• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.15-22
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• 1995

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.37-44
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• 2012

Recently, due to developments in construction technology, the use of high-performance concrete became popular. High-performance concrete when compared to the ordinary concrete can better satisfy required performances by using mineral admixture and superplasticizer. Various studies on the effect of admixture materials on the quality of high-performance concrete have been reported. But there exist limited number of reported results on the effect of cement qualities, which is the most important constituent material in concrete. Therefore, in this study, the relationship between the quality of cement and the flowability of high flowing concrete is investigated. Qualities of domestically produced cement were identified, and then the influence of the qualities of cement on the flowability of high flowing concrete is evaluated. The result showed that the dosage of required superplasticizer was dependent on cement fineness, to brain, free-CaO, and interstitial phase, which all trigger initial hydration process of cement. Particularly, the results showed that fineness of cement has a high impact on the dosage of the superplasticizer. For strength property of concrete, the dosage of superplasticizer had a significant effect on the early age strength, but had negligible effect in the long term strength.

• Magazine of the Korea Institute for Structural Maintenance and Inspection
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• v.18 no.4
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• pp.2-8
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• 2014

본 고는 동절기 이후 무근 콘크리트의 상부에서 쉽게 발생하는 스케일링 현상에 주목하여 무근 콘크리트의 동해 발생원인을 고찰하고, 이에 대한 내구성을 향상시키기 위한 방안을 기존문헌조사를 통하여 1) 강도향상, 2) 진공배수공법 적용, 3) 흡수방지재 시공의 방법을 선정하였다. 그 후 각 방법의 동결융해저항성 향상 평가를 정량적으로 평가하기위하여 동결융해 시험을 통한 상대동탄성계수를 측정하였다. 그 결과 1), 2)번의 경우 동탄성계수가 약 15% 향상, 3)의 경우 강도에 따라 7~13%향상됨을 실험적으로 확인하였다. 따라서 상기의 방법 모두 무근 콘크리트의 동결융해 저항성 향상에 유효한 방법으로 판단되며, 이를 통해 무근콘크리트의 빈번히 발생하는 품질저하 및 이로인한 유지보수비용 절감을 도모할 수 있을 것으로 사료된다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.247-248
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• 2009

Testing standards both nationally and abroad for high flowing concrete are presented about slump flow and the time to reach 500 mm. However, the slump flow testing method to measure flow properties of high flowing concrete results in measurement error due to the differences in each person's perception of the test. This study introduced laser diode to reduce such testing errors from personal differences in experimental procedure.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.629-636
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• 2001

To apply the research results to the design and the construction of the high rise buildings, long-term behavior of reinforced concrete structure have been widely studied. However, shoring and reshoring at early ages have not been considered in the most of studies. The removal of forms and shores has been dealt with one construction sequence. i.e. the deformation occurred at the early age before the removal of shore has been neglected. In this paper, two-dimensional frame analysis program for long-term behavior of reinforced concrete was developed. In the developed program, construction sequence including the settlement and the removal of shores is considered to predict axial force variation due to forms ,shores, and time-dependent concrete stiffness. Analysis results show that the time-dependent axial force of shores is reduced, and the redistributed axial force of the interior column is greater than the value by elastic analysis and that of the exterior column is smaller. In order to demonstrate the validity of this program, the test frame was constructed in sequence of the placement of concrete, form removal, reshoring, shore removal, and the application of additional load. The proposed program predicts experimental results well.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.122-129
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• 2016

In this study, we developed a pressing device which can reproduce the pressure of concrete inside the conveying pipe as a part of the basic study to development of high fluidity concrete under high pressure pumping. Using this pressing device, we evaluated a absorption properties of aggregate that are crushed coarse aggregate, river gravel and lightweight coarse aggregate according to pressure of coarse aggregate and aggregate inside a high fluidity concrete, focused on the reduction of unit water quantity by pressure. In addition, it was evaluated the compressive strength of high fluidity concrete about before and after of pressive. Test a result, case of condition under the high pressure of 250 bar, absorption ratio of crushed coarse aggregate and river gravel were not increased above the surface absorption, absorption ratio of lightweight coarse aggregate was increased than the surface absorption.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.51-56
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• 1993

This is a part a study on the development of High-Performance Concrete ; about experimental results from several test methods to estimate workability in fresh concrete and influences of concrete mix design that affects properties of super-flowing concrete. Super-flowing concrete can be filled in a formwork without any vibration because of its excellent workability of passing narrow space and filling complicated shaped mold, new test methods should be used to estimate the workability and rhelogy in super-flowing concrete instead of slump test method in conventional concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.385-386
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• 2010

This paper was examined the autogenous shrinkage properties through the fludity properties and autogenous shrinkage volume of high fluidity concrete using limestone powder.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.276-286
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• 2021

General high fluidity concrete is the area of high strength concrete with a high amount of cement to secure the required fluidity and workability. Since most of the concrete structures currently used have normal strength, there is a limit to the practical expansion and practicality of use. Thus it is necessary to develop normal strength-high fluidity concrete with low binders that can be used not only in general buildings but also in special buildings, and can greatly reduce construction time and save labor costs. This requires to develop and apply the polycarboxylate-based superplasticizer. In this study, PCE was prepared for each combination of starting materials(WR, HB, RT) and the rheological properties of cement paste were analyzed using ringflow cone and a rotary viscometer. As a result, when PCE with a combination of WR 80%, HB 6.5%, and RT 13.5% was applied, the yield stress can be minimized while securing the plastic viscosity at level of the normal strength. In addition, high fluidity due to the high dispersion effect was confirmed.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.671-677
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• 2014

In this research, flow experiments and simulation of highly flowable concrete has been attempted using a viscoplastic particle method varying with dosages of SP admixture and water-cement (W/C) ratios. Rheological and flow characteristics of flowable concrete manufactured in domestic products of cement, aggregates, and SP admixtures were investigated by experimental programs varying with mix proportions. From experiment, the predictive model of rheological characteristics of flowable concrete has been newly proposed considering with the effects of the W/C ratio and the dosage of SP admixture, and the effect of mixing proportion has also been incorporated into shear stress and strain rate curve of flowable concrete in the current method. A series of L-box flow test of highly flowable concrete varying with dosages of SP admixture and W/C ratios was compared with the proposed model.