• Computers and Concrete
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• v.7 no.1
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• pp.17-38
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• 2010

This research aimed to investigate the influence of high-volume mineral admixtures (MAs), i.e., fly ash and slag, on the hydration characteristics and microstructures of cement pastes. Degree of cement hydration was quantified by the loss-on-ignition technique and degree of pozzolanic reaction was determined by a selective dissolution method. The influence of MAs on the pore structure of paste was measured by mercury intrusion porosimetry. The results showed that the hydration properties of the blended pastes were a function of water to binder ratio, cement replacement level by MAs, and curing age. Pastes containing fly ash exhibited strongly reduced early strength, especially for mix with 45% fly ash. Moreover, at a similar cement replacement level, slag incorporated cement paste showed higher degrees of cement hydration and pozzolanic reaction than that of fly ash incorporated cement paste. Thus, the present study demonstrates that high substitution rates of slag for cement result in better effects on the short- and long-term hydration properties of cement pastes.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1722-1729
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• 2006

Predicting the mechanical properties of the 3-D scaffold using finite element method (FEM) simulation is important to the practical application of tissue engineering. However, the porous structure of the scaffold complicates computer simulations, and calculating scaffold models at the pore level is time-consuming. In some cases, the demands of the procedure are too high for a computer to run the standard code. To address this problem, the representative volume element (RVE) theory was introduced, but studies on RVE modeling applied to the 3-D scaffold model have not been focused. In this paper, we propose an improved FEM-based RVE modeling strategy to better predict the mechanical properties of the scaffold prior to fabrication. To improve the precision of RVE modeling, we evaluated various RVE models of newly designed 3-D scaffolds using FEM simulation. The scaffolds were then constructed using microstereolithography technology, and their mechanical properties were measured for comparison.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.3
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• pp.132-145
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.499-506
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• 2007

According to the high demand of concrete structures with high performance, various studies have examined on the high performance concrete, especially high strength concrete. Various admixtures are required to produce high strength concrete and silica fume has been the most popular admixture. Recently, however, metakaolin, which is similar to silica fume in properties but cheaper, has been introduced to high strength concrete. In this study, high-strength concrete using metakaolin were studied of capillary pore structure by mercury intrusion porosimetry technique and the accelerated chloride diffusivity by electrical difference. In result, it was found that the pore structure improved and compressive strength increased and chloride diffusivity reduced as more metakaolin content was added. In addition, a regression analysis of $5{\sim}2,000nm$ pore volume and both compression strength and chloride diffusivity revealed that each these had a high correlation of about 0.76 and 0.68.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.177-190
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. Lee et al.(2016) studied for regular waves, and this study considered for irregular waves with the same numerical analysis method used for regular waves. Under the condition of the irregular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated and their results were compared with those of the regular wave field to evaluate the liquefaction potential on the seabed quantitatively. Although present results are based on a limited number of numerical simulations, one of the study's most important findings is that a more safe design can be obtainable when analyzing case with a regular wave condition corresponding to a significant wave of irregular wave.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.177-184
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• 2015

In order to use the high-volume slag cement as a construction materials, a proper activator which can improve the latent hydraulic reactivity is required. The dissolved aluminum silicon ions from ground granulated blast furnace slag (GGBFS) react with sulfate ions to form ettringite. The proper formation of ettringite can increase the early-age strength of high-volume GGBFS (80%) cement. The aim of this study is to investigate the hydration properties with sulfate activators (sodium sulfate, anhydrite). In this paper, the effects of $Na_2SO_4$ and $CaSO_4$ on setting, compressive strength, hydration, micro-structure were investigated in high-volume GGBFS cement and compared with those of without activator. Test results indicate that equivalent $SO_3$ content of 3~5% improve the early-age hydration properties such as compressive strength, heat evolution rate, micro-pore structure in high-volume GGBFS cement.

• Korean Journal of Materials Research
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• v.19 no.10
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• pp.538-543
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• 2009

Active clays, Diatomite, bentonite and zeolite were used as porous materials for fabricating hygroscopic gypsum boards. Pohang active clay and Cheolwon diatomite showed excellent characteristics of moisture adsorption and desorption. These characteristics were caused by higher surface area and pore volume of porous materials. Moisture adsorption content of gypsum board with 10% active clay(P1) was 62.0 g/m$^2$, and moisture desorption content was 50.2 g/m$^2$. Moisture adsorption content of gypsum board with 10% diatomite(P) was 59.5 g/m$^2$, and moisture desorption content was 49.0 g/m$^2$. Moisture adsorption contents of gypsum boards with porous materials were higher than that moisture desorption contents of gypsum board without porous materials. Correlation coefficient between surface area and moisture adsorption content of gypsum boards was 0.98. Also, correlation coefficient between surface area and moisture desorption content of gypsum boards was 0.97. Moisture adsorption and desorption contents were influenced by surface area and pore volume of the gypsum boards, and surface area had a larger effect on moisture adsorption and desorption.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.293-303
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• 2016

Underground $CO_2$ storage technology is one of the most effective methods to reduce atmospheric $CO_2$. In this study, $CO_2$ storage condition was simulated in the laboratory. Sandstone and shale specimens were saturated in 1M NaCl and were reacted at $45^{\circ}C$, 10 atm for 4 weeks. The physical and microstructural properties of rock specimens were measured. Variations on physical properties of shale specimens were bigger than those of sandstone specimens, such as volume, density, elastic wave velocity, Poisson's ratio and Young's modulus. Microstructure were analyzed using X-ray computed tomography. Total number of pores were decreased, and average volume, average area and average equivalent diameter of each pore were changed after $CO_2$ reaction. Swelling and leakage of clay mineral caused by $CO_2$-mineral reaction were the reason of changes. The results of this study can be applied to predict the physical and microstructural changes in underground $CO_2$ storage condition.

• Clean Technology
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• v.19 no.3
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• pp.279-286
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• 2013

Using a cation exchange resin of polystyrene-DVB copolymer as a carbon source for the production of activated carbon, the effects of operating parameters on the physical properties of activated carbon such as specific surface area and specific pore volume were experimentally studied. In carbonization process specific surface area and specific pore volume of carbonized product decreased with the increase of carbonization temperature and time. They were proportional to activation temperature and time up to the specific temperature and time in activation process. In carbonization process the increase of heating rate gave negative effect to the properties. The properties of activated product, on the contrary, increased with the heating rate in carbonization process. The properties of activated carbon manufactured with the resin exchanged with divalent cations were lower than those with raw resin.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.229-241
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• 2008

In order to investigate stabilization effect on As-contaminated soils treated by zero-valent iron(ZVI) and industrial by-products, batch tests and column tests were carried out with As-contaminated soils collected from farmland around the abandoned mine site. In batch tests, ZVI and industrial by-products(blast furnace slag, steel refining slag and oyster shell powder) were used as treatment materials to reduce As. Industrial by-products were mixed with As-contaminated soils, in the ratio of 1%, 3%, 5% and 7% on the weight base of dried soil. After incubation, all samples showed the reduction of As concentration and it was expected that ZVI and steel refining slag were effective treatment materials to remove As among treatment materials used in batch test. In column tests, columns were made by acrylic with the dimension of diameter=10cm, height=100cm, thickness=1cm and these columns were filled with untreated soils and treated soils mixed with ZVI and steel refining slag(mixing ratio=3%). Distilled water was discharged into the columns with the velocity of 1 pore-volume/day. During test, pH, EC, Eh and As concentration were measured in the regular term(1 pore-volume). As a result, ZVI and steel refining slag were shown 93%, 62% reduction of As concentration respectively by comparison with untreated soils. Therefore, if ZVI and steel refining slag are used as treatment materials in As-contaminated soils, it is expected that the As concentration in soils is reduced effectively.