• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.11-30
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• 2000

Structural properties of reinforced concrete, such as bond and shear strength, that depend on the tensile properties of concrete are much lower for high-strength concrete than would be expected based on relationships developed for normal-strength concretes. To determine the reason for this behavior, studies at the University of Kansas have addressed the effects of aggregate type, water-cementitious material ratio, and age on the mechanical and fracture properties of normal and high-strength concretes. The relationships between compressive strength, flexural strength, and fracture properties were studied. At the time of test, concrete ranged in age from 5 to 180 days. Water-cementitious material ratios ranged from 0.24 to 0.50, producing compressive strengths between 20 MPa(2, 920 psi) and 99 MPa(14, 320psi). Mixes contained either basalt or crushed limestone aggregate, with maximum sizes of 12mm(1/2in). or 19mm(3/4in). The tests demonstrate that the higher quality basalt coarse aggregate provides higher strengths in compression than limestone only for the high-strength concrete, but measurably higher strengths in flexure, and significantly higher fracture energies than the limestone coarse aggregate at all water-cementitious material ratios and ages. Compressive strength, water-cementitious material ratio, and age have no apparent relationship with fracture energy, which is principally governed by coarse aggregate properties. The peak bending stress in the fracture test is linearly related to flexural strength. Overall, as concrete strength increases, the amount of energy stored in the material at the peak tensile load increases, but the ability of the material to dissipate energy remains nearly constant. This suggests that, as higher strength cementitious materials are placed in service, the probability of nonductile failures will measurably increase. Both research and educational effort will be needed to develop strategies to limit the probability of brittle failures and inform the design community of the nature of the problems associated with high-strength concrete.

• 대한토목학회논문집
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• 제39권4호
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• pp.485-492
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• 2019

본 연구는 순환 굵은 골재의 함수상태가 콘크리트의 압축강도에 미치는 영향을 물/결합재 비와 양생 조건을 변수로 하여 평가하였다. 표건상태의 순환골재는 콘크리트의 강도발현을 저하시켰는데, 이는 순환골재의 높은 흡수율에 의한 표면수의 증가로 골재와 시멘트 페이스트 사이의 부착강도가 저하되었기 때문이다. 골재의 종류와 함수상태가 물/결합재 비의 변화에 따라 압축강도에 미치는 영향의 정도는 비슷하였다. 그러나 양생조건에 대해서는 골재의 종류에 따라 상당한 차이를 보였다. 대기양생을 시킨 경우 높은 흡수율을 가진 순환골재는 수화작용에 필요한 수분을 감소시키고, 수분증발을 증가시켜 강도발현을 저해하였다. 순환골재의 함수상태는 콘크리트의 압축강도에 상당한 영향을 줬으며, 순환골재콘크리트 생산시 골재의 흡수율에 따른 함수상태에 대한 관리가 필요하다. 또한 순환골재 콘크리트의 경우 적절한 품질관리를 위해 양생관리가 매우 중요하다.

• 산업기술연구
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• 제25권A호
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• pp.49-56
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• 2005

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. VES-LMC provides the advantage of very-early-strength, as well as high flexural strength, bond strength, durability, resistance to corrosion, reduced water permeability and resistance to damage from freeze-thaw cycles. The compressive and flexural strength of VES-LMC are 21 MPa and 4.5 MPa at 3 hours after concrete placing, respectively. However, VES-LMC would have a relatively large shrinkage at early-age because of reduced water-cement ratio, big water self-dissipation, and rapid hydration reaction. Therefore, the purpose of this study was to evaluate the early-age and restrained shrinkage of VES-LMC, having an experimental variables such as latex contents and cement types. The latex contents included 0%, 5%, 10%, 15% and 20%, and the cement types included ordinary portland cement and very-early strength cement.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.75-79
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• 2007

This paper describes the self-alignment and bonding of microparts using adhesive surface tension to assemble microsystems in air. The alignment and bonding were tested experimentally using adhesive droplets, and the resulting performance was evaluated. The adhesive, which was inorganic and water-soluble before hardening, was diluted with water to a ratio of 10:1 so that its surface tension generated a sufficient restoring force for self-alignment. The experimental results showed that the average of the alignment errors obtained using the adhesive on $1.0\times1.0\times0.15-mm$ microparts was less than $2{\mu}m$ in the X and Y directions and 0.2 degrees in the e direction. These alignment errors were almost the same as those obtained using water. The use of a suitable adhesive had no negative effects on the alignment accuracy. The average tensile strength of the adhesive bond after self-alignment was $0.61N/mm^2$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.913-916
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• 2008

변형경화형 시멘트 복합체(SHCC)의 직접인장거동은 주로 물시멘트비, 섬유와 매트릭스 간의 상호작용, 부착강도, 섬유 혼입율 등에 의해 영향을 받는다. 본 논문은 PET 및 PVA섬유를 사용한 SHCC의 직접인장거동에서 섬유의 형상비의 영향을 평가하기 위해 PET섬유의 형상비(Aspect ratio, ${\ell}/d_f$ : 150, 300, 600)를 변수로 선정하였다. 동일한 배합조건에서 PET1.5+PVA0.5-300 및 PET1.5+PVA0.5-600시험체는 PET1.5+PVA0.5-150에 비해 우수한 유사변형경화특성과 미세균열분산 특성을 보였으며, PET1.5+PVA0.5-300 및 PET1.5+PVA0.5-600 시험체는 최대인장응력시 각각 0.5, 2.0%의 변형율을 나타내었다.

• 콘크리트학회논문집
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• 제14권5호
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• pp.660-667
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• 2002

본 연구에서는 에틸렌 초산 비닐 (EVA) 재유화형 분말수지를 혼입한 초속경 폴리머 시멘트 모르타르의 응결시간, 수밀성, 염화물이온 침투에 대한 저항성, 동결음해 저항성 및 내약품성에 미치는 분말소포제 첨가율 및 폴리머-시멘트비의 영향에 대하여 검토하였다. 그 결과, 재유화형 분말수지를 혼입한 초속경 폴리머 시멘트 모르타르의 공기량은 분말소포제 첨가율 및 폴리머-시멘트비의 증가에 따라 감소하는 경향을 보였다. 재유화형 분말수지를 혼입한 초속경 폴리머 시멘트 모르타르의 응결시간은 분말소포제 첨가율에 관계없이 폴리머-시멘트비의 증가에 따라 길게 되는 경향을 보였다. 또한 재유화형 분말수지를 혼입한 초속경폴리머 시멘트 모르타르의 수밀성 및 염화물이온 침투깊이는 분말소포제 첨가율에 관계없이 폴리머-시멘트비의 증가에 따라 감소하는 경향을 보였다. 재유화형 분말수지를 혼입한 초속경 폴리머 시멘트 모르타르의 동결융해 저항성 및 내약품성의 개선은 재유화형 분말수지의 혼입에 의해 시멘트 수화룰과 골재간의 접착성이 개선되기 때문이라 판단된다.

• 콘크리트학회논문집
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• 제17권5호
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• pp.703-708
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• 2005

본 연구에서는 에틸렌 초산 비닐 (EVA) 재유화형 분말수지를 혼입한 고유동 폴리머 시멘트 모르타르의 응결 시간 수밀성, 염화물이온 침투에 대한 저항성, 동결융해 저항성 및 중성화 깊이에 미치는 분말소포제 첨가율 및 폴리머-시멘트비의 영향에 대하여 검토하였다. 그 결과, 재유화형 분말수지를 혼입한 고유동 폴리머 시멘트 모르타르의 응결 시간은 분말소포제 첨가율에 관계없이 폴리머-시멘트비의 증가에 따라 지연되는 경향을 보였다. 또한 재유화형 분말수지를 혼입한 고유동 폴리머 시멘트 모르타르의 수밀성, 염화물 이온 침투 깊이 및 중성화 깊이는 분말소포제 첨가율에 관계없이 폴리머-시멘트비의 증가에 따라 감소하는 경향을 보였다. 재유화형 분말수지를 혼입한 고유동 폴리머 시멘트 모르타르의 동결융해 저항성의 개선은 재유화형 분말수지의 혼입에 의해 시멘트 수화물과 골재간의 접착성이 개선되기 때문이라 판단된다.

• 상하수도학회지
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• 제25권5호
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• pp.681-689
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• 2011

Submerged membrane bio-reactor (SMBR) has several advantages such as high MLSS, long SRT, and low F/M ratio at wastewater treatment. So, this has widely applied over the world and many studies have been conducted. However, membrane fouling remains an inevitable problem. This study was investigated using bench-scale SMBR with three poeration modes. Raw waters were prepared by addition of starch, acetic and fibric acid to recovery water of zeolite. The efficiency of nitrification and COD were very stable as about 95% and 80%, respectively. And critical flux was 128.8L/$m^{2}$/hr. The result of biodegradability test was following values at the each mode : Ss+Xs/$C_{T}$=81.7%, 35.1% and 45.3%, $X_{I}+S_{I}/C_{T}=18.3%$, 64.9% and 54.7%. When particulate matters such as $X_{I}$ and $X_{S}$ in influent are increased, membrane fouling will take place more and more. A relative ratio of filtration resistance to the fouling occurred by the cake layer was increased when increased the portion of $X_{I}$ and polysaccharide. It was thought that the formation of cake layer was promoted due to bond between $X_{I}$ and vicid material s generated from the polysaccharide.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.762-765
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• 2004

The main objective of this study is to provide a parametric evaluation of the pull-out response of steel fibers embedded in cementitious matrices. The various parameters controlling the behavior of the bond stress versus end slip relationship are analyzed; their effects on the entire pull-out load versus end slip response and the corresponding pull-out energy up to total pull-out are investigated. Also discussed are the effects of the fiber length, the water/binder ratio of the mixtures and embedded length.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1063-1068
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• 2000

Latex modified concrete (LMC) has grown to be accepted as a standard material of construction overlaying bridge decks in America due to its superior physical and chemical properties. The properties of latex, combined with the low water-cement ratio, produce a concrete that has improved flexural, tensile, and bond strength, lower modulus of elasticity, increased freeze-thaw resistance, and reduced permeability compared to conventional concrete of similar mix design. LMC overlays have been service in excellence for 30 years on thousands of bridge in U.S.A. This may, also, prolong the life cycle of bridge deck once it is adopted in Korea. The self-contained, mobile, continuous mixer is most appropriate particularly for concrete quality assurance. Assuring quality on a bridge deck overlay project should begin in the design phase and continue after the construction is completed. Quality should be the concern of everyone involved-owner, designer, and contractor.