• 한국구조물진단유지관리공학회 논문집
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• 제3권1호
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• pp.163-169
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• 1999

The object of this study is to compare properties of massive fly-ash concrete with plain concrete. Two concrete mixtures comprising two batch each $1.0m^3$ in volume, were made from ready mixed concrete batch plant. The water-to-cementitious materials ratio was kept constant at 51.4%. Therefore, massive concrete specimen($W800{\times}D800{\times}H800mm$) was cast from ready mixed concrete to analyze history of temperature and core strength properties. Bleeding, time of slump loss and time of setting of the fresh concrete were measured. In order to estimate the properties of massive fly-ash concrete in hardened concrete, non-destructive tests such as rebound hardness, ultrasonic pulse velocity and maturity were performed and analyzed.

• 한국산업융합학회 논문집
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• 제7권4호
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• pp.331-340
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• 2004

This paper presents a feasibility study of a fresh air load reduction system by using an underground double floor space. The fresh air is introduced into the double slab space and passes through the opening bored into the footing beam. The air is cooled by the heat exchange with the inside surface of the double slab space in summer, and heated in winter. This system not only reduces sensible heat load of the fresh air by heat exchange with earth but also reduces latent heat load of the fresh air by ad/de-sorption of underground double slab concrete. In this paper, we used a model for evaluation of fresh air latent heat load reduction by hygroscopic of air to earth exchange system taking into account coupled heat and moisture transfer of underground double floor space. In conclusion it shows the validity of the proposed method for a design tool and the quantitative effect of the system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.507-512
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• 2002

In road pavements, it is known that cement concrete pavement has superior durability. But in repairing pavement, cement concrete pavement is not usually applied because of the length of time while the road is interrupted when using Ordinary and Rapid-hardening Portland Cement. And Super High Early Strength Cement and Ultra Super High Early Strength Cement are not favorable for ready mixed concrete because of rapid setting time, high slump loss and other restrictions. We developed special cement developing 1 day strength of over 30.0N/$mm^2$ to open the road within 1 day and workable time is maintained over 1 hour so that it can be used as ready mixed concrete. We performed experimental overlay construction with concrete and evaluated the properties of the fresh and hardened concrete. The flexural strength was over 5.0N/$mm^2$ and the compressive strength was over 30N/$mm^2$ at 1 day. So it is thought that the road can be open to traffic within 1 day after placement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 가을 학술발표회 논문집
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• pp.100-105
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• 1992

While there are many researches in high-strength concrete recently, average strength required is the level of 400kg/$\textrm{cm}^2$ 28days compressive strength yet. For the effective using of high strength concrete, high strength concrete of 600 to 800kg/$\textrm{cm}^2$ 28days compressive strength must be accepted, But in this high strength concrete, due to much cement content, there are the problems of high hydration heat, high viscosity and economical efficiency. To solve these problems, it is suggested the method that replacement some of cement content as flyash up-to-dately. Therefore, the aim of this study is to develop high strength concrete of 800kg/$\textrm{cm}^2$ 28days compressive strength containing fly ash. This paper is the part I that analyze the testing results of fresh concrete in various aspects.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.291-296
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• 1998

In the present study, the high strength concrete which is adequate for the long span PC beam above 40 meters has been developed. The optimum cement for high strength concerete was selected through laboratory tests and in-situ mock-up applications. The optical concrete mix design was performed, and the properties of fresh concrete and hardened concrete have been investigated. These results of laboratory study are analized and compared to domestic and foregn design codes and specifications. Finally, the developed high strength concrete was applied to half-scale PSC beams and showed good applicability in field conditions. It is conclude that hte developed high strength concrete can be applied to civil and architectural structures in the field applications.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.245-248
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• 1999

In our standard specification, the specific provision of steel fiber pavement concrete didn't describe yet. The purpose of this study presents criteria of recycled aggregate steel fiber pavement concrete including standard crushed stone steel fiber pavement concrete. This study examined a lot of factors which influence consistency of SFRC(Steel Fibre Reinforced Concrete) including crush stone and recycled aggregate. According to this examination, this study decided optimum S/α and W which are essential to pavement concrete mix proportion. Come to the conclusion, this study is expected to effect economically in recycling of resources and bring to affirmative result in aspect of environment.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.333-336
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• 1999

The crack of concrete induced by the heat of hydration is a serious problem, particularly in concrete structures such as mat-slab of nuclear reactor buildings, dams or large footings, foundations of high rise buildings, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, pre-cooling which lowers the initial temperature of fresh concrete with ice flake, pipe cooling which cools the temperature of concrete with flowing water, design change which considers steel bar reinforcement, operation control and so on. The Aim of this paper is to verify the effect of low heat blended cement in reducing thermal stress in slab type's mass concrete such as container harbor structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표회 논문집(I)
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• pp.66-71
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• 1998

Recently, it has been increased to construct massive concrete structures, like under-ground structure, offshore structure etc., ie. concrete construction have become larger and higher and are demanding lower heat concrete to prevent thermal cracking. It has been progressed to replace cements with fly-ash and slag to lower heat of hydration, but it is hard to control quality of the mineral admixtures in stage of adjusting of real construction. Application of low heat portland(Belite Rich) cement for the mass concrete is the best solution to satisfied those requirements. Here are explained the basic properties of fresh concrete as well as hardened concrete of using low heat portland cement(LHPC). Also, we compare the results of adiabatic temperature rise test using LHPC and OPC.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.1219-1224
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• 2001

In this study, concrete what plenty of fly ash used as binder is left in three condition humid condition($35^{\circ}C$), normal condition($20^{\circ}C$) and cold condition($5^{\circ}C$). Fly ash concrete is tested in fresh properties and early strength. The result of tests could give the decisive factor of form side's stripping time. The purpose of this study is presenting the stripping time data to help the construction work. The result of this study is below. 1. The plain concrete specimen in humid condition developed high strength before 5 days, then strength development is declined. 10 day strength of plain specimen is smaller than the normal condition specimen's. 2. The strength of the concrete which plenty of fly ash used is more developed than the concrete in normal condition. It says that fly ash concrete is useful in the humid condition. 3. As fly ash substitution rate is downsizing and outdoor temperature degree is low, form stripping times is getting shorter.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.669-674
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• 2002

This paper describes the properties analysis of concrete using bleeding reduction agent. According to the results, the fluidity and the air content of fresh concrete with increase of bleeding reduction agent show little difference in compare with plain concrete which does not use bleeding reduction agent. The efficiency of bleeding reduction agent is confirmed because in variation of W/C and slump, the increase of bleeding reduction agent dosage reduces bleeding remarkably. And the compressive strength of hardened concrete does not show any differences with increase the dosage of bleeding reduction agent. Bleeding reduction agent does not have bad effect on the quality of concrete such as fluidity, air content and the strength of hardened concrete and so on, the dosage of it can reduce bleeding effectively.