• Journal of Korea Foundry Society
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• v.19 no.6
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• pp.493-500
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• 1999

Squeeze casting was used for fabricating a light metal base composite having high strength and wearresistance. Reactive sintering was used to prepare the preform of Squeeze casting. To utilize Fe-Al intermetallic compounds and SiC particle as a reinforcement, there needs to prepare Fe-Al mixed powder at 50, 60, 70at.%Al, and add SiC powder to the above mixture at 4, 7, 16, 24wt.%. The prepared mixture with SiC was reactive sintered in a tube furnace at $660^{\circ}C$ to get a porous hybrid preform of intermetallic compound and SiC. The preform prepared above was placed in a metal mold, preheated at $660^{\circ}C$ AC4C matrix was injected into the mold with the temperature of the melt at $610^{\circ}C$ After these processes, 66MPa was applied to the mold for 5 minute to finish the whole procedure. The maximum reaction temperature was increased with the increased Al amount, but decreased with the increased SiC amount. The density of the preform was decreased with SiC amount increase in the compacts due to swelling of the preform. An optical microscope was applied to observe the micro structure and the dispersion of the reinforcements. To analyze phases, We utilized XRD, EDS. Hardness test were chosen to get the information of mechanical properties. There were no significant changes in micro structure between the composite and preform. However, it was shown that uniform dispersion of the reinforcers and complete infiltration of the melt into the preform were achieved through the procedure of the squeeze casting. It was observed that the hardness of the composite is decreased with increased SiC amount, resulting from the volumetric expansion of the preform.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.177-184
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• 2015

In order to use the high-volume slag cement as a construction materials, a proper activator which can improve the latent hydraulic reactivity is required. The dissolved aluminum silicon ions from ground granulated blast furnace slag (GGBFS) react with sulfate ions to form ettringite. The proper formation of ettringite can increase the early-age strength of high-volume GGBFS (80%) cement. The aim of this study is to investigate the hydration properties with sulfate activators (sodium sulfate, anhydrite). In this paper, the effects of $Na_2SO_4$ and $CaSO_4$ on setting, compressive strength, hydration, micro-structure were investigated in high-volume GGBFS cement and compared with those of without activator. Test results indicate that equivalent $SO_3$ content of 3~5% improve the early-age hydration properties such as compressive strength, heat evolution rate, micro-pore structure in high-volume GGBFS cement.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.121-127
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• 2012

Cement has been traditionally used as a main binding material of high ductile fiber reinforced cementitious composites. The purpose of this paper is to investigate the feasibility of using alkali-activated slag and polyvinyl alcohol (PVA) fibers for manufacturing high ductile fiber reinforced cementless composites. Two mixture proportions with proper flowability and mortar viscosity for easy fiber mixing and uniform fiber dispersion were selected based on alkali activators. Then, the slump flow, compression, uniaxial tension and bending tests were performed on the mixes to evaluate the basic properties of the composites. The cementless composites showed an average slump flow of 465 mm and tensile strain capacity of approximately 2% of due to formation of multiple micro-cracks. Test results demonstrated a feasibility of manufacturing high ductile fiber reinforced composites without using cement.

• Journal of Environmental Health Sciences
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• v.45 no.6
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• pp.594-604
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• 2019

Objectives: This study developed and validated an analysis method of urinary metals and metalloids that can be applied inductively with coupled plasma mass spectrometry (ICP-MS). Methods: 0.3 mL of urine was used to analyze 25 metal and metalloid compounds using ICP-MS. The validation of the analytical method included linearity, accuracy, precision, and the calculation of detection limits. In addition, a comparison test was performed with the graphite furnace atomic absorption spectrometry (GF-AAS) method, which is the current standard method, with urine samples of 66 healthy subjects. Results: The linearities (R²) of calibration curves of all 25 compounds were ≥ 0.999. Of the 25 compounds, the intra-day and inter-day accuracy% of 17 and 20 met ≤15%, respectively. In addition, fifteen compounds showed ≤15% recovery% for certificated reference materials. Intraclass correlation coefficients of the comparison between the current methods and new methods in this study were 0.952 (p-value<0.001) and 0.911 (p-value<0.001) for urinary cadmium and mercury, respectively. Conclusion: This study proposes an efficient simultaneous methodology that can analyze multi elements in smaller sample amounts. More reproduction experiments are needed in the future.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.677-680
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• 2008

The surface of particles was energetically modified by inter-grinding OPC and BFS in vibration mill for improvement of the early strength and low-heat evolution of concretes. BFS was pre-grinding in ball-mill to 2535(BS2) and 3245 $cm^2/g$(BS3), in blaine surface area. The inter-grinding time in vibration mill was changed from 10 minutes to 30 minutes. And Mixing ration of BFS to OPC was changed in 60, 70, 80%. After inter-grinding, the change of specific surface area, particle size distribution, hydration heat of cement and compressive strength of mortar were measured. As the result of comparison test with LHC, it was found that the mixture and inter-grinding time satisfying the value of over 100% of compressive strength for 7 days and under 170J/g of heat of hydration for 72 hours. and it was confirmed that the possibility of low heat slag cement utilizing blast furnace slag(BS2, BS3) with the low fineness in high volumes.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.885-888
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• 2008

In recent years, the terminology "High-Performance Concrete(HPC)" has been introduced into the construction industry. Most high-performance concretes have a high cementitious content and a low water-cementitious material ratio. The proportions of the individual constituents vary depending on local preferences and local materials. Therefore, many trial batches are usually necessary before a successful mix is developed. The objective of this experiments is to investigate the fundamental properties of high performance concrete based binary cimentitious materials such as ordinary portland cement and ground granulated blast furnace slag. The results from the study will be utilized as the basic data and guideline in making standard mixproportions and the manufacture, construction work and quality control of HPC

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.559-567
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• 2005

The objective of this study is to optimize the use of mineral admixtures (silica fume, fly ash, and blast furnace slag) in high-performance concrete for bridge deck overlay. For this purpose, high-performance concrete, incorporating mineral admixtures, was tested for compressive strength and permeability. The Box Behnken design was used to determine the optimum mix proportions of the mineral admixtures. The optimized mix compositions were then technically evaluated. Test results are compare with the performance specification for high performance concrete overlay on bridge deck. The optimum mix proportions were shown to possess acceptable properties. Also, it is possible to save the construction and materials costs result from a reduction In actual material cost and from the use of widely avaliable truck mixers instead of mobile mixers.

• Journal of Environmental Health Sciences
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• v.31 no.4 s.85
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• pp.316-321
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• 2005

4개 업종(축전지제조업, 광명단 제조업, 2차 제련업, 라디에타 제조업)에서 근무하는 총 100명의 근로자를 대상으로 8단계다단충돌기(eight stages personal cascade imparter)에 의한 입자 크기 별 납농도를 측정하였다 크기 별 납 농도는 총납(PbA), 흡입성납(IPM-PbA), 흉곽성납(TPM-PbA), 호흡성납(RPM-PbA), $1{\mu}m$ 미만의 납$(Pb_{1\mu})$ 그리고 $1{\mu}m$ 이상의 소화성납$(Pb_{ing})$이었다. 동일한 근로자(100명)를 대상으로 혈액에서 납농도를 측정하였다. 혈액 중 납은 원자흡광광도계(atomic absorption spectrometry)의 Zeeman effect graphite furnace를 이용하여 분석하였다. 총 납의 노출농도는 노출기준$(50\;ug/m^3)$을 크게 초과하였다. 평균 호흡성 납 노출농도$(115.7\;ug/m^3)$ 총 납의 노출기준을 훨씬 초과하였다. $1{\mu}m$미만의 납$(Pb_{1\mu})$ 노출농도의 범위는 0.7에서 $(492.2\;ug/m^3)$이나 되었다. 근로자의 $46\%$가 혈액 중 납 농도 40 ug/dL을 초과하였다. 60 ug/dL을 초과한 경우도 $13\%$나 되었다. 입자 크기가 큰 납인 총납, 흡입성 납 그리고 호흡성 납 농도는 혈액 중 납 농도와 유의한 상관을 보였다(p<0.0001). 그러나 가장 높은 상관은 $1{\mu}m$미만의 납$(Pb_{1\mu})$ 혈액 중 납과의 관계였다. T-test에서 $50ug/m^3$이상의 호흡성 납을 나타낸 근로자 그룹과 $50ug/m^3$ 이하의 근로자 그룹간에의 혈액 중 납 농도는 유의한 차이가 있는 것으로 나타났다(p=0.000). 이러한 연구결과는 입자크기 구분이 없는 현재의 총납에 의한 노출기준과 측정방법은 미세 납 먼지에 노출되는 근로자의 납흡수를 보호하는데 한계점이 있다는 것을 의미한다. 향후 납 입자크기는 물론 근로자의 개인적인 위생과 작업내용 등을 변수로 납 흡수에 영향을 미치는 종합적인 요인을 찾아내는 연구를 진행할 필요가 있다.

• Journal of the Korean Ceramic Society
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• v.12 no.1
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• pp.23-28
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• 1975

The object of this study is to find the optimum conditions for crystal growth and kinds of crystal in ZnO-Al2O3-SiO2 glass composition. At first, the base glass composed of ZnO (44.7%), Al2O3(14.0%) and SiO2(41.3%) was melted in propane gas furnace at 1450-150$0^{\circ}C$ for an hour, and then it was poured into the stainless steel mould heated previously at $600^{\circ}C$ to obtain the thin glass test piece. Four crystal forms from base glass such as stuffed keatite, zinc orthosilicate, zinc aluminosilicate, and cristobalite were crystallized during heat treatment between 80$0^{\circ}C$ and 110$0^{\circ}C$. For the investigation of crystal growth, X-ray diffractometer and thermal differential analysis were used and the growth rate of the four crystal forms were obtained by the method of Archimedes specific gravity and intensity comparison of X-ray diffraction peak. The results obtained were as follows. 1) Stuffed keatite peaks which started to appear after two hours at 80$0^{\circ}C$ were maximum after 11 hours and this crystal breaks down to willemite irreversibly at about 100$0^{\circ}C$. 2) Development of gahnite started at 85$0^{\circ}C$ and increased with temperature growth. 3) Stuffed keatite which had been transformed slowly into willemite at 100$0^{\circ}C$ was decreased with time and willemite increased until four hours. 4) Cristobalite began to be developed after treatment of 110$0^{\circ}C$.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.175-183
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• 2008

Domestically, application of High Flowing Self-Compacting Concrete (HSCC) is limited to building structures and it is difficult to find examples of application in civil infrastructural constructions. However, in the case of North America and Europe, by introducing precast and prestressed system, HSCC is being used for high-density reinforced bridge members. Hence it is assessed that broadening the utilization of HSCC into areas such as bridges and civil construction is required. Therefore in this research, to apply HSCC to high-density reinforced bridge members, ground granulated blast-furnace slag and fly ash were mixed in binary and ternary systems. Also the dynamical characteristics of HSCC, following 1st class regulations of Japan Society of Civil Engineers (JSCE), were assessed to enable application on high-density reinforced structures. The test results revealed ternary system mixture showed better mechanical characteristics than binary system mixture and the application on high-density reinforced precast bridge members seems possible.