• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 춘계 학술논문 발표대회
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• pp.36-37
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• 2019

In domestic construction industry progress, construction and quality control of large structures are considered to be important as the superstructure and mass scale of structures. In the case of mass concrete, high hydration heat caused by cement hydration generates temperature stress by generating internal temperature difference with the concrete surface. These temperature stresses cause cracks to penetrate the concrete structure. A method of lowering the heat generation by incorporating Urea in order to reduce the concrete temperature crack has been proposed. In this study, the heat function coefficient for the FEM temperature crack analysis of the mass concrete containing the element was derived and the adiabatic temperature rise test was carried out according to the incorporation of the element. As a result of this experiment, the maximum temperature of 41 ± 1℃ was obtained irrespective of the amount of urea, and the maximum temperature decreased by 16.9℃ in concrete containing 40kg/㎥ of urea.

• 한국환경과학회지
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• 제19권1호
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• pp.105-114
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• 2010

The objective of the paper is to experimentally investigate the compressive strength of the concrete incorporating fly ash. Ordinary Portland cement(OPC). Water to binder ratio(W/B) ranging from 30% to 60% and curing temperature ranging from $-10^{\circ}{\sim}65^{\circ}C$ were also adopted for experimental parameters. Fly ash was replaced by 30% of cement contents. According to the results, strength development of concrete contained with fly ash is lower than that of plain concrete in low temperature at early age and maturity. In high curing temperature, the concrete with fly ash has higher strength development than that of low temperature regardless of the elapse of age and maturity. Fly ash can have much effect on the strength development of concrete at the condition of mass concrete, hot weather concreting and the concrete products for the steam curing.

• 한국도로학회논문집
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• 제7권3호
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• pp.79-91
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• 2005

포틀랜드 시멘트 콘크리트 도로 포장의 온도 패턴을 콘크리트 타설시부터 최근에 개발된 저렴하며 획기적인 센서를 이용하여 측정하였으며 그 결과를 분석하였다. 콘크리트 포장의 온도 측정은 여러 다른 지역에서 여러 다른 두께를 가진 콘크리트 포장에서 수행하였다. 콘크리트 포장의 온도 패턴은 깊이방향과 콘크리트 타설시간에 따른 종방향의 변화를 고려하여 분석하였으며, 포장 표면의 반사율, 그늘, 덮음막 등이 콘크리트 포장의 온도 패턴에 미치는 영향을 분석하였다. 본 연구 결과에서 콘크리트를 타설한 날의 콘크리트 포장의 최고 온도는 종방향을 따라 타설 시간이 다름으로 인해 생기는 차이가 두드러지는 것을 알 수 있었다. 콘크리트의 영점응력온도(zero-stress temperature)는 타설한 날의 최고 온도와 직접적인 연관이 있으므로 타설 시간에 따른 최고 온도의 차이는 콘크리트 포장의 거동 및 성능에 크게 영향을 미칠 수 있다. 또한 콘크리트 포장의 표면 상태 (표면 색상, 그늘 유무, 덮음막 유무 등)도 콘크리트 포장의 온도 패턴에 큰 영향을 미치는 인자인 것으로 분석되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.128-131
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• 2004

This paper is to investigate the mock up test results of mass concrete for transfer girder using setting time difference with super retarding agent(SRA) to reduce hydration heat. According to test results, the temperature history of plain concrete without placing lift had a steep rising curvature, and plain concrete had a big temperature difference between surface and middle section of mass concrete, which may result in occurrence of temperature crack. However, considering placing method B, because setting time of middle section concrete was retarded with an increase in SRA contents, higher hydration heat temperature was observed at surface section concrete compared with that at middle section concrete at early age, which can lower the possibility of hydration heat crack. In case of placing method C, although peak temperature of hydration heat was much lower, at early age, high crack occurrence possibility of the hydration heat attributable to the big temperature difference between middle section and bottom section of concrete was expected at bottom section concrete. Therefore, the structure above the ground like transfer girder is not applicable to consider the placing method C.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.26-27
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• 2014

Study on high temperature properties of concrete and internal force estimation of structural member subjected to high temperature mainly applied high temperature strength model based on experimental results with concrete under 40MPa. However, it is reported that degradation of internal force at high temperature and spalling of ultra high strength concrete are higher than that of normal strength concrete. Therefore, this study attempts to propose compressive strength degradation model which is suitable to ultra high strength concrete comparing to existing model by evaluating high temperature properties of ultra high strength concrete.

• Advances in concrete construction
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• 제6권6호
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• pp.645-658
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• 2018

Despite being one of the most abundantly used construction materials because of its exceptional properties, concrete is susceptible to deterioration and damage due to various factors particularly corrosion, improper loading, poor workmanship and design discrepancies, and as a result concrete structures require retrofitting and strengthening. In recent times, Fiber Reinforced Polymer (FRP) composites have substituted the conventional techniques of retrofitting and strengthening of damaged concrete. Most of the research studies related to concrete strengthening using FRP have been performed on undamaged test specimens. This contribution presents the results of an experimental study in which concrete specimens were damaged by mechanical loading and elevated temperature in laboratory prior to application of Carbon Fiber Reinforced Polymer (CFRP) sheets for strengthening. The test specimens prepared using concrete of target compressive strength of 28 MPa at 28 days were subjected to compressive and splitting tensile testing up to failure and the intact pieces of the failed specimens were collected for the purpose of repair. In order to induce damage as a result of elevated temperature, the concrete cylinders were subjected to $400^{\circ}C$ and $800^{\circ}C$ temperature for two hours duration. Concrete cylinders damaged under compressive and split tensile loads were re-cast using concrete and rich cement-sand mortar, respectively and then strengthened using CFRP wrap. Concrete cylinders damaged due to elevated temperature were also strengthened using CFRP wrap. Re-cast and strengthened concrete cylinders were tested in compression and splitting tension. The obtained results revealed that re-casting of specimens damaged by mechanical loadings using concrete & mortar, and then strengthened by single layer CFRP wrap exhibited strength even higher than their original values. In case of specimens damaged by elevated temperature, the results indicated that concrete strength is significantly dropped and strengthening using CFRP wrap made it possible to not only recover the lost strength but also resulted in concrete strength greater than the original value.

• 콘크리트학회지
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• 제7권1호
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• pp.97-108
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• 1995

• 대한기계학회논문집B
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• 제22권5호
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• pp.596-606
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• 1998

Thermophysical properties and the compressive strength of concrete used in nuclear power plants in Korea were measured. The chemical composition of the concrete was also analyzed. The measured thermophysical properties include the density, the thermal conductivity, the thermal diffusivity and the specific heat for a wide temperature range of 20.deg. C to 1100.deg. C. The chemical composition of Korean concrete is similar to that of US basaltic concrete and the thermophysical properties are strongly temperature dependent. The density, the conductivity and the diffusivity decrease with an increase in temperature, and particularly the conductivity and the diffusivity are a 50-perdent decrease at 900.deg. C as compared with these values at room temperature. The specific heat increases until 500.deg. C, decreases from 700.deg. C to 900 .deg. C, and then increases again when temperature is above 900.deg. C. The measurement beyond 1100.deg. C is not acceptably accurate because the concrete decomposes to a liquid phase from a solid phase at that temperature. The results of this study can be applied, for example, to an analysis of the molten core-concrete interaction (MCCI) phenomenon of concrete structures at high temperature will also require those property data, especially for high temperature ranges.

• 한국컴퓨터산업학회논문지
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• 제9권3호
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• pp.99-104
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• 2008

매스콘크리트에서 수화열에 의한 응력은 외기온도와 콘크리트의 타설온도에 따라 변하므로 이들의 영향을 고려한 해석이 필요하다. 본 연구에서는 교각의 코핑부를 대상으로 해석을 수행하여 분석하였다. 최대 인장응력은 타설 후 2.75일을 전후하여 표면 모서리부에서 발생하며 균열지수는 계속 증가하여 균열 발생 가능성은 거의 없는 것으로 나타났다. 그리고 계절에 관계없이 콘크리트의 타설온도를 낮추면 수화열에 의한 균열 발생 가능성을 줄일 수 있는 것으로 나타났다. 따라서 콘크리트를 타설하기 전에 타설온도를 낮추기 위한 여러 가지 방안을 강구하면 수화열에 의한 균열을 최소화할 수 있다.

• 한국도로학회논문집
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• 제18권2호
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• pp.19-27
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• 2016

PURPOSES: The behavior of a concrete pavement in a tunnel was investigated, based on temperature data obtained from the field and FEM analysis. METHODS: The concrete pavement in a tunnel was evaluated via two methods. First, temperature data was collected in air and inside the concrete pavement both outside and inside the tunnel. Second, FEM analysis was used to evaluate the stress condition associated with the slab thickness, joint spacing, dowel, and rock foundation, based on temperature data from the field. RESULTS : Temperature monitoring revealed that the temperature change in the tunnel was lower and more stable than that outside the tunnel. Furthermore, the temperature difference between the top and bottom of the slab was lower inside the tunnel than outside. FEM analysis showed that, in many cases, the stress in the concrete pavement in the tunnel was lower than that outside the tunnel. CONCLUSIONS : Temperature monitoring and the behavior of the concrete pavement in the tunnel revealed that, from an environmental point of view, the condition in the tunnel is advantageous to that outside the tunnel. The behavior in the tunnel was significantly less extreme, and therefore the concrete pavement in the tunnel could be designed more economically, than that outside the tunnel.