• 콘크리트학회지
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• 제6권5호
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• pp.158-170
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• 1994

본 연구는 산업부산물의 플라이애쉬 및 실리카흄을 이용한 고성능$\cdot$고품질의 건재의 제조 및 응용을 위하여 보강재로서 PAN계 및 Pitch계 탄소섬유를 사용하여 건재용 탄소섬유보강 실리카흄$\cdot$시멘트 복합체 및 플라이애쉬$\cdot$시멘트 복합체를 제조하여 배합조건별 동복합체의 물리적 역학적 특성에 관한 연구를 수행하였다. 시험결과, 탄소섬유보강 실리카흄$\cdot$시멘트 복합체의 휨강도, 휨인성 및 휨변형 특성은 탄소섬유 혼입율증대에 수반하여 현저히 증가하는 경향을 나타내었고, 또 이들 값은 PAN계 CF를 사용한 경유가 Pitch계 CH를 사용한 경우에 비하여 높게 나타났다. 한편, 플라이애쉬$\cdot$시멘트 복합체는 플라이애쉬 대체율의 증가에 따라 물(플라이애쉬+시멘트)비는 증가하였으나, 압축$\cdot$휨강도 및 겉보기 비중은 저하하였으며 촉진양생은 경우가 습윤양생한 경우에 비하여 우수한 압축강도 및 휨강도를 나타내었다. 또한, 기존ALC의 대체를 위한 경량 플라이애쉬\ulcorner시멘트 복합체를 개발하였고, 그 최적배합조건을 제시하였다.

• 한국세라믹학회지
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• 제39권6호
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• pp.540-549
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• 2002

본 실험에서는 Impedance Spectroscopy(IS)를 이용하여 플라이 애쉬, 고로 슬래그, 실리카 퓸 등의 혼합재가 치환 첨가된 포틀랜드 시멘트의 수화거동을 검토하였다. 플라이 애쉬 및 고로 슬래그가 시멘트에 치환 첨가될 경우, 수화 초기 IS 의 전기적 변수, $R_{t(s+1)}$과 $R_{t(s+1)}$의 증가폭이 감소하였다. 이것은 동일한 W/C비에서 혼합재를 포함한 시멘트의 수화가 늦게 진행되고 있음을 보여준다. 그러나, 실리카 퓸의 경우 초기에 매우 빠른 포졸란 반응성으로 인하여 플라이 애쉬 및 고로 슬래그가 첨가된 경우에 비해 큰 폭의 $R_{t(s+1)}$ 및 $R_{t(s+1)}$ 변화를 확인 할 수 있었다. OPC-플라이 애쉬계의 경우 반원과 직선 영역 사이에서 특이 할만한 평할한 곡선 영역이 출현하였으며, 수화가 진행되고 플라이 애쉬의 치환첨가량이 증가할수록 그 영역이 증가하였다.

• 한국산업보건학회지
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• 제10권2호
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• pp.150-164
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• 2000

This study was conducted at occupational health laboratories in Seoul and Gyunggi district area from December, 1999 to January, 2000. The main purpose of this study was to survey the actual condition of safety and health by questionnaire and checklist and to assess the performance of fume hoods and the airborne exposures to chemicals in the laboratories. The chemicals in the cabinet were not classified by hazardous properties and the compressed gases were not stored safely. The prevalences of laboratories having first aid kits, fire extinguishers, and safety showers were found to be 18%, 55%, and 9%, respectively. Most laboratory workers were not educated for safety and health. Also, there was no performance evaluation for hazards and risks. The fume hoods in laboratories had not been annually inspected by checklist and the face velocity had been checked more than one time in the previous year for only 18% of them. Five percent of fume hoods had the face velocity more than 4.0 m/sec and 17% had no capture performance. Detected organic solvents were methylenechloride, acetone, ethylbenzene, isopropanol, xylene, methylisobutylketone, trichloroethylene, and toluene. The concentrations of organic solvents were much less than the occupational exposure limits proposed by the Ministry of Labor in Korea. This study showed that the actual condition of safety and health was not appropriate for laboratory workers. It is recommended that laboratory workers should be educated for the treatment and storage of hazardous chemicals and compressed gases to improve the working environment of the occupational safety and health laboratories.

• 한국산업보건학회지
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• 제20권1호
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• pp.63-69
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• 2010

This study was conducted to compare the concentration of various air contaminants in nine different laboratories during routine activities. Volatile organic compounds (VOC) were sampled and analyzed using NIOSH Method 1500 and asbestos fibers were sampled and analyzed using NIOSH Method 9002 and 7400. Detectable levels of acetone, toluene and ethanol were found in all the laboratories and xylene and n-hexane were detected in eight of the nine laboratories. All the VOC concentrations were well below the Korean Ministry of Labor's Exposure Limit and American Conference of Governmental Industrial Hygienists' (ACGIH) Threshold Limit Values (TLVs). Total VOC concentrations at the university laboratories were significantly higher than those at governmental agency laboratories. Airborne fiber concentrations were below 0.01 fibers/cc, while the concentration of chrysotile was 2% in insulation materials sprayed on the ceiling of one laboratory. While all the governmental agency laboratories (n=4) had fume hoods, two out of the five university laboratories did not have fume hoods. The capture velocity of half of the fume hoods were below the maintenance standard(0.4 m/sec). In conclusion, the study suggests that the current controls in place at both university and government agency laboratories are not sufficient in limiting exposure to harmful chemicals to non-detectable levels, though they appear to be adequate in protecting workers to levels below applicable occupational exposure limits. The study also suggests that researchers working in university laboratories may be exposed to greater levels of contaminant than those working in government agency laboratories.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.906-915
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• 2006

In this study, Field test was performed using high-quality additions and accelerators to obtain the improvement of the strength on domestic shotcrete and quality test based on EFNARC was performed. In addition, Deterioration test that combined the Freezing-thawing and Carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of field test, a promotion ratio of early strength is $90\sim97%$ in case of using alkali-free accelerators. And a compressive strength of shotcrete using Micro-silica fume was $45.2\sim55.8MPa$ and the flexible strength was $5.01\sim6.66MPa$, so a promotion ratio of strength was $37\sim79%$, $17\sim61%$ respectively. It was showed that increment effect of strength by the Micro-silica fume replacement of $7.5\sim10%$ for cement mass was remarkable. It was also realized that application of Micro-silica fume to shotcrete reduced deterioration and improved a long-term durability of shotcrete.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• Environmental Engineering Research
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• 제22권2호
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• pp.216-223
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• 2017

For the prediction of the ventilation rate for removing the non-isothermal concentrated fume from the semi-enclosed space, the computational fluid dynamics (CFD) analysis was done. Securing the proper ventilation conditions in emergency state such as in fire is crucial factor for the protection of the resident in the space. In the analysis for the determining the proper ventilation rate, the experimental study had the limitation for simulating the versatile conditions of fume development. The theoretical and computational method had been chosen as the alternate tool for the experimental analysis. In this study, the CFD analysis was done on the defined model which already had been done the experimental analysis by the previous workers. By comparing the prediction on the plume heights and the ventilation rates by the CFD analysis at, and in the parametric model of $1m^3$ with those of the previous experimental works, the feasibility of the computational analysis was evaluated. For the required ventilation rate analyzed by the CFD analysis was over predicted in 7.1% difference with that of the experimental results depending on the different plume height. With the comparison with the analytical Zukoski model at, the CFD analysis on the ventilation was under predicted in 8.3%. By the verification of the feasibility of the CFD analysis, the extended analysis was done for getting the extra information such as the water vapor distribution and $CO^2$ distribution in the semi-enclosed spaces.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.521-524
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• 2008

최근 고층 구조물이 많이 건설되면서 콘크리트의 내구성 향상에 대한 요구가 증가하고 있다. 이에 따라 고성능 콘크리트에 대한 관심이 높아지고 있다. 최근, 실리카 흄과 같은 수준의 강도나 내구성을 확보하면서 경제적 측면에서 좀 더 유리한 메타카올린이 새로운 혼화재로 가치를 높게 평가되고 있다. 따라서, 본 연구에서는 메타카올린과 실리카 흄의 시공성, 강도 및 염화물 저항성, 50${\mu}m$이상의 거대공극 구조를 비교 평가하였다. 연구결과에 따르면, 메타카올린은 실리카 흄과 동일한 수준의 시공특성을 보인다. 강도 특성의 경우 메타카올린의 대체가 가장 높은 강도를 보였다. 장 단기 염화물 저항성에서도 메타카올린의 대체가 뛰어난 성능을 보였다. 결과적으로 메타카올린 10%의 대체는 강도 및 염화물 저항성 측면에서 가장 우수한 성능을 보인다.

• Advances in concrete construction
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• 제5권1호
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• pp.65-74
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• 2017

This study was focused on the use of partial replacement of cement with glass powder in high strength concrete and also copper slag as a partial replacement of coarse sand in concrete. The high strength concrete was prepared with different mineral admixtures like silica fume, fly ash and rice ash husk in different proportions. An experimental investigation has been carried to study about the effect of glass powder on high strength copper slag concrete. The range of glass powder was 10%, 15% and 20% as a replacement of cement. The range of copper slag was 0%, 20%, 40% and 60% as a replacement of natural sand. In addition to the different percentage of fly ash, silica fume, and rice husk ash 5% and 10% was also studied in copper slag concrete. Thus, a total of 51 cubes were casted and compressive strength test was performed on them. The result of the study shows that the value of average compressive strength of concrete after addition of 10%, 15% and 20% of glass powder are 70.47, 72.01 and 73.31 respectively. The value of average compressive strength after addition of 20%, 40% and 60% copper slag as a replacement of sand are 72.18, 74.38 and 73.08 respectively. The value of average compressive strength after addition of 5% and 10% fly ash as a replacement of cement are 71.56 and 73.22. The value of average compressive strength after addition of 5% and 10% silica fume as a replacement of cement are 72.33 and 73.53. The value of average compressive strength after addition of 5% and 10% rice husk ash as a replacement of cement are 72.86 and 69.49. At the level of 20% replacement of cement by glass powder meets maximum strength as compared to that of controlled concrete and copper slag high strength concrete.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.339-354
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• 2019

Reusing building materials and concrete of old buildings can be a promising strategy for sustained development. In buildings, the performance of materials under elevated temperatures is of particular interest for determining fire resistance. In this study, the effect of pozzolan and aggregate type on properties of concrete exposed to fire was investigated. In doing so, nanosilica with cement-replacement levels of 0, 2, and 4% as well as silica fume and ultrafine fly ash with cement-replacement levels of 0, 7.5, and 15% were used to study effect of pozzolan type, and recycled refractory brick (RRB) fine aggregate replacing natural fine aggregate by 0 and 100% was utilized to explore effect of aggregate type. A total of 126 cubic concrete specimens were manufactured and then investigated in terms of compressive strength, ultrasonic pulse velocity, and weight loss at $23^{\circ}C$ and immediately after exposure to 400 and $800^{\circ}C$. Results show that replacing 100% of natural fine aggregate with recycled refectory brick fine aggregate in the concretes exposed to heat was desirable, in that it led to a mean compressive strength increase of above 25% at $800^{\circ}C$. In general, among the pozzolans used here, silica fume demonstrated the best performance in terms of retaining the compressive strength of heated concretes. The higher replacement level of silica fume and ultrafine fly ash pozzolans in the mixes containing RRB fine aggregate led to a greater weight loss rate, while the higher replacement level of nanosilica reduced the weight loss rate.