• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2000년도 추계학술발표회 초록집
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• pp.12-12
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• 2000

This paper investigated the effect of the film deposition rate for $CrN_x$ microstructure and mechanical properties. For these purpose, pure Cr an stoichiometric CrN films were deposited with various target power density on Si hardened M2 tool steel. The variation of ni trogen concentration in $CrN_x$ f analyzed by AES and deposition rate was calculated by measuring of thickness using ${\alpha}-step$ profilometer. The microstructure was analyzed by X-Ray Diffract and Scanning Electron Microscopy(SEM), and mechanical properties were evalua residual stress, microhardness and adhesion tests. Deposition rate of Cr and CrN increased as an almost linear function of target power density from $0.25\mu\textrm{m}/min$ and $0.15\mu\textrm{m}/min$ to $0.43\mu\textrm{m}/min$. Residual stresses of Cr and CrN films were from tensi Ie to compressive stress with an increase of deposi tion rate a compressive stresses were increased as more augmentation of deposition r maximum hardness value of $2300kg/\textrm{mm}^2$ and the best adhesion strength correspond HF 1 were obtained for CrN film synthesized at the highest target densitY($13.2W/\textrm{mm}^2$) owing to high residual compressive stress and increasing mobility.

• 한국응용과학기술학회지
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• 제19권2호
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• pp.117-122
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• 2002

A silicone softner (SS-5), a permanent press (PP) finish, was prepared by blending silicone oil KF-96 (as a lubricating component) and beef tallow hardened oil (as a softening component) which was synthesized from fatty polyamide salts. The prepared SS-5 and the PP finishing resin were applied to PP finishing cotton cloth and P/C gingham sample by one-bath method. The properties such as crease recovery, tear strength, and bending resistance were tested. The samples treated with SS-5 and PP finishing resin showed improved properties when comparing with the untreated ones, with the ones treated only with PP finishing resin, with ones treated with commercial PP finishing softners and PP finishing resin. The grades of fabric samples treated with 3% SS-5 were fifth grade in the bending resistance test.

• Structural Engineering and Mechanics
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• 제59권1호
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• pp.133-151
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• 2016

Self-Compacting Concrete (SCC) has been originally developed in Japan to offset a growing shortage of skilled labors, is a highly workable concrete, which is not needed to any vibration or impact during casting. The utilizing of fibers in SCC improves the mechanical properties and durability of hardened concrete such as impact strength, flexural strength, and vulnerability to cracking. The purpose of this investigation is to determine the effect of steel fibers on mechanical performance of traditionally reinforced Self-Competing Concrete beams. In this study, two mixes Mix 1% and Mix 2% containing 1% and 2% volume friction of superplasticizer are considered. For each type of mixture, four different volume percentages of 60/30 (length/diameter) fibers of 0.0%, 1.0%, 1.5% and 2% were used. The mechanical properties were determined through compressive and flexural tests. According to the experimental test results, an increase in the steel fibers volume fraction in Mix 1% and Mix 2% improves compressive strength slightly but decreases the workability and other rheological properties of SCC. On the other hand, results revealed that flexural strength, energy absorption capacity and toughness are increased by increasing the steel fiber volume fraction. The results clearly show that the use of fibers improves the post-cracking behavior. The average spacing of between cracks decrease by increasing the fiber volume fraction. Furthermore, fibers increase the tensile strength by bridging actions through the cracks. Therefore, steel fibers increase the ductility and energy absorption capacity of RC elements subjected to flexure.

• Advances in concrete construction
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• 제5권6호
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• pp.575-586
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• 2017

The disposal of polythene waste and fly ash is causing serious threat to the environment. Aim of this study is to decrease environmental pollution by using polythene waste and fly ash in concrete. In this study, cement was partially replaced with 0%, 5%, 10%, 15% and 20% fly ash (by weight) and plastic waste was added in shredded form at 0.6% by weight of concrete. The specimens were prepared for the concrete mix of M25 grade and water to cementitious material ratio (w/c) was maintained as 0.45. Fresh concrete property like workability was examined during casting the specimens. Hardened properties were found out by carrying out the experimental work on cubes, cylinders and beams which were cast in laboratory and their behavior under test were observed at 7 & 28 days for compressive strength and at 28 days for density, flexural strength, dynamic modulus of elasticity, abrasion resistance, water permeability and impact resistance. Overall results of this study show that addition of 0.6% (by weight of the concrete) plastic waste with 10% (by weight of cement) replacement of cement by fly ash result an improvement in properties of the concrete than conventional mix.

• Steel and Composite Structures
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• 제39권3호
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• pp.307-318
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• 2021

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

• Advances in concrete construction
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• 제11권1호
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• pp.59-71
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• 2021

This research aims to study the utilization of olive waste ash (OWA) in the production of concrete as a partial substitute for cement. Effects of using OWA on the physical and mechanical properties of concrete mixtures have been investigated. This is done by carrying out tests involving the addition of various percentages of OWA to cement (0%, 5%, 10% and 15%). For each percentage, tests were performed on both fresh and hardened concrete; these included slump test, unit weight test and compressive strength test after 7, 28 and 90 days. Durability tests were investigated in solutions containing 5% NaOH and MgSO4 by weight of water. In addition, resistance to high temperatures was tested by subjecting the cubes to high temperatures of up to 170℃. The results of this research indicate that a higher percentage of OWA gives a lower compressive strength and lower workability but higher performance in terms of durability against both different weather conditions and high temperatures.

• Steel and Composite Structures
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• 제43권3호
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• pp.389-401
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• 2022

This study investigated the flowability and mechanical properties of cost-effective steel fiber reinforced ultra-high performance concrete (UHPC) by using locally available materials for field-cast application. To examine the effect of mixture constituents, five mixtures with different fractions of silica fume, silica powder, ground granulated blast furnace slag (GGBS), silica sand, and crushed natural sand were proportionally prepared. Comprehensive experiments for different mixture designs were conducted to evaluate the fresh- and hardened-state properties of self-consolidating UHPC. The results showed that the proposed UHPC had similar mechanical properties compared with conventional UHPC while the flow retention over time was enhanced so that the field-cast application seemed appropriately cost-effective. The self-consolidating UHPC with high flowability and low viscosity takes less total mixing time than conventional UHPC up to 6.7 times. The X-ray computed tomographic imaging was performed to investigate the steel fiber distribution inside the UHPC by visualizing the spatial distribution of steel fibers well. Finally, the tensile stress-strain curve for the proposed UHPC was proposed for the implementation to the structural analysis and design.

• Advances in concrete construction
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• 제16권1호
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• pp.1-20
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• 2023

This study presents the experimental results performed to evaluate the effects of Polyvinyl-alcohol (PVA) and Polypropylene (PP) fibers on the fresh and residual mechanical properties of the hybrid fiber reinforced SCC before and after the exposure of 250℃, 500℃ and 750℃ temperatures. The compressive and splitting tensile strength, modulus of rupture (MOR), ultrasonic pulse velocity (UPV) as well as toughness and weight loss were investigated at different temperatures. PVA and PP fibers were added into SCC mixtures having only macro steel fiber and also having binary hybridization of both macro and micro steel fiber. The results showed that the use of micro steel fiber replaced by macro steel fiber improved the fresh and hardened properties compared to the use of only macro steel fiber. Moreover, it was emphasized that PVA or PP enhanced the residual flexural performance of SCC, generally, while it negatively influenced the workability, weight loss, UPV and the residual strengths with regards to the use of single steel fiber and binary steel fiber hybridization. Compared to the effect of synthetic fibers, PP had slightly more positive effect in the view of workability while PVA enhanced the residual mechanical properties more.

• 콘크리트학회논문집
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• 제21권1호
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• pp.29-35
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• 2009

최근 전 세계적으로 우수한 성능을 인정받는 플라이애쉬는 시멘트의 대체재로 많은 연구와 적용사례가 늘어나고 있으나, KS L 5405에 규정된 분말도 $3,000{\sim}4,500\;cm^2/g$급인 플라이애쉬를 단위시멘트량의 20% 전후로 치환하여 사용하고 있어 그 이상의 분급에 관한 규정은 부족한 실정이다. 따라서, 본 연구에서는 3성분계 콘크리트의 특성에 미치는 고분말도 플라이애쉬의 치환율 및 물-결합재비 영향을 분석하기 위해 분말도 4000, 6000, 8000급과 치환율 15, 30, 45%의 3수준으로 설정하였으며, 물-결합재비는 40, 50%의 2수준으로 실험한 결과, 굳지않은 콘크리트의 성상에서 플라이애쉬의 치환율과 분말도가 높을수록 유동성이 향상되는 경향을 나타내었으나, 물-결합재비가 높을수록 현저히 낮아지는 것으로 나타났다. 또한, 공기량은 플라이애쉬의 치환율과 분말도가 증가하고 물-결합재비가 낮아짐에 따라 감소하는 경향을 나타내었고, 플라이애쉬의 치환율과 분말도가 높을수록 응결이 촉진되는 현상을 나타내었으며, 물-결합재비에 관계없이 플라이애쉬의 치환율이 높을수록 수화열 저감을 확인할 수 있었다. 또한, 강도특성에서는 치환율과 물-결합재비가 높아질수록 강도가 낮아지는 경향을 나타내었다.

• 콘크리트학회논문집
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• 제27권3호
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• pp.229-236
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• 2015

콘크리트는 압축강도가 증가할수록 취성적인 성질이 두드러지는데, 이를 보완하기 위해 강섬유를 혼입하여 콘크리트에 연성을 부여하는 강섬유 보강 콘크리트에 대한 연구가 진행되고 있다. 강섬유 보강 콘크리트는 섬유 혼입률에 따라 역학적 특성이 달라지며, 일반적으로 1.5%의 혼입률이 가장 효과적인 것으로 알려져 있다. 섬유 혼입률 2%를 초과하게 되면 섬유 뭉침현상이 발생하는데, 이로 인해 역학적 특성이 저하된다. 본 연구에서는 2% 이상의 높은 혼입률에서 섬유의 분산성을 향상시키기 위해 굵은 골재 크기를 변수로 재령에 따른 강섬유 보강 콘크리트의 압축거동에 대해 평가하였다. 굵은 골재 크기에 따른 굳지 않은 성상, 압축강도, 탄성계수 및 압축인성 등을 평가한 결과 섬유 혼입률이 증가할수록 공기량은 증가하였으며, 공기량이 증가함에 따라서 슬럼프는 감소하였다. 또한 골재 크기가 압축강도 및 탄성계수에 미치는 영향은 미소하였지만, 섬유의 분산성을 향상시켜 압축인성 및 최대하중 이후 거동에 영향을 끼치는 것으로 나타났다. 또한 강섬유 보강 콘크리트의 압축인성은 재령이 지날수록 감소하게 되는데, 굵은 골재 크기가 감소할수록 압축인성의 감소율이 줄어들어 보다 안정적인 것으로 나타났다. 따라서 본 연구에서 나타난 것과 같이 강섬유 보강 콘크리트의 굵은 골재 크기를 조절하여 높은 혼입률을 갖는 강섬유 보강 콘크리트의 섬유 분산성과 연성적인 거동을 부여할 수 있을 것으로 판단된다.