• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.299-306
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• 2017

In this research, it was examined chloride ion penetration resistance of slag-replaced concrete and cementless slag concrete considering marine environmental exposure conditions of splash zone, tidal zone and immersion zone. In the design strength of grade 24 MPa, the specimens were tested to determine their compressive strength, scanning electron microscopy images and chloride migration coefficient. Further, chloride ion penetration depth and carbonation depth of specimens exposed to marine environment were measured. Experimental results confirm that chloride migration coefficient of specimens tended to decrease with increasing the replacement ratio of ground granulated blast-furnace slag in accelerated laboratory test. In addition, the specimens exposed to the tidal zone were found to be the greatest chloride ion penetration depth compared to splash zone and immersion zone. On the other hand, the chloride ion penetration depth of the specimens exposed to splash zone tended to increase with increasing the replacement ratio of ground granulated blast-furnace slag in contrast with the results for the tidal zone and immersion zone.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.801-809
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• 2006

Epoxy resin has widely been used as adhesives and corrosion-resistant paints in the construction industry for many years, since it has desirable properties such as high adhesion and chemical resistance. Until now, in the production of conventional epoxy cement mortars, the use of any hardener has been considered indispensable for the hardening of the epoxy resin. However we have noticed the fact that even without any hardener, the hardening process of the epoxy resin can proceed by the action of hydroxides in cement mortars. As a result the disadvantages of the two-component mixing of the epoxy resin and hardener have been overcome. The purpose of this study is to evaluate the mechanical properties and durability of epoxy cement mortar without a hardener exposed at indoor and outdoor for one year. The epoxy cement mortars without and with a hardener were prepared with various polymer-cement ratios, and tested for weight change, flexural and compressive strengths, water absorption, carbonation depth and pore size distribution. Especially, the basic properties of the epoxy cement mortars without hardener are discussed in comparison with ones with the hardener. From the test results, it is concluded thai the epoxy cement mortars without a hardener exposed at indoor and outdoor for one year have higher strength and better durability than ones with the hardener within the polymer-cement ratios of 10 to 20%.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.375-381
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• 2008

Various problems such as durability degradation may happen when extra water is added to concrete. Because of these reasons, the change of water content is managed by using rapid evaluation method of unit water content such as electric capacity method, heat drying method making use of micro wave, unit capacity mass method among various methods. Especially, in Japan, guidance for the change of water content ($\pm$ 10, 15, 20 kg/$m^3$ etc.) were regulated and used. However, it is the real situation that the guidance which were regulated in South Korea evaluate suitability only considering production and measurement error under the circumstances which are not considering the degree of durability degradation. Therefore, this study tries to investigate the influence of addition of extra water in the concrete on the durability degradation of concrete when it was added by artificial manipulation or by management error. From the test results, a guideline of the contents of extra water for the quality control is suggested with the consideration of the degree of durability degradation and the probable error resulted from the addition of extra water. The contents of extra water for tests are set as 0, 15, 25, 35 kg/$m^3$. To examine the durability degradation of concrete, freezing and thawing, carbonation, chloride penetration and compressive strength are tested.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.311-320
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• 2011

Fly ash (FA), byproduct from power plant has been actively used as mineral admixture for concrete. However, since bottom ash (BA) is usually used for land reclaim or subbase material, more active reuse plan is needed. Pond ash (PA) obtained from reclaimed land is mixed with both FA and BA. In this study, 6 PA from different domestic power plant are prepared and 5 different replacement ratios (10%, 20%, 30%, 50%, and 70%) for fine aggregate substitutes are considered to evaluate engineering properties of PA as fine aggregate and durability performance of PA concrete. Tests for fine aggregate of PA for fineness modulus, density and absorption, soundness, chloride and toxicity content, and alkali aggregate reaction are performed. For PA concrete, durability tests for compressive strength, drying shrinkage, chloride penetration/diffusion, accelerated carbonation, and freezing/thawing are performed. Also, basic tests for fresh concrete like slump and air content are performed. Although PA has lower density and higher absorption, its potential as a replacement material for fine aggregate is promising. PA concrete shows a reasonable durability performance with higher strength with higher replacement ratio. Finally, best PA among 6 samples is selected through quantitative classification, and limitation of PA concrete application is understood based on the test results. Various tests for engineering properties of PA and PA concrete are discussed in this paper to evaluate its application to concrete structure.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.349-355
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• 2016

This study is about the reuse of bottom ash, which is released as a necessity in thermal power plant. In general, coal-ash are classified as fly-ash, bottom-ash, cinder-ash. Of these, a large amount of fly ash is being recycled as cement substitutes. While, recycling rates of bottom ash are the lowest due to its porosity and high absorption. In this study, the durability of the concrete using bottom ash as a concrete fine aggregate was evaluated. The using level of the bottom ash ranges to step-by-step from 0% to 30%. According to the result of the durability test, regardless of the presence of the bottom ash, freeze-thaw durability could be secured by air entrainment. In case of the resistance to chloride ions penetration, the length change, and the effects on heavy metals, the replacement of bottom ash as fine aggregate was not critical. Although carbonation penetration was higher as the replacement level of bottom ash increased, the experiment showed that it could be possible to use bottom ash as concrete fine aggregate with proper mix design.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.265-271
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• 2015

This study is intended to produce a PC (Precast Concrete) member without a steam curing process in developing the high early strength concrete satisfying the condition of 10MPa in compressive strength at the age of 6 hours, and is intended to ensure economic feasibility by increasing the turnover rate of concrete form. Hence, high early strength cement with high $C_3S$ content and the hardening accelerator of powder type accelerating the hydration of $C_3S$ was used. And the properties of concrete were evaluated according to the hardening accelerator mixing ratio (0, 1.2, 1.6, 2.0). No big difference was found from the tests of both slump and air content. When 1.6 % or higher amounts of the hardening accelerator were mixed, the compressive strength of 10MPa was achieved at the age of 6 hours. From the test results of autogenous (drying) shrinkage and plastic shrinkage, it can be seen that there was a difference according to hydration reaction rate due to the addition of the hardening accelerator. However, it was shown that no problem arose with crack and durability. And it was shown that resistance to freezing-thawing, carbonation, and penetration were excellent.

• Science of Emotion and Sensibility
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• v.24 no.4
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• pp.149-156
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• 2021

The mechanical properties of a woven fabric made of SiC (silicon carbide) fibers were determined in this study using the KES-FB system. The woven fabric is used in high heat settings above 1500℃. Composite spun yarns were used to create SiC fibers. By analyzing the wearing properties, we studied the prospect of using the textiles as fire-retardant work clothes. Mechanical properties determine the wearing attributes. Therefore, the tensile linearity (LT), tensile resilience (RT), and shear stiffness (G) values of the fabric varied according to the yarn type (filament or spun yarn). The thickness, weight per square meter, and density of the fabric were found to have an effect on the shear hysteresis (2HG) and compression resilience (RC) values. In terms of wearable clothing qualities, the fabric qualities of the SiC composite yarn demonstrated the highest ratio of compressive energy to thickness (WC/T), which indicates bulkiness. The fabric manufactured from SiC composite yarns passed the KFI criteria for carbonation length and cumulative flame time in the flame-retardant test. Therefore, we discovered that the material can be used as a fire-resistant work cloth.