• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.4
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• pp.349-360
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• 2009

Purpose: As the esthetic demands of dental implant patients are increased, the demands of zirconia as implant abutment material are also increased. It has non-metalic color, good biocompatibility, high strength and high toughness. Even thought the advatage of zirconia abutment, there are a few studies about mechanical properties of zirconia abutment. This study evaluated the mecanical strength with compressive bending strength and endurance limit of implant-zirconia abutment assembly. Materials and Methods: Static and cyclic loading of implant-Zirconia abutment assembly were simulated under worst case condition according to ISO. Test groups were implants of external butt joint with straight regular diameter and angled regular diameter zirconia abutment, implant of external butt joint with narrow straight diameter zirconia abutment and implant of internal conical joint with straight narrow diameter zirconia abutment. All test group were evaluated the mecanical strength with compressive bending strength and endurance limit. After fatique testing, fracture surface were examined by SEM. Results: The compressive bending strengths exceed 927N. Regular diameter zirconia abutment were stronger than narrow diameter zirconia abutment(P<.05). The endurance limits ranged from 503N to 868N. Conclusion: Within the limitation of this study, zirconia implant abutment exceeded the estabilished values for maximum incisal biting forces reported in the literature.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.529-539
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• 2004

The corrosion of steel rebars has been the major cause of reinforced concrete deterioration. FRP(Fiber-reinforced polymer) rebar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP rebar is prone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Therefore, the USA, Japan, Canada, UK. etc are using environmental reduction factor. Although difference design guidelines were drawn in many, including USA, Japan, Canada, UK etc, recommendations and coefficients that could take into account the long-term behavior of FRP reinforcement were not well defined. This study focuses on recommendation of environmental reduction factor of FRP rebar. Environment reduction factor were decided using durability test result. FRP rebars were subjected to twelve type of exposure conditions including alkaline solution, acid solution, salt solution and deionized water etc. The water absorption behavior was observed by means of simple gravimetric measurements and durability properties were investigated by performing tensile, compressive and short beam tests. Based on the experimental result, environmental reduction factor of hybrid FRP rebar(A), and (C) and CFRP rebar was decided as 0.85. Also, hybrid FRP rebar(B) and GFRP rebar were decided as 0.7 for the environmental reduction factor

• Korea journal of population studies
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• v.18 no.1
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• pp.119-165
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• 1995

가구는 주택과 내구소비재 구입의 단위가 되기 때문에 장래의 가구수에 대한 자료는 정부가 주택정책을 수립하거나, 기업체가 가전제품이나 가구를 생산하는 장기 계획을 짜는 데 필요불가결한 정보 중 하나이다. 우리 나라는 현재 심각한 주택난을 겪고 있으며 이 주택난은 가구의 급증과 떼어 놓고 생각할 수 없다. 최근 우리 나라의 주택난 해소에 대한 합리적인 대책을 수립하자면 정확하고 상세한 가구추계가 요청된다. 그리고 경제적으로 취약한 계층인 노년인구가 급증하고 있는 것과 관련해서 노인가구의 증가가 예상되고 있는데 이들을 대상으로 하는 각종 사회복지정책의 수립에는 전반적인 가구구조와 노인가구에 관한 정확한 예측이 절실하게 요청되고 있다. 본 연구는 단순한 가구수 추계뿐만 아니라 가구구조 및 혼인상태별로 다양하게 가구수를 추계할 수 있는 비교적 간편하면서도 신뢰성을 인정받고 있는 고노(Kono)의 확장된 가구주율법을 사용하고 최근의 센서스 자료를 활용하여 가구수 추계를 실시하였다. 이 연구에서는 지난 30년간의 가구구조의 변동을 분석하고 1990년 이후 10년간 우리 나라의 시·도별 가구수를 전망하며, 노인가구를 위시한 가구형태별, 가구규모 및 혼인상태별로 가구수를 추계하고 있다. 아무쪼록 이 연구결과가 지방자치화에 따른 지역 주택정책 수립 및 노인복지 등 각종 사회복지정책의 수립에 필요한 자료로써 널리 활용되기를 바란다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.05a
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• pp.59-62
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• 2019

인천신항 내 기존 준설토 투기장은 2018년에 수토가 완료 될 예정이므로 향후 항만개발과 운영시 발생되는 준설토의 원활한 처리를 위해서는 신규 준설토 투기장 조성이 필요하다. 투기장 조성을 위해서는 중 장기적인 준설토 처리방안 등을 고려한 항만기능 향상과 경쟁력 강화를 위한 준설토 투기장 호안 축조가 선행되어야 하기 때문에 극동건설 컨소시움에서는 퍼펙트델타라는 설계컨셉을 수립하고 내구성과 안전성을 강화한 설계, 조기수토 공간확보 및 수토용량 증대, 자연과 인간 도시가 함께하는 환경 친화적인 설계, 현장여건에 가장 적합한 설계를 구현하였다.

• Journal of the Korean Applied Science and Technology
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• v.32 no.2
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• pp.188-193
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• 2015

Blast Furnace Slag is good for enhancing the qualities of concrete such as reducing hydration heat increasing fluidity, long-term strength and durability, but it has some problems: construction time is increased or the rotation rate of form is decreased due to low development of early strength. In this study, an aqueous alkali solution for alkali activated reaction was obtained by the electrolysis using concentrated water discharged from seawater desalination process. Prepared aqueous alkali solution was applied to produce mortars using blast furnace slag. The results can be summarized as follows : For the mortar, compressive strength was decreased below 2% of NaOH and increased below 6% of NaOH. And compressive strength was increased gradually with increasing NaOCl contents. However, NaCl contents of mortars caused a decrease of 28days strength above early strength.

• Journal of the Korean GEO-environmental Society
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• v.10 no.4
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• pp.25-31
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• 2009

In this study, the problem of existing soil pavement is a long-term durability lack and crack occurrence. It complements in order to develop the environmental soil pavement material which composites readily blended mineral binder of liquid and decomposed granite soils. It was estimated optimal mixture proportion for unconfined compressive strength, permeability, $Cr^{6+}$detection test, SEM test with age, freezing and thawing test. It resulted mixture proportion of powder types mineral binder for rates of cement : fly ash : plaster was optimal rates of 50 : 33 : 7, and $Cr^{6+}$detection test as a result was a slight production. SEM test with 3days as a result was made Ettringite. It was found that this material was early development of early-strength for chemical. This study indicated that it will execute field appliciability Evaluation test, examination of soil pavement method with decomposed granite soils and mineral binder.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.135-144
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• 2004

Since Modern bridges have a tendency to make the spans continuous and longer, the effect of concrete shrinkage and creep is very important and must be evaluated appropriately for the durability and safety of steel-concrete composite bridges. However, highway design specification in current use prescribes $180^{1\;2}$ as the final shrinkage strain. which is for less value than one resulted from many experimental researches and cause some problems in the construction of composite bridges due to the understimation of shrinkage strain. Thus, in this paper nonlinear analysis with time-steps applying the CEB-FIP(90) provision have been conducted for plate girder bridge, box girder bridge and Preflex beam bridge and the linear equivalent shrinkage strain for the design of composite bridges. which produces the stress equal to the values from the nonlinear analysis, has been calculated by comparing the results with the values following highway design specification. The results yield appropriately double values than $180^{1\;2}$ which highway design specification prescribes.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.143-152
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• 2005

Shotcrete for support of tunnel structures may contact with groundwater. The hazardous components in groundwater may cause corrosion of shotcrete. Also, the hazardous components may deteriorate the engineering properties of shotcrete, such as compressive strength, bond strength, flexural strength and so forth. The more the effect of the hazardous components on the shotcrete may increase, the more the stability of tunnel structure may decrease. The specimens were artificially immersed in various chemical solutions including hazardous components after the specimens were made at the tunnel construction site. It was performed to analyze the effect of the hazardous components in ground water on the engineering properties of shotcrete. The uniaxial compressive strength test, XRD, SEM were conducted to evaluate the durability and corrosion of shotcrete.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.5
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• pp.385-392
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• 2014

The isolators have been generally used to reduce a seismic force. If the isolators apply to the nuclear power plants(NPPs), the durability and capacity for the structures and equipments should be ensured during the life time. In this study, the long-term behavior of isolated NPPs was analyzed for ensuring the seismic safety. The properties of isolator due to the age-related degradation were analyzed. And the seismic behavior of isolated buildings was analyzed by considering the aging of rubber bearings in different temperature environments. According to the analysis results, the natural frequency of structures was increased with time. But the maximum acceleration and maximum displacement of isolated structures have not changed significantly. Although the damaged of structure did not occurred by aging of isolators, it was presented that the spectral acceleration at the target frequency of isolated structure increased with the temperature. Therefore the isolators in the isolated buildings should be carefully designed and manufactured considering the temperature-dependancy of rubber material.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.441-444
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• 2008

This study was conducted to develop self-repairing ability for concrete so that inspection could be available even in the event of minute cracks, for more economic concrete structure maintenance and longevity. This is a basic attempt to develop self-repairing concrete using the biochemical reaction of bacteria through an innovative method. In this study, the characteristics and problems posed by self-repairing concrete as proposed in international scientific journals were examined, and the potential of new concrete reformation and performance improvement using bio-mineralization was explored. Bio-mineralization, which is an action of creating bio-minerals using an organism, was proposed. A new concept of bacteria such as bacillus pasteurii using bio-mineralization that precipitates calcium carbonate, as well as the possibility of mechanical performance and durability of concrete and repair of cracks, was introduced. Directions for further study through basic experiments and developmental feasibility of self-repairing concrete were also presented.