• Architectural research
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• v.15 no.1
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• pp.53-58
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• 2013

High strength concrete is being used increasingly in mass structure projects. The purpose of this study is to investigate the influence of temperature during mixing, placing and curing on the strength development, hydration products and pore structures of high strength concrete in mass structures. The experiments were conducted with two different model walls, viz.: 1.5 m and 0.3 m under typical summer and winter weather conditions. The final part of this study deal with the clarification of the relationship between the long-term strength loss and the microstructure of the high strength concrete at high temperatures. Test results indicated that high elevated temperatures in mass concrete structures significantly accelerate the strength development of concrete at the early ages, while the long-term strength development is decreased. The long-term strength loss is caused by the decomposition of ettringite and increased the total porosity and amount of small pores.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.13.2-17
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• 2003

When fresh concrete is exposed to low temperature, the concrete may suffer frost damage due to freezing at early ages and strength development may be delayed. One of the solution methods to resolve these problems is to lower freezing temperature of concrete by the use of chemical admixture called Accelerators for Freeze Protection. In this study, it was the results of appling cold weather concrete using Accelerator for Freeze Protection in the Daewoo Trump world field. Before the application of the cold weather concrete using accelerator for freeze protection, we executed the some test in the laboratory and mock-up test in the field. We examined the manifestation of compressive strength complying with the amount of Accelerators for Freeze Protection and curing conditions, and then made a selection of most suitable amount of Accelerators for Freeze Protection.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.99-105
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• 1993

The purpose of this fundamental study is to investigate the mechanism of high strength concrete using the high calcium sulfate cement from a point of view in cement hydration and micro structure. As a results, it was found that the internal pores of concrete are decreased by using the high calcium sulfate cement, because the hydrates of Ettringite which is densified in structure is much formed in early ages at steam curing. In addition to the ettringite needs the 32 times of free water formed mixing water for hydration. This effect are not only decreased the water to cement ratio and also increase to comp, strength of concrete. It was conclude that these above the two facts are the main mechanism of high strength concrete using high calcium sulfate cement.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.193-198
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• 1998

In this study, the change of concrete temperature, strain and thermal stress were measured by using the embedded type concrete gauges in tendon gallery wall of containment building. A finite element analysis was performed to clarify the thermal behavior of concrete. The analytic and test results were investigated to improve the validity of analytic method. According to the test results, concrete temperature, strain and thermal stress were strongly affected by measuring point and environment condition of member. And the thermal stress was developed in the member which was not demoulded at early ages. This is caused by the change of internal temperature and restrained condition. A finite element effectively interpreted the test results by estimating the concrete properties and the site condition.

• International Journal of Concrete Structures and Materials
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• v.10 no.3
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• pp.257-269
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• 2016

Early-strength-concrete (ESC) made of Type I cement with a high Blaine value of $500m^2/kg$ reaches approximately 60 % of its compressive strength in 1 day at ambient temperature. Based on the 210 compressive test results, a generalized rateconstant material model was presented to predict the development of compressive strengths of ESC at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) and maximum temperatures (20, 30, 40, 50 and $60^{\circ}C$) for design compressive strengths of 30, 40 and 50 MPa. The developed material model was used to find optimum curing regimes for precast prestressed members with ESC. The results indicated that depending on design compressive strength, conservatively 25-40 % savings could be realized for a total curing duration of 18 h with the maximum temperature of $60^{\circ}C$, compared with those observed in a typical curing regime for concrete with Type I cement.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.267-270
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• 2005

Recently, the damaged concrete structures are often strengthened or repaired using the polymer concrete or the polymer cement mortar. In the repaired concrete structures at early ages, internal stresses could be developed due to the differential drying shrinkage of the repair material. Due to the difference of the thermal coefficients of the repair material and existing concrete, additional stresses also could be developed as the structures are subjected to the ambient temperature changes. Theses environmentally-induced stresses can sometimes be large enough to cause damage to the structures, such as debonding of the interface between the two materials. In this study, a rational procedure was developed where anchors can be designed and installed to prevent damages in such structures by thermally-induced stresses. Finally, through the experimental and numerical study, the effects of the repair method using anchors with debonding was investigated and discussed the results.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1267-1272
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• 2000

When fresh concrete is exposed to low temperature, the concrete may suffer frost damage due to freezing at early ages and strength development may be delayed. These are problems on cold weather concrete. One of the solution methods for resolving these problems has been to reduce the freezing temperature of concrete by the use of chemical admixtures called Accelerators for freezing resistance. Therefore, in this study, we executed freezing temperature of mortar, setting and strength properties with using water reducing accelerator and accelerators for freezing resistance which are producted internationally. As a result of this experiment, the freezing temperature of mortar is lower and the setting property is promoted when the admixing content of accelerators for freezing resistance is increased. Moreover, the compressive strength of mortar used accelerators for freezing resistance represented the result which is similar with result of analysis of compressive strength increase with using logistic curve formula, but in the case of plain and using water reducing accelerator, there is no relation between logistic curve formula, maturity and compressive strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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• pp.71-72
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• 2010

The study is compared temperature history and strength of concrete followed by covering method of insulation curing of cold weather concrete with double bubble sheet. The results were as follows. First of all, in temperature history of concrete, the internal temperature of concrete fell down to $0^{\circ}C$ before/after 60 hours, having nothing to do with covering method. The study could see that, when sheet was isolated, it fell down to low temperature quickly in early curing. When the study measured compressive strength of core specimen, there were no large differences among placing methods. However, compressive strength fell down in all ages when sheet was isolated.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.309-312
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• 2000

Nonuniform temperature distribution due to hydration heat induces thermal stress in mass concrete. At early ages, such thermal stress may induce thermal cracks which can affect on the durability ad safety of the structure. Steel fiber reinforced concrete may be useful when a large amount of energy has to be absorbed, when a high tensile strength and reduced cracking are desirable, of an improvement of thermal conductivity is desirable. In LG IPP Project, the upper part(50cm) of turbine foundation was replaced with steel fiber reinforced concrete to reduce the thermal crack induced by hydration heat. It was shown that the thermal crack control could be successfully achieved by steel fiber reinforced concrete.

• Computers and Concrete
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• v.6 no.4
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• pp.269-280
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• 2009

In this paper an experimental study of the influence of hot springs curing upon concrete properties was carried out. The primary variables of the investigation include water-to-binder ratio (W/B), pozzolanic material content and curing condition. Three types of hot springs, in the range $40-90^{\circ}C$, derived from different regions in Taiwan were adopted for laboratory testing of concrete curing. In addition, to compare with the laboratory results, compressive strength and durability of practical concrete were conducted in a tunnel construction site. The experimental results indicate that when concrete comprising pozzolanic materials was cured by a hot spring with high temperature, its compressive strength increased rapidly in the early ages due to high temperature and chloride ions. In the later ages, the trend of strength development decreased obviously and the strength was even lower than that of the standard cured one. The results of durability test show that concrete containing 30-40% Portland cement replacement by pozzolanic materials and with W/B lower than 0.5 was cured in a hot spring environment, then it had sufficient durability to prevent steel corrosion. Similar to the laboratory results, the cast-inplace concrete in a hot spring had a compressive strength growing rapidly at the earlier age and slowly at the later age. The results of electric resistance and permeability tests also show that concrete in a hot spring had higher durability than those cured in air. In addition, there was no neutralization reaction being observed after the 360-day neutralization test. This study demonstrates that the concrete with enough compressive strength and durability is suitable for the cast-in-place structure being used in hot spring areas.