• International Journal of Railway
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• v.4 no.4
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• pp.86-92
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• 2011

Chloride ion diffusion at the corner of rectangular-shaped concrete structures is presented. At the corner of rectangular-shaped concrete, chloride ion diffusion is in two-dimensional process. Chloride ions accumulate from two orthogonal directions, so that corrosion-free life of concrete structures is significantly reduced. A numerical procedure based on finite element method is used to solve the two-dimensional diffusion process. Orthotropic property of diffusion coefficient of concrete is considered and chloride ion profile obtained from numerical analysis is used to produce transformed diffusion coefficient. Comparisons of experimental data are also carried out to show the reliability of proposed numerical analysis. As a result of two-dimensional chloride diffusion, corrosion-free life of concrete structure for railway is estimated using probability of corrosion initiation. In addition, monographs that produces transformed diffusion coefficient and corrosion-free life of concrete structure are made for maintenance purpose.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.254-260
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• 1997

Chloride-induced corrosion of reinforcement is one of the main factors which cause the deterioration of concrete structures. Durability and service lives of the concrete sturctures should be predicted in order to minimize the risk of corrosion of reinforcement. The objective of this study is to suggest the basis of analytical methods of predicting the corrosion threhold time of concrete structures. Based on the chemistry and physics of chloride ion transport and corrosion process, chloride intrusion with various exposure conditions, variability of diffusivity and transport of pore water in concrete are taken into consideration in applying finite element formulation to the predicion of corrosion threhold time. The effects of main factors on the prediction of chloride intrusion and corrosion threhold time are examined. In addition, after chloride diffusivities of several mixture proportions with different parameters are measured by chloride diffusion test, the exemplary anayses of corrosion threhold time of those mixture proportions are carried out.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.193-203
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• 1999

The corrosion of steel reinforcements in concrete is of great concern in recent years. This study is focused on the corrosion behavior of steel bars induced by internal chlorides in concrete at early ages. The main objective of this study is to determine the chloride thresholds causing depassivation and active corrosion of steel reinforcement in concrete. To examine the threshold concentration of chloride ion, the half-cell potential, chemical composition of expressed pore solutions of concrete and the rate of corosion area of the specimens were measured. Major variables include the added amount of chlorides in concrete, types of binders, and water-to-binder ration. From the present comprehensive experimental results, the factors influencing chloride-induced corrosion are investigated, and the chloride thresholds causing active corrosion of steel bars are proposed. The present study will enable to specify the realistic chloride limit in concrete which can be used in the future technical specification.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.553-557
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• 2022

The present study evaluate the chloride extracion under electrochemical chloride extraction method. Chloride was penetrated into the concrete from external reservoir using a 4M NaCl solution, and an electrochemical chloride extraction method was applied after the curing period of 1 year. The current density was constantly kept 1000 mA/m² for coulostatic application with the variation in potential difference. The duration of the ECE treatment was 2, 4, 8 weeks, respectively. The residual chloride concentration at all depths decreased, and the chloride concentration decreased as the application period increased. After the application period of 8 weeks, 62.9 to 77.6 % of chloride extracted in the total chloride profile, and 77.7 to 99.5 % of chloride extracted in the free chloride profile. In particular, the concentration of free chloride at a depth of 7 mm or more from the concrete surface was 0.01 % or less by cement. In addition, it was confirmed that the bound chloride could be extracted by the electrochemical chloride extraction.

• Resources Recycling
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• v.16 no.1 s.75
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• pp.37-43
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• 2007

It was studied to prepare anhydrous magnesium chloride which could used as the raw material of a fused salt electrolysis of magnesium by dehydration of magnesium chloride hydrate. The dehydration was carried out in a tube furnace at $350{\sim}580^{\circ}C$. It was confirmed that magnesium chloride hydrate was oxdized to magnesia through the dehydration in ambient atmosphere, but anhydrous magnesium chloride could be obtained in hydrogen chloride gas atmosphere. And the crystallity of the product increased with increasing temperature and time of dehydration. All of the un-reacted hydrogen chloride gases which were generated during the dehydration in hydrogen chloride gas atmosphere could be recovered as hydrochloric solution, and it could be reused for chlorination of magnesia to prepare magnesium chloride hydrate.

• Food Science and Preservation
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• v.18 no.5
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• pp.678-683
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• 2011

The effects of coagulant types (magnesium chloride, calcium chloride, calcium sulfate, glucono-${\delta}$-lactone) on yield, quality properties and storability of astringent persimmon powder added tofu were investigated. Yield, hardness, chewness, crispness, and overall acceptability of tofu coagulated by glucono-${\delta}$-lactone were higher than those coagulated by the others. L value, a value, pH, soaking-solution turbidity, and total aerobic bacteria of glucono-${\delta}$-lactone coagulated tofu were lower than those coagulated by the others. Calcium sulfate and calcium chloride coagulated tofu showed relatively high L and b values. Magnesium chloride coagulated tofu had higher sensory score for firmness, taste, overall acceptability than calcium chloride and calcium sulfate coagulated tofu, but there was no significant difference between magnesium chloride and glucono-${\delta}$-lactone. The results suggested that glucono-${\delta}$-lactone and magnesium chloride were found to be the suitable coagulants for processing of the persimmon powder added tofu.

• Journal of the Korean Society of Safety
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• v.22 no.3 s.81
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• pp.57-64
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• 2007

Recently, the corrosion of concrete structures has received great attention related with the deterioration of sea-side structures, such as new airport, bridges, and nuclear power plants. In this regards, many studies have been done on the chloride attack in concrete structures. However, those studies were confined mostly to the single deterioration due to chloride only, although actual environment is rather of combined type. The purpose of the present study is, therefore, to explore the influences of carbonation and freezing-thawing action to chloride attack in concrete structures. The test results indicate that the chloride penetration is more pronounced than the case of single chloride attack when the carbonation process is combined with the chloride attack. It is supposed that the chloride ion concentration of carbonation region is higher than the sound region because of the separation of fixed salts. Though the use of fly ash pronounces the chloride ion concentration in surface, amounts of chloride ion penetration into deep region decreases with the use of fly ash. The small reduction of relative dynamic elastic modulus induced from freezing-thawing increases the chloride ion penetration depths much. The present study allows more realistic assessment of durability for such concrete structures which are subjected to combined attacks of both chlorides and carbonation or freezing-thawing but the future studies for combined environment will assure the precise assessment.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.58-66
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• 1999

The catalytic oxidation of vinyl chloride was investigated over $CrO_x$ impregnated on $Al_2O_3$ at temperature between 200 and $400^{\circ}C$. The major carbonaceous products were CO and $CO_2$, and the selectivity of $CO_2$ was gradually increased with increasing reaction temperature, while that of CO was dropped consequently. This suggests that CO is the first product which is further oxidized to $CO_2$ in the oxidation of vinyl chloride over $CrO_x/Al_2O_3$. The addition of HCl in the feed didn't affect the conversion of vinyl chloride, but the selectivity of $CO_2$ decreased by adding HCl. It implies that HCl inhibits, the complete oxidation of vinyl chloride to $CO_2$. When oxidizing vinyl chloride in dry air, significant amounts of $Cl_2$ were observed, while no $Cl_2$ was detected in the humid condition. The activities of several catalysts including various precious metals and other transition metal oxides were measured, it was found that the catalytic activity of 12% $CrO_x/Al_2O_3$ was higher than other catalysts except 1% $Pt/Al_2O_3$. The reaction rate of 12% $CrO_x/Al_2O_3$ was 1.2 times lower than that of 1% Pt/alumina, but it was 3 to 8 times more active than other catalysts for vinyl chloride oxidation at $275^{\circ}C$.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.367-375
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• 2007

Critical chloride content for corrosion initiation is a crucial parameter in determining the durability and integrity of reinforced concrete structures, however, the value is still ambiguous. Most of the studies reporting critical threshold chloride content have involved the experimental measurement of the average amount of the total chloride content at arbitrary time. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on critical threshold chloride content. Furthermore, the studies have tried to define the critical chloride content within the scope of their experimental concrete mix proportion at arbitrary time. However, critical chloride content for corrosion initiation is known to be affected by a lot of factors including cement content, type of binder, chloride binding, concentration of hydroxyl ions, and so on. It is necessary to define the unified formulation to express the critical chloride content for various mix proportions of concrete. The purpose of this study is to establish an analytical formulation of the critical chloride content of concrete. In this formulation, affecting factors, such as mix proportion, environment, chemical evolution of pore solution with elapsed time, carbonation of concrete and so on are taken into account. Based on the Gouda's experimental results, critical chloride content is defined as a function of $[Cl^-]$ vs. $[OH^-]$ in pore solution. This is expressed as free chloride content with mass unit to consider time evolution of $[OH^-]$ content in pore solution using the numerical simulation programme of cementitious materials, HYMOSTRUC. The result was compared with other experimental studies and various codes. It is believed that the approach suggested in this study can provide a good solution to determine the reasonable critical chloride content with original source of chloride ions, for example, marine sand at initial time, and sea water penetration later on.

• Korean Journal of Plant Resources
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• v.26 no.6
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• pp.695-700
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• 2013

Flax (Linum usitatissimum L.) has been used for the only edible oil in Korea. We carried out the field experiment in order to investigate the possibly combined effects of mepiquat chloride (MC) and trinexapac-ethyl (TE) on oil composition, lignan content, seed yield and endogenous gibberellins content of flax cultivar. Plant growth retardants mepiquat chloride (300 and 600 ppm) and trinexapac-ethyl (100, 200 and 300 ppm) were foliar-sprayed to flax plant at 50days after seeding. The plant height was decreased in the combination of mepiquat chloride 600 ppm with trinexapac-ethyl 100, 200 and 300 ppm. Mepiquat chloride treatment combined with trinexapac-ethyl observed the highest response on seed yield, followed by mepiquat chloride 300 ppm with trinexapac-ethyl 100 ppm, mepiquat chloride 300 ppm with trinexapac-ethyl 200 ppm and mepiquat chloride 300 ppm with trinexapac-ethyl 300 ppm. Lignan content was increased in all of the combination treatments. It concludes that the combination of mepiquat chloride 300 ppm with trinexapac-ethyl 300 ppm will be useful to increasing oil and lignan content in flax plants.