• Advances in materials Research
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• v.9 no.3
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• pp.219-231
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• 2020

The aim of this study is to investigate the durability of fly ash based geopolymer mortar with and without protective coatings in aggressive chemical environments. The source materials for geopolymer are Fly ash and Ground Granulated Blast furnace Slag (GGBS) and they are considered in the combination of 80% & 20% respectively. Two Molarities of NaOH solution were considered such as 8M and 10M. The ratio of binder to sand and Sodium silicate to Sodium hydroxide solution (Na₂SiO₃/NaOH) are taken as 1:2 and 2 respectively. The alkaline liquid to binder ratio is 0.4. Compressive strength tests were conducted at various ages of the mortar specimens. In order to evaluate the performance of coatings on geopolymer mortar under aggressive chemical environment, the mortar specimens were coated with two different types of coatings such as epoxy and Acrylic. They were then subjected to different chemical environments by immersing them in 10% standard solutions of each ammonium nitrate, sodium chloride and sulphuric acid. Drop in compressive strength as a result of chemical exposure was considered as a measure of chemical attack and the drop in compressive strength was measured after 30 and 60 days of chemical exposure. The compressive strength results following chemical exposure indicated that the specimens containing the acrylic coating proved to be more resistant to chemical attacks. The control specimen without coating showed a much greater degree of deterioration. Therefore, the application of acrylic coating was invariably much more effective in improving the compressive strength as well as the resistance of mortar against chemical attacks. The results also indicated that among all the aggressive attacks, the sulphate environment has the most adverse effect in terms of lowering the strength.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.639-647
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• 2009

In order to evaluate the durability of reinforced concrete structures under chloride attack from sea water and frost damage, it is important to analyze both the microstructural characteristics of concrete and its diffusion resistance of concrete against chloride ingress. In this study, a relation between micro-pore structures of concrete obtained by the Mercury Intrusion Porosimetry and accelerated chloride diffusivity as well as long term chloride diffusivity were studied for ground granulated blast furnace slag(GGBS) concrete. Different water-cement ratio of 40, 45, 50% and different unit cement concrete of 300, 350, 400 or 450 kg/$m^3$ of the GGBS concrete along with OPC concrete were used and freeze and thawing, and the change in diffusivity and microstructure were observed for both GGBS concrete and damaged GGBS concrete due to rapid freezing and thawing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1805-1813
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• 2010

This paper presented regarding an parametric study to investigate seismic capacity evaluation of semi-rigid steel frame infilled with composit panel. In order to propose the optimum retrofit of the steel frame, we analysed the various pattern of retrofitted steel frame subjected to weak/medium earthquake. Steel frame with composit panel was analysed by Time history analyses analysis. The model were analysed using the suites of ground motion developed by NEHRP project on steel moment resisting frame. These earthquakes consist of 20 horizontal ground acceleration record each, i.e., a 10%, 50% probability of accidence in a 50 year period. We considered the semi-rigid connection which are commonly used in field, and modeled the nonlinear connection element (GAP) between panel and frame. It was shown that how is the steel frame with composit panel effected. We also examined the response of retrofitted frame.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.4
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• pp.67-75
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• 2008

In construction facilities such as bridges, the fluid boundary layer(or water film) is formed at the structure-soil interface by the inflow into the system due to rainfall or/and rising ground-water. As a result, the structure-soil interaction(SSI) state changes into the structure-fluid-soil interaction(SFSI) state. In general, construction facilities may be endangered by the inflow of water into the soil foundation. Thus, it is important to predict the dynamic SFSI responses accurately so that the facilities may be properly designed against such dangers. It is desired to have the robust tools of attaining such a purpose. However, there has not been any report of a method for the SFSI analyses. The objective of this study is to propose an efficient method of finite element modelling using the new interface element named hybrid interface element capable of giving reasonable predictions of the dynamic SFSI response. This element enables the simulation of the limited normal tensile resistance and the tangential hydro-plane behaviour, which has not been preceded in the previous studies. The hybrid interface element was tested numerically for its validity and employed in the analysis of SFSI responses of the continuous bridge subjected to seismic load under rainfall or/and rising ground-water condition. It showed that dynamic responses of the continuous bridge resting on direct foundation may be amplified under rainfall condition and consequently lead to significant variation of stresses.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1415-1426
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• 2008

Stone columns, locally called "GCP (granular compaction pile)" can be used to improve strength and resistance against lateral movement of a foundation soil like rigid piles and piers. Also installation of such a discrete column facilitates drainage, and densifies and reinforces the soil in the sense of ground improvement. The integrity of the GCP has been indirectly controlled with the records of each batch including depth and the quantity of stone filled. An integrity testing was attempted using crosshole S-wave logging. The method is conceptionally same as the crosshole sonic logging (CSL) for drilled piers. The only and critical difference is that S-wave should be used in the logging, because P-wave velocity of the stone column is less than that of ground water. The crosshole sonic logger does not have the capability to measure S-wave propagating through the skeleton of crushed stone. An electro-mechanical source, which can generate either P- or SH-waves, and a 1-D geophone were used to measure SH-waves. Two 76mm diameter cased boreholes were installed 1 meter apart across the nominal 700mm diameter stone column. At every 10cm of depth, shear wave was measured across the stone column. One more borehole was also installed 1 meter outward from the one of the above boreholes to measure the shear wave profile of the surrounding soil. The diametric variation of the stone column with respect to depth was evaluated from the shear wave arrival times across the stone column, and shear wave velocities of crushed stone and surrounding soil. The volume calculated with these variational diameters is very close to the actual quantity of the stone filled.

• Journal of Environmental Health Sciences
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• v.40 no.3
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• pp.225-233
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• 2014

Objective: This study was performed in order to investigate the distribution of antibiotic resistant E. coli and water quality in waterscape facilities. Methods: Nine waterscape facilities were selected and classified into three types: ground, wall and general fountain. The items analyzed in this study were pH, turbidity, $KMnO_4$ consumption, total colony, total coliforms, fecal coliforms and E. coli. Additionally, an antibiotic resistance test on E. coli was performed. Results: There were no sampling sites that exceeded the permitted limits of water quality, but the concentration of pollutants was high at the beginning operation in June. Moreover, concentration of turbidity, $KMnO_4$ consumption and total colony were higher in ground fountains than in wall and general fountains. Five species of antibiotic resistant E. coli were detected from three sampling sites. Conclusions: The waterscape facilities were significantly contaminated with water microorganisms, especially total colony, total coliforms and fecal coliforms. Disinfection and filtration systems to remove pollutants should be installed for safe waterscape facilities.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.530-538
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• 2007

An inductor library for efficient low cost RFIC design has been developed based on a standard digital 0.18 ${\mu}m$ CMOS process. The developed library provides four structural variations that are most popular in RFIC design; standard spiral structure, patterned ground shield(PGS) structure to enhance quality factor, stacked structure to enable high inductance values in a given silicon area, multilayer structure to lower series resistance. Electromagnetic simulation, equivalent circuit, and parameter extraction processes have been verified based on measurement results. The extensive measurement and simulation results of the inductor library can be a great asset for low cost RFIC design and development.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.10
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• pp.1364-1370
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• 2014

Power system fault analysis has been based on symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. Obtaining accurate line impedances as possible are very important for estimating fault current magnitude and setting distance relay accurately. Especially, accurate calculation of zero sequence impedance is important because most of transmission line faults are line-to-ground faults, not balanced three-phase fault. Since KEPCO has started measuring of transmission line impedance at 2005, it has been revealed that the measured and calculated line impedances are well agreed within reasonable accuracy. In case of underground transmission lines, however, large discrepancies in zero sequence impedance were observed occasionally. Since zero sequence impedance is an important input data for distance relay to locate faulted point correctly, it is urgently required to analyze, detect and consider countermeasures to the source of these discrepancies. In this paper, development of pre/post processor to ATP (Alternative Transient Program) version of EMTP (Electro-Magnetic Transient Program) for sequence impedance calculation was described. With the developed processor ATP-cable, effects of ground resistance and ECC (Earth Continuity Conductor) on sequence impedance were analyzed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3587-3595
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• 2015

Low-carbon eco-friendly precast concrete (PC) box structure has been recently was developed as an low-cost infrastructure of near-surface transit system. The concrete of PC box was manufactured by industrial byproducts such as ground granulated blast furnace (GGBF) slag, flyash and rapid-cooling electric arc furnace (EAF) oxidizing slag, its mechanical property and durability were estimated in this study. Based on the mechanical and durability tests, it is found that low-carbon eco-friendly concrete shows high initial compressive strength, more than 90% of design strength (35MPa), and high resistance to salt-attack, chemical- attack and freeze-thaw. Therefore, low-carbon eco-friendly PC box concrete technology is expected to contribute to the railway with low environmental impact.

• Journal of the Korean Geotechnical Society
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• v.35 no.10
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• pp.67-78
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• 2019

The efficiency of suppressing fine dust was evaluated by conducting indoor and field experiments for the ground treated with EICP solution, which is an eco-friendly ground improvement method. In laboratory experiments, the EICP solution was prepared with inexpensive materials for the field applicability, and the optimal mixing ratio and optimal spraying volume of EICP solution were calculated. The optimum amount of calcium carbonate was shown when the ratio of urea/calcium chloride and white powder were 1.5 and 15 g/L, respectively. The optimum spraying amount of the EICP solution was $7L/m^2$ determined by fine dust suppression and cone tip resistance experiments. The spraying of water and EICP solution was conducted at the test-bed where dump trucks pass for the effect of suppressing fine dust of each method. The effective fine dust suppression method can be chosen depending on the situation of the site.