• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.12
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• pp.165-172
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• 2019

The aim of the research is to evaluate the influence of various replacing ratios of supplementary cementitious materials(SCMs) such as fly ash(FA), blast furnace slag(BS), and both FA and BS on general properties including segregation resistance as a powder based high fluidity concrete of normal strength grade with water-to-cement ratio 0.40. Specifically, by replacing the SCMs with low density powders, it was assessed that the decreased segregation resistance due to the decreased viscosity by J-ring test. As a result of the experiment, from the general test, the mixtures with SCMs showed increased segregation resistance by increased viscosity as the references, while some segregation was shown from J-ring test due to the decreased density of fresh state mixture related with the capacity of delivering coarse aggregate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.4
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• pp.449-455
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• 2022

Concrete is the most widely used construction material. The heavy self-weight of concrete may offer an advantage when developing high compressive strength and good dimensional stability. However, it is limited in the construction of super-long bridges or very high skyscrapers owing to the substantially increased self-weight of the structure. For developing lightweight concrete, various lightweight aggregates have typically been utilized. However, due to the porous characteristics of lightweight aggregates, the strength at the composite level is generally decreased. To overcome this intrinsic limitation, this study aims to develop a construction material that satisfies both lightweight and high strength requirements. The developed cementitious composite was manufactured based on a high volume usage of hollow glass microspheres in a matrix with a low water-to-cement ratio. Regardless of the tested hollow glass microspheres from among four different types, compressive strength outcomes of more than 60 MPa and 80 MPa with a density of 1.7 g/cm³ were experimentally confirmed under ambient and high-temperature curing, respectively.

• Structural Engineering and Mechanics
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• v.85 no.1
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• pp.29-53
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• 2023

High-strength shielding concrete against gamma radiation is a priority for many medical and industrial facilities. This paper aimed to investigate the gamma-ray shielding properties of high-strength hematite concrete mixed with silica fume (SF) with nanoparticles of lead dioxide (PbO₂), tungsten oxide (WO₃), and bismuth oxide (Bi₂O₃). The effect of mixing steel fibres with the aforementioned binders was also investigated. The reference mixture was prepared for high-strength concrete (HSCC) containing 100% hematite coarse and fine aggregate. Thirteen mixtures containing 5% SF and nanoparticles of PbO₂, WO₃, and Bi₂O₃ (2%, 5%, and 7% of the cement mass, respectively) were prepared. Steel fibres were added at a volume ratio of 0.28% of the volume of concrete with 5% of nanoparticles. The slump test was conducted to workability of fresh concrete Unit weight water permeability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity tests were conducted to assess concrete's engineering properties at 28 days. Gamma-ray radiation of 137Cs emits photons with an energy of 662 keV, and that of 60Co emits two photons with energies of 1173 and 1332 keV were applied on concrete specimens to assess radiation shielding properties. Nanoparticles partially replacing cement reduced slump in workability of fresh concrete. The compressive strength of mixtures, including nanoparticles was shown to be greater, achieving 94.5 MPa for the mixture consisting of 7.5 PbO2. In contrast, the mixture (5PbO₂-F) containing steel fibres achieved the highest values for splitting tensile, flexural strength, and modulus of elasticity (11.71, 15.97, and 42,840 MPa, respectively). High-strength shielded concrete (7.5PbO2) showed the best radiation protection. It also showed the minimum concrete thickness required to prevent the transmission of radiation.

• Korean Journal of Veterinary Research
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• v.63 no.1
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• pp.3.1-3.9
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• 2023

The efficiency of somatic cell nuclear transfer (NT) in pigs is low and requires enhancement. We identified the most efficient method for zona pellucida (ZP) removal and blastomere aggregation in pigs and investigated whether the aggregation of NT and parthenogenetic activation (PA) of blastomeres could reduce embryonic apoptosis and improve the quality of NT-derived embryos by investigating. Embryonic developmental competence after ZP removal using acid Tyrode's solution or protease (pronase E). The embryonic developmental potential of NT-derived blastomeres was also investigated using well-of-the-well or phytohemagglutinin-L. We analyzed apoptosis in aggregate-derived blastocysts. The aggregation rate of protease-treated embryos was lower than that of Tyrode's solution-treated embryos (69.2% vs. 88.3%). No significant difference was observed between phytohemagglutinin-L and well-of-the-well (35.7%-38.5%). However, 2P1N showed a higher number of blastocysts compared to 3N (73.8% vs. 24.3%) and an increased blastocyst diameter compared to the control and 1P2N (274 ㎛ vs. 230-234 ㎛). In blastomeres aggregated using phytohemagglutinin-L, the apoptotic cell ratio was significantly higher in 1P2N and 3N than in 3P (5.91%-6.46% vs. 2.94%, respectively). Our results indicate that aggregation of one NT embryo with two PA embryos improved the rate of blastocysts with increased blastocyst diameter.

• Advances in concrete construction
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• v.13 no.2
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• pp.123-132
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• 2022

This paper aims to adapt Multilinear regression (MLR) to predict the strength and toughness of SIFCON containing various pozzolanic materials. Slurry Infiltrated Fibrous Concrete (SIFCON) is one of the most common terms used in concrete manufacturing, known for its benefits such as high ductility, toughness and high ultimate strength. Assessment of compressive strength (CS.), flexural strength (F.S.), splitting tensile strength (STS), dynamic elasticity modulus (DME) and impact energy (I.E.) using the experimental approach is too costly. It is time-consuming, and a slight error can lead to a repeat of the test and, to solve this, alternative methods are used to predict the strength and toughness properties of SIFCON. In the present study, the experimentally investigated SIFCON data about various mix proportions are used to predict the strength and toughness properties using regression analysis-multilinear regression (MLR) models. The input parameters used in regression models are cement, fibre, fly ash, Metakaolin, fine aggregate, blast furnace slag, bottom ash, water-cement ratio, and the strength and toughness properties of SIFCON at 28 days is the output parameter. The models are developed and validated using data obtained from the experimental investigation. The investigations were done on 36 SIFCON mixes, and specimens were cast and tested after 28 days of curing. The MLR model yields correlation between predicted and actual values of the compressive strength (C.S.), flexural strength, splitting tensile strength, dynamic modulus of elasticity and impact energy. R-squared values for the relationship between observed and predicted compressive strength are 0.9548, flexural strength 0.9058, split tensile strength 0.9047, dynamic modulus of elasticity 0.8611 for impact energy 0.8366. This examination shows that the MLR model can predict the strength and toughness properties of SIFCON.

• Steel and Composite Structures
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• v.51 no.3
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• pp.243-260
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• 2024

Thirteen self-compacting recycled concrete filled aluminium tubular (SCRCFAT) columns were tested under concentric compression loads. The effects of the replacement ratio of the recycled concrete aggregate (RCA) and steel fibre (SF) reinforcement on the structural performance of the SCRCFAT columns were studied. A control specimen (C000) was cast with normal concrete without SF to be reference for comparison. Twelve columns were cast using RCA, six columns were cast using concrete incorporating 2% SF while the rest of columns were cast without SF. Failure mode, ductility, ultimate load capacity, axial deformation, ultimate strains, stress-strain response, and stiffness of the SCRCFAT columns were studied. The results showed that, the peak load of tested SCRCFAT columns incorporating 5-100 % RCA without SF reduced by 2.33-11.28 % compared to that of C000. Conversely, the peak load of tested SCRCFAT columns incorporating 5-100% RCA in addition to 2% SF increased by 21.1-40.25%, compared to C000. Consequently, the ultimate axial deformation (Δ) of column C100 (RCA=100% and SF 0%) increased by about 118.9 % compared to C000. The addition of 2% SF to the concrete mix decreased the axial deformation of SCRCFAT columns compared to those cast with 0% SF. Moreover, the stiffness of the columns cast without SF decreased as the RCA % increased. In contrast, the columns stiffness cast with 2% SF increased by 26.28-89.7 % over that of C000. Finally, a theoretical model was proposed to predict the ultimate loads tested SCRCFAT columns and the obtained theoretical results agreed well with the experimental results.

• KDI Journal of Economic Policy
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• v.14 no.1
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• pp.89-119
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• 1992

This paper purports to analyze the economic rationale of compensating balance requirements and its impact on money supply. This practice has recently been severely criticized for artificially increasing the money supply and, therefore, limiting the nation's aggregate lending policy under the tight constraint of the given money supply target. A review of the existing literature implies that compensating balance requirements is a banking practice which leads to corrections in the distortion of financial resource allocation due to the imperfection of financial market stemming from asymmetric information and/or financial regulations on deposit and lending rates. Therefore, the economic rationale of this practice is deemed to improve the efficiency of financial resource allocation. On the other hand, the macroeconomic impact of compensating balance requirements on the money supply depends on the impact on the money multiplier, which in turn depends on the desired ratio of deposit that people wish to maintain on the money borrowed from the banking system, and on the desired reserve ratio that the banking system would like to hold for deposit withdrawal. If the compensating balance requirements could increase the desired ratio of deposit to borrowing (bank lending), it will increase the available amount of total reserve within the banking system and, in turn, the money multiplier. However, this channel has not been fully analyzed in the literature, and the direction of the effect is ambiguous. If the practice could reduce the turn-over rate of deposit and, thereby, reduce the desired reserve ratio of the banking system, then it will also increase the money multiplier. While this channel operates unambiguously toward increasing the money multiplier, this effect will be limited by the extent that the banking system holds the excess reserve over the required reserve because the excess reserve will set the maximum amount for the desired reserve to fall. This paper tries to determine the effect on the money supply by empirically estimating the multiplier and the desired ratio of deposit to lending equations as functions of the ratio of compensating balance to the related lending, which is not observable and is estimated for the regression purpose. The results suggest that the effect of compensating balance requirements on the money supply in Korea does not exist or is very tenuous even if it could operate. Therefore, this paper concludes that the well publicized policy of cross cancelling the compensating balance and the related lending will not be effective at controlling the money supply and increasing the amount of loans without expanding the money supply.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.56-62
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• 2018

In this study, an artificially formed Gap graded soil, designed to increase its shear strength, was analyzed to determine the strength parameters through direct shear tests. Uniform and fine grain size samples were compared to the Gap graded soil to investigate the increase in the shear strength. Plate loading tests were conducted using 13mm and 19mm aggregates to confirm the reproducibility of the strength enhanced samples for site application. This test confirmed that the particle size ratio and the internal friction angle are correlated to the shear strength, and the shear resistance angle significantly increased in the specific particle size ratio range. The calculation of the ultimate bearing capacity by the plate load test demonstrated that the grain size adjustment method greatly influences the strength increase rate. Therefore, the findings were verified and it was confirmed that a high shear strength is achievable despite the existence of a poor particle size distribution.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.549-556
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• 2003

Various researches on the application of polymer dispersions to the cement mortar and concrete have been practised in many countries like America, Japan and Germany and so on because of high performance and good modification effect of these. In this study, SBR, Polymer dispersion that widely used in situ is employed that the self-flowability may be induced in the cemen mortar. In order to comprehend and investigate the modification of cement mortar with self-flowability by SBR and properties and fracture mode of adhesive strength in tension of that, experimental parameter was set as SBR solid-Cement ratio(S/C) and Cement:Fine aggregate(C:F) and the experiments such as Unit weight, Flow, Consistency change, Crack resistance and Segregation that inform on the general properties have been done. In addition of that, Adhesion in tension is measured with a view to comprehending the properties and fracture mode in tensile load. Consistency change of cement mortar modified by SBR did grow better as the ratio of SBR solid-Cement increased and was much superior to that of resin based flooring such as polyurethane and epoxy which recorded the loss of consistency in 90min. after mixing. Adhesive strength in tension increased with continuity in the curing age and showed the maximum in case of C:F=1:1 and S/C=20%. As the increase of curing age, the fracture mainly happened in the concrete substrate and the interface between the specimen and concrete substrate.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.179-188
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• 2007

Recently, the concern on the receipt of poor ready-mixed concrete in the construction field and the durability of concrete has been increased. Based on the such background, a large number of measuring methods of water content for fresh concrete have been developed and enforced in a developed country. In this study, to investigate practicality for quality control of ready-mixed concrete among various water content measurement techniques, microwave range method, air meter method and capacitance measurement method as measuring methods of water content were selected. Then, it was evaluated estimating performance of water content according to the change of binder types, fine aggregate types, absorption ratio, water content and water-binder ratio in series I and II. Also, it was examined influence on error occurrence of water content according to change of properties of used materials in series III. Finally, based on this study, it was proposed fundamental data to utilize measurement technique of water content to quality control of ready-mixed concrete in construction field.