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장복기 한국세라믹학회 1988 한국세라믹학회지 Vol.25 No.5
Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.
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장복기,윤정한,Chang, Pok-Kie,Yoon, Chung-Han 한국세라믹학회 2002 한국세라믹학회지 Vol.39 No.5
This paper addresses the hydrothermal reactivity of blast furnace slag and fly ash with lime, respectively. The test conditions were CaO-to-$SiO_2$ ratio (C/S), autoclaving temperature ($140{\circ}C$ and $180{\circ}C$) and time (20 to 60h). The study was carried out in terms of the hydrothermal reactivity between $SiO_2$ contained in each hydraulic material and (pure) lime and the compressive strength of autoclaved specimens. Porosity measurement and the XRD analysis were also made in order to ascertain the hydraulicity of the siliceous materials. Compressive strength of the specimens was interpreted in terms of porosity and the reactivity of CaO and $SiO_2$. And the XRD analysis showed the C/S change of the hydrates in the course of autoclaving process. $SiO_2$ in the blast furnace slag was more reactive with CaO than that in the fly ash and consequently the blast furnace slag specimens resulted in much higher compressive strength. A maximum compressive strength of $807kg/cm^2$ was obtained for the blast furnace slag at the autoclaving condition of $180{\circ}C$ and 40 h, while only $397kg/cm^2$ was maximally to achieve with fly ash. 고로슬래그와 플라이 애쉬의 석회 반응성을 수열조건 하에서 각각 고찰하였다. 수열반응 조건은 CaO-$SiO_2$ 비(C/S), 수열온도($140{\circ}C$와 $180{\circ}C$)및 반응시간(20~60시간)이었다. 수열반응성은 각 수경성 재료에 함유된 $SiO_2$와 (순수)석회 사이의 반응률 및 반응 시편의 압축강도를 측정하여 조사하였다. 그리고 본 반응성 고찰을 위하여 기공률 측정 및 XRD 분석도 수행하였다. 압축강도 물성은 시편의 기공률 및 CaO-$SiO_2$ 반응성과 연계하여 고찰하였으며, XRD 분석으로 수열반응 중 C/S가 변화함을 확인할 수 있었다. 고로슬래그 중의 $SiO_2$는 플라이 애쉬에 함유된 $SiO_2$ 보다 석회반응성이 우수하여 전자의 경우 시편은 훨씬 높은 강도를 나타내었다. 수열반응 온도 $180{\circ}C$ 및 40시간의 조건에서 고로슬래그는 최고 강도 $807kg/cm^2$을 나타냈으며, 플라이 애쉬의 경우 최고 강도는 $397kg/cm^2$ 이었다.
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장복기,백용혁,문종하,이종호 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.6
The mechanical properties of Al2O3-ZrO2 composites fabricated by RBAO(reaction bonded aluminium oxide) process were investigated. As the amount of ZrO2 increased the sinstered density of Al2O3-ZrO2 composites decreased slightly, but wear resistance was enhanced. Bending strength of Al2O3-ZrO2 composites increased in proportion to the amount of al in case of a fixed ZrO2 content. When the amount of Al was fixed bending strength reached its maximum value at 25 wt% ZrO2. The fracture toughness(K1c) increased with increasing content of ZrO2, but decreased with increasing Al amount. On the other hand, the fracture mode of Al2O3-ZrO2 composites was the mixed mode of inter-and transgranular fracture.
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장복기,김윤주 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.7
포틀랜드 시멘트 양(중량)을 플라이 애쉬로 50 wt%까지 치환한 페이스트, 모르터 내지 콘크리트 시편을 만들어 플라이 애쉬가 모르터/콘크리트의 온도, 자유석회량 및 강도 등에 미치는 영향을 조사하였다. 페이스트의 수화열을 측정하여 환산식에 따라 일반 포틀랜드 시멘트 콘크리트의 경우와 비교할 때, 플라이 애쉬를 50 wt% 함유한 콘크리트의 양생 7일 온도(상승)는 약 45% 저하되었다. 전자의 경우 온도 상승은 33.4$^{\circ}C$이며 후자의 경우는 18.7$^{\circ}C$였다. 한편 철근 콘크리트의 제조에 사용되는 시멘트의 플라이 애쉬 함유량은 철근부식의 방지를 위하여 30 wt%를 초과하지 않는 게 바람직하다. 플라이 애쉬를 혼합한 콘크리트의 강도가 순수 포틀랜드 시멘트 콘크리트의 강도보다 양호하기 위해서는 양생기간이 28일 이상 되어야 한다. 그리고 플라이 애쉬 50 wt%를 함유한 시멘트를 가지고도 360 kg/$\textrm{cm}^2$ 이상의 28일 강도를 얻을 수 있었다. Cement paste, mortar or concrete specimens, substituting the content of Portland cement with fly ash up to 50 wt%, were prepared to investigate the effect of fly ash on the temperature, free lime content and strength etc. of mortar/concrete. Being compared with the concrete made of ordinary Portland cement, temperature increment of the concrete containing 50 wt% fly ash reduced, according to appropriate conversion formulae, to about 45% at the 7 days curing time: the temperature increment of the former amounted to 33.4$^{\circ}C$, while that of the latter only to 18.7$^{\circ}C$. On the other hand, it is better to control the content of fly ash in the cement that is used for reinforced concrete not to exceed 30 wt%. In this study, more than 28 days curing time is necessary in order that the strength of concrete made of fly ash cement will be higher than that of pure Portland cement. In addition, 28-days concrete strength higher than 360 kg/$\textrm{cm}^2$ could be easily achieved even with 50 wt% fly ash cement.
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유기 및 무기 섬유로 보강한 포트랜드 시멘트의 물성 연구
장복기,김윤주,Chang Pok-Kie,Kim Yun Ju 한국세라믹학회 2004 한국세라믹학회지 Vol.41 No.9
본 연구에서는 무기(강, 아스베스트와 카본) 및 유기(폴리아크릴과 폴리아마이드) 섬유가 포트랜드 시멘트의 물성 보강에 미치는 영향을 조사하였다. 각 시편의 하중-변형 관계도로부터 굽힘강도, 탄성계수, 파괴에너지 및 파괴인성 값을 구하여 서로 비교하였다. 그리고 따로 충격에너지 실험도 수행하였으며 파괴에너지와 비교하였다. 휨강도 개선에는 무기(아스베스트) 섬유보강이 가장 효과적이었으며, 충격에너지의 보강섬유로는 유기(폴리아크릴) 섬유가 가장 좋았다. 한편 강 섬유는 휨 강도와 충격에너지 양자를 동시에 보강하는 데에 가장 적합했다. 또한 강 섬유는 모든 섬유 중에서 가장 높은 파괴에너지와 파괴인성 값을 나타내었다. In this study, inorganic (steel, asbestos and carbon) and organic (polyacryl and polyamide) fibers were used to investigate their reinforcing effects of the physical properties of Portland cement. From the load-displacement curve of each reinforced specimen, fracture strength, Young's module, fracture energy and fracture toughness were computed and compared with each other. In addition, the experiment of their impact toughness was carried out and compared with the fracture energy. For the improvement of fracture strength the inorganic (asbestos) fiber reinforcement was most effective, while the best reinforcing effect of impact toughness was achieved by organic (polyacryl) fiber. And steel fiber proved to be most adequate for improvement of both fracture strength and impact toughness. Steel fiber also showed the highest fracture energy and fracture toughness among all of the fibers.
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장복기,임용무 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.5
Glasses showing the composition of blast furnace slag were made in the laboratory, and the effect of the chemical composition on the latent hydraulic activity of the slags was examined. The latent hydraulicity was greatly influenced by the composition change, the optimal characteristic of the hydraulicity was achieved at the slag composition of 47CaO:20Al2O3:33SiO2. The content of CaO and Al2O3 were not equivalent to the hydraulic activity of the slags as the b-formula (KS L 5210) indicates. Good latent hydraulicity was shown when Al2O3 was richly contained at the high (CaO+Al2O3):SiO ratio, while the more the MgO content was, the more negative the result turned out.
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장복기,임재봉 한국세라믹학회 1990 한국세라믹학회지 Vol.27 No.6
The microstructural dependence of thermal conductivity of a high-alumina (ca. 70%) heat-insulating frebricks(ca. 75%porosity) was investigated under special consideration of the tailored-pore shape effects. Pores different shape could be incorporated into the insulators through pore formers : Styrofoam produces spherical pores while saw dust results in parallel plate pores. Concerning the pore-shape effectiveness of thermal insulation, the specimen with irregular plate pores showed much lower values of heat conductivity than those with spherical pores, the values being 0.31 to 0.38 at $600^{\circ}C$ and 0.35 to 0.47 at 100$0^{\circ}C$, respectively. On the contrary, however, other material properties such as strength and softening temeprature under load were turned out to be better in the case of the spherical pores.
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