• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.145-152
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• 2023

In this study, microscopic observation was made on the surface of cement paste immersed in an aquatic environment for 100 days at electrochemical treatment to mitigate the leaching of alkali ions. To quantitatively rank the hydration products, unhydrated grains and porosity in the interfacial region, the backscattered electron(BSE) images were obtained by scanninng electron microscopy. As a result, it was found that the porosity on the surface was significantly reduced by the electrochemical treatment, while unhydrated grains were more or less increased presumably limited hydration reaction under electric charge. At electrochemical treatment, Ca²⁺ ions present in C-S-H gel could be precipitated with OH^- to form Ca(OH)₂ then to lower C-S-H gel and simultaneously to enhance Ca(OH)₂. Substantially, the risk of alkali leaching could be lowered by the limited ionized matrix under electrochemical treatment.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.364-372
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• 2023

By applying coarse-grained limestone and unprocessed coal ash as sintering raw materials for cement clinker, the microstructure and distribution of chemical components of cement clinker were compared and examined. Samples using coarse limestone as a raw material for cement clinker showed a decrease in sinterability compared to samples using reagent-grade raw materials. Samples using coal ash showed a tendency for some increase in sinterability. In samples using coarse limestone and coal ash, the formation of Belite was high at 1350 ℃. The conversion rate from Belite to Alite was high in the range of 1350~1450 ℃. Samples using coal ash showed stable formation of interstitial phase in the range of 1350 to 1450 ℃. The microstructure and chemical composition distribution of cement clinker sintered at 1350~1450 ℃ showed that all samples showed a form and composition distribution in which the calcium silicate phase and interstitial phase were clearly distinguished.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.47-52
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• 2024

The demand for FRPs that are corrosion-free and have an excellent tensile strength-to-weight ratio. However, there is a lack of research on the mechanical properties of FRP in the form of rebars, especially the changes in performance due to heating. Therefore, in this paper, 60 tensile and compression specimens of CFRP rebars with a diameter of 12 mm were fabricated and subjected to direct tensile and direct compression tests, and their performance was evaluated according to the heating temperature. It was found that as the heating temperature increases above 300 ℃, the performance decrease becomes larger due to the burning of epoxy. The compressive strength was found to be much lower than the tensile strength, but the modulus of elasticity was found to be the same in tension and compression.

• Journal of the Korea Institute of Building Construction
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• v.18 no.5
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• pp.403-412
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• 2018

Recently, needs for utilization of recycled aggregate have been increasing. However, its utilization has been limited due to its high alkalinity, which mostly came from the unremoved cement paste particles that were attached at the surface of recycled aggregate. Various efforts has been made to reduce its alkalinity by using $CO_2$, but currently available methods that uses $CO_2$ generate the problem with pH recovery. Considering the fact that supercritical $CO_2$ ($scCO_2$) can provide more rapid carbonation of cement paste than by normal $CO_2$, $scCO_2$ was utilized in this work. The reaction between $scCO_2$ and hydrated cement paste has been systematically evaluated. According to the results, it was found that powder type showed higher carbonation compared to that of cube specimens. It seems the carbonation by $scCO_2$ has occurred only at the surface of the specimen, and therefore still showed some amount of $Ca(OH)_2$ calcium aluminates after reaction with $scCO_2$. With powder type specimen, all $Ca(OH)_2$ was converted into $CaCO_3$. Moreover, additional calcium that came from both calcium aluminate hydrates and calcium silicate hydrates reacted with $scCO_2$ to form $CaCO_3$. After carbonation with $scCO_2$, the powder type specimen did not show pH recovery, but cube specimens did show due to the presence of portlandite.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.349-356
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• 2018

In this study, material properties of steel fiber reinforced high strength concrete (FRHSC) with the compressive strength of about 120MPa were modeled. Steel fiber content of 1.0%, 1.5%, and 2.0% was considered as experimental variable. First of all, compressive strength tests were carried out to determine compressive characteristics of concrete, and compressive stress-strain curves were modeled. For conventional concrete with moderate compressive strength, the stress-strain curves are in the form of parabolic curves, but in the case of high strength concrete reinforced with steel fiber, the curves increase linearly in the form of the straight line. In addition, to understand the tensile properties of FRHSC, the crack mouth opening displacement (CMOD) test was performed, and the tensile stress-CMOD curve was calculated through inverse analysis. When the steel fiber content increased from 1.0% to 1.5%, there was a significant difference of tensile strength. However, when the amount of steel fiber was increased from 1.5% to 2.0%, there was no significant difference of tensile strength, which might result from the poor dispersion and arrangement of steel fiber in concrete.

• Journal of the Korean housing association
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• v.17 no.5
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• pp.117-126
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• 2006

Although we have seen recently increasing number of eco-villages, any eco-village is not registered in Global Eco-village Network. It is important to review the definition of eco-villages and to provide useful basic information for future eco-villages. The main research aim is to analyze landscape characteristics of community garden and common spaces and to identify ecological symbolism of landscape created by residents in eco-villages. Seven eco-villages in Germany, Denmark and UK were selected and the following aspects were investigated through field survey; the settlement background, social and economical aspect, architectural specifications, recycled energy, and landscape characteristics of external spaces in eco-villages. The result indicated that the landscape of eco-village did intend neither to return to primitive society nor to control nature by technology. It intended to coexistence with nature. Primitive nature is symbolically restored and people who have it in mind strongly intend to grow together this common sense. Landscape creation has important role in creating common relationship between human living and nature. When we regard it conceptually as the eco-symbolism in landscape design of community garden, it presented the meaningful relationship with landscape and human life. It is not expression of landscape materiality and designed form but sense of place and landscape image. Landscape design would be expected to reveal the life stage and cycle from designed physical form and materiality through as time goes by when it is part of environmental circulation process by means of human living as meaningful relationship.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1551-1561
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• 2012

Boat or yacht hulls are mainly built using FRP composite materials. FRP boat hull manufacturing has been restricted since 2000 under international regulations on ocean environment safety. FRP composite materials cannot be recycled and require more than 100 years to biodegrade. Therefore, alternatives to FRP have been proposed by many boat builders. Steel, aluminum, and FRP are commonly used as boat hull materials. Their design specifications are proposed as Korean register of shipping. However, the design specifications for inexpensive materials for a small boat have not yet been studied. Small shipbuilders manufacture and sell HDPE canoes or HDPE kayaks. In this study, a hull form was designed based on actual boats. The thickness of an HDPE boat hull was determined based on ISO 12215-5 structural design specifications.

• Steel and Composite Structures
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• v.51 no.3
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• pp.337-349
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• 2024

The growing quantity of tires and building trash piling up in landfills poses a serious threat to the stability of the ecosystem. Researchers are exploring ways to reduce and use such byproducts of the construction industry in an effort to promote greener building practices. Thus, using recycled crumb rubber from scrap tires in concrete manufacturing is important for the industry's long-term viability. This study examines the proportion of waste rubber in fiber form, specifically at weight percentages of 5%, 10%, and 15%. Moreover, the study examines the shear behavior of reinforced concrete beams. A total of twelve RC beam specimens, each sized 100 mm by 150 mm by 1000 mm (w × d × L), were constructed and positioned to the test. Various mixtures were designed with different levels of scrap tire rubber content (0%, 5%, 10%, and 15%) and Stirrup Vol. Ratio (2.10, 2.80, and 3.53) in reinforced concrete beams. The findings indicate that the inclusion of scrap rubber in concrete leads to a decrease in both the mechanical characteristics and weight of the material. This is mostly attributed to the lower strength and stiffness of the rubberized concrete. Furthermore, estimations generated by a variety of design codes were examined alongside the obtained data. In order to make a comparison between the estimates provided by the different codes such as ACI 318-14, CEB-FIB and Iranian national building codes, a calculation was done to determine the ratio of the experimental shear strength to the anticipated shear strength for each code.

• Advances in environmental research
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• v.7 no.1
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• pp.39-52
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• 2018

Direct membrane filtration (DMF) of wastewater has many advantages over conventional biological wastewater treatment processes. DMF is not only compact, but potentially energy efficient due to the lack of biological aeration. It also produces more biosolids that can be used to produce methane gas through anaerobic digestion. Most of ammoniacal nitrogen in wastewater is preserved in effluent and is used as fertilizer when effluent is recycled for irrigation. In this study, a technical feasibility of DMF was explored. Organic and nitrogen removal efficiencies were compared between DMF and membrane bioreactor (MBR). Despite the extremely high F/V ratio, e.g., $14.4kg\;COD/m^3/d$, DMF provided very high COD removal efficiencies at ~93%. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) were less in DMF sludge, but membrane fouling rate was far greater than in MBR. The diversity of microbial community in DMF appeared very narrow based on the morphological observation using optical microscope. On the contrary, highly diverse microbial community was observed in the MBR. Microorganisms tended to form jelly globs and attach on reactor wall in DMF. FT-IR study revealed that the biological globs were structurally supported by feather-like materials made of secondary amines. Confocal laser scanning microscopy (CLSM) study showed microorganisms mainly resided on the external surface of microbial globs rather than the internal spaces.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1129-1131
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• 2002

Zinc Air battery obtain their energy density advantage over the other batteries by utilizing ambient oxygen as the cathode materials, and reusing cathode as recycled form. And specific capacity of zinc powder is as high as 820mAh/g. When Zinc Air battery discharged by low rate current discharge voltage profile has very flat pattern until end of voltage. But, when Zinc Air battery discharged by high rate current discharge voltage and capacity become lower. Therefore, we focused on effects of catalyst size in cathode. So we examined performance of zinc air batteries, average discharge voltage, capacity, energy, resistance. And we also obtained resistance by the GSM pulse discharge. So we have got optimum size of catalyst for Zinc Air battery.