• Geomechanics and Engineering
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• v.8 no.6
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• pp.859-872
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• 2015

Pebble matrix filtration (PMF) is a water treatment technology that can remove suspended solids in highly turbid surface water during heavy storms. PMF typically uses sand and natural pebbles as filter media. Hand-made clay pebbles (balls) can be used as alternatives to natural pebbles in PMF treatment plants, where natural pebbles are not readily available. Since the high turbidity is a seasonal problem that occurs during heavy rains, the use of newly developed composite clay balls instead of pure clay balls have the advantage of removing other pollutants such as natural organic matter (NOM) during other times. Only the strength properties of composite clay balls are described here as the pollutant removal is beyond the scope of this paper. These new composite clay balls must be able to withstand dead and live loads under dry and saturated conditions in a filter assembly. Absence of a standard ball preparation process and expected strength properties of composite clay balls were the main reasons behind the present study. Five different raw materials from industry wastes: Red Mud (RM), Water Treatment Alum Sludge (S), Shredded Paper (SP), Saw Dust (SD), and Sugar Mulch (SM) were added to common clay brick mix (BM) in different proportions. In an effort to minimize costs, in this study clay balls were fired to $1100^{\circ}C$ at a local brick factory together with their bricks. A comprehensive experimental program was performed to evaluate crushing strength of composite hand-made clay balls, using uniaxial compression test to establish the best material combination on the basis of strength properties for designing sustainable filter media for water treatment plants. Performance at both construction and operating stages were considered by analyzing both strength properties under fully dry conditions and strength degradation after saturation in a water bath. The BM-75% as the main component produced optimum combination in terms of workability and strength. With the material combination of BM-75% and additives-25%, the use of Red Mud and water treatment sludge as additives produced the highest and lowest strength of composite clay balls, with a failure load of 5.4 kN and 1.4 kN respectively. However, this lower value of 1.4 kN is much higher than the effective load on each clay ball of 0.04 kN in a typical filter assembly (safety factor of 35), therefore, can still be used as a suitable filter material for enhanced pollutant removal.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.469-483
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• 2018

Steel bars have been widely used as the primary reinforcement for Precast Segmental Concrete Lining for TBM Tunnels. Previously, studies have been carried out to gauge the potential for steel fiber reinforcement to replace the use of steel bar reinforcements in the segmental lining to reduce the amount of the steel bar reinforcement. Steel fiber reinforcements have been investigated and widely applied to SFRC TBM linings to improve the constructability of SFRC TBM linings worldwide. However, the steel fiber reinforcement often caused punctures to the water membranes inside tunnel lining and had long-term durability deterioration issues caused by steel corrosion, as well as cosmetic problems. Therefore, this paper sought to gauge the potential of synthetic fiber reinforcements, which have proven to be very attractive substitutes for steel fiber reinforcements. This study analyzed the performance of both steel and synthetic fiber reinforcements in segmental linings and evaluated the applicability of the fiber reinforcements to the TBM Precast Concrete Segmental Linings of TBM tunnels. As a conclusion, this study demonstrates that the potential use of steel and synthetic fibers in various combination, can substitute the rebar reinforcement in the concrete mix for segmental concrete linings.

• Korean Journal of Heritage: History & Science
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• v.53 no.1
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• pp.34-51
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• 2020

In order to clarify the lime-based building method used in the Joseon Dynasty, lime materials, production techniques, and mixing methods recorded in ancient literature were examined. In ancient Joseon Dynasty literature, the use of low grade limestone as a raw material was recorded, and the use of pozzolanic materials such as Hwangtoh, white clay, and roof tile powder as mixing aids to enhance the strength of lime was recorded. In addition, various lime hydration and mixing methods were recorded, and based on re-experiments carried out with regards to this, a physical property evaluation was deemed to be required in accordance with the various types of raw lime materials, lime hydration methods, and mixture ratios. In the early Joseon Dynasty, lime was used for various aspects, but frequent problems were experienced due to lack of supply and poor production techniques. In the late Joseon Dynasty, lime production techniques developed along with mass production. Based on analysis of the manufacturing techniques of Hoegwagmyo lime mortar in the 16^th and 18^th centuries during the Joseon Dynasty, it was found that mixing ratios and the methods described in the ancient literature had been applied. It was confirmed that the mixing ratio differed depending on mixing materials and lime quality. Since the mixing ratio of Hoegwagmyo lime mortar changed over time and it was produced strictly on the basis of a guidebook, it is believed that if continuous scientific analysis of the Hoegwagmyo lime mortar production method were carried out, this would be helpful for ascertaining the chronological methodology of Hoegwagmyo.

• Resources Recycling
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• v.25 no.2
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• pp.60-68
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• 2016

In this study, earlier analyzed tetrapod, one of an original group of offshore constructions studied for manufacturability of the concrete using the properties of steel making slag aggregate. steel making slag aggregate assessment, RCS and Blast Furnace Slag : the 20 mm air-cooled slag and combinations by 50 %, aggregate properties on the most appropriate for the properties of recycled aggregate concrete optimal mix, and assessing it. Properties of concrete used to be derived are judged as to bury the studies show that the hollowing-out of the RCS, plastic sole use is in the workability of the aggregate, plastic in the 20 mm slag also assessed to be a slight disadvantage, but RCS by mixing air-cooled coarse and 50 percent to 20 percent 50 mm. Thus, steel making slag marine structures using recycled aggregate, in rapid chilled slag or air-cooled slag. The sole use of the aggregate them than to combine the aggregate of concrete. After they satisfy the quality standard quality shall be used will aggregate steel making slag who meet the criteria concrete manufacturing in general or par with the aggregate of concrete. Performance was assessed as to develop a more than that.

• Informatization Policy
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• v.27 no.1
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• pp.92-114
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• 2020

The purpose of this study is to analyze people's motivations to use the National Petition service of CheongWaDae, the Presidential Office of Korea. The online space has been used as a testbed of deliberative democracy. In fact, a wide variety of public opinions are being formed and gaining sympathy through the E-Petitions and Daum's Agora. In this regard, President Moon's government launched a petition site to gather public opinions. For any petition agreed on by more than 20,000 people within 30 days, the relevant ministry or the President's office must provide answers or feedback. This study wants to figure out how this National Petition is different from previous platforms like Agora or E-Petitions and why it is so well-received by people. This study uses a mix of both qualitative and quantitative methods. First, we conducted a focus group interview to factorize experiences of using the National Petition into measurable constructs. Second, we did a survey o 156 Koreans who had experienced the National Petition. Results show that symbolism, usefulness, gratification, and trust have positive impact on continuous usage intention. This study argues that symbolism, usefulness, gratification, and trust factors should be in place rather than technical aspects in order to increase the actual participation of users on the online platform of deliberative democracy. In addition, this study is meaningful in that it examined how different the CheongWaDae's National Petition is from the existing platforms for collecting public opinions and analyzed factors that encourage continuous use.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.29-36
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• 2015

In this study, to examine the use of sulfur polymer as a coating agent for concrete, durability and hazard evaluations were performed. The result of the evaluation indicated that the chemical resistance of the coating agent for concrete was outstanding against acidic, base, and alkaline solutions. The evaluation of the bond strength after an accelerated weathering test depending on the mixing condition indicated that the most outstanding strength characteristic was obtained when silica powder and fly ash were mixed at the same time. The bond strength exceeded 1 MPa in every mixing condition even after the repeated hot and cold treatment of the coating agent specimen for concrete, and the SFS mix proportion showed the highest bond strength. The examination of the accelerated carbonation and chloride ion penetration resistance of the concrete coated with the coating agent indicated that the specimen coated with the coating agent using silica powder as a filler showed the most outstanding durability. When a fish toxicity test was performed to examine the hazard of the use of the functional polymer as a coating agent for concrete, the functional polymer was found to have no effect on the organisms. When the chemical resistance, freezing and thawing resistance, carbonation, and chloride ion penetration resistance of the coating agent were considered, substituting silica powder and fly ash as the fillers of the functional polymer by 20%, respectively, was the optimal level in the range of this study.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.5
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• pp.492-501
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• 2001

The use of alginate impression materials today is prevalent because of its efficiency and simplicity in clinical settings. Unfortunately, the simplicity of the procedure tends to lull the dentist into a sense of well-being, and lead him into using careless or sloppy technique. Alginate impression materials are used to fabricate diagnostic and preliminary casts, and the final cast. Incorrect use of this material is known to affect the accuracy of the final prosthesis. The purpose of this study was to compare the effect of different mixing methods of alginate impression material and tray adhesive on the accuracy of the stone cast produced by each method. A total of 30 stone casts were produced by using 3 different types of mixing methods (10 stone cast for each mixing method, respectively). The first method utilized an automatic-mixing machine to mix alginate while the second method was carried out manually, strictly following manufacturer's instructions. The third method also involved manual mixing, but did not follow the manufacturer's instructions and was done in a random fashion. Also, 20 additional stone casts were produced by using alginate with or without tray adhesives were included in the study to evaluate effects of tray adhesives on the accuracy of alginate impression. 10 stone casts were produced by adding tray adhesives to the interior surface of the impression tray prior to taking the impression. The other 10 excluded this step. A total of 50 stone casts were analyzed by the three-dimensional measuring machine to measure and compare the dimensional changes of the impression material of each group. The results are as follows. 1. No significant difference was found between the automatic mixing group and the manually-mixing group(p>0.05). 2. For the group that followed manufacturer's instructions, less dimensional changes were record ed than the group that didn't in measuring distanced 4(p<0.05). 3. The group that used tray adhesives showed less dimensional changes(p<0.05). The findings revealed that mechanical methods of mixing alginate impression materials had little influence on dimensional changes. However, it is proven that following manufacturers instructions in alginate impression taking is an important step in acquiring accurate impressions and tray adhesives may play an important role in enhancing the results.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.842-846
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• 2016

It's possible for a human to breathe under water, but the amount of dissolved oxygen in the water is small and a large amount of water is necessary to obtain sufficient dissolved oxygen from water. So, large separation system with large water pumps, having large surface areas, and large battery sources are needed. Exhalation gases are used to solve this problem. Theses gases contain some oxygen, nitrogen, and carbon dioxide; they contain less oxygen and more carbon dioxide compared to air. Therefore, reduction of the amount of carbon dioxide is necessary. If exhalation gases are employed appropriately, the separation device can be made more compact. Inlet water mixed with exhalation gases is supplied into the separation device, and dissolved gases are separated from the mixed water as it passes through the device. The inlet part of a typical separation system with a water delivery pump before the membrane module has more than one atmosphere. Hence, a compressor is used to mix the exhalation gases. In this study, the pressure at the inlet due to the use of a suction pump after the membrane module was less than one atmosphere; hence, compressors were not required. Separation characteristics were studied using a separation device without a compressor. The use of exhalation gases led to an increase in the amount of dissolved gases being separated. As the amount of inlet exhalation gases was increased, the separation of dissolved gases was increased as well.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.807-812
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• 2007

With the advent of Electronic Chart Display and Information Systems(ECDIS) and Automatic Identification Systems (AIS) as the principal navigation equipment of E-navigation strategy, mariners will begin to practice "e-navigation" and increasingly rely upon these systems to navigate safely and efficiently. However, these electronic systems require "e-inputs" in order to function. At present, the choices for e-input are limited, and they are installation dependent. This means that the mariner must be suitably equipped in order to use an alternative e-input. If the primary e-input is lost, and the vessel is not equipped to make use of suitable alternative e-inputs, then continued operations will have to be done the "old fashioned way" using conventional navigation The final objective is a recommendation of dual harbor positioning system on the most appropriate mix of positioning systems to satisfy the marine needs for radionavigation, positioning services.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.117-124
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• 2009

The purpose of the study was to improve quality of high volume fly ash concrete. The study evaluated on the possibility of early quality improvement of high volume fly ash concrete with early strength gain admixture ('GA' below) developed by the preceding research. The study regarded applying naphthalene admixture ('NA' below) to mix proportion substituting FA 15 % to be plain. In the event of substituting FA 20, 25 and 30 %, the study compared engineering properties of concrete with plain by applying GA. Because of features of fresh concrete, fluidity falls down when GA is applied. Therefore, its use amount shall be increased. Only, in W/B 60 %, it was beneficial since slump loss was reduced about 35~70 mm than plain. The study could see that AE use should be increased proportionally since air content was reduced by coming from AE absorption operation of unburned coal content included in FA according to an increase in the amount of FA use. Reduction effect of bleeding could be anticipated since the amount of bleeding appeared at least in FA 20 %. Because of hardened concrete, time of setting appeared in the same level as plain when GA was applied. Therefore, it is judged that delay of setting can be reduced. In compressive strength, the study could check the same strength development as plain when GA was applied, having nothing to do with W/B and curing temperature. However, it is thought that we shall pay attention to GA use in the event of FA 30 % substitution. Freezing and melting resistance had less early value than plain. However, it is judged that there will be no problem of frost resistance since there is no a large difference between freezing and melting resistance and plain in overall. In accelerated neutralization, it was analyzed that a problem of weakening in neutralization appointed as a demerit when FA was applied in mass in proportion with GA use could be settled to some extent.