• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.793-801
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• 2005

This study investigates fundamental properties of recycled aggregate concrete which incorporated 100% recycled coarse aggregate and various amount of recycled fine aggregate. In addition, for the purpose of the improvement of long term strength and durability, a part of cement was replaced with fly ash. Compressive strength and resistance to chloride ion penetration and carbonation were investigated. When the coarse aggregate was completely replaced with the recycled the replacement ratio of the fine aggregate with the recycled was recommended to be limited below 60% in the consideration of strength. The strength of the steam-cured specimen was very comparable to the wet-cured at 28 days. As fly ash content increased the resistance to chloride ion penetration was increased. The chloride ion penetrability based on the charge passed was found to be low at 21 days and very low at 56 days, respectively. Carbonation depth and carbonation velocity coefficient increased as the fly ash content increased and the relationship between the carbonation depth and recycled fine aggregate replacement ratio was not clear. Up to 28days, however, the measured carbonation depth was mostly less than 10mm which could be considered as low.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.23-31
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• 2004

Normally, coating is used for protecting reinforced concrete. For this purpose, both organic and inorganic coatings are used. The advantages of inorganic coatings are lower absorption of UV, non-burning etc. On the other hand, organic coatings have the advantage of low permeability of $CO_2, SO_2$ and water. Organic coatings provide better protection for reinforced concrete. However, organic coatings such as epoxy, urethane and acryl reduce long-term adhesive strength by the difference of their thermal expansion coefficients and elastic modules from those of concrete, and the formed coating cover of these is blistered by poor breathing. Also, when organic coatings are applied to the wet surface of concrete, they have a problem with adhesion. In this study, a new coating material for protecting concrete was hybridized with polymer and ceramics. And tests were carried out on its physical and durable characteristics, and safety characteristic on elution. All results were compared with organic coating materials and epoxies and showed that the performance of the developed coating material was not inferior to that of other organic coatings in protecting concrete. On the other hand, safety characteristic on elution was superior to epoxies which were used in this study. So, the developed coating material was considered as a suitable protecting coating material which have advantages of inorganic and organic coatings for protecting underground concrete structures, especially in contact with water.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.175-181
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• 2019

In the case of a conventional single stage decompression regulator used for large depressurization in the hydrogen fuel cell system of a fuel cell electric vehicle (FCEV), problems can arise, such as pulsation, slow response, hydrogen brittleness, leakage, high weight, and high cost due to high decompression. Most of these problems can be overcome easily using two decompression mechanisms (two-stage structures). In addition, a wide outlet-pressure control range can be secured if an electronic solenoid is applied to the second decompression. Accordingly, it is necessary to improve the precision of the outlet pressure of a two-stage pressure-reducing regulator and develop techniques, such as leakage prevention, durability, light weight, and price reduction. Therefore, to improve the outlet pressure accuracy and prevent leakage, the structural part before and after decompression to improve the air tightness were divided and the analysis was carried out assuming that the valve part was closed (open ratio: 0%) after each initial internal pressure application.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.4
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• pp.191-203
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• 2018

Identify the effects of ISO quality management system on the durability of the enterprise by applying it to early startups and small - and medium-sized enterprises. In particular, the quality management system of a technology start-up small and medium sized companies is important in applying the management system to the financial, management and quality control services rather than to research and development. The quality management system is applied to the medical equipment manufacturers, mobile phone brokers, foreign Chinese companies, and components manufacturers for diesel engines.Try it. Check the case where the quality management system has been applied to the company concerned and the nonconformities have been improved. In addition, the success of the project was determined by applying the quality control system to maintain the stability and perpetuation of the company through the case of the failed selection. The company explains that recently, it must appoint internal auditors to carry out continuous improvement activities and that those who want the development and continuity of the company must reflect the quality management system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.475-481
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• 2013

Although the lightly burnt MgO at $850{\sim}1000^{\circ}C$ has expansibility, it does not lead to unsound concrete. The expansion of MgO could compensate for shrinkage of concrete for a long-term, because the hydration of MgO occurs at a slow pace. Recently, the study and application of mineral admixture such as fly ash and blast furnace slag have increased for the hydration heat reduction, durability improvement, and reducing $CO_2$ emission in the construction industry. Thus, it is necessary to research on the concrete that contains both a mineral admixture and MgO as an expansion agent. This study investigates fundamental properties of fly ash concrete with lightly burnt MgO through various experiments. The adiabatic temperature test results showed that the fly ash concrete with MgO of the 5% replacement ratio had the slower pace of the temperature rise and the lower final temperature than the fly ash concrete. The influences of MgO on long-term compressive strength varied depending on water-binder ratio, and the long-term length change test results indicated the expansion effects of the FA concrete containing MgO.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.117-124
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• 2019

Military Vehicles of the Korean army had been developed before 2004 and used manual transmissions. Manual transmissions contain a clutch system regulating the force from engine to transmission. In this study, a 2.5-ton military vehicle's clutch system was investigated. The existing clutch system had the characteristics that need to adjust the clearance between the clutch cover and release bearing. Improper clearance led to early wear of the clutch disk and failure of the clutch cover. To solve these problems, an improved clutch system was suggested and tested. The improved clutch system contains auto adjustment of the clearance and an enhanced clutch disk. To verify the improved clutch systems, 2 stage tests were conducted: an accelerated life test of the clutch system, and a driving test by trainee of driving more than 3,000km. As a result, the problems caused by the improper clearance adjustment were solved and this design was verified.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.6
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• pp.129-134
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• 2021

Recently, the demand for electricity is gradually increasing due to the rapid industrial development and the improvement of living standards. In the case of Korea, which is highly dependent on fossil fuels due to such a surge in electricity demand, reduction and freezing of greenhouse gas emissions due to international environmental regulations will immediately lead to a contraction in industrial activities. Accordingly, there are many difficulties in competition with advanced countries that want to link the environment with the country's industrial production activities, and the development of alternative energy as a countermeasure is of great interest around the world. Among these new power generation methods, small-scale power generation facilities with relatively small capacity include photovoltaic generation, wind power generation, and fuel cell generation. Among them, the fuel cell attracts the most attention in consideration of continuous operation, high power generation efficiency, and long-term durability, which are important factors for practical use. Therefore, in this paper, the fuel cell power generation system was researched and constructed by designing the power conversion circuit necessary to finally obtain the AC power used in our daily life by using the DC power generated from the fuel cell as an input.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.1
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• pp.9-20
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• 2023

For highway concrete structures, the deterioration of the structure is accelerated due to the increase in the use of deicing materials, and sectional repair work is being frequently carried out to restore performance. However, after the repair work, re-damage such as cracks, delamination, and poor bond performance is exhibited in the repaired sectional area. In this study, overseas repair material requirements were first analyzed, and present domestic requirements were improved repair material performance through field surveys of common concrete structures, laboratory experiments, and test construction on a disused concrete bridge. In addition, performancebased quality requirements were presented so that all materials that meet the required performance can be applied, and different test methods for each material were unified into concrete test methods for consistent test results analysis. The considered performance requirements were compression strength, bending strength, and bond strength for structural properties, and length change rate, crack resistance, thermal expansion coefficient, and elasticity coefficient were for dimensional behavior. For resistance to chloride penetration resistance and freeze-thaw resistance were presented as durability. The proposed requirements for concrete repair materials are expected to contribute to the improvement of the quality of concrete sectional repair work in Korea.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5915-5922
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• 2013

In this study, with the aim of improving the performance of shale to allow for its use as coarse aggregate for concrete, we coated shale aggregates with water repellents and polymers and evaluated their physical properties such as density, water absorption rate, wear rate, and stability depending on the coating method. In addition, the effects of the performance improvement were evaluated by assessing the properties of fresh concrete produced by varying the shale substitution ratio, as well as the compressive strength, flexural strength, and freeze-thaw resistance according to curing ages. The test results revealed that the absolute dry densities of all coated aggregates satisfied the standard density for coarse aggregates for concrete(>$2.50g/cm^3$),and the absorption rate of the shale aggregate coated with water repellent decreased by about 50% compared with that of uncoated shale. The wear rate of the polymer-coated shale decreased by up to 13.0% compared with that of uncoated shale. All coated aggregates satisfied the stability standard for coarse aggregates for concrete(${\leq}12$). The water repellent-induced performance improvement decreased the shale aggregates' slump by about 20~30mm compared with that of the uncoated shale aggregates, and the air content of the repellent-coated shale aggregate increased by up to 0.9% compared with that of the uncoated shale aggregate. The compressive strength of the polymer-coated shale aggregates at a curing age of 28 days was RS(F) 95.7% and BS(F) 90.0%, and the flexural strength was RS(F) 98.0 % and BS(F) 92.0% of the corresponding values of concretes produced using plain aggregates. Furthermore, the concrete using polymer-coated shale aggregates showed a dynamic modulus of elasticity of RS(F) 91% and BS(F) 88% after 300 freeze-thaw cycles, thus demonstrating improved freeze-thaw durability.