• 콘크리트학회지
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• 제16권5호
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• pp.64-72
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• 2004

• Earthquakes and Structures
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• 제18권4호
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• pp.451-466
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• 2020

In this paper, the effect of Engineered Cementitious Composites (ECC) on the lateral strength of a bearing unreinforced Masonry (URM) wall, was experimentally and numerically investigated. Two half scale solid walls were constructed and were tested under quasi-static lateral loading. The first specimen was an un-retrofitted masonry wall (reference wall) while the second one was retrofitted by ECC mortar connected to the wall foundation via steel rebar dowels. The effect of pre-compression level, ECC layer thickness and one or double-side retrofitting on the URM wall lateral strength was numerically investigated. The validation of the numerical model was carried out from the experimental results. The results indicated that the application of ECC layer increases the wall lateral strength and the level of increment depends on the above mentioned parameters. Increasing pre-compression levels and the lack of connection between the ECC layer and the wall foundation reduces the influence of the ECC mortar on the wall lateral strength. In addition, the wall failure mode changes from flexure to the toe-crashing behavior. Furthermore, in the case of ECC layer connected to the wall foundation, the ECC layer thickness and double-side retrofitting showed a significant effect on the wall lateral strength. Finally, a simple method for estimating the lateral strength of retrofitted masonry walls is presented. The results of this method is in good agreement with the numerical results.

• 한국전산구조공학회논문집
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• 제22권6호
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• pp.597-605
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• 2009

본 연구에서는 철근 보강된 Engineered Cementitious Composite(ECC) 면내요소에 대한 2축응력 상태에서의 면내전단거동에 관한 예측 모델을 제시하였다. 기존의 철근콘크리트와 상이한 특성, 즉 ECC 요소의 복수미세균열 현상에 의한 높은 연성의 인장 거동, 일반 콘크리트에 비하여 연성적인 압축 연화 거동, 그리고 ECC 균열면에서의 전단전달 거동 특성 등을 모델에 반영하였다. 면내 순수전단거동에 대한 실험 및 해석결과를 통하여 개발된 R-ECC-MCFT 모델은 ECC 면내전단거동 예측에 효과적인 것으로 평가되었다. 또한 철근 보강된 ECC 면내요소는 철근콘크리트 면내요소에 비하여 최대전단강도 및 전단변형률이 증가하기 때문에 면내전단변형에서 높은 연성을 확보하는 것으로 평가되었다.

• Composites Research
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• 제23권3호
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• pp.50-57
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• 2010

섬유 보강 시멘트계 복합재료의 성능 예측 및 평가에 있어서 중요한 영향을 미치는 섬유 분포 특성을 정량적으로 평가하기 위해서는 복합재료의 단면 이미지에서 섬유를 정확히 검출하여야 한다. 이 논문은 형광원리를 이용하여 합성섬유를 매트릭스로부터 개별적으로 검출하기 위한 기초 연구로써 섬유 보강 시멘트계 복합재료 중의 하나인 ECC에 일반적으로 사용되는 PVA 섬유, PET 섬유, PE 섬유, 그리고 PP 섬유의 형광특성을 분석하였다. 또한 하이브리드 된 경우 합성섬유들 간의 상대 형광 광도값의 차이를 비교하여 종류별로 구분하기 위한 최적의 파장대를 선정하였으며, 그 파장대에서 두 분류대상을 구별할 수 있는 최적의 경계값을 통계적 방법을 이용하여 산출하였다. 또한 형광 현미경을 이용하여 각 섬유를 촬영하여 상대적인 밝기값을 비교하였다.

• 콘크리트학회지
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• 제18권1호
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• pp.28-35
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• 2006

• 한국구조물진단유지관리공학회 논문집
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• 제13권6호통권58호
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• pp.88-96
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• 2009

본 연구에서는 RC구조물의 내구 및 내화성능을 동시에 향상시킬 수 있는 고인성 모르타르 (FR-ECC) 를 개발하여, 이를 RC구조물의 보수재료로서 사용하기 위한 실험적 연구를 실시하였다. 즉, FR-ECC를 이용하여 제조한 콘크리트 시험체의 강도, 열적특성, 모의부재의 철근부식특성, 내화성능 등에 대하여 검토하였으며, FR-ECC의 현장적용 가능성에 대해서도 평가하였다. 그 결과, FR-ECC는 기존 보수 모르타르에 비해 우수한 강도 및 내구성능을 보유하고, 휨균열 발생 후에도 외부열화 인자의 침입을 억제하여 철근부식을 방지하는 것으로 나타났다. 또한 FR-ECC를 적용한 부재는 ISO 834 가열조건에서도 우수한 내화성능을 갖는 것으로 나타났으며, 뿜칠성능 등의 현장시공 성능에서도 우수한 특성을 나타냈다.

• 비파괴검사학회지
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• 제27권2호
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• pp.148-156
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• 2007

섬유복합재료의 역학적인 관점에서 볼 때 PVA-ECC (polyvinyl alcohol-engineered cementitious composite)의 섬유분산성 평가는 매우 중요한 요소이다. 그러나 PVA 섬유의 낮은 명암비 때문에 시멘트계 재료와 섬유를 구별하기가 어려우므로, PVA-ECC의 섬유분산성 평가를 하기에는 어려운 점이 있다. 이 연구에서는 이러한 문제점을 해결하기 위하여 PVA-ECC 내의 섬유분산성을 평가할 수 있는 새로운 방법을 제시하였다. 형광의 원리를 이용하여 섬유복합재료 단면에서 PVA 섬유가 초록빛을 발하는 이미지를 얻었고, PVA-ECC 시편에 대한 섬유분산성은 형광 현미경에 부착된 CCD (charge coupled device) 카메라를 통하여 얻어진 이미지를 이미지 프로세싱 기법과 통계적인 방법을 이용하여 평가하였다. 또한 형상분석을 통하여 섬유의 방향성이 분산성에 미치는 영향을 파악하였으며, 판별함수기법과 분수령 알고리즘을 이용하여 섬유 검출 성능을 향상시킬 수 있는 기법을 제시하였다.

• Structural Engineering and Mechanics
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• 제62권1호
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• pp.21-31
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• 2017

Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength ($f_{ECC}$), maximum aggregate size ($D_{max}$) and slag amount (${\phi}$) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.575-589
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• 2022

In order to enhance the greenness in the strain-hardening composites and to reduce the high cost of typical polyvinyl alcohol fiber reinforced engineered cementitious composite (PVA-ECC), an affordable strain-hardening composite with green binder content has been proposed. For optimizing the strain-hardening behavior of cementitious composites, this paper investigates the effects of polypropylene fibers on the first cracking strength, fracture properties, and micromechanical parameters of cementitious composites. For this purpose, digital image correlation (DIC) technique was utilized to monitor crack propagation. In addition, to have an in-depth understanding of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. To understand the effect of fibers on the strain hardening behavior of cementitious composites, ten mixes were designed with the variables of fiber length and volume. To investigate the micromechanical parameters from fracture tests on notched beam specimens, a novel technique has been suggested. In this regard, mechanical and fracture tests were carried out, and the results have been discussed utilizing both fracture and micromechanical concepts. This study shows that the fiber length and volume have optimal values; therefore, using fibers without considering the optimal values has negative effects on the strain-hardening behavior of cementitious composites.

• Advances in concrete construction
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• 제6권2호
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• pp.199-220
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• 2018

In this study, the effects of sulphuric acid on the mechanical performance and the durability of Engineered Cementitious Composites (ECC) specimens were investigated. The carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) fabrics were used to evaluate the performances of the confined and unconfined ECC specimens under static and cyclic loading in the acidic environment. In addition, the use of CFRP and BFRP fabrics as a rehabilitation technique was also studied for the specimens exposed to the sulphuric acid environment. The polyvinyl alcohol (PVA) fiber with a fraction of 2% was used in the research. Two different PVA-ECC concretes were produced using low lime fly ash (LCFA) and high lime fly ash (HCFA) with the fly ash-to-OPC ratio of 1.2. Unwrapped PVA-ECC specimens were also produced as a reference concrete and all concrete specimens were continuously immersed in 5% sulphuric acid solution ($H_2SO_4$). The mechanical performance and the durability of specimens were evaluated by means of the visual inspection, weight change, static and cyclic loading, and failure mode. In addition, microscopic changes of the PVA-ECC specimens due to sulphuric acid attack were also assessed using scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that PVA-ECC specimens produced with low lime fly ash (LCFA) showed superior performance than the specimens produced with high lime fly ash (HCFA) in the acidic environment. In addition, confinement of ECC specimens with BFRP and CFRP fabrics significantly improved compressive strength, ductility, and durability of the specimens. PVA-ECC specimens wrapped with carbon FRP fabric showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabric. Both FRP materials can be used as a rehabilitation material in the acidic environment.