• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1101-1104
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• 2008

Recently, active researches are conducted on high performance concrete(HPC) exhibiting high strength and high fluidity. These researches are resulting in increased applications on real structures. In order to satisfy the required performances, HPC makes use of large quantities of binder and presents low water-cementitious material ratio. Such mixing is increasing significantly the autogenous shrinkage, which subsequently is likely to favor the potential development of cracks. Therefore, we investigated the effect of used materials and mix proportions on the shrinkage properties of HPC, and of the use of expansive additives and shrinkage reducing agents on the HPC. The autogenous shrinkage of HPC using blast furnace slag are tend to be increased, in some case have the potential development of cracks by only the autogenous shrinkage. Also the using method in combination with expansive additive and shrinkage reducing agent is more effective than the separately using method of that.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.16-20
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• 2018

Steel Fiber reinforced self-compacting concrete (SFRSCC) has been widely used in a number of structures, such as ordinary civil infrastructures, sky scrapers, nuclear power plants, hospitals, dams, channels and etc. Thanks to its short and discrete reinforcing fibers, its performance, including tensile strength, ductility, toughness and flexural strength gets much better in comparison with ordinary self-compacting concrete (SCC) without any reinforcing fibers. Despite all these aforementioned advantages of SFRSCC, its performance highly depends on fiber's orientation. In case of short discrete fibers, the orientation of fibers is completely random and cannot be controlled during pumping process. If fibers distribution inside hardened state concrete are randomly distributed, it leads to less resistance potential of concrete element, especially in terms of flexural and tensile strength. The maximum expected strength may not be achieved. Therefore, fiber alignment has been considered as one of the important factors in SFRSCC. To address this issue, this study investigates the effects of concrete matrix's density and inlet velocity on fiber alignment during the pumping process using a finite element method.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.9 no.6
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• pp.711-718
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• 2019

Spectrum analyzer and electromagnetic field meter were used to investigate the EM generation behaviour in different types of home electrical appliances. During microwave oven operation, the EM power measured at a point 30cm apart was measured in the range of 8~11mW/㎡, the strength of the low frequency magnetic field was 60~80mG and the electric field strength was measured at 150~160V/m. For smart phone wireless charging pad, it was measured at an electromagnetic power of 0.4mW/㎡, an electric field of 160 V/m and a magnetic field of 1mG at a point 10cm away. For microwave oven and wireless charging pad, if used within 10cm, the size of the electric field has been measured at a large value that exceeds the human body protection standard and may be hazardous to humans. On the other hand, home appliances such as TVs, hairdryers and refrigerators all showed very low levels of electromagnetic waves, electric fields and magnetic fields, with no harmful effects seen. For electromagnetic shielding, the metal Cu fabric and metal foil had a high level of EM shielding, while polymer films had a low EM shielding characteristic.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.50-57
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• 2018

The purpose of this study is to evaluate the practical application of the self consolidating concrete for the steel concrete pannel (SCP) in module LNG storage tank proposed in the previous research. We evaluated the physical properties and filling performance of developed concrete for the SCP module. First, a slump flow test was conducted to evaluate the performance of the proposed guidelines for the filling test. As a result, all of the concrete used showed satisfactory performance. Based on the results of the previous study, it was found that the reliability of the required time measured by the $T_{500}$ test and the rheometer results measured before and after pumping was 0.94 which means the separation and blocking should not occur. The L-box test and the U-box test were conducted before and after pumping. All of the guidelines suggested showed satisfactory performance. SCP module for LNG storage tanks was fabricated on actual size scale to evaluate the practical application at the final site. As a result, it was confirmed that satisfactory filling performance was obtained in all the specimens.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.1
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• pp.76-79
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• 2017

This paper presents the electromagnetic shielding structure for low frequency wireless power transfer system with magnetic induction method using soft magnetic materials. Soft magnetic materials have advantages such as high permeability and low magnetic loss, but have undesirable effect of power loss by eddy current. To overcome this, we proposed the patterned soft magnetic material to suppress the eddy current path. For validity of this paper, we simulated the coil transfer efficiency and the radiated electromagnetic field, and fabricated the proposed structure using 79-permalloy. The measured results shows good agreements with the simulated results and reduction of the radiated electromagnetic field compared to commercial ferrite plate.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.6
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• pp.578-583
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• 2016

In this paper, we propose a multi-mode wireless power transfer (WPT) system with a dual loop structure. The proposed multi-mode WPT system consist of outer loop module which can operate at two different frequency bands including 6.78 MHz magnetic resonance WPT mode and 13.56 MHz near field communication (NFC) mode and inner loop module connected with outer loop which can operate at two different frequency bands including WPC mode and PMA mode based on inductive coupling standards. In order to be able to embed this system into smartphone battery back cover, the electrical designs are optimized and then the size was fixed $45{\times}90{\times}0.35mm3$ (including ferrite sheet) which is the same commercial smartphone. The proposed multi-mode WPT module can cover WPC and PMA mode based on inductive coupling. Moreover, it has more than 20 dB return loss characteristics at two different frequency bands including 6.78 MHz and 13.56 MHz, and shows more than 70 % transfer efficiency between resonant coils at 6.78 MHz in magnetic resonant charging environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.382-390
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• 2017

In this paper, we consider particular exposure scenarios to evaluate human effects for inductive commercial wireless charging device operating at low frequency. The coil used in this study is the A10 model in Qi standard proposed by WPC(Wireless Power Consortium), and input power is 5 W to the operating frequency of 155 kHz. In perfectly aligned condition, the max leakage magnetic field is $257.58{\mu}T$ which is obtained at the side of the device, and it is exceeded about 7.4 times of the ICNIRP 1998 reference level. The SAR is evaluated with homogeneous phantom which has electric constants of wet skin. The max value of the SAR is $134.47{\mu}W/kg$ which is obtained at the side of the device also, and it is much lower than the international guidelines. Especially, it showed higher SAR values in case of misalignment condition, so we will need to consider the misalignment condition importantly when we evaluate human effects for wireless power transfer system.

• Proceedings of the KACD Conference
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• 2008.05a
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• pp.204-212
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• 2008

The purpose of this study was to compare the apical microleakage in root canal filled with Resilon by methacrylate-based root canal sealer or 2 different self-adhesive resin cements. Seventy single-rooted extracted human teeth were sectioned at the CEJ perpendicular to the long axis of the roots with diamond disk. Canal preparation was performed with crown-down technique using Profile NiTi rotary instruments and GG drill. Each canal was prepared to ISO size 40, .04 taper and 1 mm short from the apex. The prepared roots were randomly divided into 4 experimental groups of 15 roots each and 5 roots each for positive and negative control group. The root canals were filled by lateral condensation as follows. Group 1: Gutta-percha with AH-26, Group 2: Resilon with RealSeal primer & sealer, Group 3: Resilon with Rely-X Unicem, Group 4: Resilon with BisCem. After stored in $37^{\circ}C$, 100% humidity chamber for 7 days, the roots were coated with 2 layers of nail varnish except apical 3 mm. The roots were then immersed in 1% methylene blue dye for 7 days. Apical microleakage was measured by a maximum length of linear dye penetration after roots were separated longitudinally. One way ANOVA and Scheffe's post-hoc test were performed for statistical analysis. Group 1 showed the least apical leakage and there was no statistical significance between Group 2, 3, 4. According to the results, the self adhesive resin cement is possible to use as sealer instead of primer & sealant when root canal filled by Resilon.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.85-88
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• 2006

This study describes the optimum mix proportion of the high strength and self-compacting concrete placed in main structures of LNG above tank. This concrete requires high strength level about $60{\sim}80MPa$, low hydration heat, balance between workability and consistency without vibrating in the actual work. For this purpose, low heat portland cement and fly ash are selected and design factors including water-binder ratio, replacement ratio of fly ash are tested. As experimental results, low heat portland cement shows lower the confined water ratio than another cement type and the optimum replacement ratio of fly ash in order to improve properties of the binder-paste shows 10% by cement weight considering test results of the confined water ratio$({\beta}p)$. Also, flowability of the high strength and self-compacting concrete by using fly ash about $10{\sim}20%$ is improved. The replacement ratio of fly ash 10% and water-binder ratio $25{\sim}27%$ are suitable to the design strength 80MPa and cost, In case of the design strength 60MPa, the replacement ratio of fly ash and water-binder ratio show 20% and $25{\sim}30%$ separately. Based on the results of this study, the optimum mix proportions of the high strength and self-compacting concrete will be applied to the construction of LNG above tank as a new type.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.485-488
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• 2006

This research has evaluated flowability of ultra flowing self-compacting concrete, which is limitedly used for traditional building structures, in accordance with the first class regulations of Japan Society of Civil Engineering(JSCE) that can be applied to overcrowding-arrangement of bar, as a part of application methods that ultra flowing self-compacting concrete is applied to both precast and prestress bridge structures. The experimental results show that the flowability is acceptable in ternary blended among binary and ternary blended mixings, which satifies the first class regulation of JSCE. It is also concluded to use fly ash to increase viscosity of concrete in the case of segregation resistance because of low viscosity in the mixture of slag from blast furnace and limestone micropowder. Satisfying goals of every mixing after U-box self-compacting experiment, we conclude that ultra flowing self-compacting concrete is applicable to bridges and civil constructions of overcrowding arrangement of bar with evaluation of flowability of ultra flowing self-compacting concrete.