• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.66-74
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• 2016

The objective of this study is the investigation of the influence of carbonation on the penetration of chloride ions in reinforced concrete sections for different mix proportions and environmental conditions. A comprehensive numerical model based on the change of the pore structure and the chemical equilibrium was used for this combined action of carbonation and chloride ingress. The empirical formulae of some parameters in this model are estimated according to numerous experimental data. And, a set of data analysis is carried out to simplify the estimation of model variables to reduce the computational cost. A coupled simulation of the transports of carbon dioxide, chloride ions, heat and moisture is carried out. Then, the parametric analysis is given and the numerical results show that the effect of carbonation of the free chloride ingress is significant and depends on the binder types and concrete mix proportion.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.141-150
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• 2017

Geosynthetics are generally utilized to restrain the leakage of leachate and other contaminants during the construction of offshore waste landfill. Therefore, geosynthetic-soil interface is formed inevitably. In this study, 2 dimensional numerical analysis is performed to assess the dynamic behaviour of the offshore waste landfill including geosynthetic-soil interface. Offshore waste landfill can be divided into rubble mound revetment and retaining wall types and analyzed on each type. Effective stress analysis is conducted to consider the variation of pore water pressure and axial force and shear displacement of the interface are compared based on the characteristics of seismic frequency. Consequently, retaining wall type demonstrates more stable behavior against liquefaction potential and favorable forces and shear displacement.

• Journal of the Korea Institute of Building Construction
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• v.20 no.4
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• pp.321-330
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• 2020

The addition of a limestone filler(LF) to fill into the voids between cement and aggregate particles can reduce the cementitious paste volume. In previous studies, it has been found that the addition of LF to reduce the cementitious paste volume would substantially increase the compressive strength, and reduce the heat generation. This paper aim to evaluate the influence of LF contents on the hydration kinetics and compressive strength. Hydration kinetics were evaluate using heat of hydration, ignition loss and thermal analysis. The heat of hydration was measured using Isothermal Calorimetry. The degree of hydration was measured using ignition loss. Hydration product analysis was carried out by Thermal Gravimetric and Differential Thermal Analysis. The results show that the addition of LF reduces not only the initial setting time and heat of hydration peak, also degree of hydration and rate of strength development at early age increase with the addition of LF. It can be concluded the LF fills the pore between cement particles due to formation of carboaluminate, which may accelerate the setting of cement pastes.

• Journal of the Korean Geosynthetics Society
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• v.12 no.1
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• pp.51-61
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• 2013

This paper presents results from a study undertaken to quantitatively evaluate the geotextile pore sizes using optical image analysis. The evaluation was conducted by observing surfaces of coupons cut from resin-impregnated specimens of geotextile-geomembrane layered under various load conditions. Stereological concepts were applied to collect representative specimens from a series of laboratory tests. The sizes of voids enclosed by filaments were expressed in terms of the largest inscribing opening size (LIOS) distribution. The opening diameter corresponding to the 50% cumulative frequency decreased by about 45mm as the load increased from 10 to 300kPa and recovered to about 90% of its initial state on unloading back to 10kPa. The average void size was reduced by 32 and 16.5% as the geotextile was sheared against a textured geomembrane under normal stresses of 100 and 300kPa, respectively. The results showed how the LIOS distribution varied as a function of normal stress and interface shear displacement against a smooth and a textured geomembrane surfaces.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.55-63
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• 2020

In this study, a scaled model test of the shaking table and a seismic analysis considering effective stresses were performed to reveal the dynamic behavior characteristics of box structures deep located in multi-layered soils upon seismic loading. The input seismic wave was operated below the ground using five seismic waves, including long period wave (Hachinohe), short period wave (Ofunato), artificial wave and real earthquakes that occurred in Gyeong-ju and Po-hang. As a result of model test and numerical analysis, the vertical displacement of box structures upon seismic loading was greater than that of horizontal direction, and it was confirmed that an increase of excess pore water pressure below the foundation ground caused a displacement. In addition, behavior of the ground and structures during artificial seismic wave appeared to be larger than real earthquake wave.

• Journal of the Korean Chemical Society
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• v.61 no.6
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• pp.339-345
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• 2017

Carbonaceous adsorbent (CA-WTP) was prepared by heat treatment at $400^{\circ}C$ for 2 h in N2 atmosphere using waste tire powder (WTP). WTP and CA-WTP were first characterized by thermo-gravimetric analysis (TGA), energy dispersive X-ray spectrometer (EDS), scanning electron microscopy (SEM), specific surface area analysis (BET) and FT-IR spectroscopy. Then, they were tested as adsorbents for removal of Cd in water. CA-WTP exhibited much higher specific surface area and total pore volume than WTP itself and showed higher adsorption capacity for Cd. Equilibrium data of adsorption were analyzed using Freundlich and Langmuir isotherm models. It was seen that both Freundlich and Langmuir isotherms have correlation coefficient $R^2$ value larger than 0.95. The results of studies indicate that CA-WTP developed from WTP by heat treatment could be used as efficient adsorbent for the removal Cd from water.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3C
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• pp.113-120
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• 2012

An actual slope failure was analyzed in residual soils at Jinju. Due to rainfall infiltration, the safety factor decreases in the unsaturated layers, since the effective stress and shear strength decrease. In this study, the effective stress is based on suction stress using soil water retention curve. Unsaturated properties were evaluated on soil water retention curve, hydraulic conductivity and shear strength with samples from the site. After infiltration analysis of unsaturated flow under the actual rainfall, the distribution of pore water pressure could be calculated in the slope layers. In the stress field of finite elements, an elastic analysis calculated total stress distribution in the layers and also shear stresses on the slip surface using elastic model. On the slip surface, suction stress and effective stress evaluated the shear strength. As a result, the factor of safety was calculated due to rainfall, which could simulate the actual slope failure. In particular, it was found that the suction stress increases and both the effective stress and the shear strength decrease simultaneously on the slip surface.

• Environmental Analysis Health and Toxicology
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• v.26
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• pp.12.1-12.7
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• 2011

Objectives: Perchlorate is an emerging contaminant that is found everywhere, including various foods. Perchlorate is known to disturb the production of thyroid hormones and leads to mental disorders in fetuses and infants, as well as metabolic problems in adults. In this study, we attempted to establish an LC-MS/MS method for measuring perchlorate in dairy products and used this developed method to investigate perchlorate levels in Korean milk and yogurt samples. Methods: The developed method of perchlorate analysis requires a shaker and 1% acetic acid/acetonitrile as the extracting solvent. Briefly, the samples were extracted and then centrifuged (4000 rpm, 1hour), and the supernatant was then passed through a $Envi^{TM}$ Carb SPE cartridge that had been prewashed sequentially with 6 mL of acetonitrile and 6 mL of 1% acetic acid in water. The final volume of the sample extract was adjusted to 40 mL with reagent water and the final sample was filtered through a 0.20-${\mu}m$ pore size PTFE (Polytetrafluoroethylene) syringe filter prior to LC-MS/MS. Results: The average levels of perchlorate in milk and yogurt samples were $5.63{\pm}3.49\;{\mu}g/L$ and $3.65{\pm}2.42\;{\mu}g/L$, respectively. The perchlorate levels observed in milk samples in this study were similar to those reported from China, Japan, and the United States. Conclusions: The exposure of Koreans to perchlorate through the consumption of dairy products was calculated based on the results of this study. For all age groups, the calculated exposure to perchlorate was below the reference of dose (0.7 ${\mu}g/kg$-day) proposed by the National Academy of Science, USA, but the perchlorate exposure of children was higher than that of adults. Therefore, further investigation of perchlorate in other food samples is needed to enable a more exact assessment of exposure of children to perchlorate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.9
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• pp.642-648
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• 2019

In this study, Image-based computational analysis using the developed models was performed to predict the degradation of effective properties by ablation. The ablation tests of carbon/phenolic composites were performed using a 0.4 MW arc-heated wind tunnel. The carbon/phenolic composite samples were scanned using the micro-computed tomography (Micro-CT) to analyze the ablation characteristics according to a duration time of the ablation test. By calibrating the scanned images, computational models were developed that reflect the actual microstructure of the ablation composites. Also, nine computational models that reflect the actual pore shape were developed using the created cross-sectional images. Image-based computational analysis using the developed models was performed to predict the degradation of effective properties by ablation and the decrease of effective properties was confirmed with increase of porosity.

• Structural Engineering and Mechanics
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• v.69 no.5
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• pp.537-545
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• 2019

Stress analysis of bottom-hole rock has to be considered with much care to further understand rock fragmentation mechanism and high penetration rate. This original study establishes a fully coupled simulation model and explores the effects of overburden pressure, horizontal in-situ stresses, drilling mud pressure, pore pressure and temperature on the stress distribution in bottom-hole rock. The research finds that in air drilling, as the well depth increases, the more easily the bottom-hole rock is to be broken. Moreover, the mud pressure has a great effect on the bottom-hole rock. The bigger the mud pressure is, the more difficult to break the bottom-hole rock is. Furthermore, the maximum principal stress of the bottom-hole increases as the mud pressure, well depth and temperature difference increase. The bottom-hole rock can be divided into three main regions according to the stress state, namely a) three directions tensile area, b) two directions compression areas and c) three directions compression area, which are classified as a) easy, b) normal and c) hard, respectively, for the corresponding fragmentation degree of difficulty. The main contribution of this paper is that it presents for the first time a thorough study of the effect of related factors, including stress distribution and temperature, on the bottom-hole rock fracture rather than the well wall, using a thermo-poroelastoplasticity model.