• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.293-296
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• 2004

In this study, to investigate autogenous shrinkage behavior of 120MPa UHSC at early ages, free and restrained shrinkage tests are performed for various strength levels(50MPa, 80MPa, 120MPa). For 120MPa, the effect of fly ash on autogenous shrinkage was also investigated. In order to assess the potential for early-age cracking in concrete and a mixtures susceptibility to shrinkage cracking, restrained ring test was carried out. Test results show that autogenous shrinkage of UHSC was much higher than that of HSC, VHSC and fly ash delayed cracking age in UHSC by decreasing autogenous shrinkage.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.85-95
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• 2015

PURPOSES : Recently, bonded concrete overlay has been used as an alternative solution in concrete pavement rehabilitation since its material properties are similar to those of the existing concrete pavements. Deteriorated concrete pavements need rapid rehabilitation in order to prevent traffic jams on Korean expressways. Moreover, speedy and effective repair methods are required. Therefore, the use of bonded concrete overlay with ultra-rapid hardening cement has increased in an effort to reopen promptly the expressways in Korea. However, mobile mixer is required for ultra-rapid hardening cement concrete mixing in the construction site. The use of mobile mixer causes various disadvantages aforementioned such as limitation of the construction supply, open-air storage of mixing materials, increase in construction cost, and etc. In this study, therefore, hydration accelerator in-situ mixing on polymer modified concrete produced in concrete plant is attempted in order to avoid the disadvantages of existing bonded concrete overlay method using ultra-rapid hardening cement. METHODS : Bonded concrete overlay materials using ultra-rapid hardening cement should be meet all the requirements including structural characteristics, compatibility, durability for field application. Therefore, This study aimed to evaluate the application of hydration accelerator in-situ mixing on polymer modified concrete by evaluating structural characteristics, compatibility, durability and economic efficiency for bonded concrete overlay. RESULTS : Test results of structural characteristics showed that the compressive, flexural strength and bond strength were exceed 21MPa, 3.15MPa and 1.4MPa, respectively, which are the target strengths of four hours age for the purpose of prompt traffic reopening. In addition, tests of compatibility, such as drying shrinkage, coefficient of thermal expansion and modulus of elasticity, and durability (chloride ions penetration resistance, freezing-thawing resistance, scaling resistance, abrasion resistance and crack resistance), showed that the hydration accelerator in-situ mixing on polymer modified concrete were satisfied the required criteria. CONCLUSIONS : It was known that the hydration accelerator in-situ mixing on polymer modified concrete overlay method was applicable for bonded concrete overlay and was a good alternative method to substitute the existing bonded concrete overlay method since structural characteristics, compatibility, durability were satisfied the criteria and its economic efficiency was excellent compare to the existing bonded concrete overlay methods.

• Journal of Powder Materials
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• v.11 no.1
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• pp.28-33
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• 2004

In the present study, the focus is on the analysis of carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fined TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. The synthesized titanium-cobalt-oxygen based oxide powder has a mixture of $TiO_2$ and $CoTiO_3$. This oxide powder was transformed to a mixed state of titanium car-bide and cobalt by solid carbon through four steps of carbothermal reduction steps with increasing temperature; reduction of $CoTiO_3$ to $TiO_2$ and Co, reduction of $TiO_2$, to the magneli phase($Ti_nO_{2n-1}$, n>3), reduction of the mag-neli phase($Ti_nO_{2n-1}$, n>3) to the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases, and reduction and carburization of the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases to titanium carbide.

• Journal of Powder Materials
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• v.12 no.5 s.52
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• pp.336-344
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• 2005

In the present study, the focus is on the effect of cobalt oxide powder in the carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fine TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under flowing argon atmosphere. Changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. Titanium-cobalt-oxygen based oxide powder desalted at $600^{\circ}C$ had a mixture of $TiO_2\;and\;Co_{3}O_4$. And the one desalted at $800^{\circ}C$ had a mixture of $TiO_2\;and\;CoTiO_3$. In the case of the former powder, the reduction of cobalt oxide powder in the titanium-cobalt-oxygen based oxide powder occurred at lower temperature than the latter one. However, the carbothermal reduction of titanium dioxide powder in the titanium-cobalt-oxygen based oxide powder with a mixture of $TiO_2\;and\;Co_{3}O_4$ occurred at higher temperature than the one with a mixture of $TiO_2\;and\;CoTiO_3$. And also, the former powder showed a lower TiC formation ability than the latter one.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.725-728
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• 2008

Most of shrinkage is mainly caused by autogenous shrinkage in Ultra high strength steel-fiber reinforced cementitious composites(UHSFRC). water to binder ratio is very low, about 0.2. It occurs faster hydration and cause a large amount of autogenous shrinkage in early ages. the large autogenous shrinkage can cause harmful cracks in a structure and deteriorate the designed structural performance. therefore it is very important to predict the autogenous shrinkage accurately. The study about the autogenous shrinkage of UHSFRC was carried out in this paper. through comparing with JSCE recommendations for UHSFRC, it was found out that UHSFRC in this study showed higher autogenous shrinkage than that of JSCE. And Applicability of early proposed models by some researchers was also investigated. the analytical results let us know that Miyazawa's model showed the best agreement with the experimentally obtained autogenous shrinkage of UHSFRC.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.246-252
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• 2021

The basic properties and volume stability of the ultra-rapid setting cement mortar containing low-quality recycled aggregate with a higher water absorption and lower specific gravity than relavent Korea Standard were experimentally confirmed. The mix proportion without recycled aggregate followed that of the general repair mortar used in the fields. 15% and 30% of the fine aggregate was substituted by the recycled aggregate in the mixtures with and without latex emulsion, and properties and characteristics of the mortar including mortar flow, setting time, compressive and flexural strength, and linear deformation under sealed and unsealed conditions were evaluated. It was confirmed that when low-quality recycled aggregate was used by 30%, there were risks of decrease in the early-age strength by up to 50% within 24h and increases in drying shrinkage by up to 2 times for 2 weeks compared to the the mixtures without the recycled aggregate.

• FOCUS: LIFE SCIENCE
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• no.1
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• pp.1.1-1.4
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• 2024

This article provides comprehensive guidance on the maintenance, cleaning, regeneration, and storage of silica-based HPLC (High-Performance Liquid Chromatography) columns. The general considerations emphasize the importance of using in-line filters and guard cartridges to protect columns from blockage and irreversible sample adsorption. While these measures help, contamination by strongly adsorbed sample components can still occur over time, leading to an increase in back pressure, loss of efficiency, and other issues. To maximize column lifetime, especially with UHPLC (Ultra-High Performance Liquid Chromatography) columns, it is advisable to use ultra-pure solvents, freshly prepared aqueous mobile phases, and to filter all samples, standards, and mobile phases. Additionally, an in-line filter system and sample clean-up on dirty samples are recommended. However, in cases of irreversible compound adsorption or column voiding, regeneration may not be possible. The document also provides specific recommendations for column cleaning procedures, including the flushing procedures for various types of columns such as reversed phase, unbonded silica, bonded normal phase, anion exchange, cation exchange, and size exclusion columns for proteins. The flushing procedures involve using specific solvents in a series to clean and regenerate the columns. It is emphasized that the flow rate during flushing should not exceed the specified limit for the particular column, and the last solvent used should be compatible with the mobile phase. Furthermore, the article outlines the storage conditions for silica based HPLC columns, highlighting the impact of storage conditions on the column's lifetime. It is recommended to flush all buffers, salts, and ion-pairing reagents from the column before storage. The storage solvent should ideally match the one used in the initial column test chromatogram provided by the manufacturer, and column end plugs should be fitted to prevent solvent evaporation and drying out of the packing bed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1600-1604
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• 2017

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile and many other applications due to their excellent physical and electronic properties. Especially, Mo-Cu composites with 5~20 wt% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength and prominent electrical and thermal conductivity. In most of the applications, high dense Mo-Cu materials with homogeneous microstructure are required for high performance, which has led in turn to attempts to prepare ultra-fine and well-dispersed Mo-Cu powders in different ways, such as spray drying and reduction process, electroless plating technique, mechanical alloying process and gelatification-reduction process. However, most of these methods were accomplished at high temperature (typically degree), resulting in undesirable growth of large Cu phases; furthermore, these methods usually require complicated experimental facilities and procedure. In this study, Mo-Cu alloying were prepared by planetary ball milling (PBM) and spark plasma sintering (SPS) and the effect of Cu with contents of 5~20 wt% on the microstructure and properties of Mo-Cu alloy has been investigated.

• Clean Technology
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• v.7 no.1
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• pp.13-25
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• 2001

With fast advancement of fine machineries and semiconductor industries in recent decades, the ultra-cleaning of organic chemicals, submicron particles from contaminated unit equipments and products such as silicon wafers becomes one of the most important steps for further advancement of such industries. To date, two kinds of ultra cleaning techniques are used; one is the wet-cleaning and the other is the dry cleaning. In case of wet cleaning, removal of organic contaminants and submicron particles is made by DIW with additives such as $H_2O_2$, $H_2SO_4$, HCl, $NH_4OH$ and HF, etc. While the wet cleaning method is most widely adopted for various occasions, it is inevitable to discharge significant amount of toxic waste waters in environment. Dry cleaning is an alternative method to mitigate environmental pollution of the wet cleaning with maintaining comparable degree of cleaning to the wet cleaning. Although there are various concept of dry cleaning have been devised, the dry cleaning with environmentally-benign solvent such as carbon dioxide proven to show high degree of cleaning from the contaminated porous surface as well as from the bare surface. Thus, special global attention has been placing on this technique since it has important advantages of simple process schemes and no environmentally concern, etc. Thus, this article critically reviews the state-of-the-art of the supercritical fluid drying with emphasis on the thermo-physical characteristics of the supercritical solvent, environmental gains compared to other dry cleaning methods, and the generic aspects of the basic design and processing engineering.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.