• Journal of the Korean Ceramic Society
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• v.52 no.2
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• pp.140-145
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• 2015

In this study, we verified the relationship among the electrical conductivity, chemical durability, and structure of conductive vanadate glass in which $BO_3$ and $BO_4$ and $V^{4+}$ and $V^{5+}$ coexist simultaneously. We prepared samples of vanadium borophosphate glass with various compositions, given by $50V_2O_5-xB_2O_3-(50-x)P_2O_5$(x = 0 ~ 20 mol%) and $70V_2O_5-xB_2O_3-(70-x)P_2O_5$(x = 0 ~ 10 mol%), and analyzed the electrical conductivity, chemical durability, FT-IR spectroscopy, thermal properties, density, and molar volume. Substituting $B_2O_3$ for $P_2O_5$ was found to improve the electrical conductivity, chemical durability, and thermal properties. From these results, we can draw the following conclusions. First, the electrons shift from the electron rich $V^{4+}$ to the electron deficient $BO_3$ as the $B_2O_3$ content increases. Second, the improvement in chemical durability and thermal properties is attributed to an increase in cross-linked structures by changing from a $BO_3$ structure to a $BO_4$ structure.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.540-545
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• 2010

As the urban railroad durability period law has revised on march 19, 2009, the life cycle of urban railroad cars has lengthened to 40 years for the longest period. It seems to be attributed to the development of railroad car making technique along with their durability being longer thanks to the quality improvement of their materials and parts. As the stability of urban railroad cars is directly linked to the safety of passengers, safety should be considered first, and more precise examination is necessary for endurance extension. Hereupon, the rolling stocks with their durability near expiration should get precise diagnosis following the revised "RDG for urban railroad cars" This study aims to suggest a diagnosis method for the institute and the urban railroad operating body which enforce the revised diagnosis, through the case of Busan transportation corporation which firstly started the revised diagnosis after the durability related law has been revised.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.79-88
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• 2007

Concrete structures undergo degradation of durability performance and it generally propagates to the structural problems. Recently. a lot of materials for surface protection for concrete are developed, however, performance is not clearly improved due to the difficulties such as repair construction technique and quality of materials for repairing. In this study, liquid inorganic impregnant for concrete structures is developed and durability performance for impregnated concrete specimens is carried out. Furthermore, the performances of the concrete specimens with developed impregnant is also compared with those of the specimens with impregnant conventionally used. Additional CSH gel is formed through the reaction of calcium hydroxide ($Ca(OH)_2$) and impregnant with silicate. As a result of the reaction, impregnated concrete is evaluated to have more denser surface and resistance to deterioration. Finally it is experimentally verified that the concrete specimens with developed impregnant show better durability performance than normal specimens and those with conventional impregnant.

• Resources Recycling
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• v.24 no.1
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• pp.28-34
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• 2015

Generally, when using copper slag mixed into the concrete, due to higher weight of copper slag, a reduction in the compressive strength and durability of the hardened concrete to increased bleeding is caused. In this study, hence copper slag, a kind of by-product was used as an alternative to the fine aggregate, it was carried out in combination with the use of fly ash in eliminating disadvantage and recycling aspects. As a result of this study, the mixing of fly ash is decreased in the 50% of bleeding, 5% of drying shrinkage, 30% of carbonation test and improvement of 10% of compressive strength than that of copper slag only at most.

• Architectural research
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• v.7 no.1
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• pp.49-54
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• 2005

Conventional studies have focused on the reduction in the water-cement ratio, the use of various admixtures, etc., to ensure the durability of reinforced concrete structures against such deterioration factors as carbonation and chloride attack. However, improvement in the concrete quality alone is not considered sufficient or realistic for meeting the recent demand for a service life of over 100 years. This study intends to improve the durability of reinforced concrete structures by improvement in the reinforcing steel, which has remained untouched due to cost problems, through subtle adjustment of the steel components to keep the cost low. As a fundamental study on the performance of Cr-bearing rebars in steel reinforced concrete structures exposed to corrosive environments, The test specimens were made by installing 8 types of rebars in concretes with a chloride ion content of 0.3, 0.6, 1.2, 2.4 and $24kg/m^3$. Corrosion accelerated curing were then conducted with them. The corrosion resistance of Cr-bearing rebars was examined by measuring crack widths, half-cell potential, corrosion area and weight loss after 155 cycles of corrosion-accelerating curing. The results of the study showed that the corrosion resistance increased as the Cr content increased regardless of the content of chloride ions, and that the Cr-bearing rebars with a Cr content of 5% and 9% showed high corrosion resistance in concretes with a chloride ion content of 1.2 and $2.4kg/m^3$, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.429-432
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• 2008

Large area members such as foundation concrete of underground structures in power plants have an effect on structural stability and durability of the structure due to danger of crack occurrence and shrinkage crack that occur owing to the difference of temperature by heat of hydration between inside and outside of the members at initial age. And a construction for waterproofness is performed additionally to protect marine structures from osmosis of seawater because the structures adjoin below the surface of sea. So, if a rise of the heat of hydration, crack, and corrosion of bars are controled effectively using a composite such as fluosilicate salt in concrete production process of a initial construction, expenses are cut down and construction hours are reduced by securing durability through improvement of watertightness. The property tests of adiabatic temperature by hydration are carried out at initial age about standard concrete and test concrete using a fluosilicate salt composite to evaluate an effect on improvement of watertightness for concrete structures in this study. And the experiments such as a permeability test of hardened concrete, a water absorption test, a compression strength test and a elongation test are carried out and the results from these are described.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.5
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• pp.545-551
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• 2013

In this study, shot peening technique was employed with shot peening time for durability improvement and surface modification of copper alloy to investigate the electrochemical characteristics and microstructural variations. As a result of shot peening, roughness was distributed over the surface, and homogenization phenomenon was observed with increasing shot peening time due to the enhancement of coverage. The results revealed that hardness increased for shot peened specimens and particularly 3.5 mins of shot-peening time represented a hardness improvement of 52 %, showing similar electrochemical characteristics to that of the un-peened surface.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.219-224
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• 2017

This paper investigates equivalent stress and deformation happening at inner fiber structure when the tensile force acts on the specimen with arch type composed of carbon fiber. The countless many each fiber is applied on the unidirectional axis at CFRP and has the high specific strength and stiffness by comparing with iron. In this study, the distribution of stress due to radius is investigated at the structure of arch type composed with the optimum stacking angle of $60^{\circ}$. And the durability is seen to be lower as the radius increases at the same stacking angle. By applying the result of this study to the design of structure with arch type, it can be devoted to the safe design for the prevention of damage and the durabilty improvement. And it is possible to be grafted onto the convergence technique at the designed factor and show the esthetic sense.

• Advances in concrete construction
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• v.11 no.2
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• pp.173-181
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• 2021

The main objective of this work is to contribute to the valorization of plastic and glass waste in the improvement of concrete properties. Waste glass after grinding was used as a partial replacement of the cement with a percentage of 15%. The plastic waste was cut and introduced as fibers with 1% by the total volume of the mixture. Mechanical and durability tests were conducted for various mixtures of concrete as compressive and flexural strengths, water absorption, ultrasonic pulse velocity, and acid attack. Also, other in-depth analyses were performed on samples of each variant such as X-ray diffraction (XRD), thermogravimetric analysis (DSC-TGA), and scanning electron microscope (SEM). The results show that the addition of glass powder or plastic fibers or a combination of both in concrete improved in the compression and flexural strengths in the long term. The highest compressive strength was obtained in the mix which combines the two wastes about 26.72% of increase compared to the control concrete. The flexural strength increased in the mixture containing the glass powder. Therefore, the mixture with two wastes exhibits better resistance to aggressive sulfuric acid attack, and incorporating glass powder improves the ultrasonic pulse velocity.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.157-164
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• 2014

Ground granulated blast-furnace slag (GGBS) is a green construction material used to produce durable concrete. The secondary pozzolanic reactions can result in reduced pore connectivity; therefore, replacing partial amount of Portland cement (PC) with GGBS can significantly reduce the risk of sulfate attack, alkali-silica reactions and chloride penetration. However, it may also reduce the concrete resistance against carbonation. Due to the time consuming process of concrete carbonation, many researchers have used accelerated carbonation test to shorten the experimental time. However, there are always some uncertainties in the accelerated carbonation test results. Most importantly, the moisture content and moisture profile of the concrete before the carbonation test can significantly affect the test results. In this work, more than 200 samples with various water-cementitious material ratios and various replacement percentages of GGBS were cast. The compressive strength, electrical resistivity, chloride permeability and carbonation tests were conducted. The moisture loss and microstructure of concrete were studied. The partial replacement of PC with GGBS produced considerable improvement on various properties of concrete.