• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.112-119
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• 2020

In this study, cellulose-based bacterial pellets was used for the self-healing concrete manufacturing. The pellet is composed of complex cultured bacterial spore powder, methyl cellulose, two kinds of PVA nutrients and water, and is extruded through a hydraulic press to have a shape of 2mm in diameter to 3 to 4mm in length. Cellulose pellets expand at neutral pH, release bacteria and nutrients, and do not react in a basic environment, increasing the long-term survival rate of bacteria in cement mortar. In addition, pellet self-healing performance of pellet mortar was significantly higher than that of control mortar. Cellulose-based pellets are a new type of bacterial carrier system that will help develop self-healing concrete in the future by improving and optimizing pellets.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.429-438
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• 2003

The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for the unidirectional and satin-weave, continuous glass-fiber reinforced plastic(UD-GFRP and SW-GFRP) tensile specimens. Reflection and transmission optical microscopy was used for investigation of the damage zone of specimens. AE signals were classified as different types by using short time fourier transform(STFT) : AE signals with high intensity and high frequency band were due to fiber fracture, while weak AE signals with low frequency band were due to matrix and interfacial cracking. The feature in the rate of hit-events having high amplitudes showed a process of fiber breakages, which expressed the characteristic fracture processes of individual fiber-reinforced plastics with different fiber orientations and with different notching directions. As a consequence, the fracture behavior of the continuous GFRP could be monitored as nondestructive evaluation(NDE) through the AE technique.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.41-48
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• 2016

This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1195-1196
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• 2015

최근 급격한 산업사회의 발달로 인해 전력기기의 종류와 설치개수가 꾸준히 증가하고 있다. 수많은 고전압 전력기기의 운용으로 인해 발생되는 온실가스는 지구온난화와 같은 환경파괴를 유발시키는 등의 문제를 발생시키고 있다. 고전압 전력기기의 전기적 절연을 위해 주로 사용되는 SF6와 같은 기체 절연체는 온실가스를 유발시키며, 현재 여러 나라에서는 고전압 전력기기로부터 방출되는 CO2의 양을 최소화하기 위한 많은 연구가 진행되고 있다. 특히, 일본 교토에서 180여개의 국가가 온실가스 감축의 의무를 나누고자 교토의정서를 채택하였고, 온실가스를 유발하는 SF6를 대체할 수 있는 친환경 기체 절연체에 대한 연구가 활발히 진행 중이다. 그 중에서도 본 연구에서는 친환경 기체 절연체인 Dry-air의 절연파괴와 부분방전 개시전압 특성을 분석하였다. 다양한 구 전극의 크기와 전극 사이 간격 조건에서 AC 절연파괴 및 부부방전 개시전압에 대한 실험을 수행하였다. 또한, 유한요소해석을 통해 산출한 전계 이용률을 고려하여 절연파괴와 부분방전 개시전압에 대한 특성을 분석하였다. 실험결과, 구 전극의 크기와 전극 사이 간격이 증가할수록 절연파괴와 부분방전 개시전압의 크기가 커지는 것을 알 수 있으며, 부분방전이 먼저 개시되고 절연파괴로 이어는 경향을 확인할 수 있었다. 또한, 전계 이용률이 0.52 이상에서는 부분방전이 개시되지 않고 곧바로 절연파괴로 이어지는 것을 확인할 수 있었다.

• Fire Science and Engineering
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• v.24 no.3
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• pp.72-77
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• 2010

Honeycomb core structure with its excellent stiffness and strength is being utilized in many fields such as interior building material. Because it is inexpensive and renewable, honeycomb paper production is economically and environmentally helpful. However, the paper needs to be fireproofed because it is vulnerable to fire. In this study, we have undergone the performance evaluation process of the honeycomb paper which is widely used as interior material of a fire door and packing material. Four kinds of honeycomb (a honeycomb made of flame-resistant paper; a honeycomb attached with conventional flame-resistant film made in the laboratory; honeycomb impregnated with flame retardant; a honeycomb attached with flame-resistant film after impregnating fire retardant) were used in the study to compare the fire retardant performance. As a result, the honeycomb with impregnated flame retardant showed the highest performance. The flame-resistant film was effective in delaying the igniting time but had a negative effect on the rate of heat and smoke production.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.60-67
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• 2019

To understand the low frequency instability(LFI) characteristics in hybrid rockets combustion, effects of equivalence ratio variations on the phase shift between pressure and heat release oscillations were investigated by using the direct numerical simulation. The change in the equivalence ratio of the main chamber was simulated by the temperature and composition variation of the combustion gas introduced into the post-combustion chamber. In the results, additional combustion appeared along with vortex generation at the backward step, and combustion pressure and heat release oscillations were observed as the vortex moved. In addition, the results confirmed that the phase difference between the pressure and heat release oscillation shifts because of the changes in the propagation velocity of pressure wave as the temperature of combustion gas changes.

• Journal of the Economic Geographical Society of Korea
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• v.25 no.3
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• pp.299-319
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• 2022

Since 2010, there have been phenomena that the recession of key industries has spreaded into a regional crisis, affecting the overall regional economy in Korea. The purpose of this study is to analyze how the regional industrial structure and manufacturing competitiveness has been changed in Gunsan, which is in crisis due to the decline of the shipbuilding and automobile industries. As a result, the pace of change in industrial structure of Gunsan has accelerated, and this is because the mass employment released from the key industries has been absorbed into other industries, but there were no manufacturing fields that could replace the recession of the key industries. Among the manufacturing of Gunsan, the degree of specialization of the basic industries has been gradually weakened, and in addtion, the weakening of location competitiveness has brought a negative impact on the growth rate differential of the manufacturing. It is necessary to closely examine changes in characteristics of regional industrial structure for Gusan to find an alternative direction in order to respond to the manufacturing crisis.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.8
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• pp.553-563
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• 2011

This study investigated the effects of elevated $CO_2$ and nitrogen addition on the anaerobic decomposition mediated by microorganisms to determine the microbial metabolic pathways in the degradation of organic matters of the sediments. There were statistically significant differences(P < 0.05) in the rates between denitrification and methanogenesis upon increased $CO_2$ concentration, nitrogen addition, in the presence of plants. Based on the assumption that anaerobic degradation of organic matter mainly occurs through denitrification, iron reduction, and methanogenesis, methanogenesis is the dominant pathways in the decomposition of organic matter under the condition of elevated $CO_2$ and nitrogen addition. In addition, the altered environment increased anaerobic carbon decomposition. Therefore, it can be concluded that freshwater wetland sediments have positive effects on the global warming by the increased methanogenesiss as well as increased anaerobic carbon decomposition.

• Resources Recycling
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• v.29 no.3
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• pp.51-60
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• 2020

This study was carried out to get the optimum conditions for manufacturing high refractive glass beads from waste fluorescent lamp glass. Chemical composition, X-ray diffraction pattern, particle size distribution, refractive index of glass beads, and the effect of air mixing ratio and ejection rate were investigated. The obtained results are as follows. The X-ray diffraction pattern and chemical composition of glass beads made of waste fluorescent glass are similar to common glass except ReO₂ 0.0108 wt%, BaO 0.071 wt%, NiO 0.0039 wt% and CaO 7.8 wt% but 11.7 wt% of common glass. The glass beads made of waste fluorescent lamp glass have the narrower particle size distribution of and the higher refractive index than the glass beads made of common glass. The optimal conditions of kiln operation for manufacturing glass beads from waste fluorescent lamp glass are 20 m/sec of ejection rate, 1.7 of air mixing ratio, and 940℃ of temperature.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.149-163
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• 2021

Damage characteristics of granite, marble and sandstone whose properties were different were investigated by uniaxial compression test and cyclic loading-unloading test. Strength, elastic constants and damage threshold stresses were measured by uniaxial compression test and were compared with those measured by cyclic loading-unloading test. Average rock strengths measured by cyclic loading-unloading test were either lower than or similar with those measured by uniaxial compression test. Rocks with high strength and low porosity were more sensitive to fatigue than that with low strength and high porosity. Although permanent strains caused by cyclic loading-unloading were different according to rock types, they could be good indicators representing damage characteristics of rock. Damage threshold stress of granite and marble might be measured from stress-permanent strain curves. Acoustic emissions were measured during both tests and felicity ratios which represented damage characteristics of rocks were calculated. Felicity ratio of sandstone which was weak in strength and highly porous could not be calculated because of very few measurements of acoustic emissions. On the other hand, damage threshold could be predicted from felicity ratios of granite and marble which were brittle and low in porosity. The deformation behaviors and damage characteristics of rock mass could be investigated if additional tests for various rock types were performed.