• Title, Summary, Keyword: 수분확산

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Moisture Diffusion of Concrete an Early Ages Considering Self-deseccation (자체건조를 고려한 초기재령 콘크리트의 수분확산)

  • 김진근;이칠성
    • Magazine of the Korea Concrete Institute
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    • v.10 no.5
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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.

Prediction of Time-dependent Moisture Diffusion Coefficient in Early-age Concrete (초기재령 콘크리트의 시간 의존적인 수분확산계수 예측에 관한 연구)

  • Kang, Su-Tae;Kim, Jin-Keun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.9 no.4
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    • pp.141-148
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    • 2005
  • The nonlinear humidity distribution occurs due to the moisture diffusion when a concrete is exposed to an ambient air. This nonlinear humidity distribution induces shrinkage cracks on surfaces of the concrete. Because shrinkage cracks largely affect the durability and serviceability of concrete structures, the moisture diffusion in concrete must be investigated. The purpose of this paper is to propose a model of the moisture diffusion coefficient that governs moisture diffusion within concrete structures. To propose the model, numerical analysis was performed with several experiments. Because the moisture diffusion coefficient is changed with aging, especially at early ages, the proposed model includes aging effect by terms of the porosity as well as the humidity of concrete.

A Study on the Dry Shrinkage and Moisture Diffusion Coefficient of Polymer-Modified Mortars by the Moisture Diffusion (수분확산에 의한 폴리머 시멘트 모르터의 건조수축과 확산계수에 관한 연구)

  • 조영국;소양섭
    • Magazine of the Korea Concrete Institute
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    • v.8 no.5
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    • pp.145-154
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    • 1996
  • Polymer-modified mortars have an excellent water proofness and water retentivity. Therefore, the study on the moisture diffusion behavior- is very important. The purpose of' this study is to investigate the effects of relative humidity and moisture content in mortars on the moisture diffusion, and the relationship between the shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H and 80% R.H. The pore size distribution of the polymer-modified mortars was also measured. From the test results, the relative humidity and moisture content in mortars influenced on the moisture diffusion of polymer-modified mortars. The shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H. was bigger than that cured at $20{\circ}C$ 80% R.H.. and decreased with increasing polymer-cement ratio regardless of polymer type.

A Moisture Diffusivity Model of Hardening Concrete (경화하는 콘크리트의 수분확산도 모형)

  • Jeong, Jin-Hoon
    • International Journal of Highway Engineering
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    • v.7 no.1
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    • pp.31-38
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    • 2005
  • Concrete has higher vapor pressure than its surrounding ambient air immediately after placement. Moisture at concrete surface evaporates to the ambient air to adjust equilibrium of the vapor pressure between them. The moisture inside the concrete moves to the surface because the evaporation at the surface causes gradient of vapor pressure inside the concrete. Plastic cracking, degree of hydration, strength development, and others caused by velocity of the moisture movement significantly influences quality of concrete. In this paper, the moisture diffusivity of early-age concrete was back-calculated using governing equation of the moisture diffusion, and temperature and relative humidity of concrete measured in a laboratory. The moisture diffusivity of the concrete was modeled using the back-calculated moisture diffusivity. The relative humidity of the concrete calculated by finite element method (FEM) using the modeled moisture diffusivity as Input data coincided with the measured relative humidity well.

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A Study on te Water Diffusion of Polymer-Modified Mortars in Drying Process (건조과정에 있어서 폴리머 시멘트 모르터의 수분확산에 관한 연구)

  • 조영국;소양섭
    • Magazine of the Korea Concrete Institute
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    • v.8 no.5
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    • pp.135-143
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    • 1996
  • Diffusion of water in hardened cement concrete and mortar influences on the dry shrinkage. creep. modulus of' elasticity, etc. In general, water loss through drying process in polymer-modified concrete and mortar is small compared with that of unmodified concrete and mortar due to the films formed by polymer as cement modifieder. The purpose of this study is to investigate the diffusion process of water in the polymer-modified mortars. The polymer-modified mortars using three polymer dispersions and epoxy resin are prepared with various polymer-cement ratios, and water diffusion coefficient of polymer-modified mortars according to inside water content is calculated. From the test results, the water diffusion coefficient of polymer modified mortars i s smaller than that of unmodified mortars and decreases with increasing polymer cement ratio.

Mass Transfer Characteristics in the Osmotic Dehydration Process of Carrots (당근의 삼투건조시 물질이동 특성)

  • Youn, Kwang-Sup;Choi, Yong-Hee
    • Korean Journal of Food Science and Technology
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    • v.27 no.3
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    • pp.387-393
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    • 1995
  • Diffusion coefficients of moisture and solid, reaction rate constants of carotene destruction, and the fitness of drying models for moisture transfer were determined to study the characteristics of mass transfer during osmotic dehydration. Moisture loss and solid gain were increased with increase of temperature and concentration; temperature had higher osmotic effect than concentration. Diffusion coefficient showed similar trend with osmotic effect. Diffusion coefficients of solids were larger than those of moisture because the movement of solid was faster than that of moisture at the high temperature. Reaction rate constants were affected to the greater extent by concentration changes than by temperature changes. Arrhenius equation was applied to determine the effect of temperature on diffusion coefficients and reaction rate constants. Moisture diffusion required high activation energy in $20^{\circ}Brix$, while relatively low in $60^{\circ}Brix$. To predict the diffusion coefficients and reaction rate constants, a model was established by using the optimum functions of temperature and concentration. The model had high $R^2$ value when applied to diffusion coefficients, but low when applied to reaction rate constants. Quadratic drying model was most fittable to express moisture transfer during drying. In conclusion, moisture content of carrots could be predictable during the osmotic dehydration process, and thereby mass transfer characteristics could be determined by predicted moisture content and diffusion coefficient.

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Development of Testing and Analysis Model for Evaluation of Absorbed Water Diffusion into Concrete (콘크리트 흡수 수분확산계수 산정을 위한 실험 및 수치해석 모델 개발)

  • Park, Dong-Cheon;Ahn, Jae-Cheol
    • Journal of the Korea Institute of Building Construction
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    • v.11 no.4
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    • pp.371-378
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    • 2011
  • Concrete is affected by various deterioration factors, such as $CO_2$ and chloride ions from the sea, which cause carbonation and salt attack on concrete. These deterioration phenomena cause steel corrosion in RC structures. Although a great deal of research has been carried out in this area thus far, it is difficult to know the point at which corrosion will occur to a reinforced bar. As the diffusion of deterioration factors depends on the water content in concrete, it is imperative to assess the condition of absorbed water content. A mass measuring method was applied to calculate the absorbed water diffusion coefficient, as well as non-linear finite element method(FEM) analysis. As a result, it was found that W/C and unit water content in concrete mixture affect the diffusion coefficient decision.

Effects of Moisture Content in Concrete on Diffuse Ultrasound (확산초음파의 콘크리트 함수율에 대한 의존성)

  • Ahn, Eunjong;Shin, Myoungsu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.1
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    • pp.142-147
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    • 2020
  • This study investigates the effects of moisture content on diffuse ultrasound to be applied for the evaluation of micro-structural damage in concrete subjected to various environmental conditions. We monitored diffuse wave parameters for concrete samples in process of water saturation for 5 days. Dried samples were immersed in a water bath, and the change of moisture content in concrete were estimated by measuring the change of mass. For the diffuse wave analysis, a frequency range of 500 kHz, which represents a scattering regime of ultrasound in concrete, was selected. The test results reveal that the ultrasonic diffusivity slightly changed, and the ultrasonic dissipation significantly increased by approximately 120% in the process of water saturation. Therefore, the moisture content in concrete should be considered for the evaluation of micro-structural damage using diffuse wave techniques.

Development of System for Measuring Evaporation Rate through Porous Medium in Fuel Cells (연료전지 다공성막을 통한 수분증발량의 정량적 측정에 관한 실험적 연구)

  • Kim, Jong-Rok;Kim, Moo-Hwan;Son, Sang-Young
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.6
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    • pp.579-582
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    • 2012
  • Removing residual water in a fuel cell is a critical operational process for managing its performance and controlling its lifetime. Understanding the mechanism of water transport in fuel cells is essential for the design of the water removal process. In this study, an experimental method for measuring the water evaporation rate through a gas diffusion layer, which is a porous medium, under steady-state conditions was developed. Experimental bench tests were conducted to apply the developed method. Then, the effects of various parameters of the drying gas and the gas diffusion layer were experimentally measured. The water evaporation rate increased as the humidity of the drying gas decreased and the flow rate of the drying gas increased. In addition, a thinner gas diffusion layer yielded a higher water evaporation rate.

Estimations of Moisture Profiles During Wood Drying Using an Unsteady-State Diffusion Model (II) - Experimental Verification for Red Oak - (비정상(非正常) 상태(狀態)의 확산(擴散)모델을 이용한 수분(水分) 경사(傾斜)의 예측(豫測) (II) - 실험적(實驗的) 검증(檢證) -)

  • Park, Jung-Hwan;Smith, William B.
    • Journal of the Korean Wood Science and Technology
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    • v.24 no.3
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    • pp.37-44
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    • 1996
  • 포수상태(包水狀態)의 루부라참나무(Quercus rubra) 시험편을 3가지 등온조건(等溫條件)에서 건조한 결과를 비정상상태(非正常狀態)의 확산(擴散)모델로 추정한 결과와 비교하였다. 표면이 충분히 젖은 상태인 건조초기에는 불안정(不安定)한 확산현상(擴散現象)이 관찰되었으나, 함수율(含水率)별 건조속도의 변이를 Fick's의 확산법칙과 비교할 때 유사한 형태를 보였다. 실험에서 얻은 건조조건별 건조곡선은 확산모델의 수치해석(數値解析) 결과와 거의 일치하였으며, 같은 평위함수율(平衛含水率) 조건에서 건조온도의 증가는 목재표면 보다 내부의 함수율 변화에 더 크게 영향하여 결과적으로 낮은 온도에서의 건조조건이 목재 내의 수분경사(水分傾斜)를 급하게 하는 것으로 밝혀졌다. 본 연구를 통해 목재 건조 중의 내부에 발생하는 수분경사를 추정하는데 비정상상태의 확산모델이 모든 함수율 범위에 걸쳐 유용하게 사용될 수 있음이 밝혀졌다.

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