• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.101-109
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• 2008

Many researchers have reported that adding steel fiber to concrete improved its tensile and flexural strength significantly, but relatively few studies have been made on the compressive behavior of steel fiber-reinforced concrete. It is still less in case of high strength steel fiber-reinforced cementitious composites(SFRC). The main objective of this research is to examine the effect of adding steel fiber on the compressive strength of high strength SFRC using fiber reinforcing index(RI, $V_f(I_f/d_f)$). It was found from the study that compressive strength was noticeably increased in proportion to RI. In conclusion, the relationship between Reinforcing Index(RI) and compressive strength in case of high strength steel fiber-reinforced cementitious composites was suggested.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.543-550
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• 2005

In the present work, modulus of rupture (MOR), flexural toughness properties $(I_{30}\;and\;W_{2.0})$ and workability (slump) of high performance hybrid fiber reinforced concrete (HPHFRC) mixed with micro-fiber (carbon fiber) and macro-fiber (steel fiber), and replaced with a fine mineral admixture such as silica fume (SF) are characterized through the analysis of variance (ANOVA). Data of MOR, $I_{30}(or W_{2.0})$ and slump are used as the characteristic values to estimate flexural performance and workable property of HPHFRC. Specially, an experimental design was Planned according to the fractional orthogoanl nay method to reduce experimental number of times. The experimental results show that steel fiber is a considerable significant factor in MOR and I30 $(W_{2.0})$. Based on the significance of experimental factors about each characteristic factors, the following evaluation can be used: Experiment factors which reduce slump most remarkably are carbon fiber, steel fiber, silica fume order.; Those that improve MOR most significantly are silica fume $({\fallingdotseq}\;carbon\;fiber)$, steel fiber order; Those that increase flexural toughness most distinctly are silica fume, carbon fiber, steel fiber order. It is obtained that the combination of steel fiber $1.0\%$, carbon fiber $0.25\%$ and silica fume $5.0\%$ is the experimental condition that improve MOR and flexural toughness excellently with workability ensured within the experiment.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.249-257
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• 2008

Various methods have been used to reinforce the cementitious material such as mortar and concrete that have weak tensile strength. Major reinforcing method is to mix matrix with fibers which have strong tensile strength. Recently, micro-fiber reinforced mortar has been studied which removes coarse aggregate and uses micro-fiber with small diameter in order to homogenize the matrix properties and maximize the performance of fiber. Performance of micro-fiber reinforced mortar showing multiple cracking behavior is hardly represented only by the flexural toughness. Therefore, This paper reports the cracking behavior as well as mechanical behavior for various mixtures which have different fiber type and mixture proportions to find the proper parameter representing the cracking characteristic. Correlations between flexural toughness and various cracking characteristics such as cracking area, width and number are explored. As a result, it is found that flexural toughness, volume of fiber and number of cracks are suitable for representing the characteristics of micro-fiber reinforced mortar.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.387-397
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• 2015

In the present study, to enhance the constructability, a composite slab system using deck plate and micro steel fiber concrete was studied. In the proposed slab system, on-situ re-bar placement is not required. Steel fibers replace the temperature reinforcement. The present study focused on the crack control at the slab top in the continuous composite slab without spliced bars. Eight continuous slabs with various parameters were tested under vertical loading. The test parameters were the amount and types of micro steel fibers, types of deck plate, and the use of top bars in the continuous slab. To evaluate the crack resistance of the slabs, crack widths were measured in the continuous slabs. The test results showed that although the top spliced bars were not used, cracking were restrained by large flexural stiffness of the composite sections.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2000.11a
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• pp.141-141
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• 2000

한지의 제조에 있어서 부원료인 점질물은 초지시 매우 중요한 역할을 하는데 그 주된 역 할은 다음과 같다. 먼저 점질물은 섬유의 분산을 용이하게 하고 종이의 강도를 증가시키며, 양지와는 달리 박엽지의 제조가 편리하고, 종이의 경도를 증가시키며, 습지의 처리를 용이하 게 하며, 점성으로 인하여 섬유의 침전올 방지하고, 종이의 광택을 향상시키는 둥 매우 중요 한 역할을 한다. 그러나 한지 제조시 이러한 식물성 점제의 미묘한 작용은 현재 대다수의 한지 제조 공장에서 사용하고 있는 합성점제인 PAM이나 PEO 등의 합성 고분자 화합물에 서는 기대하기 어려운 작용이라 여겨진다. 이와 같은 사실에서 본 연구에서는 전통적인 천 연점질물인 황촉규근의 점질물과 합성점제인 PAM 및 우리 나라에서 전혀 사용되지 않고 있는 나무수국 내수피의 점질물을 이용하여 한지를 제조하고 이들 한지의 특성을 SEM 및 A AFM(Atomic Force Microscopy)를 이용하여 분석하였다. 먼저 각각의 점질물로 제조한 한지를 SEM으로 관찰한 결과 닥나무 인피섬유의 최외층에 투명막이 존재하는 사실을 발견할 수 있었다. 이러한 투명막은 닥나무나 뽕나무 인피섬유에 만 존재하고 삼지닥나무나 산닥나무 둥과 같은 기타 인피섬유에는 존재하지 않으므로 한지 의 원료 섬유의 식별에 매우 중요한 요소가 된다. 또한 이러한 투명막은 섬유간 결합을 증 대시켜 한지의 강도 발현에 기여한다고 사료된다. 천연점질물인 황촉규근과 나무수국 점 질물을 이용하여 제조한 한지를 SEM 및 SEM-EDXA를 이용하여 분석한 결과, 황촉규근 점질물로 제조한 한지에는 상당량의 전분입자가 폰재하고 있었으며 나무수국 점질물로 제 조한 한지에는 침상의 수산칼슐 결정이 상당량 존재하고 있는 사실을 발견하였다. 이러한 사실은 한지 제조시 사용된 점질물의 식별에 중요한 요소라 사료된다. 한지의 원료인 닥나무 인피펄프와 침엽수 미표백 크라프트 펄프를 AFM을 이용하여 분석 한 결과, 닥나무 인피펄프의 마이크로피브릴 폭은 5-10nm로 Sw-UKP의 마이크로피브릴 폭 lO-20nm보다 매우 가늘고, 치밀한 세포벽 구조를 하고 있었다. 닥나무 인피펄프의 이러 한 세포벽 구조 및 마이크로피브렬의 형태가 Sw-UKP보다 높은 섬유강도를 나타내는 원인 이라 사료된다. 각각의 점질물을 이용하여 제조한 한지의 섬유표면을 AFM을 이용하여 관 찰한 결과, 원료펄프의 표면관찰에서와는 달리 초지시 사용된 점질물이 섬유표면을 피복하 고 있어 명확한 형태의 마이크로피브렬을 관찰할 수 가 없었다. 따라서 점질물의 이러한 역 할이 한지의 강도 및 보존성 향상에 기여하리라 사료된다.

• Magazine of RCR
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• v.18 no.4
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• pp.56-63
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• 2023

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.233-240
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• 2012

Hybrid SHCC is being researched actively for its excellent performance in controlling macro and micro cracks using macro and micro fibers, respectively. However, a significant autogenous shrinkage of SHCC is expected since it possesses high unit cement volume in its mix proportion, resulting in autogenous shrinkage cracks. Therefore, this study was performed to evaluate mechanical property of shrinkage-reducing type hybrid SHCC mixed together with steel fiber and PE fiber with excellent micro/macro crack controlling performance. In order to evaluate mechanical property of shrinkage-reducing type hybrid SHCC, replacement ratios of 0% and 10% of expansive admixture and water to binder ratios of 0.45, 0.3, and 0.2 were considered as variables. Then, shrinkage, compressive, flexural, and direct tensile tests were performed. The test results showed that mix proportion with W/B 0.3 significantly improved mechanical performance by using 10% replacement of expansive admixture.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.98-105
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• 2017

In this study, the fiber blending ratio and strain rate effect on the tensile behavior of hybrid fiber reinforced cement composite was evaluated. Hooked steel fiber and polyvinyl alcohol fiber were used for reinforcing fiber. The fiber blending ratio of HSF+PVA were 1.5+0.5, 1.0+1.0 and 0.5+1.5vol.%. As a results, the tensile strength, strain capacity and fracture toughness of the hooked steel fiber reinforced cement composites were improved by the increase of the bond strength of the fiber and the matrix according to increase of strain rate. However, the tensile stress sharply decreased after the peak stress because of the decrease in the number of straightened pull-out fibers by micro cracks in the matrix around hooked steel fiber. On the other hand, PVA fiber showed cut-off fracture at strain rate $10^{-6}/s$ with multiple cracks. However, at the strain rate $10^1/s$, the multiple cracks and strain capacity were decreased because of the pull-out fracture of PVA fiber. The HSF1.5PVA0.5 shown the highest tensile strength because the PVA fiber suppressed the micro cracks in the matrix around the hooked steel fiber and improved the pull-out resistance of hooked steel fiber. Thus, DIF of strain capacity and fracture toughness of HSF1.5PVA were greatly improved. In addition, the synergistic response of fracture toughness was positive because the tensile stress was slowly decreased after the peak stress by improvement of the pull-out resistance of hooked steel fiber at strain rate $10^1/s$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.49-56
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• 2015

Ultra-High Strength Concrete(UHPC) has ultra-high material performance including high strength and high flowability. On the other hand it is less ductile than high ductile fiber reinforced cementitious composite. This study investigated the effect of combination of steel fiber and micro fiber on the tensile behavior of UHPC. Four types of UHPC containing combination of steel fiber, polyethylene(PE), polyvinyl alcohol(PVA), and basalt fiber were designed. And then uniaxial tension tests were performed to evaluate the tensile behavior of UHPC according to combination of fibers. And density was measured to evaluate whether micro fiber induces unintentional high pore or not. From the test results, it was exhibited that PE fiber with high strength is effective to improve the tensile behavior of UHPC and basalt fiber is effective to increase the cracking and tensile strength of UHPC. Furthermore, it was also verified that micro fiber does not make high pore.