• Corrosion Science and Technology
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• v.4 no.2
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• pp.69-74
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• 2005

The carbonation of concrete is one of the major factors that cause durability problems in concrete structures. The rate of carbonation depends largely upon the diffusivity of carbon dioxide in concrete. The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. To this end, several series of tests have been planned and conducted. The test results indicate that the diffusion coefficient increases with the increase of water-cement ratio. The diffusion coefficient decreases with the increase of relative humidity at the same water-cement ratio. The diffusion of carbon dioxide reached the steady state within about five hours after exposure. The content of aggregates also influences the diffusivity of carbon dioxide in concrete. It was found that the diffusion coefficient of cement paste is larger then that of concrete or mortar. The quantitative values of diffusivity of carbon dioxide in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.669-674
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• 2003

The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. The test results indicate that the diffusion coefficient increases with the increase of water-cement ratio. The diffusion coefficient decreases with the increase of relative humidity at the same water-cement ratio. The diffusion of carbon dioxide reached the steady-state within about five hours after exposure. It was found that the diffusion coefficient of cement paste is larger then that of concrete or mortar. The quantitative values of diffusivity of carbon dioxide in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Membrane Journal
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• v.25 no.3
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• pp.248-255
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• 2015

Aminated polyetherimide membrane synthesized in the laboratory according to amine ratio was used for measurement of gas permeability, diffusivity, and solubility about carbon dioxide, nitrogen, methane, oxygen, and sulfur dioxide with Time-lag method at room temperature. Generally, gas permeability is totally decreased because the more amination rate reacted to the main chain of amine groups, the more intermolecular space became narrow. However, gas permeability of sulfur dioxide was increased due to combination of sulfur dioxide and amine groups have acid and base properties respectively. Diffusivity and solubility of dry gas are totally decreased excluding sulfur dioxide as increasing amination rate. In case of sulfur dioxide, however, diffusivity as well as solubility was increased as increasing amination rate. Selectivity of carbon dioxide/nitrogen showed 60 when amination rate was 3. In case of humid gas, gas permeability of carbon dioxide was 70 barrer when relative humidity showed 100, and selectivity with nitrogen approximately showed 18.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.778-784
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• 2003

The carbonation of concrete is one of the major factors that cause durability problems in concrete structures. The rate of carbonation depends largely upon the diffusivity of carbon dioxide in concrete. The purpose of this study is to identify the diffusion coefficients of carbon dioxide for various concrete mixtures. To this end, several series of tests have been planned and conducted. The test results indicate that the diffusion of carbon dioxide reached the steady-state within about five hours after exposure. The diffusion coefficient increases with the increase of water-cement ratio and decreases with the increase of relative humidity at the same water-cement ratio. The content of aggregates also influences the diffusivity of carbon dioxide in concrete. It was found that the diffusion coefficient of cement paste is larger than that of concrete or mortar. The experimental study of carbon dioxide diffusivity in this study will allow more realistic assessment of carbonation depth in concrete structures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.639-647
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• 2017

This basic study is focused on the physically removal method of carbon dioxide from the decomposition of ammonium carbarmate to prevent the recombination of ammonium salts. A basic visual experimental set-up was designed and constructed to observe the recombination phenomena from the proper composition of ammonia gas, carbon dioxide gas, and compressed air dilution gas. To quantify the recombination phenomena, a simple device was designed to measure the weight change under severe cases for three different tube sizes. The temperature and pressure in the visual tube and the volumetric flow rates of the nitrogen dilution gas were studied and the conditions to avoid recombination were analyzed according to mean free path theory. Diffusivity values based on the Chapman-Enskog theory were calculated from the experimental data. These value may serve as an index for the prevention of recombination.

• Clean Technology
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• v.13 no.4
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• pp.244-250
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• 2007

Sorption of C. I. Disperse Yellow 54 dye in poly(trimethylene terephthalate) (PTT) and poly (ethylene terephthalate) (PET) textile fibers were measured at various pressures, temperatures, and times in the presence of supercritical carbon dioxide and thereby the diffusivities of the dye in the fibers were calculated. The diffusivity of dye in the polymeric fibers was very low, only in the order of $10^{-12}\;cm^2/sec$, but increased with increasing temperature at constant pressure and with increasing pressure at constant temperature. The diffusivity in PTT fibers were about 1.5 to 3 times as large as that in PET fibers. As the fiber was very thin, the dye distribution in the fiber was almost uniform everywhere inside the fiber.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.163-168
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• 2002

Through the developing measuring system of gas diffusivity, the experiments on carbon dioxide diffusivity in concrete carry out. From this, some important results was achieved. First, the times of reaching the steady state condition don't depend on the water/cement ratio with linearity. But, for the 0.42 w/c ratio the duration of the non-steady state condition is long. Second, in constant relative humidity, the diffusion coefficient shows linearity for the w/c ratio. Third, for the same w/c ratio, the influence of relative humidity on the diffusivity is very large. This shows the importance of the environmental condition for the carbonation. This study on $CO_2$ diffusivity in concrete is the first attempt within a country and will be important data.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.4
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• pp.63-65
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• 2008

The increased interest in reducing the environmental effects caused by releasing organic compounds and aqueous waste has motivated the development of polymeric materials in supercritical fluids. Recently, supercritical fluids have been used in material synthesis and processing because of their special properties, such as high diffusivity, low viscosity, and low surface tension. Supercritical carbon dioxide is the most attractive because it is non-toxic, non-flammable, and has moderate critical temperature and critical pressure values. Supercritical carbon dioxide can also swell most polymers. In this study, we prepared polymer/clay nanocomposites using supercritical fluids. Cloisites 10A, 15A, 25A, and 30B used in this study are montmorillonites modified with a quaternary ammonium salt. The nanocomposites of polymer/clay were characterized by X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.443-453
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• 2003

The diffusivity of carbon dioxide in concrete is very important in that it directly affects the degree of carbonation in concrete structures. The purpose of the present study is to explore the diffusivity of carbon dioxide and to derive a realistic equation to estimate the diffusion coefficient of carbon dioxide in concrete. For this purpose, several series of concrete specimens have been tested. Major test variables were the water-cement ratios. The total porosities and the diffusion coefficients of carbon dioxide were measured for the specimens. The present study indicates that the measured porosities agree well with the calculated ones. The effects of porosity and relative humidity on the diffusion coefficient of carbon dioxide were examined. A prediction equation to estimate the diffusion coefficient of carbon dioxide was derived and proposed in this study. The proposed equation shows reasonably good correlation with test data on the $CO_2$ diffusion coefficient of concrete

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.143-150
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• 2014

Recently, supercritical fluid process has been widely used in material synthesis and processing due to their remarkable properties such as high diffusivity, low viscosity, and low surface tension. Supercritical carbon dioxide is the most attractive solvent owing to their characteristics including non-toxic, non-flammable, chemically inert, and also it has moderate critical temperature and critical pressure. In addition, supercritical carbon dioxide would dissolve many small organic molecules and most polymers. In this study, we have prepared the poly (ethylene oxide)/clay nanocomposites using supercritical fluid as a carbon dioxide. Commercialized Cloisites-15A and Cloisites-30B used in this study, which are modified with quaternary ammonium salts. The nanocomposites of polymer/clay were characterized by XRD, TGA and DSC. Poly (ethylene oxide)/clay nanocomposites by supercritical fluid show higher thermal stability than nanocomposites prepared by melt process. In addition, supercritical fluid process would be increased dispersibility of the nanoclay in the matrix.