• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.655-660
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• 2002

Major deterioration in concrete structures are salt attack and carbonation. Especially severe problems due to carbonation occur in tile concrete structures of city, tunnel, underground structures. Cracks in concrete during service life including early age due to hydration heat and/or shrinkage accelerate the diffusion of concrete so that the deterioration is also accelerated. In this study, carbonation depths of both non-cracked concrete and cracked concrete are evaluated and weight change test and TGA are carried out. Through the tests, a relation between water-cement ratio and carbonation depth is derived and also carbonation increase rate is derived in the function of crack width.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 봄 학술발표회 논문집
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• pp.209-214
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• 1994

The heat of hydration of cement causes the intemal temperature rise at early age, particulay in massive concrete structures. As the results of the temperature rise and restraint condition, the thermal stress amy induce cracks in concrete. The prediction of the thermal stress is very important in design and consturction slages in order to control the cracks in mass concrete. In this study, the temperature rise of high strength concrete due to the heat of hydration is investigated. Test variables are type and content of binder. As the results, the temperature rise is imcreased with increasing cement content. However, the increament is decreased in higher cement comtnet range. Fly ash is effictive in the reduction of hydration heat.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.29-34
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• 2002

The heat of hydration of cement causes the internal temperature rise at early age, paticular in massive concrete structures. As the results of the temperature rise and restraint condition, the thermal stress may induce cracks in concrete. The prediction of the thermal stress is important in design and construction stages in order to control the cracks in mass concrete. It is poor economy to analysis for prediction of the thermal stress on each design or construction. In this study, the hydration heat and thermal stress analysis is performed by ABAQUS program, as a results of thermal analysis, the formula of size-placing depth relationship is proposed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 봄 학술발표회 논문집
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• pp.107-113
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• 1992

The heat of hydration of cement the causes the internal temperature rise at early age, particulary in massive concrete structures such as a mat-slab of nuclear reactor building or a dam or a large footing. As the result of the temperature rise and restraint of foundation, the thermal stress enough to induce concrete cracks can occur. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, more creep and shrinkage take place at elevated temperatures in young concrete, Thus the effect of creep and shrinkage must be considered for checking the safety and servicebility(crack, durability and leakage).

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.273-276
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• 2004

Recently. cold weather constructions were popularized because of the importance of construction term. The special method about mix design and curing of concrete was being planned to conduct cold weather constructions, but these method were not considered in a low temperature time. A Strength revelation of concrete is delayed in a curing condition of low temperature. If a construction was loaded in this case, cracks or remaining deformations are generated in a construction. So, a strength revelation characteristic in early age was investigated to secure early strength of concrete in curing condition of a low temperature. In this study, the method about concrete mix design was presented to secure construction safety in a low temperature time.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
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• pp.67-72
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• 1992

The heat of hydration of cement causes the internal temperature rise at early age, particulary in massive concrete structures such as a footing of nuclear reactor building or a dam. As the result of the temperature rise and restraint of foundation, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, in case of young concrete, creep effect by the temperature load is larger than That of old concrete. Thus the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This study is composed of two items. The first, it is to develop a finite element program which is capable of simulating the temperature history in mass concrete. The second, when the thermal stress of mass concrete structures considering creep is calculated by using the modified elastic modulus due to the inner temperature change. It is shown that the analytical results of this study is in comparably good agreement with JCI's analytical results.

• 한국건축시공학회지
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• 제10권4호
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• pp.113-122
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• 2010

In this study, 150MPa ultra-high-strength concrete was manufactured, and its performance was reviewed. As technically meaningful autogenous shrinkage reportedly occurs at a W/B ratio of 40% or less, although it occurs in all concrete regardless of the W/B ratio, the effects of the use of expansive admixture and shrinkage reducer, or of the friction and restraint of forms that may result in the effective reduction of autogenous shrinkage, were reviewed. As a result, considering the flow and strength characteristics, it was found that the slump flow time was shorter with expansive admixture, and shortest with shrinkage reducer. All specimens with $30kg/m^3$ expansive admixture showed high strength at early material age. Their strength decreased due to the expansion cracks when there was excessive use of expansive admixture, and the use of shrinkage reducer did not influence the change in the strength according to the material age. The expansive admixture had a shrinkage reduction effect of 80%, while the shrinkage reducer had a shrinkage reduction effect of 30%, indicating that the expansive admixture had a stronger effect. It seems that mixing the two will have a synergistic effect. The shrinkage reduction rate was highest when the W/B ratio was 20%. The form suppressed the expansion and shrinkage at the early period, and the demolding time did not significantly influence the shrinkage. The results of the study showed that the excessive addition of expansive admixture leads to expansion cracks, and the expansive admixture and shrinkage reducer have the highest shrinkage reduction effect when they are mixed.

• 한국도로학회논문집
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• 제6권4호
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• pp.75-89
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• 2004

콘크리트 포장의 장기 공용성은 시공조건과 환경조건에 크게 좌우된다. 즉 초기에 무작위 균열이나 균열틈이 많이 벌어진 경우 포장수명을 저감시키는 원인이 된다. 시공당시의 온도와 습도, 시멘트와 골재의 종류, 양생조건들은 콘크리트포장의 품질에 영향을 미치는 중요한 요소이다. 그 중에서도 대기온도와 수화열의 증가에 의한 높은 온도차이는 심각한 초기균열을 발생시키는 원인이 되는 것으로 알려져 있다. 본 연구에서는 차광막을 사용하여 콘크리트 슬래브의 온도를 제어하여 초기균열이 발생할 가능성을 낯추고 슬래브질이의 온도차이에 의해 발생되는 curling stress를 줄일 수 있었고, 강도에 있어서는 차광막 설치 구간이 일반시공구간보다 장기강도를 크게 할 수 있음을 확인하였다. 또한 콘크리트포장의 포설 후 72시간의 강도 및 응력을 예측하는 프로그램인 HIPERPAV를 사용하여 초기에 균열이 발생할 가능성을 비교해본 결과 차광막을 설치한 구간이 본 시험시공의 예에서 균열이 발생하지 않을 가능성(reliability)이 차광막을 설치하지 않은 구간(일반시공구간) 72.5%. 차광막설치 구간 95%로 나타나 차광막설치 구간이 차광막을 설치하지 않은 구간보다 균열이 발생하지 않을 가능성을 크게 증가시킬 수 있을 것으로 분석되었다.

• 대한토목학회논문집
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• 제14권4호
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• pp.771-781
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• 1994

매스콘크리트에서 시멘트의 수화반응에 의해 발생되는 열은 약재령 콘크리트(young concrete)에서 내부온도의 증가와 체적변화를 초래하므로 외적인 구속이 존재하면 구조물에는 인장응력이 발생하고 이는 구조물에 균열을 일으킬 수 있다. 따라서 매스콘크리트의 설계와 시공단계에서 균열을 제어하기 위해서는 온도응력을 정확하게 예측하는 것이 매우 중요하다. 또한 약재령 콘크리트에서는 크리이프 효과가 노재령 콘크리트(old concrete)의 경우에 비하여 현저하게 크므로 이를 반드시 고려하여야 할 것이다. 이 논문은 매스콘크리트에서의 온도에 관한 시간이력을 구하고 크리이프와 각 요소의 온도를 고려한 탄성계수를 적용하여 온도응력을 구하는 유한요소 프로그램을 개발하는데 그 목적이 있다. 개발된 프로그램의 해석결과를 문헌의 자료들과 비교해 볼 때 온도균열의 제어에 가장 중요한 내부에서의 온도이력과 응력이 실험결과와 잘 부합되고 있다. 따라서, 이 논문의 해석방법은 매스콘크리트 구조물의 설계와 시공단계에서 균열의 제어를 위해 유용하게 사용될 수 있을 것이다.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.159-167
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• 2003

Cracks in reinforced concrete structures reduce overall durability by allowing the penetration of water and aggressive agents, thereby accelerating the deterioration of the reinforcing steel. Highway pavement and bridge decks are especially susceptible to this type of deterioration since these structures exhibit high rates of shrinkage and are frequently exposed to aggressive environmental conditions. The objectives of this investigation included the development of experimental procedures for assessing shrinkage cracking potential of recycled aggregate concrete, the evaluation of mix composition on shrinkage cracking potential, and the development of theoretical models to simulate early-age cracking behavior. Specifically, the influences of shrinkage-reducing admixture(SRA) and recycled aggregate concrete were investigated. The shrinkage-reducing admixture substantially reduces free shrinkage and restrains shrinkage cracking while providing similar mechanical properties. A fracture mechanics modeling approach was developed to predict the behavior of a variety of restrained concrete specimens. This modeling approach was used to successfully explain experimental results from a variety of mixture compositions. The model was used to demonstrate the influence of material and structural properties on the potential for cracking.