• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.695-702
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• 2005

It is known that latex-modified concretes were increased their durability and permeability by added latex. The purpose of this study was to analysis the air void systems in latex-modified concretes using a reasonable and objective image analysis method with main experimental variables such as water-cement ratios, latex contents(0%, 15%) and cement types(ordinary portland cement, high-early strength cement and very-early strength cement). The results are analyzed spacing factor, air volume after hardened, air distribution and structure. Also, air void systems and permeability of latex-modified concretes were compared with correlation. The results are as follows; The same w/c ratio LMC showed better air entraining effect than OPC with AE water reducer. The VES-LMC showed that the number of entrained air below $100{\mu}m$ increased more than four times. In the HES-LMC, micro entraining air having range from 50 to $500{\mu}m$ increased above 7 times without antifoamer. Though spacing factor was measured low, latex-modified concretes were showed that permeability was good. It is considered that air void system does not have an effect on the property of latex-modified concretes but latex film is more influenced in the their durability.

• Magazine of the Korea Concrete Institute
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• v.6 no.2
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• pp.97-107
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• 1994

The objective of this study is to develop polymer-impregnated concrete(PIC), which is a newly developed composite material made by impregnating polymer impregnanls into hardened normal concrete, and to develop analytical techniques for its proper applications. Crystalline methyl methacrylate(MMA) is chosen as a monomer of polymer impregnants. The corrlpositions of polymer impregnants and producing processes are developed by analyzing the effects of penetration, polymerization, thermal safety, and strengthening characteristics. On t he basis of experimental results of this study, various strength characteristics and stress strain constitutive relations are formulated in terms of the compressive strength of normal concrete and the polymer loadings, which can be applied for analysis and design of PIC members. In order to provide a model for fracture analysis of flexural members, fracture toughness, fracture energy, critical crack width, and tension softening relations near crack tip are also formulated in terms of member depth, initial notch depth, and the flexural strength of normal concrete. The structural analysis procedure and the finite element computer program developed in the study are applicable to evaluate elastic behavior, ultimate strength, and tension softening behavior of MMA type PIC structural members subject to various loading conditions. The accuracy and effectiveness of the developed computer program is examined by comparing the anal ytical results with the experimental results. Therefore, it is concluded that the developed structural analysis procedure and the finite element computer program are applicable to analysis and design of in-situ and precast PIC structural members.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.131-139
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• 1994

The min aim of thls study was to evaluate the effect of particle slze of the fly ash as a cement additive. Experimental work was carried out with three different sizes of fly ash. 18.58, 8.95 and 4.02{$mu}m$ in average radius. Namely, the effect of particle size variation of fly ash on the physical properties of cement paste was investigated. The jluidity was decreased with increasing the addition of fly ash to cement paste regardless of the particle size variation. The decrement of the fluidity of the pulverized fly ash was higher than that of the spherical fly ash. On the other hand, the pozzolan reactivity increased with lowering particle size. In the case of specimens with 5% up to 10% addition of fly ash having a particle size of 4.02{$mu}m$. the compressive strength was increased as compared with the plain specimens before curing for 28 days and showed higher value above 800kg /$cm^2$ when cured for 60 days.This increased compressive strength was ascribed to both the closer packlng of fine particles and the pozzolan reactivity of fly ash. These results were comfirmed by measuring both the porosity of the specimens and Ca(OH ), contents remained in specimens. This work showed that could be effectively ut~lized as a blending material without any de crease in the strength of early hydration stage if we can control the particle size of fly ashes by sizing or pulverizing.

• Journal of Conservation Science
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• v.25 no.4
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• pp.421-430
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• 2009

This research was carried out focusing on the urgent treatment and related studies for paint scribbling on Samjeondobi Monument (Historic Sites No. 101) in 2007. Before the preliminary test, the paint lacquer used on the surface of Samjeondobi Monument was analyzed. The paint lacquer turned out to be the paint lacquer spray composed of $Pb_3O_4$ used for the red pigment in the market. It was proved that the poultice used with the organic solvent was the best way to remove the paint pollutants following the preliminary test for the removal of paint pollutants which was performed with various removal methods by the laser, etc. However, the removing the paint pollutants was found in difficulty in contrast to the preliminary tests because the paint on the spot was hardened so rapidly over time that there was difference from the situation of the laboratory. For that problem, the poultice method with ethylene dichloride of main component from Remover (goods in the market) was the most efficient, therefore the pollutants were removed with the solution of alkyds resin and nitrocellulose and the rest part was removed by the $Laponite^{(R)}$ RD.

• Korean Journal of Food Science and Technology
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• v.49 no.1
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• pp.85-89
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• 2017

This study was conducted to prevent hardened texture in retorted frozen seafoods such as small octopus, squid, and top shell by adding sorbitol; the strength of mechanical hardness and other qualities were measured. The hardness of the 3 kinds of seafood pretreated with 2-4% (w/w) sorbitol solution decreased by 9-36% compared to the control. The hardness of retorted frozen octopus, squid, and top shell treated with sorbitol solution upon freezing significantly decreased to 1670, 1015, and $521g_f/cm^2$ compared to levels in untreated food of 1841, 1291, and $815g_f/cm^2$ (p<0.05), respectively. Yields based on weight in retorted seafood treated with sorbitol were increased by 2-5% compared to untreated samples. Additionally, the overall preference of texture was 0.4 points higher than that of control samples in descriptive sensory evaluation (p<0.05). The tissue softening of pretreated seafood was based on decreased dewatering due to the formation of small ice crystals during freezing as a result of sorbitol treatment.

• Horticultural Science & Technology
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• v.19 no.3
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• pp.315-319
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• 2001

The study was carried out to develop a simple and efficient system to regenerate plants from cotyledon and hypocotyl tissues of Chinese cabbage (Brassica campestris L. ssp. pekinensis cv Seoul). Among the various combinations of naphthalene acetic acid (NAA) and 6-benzyladenine (BA) tested, the best shoot induction medium for cotyledon, with 2.67 shoots per explants, contained $2.0mg{\cdot}L^{-1}$ NAA, $1.0mg{\cdot}L^{-1}$ BA and $16.7mg{\cdot}L^{-1}$ $AgNO_3$. The shoot induction medium with $1.0mg{\cdot}L^{-1}$ NAA, $5.0mg{\cdot}L^{-1}$ BA and $16.7mg{\cdot}L^{-1}$ $AgNO_3$, was best for shoot induction from hypocotyl explants, with 1.87 shoots per explants. After shoot induction, regenerated shoots were excised and rooted on rooting medium. Rooted plantlets were then hardened in the high humidity growth chamber and transplanted to pots, and then grown in the greenhouse. Regenerated plants appeared phenotypically normal and there were no changes in chromosome number.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.811-823
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• 2019

Slip form method is applied to many cases of a shaft these days because it is safer, more economical and faster than cast-in-place method. Slip-up height of the method is approximately 2.5 to 4.0 m/day. If the temperature of concrete is outside the range of 10 to 30℃, the effects of changes in strength or elastic characteristics are significant. Therefore, it is difficult for slip-up speed to be higher than 3 m/day during winter construction. In addition, concrete has heat caused by hydration, which causes temperature cracking of hardened concrete. Therefore, temperature control of concrete curing is necessary for the continuous slip-up of slip form. In this study, the rebound hardness, time of ultrasonic waves propagation, heat of hydration, and external temperature are measured by developing heating panels and test devices for the continuous slip-up. Based on this, heating slip form is manufactured; this was applied to "Kimpo sites" and "Sinwol sites". The compared slip-up speed samples were 1.9 m/day or 0.200 m/hr on average at Gimpo sites (08:00~17:30) and 2.0 m/day or 0.210 m/hr at Sinwol sites.

• Resources Recycling
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• v.19 no.5
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• pp.50-57
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• 2010

Ternary blended concrete(TBC), which contains both fly ash and granulated blast furnace slag, has an initial cost effective and is environment friendly. Furthermore, it has a lot of technical advantages such as the improvement of long term compressive strength, high workability, and the reduction of hydration heat. However, as the use and study on the performance of ternary blended concrete is limited, it is low short term compressive strength. This study was performed to evaluate the characteristics which are a long and short term compressive strengths, permeability and chemical attacks resistance of hardened high early concrete containing slag powder and fly-ash using high early strength cement(HE-TBC). Replacement rate of FA is fixed on 10% and replacement rate of slag powder are 0%, 10%, 20% and 30%. The test results showed that compressive and flexural strength of HE-TBC increased as the slag contents increased from 0% to 30% at the short term of curing. The permeability resistance of HE-TBC(fly ash 10%, blast 30%) was extremely good at the short and long terms. However, high early strength ternary blended concrete had weak on carbonation of chemical attack.

• Conservation Science in Museum
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• v.17
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• pp.101-116
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• 2016

Ceramic cultural artifacts restored with gypsum-based materials are prone to decay over time due to gypsum's natural absorption and release of atmospheric moisture, often leading to distortion and peeling of painted layers. This study proposes a new restoration material which utilizes extra hard stone, significantly superior in strength to regular gypsum. In order to enhance its physical properties and make it suitable for restoration of ceramics, extra hard stone is mixed with metakaolin. This mixture far surpasses regular gypsum in compressive strength(119MPa vs. 26MPa) while also maintaining a much lower wear rate(0.88% vs. 2.53%). Furthermore, the water absorption rate(2.9%) of the mixed material is over five times lower than that of regular gypsum(17.2%). When examined using a SEM(Scanning Electron Microscope), this mixture also proved superior to extra hard stone in terms of hardened density. The addition of metakaolin increases the mixture's strength and water resistance over that of extra hard stone and also improves its surface density, making it ideal for the restoration of ceramics. It has already been used to repair ceramic objects in the Museum's collection: Clay basin(sinan 18892), Buncheong ware bottle with incised peony design(jubsu 2034), Buncheong ware bowl with chrysanthemum(jubsu 1730). Results thus far have shown the mixture to be easy to inject and layer as well as harden into an even surface, which allows for smooth application of paint for color matching.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.631-637
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• 2006

In this study, fundamental properties such as fresh and hardened performance of concrete mix(specification : 25-24-18) added fluorine-silicate hybrid based crack reducing agent(FS) were measured. Addition of FS ranged from 0.5% to 2.0% at intervals 0.5% based on cement weight. Adequate dosage(0.5%) of FS derived from basic properties measurements applied and compared resistance for shrinkage crack. The permeability of concrete in the absence(24-S-0.0) and presence(24-S-0.5) of evaluated at a mock-up sized concrete. Concrete added FS improved resistance for shrinkage crack and consequently crack number, length and area decreased to $50{\sim}74.4%$ compared non-added. As well, by the addition of FS, the resistance for permeability and penetration depth to concrete surface region increased 67% and 40%, respectively. Therefore it was confirmed that shrinkage crack resistance and permeability of concrete could be improved by the addition of FS.