• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.266-267
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• 2014

In order to develop concrete generating compressive strength of 10MPa~15MPa aging for 6hours in the room temperature curing, Hardening accelerator containing Ca²⁺ mixed with rapid hardening portland cement containing C₃S in quantity. The result was that the more addictive contents of Hardening accelerator is, the more greatly early compressive strength was improved. That's because the composition of Ca(OH)₂ was mass-produced at early-ages.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.131-132
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• 2021

In this study, as part of the study to reduce and integrate heat of hydration of concrete, the performance change of super retarding agent is examined in the mortar area under high temperature conditions. It was confirmed that the setting time delay can be adjusted from several hours to several days depending on the high temperature and the change of super retarding agent mixing rate. With the increase of super retarding agents, the early age strength was delayed while at 28 days the use of super retarding agent results in an increase of strength remakably.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.211-215
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• 1996

This paper presents comparisons of pullout load of concrete with compressive strength of cylinders and cores, pulse velocity, and rebound number. A pullout test, which is a relatively new nondestructive technique, measures with a special tension ram the force required to pullout a specially shaped steel rod whose enlarged end has been cast into a concrete block. In this study 3 concrete mixes(normal strength, high-strength & super-high-strength) were made. From each mix, one 100$\times$70$\times$20 concrete block, 24 cylinders$(\phi10mm)$were casted. Each tests were performed on the concrete blocks at 3, 7, 28, and 91days. The test data shows that the pullout test is superior to the rebond hammer and the pulse velocity measurements on the evaluation of concrete strength. The pullout test is satisfactory for estimating the strength of in situ concrete at both early and late age, and its results can be reproduced with an acceptable degree of accuracy.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.47-50
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• 2009

The existing techniques used to estimate and manage the compressive strength of concrete do not include the environmental factors that influence the development of compressive strength and the compressive strength itself. Thus, it is necessary to develop a reasonable yet simple way to measure the compressive strength of concrete structures at construction sites by considering concrete's mechanical properties and curing environment. This study was conducted to propose an acrylic form and a junction isolation mold with crack-inducing boards that uses non-destructive methods to create and collect concrete test samples that are cured in the same condition as the actual concrete structures. junction isolation molds were used in high-strength and super high-strength concrete to evaluate the reliability of compressive strength evaluation on the test sample. The following were the findings of this study:

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.73-76
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• 2009

In ultra-high-strength concrete, chemical shrinkage is larger than drying shrinkage due to using a large amount of cement and admixtures, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain of ultra-high-strength concrete. So, this study have prepared super-high-strength concrete with specified mixing design strength of over 100MPa and have evaluated a method of reducing chemical shrinkage by using expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by chemical shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher than previous research that used only expander or shrinkage reducing agent. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.57-60
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• 2009

In ultra-high-strength concrete, autogenous shrinkage is larger than dry shrinkage due to the consume of a large amount of cement and cementitous material, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain for ultra-high-strength concrete. So, this paper have prepared super-high-strength concrete with specified mixing design strength of over 150MPa and have evaluated a method of reducing autogenous shrinkage by utilizing expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by autogenous shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher when the contents of the expander material were higher. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.463-468
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• 1999

The slurry wall of Inchon LNG receiving terminal tank will be planned the super flowing concrete having properties of high strength (required strength 520kg/$\textrm{cm}^2$), no-vibrating and massive structure in the underground. For the performance of this concrete, we investigate and select all materials, the optimum mix design and sensibility test in the laboratory. As test results, we choose portland blast-furnace slag cement and lime stone powder(L.S.P) as cementitious materials, W/C 41%(W/B 35.4%), S/a 50.8% and unit volume of coasre aggregate 0.30 as optimum mix design. Also test result of the fresh and hardened concrete are satisfied with specifications of slurry wall.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.757-762
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• 2001

CFT concrete has high flowing, high strength and resistance to material separation to use skyscraper structure. It is considered that concrete could fill the lower part of Diaphragm up. This kinds of CFT concrete hardly apply to building below 20 stories. Using the common use strength concrete to building below 20 stories brings to reduce construction cost. This concrete is needed that valid fluidity and packing ability with unit cement content as common use strength concrete. Offering a fundamental data and proportioning in CFT concrete of below 20 stories, it is executed basic property test, analysis of proportioning and mock up test.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.709-712
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• 2008

RC super tall buildings are planned and constructed recently in domestic area. Concrete is characterized by time dependant material such as creep and shrinkage. For this properties of concrete, differential shortening is one of the main issues on super tall buildings construction. This study includes material research, which is performing as a pre design stage to solve differential shortening on Lotte Super Tower Jamsil core structure(50, 60, & 70 MPa). The major part of this study is composed with comparison and analysis between experimental data and predicted data on total shrinkage and total compliance which were used on design stage. Four models, ACI209R Model, Ba${\check{z}}$ant-Baweja B3 Model, CEB MC99 Model, & GL2000 Model, were employed to predict them. It also tries to seek a proper model for high strength and high performance concrete in the case of no concrete test.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.05a
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• pp.193-197
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• 2008

Recently, it increases in use of CFT(Concrete filled steel tube, below CFT) that is an excellent internal force and deformation capacity because material and method are required to be diversification and High-Performance according to increase the super-high structure. And it is proposed to use high-strength Concrete Filled steel Tube Column. But it is difficult quantitative evaluation about fire-resist performance of CFT because steel tube bind concrete. Also, the case of high strength CFT is feared that spalling occur inside. Therefore, this study made CFT specimen that determine the factor(which is strength of concrete) and then CFT column was exposed to heating controlled as closely as possible the ISO-834 standard fire curve. Also, it tried to analyze internal temperature through nonlinear transient heat flow analysis.