• Journal of the Korea Institute of Building Construction
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• v.14 no.5
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• pp.397-405
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• 2014

There are many literatures reporting that the service life of re-bars in concrete structures is reduced in the oceanic environment due to chloride attack. To solve this problem, this study used geo-polymer as a mix material for concrete to increase its resistance to salt damage, and the external voltage method, one of the electric methods, is was applied to evaluate the likelihood of re-bars in the oceanic structure being exposed to the extreme salt environment. The items evaluated include the natural potential of re-bars and the corrosion rate. The results of the tests showed that in all of the salt environmental conditions (submerged zone, tidal zone, and crack), the tested materials were remarkably effective compared with ordinary concrete. The corrosion protective property was found not only in the evaluation of the natural potential but also in the evaluation of the corrosion rate, suggesting that the external voltage method can be used stably for geo-polymer RC structures in an extreme salt environment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.280-286
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• 2006

As a way to expand electric capacity in conductor with electric power demand, STACIR/AW (Super Thermal-resistant Aluminum-alloy Conductors Aluminum-clad Invar-Reinforced) conductor which has high electric current and heat resistance characteristics have been developed. STACIR/AW power line is mechanical composite wire composed of steel cores for dip control and aluminum conductors for sending electric current. Recently, to ensure stable operation and prediction of wire life span of STACIR/AW conductor, a heat property of STACIR/AW conductor have been investigated. In the present work, a change of essential property with long term-heat exposure of STACIR/AW conductor and its structure material, INVAR wire and Al conductor, have been investigated. INVAR/AW is approximately $3.2\;{\mu}m/m^{\circ}C$. thermal expansion coefficient of INVAR/AW wire increases with time of heat exposure. the thermal expansion coefficient of INVAR/AW is markedly influenced by heat and mechanical treatment. creep rate(0.242) of STACIR/AW $410\;mm^2$ conductor at room temperature is much higher than that(0.022) at $210\;^{\circ}C$ STACIR/AW $410\;mm^2$ conductor has minimum creep rate at operating temperature. To lower creep rate with increase temperature is more unique characteristics in STACIR/AW. It is expected that STACIR/AW turned its tension to INVAR/AW at the transition temperature. at room temperature, the tension apportionment of INVAR/AW in STACIR/AW is about $50\;\%$. but whole tension of STACIR/AW is placed on the INVAR/AW alone of core metal above transition temperature.

• Journal of Adhesion and Interface
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• v.10 no.4
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• pp.182-190
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• 2009

In this work, effect of antistrip additives to reduce moisture damage of asphalt mixture were studied. Asphalt antistripping agents were prepared by condensation of formaldehyde with tetraethylene pentamine (TEPA), triethylenetetramine (TETA) and bis(hexamethylene)-triamine (BHMT), respectively. And also the metal type antistripping agent was prepatred by neutralization of stearic acid or palmitic acid with metal hydroxide. Mechanical characteristics of the asphalt mixture added antistripping agent were evaluated with Marshall stability, submerging residuals and coating rate. It was found that antistripping agent prepared in this study reduced moisture damages of asphalt mixtures. In particular, asphalt mixtures added BHMT and C/S (Calcium stearate hydroxide) antistripping agent showed highest submerging and coating rate. Because BHMT and C/S type antistripping agent was to improve bonding between asphalt and aggregate owing to increase of amine concentration and role of metal surfactant.

• Membrane Journal
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• v.25 no.3
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• pp.256-267
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• 2015

The goal is to compare two different aeration strategies for a pilot scale operation of submerged microfiltration with respect to the minimization of membrane fouling. A constant aeration (65 L/min) was examined parallel with a step-wise increase in airflow rate (40 to 65 L/min). The airflow rate was stepped to a higher rate every 5 min and the step-aeration cycles were repeated at regular intervals of 15 min. The comparative filtration runs were conducted with synthetic water containing powdered activated carbon (~10 g/L) and/or kaolin (~20 g/L) at a constant flux of 80 LMH. The extent and mechanisms of fouling in the microfiltration were identified by determining hydraulic resistance to filtration and the fouling reversibility after cleaning. Results showed that the step-aeration effectively alleviated fouling in the microfiltration of synthetic water compared to when using constant aeration. A substantial decrease in fouling was achieved by combining with coagulation using aluminum salts regardless of the aeration strategies. The constant aeration resulted in increased pore blocking likely due to increased accumulation of particles on the surface of membrane.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.2
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• pp.92-98
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• 2011

The influence of the cooling condition after solution treatment on the high temperature fatigue resistance of 23Cr-26Ni heat resistant steel was investigated. Two different cooling conditions were applied to the steel after solution treatment at $1200^{\circ}C$ for 3 hours. One specimen was water quenched immediately after the solution treatment. The other one was furnace cooled at a rate of $0.5^{\circ}C/min$ down to $750^{\circ}C$ after the solution treatment. Then, both specimens were aged at $750^{\circ}C$ for 5 hours. Under two different heat treatment conditions, the low cycle fatigue (LCF) test was performed at $600^{\circ}C$ and room temperature (RT). Only cyclic hardening continued from the beginning until fracture at all strain amplitudes during LCF at $600^{\circ}C$. This phenomenon was attributed to the increase in the dislocation density due to cyclic deformation, which resulted in the interaction between the newly created dislocations and precipitates. Cyclic hardening followed by saturation and cyclic softening was observed at RT. Cyclic softening was attributed to the dislocation annihilation rate exceeding the dislocation generation rate. Other probable factor for cyclic softening was some cavities formed around grain boundaries after 20 cycles. WQ and FC have a similar LCF behavior at RT and $600^{\circ}C$ as shown in the cyclic stress response curves.

• Nuclear Engineering and Technology
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• v.21 no.3
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• pp.165-170
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• 1989

The strain rate effects on fracture toughness and fracture resistance characteristics of A533B-1 nuclear pressure vessel steels were examined in the quasi-dynamic test conditions through the microscopic investigation of the intense strain region around crack tip and the microroughness of fracture surface. J-value calculated from the recrystallization etch technique was the same as calculated from the modified-J when the crack extension is less than 1.5mm in a 1/2T-CT specimen. Local fracture strain was calculated from the fracture surface micro-roughness. The local strains were calculated to be the values of 1.8 and 2.0 and were much higher than the macroscopically measured values. It was nearly independent on strain rate and was regarded as a material constant in ductile dimpled rupture. The fracture toughness increased with increase in strain rate while the tearing modulus showed little variation.

• Nuclear Engineering and Technology
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• v.25 no.4
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• pp.507-514
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• 1993

Titanium tubes have recently been used in condensers of nuclear power plants since titanium has very good corrosion resistance to seawater. However, when it is connected to Cu alloys as tube sheet materials and these Cu alloys are connected to carbon steels as water box materials, it makes significant galvanic corrosion on connected materials. It is expected from electrochemical tests that the corrosion rate of carbon steel will increase when it is galvanically coupled with Ti or Cu in sea water and the corrosion rate of Cu will increase when it is coupled with Ti, if this couple is exposed to sea water for a long time. It is also expected that the surface area ratios, R$_1$(surface area of carbon steel/surface area of Ti) and R$_2$(surface area of carbon steel/surface area of Cu) are very important for the galvanic corrosion of carbon steel and that these should not be kept to low values in order to minimize the galvanic corrosion on the carbon steel of the water box. Immersed galvanic corrosion tests show that the corrosion rate of carbon steel is 4.4 mpy when the ratio of surface area of Fe/ surface area of Al Brass is 1 while it is 570 mpy when this ratio is 10$^{-2}$ . The galvanic corrosion rate of this carbon steel is increased from 4.4 mpy to 13 mpy at this area ratio, 1, when this connected galvanic specimen is galvanically coupled with a Ti tube. This can be rationalized by the combined effects of R$_1$ and R$_2$ on the polarization curve.

• Journal of the Society of Disaster Information
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• v.15 no.2
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• pp.292-300
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• 2019

Purpose: To reduce the noise and vibration of reinforced concrete slab structures, the damping performance is to be performed experimentally after installing hollow core or filling it with liquid. Method: Using the hollow rate as an experimental variable, the damping ratio and stiffness of each test specimen at impact load are obtained to determine the difference between the damping ratio and stiffness of the numerical analysis. In addition, the damping effects are reviewed by comparing the difference in the damping ratio and stiffness of a test specimen filled with liquid 50% of the study. Results: Since the difference in resistance between a specimen with or without hollow core is 5%, it is judged that there is no structural problem, and the injection of liquid into the hollow core can increase the damping ratio, which can reduce noise or vibration. Conclusion: At less than 20% of hollow rate, there was little damping effect, and at 30%, damping effect was found. However, if liquid is injected into the hollow core of the specimen, damping rate is shown to increase, and the injection of liquid into the hollow part is believed to reduce noise or vibration.

• Journal of the Korean GEO-environmental Society
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• v.23 no.5
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• pp.33-39
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• 2022

For a slag-cement-bentonite (slag-CB) cut-off wall, GGBS replaces a part of the cement mixed to build a CB cut-off wall, which is used to block the flow and leakage of pollutants or groundwater; prevent seawater infiltration; and repair or reinforcement an aged embankments. Slag-CB cut-off walls are used in various applications in different fields where groundwater control is required due to its excellent characteristics. Such properties include high strength, low permeability, high durability and chemical resistance. However, despite these advantages, slag-CB cut-off walls are not extensively studied in Korea and thus are not applied in many cases. Particularly, GGBS, which replaces cement in a mixture, has different properties depending on its country of production. Consequently, it is necessary to perform various studies on slag-CB cut-off walls that use GGBS produced in Korea in order to increase its usability. This study has evaluated the bleeding rate, setting time, strength, and permeability in relation to the cement replacement rate of GGBS produced in Korea for slag-CB cut-off walls, with the aim to increase its usability. The evaluation found that slag-CB cut-off walls, made of a mixture containing GGBS produced in Korea, have a lower bleeding rate and permeability, and higher strengththan CB cut-off walls. It was also analyzed that such improved performance is more effective with a higher cement replacement rate of GGBS.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.99-106
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• 1987

Annealing were performed to investigate the behaviors of the residual stress remaining on the member of a steel structure. According to the fatigue test, the welding part has higher fatigue crack growth rate than the base metal part because the hardening of welding part reduce fracture toughness. However, the heat treatment decrease the hardness and increase the resistance to failure. Thus, the fatigue crack growth rate is improved and it reaches the minimum at $650^{\circ}C$. Elber' s equation includes the effect of the crack-close so that this equation provides a lower the fatigue crack growth rate than Paris-Erdogan' s equation, the Elber's curves show no significant difference to indentify the effect of the residual stress. The Pop loading along the crack length increases as the hardness goes higher. The heat treatment not only decrease the hardness, and the fatigue crack growth rate, but increase the absorption energy and fracture toughness on the member of a steel structure. As the result, the heat treatment produces the resistant ability to cracking which can reduce the degree of danger to failure.