• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문발표회
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• pp.59-62
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• 2003

Kinds, shapes and fraction ratios of fibers have influence on properties of HPFRCC(High-Performance Fiver Reinforced Cementitious Concrete ) like bending strength, strain capacity and fracture toughness. For example, hydrophilic fibers have different chemical bond strength from hydrophobic fibers, fiber shapes influence on fiber pull-out and rupture, and fiber volume fraction influence on bending strength. In this study, to estimate influences of kinds, shapes and fraction ratios of fibers, we make HFRCC with 3 kind of fiber in various volume fraction of fiber and compare cracking, bending strength and fracture toughness. As the results, bending strength of HPFRCC was increased as fiber volume fraction was Increase and fiber tensile strength was increase, and strain capacity and fracture toughness of HFRCC was higher in fiber pull-out fracture than in fiber rupture fracture. And HFRCC showing pseudo strain hardening has higher fiber reinforce efficiency than others.

• 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.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문 발표회
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• pp.59-62
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• 2003

Kinds, shapes and fraction ratios of fibers have influence on properties of HPFRCC(High-Performance Fiver Reinforced Cementitious Concrete) like bending strength, strain capacity and fracture toughness. For example, hydrophilic fibers have different chemical bond strength from hydrophobic fibers, fiber shapes influence on fiber pull-out and rupture, and fiber volume fraction influence on bending strength. In this study, to estimate influences of kinds, shapes and fraction ratios of fibers, we make HFRCC with 3 kind of fiber in various volume fraction of fiber and compare cracking, bending strength and fracture toughness. As the results, bending strength of HPFRCC was increased as fiber volume fraction was increase and fiber tensile strength was increase, and strain capacity and fracture toughness of HFRCC was higher in fiber pull-out fracture than in fiber rupture fracture. And HFRCC showing pseudo strain hardening has higher fiber reinforce efficiency than others.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.937-940
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• 2006

According to the analysis of tension failure mechanism of UHSC specimen, one modified model based on ACK model by the introduction of partial debonding energy of non-first cracks and by the application of steel fiber number on unit area is presented in this paper. It can be used to explain the evolution mechanism of multiple cracking and pseudo strain hardening of UHSC. From the numerical results, to increase steel fiber length and to reduce steel fiber diameter in some region all can reduce the fiber volume fraction with the same multiple cracks for economic design of UHSC.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.740-743
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• 1995

The analysis model is the power law creep material containing an elliptical rigid inclusion subjected to the arbitrarily directional stress on infinite boundary. The stress analysis is performed using the conformal mapping function and complex pseudo-stress function. The stress distributions near an elliptical rigid inclusion are obtained with various ellipse shapes, strain hardening exponents and directions of applied stress.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.257-260
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• 2006

Coupled shear walls consist of two or more in-plane walls inter-connected with coupling beams. In order to effectively resist seismic loads, coupling beams must be sufficiently stiff, strong and posses a stable load-deflection hysteretic response. Much of requirements to the civil and building structures have recently been changed in accordance with the social and economic progress. Ductility of high performance fiber reinforced cementitious composites(HPFRCCs), which exhibit strain hardening and multiple crackling characteristics under the uniaxial tensile stress is drastically improved. This paper provides background for design guidelines that include a design model to calculate the shear strength of pseudo strain hardening cementitious composite steel coupling beam.

• 콘크리트학회논문집
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• 제24권4호
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• pp.361-368
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• 2012

보수 보강재는 강도, 안정성, 내구성, 모재와의 부착력 등 많은 특성이 필요하며, 최근 변형경화형 시멘트 복합체(strain-hardening cement-based composite, SHCC)가 기존의 재료를 대체할 수 있는 성능으로 많은 연구가 이루어지고 있다. 팽창형 SHCC는 팽창재를 이용하여 수축이 발생하는 SHCC의 단점을 보완하여 성능을 개선시킨 복합체로 이를 이용해 보강재의 성능을 만족시키면서 동시에 강도 증진 효과를 가져올 수 있을 것으로 예상된다. 따라서 이 연구에서는 SHCC 보강재의 강도, 팽창재 대체 여부 및 보강 두께를 변수로 하여 휨 성능을 평가하였으며, 실제 보강에 적용 시 기초 자료로 활용하고자 한다.

• 한국구조물진단유지관리공학회 논문집
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• 제16권2호
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• pp.95-103
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• 2012

변형경화형 시멘트 복합체(SHCC)는 직접인장 상황에서 FRCCs에 비해 우수한 변형경화 특성을 갖는 재료이다. 하지만 SHCC는 일반적인 콘크리트에 비해서 시멘트비율이 높은 부배합 이며, 이에 따라서 자기수축이 큰 특성을 갖는 재료이다. 따라서 시멘트 복합체 내에 팽창재를 대체함으로써 수축저감을 통한 성능향상을 기대하였다. 이 연구에서는 각 강도별 SHCC의 배합에 팽창재를 대체함에 따른 역학적특성을 평가하고자 하였다. 시험결과 설계기준 압축강도 70MPa 배합이 압축, 인장, 휨, 시험에서 우수한 역학적 특성을 나타내었으며, 균열 특성에서는 팽창재를 대체한 SHCC가 균열분산 및 연성에서 우수한 특성을 나타내었다.

• Advances in nano research
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• 제15권5호
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• pp.467-484
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• 2023

Despite the significant features of fiber-reinforced cementitious composites (FRCCs), including better mechanical, fractural, and durability performance, their high content of cement has restricted their use in the construction industry. Although ground granulated blast furnace slag (GGBFS) is considered the main supplementary cementitious material, its slow pozzolanic reaction stands against its application. The addition of nano-sized mineral modifiers, including nano-silica (NS), is an alternative to address the drawbacks of using GGBFS. The main object of this empirical and numerical research is to examine the effect of NS on the strain-hardening behavior of cementitious composites; ten mixes were designed, and five levels of NS were considered. This study proposes a new method, using a four-point bending test to assess the use of nano-silica (NS) on the flexural behavior, first cracking strength, fracture energy, and micromechanical parameters including interfacial friction bond strength and maximum bridging stress. Digital image correlation (DIC) was used for monitoring the initiation and propagation of the cracks. In addition, to attain a deep comprehension of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. It was discovered that using nano-silica (NS) in cementitious materials results in an enhancement in the matrix toughness, which prevents multiple cracking and, therefore, strain-hardening. In addition, adding NS enhanced the interfacial transition zone between matrix and fiber, leading to a higher interfacial friction bond strength, which helps multiple cracking in the composite due to the hydrophobic nature of polypropylene (PP) fibers. The findings of this research provide insight into finding the optimum percent of NS in which both ductility and high tensile strength of the composites would be satisfied. As a concluding remark, a new criterion is proposed, showing that the optimum value of nano-silica is 2%. The findings and proposed method of this study can facilitate the design and utilization of green cementitious composites in structures.

• 대한기계학회논문집A
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• 제22권2호
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• pp.408-415
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• 1998

The analysis model is the power law creep material containing an elliptical rigid inclusion subjected to the arbitrarily directional stress on infinite boudary. The stress analysis is performed using the conformal mapping function and complex pseudo-stress function. The stress distributions near an elliptical rigid inclusion are obtained with various ellipse shapes, strain hardening exponents and directions of applied stress.