• Structural Engineering and Mechanics
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• 제37권5호
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• pp.459-473
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• 2011

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.

• 콘크리트학회지
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• 제5권3호
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• pp.152-160
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• 1993

양생 초기에 있어서 콘크리트의 투수계수는 콘크리트의 건조수축에 영향을 미치는 요인으로서 콘크리트내의 물의 이동과 관련된 중요한 변수이다. 콘크리트의 특수성에 관한 연구는 주로 콘크리트의 건조수축이나, 동결융해에 대한 내구성 등과 연관되어 있다. 이들 대부분의 측정결과는 염소 이온등을 이용한 간접 측정방법이거나 충분히 양생된 안정한 콘크리트를 대상으로 하는 것이 대부분이므로 양생초기의 콘크리트의 투수계수에 관한 연구는 거의 없다고 할 수 있다. 본 연구에서는 싸이크로미터라는 수리에너지를 측정하는 쎈서를 이용하여 콘크리트의 투수계수의 측정을 시도하였다. 콘크리트의 투수계수와 확산계수를 측정하기 위한 세가지의 방법을 제시하였으며, 이를 적용하는 실험도 실시하였다. 또한 투수계수와 확산계수간의 변환을 위한 등온 흡수선을 개발, 적용하였다.

• Steel and Composite Structures
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• 제26권3호
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• pp.303-314
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• 2018

Drying shrinkage in concrete caused by drying and the associated decrease in moisture content is one of the most important factors influencing the long-term deflection of steel-concrete composite slabs. The presence of profiled steel decking at the bottom of the composite slab causes non-uniform drying from top and bottom of the slab resulting non-uniform drying shrinkage. In this paper, a hydro-mechanical analysis method is proposed to simulate the development of non-uniform shrinkage through the depth of the composite slab. It also demonstrates how this proposed analysis method can be used in conjunction with previously presented structural analysis model to calculate the effects of non-uniform shrinkage on the long-term deflection of the slab. The method uses concrete moisture diffusion model to simulate the non-uniform drying of composite slab. Then mechanical models are used to calculate resulting shrinkage strain from non-uniform drying and its effect on the long-term behaviour of the composite slabs. The performance of the proposed analysis method is validated against experimental data.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.109-112
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• 2004

It was found from the previous experimental studies that the long-term deformation of SRC columns was quite different from that of RC columns. A new approach method is needed to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the difference between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of RC columns due to the presence of a flange, which interferes with the moisture diffusion of concrete. This different relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns.

• 한국안전학회지
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• 제23권5호
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• pp.84-90
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• 2008

The occurrence of longitudinal cracking in concrete deck of box girder bridge is affected by many factors, but the most important factors are the shrinkage and thermal gradient of deck slabs. In this study, therefore, the tensile stresses at the bottom of deck were calculated from the experimental data(autogeneous shrinkage, drying shrinkage, and thermal gradient of deck slab). Also, the possibility of longitudinal cracks at bottom of deck was estimated. For this purpose, full-scale box girder segments have been fabricated and tested. The thermal gradients and shrinkage strains of deck slabs were measured after placement of concrete. Also, analytic program was conducted for the evaluation of longitudinal cracking in bridge deck considering differential shrinkage induced from non-uniform moisture distributions in concrete.

• Journal of the Korean Wood Science and Technology
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• 제40권5호
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• pp.352-362
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• 2012

Mass transfer behavior in wood was estimated through its microscopic structure. The diffusion coefficients which were decided by theoretical equations are influenced by different anatomical properties of wood. From the experiment, the moisture flux was linear to the square root of time. The diffusion coefficients had a regular tendency during the time elapse. During the modeling, it is necessary to understand the limitation of parameters and consider the particular situation to be simulated. In hardwood, because the apertures were not considered, tangential mass transfer simulation was totally different from experiment. As a result, a hardwood model design should consider the apertures which are even on the fiber walls.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.635-640
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• 2001

In this study, a mathematical model is established for prediction of chloride penetration in unsaturated cracked early-age concrete. The model is combined with models for thermo-hygro dynamic coupling of cement hydration, moisture transport and micro-structure development. Chloride permeability and water permeability at cracked early-age concrete specimens are evaluated using a rapid chloride permeability test and a low-pressure water permeability test, respectively. Then, a homogenization technique is introduced into the model to determine equivalent diffusion coefficient and equivalent Permeation coefficient. Increased chloride transport due to cracks at the specimen could be predicted fairly well by characterizing the cracks using proposed model. Proposed model is verified by comparing diffusion analysis results with test results.

• 한국안전학회지
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• 제23권4호
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• pp.59-66
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• 2008

Recently, the deterioration of reinforced concrete structures, primarily due to corrosion of steel reinforcement, has become a major concern. Chloride-induced deterioration is the most important deterioration phenomenon in reinforced concrete structures in harsh environments. For the realistic prediction of chloride penetration into concrete, a mathematical model was developed in which the effects of diffusion, chloride binding and convection due to water movement can be taken into account. The aim of this research was to reach a better understanding on the physical mechanisms underlying the deterioration process of reinforced concrete associated with chloride-induced corrosion and to propose a reliable method for estimating these effects. Chloride concentrations coming from de-icing salts are significantly influenced by the exposure conditions such as salt usage, ambient temperature and repeated wet-dry cycles.

• 콘크리트학회지
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• 제10권5호
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• pp.189-195
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• 1998

콘크리트 구조물이 초기재령에서 외기에 노출될 때, 수부확산으로 인하여 수분의 이동이 일어나고, 또한 자체건조도 발생한다. 이러한 콘크리트 내부의 수분확산과 자체건조에 의하여 콘크리트의 위치에 따라 상대습도가 변호한다. 특히 고강도 콘크리트의 경우에 단위 시멘트량을 많이 사용하기 때문에 , 초기재령에서 콘크리트 단면의 수분분포는 자체건조에 의하여 큰 영향을 받는다. 본 연구에서는 초기재령에서 외기에 노출된 콘크리트 내부의 여러 위치에서 상대습도를 측정하였다. 또한 자체건조로 인한 콘크리트의 상대습도 변화를 측정하여 초기재령에서 수분확산과 자체건조가 콘크리트 내부의 각 위치에서 상대습도에 미치는 영향을 검코하였다. 그리고 수분확산 이론에 의하여 해석결과와 실험결과를 비교하여 \ulcorner재령에서 수분확산 이론의 타당성을 검증하였다. 저강도 콘크리트 단면의 수분분포는 주로 수분확산에 의하여 영향을 받았으며, 자체건조의 영향은 매우 작게 나타났다. 그렇지만 고강도 콘크리트는 수분확산 뿐만 아니라 자체건조에 의하여도 영향을 받았다. 또한 수분확산 이론에 의한 해석결과는 실험결과를 잘 예측하였다.

• 한국수소및신에너지학회논문집
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• 제16권1호
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• pp.82-91
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• 2005

Polymer membrane needs to maintain appropriate moisture. Insufficient moisture causes low conduction of hydrogen ion because of increased contact resistance between electrode and membrane by shrinking membrane, and abundant moisture decreases fuel cell performance as difficulty of diffusion reacting gas. Therefore, water controlling system is very consequential for the polymer membrane fuel cell. If hollow fiber membrane humidification is used between fuel and air lines, it is possible to supply heat to fuel and air by using thermal exchanger. It can supply appropriate humidity depending on operating temperature, and can recover heat from exhaust gas which contains water vapor and air. Because of simple structure of humidification system, this system can be easily applied in the PEMFC and cut down cost.