• Advances in concrete construction
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• 제7권1호
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• pp.31-37
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• 2019

This paper evaluates the workability and hardened properties of self-compacting concrete (SCC) containing silica fume as the partial replacement of cement. SCC mixtures with 0, 2, 4, 6, 8 and 10% silica fume were tested for fresh and hardened properties. Slump flow with $T_{500}$ time, L-box and V-funnel tests were performed for evaluating the workability properties of SCC mixtures. Compressive strength, splitting tensile strength and modulus of rupture were performed on hardened SCC mixtures. Experiments revealed that replacement of cement by silica fume equal to and more than 4% reduced the slump flow diameter and increased the $T_{500}$ and V-funnel time linearly. Compressive strength, splitting tensile strength and modulus of rupture increased with increasing the replacement level of cement by silica fume and were found to be maximum for SCC mixture with 10% silica fume. Further, residual hardened properties of SCC mixture yielding maximum strengths (i.e., SCC with 10% silica fume) were determined experimentally after heating the concrete samples up to 200, 400, 600 and $800^{\circ}C$. Reductions in hardened properties up to $200^{\circ}C$ were found to be very close to normal vibrated concrete (NVC). For 400 and $600^{\circ}C$ reductions in hardened properties of SCC were found to be more than NVC of the same strength. Explosive spalling occurred in concrete specimens before reaching $800^{\circ}C$.

• 콘크리트학회논문집
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• 제28권4호
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• pp.395-405
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• 2016

이 연구에서는 태양열 에너지 저장용도로 사용하기 위한 섬유보강 모르타르의 열적 및 역학적 특성을 파악하였다. 다양한 시멘트 복합재료의 배합이 섬유보강 모르타르의 열적 및 역학적 특성에 미치는 영향을 파악하기 위한 실험연구를 수행하였다. 섬유보강 모르타르의 역학적 특성으로서 열싸이클 전과 후의 압축강도 및 인장강도를 측정하였다. 또한, 섬유보강 모르타르의 열적 특성으로서 열전도율과 비열을 측정하였다. OPC와 그라파이트를 포함한 배합의 잔류압축강도가 가장 크게 나타난다. 알루미나 시멘트를 혼합한 배합의 비열이 크게 나타나며, 이는 알루미나시멘트가 열저장 시스템의 효율적인 축열과 방열에 유리함을 의미한다. 또한, 그라파이트의 첨가는 섬유보강 복합재료의 비열을 증가시킨다. 실험연구결과는 콘크리트를 $450^{\circ}C$ 이상의 열저장 매체로 활용하기 위한 프로토타입 시스템 설계에 실제적인 기초자료로 활용될 수 있을 것으로 사료된다.

• Journal of the Korean Statistical Society
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• 제11권1호
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• pp.36-44
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• 1982

A new design concept, called axis-slope-rotatability, is presented for the design of experiments with mixtures. This is an analogue of the Box-Hunter (1957) rotatability for second order response surface designs. By choice of design, it is possible to make the variance of the estimated slopes along the component axes constant for all axial points equidistant from the center point of the factor space. This property is called axis-slope-rotatability for mixture experiments. When the Scheffe's second degree polynomial is used, it is shown that some symmetry conditions are sufficient for axis-slope-rotatability. Several designs having this property are illustrated.

• 한국도로학회논문집
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• 제10권1호
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• pp.75-85
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• 2008

아스팔트 혼합물의 수분손상은 물의 침투로 인해 아스팔트 피막과 골재 사이의 부착력이 손실되면서 발생하는 현상으로서, 이는 아스팔트 포장의 주요 파손형태 중 하나인 포트흘의 주요원인으로 알려져 있다. 이에 본 연구는 반복적인 수침에 의한 수분손상이 일반 아스팔트 혼합물의 재료물성에 미치는 영향을 평가하고자 수행하였다. 이를 위해 기존의 수분손상 시험법인 수정 라트만 시험의 수분 동결-응해 방법을 반복적으로 적용한 일반 아스팔트 혼합물을 대상으로 간접인장시험에 의한 상온물성의 변화특성을 평가하였다. 이를 통해 일반 아스팔트 혼합물의 상온물성은 수침횟수의 증가에 따라 초기에는 급격하게 감소하다가 이후 완만한 감소추세를 나타내었으며, 초기 수분손상에서 물성값의 약 50% 이상이 손실되는 것으로 관측되었다. 또한 파괴시점을 고려한 아스팔트 혼합물의 조기 수분손상 특성을 파악하는데, $25^{\circ}C$의 파괴 에너지와 크리프 변형 에너지를 이용한 재료물성의 손상비가 가장 높은 상관성을 나타내는 것으로 평가되었다.

• 한국도로학회논문집
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• 제20권1호
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• pp.27-33
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• 2018

PURPOSES : The purpose of this study is to estimate the optimum content of an inorganic additive for cold-recycled asphalt mixtures and evaluate its performance. METHODS : An indirect tensile test, a tensile-strength ratio test, and an indirect tensile-fatigue test were conducted on cold-recycling asphalt mixtures with various additives. RESULTS : The laboratory performance tests indicated that granulated blast-furnace slag mixed with inorganic and cement activators provided optimum performance. The performance results of the cold-recycled asphalt pavement were similar to the inorganic and cement activators' performance in terms of the indirect tensile strength, tensile strength ratio, and indirect tensile-fatigue test. CONCLUSIONS : Overall, the performance of a cold-recycled asphalt mixture using inorganic additives and emulsion asphalt was comparable to a warm-recycled asphalt mixture. However, more experiments aimed at improving its performance and studying the effect of the inorganic additives must be conducted.

• Korean Membrane Journal
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• 제6권1호
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• pp.55-60
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• 2004

In recent years, an increasing interest in membrane technology has been observed in chemical and environmental industry. Membrane technology has advantages of low cost, energy saving and environmental clean technology comparing to conventional separation processes. Pervaporation is one of new advanced membrane technology applied for separation of azeotropic mixtures, aqueous organic mixtures, organic solvent and petrochemical mixtures. Sodium alginate composite membranes were prepared for the enhancement of long-term stability of pervaporation performance of water-ethanol mixture using pervaporation. Sodium alginate membranes were crosslinked with CaCl$_2$ and coated with polyelectrolyte chitosan to protect washing out of calcium ions from the polymer. The surface structures of PAN and hydrolysed PAN membrane were confirmed by ATR Fourier transform infrared (FT-IR). A field emission scanning electron microscopy (FE-SEM; Jeol 6340F) operated at 15 kV. Concentration profiles for Ca in the membrane surface and membrane cross-section were taken by an energy dispersive X-ray (EDX) analyser (Jeol) attached to the field emission scanning electron microscopy (Jeol 6340F). Pervaporation experiments were done with several operation run times to investigate long-term stability of the membranes.

• International Journal of Concrete Structures and Materials
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• 제8권1호
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• pp.27-41
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• 2014

The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects were identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stress-strain relationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members strengthened with hybrid FRP sheets and either carbon or glass FRP sheets.

• Asian-Australasian Journal of Animal Sciences
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• 제17권4호
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• pp.473-478
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• 2004

Processing and storage of the silage from agricultural by-products were studied in two experiments. The first experiment was conducted to investigate the chemical composition and degradability of various silages with varying ensiling times. The experiment was a 5$\times$3 factorial design, completely randomized, with factor A as the different formulated mixtures by varying level of urea addition (0, 0.5, 1.0, 1.5 and 2.0%) and factor B as the time of ensiling. Chemical composition changed little with time and varied only slightly with levels of urea in the mixtures. Dry matter (DM) degradability increased with increasing cassava levels while crude protein degradability and pH level increased with increasing urea addition. By using 'Flieg point', which relates to organic acid yields, there were no significant difference among ensiled mixtures and times of ensiling. Therefore it can be concluded that the 5th silage formulation is the most appropriate since its DM and crude protein (CP) degradability were highest. The second experiment was carried out to determine the quality of the 5th silage mixtures (from the previous trial) after being stored for up to 6 months. The experiment was a complete randomized design with samples taken at monthly intervals up to 6 months and subjected to laboratory and degradability analyses. The results showed no significant (p>0.05) difference in chemical composition except for increased neutral detergent fiber and acid detergent fiber percentage in association with increasing storage time. There were no significant (p>0.05) differences in 'Flieg point' among times of storage. In conclusion, this experiment showed that the silage from agricultural by-products can be stored for more than 6 months.

• Structural Engineering and Mechanics
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• 제88권2호
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• pp.141-157
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• 2023

In the present paper, the effect of recycled aggregates on the rheological and mechanical properties of self-consolidating concrete is investigated experimentally and numerically. Hence, the specimen with two types of recycled aggregates, i.e., known and unknown resistance origins, are utilized for the studied specimens. The experiments in this study are designed using the Box-Behnken method, which is one of the response surface methods. Input variables in mixtures include silica fume in the range of 5-15% as a percentage substitute for cement weight and recycled coarse and fine aggregates in the range of 0-50% for both series of recycled materials as a substitute for natural materials. The studied responses are slump flow, V funnel, compressive strength, tensile strength, and durability. The results indicate that the increase in the amount of recycled aggregates reduces the rheological and mechanical properties of the mixtures, while silica fume effectively improves the mechanical properties. In addition, the results demonstrate that the fine recycled aggregates affect the total response of the concrete significantly. The results of tensile and compressive strengths indicate that the mixtures including 50% recycled materials with known resistance origin demonstrate better responses up to 8 and 10% compared to the materials with unknown resistance origins, respectively. Recycled materials with a specific resistance origin also show better results than recycled materials with an unknown resistance origin. Durability test results represent those concretes containing recycled coarse aggregates have lower strength compared to recycled fine aggregates. Also, a series of mathematical relationships for all the responses are presented using variance analysis to predict mixtures' rheological and mechanical properties.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.533-540
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• 2000

Lightning impulse $(1.2/44[\mus])$ and damped oscillating impulse $(Osc./44[\mus])$ : 0.83[MHz]) breakdown characteristics in sulphur-hexafluoride/nitrogen (SF6-N2) mixtures were investigated. The predischarge currents were observed to clarify the breakdown mechanism. th experiments were carried out under nonuniform electric fields disturbed by a needle-shaped protrusion whose length and diameter are 10[mm] and 1[mm] at total gas pressure up to 0.5[MPa] with nitrogen concentrations varying from 5 to 20[%] in the mixture. The electrical breakdowns of SF6-N2 mixtures for both the positive and negative polarities develop with steplike pulses in leader mechanism and the breakdown voltage -time (V-t) characteristics were affected by the space charge. The voltage-time curves for the negative oscillating impulse voltage were extended over the longer time range. The minimum breakdown voltages for the negative lightning and oscillating impulse voltage were higher than those for the positive ones. in particular the positive breakdown voltages were independent of the gas pressure.