• 한국지반신소재학회논문집
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• 제14권4호
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• pp.105-115
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• 2015

본 연구에서는 매크로섬유를 PP섬유로 대체하여 유기계 섬유들인 PVA섬유 6mm와 PP섬유 50mm로 하이브리드 보강된 콘크리트의 역학적 특성을 파악하기 위해 섬유의 체적비를 주요변수로 하이브리드 섬유 보강 콘크리트(HFRC) 4배합과 섬유가 없는 Plain콘크리트 1배합을 실험하여 비교하였다. 섬유의 체적비를 1%미만으로 제한하였다. 연구결과 유기계 섬유의 하이브리드 보강은 콘크리트의 강성 및 연성거동을 강섬유만큼 극대화시키지는 못하지만, Plain콘크리트와 비교시 매우 진전된 연성거동을 보이며 휨 인성지수와 등가휨강도 사이의 의미 있는 관계를 확인하였다. 그리고 유기계 섬유로 하이브리드 보강한 콘크리트에서도 섬유의 체적비가 증가할수록 연성이 증가하였고 섬유의 하이브리드를 위해 사용한 마이크로섬유인 PVA섬유보다 매크로섬유인 PP섬유가 콘크리트의 휨 거동에 미치는 영향이 크며, 염분침투시험에서도 섬유의 혼입이 염분침투를 억제하는 효과가 있는 것으로 확인되었다.

• 한국건축시공학회지
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• 제10권2호
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• pp.59-66
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• 2010

본 연구에서는 흡착 및 내열, 내화성이 우수한 카본블랙을 이용하여, 콘크리트의 제반성능을 파악하여, 콘크리트용 혼화재료로써 활용가능성 여부를 판단하고자 함이 본 연구의 목적이다. 실험결과 굳지 않은 콘크리트에서는 흡수율 및 미립분의 카본블랙의 충전효과로 인하여 슬럼프증가 및 공기량 감소를 나타내었으며, 블리딩, 관입저항에 의한 응결시간은 양호한 결과로 나타났다. 또한 경화콘크리트의 강도 특성에는 Plain보다 높은 강도를 나타내었으며, 포졸란 반응에 의해 장기강도로 갈수록 강도발현이 높게 나타났다. 또한 약 $850^{\circ}C$내외의 가열 후의 압축강도에서 치환율이 증가할수록 내화, 내열성이 높게 나타났으며, 건조수축 역시 양호하게 나타났고, CO, $CO_2$, 포름알데히드의 환경성 평가도 Plain보다 양호한 결과로 나타났다. 이상 결과를 종합하면, 고강도의 배합설계를 고려한 적절한 AE감수제를 사용할 경우 카본블랙이 콘크리트용 혼화재로써 사용이 가능할 것으로 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.515-520
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• 2001

Mass concrete is placed considering placing lifts in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.707-710
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• 2004

This paper reported the results of mock-up test on mass concrete for transfer girder using setting time difference of super retarding agent(SRA). According to test results, two mock-up structures were made. Plain concrete without placing layer reached maximum temperature after 24hours since placement and caused surface hydration cracks at top section. However, concrete with placing layer reached maximum temperature after 72hours and surface temperature was higher than center temperature, which did not cause surface crack. After form removing, no crack was observed at side surface of plain concrete, while concrete using SRA at mid section had surface scaling and settling crack. According to coring results, concrete with placing layer had a penetration crack from top section to bottom section. Therefore, the setting time difference method to reduce hydration heat will have difficulty in applying the mass concrete for transfer girder.

• 한국건축시공학회지
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• 제4권2호
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• pp.129-136
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• 2004

High fluidity concrete(HFC) requires high dosage of superplasticizer to acquire sufficient fluidity, and high contents of fine powder and viscosity enhancing admixtures to resist segregation. The use of high amount of admixtures to make HFC at batcher plant in ready mixed concrete company is one of the reasons to raise the manufacturing cost of HFC. For this reason, new type of manufacturing method of HFC are described using both flowing concrete method and segregation reducing superplasticizer(SRS) in order to gain economical profit and offer the convenience for quality control.. As dosage of melamine based superplasticizer increases, it shows that fluidity and bleeding increase, while air contents and ratio of segregation resistance decrease. It also shows that addition of viscosity agent into superplasticizer reduce bleeding and improve segregation resistance of concrete. Dosage of AE agent into superplasticizer containing viscosity agent recovers loss of air contents during flowing procedure. Combination of proper contents of superplasticizer, viscosity agent and AE agent make possible to develope segregation reducing type superplasticizer. Compressive strength of high fluidity concrete applying flowing method with it is higher than that of base concrete. No differences of compressive strength between compacting methods are found. For the estimation of construction cost of high fluidity concreting using segregation reducing type superplasicizer, under same strength levels, although material cost of high fluidity concrete is somewhat higher than that of plain concrete due to segregation reducing type superplasticizer cost, labor cost and equipment cost of high fluidity concrete is cheaper than that of plain concrete. However, based on the strength differences, high fluidity concrete shows lower material cost, labor cost and equipment cost than that of plain concrete due to decreasing in size of member and re-bar caused by high strength development of concrete.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.469-474
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• 2001

Mass concrete is placed considering placing lifts in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2002년도 학술논문발표회
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• pp.41-45
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• 2002

Placing lift is applied to place mass concrete in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

• 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.663-668
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• 2002

In this paper, insulating effects and strength development of concrete placed at mock up model structure are discussed using anti freezing agent and insulating forms. According to test results, concrete containing 8% of anti freezing agent shows lower freezing temperature, earlier setting time and higher strength development than plain concrete. As for the temperature history of mock up structures, when plain concrete is placed at euro form, the temperature drops to -4${\circ}$ before early 24 hours, and when concrete containing anti freeze agent at euro form, it to -3${\circ}$ before early 24 hours. Nevertheless, when concrete containing anti freeze agent is placed at insulating form, it does not go below zero, and the concrete containing anti freeze agent enhances higher strength development.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 춘계 학술논문 발표대회
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• pp.90-91
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• 2014

In this study, the effect of very fine sand on drying shrinkage cracking of concrete was experimentally evaluated. As a result of the study, the time-to-cracking of concrete used very fine sand was shorter than plain concrete. Also, the stress rate of concrete used very fine sand was higher than plain concrete. It was due to the increase of water content when very fine sand was used in concrete. In conclusion, the use of very fine sand can lead the increase of water content to meet the target slump and higher potential of cracking of concrete.