• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.241-242
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• 2009

This study showsUltra high performance concrete with steel fiber to obtain the high ductillity. the results of high strength concrete specimences with existing steel fiber and liquid metal fiber were compared with them of plain high strength mortal through bending test. The result that the ductility of high strength concrete with liquid metal fiber was superior to that with bundrex steel fiber was found through toughness test mathod like ASTM C 1018, JSCE-SF4.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.93-94
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• 2012

In this study, prediction of later-age compressive strength of ultra-high strength concrete, based on the accelerated strength of concrete cured in 80℃ warm water was investigated. As a result, the nature of ultra-high strength concrete showed a rapid early strength enhancement, compressive strength using warm water method of 80℃ at 2days is same compressive at 28days using standard curing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.69-75
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• 2017

Ultra-high performance concrete and high ductile cementless composite are considered as promising construction materials because those exhibits higher performance in terms of high strength and high ductility. The purpose of this study is to investigate experimentally the compressive strength and tensile behavior of ultra-high performance concrete and high ductile cementless composite. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the compressive strength and tensile strength of alkali-activated slag based high ductile cementless composite were lower than those of ultra-high performance concrete. However, the tensile strain capacity and toughness of alkali-activated slag based high ductile cementless composite were higher than those of ultra-high performance concrete. And it was exhibited that a high ductility up to 7.89% can be attainable by incorporating polyethylene fiber into the alkali-activated slag based cementless paste.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.290-297
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• 2017

The flexural behavior tests of UHPC segmental U-girder and composite U-girder which has 160MPa compressive strength and 15.4m length were carried out. The test variables are volume fraction of steel fibers and slab over the U-girder. Each U-girder has longitudinal re-bars in web and lower flange. PS tendons which has 2 of 15.2mm diameter in upper flange and PS tendons which has 7 of 15.2mm diameter in lower flange were arranged and prestressed at onetime in U-girder connection stage. Enough strong prestressing force which applied to U-girder due to ultra high performance concrete strength can withstand the self weight and dead load in U-girder stage. By comparison with the brittle behavior of U-girder, composite U-girder showed the stable and ductile behavior. After the construction of slab over U-girder, flexural load capacity of composite U-girder can bear the design load in final construction stage with only one time prestressing operation which already carried out in U-girder stage. This simple prestressing method due to the ultra high strength concrete have the advantage in construction step and cost. The shear key which has narrow space has the strong composite connection between ultra high strength concrete U-girder and high strength concrete slab didn't show any slip and opening right before failure load.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.3-9
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• 2013

In ultra high strength concrete, when electric arc furnace oxidizing slag is substituted for sea sand as fine aggregate, compressive strength was improved about 15 MPa. To figure out the cause of the improvement in compressive strength, this study considered the dissolution characteristics of Ca component in fine aggregate and examined the microstructure, porosity, microhardness, and Ca/Si mole ratio on the interface of fine aggregate and paste. And to examine the mechanism of strength improvement resulted from the shape of fine aggregate, this study measured the surface roughness of fine aggregate with AFM. According to the result of this experiment, the mechanisms of strength improvement in ultra high strength concrete resulted from the use of electric arc furnace oxidizing slag as fine aggregate can be divided into chemical and physical mechanisms. In the chemical mechanism, the soluble Ca component contained in electric arc furnace oxidizing slag is dissolved and forms a hydrate between fine aggregate and paste to improve the interlocking strength of fine aggregate-paste. Also, it makes the microstructure around the fine aggregate. And in the physical mechanism, electric arc furnace oxidizing slag has a twice greater surface roughness than sea sand, so the interlocking strength between fine aggregate and paste increases, which contributes to the development of compressive strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.536-544
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• 2016

Recently, with the increase in the number of high rise and huge scaled buildings, ultra-high strength concrete with 80~100 MPa has been used increasingly to withstand excessive loads. Among the components of concrete, the effects of the kinds and properties of fine aggregates on the performance and economic advantages of ultra-high strength concrete need to be evaluated carefully. Therefore, this study examined the effects of the type of fine aggregates and mixing methods on the engineering properties of ultra-high strength concrete by varying the fine aggregates including limestone fine aggregate (LFA), electrical arc slag fine aggregate (EFA), washed sea sand (SFA), and granite fine aggregate (GFA) and their mixtures. Ultra-high strength concrete was fabricated with a 20 % water to binder ratio (W/B) and incorporated with 70 % of Ordinary Portland cement: 20 % of fly ash:10 % silica fume. The test results indicate that for a given superplasticizer dose, the use of LFA resulted in increases in slump flow and L-flow compared to the mixtures using other aggregates due to the improved particle shape and grading of LFA. In addition, the use of LFA and EFA led to enhanced compressive strength and a decrease in autogenous shrinkage due to the improved elastic properties of LFA and the presence of free-CaO in EFA, which resulted in the formation of C-S-H.

• 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.

• 전기의세계
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• v.37 no.7
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• pp.4-11
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• 1988

본고에서는 초고압기술 중 전기응력에 대해서 주로 논하고자 한다. 절연체의 전기강도는 여러가지의 환경적인 요소들에 따라서 크게 영향을 받으므로 절연체의 전기강도를 수량적으로 정의하기 위해서는 요소들의 영향을 충분히 알아야 할 것이다. 이들 요소 중 전기응력에 관련된 것들은 전압의 크기 및 파형이므로 초고압계통에서 사용되는 절연체가 그 초고압ㅇ 잘 견딜 수 있는 지를 알기 위해서는 그 초고압계통에서 일어날 수 있는 지를 확인해야 할 것이다. 그러므로 전기응력에 관한 한 초고압에서 중요한 문제는, 초고압계통에서 일어날 수 있는 파형을 해석하고, 그 파형을 어떻게 실험실에서 모의 하여 발생하고, 발생된 전압을 정확하게 측정하는 기술이라 하겠다. 이러한 관점에서 본고에서는 현재 전력계통 분야의 세계각국의 초고압연구를 간략하게 소개한 후 초고압 발생 및 측정에 대해서 논하고자 한다.

• Cement Symposium
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• no.15
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• pp.26-27
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• 1987

• Cement
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• s.153
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• pp.44-49
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• 2000