• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.805-808
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• 2008

본 연구에서는 BS와 FA를 치환한 3성분계 고성능 콘크리트의 개발을 위해 기초적 특성을 분석하였는데, 그 결과를 요약하면 다음과 같다. 굳지않은 콘크리트 특성으로, 유동성은 혼화재 치환율이 증가할수록 OPC보다 증가하는 것으로 나타났고, 공기량은 전반적으로 혼화재 치환율이 증가할수록 감소하는 경향을 나타내었다. 경화 콘크리트 특성으로, 압축강도는 BS와 FA의 치환율이 증가할수록 초기재령에서는 OPC보다 저하하는 것으로 나타났으나, 재령 28일에서는 OPC과 유사하거나 그 이상으로 증가하는 것으로 나타났다. 특히 B30F15일때 재령 28일에서 OPC보다 약 15% 정도 높은 최대 압축강도 값을 발휘하였다.

• Computers and Concrete
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• 제6권1호
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• pp.1-18
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• 2009

Chloride diffusivity of concrete is a crucial material parameter for service life determination and durability designing of marine concrete. Many research works on this issue have been conducted, varying from empirical solutions obtained experimentally to image analysis, based on multi-scale modeling. One of the simple approaches is to express the chloride diffusivity of concrete by a multi-factor function, however, the influences of various factors on the chloride diffusivity are ambiguous. Furthermore, the majority of these research works have not dealt with the carbonation process of concrete, although this process affects the chloride diffusivity of concrete significantly. The purpose of this study is to establish a simple approach to calculate the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should be defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, a lot of parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

• Advances in concrete construction
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• 제5권4호
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• pp.359-375
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• 2017

This paper presents a study of the properties and behavior of self-compacting concretes (SCC) in the hot climate. The effect of curing environment and the initial water curing period on the properties and behavior of SCC such as compressive strength, ultrasonic pulse velocity (UPV) and sorptivity of the SCC specimens were investigated. Three Water/Binder (W/B) ratios (0.32, 0.38 and 0.44) have been used to obtain three ranges of compressive strength. Five curing methods have been applied on the SCC by varying the duration and the conservation condition of SCC. The results obtained on the compressive strength show that the period of initial water curing of seven days followed by maturation in the hot climate is better in comparison with the four other curing methods. The coefficient of sorptivity is influenced by W/B ratio and the curing methods. It is also shown that the sorptivity coefficient of SCC specimens is very sensitive to the curing condition. The SCC specimens cured in water present a low coefficient of sorptivity regardless of the ratio W/B. Furthermore, the results show that there is a good correlation between ultrasonic pulse velocity and the compressive strength.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 춘계 학술논문 발표대회
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• pp.313-314
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• 2013

The study carried out the experiment with presenting as the fundamental data for developing non-cement by using red mud generated in blast furnace slag and bauxite generated in the process of manufacturing the pig iron process of manufacturing Al(OH)₃/Al₂O from as the binding material using the accelerator of NaOH. After fixing the thing and the NaOH adding the blast furnace slag and NaOH 10, 20, 30 (%) with 10, 20, 30 (%) substituted the red mud in the blast furnace slag and the experimental method carried out the experiment. And it measured the flexural strength and compressive strength and took a photograph EDS analysis and SEM. Consequently, the compressive strength was improved as the addition rate of the NaOH was high and the compressive strength according to the replacement ratio of the red mud was degraded. This is determined that film of the blast furnace slag is destroyed and it makes the hydration reaction condition and the intensity is revealed.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.295-296
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• 2006

High hardness of P/M parts can be obtained in the cooling section of the sintering furnace by using sinter hardenable materials, thus the post-sintering heat treatment can be eliminated. However, the sinter hardened materials would have difficulties in secondary machining if it is required, which will limit the applications of sinter hardenable materials in the machined parts. Recent development in warm compaction technology can enable us not only to achieve the high green density up to $7.4\;g/cm^3$, but also the high green strength which is needed for green machining. Therefore by using warm compaction technology, the green machining can be applied to sinter hardenable materials for the high density, strength and hardness P/M parts. In the present study, a pre-alloyed steel powder, ATOMET4601, was used by mixing with 2.0% copper, 1.0% nickel, 0.9% graphite and a proprietary lubricant using a binder treatment process - FLOMET. The specimens were compacted and green machined with different machining parameters. The machined surface finish and part integrity were evaluated in selecting the optimal conditions for green machining. The possibility of applying the green machining to the high-density structural parts was explored.

• 한국자동차공학회논문집
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• 제2권6호
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• pp.87-93
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• 1994

This paper describes on the establishment of an optimal internal grinding conditions for the purpose of improving the grinding efficiency against to the high-speed grinding. Through the fundamental grinding tests for the brittle and hardened material, we are concluded that high-speed internal grinding is effective to improve the grinding accuracy as well as the grinding efficiency. The obtained results are as follows: (1) Under the speed ratio $(V_w/V_g)$ is constant, it is possible to increase the grinding efficiency with satifying the constraint conditions. (2) Increasing the wheel velocity, surface roughness and out-roundness are improved. (3) Under the wheel depth of cut is constant and increasing the speed ratio, workpiece residual stress is decreased. The described method, in this paper, is capable of determining the optimum internal grinding conditions taking into account some constraint conditions, and practical algorithm for optimum internal grinding conditions are presented.

• 한국재료학회지
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• 제12권7호
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• pp.568-572
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• 2002

Plasma sulfnitriding technology was employed to harden the surface of SKD61 steel. The plasma sulfnitriding was performed with 3 torr gas pressure at $580^{\circ}C$ for 20 hours. Plasma sulfnitriding resulted in the formation of very thin $2-3\mu\textrm{m}$ FeS sulfide layer on top of $15-20\mu\textrm{m}$ compound layer, which consisted of predominantly $\varepsilon$- $Fe{2-3}$ N and a second phase of $\Upsilon'-Fe_4$N. In comparision with plasma nitriding treatment, plasma sulfnitriding treatment showed better surface roughness and corrosion resistance due to the presence of the thin FeS layer. which coated microvoids and microcracks on top of the nitrided layer. It was also found that plasma sulfnitrided sample showed better wear resistance due to the presence of the thin FeS layer which acted as a solid lubricant.

• Advances in concrete construction
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• 제5권1호
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• pp.17-29
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• 2017

Geopolymer concrete is environmentally friendly and could be considered as a construction material to promote the sustainable development. In this paper fly ash based geopolymer concretes with different percentages of alccofine were made by mixing sodium hydroxide and sodium silicate as an alkaline activator and cured at ambient as well as heat environment in an electric oven at $90^{\circ}C$. Effects of various parameters such as the percentage of alccofine, curing temperature, a period of curing, fly ash content, was studied on compressive strength as well as workability of geopolymer concrete. The study concludes that the presence of alccofine improves the properties of geopolymer concrete during a fresh and hardened state of concrete. Geopolymer concrete in the presence of alccofine can be used for the general purpose of concrete as required compressive strength can be achieved even at ambient temperature. The 28 days compressive strength of 73 MPa, when cured at 90-degree Celsius, confirmed that it is also very suitable for precast concrete components.

• 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.

• 한국정밀공학회지
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• 제13권12호
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• pp.151-157
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• 1996

The tool condition monitoring is one of the most important aspects to improve productivity and quality of workpiece. In this study, the wear of ceramic tool (A1$_{2}$0$_{3}$-TiC Series) cutting the hardened die material(SKD11) was investigated. Flank wear was more dominant than crater wear. Therefore the modeling of cutting force related to flank wear has been performed. The cutting force model was construct- ed by an assumption that the stress distribution on the tool face is affected by tool wear. The relationship between characteristics as cutting force and tool wear can be suggested by machining parameters depending on cutting conditions. Experiments were performed under the various cutting conditions to ensure the validity of force models. The theoretical predictions on the flank wear are approximately in good agreement with experimental results.