• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.315-325
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• 2017

The purpose of the paper is to determine the influence of two widely used steel fibers and polypropylene fibers on the sulphate crystallization resistance, freeze-thaw resistance and surface wettability of ultra-high performance concrete (UHPC). Tests were carried out on cubes and cylinders of plain UHPC and fiber reinforced UHPC with varying contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Extensive data from the salt resistance test, frost resistance test, dynamic modulus of elasticity test before and after freezing-thawing, as well as the contact angle test were recorded and analyzed. Fiber hybridization relatively increased the resistance to salt crystallization and freeze-thaw resistance of UHPC in comparison with a single type of fiber in UHPC at the same fiber volume fraction. The experimental results indicate that hybrid fibers can significantly improve the adhesion properties and reduce the wettability of the UHPC surface.

• Advances in concrete construction
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• 제9권4호
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• pp.375-386
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• 2020

In the present study, the effect of basalt, glass, and hybrid glass-basalt fibers on mechanical properties and fracture behavior of self-compacting concrete (SCC) mixes have been assessed at room and elevated temperatures. To do so, twelve mix compositions have been prepared such that the proper workability, flowability, and passing ability have been achieved. Besides, to make comparison possible, water to binder ratio and the amount of solid contents were kept constant. Four fiber dosages of 0.5, 1, 1.5, and 2% (by concrete volume) were considered for monotype fiber reinforced mixes, while the total amount of fiber were kept 1% for hybrid fiber reinforced mixes. Three different portions of glass and basalt fiber were considered for hybridization of fibers to show the best cocktail for hybrid basalt-glass fiber. Test results indicated that the fracture energy of mix is highly dependent on both fiber dosage and temperature. Moreover, the hybrid fiber reinforced mixes showed the highest fracture energies in comparison with monotype fiber reinforced specimens with 1% fiber volume fraction. In general, hybridization has played a leading role in the improvement of mechanical properties and fracture behavior of mixes, while compared to monotype fiber reinforced specimens, hybridization has led to lower amounts of compressive strength.

• Composites Research
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• 제36권6호
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• pp.383-387
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• 2023

탄소섬유 복합재료는 우수한 물성을 바탕으로 산업 전반에 활용되고 있으나 취성이 강하다는 단점이 있다. 연신율이 높은 소재와의 하이브리드화를 통해 강도는 다소 감소되더라도 파괴인성을 향상시킬 수 있다. 이 연구에서는 탄소섬유와 아라미드섬유를 하이브리드한 적층 판재의 물성을 평가하되, 적층 순서를 다르게 하여 이종 재료와의 계면 형성 정도를 조절하였다. 그 결과 25%의 아라미드 섬유 포함 시 순수 탄소섬유 대비 최대 63%의 Izod 충격강도의 향상을 확인할 수 있었으며, 중간 정도의 복잡도를 가진 적층순서 [CF/CAF₂/CF]_s 에서 가장 우수하였다. 그러나 전체적인 복합화 효과는 부정적인 것으로 분석되었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.1.2-1.2
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• 2011

Electrohydrodynamics is a good approach to produce uniform-sized colloids and fibers in a continuous process. The dimension can be controlled from tens of nanometers to a few micrometers. The structure of the colloids and nanofibers from electrohydrodynamics has been diversified according to the uses. Especially, core-shell structure and hybridization with functional nanomaterials are fascinating due to their possible uses in drug-delivery systems, multifunctional scaffolds, organic/inorganic hybrids with new functions, and highly sensitive gas- or bio-sensors. This talk will present the structural variations in the colloids and fibers by simply employing phase separation during electrohydrodynamic process and demonstrate their possible applications.

• 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.

• Advances in concrete construction
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• 제3권1호
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• pp.15-37
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• 2015

Ongoing efforts for improved fracture toughness of engineered cementitious materials address the inherent brittleness of the binding matrix at several different levels of the material's geometric scale through the addition of various types of reinforcing fibers. Crack control is required for crack widths that cover the entire range of the grain size spectrum of the material, and this dictates the requirement of hybrid mixes combining fibers of different size (nano, micro, macro). Use of Carbon Nano-Tubes (CNT) and Carbon Nano-Fibers (CNFs) as additives is meant to extend the crack-control function down to the nanoscale where cracking is believed to initiate. In this paper the implications of enhanced toughness thus attained at the material nanostructure are explored, with reference to the global smeared constitutive properties of the material, through consistent interpretation of the reported experimental evidence regarding the behavior of engineered cementitious products to direct and indirect tension.

• International Journal of Concrete Structures and Materials
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• 제9권4호
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• pp.475-486
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• 2015

Mode II fracture toughness ($K_{IIc}$) of fiber reinforced concrete (FRC) has been widely investigated under various patterns of test specimen geometries. Most of these studies were focused on single type fiber reinforced concrete. There is a lack in such studies for hybrid fiber reinforced concrete. In the current study, an experimental investigation of evaluating mode II fracture toughness ($K_{IIc}$) of hybrid fiber embedded in high strength concrete matrix has been reported. Three different types of fibers; namely steel (S), glass (G), and polypropylene (PP) fibers were mixed together in four hybridization patterns (S/G), (S/PP), (G/PP), (S/G/PP) with constant cumulative volume fraction ($V_f$) of 1.5 %. The concrete matrix properties were kept the same for all hybrid FRC patterns. In an attempt to estimate a fairly accepted value of fracture toughness $K_{IIc}$, four testing geometries and loading types are employed in this investigation. Three different ratios of notch depth to specimen width (a/w) 0.3, 0.4, and 0.5 were implemented in this study. Mode II fracture toughness of concrete $K_{IIc}$ was found to decrease with the increment of a/w ratio for all concretes and test geometries. Mode II fracture toughness $K_{IIc}$ was sensitive to the hybridization patterns of fiber. The (S/PP) hybridization pattern showed higher values than all other patterns, while the (S/G/PP) showed insignificant enhancement on mode II fracture toughness ($K_{IIc}$). The four point shear test set up reflected the lowest values of mode II fracture toughness $K_{IIc}$ of concrete. The non damage defect concept proved that, double edge notch prism test setup is the most reliable test to measure pure mode II of concrete.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.33-41
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• 2016

Ultra-high performance concrete (UHPC) is one of the most promising construction materials because it exhibits high performance, such as through high strength, high durability, and proper rheological properties. However, it has low tensile ductility compared with other normal strength grade high ductile fiber-reinforced cementitious composites. This paper presents an experimental study on the tensile behavior, including tensile ductility and crack patterns, of UHPC reinforced by hybrid steel and polyethylene fibers and incorporating plastic beads which have a very weak bond with a cementitious matrix. These beads behave as an artificial flaw under tensile loading. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the tensile behavior including tensile strain capacity and cracking pattern of UHPC investigated in this study can be controlled by fiber hybridization and artificial flaws.

• 콘크리트학회논문집
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• 제23권4호
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• pp.405-411
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• 2011

철근콘크리트 구조물의 보강에 자주 사용하는 탄소 섬유나 유리 섬유 대신에 이 두 가지 섬유를 동시에 사용하여 하이브리드 효과를 얻기 위한 연구를 시도하였다. 하이브리드 효과를 얻기 위해서는 탄소 섬유와 유리 섬유를 적절한 비율로 조합해야 되며, 이러한 비율로 제작된 실험체를 이용하여 하이브리드 FRP 직접 인장 실험을 수행할 수 있다. 하이브리드 FRP 실험체는 직조된 섬유 시트를 이용하는 현장과 다르게, 섬유를 직접 조합해야 하는 이유로 작업이 쉽지 않다. 따라서 이 연구에서는 고강도 탄소 섬유와 E형 유리 섬유의 조합에 따른 1축 직접 인장 실험체의 제작 방법을 제안하여 실험을 통하여 하이브리드 효과를 분석하였다. 하이브리드 FRP로 가장 적합한 섬유 조합은 연성 지수, 탄성계수 및 응력-변형률 곡선을 비교한 결과 연성 K형 에폭시를 사용한 유리 섬유 : 탄소 섬유 = 9 : 1(체적비)가 가장 적합한 것으로 평가되었다.

• 한국식물학회:학술대회논문집
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• 한국식물학회 1998년도 The 12th Symposium on Plant Biotechnology Vol.12
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• pp.61-70
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• 1998

Genome and chromosome analyses in plants using fluorescence in situ hybridization (FISH) and immuno-staining (IMS) methods are reviewed by presenting the recent results obtained by the Chromosome Link, a group of chromosome and genome researchers. FISH is now effective to detect unique nucleotide sequences with 153 bp on the extended DNA fibers. Genomic in situ hybridization (GISH) also allows painting plant chromosomes of different genomes. GISH is quite effective to detect the genomic differentiation in the individual chromosomes within a nucleus. Three dimensional (3D) analyses are now available by confocal microscopy and a deconvolution system. These techniques are invaluable to visualize both the structural and functional dynamics within a nucleus. 3D-FISH revealed the spatial differentiation of different genomees within a nucleus. 3D-FISH also proved structural partition of centromeric and telomeric domains within a barely nucleus. The dynamic acetylation of histone H4 at the specific regions of a genome during a cell cycle is also analyzed using 3D-IMS. It is anticipated that these methods will provide us powerful tools to understand the structural and functional significance of plant chromosomes and genomes.