우에는 비합리적인 가정이다. 본 연구에서는. 추진제의 응축 영역에서 분포 화학 반응이 발생하여, 기체 영역에서 화학반응에 의한 연소가 진행되는 경우, 복사 열전달의 교란에 대한 추진제의 응답함수를 수치적으로 계산하였다. 이때 기체 영역에서 발생하는 연소 반응은 De Luca 등에 의하여 제안된 실험적 모델인 $\alpha$ $\beta$ ${\gamma}$ 화염 모델을 사용하였으며, 추진제 표면에서의 열전달 균형에 의한 경계 조건을 사용하였다. 그러나 외부로부터 입사되는 복사광 레이저와 기체 영역의 상호 간섭은 고려하지 않았다. 수치 계산에 의한 응답 함수의 특징은 단열 조건이 사용된 이론적 응답 함수에 비하여 낮은 값을 나타내었으며, 최대치를 보이는 주파수 영역도 이론 함수에 비하여 다른 값을 보여주고 있다.연구 분석 결과 기술적 문제점으로는 배기 가스온도가 낮은데 따른 출구 부분의 Bearing, Sealing이 문제가 될 수 있다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.가 작으며, 본 연소관에 충전된 RDX/AP계 추진제의 경우 추진제의 습기투과에 의한 추진제 물성 변화는 미미한 것으로 나타났다.의 향상으로, 음성개선에 효과적이라고 사료되었으며, 이 방법이 편측 성대마비 환자의 효과적인 음성개선의 치료방법의 하나로 응용될 수 있으리라 생각된다..7%), 혈액투석, 식도부분절제술 및 위루술·위회장문합술을 시행한 경우가 각 1례(2.9%)씩이었다. 13) 심각한 합병증은 9례(26.5%)에서 보였는데 그중 식도협착증이 6례(17.6%), 급성신부전증 1례(2.9%), 종격동기흉과 폐염이 병발한 경우와 폐염이 각 1례(2.9%)였다. 14

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.152-160
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• 2021

Converter steel slag(BOF slag) is a vast amount of solid waste generated in the steelmaking process which has very low utilization rate in Korea. Due to the presence of free CaO which can derive bad volume stability in BOF slag, it usually land filled. For recycling BOF and identify its applicability as fine aggregate, this study investigates the fundamental characteristics of mortar with cement replaced ferronickel slag(FNS), which has the potential to be used as a binder. The results suggest that the mineral phases of BOF slag mainly include larnite(CaSiO₄), mayenite(Ca₁₂Al₁₄O₃₃) and wuestite(FeO) while olivine crystallines are shown in FNS. The results of flow and setting time reveals that the flowability and process of hardening increased when the amount of FNS and BOF slag incorporated was increased. The length change shows that the amount of change in the length of the mortar was almost constant regardless of mix proportion while compressive strength was reduced. Micro structure test results revealed that FNS or/and BOF slag mix took a long time to react in the cement matrix to form a complete hydration products. To achieve the efficient utilization of B OF slag as construction materials, proper replacement rate is necessary.