• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.143-148
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• 2002

Recently, to consider economical and constructive aspect, Usage of Admixture, like Blast-Furnace Slag and Fly-Ash, are increased. Blast-Furnace Slag, a by-product of steel industry, have many advantage, to reduce the heat of hydration, increase in ultimate strength and etc. But it also reduces early-age strength, it is prevented from using of Blast-Furnace Slag at cold-weather-concrete. In this study, for the purpose of increasing usage of Blast-Furnace Slag at cold-weather-concrete, it is investigated the strength properties of concrete subjected to time and period of frost damage for early age curing. According to this study, if early age curing is carried out before having frost damage, the strength of concrete, subjected to frost damage, is recovered. And that properties is not connected with the frost cause.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.287-292
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• 1999

Mass concreting in cold weather environment should be focused on the control of thermal crack caused by high hydration heat rather than curing method for protecting from frost damage at early age because the thermal stress have much influence on the quality of structure placed in cold weather. Therefore, in this paper, the control of thermal crack of mass concrete in cold weather environment are dealt with preparing the practice plan for mass concrete and placing the concrete according to the plactice plan. According to the results, we can obtain good quality mass concrete without thermal crack caused by the difference of temperature between inner part and outer part.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.10a
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• pp.125-130
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• 1990

Fly Ash in concrete is known to be effective in improving workability, the reduction of heat of hydration, increasing the long-term compressive strength, and improving durability. Recently, fly ash is consedered an essential material for the high-strength concrete. In this paper, investigations for the strength and workability characteristics was carried out when fly ash was used in the high-strength concrete. As the result, fly ash was effective in increasing the long-term compressive strength, but the short-term compressive strength was gradually decreased with increating fly ash contents. And also the use of superplasticzers was required for providing the proper workability when fly ash contents were increased. The optimum content of fly ash was about 10%.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.711-714
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• 2004

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. In order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the coefficient of air convection, which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, boiling and layer effects. Finally, the prediction model for equivalent coefficient of air convection was theoretically proposed. The coefficient of air convection in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with types of form. For determining the initial coefficient of air convection, boiling effects must be considered. The coefficient of air convection is affected by boundary layer with respect to the distance from the surface.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.643-648
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• 1997

P.C Bearing Plate method, corresponding to the existing steel plate build-up method, is developed by the very first in domestic and is applied to the foundation in the HYUNDAI building at Kang-Nam. P. C Bearing Plate produced in ourself P.C plant can stand against vertical load of 7,000ton obtaining allowable force of soil. It is possible to minmize cost expediting, do site assembling and omit unnecessary excavation work by plant prefabrication of foundation member. The purpose of this paper is to study the optimum mixing design of Ultra-high strength concrete ($\acute{f}_{C91}$= 950kg/$\textrm{cm}^2$), crack control through measuring the heat of hydration, mock up test for the optimum curing method. As mentioned above, developing the Ultra-high strength Precast Concrete Bearing Plate set up successfully in the site foundation work of the HYUNDAI Building at Kang-Nam.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1215-1220
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• 2000

Blast-Furnace Slag, a by-product of the iron or steel industry, has potential sa a cementitious material. The addition of a Blast-Furnace Slag generally reduces the heat of hydration and can confer significant improvements in resistance to sulfate attack and alkali-aggregate reaction, as well as increases in ultimate strength. But it also reduces early-age strength. In this study, for the purpose of improvement of early-age quality of Blast-Furnace Slag concrete, we choose blaine fineness of $6, 000~8, 000cm^2/g$ of Blast-Furnace Slag, and investigate the various properties of concrete. As a result, workability and early-age strength of Blast-Furnace Slag concrete were improved according to the increase of blaine fineness of Blast-Furnace Slag.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.120-123
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• 2003

In order to evaluate the applicability of steel slag aggregates for tetrapod concrete, the properties of concrete as structural material were investigated. The biochemical research of marine concrete using steel slag aggregates was also carried out. The tested concrete properties are slump, air content, compressive strength, splitting tensile strength, elastic modulus, carbonation, hydration heat, freezing and thawing, sulfate attack, drying shrinkage, etc. The biochemical experiments are carried to research the propagation and reproduction of seaweeds and survival of bottom dwelling species. According to the experimental results, the steel slag aggregate content did not have a significant effect on compressive strength, splitting tensile strength and elastic modulus. The durability of concrete was not influenced by the steel slag aggregate content. From the biochemical research, steel slag aggregate can be evaluated as the material that is ideally suited for promoting propagation and reproduction of seaweeds and survival of bottom dwelling species.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.539-545
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• 1997

Since the length of massive wall-structure is generally longer and larger than its thickness and a lift height of concrete of placement, cracks induced by hydration heat are governed by outer structural restriction rather than inner one. However, the degree of restriction control is expected to be affected by the sizes of wall thickness, length and a lift height. Thus, this analytical study aims at the development of relationship among those to minimize thermal cracks. In addition, the effect of types of cement on the thermal heats and stresses is evaluated for anti-sulphate and 2blended Portland cements concrete. It was found from analytical study that a lift height of concrete placement is the most important factor controlling thermal cracks, and the increase of lift heights is not always detrimental to structural safety.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.153-156
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• 2002

The purpose of this research was to evaluate on the properties of fresh and hardened high-performance concrete(HPC) incorporating high-reactivity metakaolin(HRM). Setting time, heat of hydration, compressive strength, resistance to chloride-ion penetration, and repeated freezing and thawing test were carried out in order to investigate the properties of fresh and hardened state concrete. The properties of the HRM concrete were also compared with those of the portland cement concrete and silica fume(SF) concrete. The laboratory test results indicate that HRM material can be used as a supplementary cementitious material to produce high-performance concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.297-302
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• 2000

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.