• Journal of the Korea Institute of Building Construction
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• v.11 no.4
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• pp.363-370
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• 2011

This study considerated reject ash, wastes of coal-fired power plants, to use mineral admixtures for cement. The pozzolan activity selected the fineness of the efficient reject ash through comparison and it compared to the fly ash that are widely used for concrete mixed material. Cement composites was prepared replacing of slag cement by fineness reject ash and fly ash, and properties of cement composites was tested by paste(setting time, fluidity, instrumental analysis) and mortar(compressive strength). Instrumental analysis results showed hydration reaction of fineness reject ash was not different from fly ash, but had more dense micro structures. Results of physical properties showed fineness reject ash shorten setting time, increased compressive strength compared by fly ash. Therefore using fineness reject ash with $6,000cm^2$/g to concrete mineral admixtures or cement composites was might be possible and could contribute to improve properties of concrete.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.584-590
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• 2014

Air-cooled slag showed grindability approximately twice as good as that of water-cooled slag. While the studied water-cooled slag was composed of glass as constituent mineral, the air-cooled slag was mainly composed of melilite. It is assumed that the sulfur in air-cooled slag is mainly in the form of CaS, which is oxidized into $CaS_2O_3$ when in contact with air. $CaS_2O_3$, then, is released mainly as $S_2O{_3}^{2-}$ion when in contact with water. However, the sulfur in water-cooled slag functioned as a constituent of the glass structure, so the$S_2O{_3}^{2-}$ ion was not released even when in contact with water. When no chemical admixture was added, the blended cement of air-cooled slag showed higher fluidity and retention effect than those of the blended cement of the water-cooled slag. It seems that these discrepancies are caused by the initial hydration inhibition effect of cement by the $S_2O{_3}^{2-}$ ion of air-cooled slag. When a superplasticizer is added, the air-cooled slag used more superplasticizer than did the blast furnace slag for the same flow because the air-cooled slag had higher specific surface area due to the presence of micro-pores. Meanwhile, the blended cement of the air-cooled slag showed a greater fluidity retention effect than that of the blended cement of the water-cooled slag. This may be a combined effect of the increased use of superplasticizer and the presence of released $S_2O{_3}^{2-}$ ion; however, further, more detailed studies will need to be conducted.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.365-372
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• 2018

3D printing technology of construction field can be divided into structural materials, interior and exterior finishing materials, and is mainly done by extruding and adapting. Particularly when it is applied as an exterior materials, it is mainly applied to an unstructured exterior materials and high accuracy is required. The exterior materials can be used as a cement composite materials, it is suitable also for a additive type manufacturing, and the role of a redispersible polymer powder is important. But, high temperatures, redispersible polymer cement base material beget dehydration and micro crack of cement matrix. In this research, we developed a EVA, EVCL redispersible polymer cement base material applicable as a 3D printing exterior materials, confirmed density and strength characteristics for application as an exterior materials, a flame retardancy test for improving the fire resistance of buildings and confirmed its possibility. From the test result, developed EVCL redispersible polymer cement mortar showed good stability in high temperatures. These high temperature stability is caused by the ethylene-vinyl chloride binding. Thus, this result indicates that it is possible to fire resistant 3D printing interior and exterior finishing materials.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.87-97
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• 2016

In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.277-282
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• 2004

In a hardened concrete, diffusion of oxygen, carbon dioxide, aggressive ions, and moisture from the environment to the concrete takes place through the pore network. It is well known that making dense cement matrix enhances the durability of concrete as well as all the characteristics including strength of concrete. In this paper,9 mix concretes with water to cementitious material ratio (40,45, and $50\%$) and replacement ratio of GGBFS (40 and $60\%$ of cement by weight) were studied on the micro-pore structure by mercury intrusion porosimetry and the accelerated chloride diffusion test by potential difference. From the results the average pore diameter and accelerated chloride diffusivity of concrete were ordered NPC > G4C > G6C. It is concluded that there is a good correlation between the average pore diameter and the chloride diffusivity, and the mineral admixtures has a filling effect, which increases the tortuosity of pore and makes large pores finer, on the pore structure of cement matrix due to the latent hydraulic reaction with hydrates of cement.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.440-452
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• 2021

Enhancement of durability and reduction of maintenance cost of concrete, with the implementation of various approaches, has always been a matter of concern to researchers. The integration of pozzolans as a substitute for cement into the concrete is one of the most desirable technique. Silica fume (SF) and colloidal nanosilica (CS) have received a great deal of interest from researchers with their significant performance in improving the durability of concrete. The synergistic role of the micro and nano-silica particles in improving the main characteristics of cemented materials needs to be investigated. This work aims to examine the utility of partial substitution of cement by SF and CS in binary and ternary blends in the improvement of the durability characteristics linked to resistance for electrochemical corrosion using electrical resistivity and half-cell potential analysis and chloride penetration trough rapid chloride penetration test. Furthermore, the effects of this silica mixture on the compressive strength of concrete under normal and aggressive environment have also been investigated. Based on the maximum compression strength of the concrete, the optimal cement substituent ratios have been obtained as 12% SF and 1.5% CS for binary blends. The optimal CS and SF combination mixing ratios has been obtained as 1.0% and 12% respectively for ternary blends. The ternary blends with substitution of cement by optimal percentage of CS and SF exhibited decreased rate for electrochemical corrosion. The strength and durability studies were found in consistence with the microstructural analysis signifying the beneficiary role of CS and SF in upgrading the performance of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.85-86
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• 2020

With the increasing importance of environmental issues, the cementitious materials with self-cleaning or photocatalytic properties by introducing TiO₂ materials have been gaining a lot of attention. In this work, the influence of TiO₂ particle size and structure on its photocatalytic effect in cement paste was investigated. The degradation of methylene blue solution was used as the parameter for evaluating the photocatalytic effect of micro-TiO2 (m-TiO₂), nano-TiO2 (n-TiO₂), and TiO₂ nanotube (TNT). Moreover, the effect of these three TiO₂ materials on the cement hydration products was characterized by X-ray diffraction (XRD) and thermgravimetric analysis (TG). According to the results, it can be found that all of the TiO₂ materials promoted the formation of hydration products, especially TNT. On the other hand, the m-TiO₂ exhibited a better photocatalytic effect compared to other materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.33-39
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• 2024

This study explores the utilization of common marine wastes, specifically seashells, such as oysters and cockles, as alternative fine aggregates in construction materials. The considered seashells were cleaned and pre-processed for use as a substitute for aggregate in mortar. Cement mortar specimens were prepared under different conditions, such as substitution ratios and the cleaning status of the seashells. The compressive strength of the mortars specimens was evaluated, and the solid and porous structures of each specimen were analyzed using microstructure analysis methods such as XRD, SEM, and micro-CT. The results confirmed that oyster and cockle seashells are composed of different calcium carbonate polymorphs, and their microstructural characteristics influence the mechanical properties of the cement mortar specimens.

• Journal of the Korean GEO-environmental Society
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• v.11 no.1
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• pp.53-59
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• 2010

In seawater deposition condition, the corrosion and chemical attack of grouts are similar to those of concrete structure. Used in domestic MSG (Micro Silica Grouting) mixtured large amounts of silicate materials containing as cement powder is $8,000cm^2/g$ of the specific surface area or more due to the high hydration activity and high-strength, high durability, and features, $C_3A$ content of less than 5% to meet the standards chemical attack of seawater was evaluated as a cement material. Therefore, in this paper, with excellent seawater attack resistant MSG in combination with rapid hardening mineral was used, those of seawater characteristics were evaluated experimentally. Typically, sodium-silicate minerals or rapid hardening cements are used in domestic. About the homogel specimens with combination of MSG and rapid hardening agents for compressive strength, weight and length change characteristics were evaluated experimentally, and so we could present the excellent seawater resistant grouts combination.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.177-183
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• 2015

In this study, the thermal conductivity, physical and mechanical properties of lightweight aggregate concretes with hollow micro sphere(HMS) are experimentally examined as a basic research for the development of structural insulation concrete. As the results of this experiment, in the case of concrete mixed with HMS, the value of slump has been reduced, so it is found that the dosage of superplasticizer should be increased. As the replacement ratio of HMS increases, it has shown that the compressive strength is somewhat decreased due to the low interfacial adhesion strength of HMS. But the thermal conductivity is found to be greatly improved with the replacement ratio of HMS increases, the thermal conductivity of HMS shows the lower value of 68% at lightweight aggregate concrete and 32% of normal concrete. Also it is found that the compressive strength is decreased and thermal conductivity is increased as the water-cement ratio increases. The most outstanding for insulation performance is observed when using 20% of HMS and 50% of water-cement ratio.