• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.11-17
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• 2011

A major source of durability problems in concrete structures is the corrosion of steel by the damage of passivity layer around steel bars. As chloride ion penetration is major cause of the destruction of passivity layer, evaluation of depth and concentration profile of chloride ion is the essential factor for the service-life estimation of concrete structure. To estimate chloride ion penetration characteristics, this paper on the basis of in-situ experimental data investigated the depth and concentration profile of chloride ion penetration. The core specimens are obtained at air-zone, splash zone, and tidal zone in Wando, Masan, Incheon, Gwangyang, and donghae harbors. Colorimentric method measured the chloride ion penetration depth and ASTM C 114 evaluated the concentration profile of chloride ion. Based on experimental data, the influence of harbor location and exposure condition on chloride ion penetration is evaluated.

• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.66-70
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• 2011

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.190-190
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• 2011

In South Korea the gross generation and heated effluent of power generation plant was 259 TWh and 4.73 billion tons in 2008. And then the waste heat from power generation was 388 TWh. It shows that the efficiency of thermal power generation plant is about 40%. Therefore to reduce $CO_2$ emission from thermal power generation plant, the energy of this heated effluent must be reused to heat buildings or farm facilities. In South Korea horticultural facilities of about 25% are heated in winter season. Total area of greenhouses which are heated is about 13,000 ha. Total heat amount needed to warm greenhouse of 13,000 ha in winter season is only 3.4% of total waste heat from power generation plant. In this study a heat pump system was designed to reuse the waste heat from power generation. Especially new heat exchanger was developed to recover the thermal energy from waste water and this model considered anti-corrosion against sea water and low cost for economic feasibility. This heat recovery system was installed in mango growing greenhouse around thermal power generation plant in Seogwipo-city, Jeju Special Self-Governing Province. The result of preliminary test shows that the heating cost of about 90% is saved as compared to boiler using tax free light oil as a fuel.

• Journal of Soil and Groundwater Environment
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• v.21 no.4
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• pp.42-49
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• 2016

Step-drawdown pumping tests for identifying the improvement of groundwater well performance after rehabilitation treatments were conducted in three longstanding wells. Three selective mechanical treatment methods including power bubble, high-voltage electric pulse, and air surging were applied to these wells and the applicability of these methods to secure additional groundwater resources were evaluated quantitatively. Commonly, drawdown at final stage of stepdrawdown pumping tests after rehabilitation decreased by as much as 0.61~0.70 meters compared to those before rehabilitation. In addition, final specific drawdown values of three wells increased from 9% to 14% after rehabilitation. Formation loss coefficient and well loss coefficient decreased to 6.1% and 60.6%, respectively, indicating some clogging materials by precipitation/corrosion/microbe within pores of aquifer materials, gravel packs, and screens were effectively removed by applied methods. Decrease of formation loss coefficient was higher in the well applied by the power bubble method meanwhile high-voltage electric pulse method demonstrated the higher decrease of well loss coefficient. Additionally secured groundwater amounts after rehabilitation ranged from 23.3 to 32.1 m³/day, which account for 8~16% of initially developed pumping rates of the wells. From the results of this study, the effective selection of rehabilitation treatments considering aquifer characteristics are expected to contribute to secure groundwater resources for irrigation as well as to plan systematic management program for groundwater resources in rural area.

• Journal of Powder Materials
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• v.22 no.2
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• pp.100-104
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• 2015

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about $42.69{\mu}m$. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at $1200{\sim}1450^{\circ}C$ and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to $1.8{\mu}m$ respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to $2.08{\mu}m$ respectively.

• Journal of Environmental Impact Assessment
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• v.18 no.3
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• pp.171-183
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• 2009

This study aims to analyze the sedimentary environment change in mid-channel bar of the lower Geum river basin after the construction of the estuary barrage using multi-temporal satellite data and GIS. The sedimentary environment changes were observed in mid-channel bar areas. The mid-channel bar F was found to have been newly formed for 10 years(1996-2006), whereas the mid-channel bar B located between mid-channel bar A and C has disappeared by erosion during the same periods. When examined by section, the areas of the mid-channel bar in the upper stream section from the Yipo's reference point generally increased due to the prevailing sedimentary environments, and those of the downstream section decreased where corrosive environments are dominant. In ternms of the centroid movement, the mid-channel bars grew up toward the downstream by switching erosion and accumulation, as sedimentation was prevailing in the downstream area of mid-channel bars and corrosion was dominant in the upper stream. Through grain size analysis, the study areas are divided into three sections according to the average grain size. In Section I, the mid-channel bars were formed as a result of sedimentary process of tides in the past. In Section II, the mid-channel bars were formed partly through the sedimentary process of rivers although the sedimentary process of tides is prevailing. In Section III, the mid-channel bars were formed mainly through the sedimentary process of rivers, even if it showed the sedimentary process of tides in the past.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.4
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• pp.119-125
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• 2007

In recent days, the consumption of stainless steel in the propulsion shafting systems for small-medium class vessel is increased due to its high corrosion protection with wear resistant properties. Unfortunately the small and medium class vessel that operated in the west-south sea area of Korean peninsula experienced heavy wear down due to the role of mud. In the event of wear or broken down, the propeller shaft must be replaced by new one, but the new shaft is very expensive and time-consuming for order made supply. In this case, the methods of built up for wear and broken shaft by welding is one of the most effective cases. In this study, the built up welding for austenitic stainless steel shaft has been accomplished by various pre-surface treatment, welding methods, post heattreatment and inspection. The results confirmed that the built-up welding was one of the effective methods for stainless steel shafting.

• Smart Structures and Systems
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• v.8 no.1
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• pp.139-155
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• 2011

Polymeric thin-film assemblies whose bulk electrical conductivity and mechanical performance have been enhanced by single-walled carbon nanotubes are proposed for measuring strain and corrosion activity in metallic structural systems. Similar to the dermatological system found in animals, the proposed self-sensing thin-film assembly supports spatial strain and pH sensing via localized changes in electrical conductivity. Specifically, electrical impedance tomography (EIT) is used to create detailed mappings of film conductivity over its complete surface area using electrical measurements taken at the film boundary. While EIT is a powerful means of mapping the sensing skin's spatial response, it requires a data acquisition system capable of taking electrical impedance measurements on a large number of electrodes. A low-cost wireless impedance analyzer is proposed to fully automate EIT data acquisition. The key attribute of the device is a flexible sinusoidal waveform generator capable of generating regulated current signals with frequencies from near-DC to 20 MHz. Furthermore, a multiplexed sensing interface offers 32 addressable channels from which voltage measurements can be made. A wireless interface is included to eliminate the cumbersome wiring often required for data acquisition in a structure. The functionality of the wireless impedance analyzer is illustrated on an experimental setup with the system used for automated acquisition of electrical impedance measurements taken on the boundary of a bio-inspired sensing skin recently proposed for structural health monitoring.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.

• Journal of the Korean Applied Science and Technology
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• v.35 no.3
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• pp.612-621
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• 2018

In this study, $TiO_2$ nanotube plate and metal electrodes(Copper, Nickel, Stainless Steel, Aluminum, Tin, Titanium) were compared on cathodic reduction of nitrate ($NO_3{^-}-N$) during electrolysis. The electrochemical characteristics were compared based on electrochemical impedance spectroscopy (EIS). The surface morphology was obtained using scanning electron microscopy (SEM) method. Brunauer-Emmett-Teller (BET) method was implemented for the specific surface area analysis of the cathodes. To study kinetics, 90 minute batch electrolysis of nitrate solution was performed for each cathodes. In conclusion, under the condition of relatively low ($0.04 A\;cm^{-2}$) current density, $TiO_2$ nanotube plate showed no surface corrosion during the electrolysis, and the reaction rate was measured the highest in the kinetic analysis.