• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.501-506
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• 1998

This paper is an experimental study on the flexural strength and ductility capacity of reinforced high performance concrete beams with the concrete which has compressive strength of 600~700kg/$\textrm{cm}^2$, slump value of 20~25cm and slump-flow value of 60~70cm. Total 8 beams with different tensile reinforcement ratio and pattern of loading were tested. Form the results of reinforced high performance concrete beams, the equivalent stress block parameters proposed by MacGregor et al. or New Zealand code are recommended to use. Also, an extreme fiber concrete compressive strain of reinforced high performance concrete beams are distributed 0.0033~0.0048. In reinforced high performance concrete beams, reinforcement ratio in order to insure curvature ductility index 2 and 4 propose by ACI code should be less than those of reinforced normal strength concrete beams.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.73-77
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• 2006

This paper shows a study of the efficiency of expansive additive and shrinkage reducing admixture in controlling restrained shrinkage cracking of high performance concrete at early age. Free autogenous shrinkage test of $100{\times}100{\times}400mm$ concrete specimens and simulated completely-restrained test with VRTM(variable restraint testing machine) were performed. Creep and autogenous shrinkage of high-performance concrete with and without expansive additive and shrinkage reducing admixture were investigated by experiments that provided data on free autogenous shrinkage and restrained shrinkage. The results showed that the addition of expansive additive and shrinkage reducing admixture effectively reduced autogenous shrinkage and tensile stress in the restrained conditions. Also, it was found that the shrinkage stress was relaxed by 90% in high-performance concrete with and without expansive additive and shrinkage reducing admixtures at early age.

• International Journal of Concrete Structures and Materials
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• v.6 no.4
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• pp.231-237
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• 2012

Recently, it has been difficult to get natural sand for concrete due to an insufficient supply in Korea. Crushed sand was thought as a substitute and previous research has been focused on low fluidity and normal compressive strength (24-30 MPa). Study on high performance concrete using crushed sand is hardly found in Korea. In this study it was investigated that the effect of the crushed sand on fluidity and compressive strength properties of high performance concrete. Blending crushed sand (FM: 3.98) produced in Namyangju, Kyunggido and sea sand (FM: 2.80) produced in Asan bay in Chungnam. The final FMs of fine aggregate were 3.50, 3.23, and 3.08. W/B was set as 0.25 to get high performance. With the test results an analysis of relationship was performed using a statistical program. It was shown that strength property of concrete using crushed aggregate at the very early age or after specific time was mainly affected by strength development properties of binders instead of the crushed sand.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.318-321
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• 2006

The objective of this study is to evaluate the optimum thickness of High Performance Concrete bridge deck pavement. The application of High Performance Concrete bridge deck pavement with micro-silica was introduced to north America in the early 1980's. In order to decide the optimum thickness of High Performance Concrete bridge deck pavement, we conducted Finite Element Method analysis with Incheon Grand Bridge constructed by SAMSUNG E&C. From the FEM results, a thickness of five centimeters of High Performance Concrete bridge deck pavement with micro-silica is considered as a resonable value compared with the conventional asphalt bridge deck pavement.

• Proceedings of the Technology Innovation Conference
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• 1998.06a
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• pp.23-37
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• 1998

Recent entrepreneurship researches emphasize the importance of entrepreneurial behaviors, entrepreurs activities. This study focused entrepreneurial behaviors, especially entrepreneurial networking for using external resources which are critical to success. This study examines the relationship between characteristics of entrepreneurial networking and performance using data from 55 new high-tech ventures in Korea. We tested hypotheses that the characteristics of entrepreneurial networking are related to the performance of new high-tech ventures using regression analysis and t-test. Major findings of this study are as follows: (1) entrepreneurial networking are related to the performance of new high-tech ventures, (2) significant differences are found in the characteristics of entrepreneurial networking between high and low-performance firms, (3) some factors are related to the entrepreneurial networking. Finally, some managerial and policy implications are presented and future research directions are suggested.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.22 no.3
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• pp.60-67
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• 2014

Technical history of VTOL aircraft is examined from the early helicopter appearance to recent experimental rotorcraft in order to distinguish the core issues of those aircraft. Performance and technological challenges of some VTOL aircraft such as tilt rotor, convertiplane, gyroplane, and coaxial helicopter are discussed. As a new generation high performance rotorcraft, Sikorsky X2 is intensively investigated. Considering the developmental history of X2, the autorotational ability at high speed is recognized as a core technology. Analytic method of autorotation and some results are shown and presents research subjects related to the future Korean high performance rotorcraft.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.73-76
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• 2005

This study aims to suggest a simple and convenient design for a mix proportion method for high performance concrete by determining the optimum fine aggregate ratio and minimum binder content based on the maximum density theory. The mix design method introduced in this study adopted the optimum fine aggregate ratio with a minimum void and binder content higher than the minimum binder content level. The research results reveal that the method helps to reduce trial and error in the mixing process and is a convenient way of producing high performance concrete with self filler ability. In an experiment based on the mix proportion method, when aggregate with the fine aggregation ratio of 41$\%$ was used, the minimum binder content of high performance concrete was 470kg/$m^{3}$ and maximum aggregate capacity was $0.657m^{3}/m^{3}$. In addition, in mixing high performance concrete, the optimal slump flow to meet filler ability was 65$\pm$5cm, V load flow speed ranged from 0.5 to 1.5.

• Journal of the Korea Institute of Building Construction
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• v.14 no.3
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• pp.273-284
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• 2014

Ultra-high-performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder ratios are 0.15 to 0.20 with 20 to 30% silica fume. In the production of ultra-high performance concrete, a significant temperature rise at an early age can be observed because of the higher cement content per unit mass of concrete. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of ultra-high performance concrete. The heat evolution rate of UHPC is determined from the contributions of cement hydration and the pozzolanic reaction. Furthermore, by combining a blended-cement hydration model with the finite-element method, the temperature history in the hardening of UHPC is evaluated using the degree of hydration of the cement and the silica fume. The predicted temperature-history curves were compared with experimental data, and a good correlation was found.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.285-288
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• 2004

Generally, the autogenous shrinkage of high performance concrete is important in that it can lead the early cracks in concrete structures. In the previous study, The. autogenous shrinakge of HPC was found to decrease with incresing expansive additive and shrinakge reduction agent. In case of combined use, the autogenous shrinakge was more reduction than in case separate use. The purpose of this study is to derive a realistic equation to estimate the autogenous shrinakge model of high performance concrete with exapnsive agent and shrinakge reduction agent. investigated the durability of high performance concrete using expansive additive and shrinkage reducing agent. The proposed equation showed reasonably good correlation with test data on autogenous shrinakge of high performance concrete with material for shrinkage reduction.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.241-244
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• 2004

The evaluation of Single or multi-degregation of concrete coated by high performance surface penetration agency was examined through various tests, i.e., carbonation, absorption, carbonation + chloride ion and carbonation + chemical solution according to various high performance surface penetration agencies and various compressive strengths of base concrete. The 2 types of high performance surface penetration agencies were used i.e., inorganic and alcohol soluble. And 2 types of compressive strength of base concrete were used such as 21 30. MPa. The characteristics of concrete coated high performance surface penetration agency was more improved than that of non-coated concrete, and especially, water soluble inorganic agency was most effective. And if compressive strength of base concrete was low, the improved effects would be larger.