• 한국구조물진단유지관리공학회 논문집
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• 제24권2호
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• pp.86-93
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• 2020

숏크리트용 콘크리트는 일반적으로 1종 보통 포틀랜드시멘트(이하 OPC)를 100% 사용한 레미콘 제품에 현장에서 별도로 숏크리트용 급결제를 약 5% 혼합하는 방식으로 사용된다. 본 연구에서는 국내에서 사용률이 높은 시멘트 광물계 급결제(calcium aluminate)를 사용한 숏크리트용 결합재로서 기존 OPC에 슬래그분말(이하 SP), 석회석분말(이하 LSP)를 첨가하여 혼합시멘트를 사용할 때의 응결 및 압축강도, 페이스트 수화물 및 공극구조에 미치는 영향을 시험 및 분석하여 재령별 수화물의 생성량과 공극구조가 숏크리트의 모르타르 성능에 미치는 영향을 파악하였다. 향후 숏크리트용 결합재로서 최적화된 결합재를 제조하는데 활용할 수 있을 것으로 기대된다.

• 한국구조물진단유지관리공학회 논문집
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• 제16권4호
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• pp.122-129
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• 2012

이 연구에서는 시멘트계 광물로 제조된 그라우트의 사용에 의해 발생되는 환경문제인 pH의 증가와 중금속오염을 MC계와 킬레이트고분자를 이용하여 평가하고자 하였다. 그라우트 재료로 보통포틀랜드시멘트와 슬래그시멘트를 사용하였고 급결재로 칼슘알루미네이트계 급결성재료의 혼합물을 사용하였으며, 중금속과 pH의 발생을 방지하기 위해 증점제를 사용하였다. 측정결과, 킬레이트고분자를 사용할 경우에 그라우트에 의한 pH의 증가가 최소화되었으며 중금속($Cr^{6+}$)은 용출되지 않았다. 그 이외의 경우에는 pH의 증가와 중금속 용출이 뚜렷이 증가하였다. 또한, 재령에 따른 중금속 발생량은 용출시험 1일에서 전 용출량의 약 97% 이상이 용출되었고 이후는 추가 발생되지 않는 것으로 나타났다. 이 연구의 결과로부터 pH의 증가와 $Cr^{6+}$과 같은 중금속의 용출을 제어하기 위해서 BSC와 킬레이트고분자를 사용하는 것이 아주 유용함을 알 수 있었다.

• 콘크리트학회논문집
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• 제17권6호
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• pp.1011-1018
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• 2005

액상 숏크리트 급결제(알칼리 알루미네이트, 2종의 알카리프리)가 시멘트 계의 수화 특성에 미치는 영향을 조사했다. 새로운 알카리프리계 숏크리트용 급결제(AF2)를 적용할 경우 기존의 알칼리 알루미네이트 급결제에 비해 초결, 종결 시간은 단축되었고, 1일 압축 강도는 유사했다. 12시간 경과된 모르타르 시편의 압축 강도는 알칼리 급결제가 첨가된 시편이 가장 높았으나, 이후 최종 강도는 알칼리 급결제를 첨가한 시편이 가장 낮았다. 그러나 알카리프리가 첨가된 AF1, AE2 시편의 압축 강도는 28일까지 plain과 유사했다. XRD와 DSC 분석을 통해 알칼리계 급결제는 주로 수산화칼슘, 알카리프리계 급결제는 에트링자이트 결정 성장으로 응결이 촉진된 것을 확인했다.

• 한국안전학회지
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• 제27권4호
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• pp.68-75
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• 2012

The biogenic corrosion of mortars adopted in sewage repair by sulfuric acid-producing bacteria was considered in this paper. Calcium aluminate cement (CAC) was known to resist microbiologically-induced corrosion significantly better than portland and blended portland cement.In this study, CAC as well portland cement mortars were tested as main binder to evaluate the corrosion resistance by the chemical immersion test. Replacement ratios of CAC were changed as 0, 20, 40, 50, 60% of OPC binder and 0, 2, 4, 6% of EVA(Ethylene Vinyl Acetate) were also adopted to increase properties of CAC repair mortars in sewage application. Setting time, compressive strength, acid resistance and adhesive strength were measured for various experiments. As a results of the experiments, the proper formulation of repair mortars was found at 40% of CAC and 4% of EVA. Finally, the CAC mortars adopted in field sewer pipe and were demonstrated to superior in adhesion and workability.

• 한국세라믹학회지
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• 제23권3호
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• pp.27-34
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• 1986

The hydration of flyash-$Ca(OH)_2-CaSO_4$.$2H_2O$ system was stuedied with varing mixing ratio of flyahs $Ca(OH)_2$ and caSO4.2H2O The samples were steam-cured for 1-7 days at 9$0^{\circ}C$. The optimum mixing composition was flyash : Ca (OH)2=65:35 with 15% $CaSO_4$.42H_2O$ added which produced the hardened material having the best compressive strength (300kg/$cm^2$) Also the low specific gravity(1, 2) of the hardened paste suggests the possibility that it can be used as a light-weight building material. The added $CaSO_4$.42H_2O$ constituted calcium-sulfo-aluminate hydrates which activates the formation of C-S-H hy-drates. Both hydrates developed the strength of hardened paste. The amount of calcium-sulfo-aluminate hydrates was increased when the $CaSO_4$.42H_2O$ was added over 15% however the increased amount did not help the development of strength because of the individually grown calcium-sulfo-aluminate hydrates.

• Advances in environmental research
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• 제5권2호
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• pp.141-151
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• 2016

Large amounts of aluminum hydroxide ($Al(OH)_3$) exist in water purification sludge (WPS) because of the added aluminum coagulant in water treatment process. Notably, $Al(OH)_3$ is an amphoteric compound, can be dissolved in its basic condition using sodium hydroxide to form aluminate ions ($Al(OH)_4{^-}$). However, in a process in which pH is increasing, the humid acid can be dissolved easily from WPS and will inhibit the recovery and reuse of the dissolved aluminate ions. This study attempts to fix this problem by a novel approach to separate $Al(OH)_4{^-}$ ions using nanofiltration (NF) technology. Sludge impurity in a alkaline solution is retained by the NF membrane, such that the process recovers $Al(OH)_4{^-}$ ions, and significantly decreases the organic matter or heavy metal impurities in the permeate solution. The $Al(OH)_4{^-}$ ion is an alkaline substance. Experimental results confirm that a recovered coagulant of $Al(OH)_4{^-}$ ion can effectively remove kaolin particles from slightly acidic synthetic raw water.

• 한국세라믹학회지
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• 제34권7호
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• pp.693-698
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• 1997

The refractive index and dispersion in the (100-x)(0.6CaO.0.4Al2O3).xSiO2(x=0~30) glasses were investigated. As the amount of SiO2 increased, the refractive index decreased. The change of refractive index was attributed to the change of the molar refraction rather than the molar volume. When the amount of SiO2 was smaller than 20 mol%, the average electronic transition energy gaps(E0) and the electronic oscillator strengths(Ed) were about 10.9($\pm$0.1) nd 18($\pm$0.5)eV, respectively. However E0 and Ed of the glass (CAS30) with 30 mol% SiO2 increased to 12.63 and 19.89eV, respectively. The similar results was observed in the variation of Abbe Number. Abbe number of the glass in the range of 0~20 mol% SiO2 was about 46 and that of CAS30 increased to 60. The zero-material dispersion wavelength({{{{ lambda }}0) of pure calcium aluminate glass was 1.8 ${\mu}{\textrm}{m}$. As the amount of SiO2 increased, the zero-material dispersion wavelength shifted to a shorter wavelength. {{{{ lambda }}0 of CAS30 was 1.5 ${\mu}{\textrm}{m}$, that is currently using for the optical telecommunication system.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.387-392
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• 2018

Various technical approaches and concepts have been proposed to develop conductive super-hydrophobic (SH) surfaces. However, most of these approaches are not usable in practical applications because of insufficient adhesion and cost issues. Additionally, durability and uniformity issues are still in need of improvement. The goal of this research is to produce a large-area conductive SH surface with improved adhesion performance and uniformity. To this end, carbon nanotubes (CNT) with a high aspect ratio and elastomeric polymer were utilized as a conductive filler and matrix, respectively, to form a coating layer. Additionally, nanoscale silica particles were utilized for stable implementation of the conductive SH surface. To improve the adhesion properties between the SH coating layer and substrate, pretreatment of the substrate was conducted by utilizing both wet and dry etching processes to create specific organic functional groups on the substrate. Following pretreatment of the surface, a zirco-aluminate coupling agent was utilized to enhance adhesion properties between the substrate and the SH coating layer. Raman spectroscopy revealed that adhesion was greatly improved by the formation of a chemical bond between the substrate and the SH coating layer at an optimal coupling agent concentration. The developed conductive SH coating attained a high electromagnetic interference (EMI) shielding effectiveness, which is advantageous in self-cleaning EMI shielding applications.

• Journal of Periodontal and Implant Science
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• 제32권4호
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• pp.769-779
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• 2002

This present study was carried out to find the effects of calcium aluminate cement($CaO\;{\cdot}\;Al_2O_3$, CAC), which has been developed with bio-compatibility and mechanical properties, in biological environments. Two different particle sizes of CAC - 3.5${\mu}m$ vs. 212${\sim}$250${\mu}m$ which is recommended in periodontal bone grafting procedures-were filled in 8mm calvarial defect in Sprague-Dawley rat. The specimens were examined histologically, especially the bone-cement interface and the response of surrounding tissues. The results are as follows; 1. In the control group, inflammatory cells were observed at 2 weeks. At 8 weeks, periosteum and dura mater were continuously joined together in the defect areas. But in the center of defect area were filled up with the loose connective tissues. 2. In the experimental group l($212{\mu}m{\sim}250{\mu}m$ particle), immature bone was formed and outermost layer was surrounded by osteoid layer at 2 weeks. Osteoblasts were arranged between immature bone and osteoid layer. And, osteoid layer was remained until 8 weeks after surgery. 3. In the experimental group 2, periosteum and dura mater lost its continuity at 2 weeks. Scattering of CAC particles and infiltration of inflammatory cells were observed, which this findings deepened at 8 weeks. The result of this study shows that when calvarial defects in white rats are filled with calcium aluminate cement of 212${\sim}$250${\mu}m$, the materials are to be bio-compatible in growth and healing on surrounding tissues. When further researches are fulfilled, such as direct bone adhesion and bone regeneration ability, it's possible that CAC could be applied to various periodontology fields in the future.

• 한국구조물진단유지관리공학회 논문집
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• 제24권4호
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• pp.1-9
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• 2020

본 연구는 철근콘크리트 구조물의 염해 내구성 향상의 일환으로써, 보통 포틀랜드 시멘트에 실험체별 다른 비율의 칼슘 알루미네이트 시멘트와 합성 CA₂를 혼입하여 혼입 비율에 따른 염소이온 고정능력을 평가하였다. 침지 후 실험체의 물리·화학적 특성을 압축강도, 공극 구조, 수화물 분석으로 염소이온침투깊이를 EPMA를 통하여 고찰하였다. 클링커 조성에 CA가 34%미만일 경우 실험체의 조밀성이나 강도 발현 양상이 구조재료로서 사용 제한이 없을 것이라고 판단되었으며 CAC와 CA₂를 5:5비율로 혼입하여 실험체에 치환한 실험체가 CAC 혹은 CA₂만 치환한 실험체보다 염소이온 침투억제능력 과 AFm상 및 프리델 염 생성이 높은 것으로 확인할 수 있었다. 결과적으로, 시멘트 페이스트 대비 칼슘 알루미네이트 클링커 치환율이 증가함에 따라 일반적으로 염소이온 고정능력이 향상하였고, CA-CA₂비율에 따라 염소이온 고정 능력 및 염소이온 침투억제 능력에 차이가 있음을 확인할 수 있었다. 실험 범위 내에서 CA-CA₂비율이 39:60이며 시멘트 페이스트 대비 10% 치환한 실험체인 M 10 가 가장 우수한 것으로 나타났다.