• Title/Summary/Keyword: calcium aluminate

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Optimization of $Nd^{3+}$ ion co-doping in $CaAl_2O_4:\;Eu^{2+}$ blue phosphor ($CaAl_2O_4:Eu^{2+}$ 청색(靑色) 형광체(螢光體)의 $Nd^{3+}$ 도핑 최적화(最適化)에 관한 연구(硏究))

  • Bartwal, Kunwar Singh;Ryu, Ho-Jin
    • Resources Recycling
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    • v.16 no.5
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    • pp.46-50
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    • 2007
  • Blue phosphor calcium aluminate, $CaAl_2O_4:Eu^{2+}$ co-doped with $Nd^{3+}$ was prepared by solid state synthesis method. Phosphor materials with 1 mol% $Eu^{2+}$ and varying compositions of $Nd^{3+}$ show high brightness and long persistent luminescence. The synthesized phosphor materials were investigated by powder x-ray diffraction (XRD), SEM, TEM, photoluminescence excitation and emission studies. Broad band UV excited luminescence of the $CaAl_2O_4:Eu^{2+}:Nd^{3+}$ was observed in the blue region (${\lambda}_{max}=440\;nm$) due to transitions from the $4f^65d^1$ to the $4f^7$ configuration of the $Eu^{2+}$ ion. $Nd^{3+}$ ion doping in the phosphor results in long afterglow phosphorescence when the excitation light is cut off.

Economic Analysis with Development of Rapid Setting Alumina-based Binder for Road Repair (알루미나계열 속경성 도로 보수재료 개발에 따른 경제성 분석)

  • Yang, Hee-Jun;Yang, Min-Jae;Hong, Sung-In;Ann, Ki-Yong
    • Journal of the Korea Concrete Institute
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    • v.29 no.1
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    • pp.3-10
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    • 2017
  • In case of Korea highways, about 60% of highways are paved by concrete and more than 50% of them were repaired due to reduction in required performance such as damage in pave or joint and delamination of cover pavement. However, repairing old material in such structure generally costs a lot of money and induces difficulty in maintenance. Thus, enhanced material for ensuring economic efficiency should be developed. The present study designed concrete mixtures with 3 levels of replacement using OPC (0, 10, 20%) in calcium aluminate cement and to evaluate material performance for load pavement, experimental works for setting time, compressive strength and flexural strength were carried out on those materials. As a result, 20% replacement for OPC was determined as an optimized material in terms of required physical performance and its unit price. Moreover, to determine cost in load pavement economy analysis using a program (CA4PRS) was conducted with widely used paving materials. Result showed that application for 20% replacement for OPC was the most efficient in economical aspect, arising from 4.052 and 1.577 billion won for total construction and user cost, respectively.

Characteristics of Manufacturing for Special Cement Using High Chlorine by-product (고염소 부산물을 이용한 특수시멘트 제조 특성)

  • Moon, Kiyeon;Cho, Jinsang;Choi, Moonkwan;Cho, Kyehong
    • Resources Recycling
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    • v.30 no.6
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    • pp.68-75
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    • 2021
  • This study aims to investigate the manufacturing process of calcium chloride-based special cement, i.e., CCA (calcium chloro aluminate, C11A7·CaCl2), which uses limestone, by using one type of random industrial by-product, domestic coal ash, cement kiln dust. The manufacturing process of was examined in detail, and the results suggested that the amount of CCA synthesized increased with an increase in the firing temperature. The manufacturing process of CCA was investigated at 1200℃, which was determined as the optimum firing temperature. The results showed that in general, the amount of CCA synthesized tended to increase with an increase in the firing time; however, the clinker melted when the firing time was more than 30 min, thereby suggesting that a firing time of less than 20 min would be suitable for the clinkering process. The optimal firing conditions for manufacturing CCA were obtained as follows: heating rate of 10 ℃/min, firing temperature of 1200 ℃, and holding time of 20 min. The results also suggest that manufacturing CCA will be easier when high chlorine-containing cement kiln dust is used.

Influence of Alkali Activator Type and Amount of Addition on CO2 Uptake of GGBFS Geopolymer Pastes Containing Zeolite (알칼리계 활성화제의 종류 및 첨가량이 고로슬래그-제올라이트 지오폴리머 페이스트의 탄소포집에 미치는 영향에 관한 연구)

  • Jang-Hyun Park;Hyo-Min Kim
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.2
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    • pp.112-119
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    • 2023
  • In this study, the variations in CO2 uptake according to the type and amount of alkali-based activator (Ca(OH)2, CSA) of geopolymer paste were evaluated. As the amount of activator added to the geopolymer paste increased, the fluidity of the paste is decreased and the compressive strength increased. According to the type of activator, it was confirmed that the addition of Ca(OH)2 had a greater effect on improving the compressive strength than CSA. As a result of changes in chemical properties according to carbonation curing, the amount of C-S-H and C-A-S-H gels produced before carbonation increased as the amount of activator increased, and amount of CaCO3 produced after carbonation increased. The reactivity of the blast furnace slag and zeolite increased due to the addition of the activator, and the reactivity tended to increase as the amount of addition increased. As a result of CO2 uptake, 10.3 wt% when Ca(OH)2 10 % was added and 8.77 wt% when CSA 10 % was added was confirmed. It increased by 421 % and 388 % respectively, compared to the case where no activator was added.

Tension-Stiffening and Cracking Behavior of 100 MPa Shrinkage-Compensated Ultra High-Strength Strain-Hardening Cement Composite (UHS-SHCC) Ties (100 MPa급 수축보상 초고강도 변형경화형 시멘트 복합체를 사용한 인장부재의 인장강성 및 균열특성)

  • Song, Young-Jae;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.25 no.4
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    • pp.371-379
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    • 2013
  • This paper investigates the cracking and tension-stiffening behavior of 100 MPa shrinkage-compensated strain-hardening cement composite (SHCC) and conventional concrete tie elements in monotonic and cyclic tension. Strain and surface crack formation of tension ties were monitored with two strain displacement transducers and a photo microscope with a lens of magnification 50 times. Three different cement composites such as conventional concrete, shrinkage-compensated SHCC, and normal SHCC were used in the tie specimens to investigate the influence of the cement composite type on the tension stiffening and cracking behavior. Test results indicated that initial shrinkage of the ultra high-strength cement composites is greatly reduced as the 10% replacement of cement by the shrinkage-compensating admixture based on calcium sulfo-aluminate (CSA). The test results on the SHCC tension ties showed that the first cracking load decreases proportionally to the initial shrinkage strain. Reinforced ultra high-strength SHCC ties with the initial shrinkage compensation exhibited improved tension stiffening and smaller crack spacings, i.e. the reduction in crack width. Cyclic loading did not have a significant effect on tension stiffening and cracking behavior of tension ties with normal concrete and SHCC materials.

Ettringite/Thaumasite Formation, Stability and Their Effect on Deterioration of Concrete (에트린자이트/사우마사이트의 형성 및 안정도와 콘크리트 성능저하에 미치는 영향)

  • 이효민;황진연
    • Journal of the Mineralogical Society of Korea
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    • v.16 no.1
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    • pp.75-90
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    • 2003
  • Ettringite and thaumasite were observed in some concrete. The morphology and occurrence of these minerals were closely examined by performing SEM/EDAX analyses. We also experimentally induced the concrete deterioration using $Na_2SO_4$ solution with application of various environmental conditions. The stability of these minerals and deterioration characteristics under applied experimental conditions were determined. Abundant ettringite formed by“through solution reaction”occurred in many open spaces, and some microscopic ettringite formed by "tophochemical replacement" of calcium aluminate also occurred in cement paste. Severe cracking of cement paste causing premature deterioration was often associated with ettringite location. Under specific condition, ettringite was transformed to thaumasite, tricthloroaluminate, or decomposed. Thaumasite occurred with association of ettrinsite in concrete containing carbonate aggregate being subject to dedolomitization or in some concrete being subject to carbonation. Thaumasite appears to be formed under the similar condition to the general ettringite forming condition, but it formed solid solution with ettringite by substituting pre-existing ettringite. Ettringite can also be transformed to trichloroaluminate in the presence of abundant chlorides, but trichloroaluminate changed back to ettringite in late sulfate attack. It is considered that the substitution reaction direction solely depend on the concentration of chloride and sulfate ion.

The Influence of PbO Content on the Crystallisation Characteristics and Dielectric Properties of Glass Frit for LTCC (LTCC용 Glass Frit의 결정화 특성 및 유전 특성에 대한 PbO 함량의 영향)

  • Park, Jeong-Hyun;Kim, Yong-Nam;Song, Kyu-Ho;Yoo, Jae-Young
    • Journal of the Korean Ceramic Society
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    • v.39 no.5
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    • pp.438-445
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    • 2002
  • In this study, the glass frit of $PbO-TiO-2-SiO_2-BaO-ZnO-Al_2O-3-CaO-B_2O_3-Bi_2O_3-MgO$ system was manufactured. The glass was melted at $1,400{\circ}C$, quenched and attrition-milled. The glass frit powder was pressed and fired for 2h at the range of $750~1,000{\circ}C$. The crystallization of glass frit began at about $750{\circ}$ and at low temperature, the main crystal phases were hexagonal celsian($BaAl_2Si_2O_8$) and alumina. As the firing temperature increased, the crystal phases of monoclinic celsian, zinc aluminate, zinc silicate, calcium titanium silicate and titania appeared. And the increase of firing temperature led to transformation of hexagonal celsian to monoclinic. The only glass frit containing 15wt% PbO had the crystal phase of solid solution of $PbTiO_3-CaTiO_3$. At the frequency of 1 MHz, the dielectric constant of glass frit crystallized was in the range of 11~16 and the dielectric loss less than 0.020. But the glass frit containing 15wt% PbO had the dielectric constant of 17~26 and loss of 0.010~0.015 because of crystal phase of solid solution of $PbTiO_3-CaTiO_3$.

A Study on Properties of High Blaine Cement for Shotcrete (숏크리트용 고분말도 시멘트의 특성)

  • Kim, Jae-Young;Kim, Teuk-Jun;Lee, Min-Suk;Ryoo, Dong-Woo
    • Journal of the Korea Concrete Institute
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    • v.22 no.5
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    • pp.633-640
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    • 2010
  • This study was performed to get basic information about properties of high blaine cement for shotcrete use. Particle size distribution, setting time and compressive strength test, analysis like as SEM, DSC thermal analysis, XRD was carried out to investigate principle properties of high blaine cement. Setting time of high blaine cement was shorter and compressive strength was higher than those of ordinary portland cement (OPC). Results of analysis showed early hydration products of high blaine cement is smaller and spread widely due to increased specific surface. From the SEM observation and analysis of DSC and XRD results, it was seen that the aluminates accelerators promoted calcium aluminium hydrates while the alkali free accelerators increased ettringite and monosulfates formation. Strength and setting time measurement of cement paste with aluminate accelerator is more effective than the alkali free accelerator in reducing the setting time and increasing early strength while alkali free accelerator is more effective in increasing the strength after 7 days.

Evaluation for Applicability as the Inorganic Binder with Rapid Setting Property for Construction Material of LFS Produced from Various Manufacturing Process (다양한 철강제조공정에서 부산되는 전기로 환원슬래그의 급경성 무기결합재로의 적용성 검토)

  • Kim, Jin-Man;Choi, Sun-Mi;Kim, Ji-Ho
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.7 no.2
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    • pp.70-77
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    • 2012
  • The Ladle Furnace Slag, about 20% of the electric arc furnace slag, has high content of free CaO and free MgO, which generates the expansion collapse by hydration reaction. Although many researchers have been endeavoring to recycle the EAF reducing slag in construction fields, there is not found the effective recycling method up to now. However, the LFS(Ladle Furnace Slag) contains mineral composition of the system of calcium aluminate with high-reactivity. Therefore, it is possible to developed the quick setting property and the high strength at the early age by the rapid cooling. This study aimed to check the reactive minerals and predict the reactivity with water on the LFS discharged from different steel product plants. The test results show that many types of LFS has hydration reactivity and can use in construction field as a inorganic binder with the rapid setting property.

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Engineering Performance and Applicability of Eco-Friendly Concrete for Artificial Reefs Using Electric Arc Furnace Slags (전기로 슬래그를 활용한 인공리프용 친환경콘크리트의 공학적 성능 및 적용성)

  • Jo, Young-Jin;Choi, Se-Hyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.3
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    • pp.533-544
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    • 2015
  • Unlike the concrete structure built on land, that exposed to the marine environment is greatly degraded in durability due to the exposure to not only the physical action caused by sea wind, tide, and wave, but also the harsh conditions, including the chemical erosion and freeze-thaw which result from $SO_4{^{2-}}$, $Cl^-$ and $Mg^{2+}$ ions in seawater. In the process of the large scaled construction of submerged concrete structures, of course environmental hazardous substance, such as alkaline (pH) and heavy metals, may be leached. Thus, this issue needs to be adequately reviewed and studied. Therefore, this study attempted to develop a CSA (Calcium Sulfo Aluminate) activator using electric arc furnace reducing slags, as well as the eco-friendly concrete for artificial reefs using electric arc furnace oxidizing slag as aggregate for concrete. The strength properties of the eco-friendly concrete exposed to the marine environment were lower than those of the normal concrete by curing 28 days. This suggest that additional studies are needed to improve the early strength of the eco-friendly concrete. With respect to seawater resistance of the eco-friendly concrete, the average strength loss against 1 year of curing days reached 8-9%. the eco-friendly concrete using high volume of ground granulated blast furnace slags and high specific gravity of electronic arc furnace oxidizing slag demonstrated the sufficient usability as a freeze-thaw resistant material. With respect to heavy metal leaching properties of the eco-friendly concrete, heavy metal substances were immobilized by chemical bonding in the curing process through the hydration of concrete. Thus, heavy metal substances were neither identified at or below environmental hazard criteria nor detected, suggesting that the eco-friendly concrete is safe in terms of leaching of hazardous substances.