• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.325-328
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• 2008

Recently increasing interest in high-rise building around the world for more than 100 floor, the trend is the increasing use of high-strength and high-flowable concrete so as of productivity improvements and cost savings to improve the performance of the early strength development. This study is to reach the optimal combination by reviewing the performance of high-rise building which is required. The results, lower the ratio of W/B was an increase in compressive strength and early strength in the use of admixture decreased in the combination of higher replacement ratio of admixture.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 1999.04a
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• pp.77-77
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• 1999

담배용 필터에 사용되고 있는 재료는 아세테이트, 종이, 폴리프로펼렌, 부직포등이 주로 이용되고 있으 며 담배연기의 흡착능을 향상시키기 위한 방법으로 활성탄 제오라이트와 같은 흡착제를 담배필터에 첨가하여 사용하고 있다. 본 실험에서는 펼터에 가장 보편적으로 많이 사용하고 있는 활성탄을 종이 제조과정에 첨가하여 나타나는 물리적 특성을 관찰하였고 제조된 종이를 담배필터에 적용하기 위하여 현행 습식 크림핑(crimping)방법과는 달리 건식 크림핑(crimping)방법을 이용한 적합한 조건을 검토하 였으며 이에 따른 담배필터에서의 연기흡착능을 분석한 결과는 다음과 같다. 1. 시트의 물리적 특성과 담배 연기성분 홉착능을 예측하기 위하여 펄프의 불성과 uv 홉착능을 분 석한 결과 Sw-BKP가 Hw-BKP에 비하여 강도적 성질이 우수하였고 또한 메틸렌불루(methylene b blue) 흡착능도 높은 경 향을 나타내 었다. 2. 활성탄 함량의 증가에 따라 섬유간의 결합력이 약화됨에 따라서 시트의 인장강도 및 파열강도가 감 소하는 경향이 가장 크게 나타났으며 평량이 펼프 배합비보다 높은 인자로 작용하였다. 또한 인자 간의 교호작용에서는 평량과 활성탄 함량에 따라서 크게 나타났으며 평량, Sw-BKP의 함량이 증가할 수록 인장강도는 증가하였다. 3. Stiffness는 활성탄 함량 펄프 배합비 평량의 순에따라 중요한 인자로 작용하였고 활성탄 함량 이 많을수록 stiffness는 감소하였으며 평 량 Sw-BKP의 함량이 높을수록 증가하였다 인자간의 교 호작용은 평량과 활성탄 함량이 다른 요인에 비하여 높은 경향을 보였다. 4. 인열강도는 활성탄 함량이 증가함에 따라 가장 크게 감소하였고 시트의 평량이 펄프 배합비보다 높은 인자로 작용하였으며 평 량 Sw-BKP의 함량이 높을수록 증가하였다 인자간의 교호작용에서는 펄프 배합비와 활성탄 함량에 따라 크게 나타났다. 5. 종이 필터지에서 시트의 평량이 bulk에 가장 큰 인자로 작용하였는데 이는 같은 두께에서 평량올 변화시킨 요인으로 판단되며 시트의 평량이 높을수록 감소하였고 활성탄 함량, Sw-BKP의 배합비 가 높을수록 증가하였다. 또한, 인자간의 교호작용은 평 량과 활성 탄 함량에 따라 크게 작용하였다. 6 6. Crimp index는 관능검사 결과로서 활성탄 함량이 증가함에 따라 현저하게 저하되었으며 평량 및 S Sw-BKP의 배합비가 높을수록 양호한 결과를 나타내었다. 인자간의 교호작용에서는 평량과 펄프 배합비에 따라 가장 높은 경향을 나타내었다. 7 활성탄을 첨가하여 제조한 종이필터의 담배 연기성분 흡착능은 acetate tow에 charcoal을 첨가한 필터에 비하여 tar흡착능이 6% 이상 향상되었고, 특히 증기상 물질(vapour phase)중 aldehyde류에 대한 제거율(removal efficiency)이 높게 나타났다. 8. 건식 크림핑 방법에 의한 담배필터 제조시 펼프의 홉착능, 시트의 강도적 특성, 크림핑 조건 및 담 배 연기성분 흡착능 등을 고려하여 적정조건을 선정하였으며, 펄프 배합비(Sw-BKP따w-BKP)는 6 65/35, 시트의 평량은 40g/$m^2$ 활성탄 함량은 10% 이었다.

• Elastomers and Composites
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• v.39 no.2
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• pp.131-141
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• 2004

The recycling of waste XLPE(crosslinked polyethylene), which is a major source of scraps from high voltage power transmission cables, has been discussed. The waste XLPE scraps were ground into fine powder with various sizes from less than $100{\mu}m$ up to about $1000{\mu}m$ using two types of tailor-made pulverizers. The compounds were prepared in a modular intermeshing co-rotating twin screw extruder at various conditions such as different compositions, types and powder sizes of waste XLPE, screw configurations and various polymer matrices (LDPE, HDPE, PP, PS). The mechanical and rheological properties and the fracture surface or the compounds were investigated. It was found that an improved impact strength was obtained from the compound with white XLPE powder pulverized from the scraps without outer/inner semi-conductive layers. Generally, the impact strength increases with the content of XLPE but decreases with the size of XLPE. Especially for LDPE, the extrusion was possible up to 80 wt% loading of XLPE. Also, the impact strength increases with the number of kneading disc blocks in the given screw configurations. The melt viscosity of the compounds increases with increasing XLPE loading. However, the higher shear thinning behavior of the compounds at common shear rates implies proper processibility of the compounds. In addition, the impact strength for other polymer matrices used increases with XLPE and it is noticeable that the impact strength of PS/XLPE (80/20 wt%) compound was improved twice that of pure PS.

• Explosives and Blasting
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• v.27 no.1
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• pp.32-37
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• 2009

To look over the effect of mixed proportion of cement, sand and water on strength, 162 tests were made for 9 mix proportions. It was observed that strength increased as water in the mixture is reduced. As a result of the control of sand ratio by 50%, the execution strength increased when the sand ratio is raised. Strength was consistent during curing period on each mix proportion, but there were sections where it suddenly increased. Poisson's ratio widely ranged from 0.13 to 0.27, and Young's modulus also broadly ranged from 13.79MPa to 33.25MPa. Poisson's ratio had nothing to do with uniaxial compressive strength, wheras Young's modulus was concerned with it. Young's modulus from theory and experiment showed similar outcome on the 3rd curing day, however, the strength from theory was higher than that from test after 3rd day. In consequence, there was a great change of strength between 3rd and 7th curing day. In addition, it is more efficient to use field strength value between the 3rd and 7th day and to apply Young's modulus on it for determining the exact time.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.373-376
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• 2008

Ultra High Strength Concrete(UHSC) is necessary a clear presentation about mechanical property that is different from normal strength concrete and an evaluation of serviceability of high rise building which is used ultra high strength concrete. To mixing ultra high strength concrete with $f_{ck}$=150MPa pre-mix cement were manufactured and experimental study were conducted to evaluated on the mixing properties and compressive strength with major variables as unit cement contents, water-binder ratio and type of pre-mix cement. As a test result, it is shown that the concrete mixing time is required about 5$^{\sim}$6 minute untill the each materials(ordinary portland cement, silica fume, blast-furnace slag powder and anhydrite) are revitalized enough. A slump flow of fresh concrete are shown about 700$^{\sim}$750mm with proper viscosity. And average value of concrete compressive strength are shown about 77% in 7days, 87% in 14days and 102% in 56days for 28days of concrete material age. From this experimental study, a proper mixture proportion of pre-mix cement are recommended about 54$^{\sim}$59% OPC, 25$^{\sim}$30% blast-furnace slag powder and 10$^{\sim}$15% silica fume for mix the ultra high strength concrete with $f_{ck}$=150MPa.

• Magazine of the Korea Concrete Institute
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• v.4 no.4
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• pp.149-160
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• 1992

콘크리트 압축강도가 설계의 규준이 될 경우 배합비를 결정하는 방법은 여러 가지가 있으나, 파괴에너지 및 탄성계수와 같은 규준이 주어질 경우 배합비 결정에 적용하는 방법은 거의 없다. 이를 위하여 본 연구는 콘크리트 재료성질의 관계에 관한 배합설계도(Mix design diagram)를 제안하였다. 이 방법은 시멘트량, 물-시멘트 비가 콘크리트의 압축강도, 탄성계수, 할렬인장강도, 파괴에너지 그리고 콘크리트 특성길이(Characteristic length)에 주는 영향을 실험에 의하여 규명하였다. 시편제작을 위하여 각기 다른 물-시멘트비와 워커빌리티를 갖는 6종류의 무근콘크리트 배합이 사용되었다.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.811-817
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• 2006

The primary purpose of this study is to estimate the guaranteed strength and construction quality of the combined high flowing concrete which is used in the slurry wall of underground LNG storage tank. The required compressive strength of this type of concrete become generally known as a non economical value because it is applied the high addition factor for variation coefficients and low reduction factor under water concrete. Therefore, after estimation of the construction quality and guaranteed strength in actual site work, this study is to propose a suitable equation to calculate the required compressive strength in order to improve its difference. Application results in actual site work are shown as followings. The optimum nix design proportion is selected that has water-cement ratio 51%, sand-aggregate ratio 48.8%, and replacement ratio 42.6% of lime stone powder by cement weight. Test results of slump flow as construction quality give average 616~634mm. 500mm flowing time and air content are satisfied with specifications in the rage of 6.3 seconds and 4.0% respectively. Results of strength test by standard curing mold show that average compressive strength is 49.9MPa, standard deviation and variation coefficients are low as 1.66MPa and 3.36%. Also test results by cored cylinder show that average compressive strength is 66.4MPa, standard deviation and variation coefficients are low as 3.64MPa and 5.48%. The guaranteed strength ratio between standard curing mold and cored cylinder show 1.23 and 1.32 in the flanks. It is shown that applied addition factor for variation coefficients and reduction factor under water concrete to calculate the required compressive strength is proved very conservative. Therefore, based on these results, it is proposed new equation having variation coefficients 7%, addition factor 1.13 and reduction factor 0.98 under water connote.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.520-527
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• 2020

Hwangtoh is the rich resource that accounts for about 15.0% of the domestic soil, and can be used as the admixture of concrete with Pozzolan characteristics if activated by rapidly freezing after burning with high temperature. In this study, the mortar curbs containing active hwangtoh were produced, based on the mixture for the mortar curbs sold on the market. The substitution rate of active hwangtoh were considered 10.0% and 25.0%, and the test items were selected to compressive and flexural strength tests, freezing/thawing resistance tests, accelerated carbonation tests, and accelerated chloride diffusion tests. In the results of the mechanical performance, it was showed that the highest strength was evaluated in OPC mixture, and the increase in strength was small by the increase of age, which was believed to be due to the fact that most of the strength in each mixture was created in three days of steam curing. The results of the freezing/thawing tests for 28 aged days showed the reduction rate of compressive strength was 85.0% or higher for all specimen, meeting the criteria presented. The accelerated carbonation tests were carried out on the specimen at 28 days of age, and the results showed that the mortar with active hwangtoh had lower carbonation resistance performance than mortar with OPC. The passed charge of each mixture was assessed in accordance with ASTM C 1202 on 28 and 91 aged days. The OPC mixture had "Low" rate and the mortar with active hwangtoh had "Moderate" rate. So it was thought that the mortar with active hwangtoh had appropriate resistance performance for chloride attack.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.101-108
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• 1998

시멘트 대체재로 사용하는 플라이애쉬(0, 10 , 30 ,50 %)를 혼입한 콘크리트의강도발현을 관찰하기 위해 각각 21$^{\circ}C$에서 수중양생과 85$^{\circ}C$에서 증기양생방법을 채택하여 실험하였다. 수중양생한 보통 콘크리트는 플라이애쉬 혼입량이 증가할수록 조기재령에서는 낮게 강도발현을 하였으나. 28일 압축강도를 기준으로 하여 물.시멘트비를 변화한 배합비(결합재량 증가)의 실험결과는 조기강도발현이 향상되었다. 특히 플라이애쉬를 30%혼입한 콘크리트는 우수하게 강도발현을 하였다. 그리고 동일한 28일 압축강도를 갖는 배합비(결합재량 증가)에서 증기양생한 플라이애쉬콘크리트는 보통콘크리트보다 강도발현이 비슷하거나 향상되었으며, 양생온도는 플라이애쉬콘크리트의 강도발현에 많은 영향을 미치는 것으로 관찰되었다.

• 레미콘
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• no.7 s.52
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• pp.26-34
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• 1997