• 콘크리트학회논문집
• /
• 제26권1호
• /
• pp.23-34
• /
• 2014

초고성능 콘크리트(UHPC)를 현장에서 타설 하기 위해서는 타설 장비, 배근 상태, 타설 환경 등 현장 조건을 고려한 유동성 조절이 필요하다. 구성 재료와 배합비가 최적화된 UHPC 제품에서 유동성 조절을 위해 현실적으로 변경 가능한 방법은 물-결합재 비(W/B) 또는 고성능 감수제 혼입률(SP/C)을 조절하는 것이며, 경제적 이유로 강섬유 혼입률도 변경 할 수 있다. 일반 콘크리트와는 달리 UHPC는 아주 작은 재료와 배합비 변화에도 굳기 전 또는 굳은 성능에 많은 차이를 나타낸다. 따라서 이 연구에서는 이러한 요인들이 UHPC의 슬럼프 플로와 공기량에 미치는 영향, 그리고 인장 및 압축 성능에 미치는 영향을 알아보았으며, 슬럼프 플로와 공기량과의 선형적인 상관관계를 이용하여 이러한 성능들을 예측할 수 있는 식을 유도 하였다. UHPC의 특성 중 하나인 자기 충전성을 만족하는 조건에서 압축강도에 관한 최적 W/B와 SP/C는 각각 16.8%와 3%로 결정 되었으며, 이러한 조건에서 측정된 공기량은 3.2~4.2%로 이 범위에서의 공기량은 압축강도에 영향을 미치지 못하는 것으로 나타났다. 휨 인장강도에 있어 W/B와 SP/C는 무시할 만큼 작은 영향을 미쳤으며, 상온 양생한 UHPC의 경우 섬유 혼입률이 휨 인장성능을 지배 하는 것으로 평가 되었다. 다만, 체적비로 1%의 강섬유가 혼입된 시편의 경우 섬유가 혼입되지 않은 시편과 달리 균열 후 연성적인 거동은 보였으나, 강도 증진에는 효과가 없는 것으로 나타났다. 반면, 체적비 2%의 강섬유가 혼입된 시편은 강도와 연성을 크게 증가시켰다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
• /
• pp.513-518
• /
• 2002

In vertical construction joint, adhesives such as epoxy, acrylic, latex, etc. have been usually used for bonding fresh concrete to hardened concrete. In this study, performance of adhesives under various application conditions was investigated through tests for slant shear and flexural strength. From the results of the tests, it is found that superior bonding performance can be obtained under good surface preparation without adhesive when high strength concrete is used.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
• /
• pp.69-72
• /
• 1999

In this study, we blended 2 grades of ultra fine cement using the results of previous stud. And the cement slurry was produced by water each water/cement ratio. The slurries were observed hydration phenomena during 28 days with SEM, XRD and DSC. The specimen made by slurry were evaluated with the hardened properties such as compressive strength, flexural strength length change and water absorption. And were tested the adhesive strength of specimen made by injecting the slurry between mortar bars.

• 대한기계학회논문집
• /
• 제3권3호
• /
• pp.116-123
• /
• 1979

On the basis of optical microscope and electro microscope observation for the fatigue fracture process of medium corbon martensitic structure produced by rapid heat treatment, mainly the abstracts of the studied results for the morphology of fatigue crack initiation process of high hardened steel are summarized as follows. Fatigue crack initiated from inclusion on the surface or subsurface. Above all the crack which initiated from inclusion exposed on the surface in as follows. (1) fatigue crack initiated from the boundary of the matrix and inclusion. (2) fatigue crack initiated at surrounding of small pit by drop out of inclusion.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1993년도 춘계학술대회 논문집
• /
• pp.13-17
• /
• 1993

Analytical models for the prediction of the size of hardened zone in laser surface hardening are presented. The models are based on the solutions to the problem of three-dimensional heat flow in plates with infinite thickness. The validity of the model was tested on medium carbon steel for Gaaussian mode of beam. Then the model for rectangular beam was used for the prediction of the size of harened zone on various hardening process parameters. From the calculation results it appeared that the size and shape of the hardened zone are strongly dependent on process parameters suchas beam mode, beam size, and traverse speed.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1995년도 추계학술대회 논문집
• /
• pp.676-679
• /
• 1995

Practically, induction surface hardening is used widely to enhance the local strength of structure. In this study, Fatigue limit and its S-T characteristic for raw and induction hardened specimen of SCM440 is studied experimentally. The life prediction was considered by Juvinall's equation and its predicted result is compared with experiment.

• 소성∙가공
• /
• 제6권5호
• /
• pp.395-399
• /
• 1997

There exists a certain functional relation between Vickers hardness and flow stress in the strain-hardened material. Using this relation, the Vickers hardness values in the strain-hardened material can be converted into the flow stress values in good approximation. Therefore, the information about the flow stress distribution in the material can be easily acquired through a forming experiment. That makes it possible to simulate the process state for a critical moment of cold forging under the given boundary conditions very quickly without calculating the foregoing history of the actual deformation from the beginning.

• 한국세라믹학회지
• /
• 제31권12호
• /
• pp.1536-1544
• /
• 1994

DSP technique was applied to improve the high strength characteristics of hardened cement paste using pozzolan materials as blending materials, and pozzolan reactivity was investigated. Pozzolanic materials such as diatomaceous earth, fly ash and hydrated silica were used as blending material. And also superplasticizer was added to cement for molding the specimens. After curing for 60 days, the specimens substituted with 10 and 15 wt% of diatomaceous earth showed better strength characteristics than the specimen with fly ash. The specimen substituted 7 wt.% of hydrated silica exhibited excellent strength with above 800 kg/$\textrm{cm}^2$.

• 한국세라믹학회지
• /
• 제28권7호
• /
• pp.509-516
• /
• 1991

The effect of various polymers on the freeze-thaw resistance of hardened cement mortar was investigated. For this study, styrene butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyvinyl alcohol (PVA) were used to prepare cement mortar specimen, and then freeze-thaw experiment was carried out. By adding SBR adn EVA to the specimen, the freeze-thaw resistance of specimens was improved, but when PVA was added to the specimen, its freeze-thaw resistance was lowered. Particularly, the specimens which were added 5, 10% of SBR and 5% of EVA showed excellent freeze-thaw resistance in the salt environment.

• 한국세라믹학회지
• /
• 제34권5호
• /
• pp.449-452
• /
• 1997

Quick hardened property and compressive strength experimented to the C4A3 quantities. Workability experimented to the hydration behavior as retarder added to the C4A3. Compressive strength reached {{{{ delta }}3h=300~350 kgf/$\textrm{cm}^2$, {{{{ delta }}6h=400~450 kgf/$\textrm{cm}^2$, {{{{ delta }}24h=500~550 kgf/$\textrm{cm}^2$. Flow loss rate reached 70.1% to retarder addition 0.12% after 15 min. Test items were SEM, XRD, TG-DTA, MCC, porosity and zeta potential.