• Computers and Concrete
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• 제7권1호
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• pp.63-81
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• 2010

We present the shape determination method of 3-D reinforcement corrosion based on observed temperature on concrete surface. The non-destructive testing for reinforcement corrosion in concrete using a heat image on concrete surface have been proposed by Oshita. The position of the reinforcement of corrosion or the cavity can be found using that method. However, the size of those defects can not be precisely measured based on the heat image. We therefore proposed the numerical determination system of the shape for the reinforcement corrosion using the observed temperature on the concrete surface. The adjoint variable method is introduced to formulate the shape determination problem, and the finite element method is employed to simulate the heat transfer problem. Some numerical experiments and the examination for the number of the observation points are shown in this paper.

• 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.

• 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.

• 설비공학논문집
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• 제11권5호
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• pp.588-597
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• 1999

Sokkuram grotto, a UNESCO cultural heritage in Kyongju Korea, was originally covered with crushed rocks over its dome with ventilating holes. The grotto was perfectly preserved for more than 12 centuries until the upper structure was replaced with a concrete dome in the early 20th century to protect from total collapse. Since then, heavy dew formed on the granite surface to seriously damage the sculptures until it was further remodeled with air-conditioning facilities in the 60s. It is considered that the original upper porous structure had a dehumidifying capability. This research is made to unveil the dehumidifying mechanism of the rock layer during the rainy season in that area. A rock layer and a concrete layer are tested in a temperature/humidity-controlled room. No dew formation is observed for the two specimen for continued sunny days or continued rainy days. However, heavy dew formed on the concrete surface for a sunny day after long rainy days. It is thought that the sun evaporates water on the ground and dew is formed at the surface as the highly humid air touches the yet cold concrete. On the contrary, no dew formation is observed for the rock layer at any time. Even in the above worst situation, air flows downward through the cool rock layer and moisture is removed before reaching inside. Temperature measurement, flow visualization, observation of dew formation and measurement of air velocity are made to verify the mechanisms.

• Coupled systems mechanics
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• 제9권2호
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• pp.163-182
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• 2020

Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by α-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in general-purpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1988-1993
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• 2023

This experimental study investigated the effect of silica fume mixed in concrete blocks on laser-induced explosion behavior. We used a 5.3 kW fiber laser as a thermal source to induce explosive spalling on a concrete surface blended with and without silica fume. An analytical approach based on the difference in the removal rate and thermal behavior was used to determine the effect of silica fume on laser-induced explosive spalling. A scanner was employed to calculate the laser-scabbled volume of the concrete surface to derive the removal rate. The removal rate of the concrete mixed with silica fume was higher than that of without silica fume. Thermal images acquired during scabbling were used to qualitatively analyze the thermal response of laser-induced explosive spalling on the concrete surface. At the early stage of laser heating, an uneven spatial distribution of surface temperature appeared on the concrete blended with silica fume because of frequent explosive spalling within a small area. By contrast, the spalling frequency was relatively lower in laser-heated concrete without silica fume. Furthermore, we observed that a larger area was removed via a single explosive spalling event owing to its high porosity.

• 원예과학기술지
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• 제31권4호
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• pp.503-511
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• 2013

본 연구는 돌나물과 한국잔디를 식재한 경량 모듈형 옥상녹화시스템의 온도저감과 열수지를 평가하였다. 식물생육은 초고와 피복율을 측정하였으며, 2012년 8월 2일부터 3일까지 48시간 동안 콘크리트와 옥상녹화 표면, 토양 속, 모듈 하부의 온도와 순복사, 증발산량을 측정하였다. 기온이 $34.6^{\circ}C$로 가장 높았던 8월 3일 15:00시의 표면온도는 콘크리트가 $57.5^{\circ}C$로 가장 높았으며, 그 다음으로 돌나물 $40.1^{\circ}C$, 한국잔디 $38.3^{\circ}C$의 순으로 옥상녹화 조성 시 큰 폭으로 온도가 저감되는 것으로 나타났다. 토양 속과 모듈 하부도 옥상녹화에 의한 온도저감 효과가 나타났으며, 한국잔디가 돌나물보다 온도저감 효과가 큰 것으로 나타났다. 콘크리트 표면과 비교하여 옥상녹화 최고 온도는 약 2시간 정도 지연되는 것으로 나타났다. 표면의 온도저감에는 식물종, 기온, 토양수분이 영향을 미치고, 모듈 하부의 온도저감에는 식물종, 기온, 토양수분, 표면온도가 유의하게 영향을 미친 것으로 나타났다. 열수지 분석결과, 현열은 콘크리트 표면이 가장 높았으며, 옥상녹화 시 감소하는 경향을 보였으며 잠열은 한국잔디가 돌나물보다 높았다. 따라서 온열환경 개선을 위해서는 한국잔디가 돌나물보다 옥상녹화 적용에 더 효과적임을 알 수 있었다.

• 환경영향평가
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• 제19권4호
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• pp.397-407
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• 2010

The increase of the solar reradiation from urban areas relative to suburban due to urbanization heats up the air temperature in urban areas and this is called the urban heat island (UHI) effect. This UHI effect has a positive relationship with the degree of urbanization. Through the studies on UHI using the satellite imagery, the effect of the surface heat radiation was observed by verifying the relationship between the air temperature and the land cover types (surface materials such as urban, vegetation, etc.). In this study, however, the surface temperature distribution was studied in terms of land use types for Seoul. Using land use types, the surface temperature in urban areas such as residential, industrial, and commercial areas in Yeongdeungpo, highly packed with industrial and residential buildings, was maximum $6^{\circ}C$ higher than in the bare ground, which indicated that the surface temperature reflected the pattern of the human-consumed energy on the areas and showed that one of the important causes influencing the air temperature except the surface heat reradiation by the sun is the anthropogenic heat. Also, the effect due to the restoration of the Chunggae stream on UHI was investigated. The average surface temperature for the Chunggae stream was reduced about $0.4^{\circ}C$ after restoration. Considering that each satellite image pixel includes mixture of several materials such as concrete and asphalt, the average surface temperature might be much lower locally reducing UHI near the stream.

• 콘크리트학회논문집
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• 제21권4호
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• pp.473-480
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• 2009

폴리프로필렌섬유와 강섬유를 혼입한 고강도콘크리트 기둥의 재하하중비에 따른 내화성능을 검증하기 위하 여 3기의 동일한 기둥시험체를 제작하여 각 시험체에 40%, 50%, 그리고 61%의 설계하중에 해당하는 고정압축하중을 재하한 후 ISO-834 표준내화곡선에 따라 180분간 내화시험을 실시하였다. 폭렬은 발생하지 않았으며, 표면부의 색은 분 홍색을 띤 회색으로 변했다. 시험체의 최대 연직방향 처짐은 1.5~2.2 mm로, 내화시험 중 화재로 인한 시험체의 강도손 실이 발생하지 않았으며, 설계하중의 61%이내에서 시험체의 내화성능은 영향을 받지 않았다. 깊이별 내부 콘크리트의 온도분포, 콘크리트 내부 수분 증발로 인한 온도상승이 변한 점 등 전반적으로 비재하 내화시험 결과와 매우 유사하였다. 180분 내화시험 후의 최종온도는 모서리철근이 491.4oC, 중앙철근이 329.0oC이며, 철근의 총 평균온도는 409.8oC이다. 전 반적인 온도분포의 경향은 비재하 내화시험과 매우 유사하였다. 모서리철근의 열에너지 유입량이 많기 때문에 중앙철 근과의 온도차(153.7oC)가 나타났으며, 가열 후 30~50분 사이에 온도상승추세가 변하였다. 이는 강섬유와 폴리프로필렌 섬유를 혼입한 콘크리트의 온도구배가 낮고, 철근으로의 수분이동과 내부 수분의 막힘현상, 그리고 수분의 기화열 때문이다.