• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.113-119
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• 2019

Many researches on alternative materials as construction materials is continuing by recycling industrial byproducts due to shortage of sitereclamation and natural aggregates. In this paper, engineering properties in early-aged OPC (Ordinary Portland Cement) and GGBFS (Ground Granulated Blast Furnace Slag) concrete are evaluated with EOS aggregate replacement. The related experiments were carried out with 0.6 of water to binder ratio, three levels of EOS replacement ratios (0%, 30% and 50%) for fine aggregate, and two levels of cement replacement with GGBFS (0% and 40%). Several tests such as slump air content, and unit mass measurement are performed for fresh concrete, and compressive strength and diffusion coefficient referred to NT BUILD 492 method are measured for hardened concrete. Through the tests, it was evaluated that the compressive strength in concrete with EOS aggregate increased to 3 days and 7 days but slightly decreased at the age of 28 days. In the accelerated chloride penetration test, GGBFS concrete showed reduced diffusion coefficients by 60 - 67% compared with OPC concrete. The lowest chloride diffusion coefficient was evaluated in the 50% replacement with EOS aggregate, which showed an applicability of EOS aggregate to concrete production.

• Journal of IKEEE
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• v.23 no.3
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• pp.1088-1091
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• 2019

In this paper, a real-time monitoring system for environmental safety by living area is proposed. The proposed system is designed to measure radiation, fine dust and basic living information (temperature) using fixed and mobile measuring equipment, and constitutes a web database that stores data received from the equipment. It also develops web programs for displaying received data on PCs and mobile phones. The results of testing the performance of the system by an authorized testing agency showed that the radiation measurement range was measured in the range of $10{\mu}Sv/h$ to 10mSv/h, which is comparable to the world's highest level, and that the accuracy was measured between ${\pm}6.7$ and ${\pm}8.7$ percent of the measurement uncertainty was measured and normal operation at or below the international standard of ${\pm}15$ percent. In addition, the temperature test was conducted on a section of $-20^{\circ}C$ to $50^{\circ}C$ and normal operation was confirmed in response to the temperature change. Stability of radiated electromagnetic waves was ensured by a suitable judgment. The product's testing in general and high and low temperature environments for about four months after the prototype was made confirmed to be more than five years of durability. The measurement range and accuracy of fine dust sensors are compared with those of companies that measure the air environment, and the performance level is similar through the air quality measurement register.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.8-15
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• 2019

When RC(Reinforced Concrete) structures are exposed to harsh environment, deterioration phenomenon occurs, and the corrosion in rebar due to chloride intrusion is known as representative deterioration, so called chloride attack. In this paper, chloride resistance performance of 2 years aged concrete is evaluated considering 3 levels of water to binder ratio(0.37, 0.42, and 0.47) and 2 levels of substitution ratio of fly ash(0% and 30%). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests referred to KS F 2405 are performed. With adaptation of the previous test results and the results from this study, time-dependent chloride diffusion characteristics are analyzed for each concrete. The FA(Fly Ash) concrete has higher chloride resistance performance than OPC(Ordinary Portland Cement) concrete. According to the evaluation standard of ASTM C 1202, the FA concrete has "Moderate" grade after 49 days while OPC concrete does "Moderate" grade after 365 days. As the results of time-parameter for chloride diffusion, OPC concrete and FA concrete show the decreasing behavior of time-parameters with increasing water to binder ratio. Also, FA concrete has 1.57~2.74 times of time-parameter than OPC concrete. That's cause is thought that the time-parameter indicates the gradient of decreasing of diffusion coefficient. FA concrete has higher time-parameters than OPC concrete by pozzolanic reaction of FA.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.92-99
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• 2021

In the case of precise safety inspection and precise safety diagnosis of a building, a condition evaluation must be conducted to determine the safety grade. Since 2004, an evaluation method using fuzzy theory has been introduced for quantitative condition evaluation,and the relationship and importance of reinforced concrete members using fuzzy theory have been applied. Generally, fuzzy theory is a method used to deal with ambiguous expressions with unclear correlations, but at the time of development, it seems that it was developed by applying fuzzy theory as an alternative in a situation where inspection and diagnosis result data were insufficient. Therefore, it is necessary to verify the relationship and importance of evaluation items derived based on the current fuzzy theory using actual inspection and diagnosis result data.In this study, the correlation between the evaluation items was derived by using the results of 19 precision safety inspections and 9 precision safety inspections and the performance score function formula, and using this, a reasonable durability score calculation formula of the member was presented.

• Journal of the Korea Institute of Building Construction
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• v.21 no.1
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• pp.31-39
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• 2021

The aim of this paper is to improve durability of cement paste by imparting hydrophobicity to the surface and sphere of cement-based materials. A cement paste mixed with a silane/siloxane-based water repellent, and the initial hydration performance, flow performance, and age-specific compressive strength were measured. In addition, the water contact angle, SEM, and XRD before and after surface polishing were measured. When 0.5% of the silane/siloxane-based water repellent was mixed into the cement paste, the compressive strength increased, but the compressive strength decreased as the mixing amount increased by 1.5% and 3.0%. When a silane/siloxane water repellent was incorporated into the cement paste, the hydrophilicity was improved and the contact angle was increased due to hydrophobicity. In addition, the contact angle after surface polishing was found to be larger than the contact angle before surface polishing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.42-49
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• 2020

This paper is a basic study to improve durability by imparting hydrophobicity to the surface and sphere of cement-based materials. A cement mortar to which a silane/siloxane-based mixed water repellent was added was prepared, and its initial hydration performance, flow performance, and compressive strength were measured. In addition, after the surface was abraded, the water contact angle and water absorption were measured. The flow of cement mortar to which the water repellent was added was found to decrease up to 1.5% in the addition amount of the water repellent agent, and increased at 3.0% in the addition amount. It was found that the setting time of the cement paste was delayed in both the initial setting and the termination when the water repellent was added. It was found that the compressive strength decreased from 3.0% of the maximum added amount of the water repellent to a maximum of 30%. The contact angle was found to increase when the water repellent was added to the cement mortar, and the contact angle after surface polishing was found to be larger than before surface polishing. The addition of the water repellent showed hydrophobicity not only on the surface but also on the surface and cross section damaged by polishing. The water absorption rate was found to decrease when the water repellent was added to the cement mortar, and the water absorption rate after surface polishing was found to be greater than before surface polishing.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.553-564
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• 2022

Concrete is a representative composite material that shows excellent performance in the construction field. However, it is a brittle and nonhomogeneous material and exhibits weak behavior against bending and tensile forces. To compensate for such weakens, fiber reinforcement has been utilized, and steel fiber has been recognized as one of the best material for such purpose. However, steel fiber can seriously affect the durability of concrete exposed to the marine environment due to the corrosion caused by chlorine ions. This study intended to evaluate the mechanical performance of steel fiber reinforce concrete during and after repeated wet/dry cycles in salt solution. According to the experimental results, there was no reduction in the relative dynamic modulus of concrete during the repeated wet/dry cycles in salt solution for 37 weeks. Flexural strength was not decreased after completion of repeated wet/dry cycles in salt solution. There was no sign of corrosion in steel fibers after visual observation of fractured surface. However, the flexural toughness was decreased, and this is because about half of the concrete specimen showed failure before reaching the maximum displacement of 3 mm. Although repeated wet/dry cycles in salt solution did not cause cracks in concrete through corrosion of steel fibers, specific attention is required because it can reduce flexural toughness of steel fiber reinforced concrete.

• Journal of the Korean Electrochemical Society
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• v.25 no.4
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• pp.154-161
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• 2022

The carbon-neutrality induced by the global warming is important for the modern society. Hydrogen has been received the attention as a new energy source to replace the fossil fuels. Polymer electrolyte membrane fuel cells, which convert the chemical reaction energy of hydrogen into electric power directly, are a type of eco-friendly power for future vehicles. Due to the sluggish oxygen reduction reaction and costly Pt catalyst in the cathode, the research related to the replacement of Pt-based catalysts has been vitally carried out. In this case, however, the performance is significantly different from each other and a variety of factors have existed. In this review paper, we rearrange and summarize relevant papers published within 5 years approximately. The selection of precursors, synthesis method, and co-catalyst are represented as a core factor, while the necessity of research for the further enhancement of activity may be raised. It can be anticipated to contribute to the replacement of precious metal catalysts in the various fields of study. The final objective of the future research is depicted in detail.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.661-666
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• 2022

This study presented the criteria for analyzing the corrosion of the powder extinguisher storage container according to the useful life, and conducted an experiment on the market area, the factory area, and the apartment building area to ensure proper performance at all times and drew the following conclusions.First, the experimental value for the degree of corrosion of external contact storage containers was found to be unsuitable in the factory area in 2014. In 2012, the experimental value for the degree of corrosion of external contact storage containers in apartment complexes was found to be inappropriate. Second, the experimental value for the dropout of the external paint in the storage container was found to be inappropriate in the factory area in 2014. In 2012, the experimental value of the degree of coating of the external paint storage container in the apartment building area was found to be inappropriate. It was analyzed that the useful life of the fire extinguisher is 10 years, and if it passes the sample test only once, it will be used for up to 13 years, but in fact, the difference varies greatly depending on the surrounding environment of the fire extinguisher place. Since the degree of corrosion of the storage container of the fire extinguisher from 8 years of the fire extinguisher's useful life is clearly decreased, it is judged that 5 years of the fire extinguisher is appropriate.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.79-89
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• 2023

Development of efficient and stable electrocatalysts for oxygen evolution reaction (OER) under acidic conditions is desirable goal for commercializing proton exchange membrane (PEM) water electroyzer. Herein, we report iridium-doped hydrogenated titanate (Ir-HTO) nanobelts as a promising catalyst with a low-Ir content for the acidic OER. Addition of low-Ir (~ 3.36 at%) into the single-crystalline HTO nanobelts with large exposed {100} facets significantly boost catalytic activity and stability for OER under acidic conditions. The Ir-HTO outperforms the commenrcial benchmark IrO₂ catalyst; an overpotential for delivering 10 mA cm^-2 current density was reduced to about 25% for the Ir-HTO. Moreover, the catalytic performance of Ir-HTO is positioned as the most efficient electrocatalyst for the acidic OER. An improved intrinsic catalytic activity and stability are also confirmed for the Ir-HTO through in-depth electrochemical characterizations. Therefore, our results suggest that low-Ir doped single-crystalline HTO nanobelts can be a promising catalyst for efficient and durable OER under acidic conditions.