• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.949-954
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• 2000

천연원료를 사용하여 $\alpha$-C$_2$S-C$_4$A$_3$S계 시멘트를 제조하였다. 클링커의 특성분석은 XRDd, FT-IR, SEM으로 행하였고 플라이애쉬 첨가에 따른 강도변화와 유동성 및 수화발열속도를 검토하였다. 그 결과 플라이애쉬 첨가시 유동성 증가 및 ettringite와 stratling계 수화물의 생성으로 초기 압축강도가 증진되었다. 플라이애쉬 5wt% 혼합시 7일 모르타르 압축강도가 224kgf/$ extrm{cm}^2$, 90일 강도는 440kgf/$\textrm{cm}^2$ 이였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.1040-1046
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• 2010

The main disadvantage of rapid setting concrete is the occurrence of cracking because of fast hydration reaction due to high thermal expansion and shrinkage. However, if the fly ash is used in concrete, it is possible to prevent cracking since the hydration heat can be decreased. Although Very-Early Strength-Latex Modified Concrete(VES-LMC) is an excellent material, occurrence of cracking has been reported because of high hydration heat. In the present study, new method which can apply the fly ash to the VES-LMC was developed. Research for the new method to improve the safety for the cracking was conducted. Safety was confirmed by reducing the shrinkage and hydration heat in the condition of overcoming the low early-age strength. Detailed conclusions are follows. Early-age compressive strength was decreased a little with increase of UFFA content. However, 28-d compressive strength was statistically insignificant regardless of UFFA contents. If the UFFA is replaced 15% to 20% of unit cement weight in concrete, maximum shrinkage can be reduced up to 43% to 47%. Usage of UFFA in VES-LMC guarantees the safety for cracking since it is very effective to control of early-age shrinkage.

• Environmental Engineering Research
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• v.25 no.2
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• pp.205-211
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• 2020

Chlorhexidine digluconate (CHD) in the aquatic environment causes irreversible change to microbes, making them resistant to biodegradation, which needs remediation other than biological process. Adsorption study was performed for the removal of CHD on fly ash (FA) as a function of pH and ionic strength. Experimental result has been validated by characterization using Scanning electron microscopy, Fourier Transform-Infrared Spectroscopy and Brunauer-Emmett-Teller. CHD adsorption with FA showed an increasing trend with an increase in pH. Variation in pH proved to be an influential parameter for the surface charge of adsorbent and the degree of ionization of the CHD molecules. The adsorption capacity of CHD decreased from 23.60 mg g-1 to 1.13 mg g-1, when ionic strength increased from to M. The adsorption isotherms were simulated well by the Freundlich isotherm model having R2 = 0.98. The Lagergren's model was incorporated to predict the system kinetics, while the mechanistic study was better explained by pseudo-second order for FA. On the basis of operational conditions and cost-effectiveness FA was found to be more economical as an adsorbent for the adsorption of CHD.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.47-54
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• 2017

Cement industry is typical carbon-emission industry. If the industrial by-products(granulated blast-furnace slag (GGBFS), fly ash, etc.) are used a large amount, it might be able to reduce cement consumption and mitigate carbon emissions. In this case, however, decrease of early strength is relatively large. Therefore, there is a limitation in increase of the amount of substitute. Considering these circumstances, it would be a good solution to reduce carbon emissions in cement industry to improve the performances of mixed cement through proper alkali-activation in Portland blended cement using GGBFS or fly ash. Therefore, this study prepared concrete in ready-mixed concrete manufacturing facilities with an addition of a binder which used 2.0% modified alkali sulfate activator after mixing Portland cement, GGBFS and fly ash in the ratio of 4:4:2 and assessed its basic properties. The results found the followings: The use of modified alkali-sulfate activator slightly reduced slump and shortened setting time. As a result, bleeding capacity decreased while early strength improved. In addition, there is no big difference in carbonation resistance. It appears that there should be continued experiments and analyses on the related long-term aged specimens.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.1
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• pp.66-74
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• 2021

The objective of this study is to evaluate the practical application potential and limitations of the modified fly ash(MFA) by vibration grinding as a partial replacement of ordinary portland cement(OPC). The test parameters investigated were the replacement level of fly ash(FA) and FA for OPC, varying from 10% to 40%, and curing temperatures of 5, 20, and 40℃. The various characteristics(including slump, air content, bleeding, setting time, compressive strength development, and hydration products) of MFA concrete were measured and then compared with those of the concrete with conventional FA. Test resul ts showed that the MFA prefers to FA in reducing the bl eeding of fresh concrete and enhancing the compressive strength gain at an early age. The compressive strength ratios between MFA and FA concrete specimens at an age of 1 day were 135%, 146%, and 111% at the curing temperatures of 5, 20, and 40℃, respectively. The corresponding ratios at an age of 28 days were approximately 110%, regardless of the curing temperatures. The X-ray diffraction analysis also revealed less calcium hydroxide products in MFA pastes than in FA pastes.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.297-310
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• 2010

This study represents basic research into the utilization of mixed ash (fly ash and bottom ash) from the ash pond of the Taean Thermal Power Plant as a construction material. We conducted physical and mechanical experiments on the mixed ash and examined its engineering characteristics in terms of its use as a material for road landfill and structure backfill. We evaluated the physical and chemical characteristics of the ash by performing tests to determine specific gravity, maximum and minimum density, liquid limit and plastic limit, grain size distribution, composition (by X-ray diffraction), and loss on ignition. We also evaluated the mechanical characteristics by testing for permeability, compaction, CBR, and tri-axial compression. The experiments on the mixed ash yielded a specific gravity of 2.18-2.20, dry density of $9.38-13.32\;kN/m^3$, modified CBR of 16.5%-21%, permeability coefficient of 1.32 to $1.89-10^{-4}cm/sec$, and drained friction angle of $36.43^{\circ}-41.39^{\circ}$. The physical and mechanical properties of the mixed ash do not meet the quality standards stipulated for road landfill and structure backfill materials. Mixed ash with a high content of fly ash failed to meet some of the quality standards. Therefore, in order to utilize the mixed ash as a material for road landfill and structure backfill, it is necessary to improve its properties by mixing with bottom ash.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.533-538
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• 2008

In order to enhance the adsorption capacity of $CO_2$, a commercial zeolite and coal fly ash were chemically modified with alkali cations (Li, K) and alkaline-earth cations (Ca, Mg). Adsorbents containing Ca and Mg showed slightly lower surface areas. The adsorption capacity at the ambient temperature was highest with Ca, then in order of Mg, Li, and K. On the contrary, regeneration efficiency of the adsorbents with Ca and Mg was relatively low, because Ca and Mg cations had stronger affinity of carbon dioxide. The affinity between cations and $CO_2$ molecule also may improve the selectivity in favor of $CO_2$ adsorption.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.307-316
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• 2019

Dam deformation should be strictly controlled for the construction of 300 m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.6
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• pp.475-482
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• 1999

The electrostatic precipitation characteristics of two kinds of fly ashes, one derived from a fluidized bed combustor(FBC), the other from a pulverized coal(PC) fired furnace, have been studied on a pilot plant. Experiments have been carried out to enhance the collection efficiency while changing the operating conditions for two kinds of coal ashes, respectively. It has been shown that collection efficiency is affected by many factors such as shape of the ashes, dust contents, humidity, and temperature, etc. Experimantal results showed that collection efficiency of the FBC ashes was higher than that of the PC fly ash in spite of the small size of the FBC ashes. The experimetal results have been applied to the collection efficiency equations to show that the modified Deutsch equation was well agreed with experiment results if modification parameter k was set to 0.6 for the fluidized bed fly ashes and to 0.43 for the pulverized coal fly ashes.

• Journal of the Korea Institute of Building Construction
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• v.16 no.4
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• pp.321-329
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• 2016

The use of ternary blended cement consisting of Portland cement, granulated blast-furnace slag (GGBFS) and fly ash has been on the rise to improve marine concrete structure's resistance to chloride attack. Therefore, this study attempted to investigate changes in chloride attack resistibility of concrete through NT Build 492-based chloride migration experiments and test of concrete's ability to resist chloride ion penetration under ASTM C 1202(KS F 2271) when 1.5-2.0% of alkali-sulfate activator (modified alkali sulfate type) was added to the ternary blended cement mixtures (40% ordinary Portland cement + 40% GGBFS + 20% fly ash). Then, the results found the followings: Even though the slump for the plain concrete slightly declined depending on the use of the alkali-sulfate activator, compressive strength from day 2 to day 7 improved by 17-42%. In addition, the coefficient from non-steady-state migration experiments for the plain concrete measured at day 28 decreased by 36-56% depending on the use of alkali-sulfate. Furthermore, total charge passed according to the test for electrical indication of concrete's ability to resist chloride ion penetration decreased by 33-62% at day 7 and by 31-48% at day 28. As confirmed in previous studies, reactivity in the GGBFS and fly ash improved because of alkali activation. As a result, concrete strength increased due to reduced total porosity.