• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.163-172
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• 2013

This paper presents a comprehensive review of recent advances in ultra-high performance concrete (UHPC). Fundamental characteristics of UHPC are elaborated with focus on its material constituents, mixing, and formulation procedures. Use of state-of-the-art materials such as carbon nanotubes or nano-silica is discussed as well, whose inclusion may enhance the performance of UHPC. The review evaluates supplementary treatment methods (e.g., pressuring curing) and identifies applicable standard test methods for determining the properties and behavior of UHPC. Site implementation is provided to link laboratory research with full-scale application. Research needs are suggested to further develop UHPC technologies from technical and socio-economical perspectives.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.55-56
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• 2011

This paper is to compare and analyze the properties of ultra high strength concrete depending on the use of SF aiming for applicability of superplasticizer containing CASB as a functional agent for strength improvement. As experimental results, in case superplasticizer containing CASB is used, regardless of W/B, settiing time was more accelerated than N, and both compressive strength and tensile strength showed an increase in their strength minutely.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.295-296
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• 2023

This study evaluated the compressive strength after making mortar with low cement composition for carbon-neutral steam curing to respond to climate change. Blast furnace slag, fly ash, and ultra-high powder fly ash were used as substitutes for cement. The cement substitute was used at 40% of the mass of cement, and after steam curing, the compressive strength was measured on the 1st, 3rd, 7th and 28th days of age. As a result of the experiment, at the age of 1 day, the mixture using only cement showed the highest strength, but from the 3rd day, the specimen using ultra-high powder showed a high strength development rate, followed by blast furnace slag and fly ash.

• Design & Manufacturing
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• v.13 no.4
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• pp.17-22
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• 2019

Currently, studies on weight reduction and fuel efficiency increase are the most important topics in the automotive industry and many studies are under way. Among them, weight reduction is the best way to raise fuel efficiency and solve environmental pollution and resource depletion. Materials such as aluminum, magnesium and carbon curing materials can be found in lightweight materials. Among these, research on improvement of bonding technology and manufacturing method of materials and improvement of material properties through study of ultrahigh strength steel sheet is expected to be the biggest part of material weight reduction. As the strength of the ultra hight strength steel sheet increases during forming, it is difficult to obtain the dimensional accuracy as the elastic restoring force increases compared to the hardness or high strength steel sheet. It is known that the spring back phenomenon is affected by various factors depending on the raw material and processing process. We have conducted analytical evaluations and studies to analyze the springback that occurs according to the cross-sectional shape of the ultra high tensile steel sheet.

• Polymer Science and Technology
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• v.8 no.2
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• pp.169-174
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• 1997

• Magazine of the Korea Concrete Institute
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• v.28 no.2
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• pp.35-40
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• 2016

• Journal of Korean Society of Water and Wastewater
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• v.37 no.5
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• pp.253-259
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• 2023

Bioreactors are devices used by sewage treatment plants to process sewage and which produce active sludge, and sediments separated by solid-liquid are treated in anaerobic digestion tanks. In anaerobic digestion tanks, the volume of active sludge deposits is reduced and biogas is produced. After dehydrating the digestive sludge generated after anaerobic digestion, anaerobic digested wastewater, which features a high concentration of organic matters, is generated. In this study, the decomposition of organic carbon and nitrogen was studied by advanced oxidation process. Ozone-microbubble flotation process was used for oxidation pretreatment. During ozonation, the TOC decreased by 11.6%. After ozone treatment, the TOC decreased and the removal rate reached 80.4% as a result of the Ultra Violet-Advanced Oxidation Process (UV-AOP). The results with regard to organic substances before and after treatment differed depending on the organic carbon index, such as CODMn, CODCr, and TOC. Those indexes did not change significantly in ozone treatment, but decreased significantly after the UV-AOP process as the linkage treatment, and were removed by up to 39.1%, 15.2%, and 80.4%, respectively. It was confirmed that biodegradability was improved according to the ratio of CODMn to TOC. As for the nitrogen component, the ammonia nitrogen component showed a level of 3.2×10² mg/L or more, and the content was maintained at 80% even after treatment. Since most of the contaminants are removed from the treated water and its transparency is high, this water can be utilized as a resource that contains high concentrations of nitrogen.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.7
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• pp.117-122
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• 2010

Recently, aspheric glass lens molding core is fabricated with tungsten carbide(WC). If molding core is fabricated with silicon carbide(SiC), SiC coating process, which must be carried out before the Diamond-Like Carbon(DLC) coating can be eliminated and thus, manufacturing time and cost can be reduced. Diamond Like Carbon(DLC) is being researched in various fields because of its high hardness, high elasticity, high durability, and chemical stability and is used extensively in several industrial fields. Especially, the DLC coating of the molding core surface used in the fabrication of a glass lens is an important technical field, which affects the improvement of the demolding performance between the lens and molding core during the molding process and the molding core lifetime. Because SiC is a material of high hardness and high brittleness, it can crack or chip during grinding. It is, however, widely used in many fields because of its superior mechanical properties. In this paper, the grinding condition for silicon carbide(SiC) was developed under the grinding condition of tungsten carbide. A silicon carbide molding core was fabricated under this grinding condition. The measurement results of the SiC molding core were as follows: PV of 0.155 ${\mu}m$(apheric surface) and 0.094 ${\mu}m$(plane surface), Ra of 5.3 nm(aspheric surface) and 5.5 nm(plane surface).

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.3.1-3.1
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• 2011

Nanoengineered materials with advanced architectures are critical building blocks to modulate conventional material properties or amplify interface behavior for enhanced device performance. While several techniques exist for creating one dimensional heterostructures, electrospinning has emerged as a versatile, scalable, and cost-effective method to synthesize ultra-long nanofibers with controlled diameter (a few nanometres to several micrometres) and composition. In addition, different morphologies (e.g., nano-webs, beaded or smooth cylindrical fibers, and nanoribbons) and structures (e.g., core-.shell, hollow, branched, helical and porous structures) can be readily obtained by controlling different processing parameters. Although various nanofibers including polymers, carbon, ceramics and metals have been synthesized using direct electrospinning or through post-spinning processes, limited works were reported on the compound semiconducting nanofibers because of incompatibility of precursors. In this work, we combined electrospinning and galvanic displacement reaction to demonstrate cost-effective high throughput fabrication of ultra-long hollow semiconducting chalcogen and chalcogenide nanofibers. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions, morphology, and crystal structures, providing a large material database to tune electrode potentials, thereby imparting control over the composition and shape of the nanostructures that evolved during galvanic displacement reaction.

• Journal of Ceramic Processing Research
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• v.19 no.6
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• pp.519-524
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• 2018

Carbon/carbon composites (C/C) have been widely studied in the aerospace field because of their excellent thermal shock resistance and specific strength at high temperature. However, they have the problems that is easily oxidized and deteriorated under atmospheric environment. In order to overcome these shortcomings, the CVD coating of ultra-high-temperature ceramics to C/C has become an important technical issue. In this study, thermodynamic calculations were performed to TaC CVD coating on C/C by FactSage 6.2 program. The Ta-C phase diagrams were constructed with the results of thermodynamic calculations in the Ta-C-H-Cl system. Based on the Ta-C phase diagram, the experimental conditions were designed to confirm the deposition of various phases such as TaC single phase, TaC + C and $TaC+Ta_2C$ by varying the composition of Ta/C ratio. The deposited films were found to be in good agreement with the predicted phases.