• Title, Summary, Keyword: 확산계수

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Relationship between Chloride Diffusivity and the Fundamental Properties of Concrete (염소이온의 확산계수와 콘크리트의 기초물성과의 관계)

  • Choi, Doo-Sun;Choi, Jae-Jin
    • Journal of Korean Society of Hazard Mitigation
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    • v.9 no.1
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    • pp.15-20
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    • 2009
  • Marine concrete structure is exposed to salt injury and deteriorated by steel corrosion due to chloride ions diffusion. It, therefore, is very important to estimate the chloride diffusivity in concrete. In this paper the compressive strength and permeable pore volume of concrete are measured and the diffusion coefficient and penetration depth of chloride ions in concrete were investigated to estimate the chloride diffusivity efficiently. To correlate these results each other, regression analysis was done. The results showed a good linear relation between chloride diffusivity and the fundamental properties of concrete and the chloride diffusivity of concrete with water-cement ratios of $40%{\sim}60%$ were about $2.5{\sim}6.6{\times}10^{-12}m^2/s$.

Chloride Diffusion in Hardened Concrete with Concrete Properties and Testing Method (콘크리트 물성 및 시험법에 따른 콘크리트 염화물 확산)

  • Yang Eun-Ik;Kim Myung-Yu;Min Seok-Hong
    • Journal of the Korea Concrete Institute
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    • v.16 no.2
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    • pp.261-268
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    • 2004
  • Corrosion of reinforcement is the main cause of damage and early failure of reinforced concrete structures. The corrosion is mainly progressed by the chloride ingress. In this paper, an experimental study is executed to investigate the effect of concrete properties and testing methods on the coefficients of chloride diffusion. Also, it is surveyed the relationship between total chloride and free chloride in concrete. According to this experiment results, W/C ratio and testing method affect chloride diffusion coefficient of concrete. As W/C ratio is increased, diffusion coefficient in concrete is also increased. Diffusion coefficient obtained by each testing method show the different values, respectively. The model equation of diffusion coefficient with W/C ratio is proposed.

Effect of Curing Condition on the Chloride ion Diffusion Coefficient in Concrete with GGBFS (양생조건이 고로슬래그 미분말을 혼입한 시멘트 콘크리트의 염화물이온 확산계수에 미치는 영향)

  • Park, Jang-Hyun;Lee, Han-Seung
    • Journal of the Korea Institute of Building Construction
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    • v.19 no.5
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    • pp.421-429
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    • 2019
  • The changes in the resistance to chloride ingress of concrete using a ground granulated blast furnace slag (GGBFS) according to curing conditions were examined. The curing conditions were divided in air-dry curing and under-water curing. Three concrete mixures with the GGBFS replacement ratio of 0%(control), 30%, and 60% were prepared. For tests, evaluations of concrete compressive strength, and chloride ion diffusion coefficient were performed. As the GGBFS replacement ratio increased, the concrete compressive strength of the in air-dry cured specimens decreased compared to under-water cured specimens. When the chloride ion diffusion coefficient was measured, the chloride ion diffusion coefficient decreased as the GGBFS replacement ratio increased. However, the diffusion coefficient of the in air-dry cured specimen was increased up to 111% compared with the under-water cured specimen.

Diffus ion-Weighted MR Imaging of Spinal Cord Infarction (척수경색의 확산강조자기공명영상)

  • 김윤정;서정진;임남열;정태웅;김윤현;박진균;정광우;강형근
    • Investigative Magnetic Resonance Imaging
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    • v.6 no.2
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    • pp.166-172
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    • 2002
  • Purpose : To evaluate the usefulness of diffusion-weighted imaging(DWI) and quantitative apparent diffusion coefficient (ADC) maps in the patients with spinal cord infarction. Materials and methods : We studied 6 patients presented symptoms with spinal cord infarction, retrospectively (3 men and 3 women). We obtained multi-shot echo planar-based, DWI using 1.5T MR scanner at 5.4 mean days after the onset of ischemic symptoms. In six patients, signal intensity was acquired at conventional b value $1000s/\textrm{mm}^2$). The ADC value for the normal spinal cord and for infarcted lesions was measured from the trace ADC maps by using regions of interest positioned over the spinal cord. We analyzed signal intensity of lesion on MRI and DWI, and compared with ADC values in infarcted lesions and normal site. Results : T1-weighted MR image showed isosignal intensity in four of six patients and low signal intensity in two of six. T2-weighted MR image demonstrated high signal intensity in all of six. All DWI were considered to be diagnostic. All of six depicted a bright signal intensity on DWI. ADC values of infarcted lesion were measured lower than that of normal spinal cord on ADC map. The differences in ADC values between infarcted and normal spinal cord were significantly different (p<0.05). Conclusion : It is possible to obtain DWI and ADC map of the spinal cord and DWI may be useful in the early diagnosis and localization of lesion site in patients with spinal cord infarction.

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Calculation of the Viscosity and Diffusion Coefficients for Some Binary Gaseous Mixtures Using the Semi-empirical Inversion Method (반실험적 반전 방법을 이용한 이성분계 기체 혼합물의 점도와 확산계수 계산)

  • Rafiee, H.R.;Heidari, N.
    • Journal of the Korean Chemical Society
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    • v.55 no.4
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    • pp.581-589
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    • 2011
  • Viscosity and diffusion coefficients for the gaseous binary mixtures of benzene- toluene, benzene-phenol and benzene-p-xylene over a wide range of temperature and composition have been predicted using the semi-empirical inversion method. The accuracies are within 3% and 4% for viscosities and diffusion coefficients, respectively.

이온채널에서 이온전류의 주기적 패턴에 대한 동역학적 격자기반 대정준 Monte Carlo 모의실험 연구

  • Jeong, Ji-Eun;Jin, Hyo-Min;Hwang, Hyeon-Seok
    • Proceeding of EDISON Challenge
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    • pp.135-139
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    • 2016
  • 본 연구에서는 동역학적 격자기반 대정준 Monte Carlo (Kinetic Lattice Grand Canonical Monte Carlo, KLGCMC) 모의실험 방법을 이용하여 모델 이온채널 내에서 KCl과 HCl의 이온 전류를 시간의 함수로 구하였다. KLGCMC 모의실험 계산 결과로부터 이온채널의 양이온 선택성이 더 큰 것을 확인 할 수 있었다. 또한 모의실험 결과를 통해 각 이온의 확산계수가 전류에 미치는 영향을 확인 할 수 있었다. $H^+$ 이온은 농도가 매우 작음에도 확산계수가 커 전체 전류에 큰 영향을 미쳤다. 반면에 확산계수가 작은 $K^+$ 이온은 이온채널 안에서 쉽게 흐르지 못하고 정체 되며, $H^+$ 이온의 전류흐름을 방해하는 것을 확인 할 수 있었고, 이로 인해 이온전류의 패턴이 시간에 따라 변화함을 알 수 있었다.

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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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Comparison of Test Methods for Evaluation of Chloride Diffusion Coefficient in Concrete (콘크리트의 염소이온 확산계수 평가를 위한 시험방법 비교)

  • Lee, Chan-Young;Kim, Hong-Sam;Kim, Jin-Cheol;Cheong, Hai-Moon;Ahn, Tae-Song
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.581-584
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    • 2008
  • Generally, durability of concrete structures under marine environment is grossly declined by detrimental ions such as chlorides, which penetrate concrete and was diffused to corrode reinforcing rod. Therefore, chloride diffusion properties in concrete are important for durability evaluation and design of concrete structure. For estimation of chloride diffusion coefficient in concrete, both evaluation methods are used for steady state and non-steady state derived from Fick's 1st and 2nd law, respectively. However, as it is very difficult to evaluate diffusion coefficient for non-steady state like service environment where concrete is actually exposed, indirect evaluation method by laboratory accelerated test is generally used. In this study, comparison of chloride diffusion behavior was investigated for fixed mix proportion and age of concrete using four accelerated test methods based on domestic and foreign standards. From test results, only relative comparison between concrete mixtures was possible using ASTM C 1202 test, and diffusion coefficient for steady state was estimated as low as 1/10 of that for non-steady state. In addition, diffusion coefficient estimated by immersion test was similar to result by NT build 492 test.

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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.

Radionuclide Diffusion in Compacted Domestic Bentonite (압축 국산 벤토나이트 내에서 방사성 핵종의 확산이동)

  • Choi, Jong-Won;Lee, Byung-Hun
    • Journal of Radiation Protection and Research
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    • v.16 no.2
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    • pp.27-39
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    • 1991
  • The diffusion of Sr-85, Cs-137, Co-60 and Am-241 in compacted domestic bentonite was studied, using a diffusion cell unit in which diffusion took place axially from the center of cylindrical bentonite sample body. The effects of compaction density and heat-treated bentonite on diffusion were analysed. And the diffusion mechanism of radionuclide was also analysed by evaluating the measured diffusivity of anion Cl-36. The apparent diffusivities obtained for Sr-85, Cs-137, Co-60 and Am-241 were $l.07{\times}10^{-11},\;6.705{\times}10^{-13},\;l.226{\times}10^{-13}\;and\; l.310{\times}10^{-14}m^2/sec$, respectively. When the as-pressed density of bentonite increased from $1.8\;to\;2.0g/cm^3$, the apparent diffusivity of Cs-137 decreased by quarter. In the case of bentonite heat-treated to $150^{\circ}C$, no significant change in diffusivity was observed, which showed the possibility that the domestic bentonite could be used as a chemical barrier to retard the radionuclide migration at below $150^{\circ}C$. From the calculated pore and surface diffusivity, the surface diffusion due to the concentration gradient of radionuclide sorbed on the solid phase was found to dominate greatly in total transport process.

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