• Structural Engineering and Mechanics
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• v.90 no.2
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• pp.107-116
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• 2024

This study examined the changes in the mechanical properties of coral concrete under different coconut fiber admixtures. To accomplish this goal, the compressive strength, splitting tensile strength, flexural strength and elastic modulus properties of coral concrete blocks reinforced with coconut fibers were measured. The results showed that the addition of coconut fiber had little effect on the cube and axial compressive strengths. With increasing coconut fiber content, the flexural strength and splitting tensile strength of the concrete changed substantially, first by increasing and then by decreasing, with maximum increases of 36.0% and 12.8%, respectively; additionally, the addition of coconut fibers resulted in a failure type with some ductility. When the coconut fiber-reinforced coral concrete was 7 days old, it reached approximately 74% of its maximum strength. The addition of coconut fiber did not affect the early strength of the coral concrete mixed with seawater. When the amount of coconut fiber was no more than 3 kg/m3, the resulting concrete elastic modulus decreased only slightly from that of a similar concrete without coconut fiber, and the maximum decrease was 5.4%. The optimal dose of coconut fiber was 3 kg/m3 in this study.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1633-1635
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• 1999

In this study, we evaluated the dependence of thickness and temperature in the breakdown strength of MDPE and effect of semiconductor. As the result, breakdown strength trend to decrease according to the increase of thickness and temperature. We obtained the result that the breakdown strength was a little lower in the structure of Semi/MDPE than Semi/MDPE/Semi, but breakdown strength of MDPE was greater both of all. The dependency of permittivity, tan ${\delta}$ and conductance on frequency and temperature were investigated. Both of the specimans showed the trend of decreased in permittivity as the temperature increased but increase as the frequency increased.

• Journal of the Korean Society of Clothing and Textiles
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• v.11 no.1
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• pp.63-69
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• 1987

Silk fibroin is likely to be hydrolyzed by acids or alkalies at high temperature, and the degree of the hydrolysis has been inferred from the changes in tensile strength and elongation. But, in this experiment, it was intended to infer that from the quantitative changes in terminal aminp group content as well as in tensile strength and elongation. Silk yarn was treated with boiling water, hydrochloric acid, and sodium hydroxide under various conditions. The boiling water somewhat degraded silk fibroin. Silk yarn treated with sodium hydroxide contained more terminal amino group than that treated with hydrochloric acid. This result agreed fairly well with the loss in weight, tensile strength, and elongation: the terminal amino group content increased with the decrease of tensile strength, elongation, and weight. The damage by sodium hydroxide to the silk fibroin was greater than that by hydrochloric acid.

• Transactions on Electrical and Electronic Materials
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• v.13 no.4
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• pp.200-203
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• 2012

Epoxy/mica composite was synthesized, in order to use it as an impregnation resin in a vacuum pressure impregnation (VPI) process, for manufacturing a high voltage rotary machine. The average particle size of the mica was 5~7 ${\mu}m$ and its content was 0, 20, 30 and 40 wt%. A plasticizer or a low molecular aliphatic epoxy was also used, to decrease the viscosity of the composite. The AC electrical breakdown strength was estimated in sphere-to-sphere electrodes, and the electrical breakdown data were estimated by Weibull statistical analysis. The electrical breakdown strength became higher with the addition of mica; and that of the system with 20 wt% mica was highest. The electrical breakdown strength of the system with an aliphatic epoxy was higher than that of the system with a, plasticizer.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.757-762
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• 2002

This study focused on the investigation of durability of latex modified concrete in the points of surface scaling resistance as cement types variated and latex content variated such as 5%, 10%, 15%, and 20%. An increasing the amount of latex produced concrete with increased flexural strength, but with slightly lower compressive strength. The increase in flexural strength might be attributed to the latex films between the hydrated cement and aggregates, and the decrease in compressive strength to the flexibility of the latex component named by Butadiene. The surface scaling resistance test was used to evaluate the durability of latex-modified concretes and rapid setting latex-modified concretes. The surface scaling resistance of LMC was quite good comparing to conventional concrete. Further, surface scaling resistance of RSLMC was improved with increasing the latex content.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.269-274
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• 1998

In this study, to increase fluidity and resistance of segregation of materials, the effect of each of the materials, which have effects on high performance concrete from investigating the properties of strength and drying shrinkage of high performance concrete made by the basic mix proportion used fly-ash and ground granulated blast-furnace slag after hardening, has been checked. According to the experimental results, fluidity on W/C = 34% was satisfied within slump-flow 65$\pm$ 5cm and U-type self-compactability difference 5cm. On the properties of strength, high performance concrete produced compressive strength over 400kg/$\textrm{cm}^2$ in 28days when powder was replaced by 40% of fly-ash and 60% of ground granulated blast-furnace slag. And compressive strength was taken over 600kg/$\textrm{cm}^2$ equal to non-replacement in 91days. Also, the length change of concrete with the addition of fly-ash was smaller than that without it. Therefore, it may be effective on the decrease of drying shrinkage volume.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.275-280
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• 1998

In this study, to increase fluidity and resistance of segregation of materials, the effect of each of the materials, which have effects on high performance concrete from investigating the properties of strength and drying shrinkage of high performance concrete made by the basic mix proportion used fly-ash and ground granulated blast-furnace slag after hardening, has been checked. By the results of this experiment, fluidity on W/C=34% was satisfied within slump-flow 65$\pm$5cm and U-type self-compacting difference 5cm. On the properties of strength, high performance concrete produced compressive strength over 400kg/$\textrm{cm}^2$ in 28days when powder was replaced by 40% of fly-ash and 60% of ground granulated blast-furnace slag. And compressive strength was taken over 600kg/$\textrm{cm}^2$ equal to non-replacement in 91days. Also, the length change of concrete with the addition of fly-ash was smaller than that without it. Therefore, it may be effective on the decrease of drying shrinkage volume.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.725-728
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• 1999

The bridge slab of express railway was designed for high strength concrete (design strength 400kgf/$\textrm{cm}^2$). In case the slab is made with the concrete using type I cement, used much amount of cement can cause cracks through concrete by hydration heat or dry shrinkage. In this study we targeted to solve above problems using type III cement. We could decrease the cement ratio in concrete using type III cement than type I cement. The concrete using type III cement showed good workability and compressive strength, and showed better properties in hydration heat and dry shrinkage than that using type I cement

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.641-646
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• 1998

The structures exposed to marine environment do not show long-term durability due to corrosion of steel and deterioration of concrete by the attack of various salts dissolved in sea water. In this study, Partial substitution of cement with fly ash(20%) or blast furnace slag(40%) was made together with the addition of 4 different corrosion-inhibitors, as a protective measure of concrete structures against chemical attack of salts. Combined effects of mineral and corrosion-inhibiting admixtures were tested by measuring the resistance and compressive strength of concretes under the simulated tidal condition, which consists of alternating 12 hour periods of immersion in artificial sea water and drying in air. Both the strength and concrete resistance were found to decrease in following order, regardless of the corrosion inhibitors the concretes with blast furnace slag, those with fly ash and those without any mineral admixtures. The interrelation between compressive strength of concrete and resistance was investigated.

• Research in Community and Public Health Nursing
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• v.22 no.3
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• pp.315-324
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• 2011

Purpose: The purpose of this study was to investigate the relationships between problem behavior, school stressor and family strength in high-school girls. Methods: Data were collected from 200 high school girls in 2008. Data were analyzed with SPSS/WIN 18.0. Results: There was a positive correlation between problem behavior and school stressor. There was a negative correlation between problem behavior and family strength. The predictors of problem behavior were school stressor, family strength, and monthly family income and these factors explained 43.0% of problem behavior. Conclusion: The findings of this study suggest the necessity of developing nursing intervention programs for enhancing high-school girls' skills in interpersonal relationship and communication to decrease school stressor and increase family strength.