• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.341-344
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• 2008

Lightweight concrete is known for its advantage of reducing the self-weight of the structures, reducing the areas of sectional members as well as making the construction convenient. Thus the construction cost can be saved when applied to structures such as long-span bridge and high rise building. However, the lightweight concrete requires specific mix design method that is quite different from the typical concrete, since using the typical mix method would give rise the material segregation as well as lower the strength by the reduced weight of the aggregate. In order to avoid such problems, it is recommended to apply the mix design method of self-consolidating concrete for the lightweight concrete. Therefore experimental tests were performed as such mechanical properties(compressive strength, dry density and structural efficiency) of concrete and dry shrinkage according to ACI committee 209.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.217-224
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• 2003

It is necessary to reduce bleeding, which is a kind of segregation of fresh concrete, for improvement of quality of concrete structure. But, besides using high qualify material and adjusting mixture ratio, there is no easy solution to reduce bleeding by now. For that reason, this study is intended to develop bleeding reduction agent and to investigate its application. The test results are following. At first, recommended mixture ratio of bleeding reduction agent is proven to be MC viscosity agent : defoaming agent : superplasticyzer of 1 : 0.004 : 0.2. It goes to prove that bleeding reduction agent does not have bad effect on the quality of concrete such as fluidity, air content and the strength of hardened concrete etc, and can reduce bleeding effectively. Therefore it is thought that bleeding reduction agent can be applied to construction field effectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.6
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• pp.411-419
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• 1999

It has been well recognized that a long term service at elevated temperature of $350^{\circ}C{\sim}550^{\circ}C$ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method (ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.19-26
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• 2014

Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.356-362
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• 2016

Light-weight concrete uses forming agents for reducing weight and high heat insulation property. However, the forming agents make problems of decreased volume and compressive strength of the concrete. This research aims to having weight-reduction and securing heat insulation property using recycled wasted form polyurethane without any forming agents. A small quantity of admixture used for constructability and avoiding material segregation. We picked admixtures from two different companies which shows evenly dispersed of wasted form polyurethane. This research conducts a study on the effect of mixing ratio of admixture on the light-weight concrete used wasted form polyurethane. As a result of the test, increased mixing ratio of the admixtures results reduced fluidity of concrete. On the other hand, percentage of moisture content and compressive strength are increased slightly. Combustibility performance and sound insulation performance are also secured, as well.

• Journal of the Korean Geographical Society
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• v.44 no.3
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• pp.282-300
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• 2009

This paper attempts to focus the ways in which Seoul as an urban space can be read and interpreted from gender perspective, assuming Seoul as a cultural text which represents modernity and post-modernity. Drawing on discussions of urban sociology and human geography which have analyzed the relationship between material spaces and social subjects, this paper explores the gendered segregation and representations of space in Seoul which has been constructed through the process of modernization. The framework of spatial interpretation of Seoul, concentrating on imageablity and legibility, consists of three dimensions; gendered division of labour and sphere, dichotomy of representations along with femininity and masculinity, and the ways of interlocking between modernity and post-modernity. In this paper, 'fl$\check{a}$nerie', Benjamin's method of interpretation of urban culture and the way of seeing with 'speculum' of Irigaray are adopted as metaphoric methodologies. It is an attempt to develop a new methodology to analyze and interpret urban space from gender-cultural perspective.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.97-107
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• 2017

Recently, there have been a lot of incidents related to ground sinks in urban areas, but restoration work is complicated and inconvenience due to on-site control, and particularly, grouting and soil filling are generally applied as recovery measures, but when the grouting or the soil filling is carried out, material segregation phenomenon occurs in the ground or a lot of restoration amount is often required, depending on the state of sinks and the existence of groundwater under the ground and the soil can be lost due to the flow of the ground water, and thus the purpose of this study is to develop a pouch-type filler applied to a trenchless method for emergency reinforcement of the ground sinks with the aim of quick recovery of the ground sink in urban areas, and as a result, it was confirmed that compression strength and the expansion ratio were different according to the temperature of ground water and the compression strength and the expansion ratio could be controlled by mixing alumina powder.

• Journal of Biomedical Engineering Research
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• v.22 no.6
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• pp.511-518
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• 2001

In vitro corrosion resistance of the commercially used 76.5wt.%Pd-17.6%Cu-7.2%Ga and 77.3%Pd-6.0%Ga dental Prostheses high-Palladium system alloys in cast, degassing and porcelain-firing heat treatment conditions were evaluated by the potentiodynamic polarization technique in the de-aerated 0.9%NaCl and a modified Fusayama electrolyte. From the corrosion rate experimental results, we found that there is a small difference in the corrosion resistance depending on the microstructure. However. it was so small that there is no significant problem as a dental material. The 77.3%Pd-6.0%Ga showed better corrosion resistance than the 76.5%Pd-11.6%Cu-7.2%Ga dental Prostheses high-palladium system alloys. These experimental observations in 76.5%Pd-11.6%Cu-7.2%Ga alleys are mainly due to a rapid quenching and Cu in the alloy which accelerate the eutectic reaction with a segregation and Precipitates in the microstructure. On the ocher hand, 77.3%Pd-6.0%Ga alloys, which are solid-solution matrix, show much better col·lesion resistance compared with that of 76.5%Pd-11.6%Cu-7.2%Ga alloys.

• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.122-128
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• 2000

Strip casting process is a new technology that makes a near net shape thin strip directly from molten metal. With this process, a large amount of energy and casting cost could be decreased from the abbreviation of reheating and/or hot rolling process. Ductile cast iron which has spheroidal graphite in the matrix is the most commercial and industrial material, because of its supreme strength, toughness, and wear resistance etc. But it cannot be produced to the thin strip owing to difficulty in rolling of ductile cast iron. In this study, ductile cast iron strips are produced by the twin roll strip caster, with different chemical compositions of C, Si, and Mn contents. And then heat-treated, microstructures and mechanical properties are examined. The microstructures of as-cast strip are that of white cast iron which consists of the mixture of cementite and pearlite, but the equiaxed crystal zone of the pearlite or segregation zone of cementite exists in the center region of the strip thickness, which cannot be observed in the rapidly solidified metallic mold cast specimens. This structure is supposed to be formed from the thermal distribution of strip and the rolling force. Comparing with the structures of each strips after heat treatment, increasing Si content makes smaller spheroidal graphite and more compact in the matrix, furthermore the less of Mn content makes the ferrite matrix be obtained clearer and easier. As a result of the tensile test of graphitization heat-treated strips, the yield strengths are about 250 MPa, the tensile strengths are about $430{\sim}500$ MPa, and the elongations are about $10{\sim}13%$. In the case of the strip which has the smaller and more compact spheroidal graphite in the ferrite matrix, the higher tensile strength and better drawability could be obtained.

• Korean Journal of Materials Research
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• v.33 no.8
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• pp.344-351
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• 2023

Cesium lead iodide (CsPbI₃) with a bandgap of ~1.7 eV is an attractive material for use as a wide-gap perovskite in tandem perovskite solar cells due to its single halide component, which is capable of inhibiting halide segregation. However, phase transition into a photo inactive δ-CsPbI₃ at room temperature significantly hinders performance and stability. Thus, maintaining the photo-active phase is a key challenge because it determines the reliability of the tandem device. The dimethylammonium (DMA)-facilitated CsPbI₃, widely used to fabricate CsPbI₃, exhibits different phase transition behaviors than pure CsPbI₃. Here, we experimentally investigated the phase behavior of DMA-facilitated CsPbI₃ when exposed to external factors, such as heat and moisture. In DMA-facilitated CsPbI₃ films, the phase transition involving degradation was observed to begin at a temperature of 150 ℃ and a relative humidity of 65 %, which is presumed to be related to the sublimation of DMA. Forming a closed system to inhibit the sublimation of DMA significantly improved the phase transition under the same conditions. These results indicate that management of DMA is a crucial factor in maintaining the photo-active phase and implies that when employing DMA designs are necessary to ensure phase stability in DMA-facilitated CsPbI₃ devices.