• Computers and Concrete
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• 제7권2호
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• pp.191-202
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• 2010

A laboratory investigation was conducted to characterize the constitutive property behavior of Cor-Tuf, an ultra-high-performance composite concrete. Mechanical property tests (hydrostatic compression, unconfined compression (UC), triaxial compression (TXC), unconfined direct pull (DP), uniaxial strain, and uniaxial-strain-load/constant-volumetric-strain tests) were performed on specimens prepared from concrete mixtures with and without steel fibers. From the UC and TXC test results, compression failure surfaces were developed for both sets of specimens. Both failure surfaces exhibited a continuous increase in maximum principal stress difference with increasing confining stress. The DP tests results determined the unconfined tensile strengths of the two mixtures. The tensile strength of each mixture was less than the generally assumed tensile strength for conventional strength concrete, which is 10 percent of the unconfined compressive strength. Both concretes behaved similarly, but Cor-Tuf with steel fibers exhibited slightly greater strength with increased confining pressure, and Cor-Tuf without steel fibers displayed slightly greater compressibility.

• 한국건설순환자원학회논문집
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• 제1권2호
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• pp.128-135
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• 2013

본 연구에서는 비정질 강섬유보강 콘크리트 슬래브의 전단성능을 분석하기 위하여 일면 전단 실험을 수행하였다. 주요 변수는 전단보강방법과 전단보강비이며, 1종류의 무전단보강실험체와 3종류의 전단보강실험체(전단철근, 0.25%, 0.5% 비정질 강섬유보강 실험체)의 일방향 슬래브 실험체를 제작하여 실험하였다. 실험결과, 0.25% 비정질 강섬유보강실험체는 전단 성능이 향상되었지만 0.5% 실험체는 0.25% 보강실험체에 비해 전단성능이 향상되지 않았다. 섬유 보강비에 따른 전단보강 효과를 파악하기 위한 추가적인 연구가 필요하다.

• Advances in concrete construction
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• 제13권1호
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• pp.35-43
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• 2022

The experimental investigations into hooked-end round steel fibers (HSF) effect on the age-dependent strengths of high volume fly ash (HVFA) concrete is studied. The concrete was prepared with class F fly ash used as partial cement replacement varied from 0% to 70% on an equal weight basis. Two percentages of HSF (i.e., 0.5% and 1.5% by volume fraction) of 50 mm length were added in plain, and 50% fly ash concrete mixes. The compressive and flexural tensile strength was determined at 7, 28, 56, and 90 days. The strength results of fly ash concrete mixes with and without steel fibers were compared with the plain concrete strength. The test results indicated that the strength of fly ash concrete is comparable with the plain concrete strength and further increases with an increase in the percentage of steel fibers. The maximum flexure strength of HVFA concrete is found with 0.5% steel fibers. It is concluded that the HVFA concrete with steel fibers of 50 mm length can effectively be used in concrete construction. The analytical models are proposed to predict the age-dependent compressive and flexural tensile strength of HVFA concrete with and without HSF. The compressive and tensile strength of HVFA concrete with HSF can be predicted using these models when the 28-day compressive strength of plain concrete is known. The present study will be helpful in the design and construction of reinforced and pre-stressed concrete structures made with HVFA and HSF.

• International Journal of Concrete Structures and Materials
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• 제3권2호
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• pp.119-126
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• 2009

This paper provides a brief summary of the performance of an innovative slip hardening twisted steel fiber in comparison with other fibers including straight steel smooth fiber, high strength steel hooked fiber, SPECTRA (high molecular weight polyethylene) fiber and PVA fiber. First the pull-out of a single fiber is compared under static loading conditions, and slip rate-sensitivity is evaluated. The unique large slip capacity of T-fiber during pullout is based on its untwisting fiber pullout mechanism, which leads to high equivalent bond strength and composites with high ductility. Due to this large slip capacity a smaller amount of T-fibers is needed to obtain strain hardening tensile behavior of fiber reinforced cementitious composites. Second, the performance of different composites using T-fibers and other fibers subjected to tensile and flexural loadings is described and compared. Third, strain rate effect on the behavior of composites reinforced with different types and amounts of fibers is presented to clarify the potential application of HPFRCC for seismic, impact and blast loadings.

• Advances in concrete construction
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• 제9권4호
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• pp.367-374
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• 2020

Concrete surfaces, industrial floors, sidewalks, roads and parking lots are typically subjected to abrasions. Many studies indicated that the abrasion resistance is directly related to the ultimate strength of the cured concrete. Chemical reactions, freeze-thaw cycles, and damages under abrasion are among many factors negatively affecting the concrete strength and durability. One of the major solutions to address the abrasive resistance of the concrete is to use fibers. Fibers are used in the concrete mix to improve the mechanical properties, strength and limit the crack propagations. In this study, implementation of the steel fibers in concrete to enhance the abrasive resistance of the concrete is investigated in details. The abrasive resistance of the concrete with and without steel fibers is studied with the sandblasting technique. For this purpose, different concrete samples are made with various hooked steel fiber ratios and investigated with the sandblasting method for two different strike angles. In total, 144 ASTM verified cube samples are investigated and it is shown that those samples with the highest steel fiber ratios have the highest abrasive resistance. In addition, the experiments determine that there is a meaningful correlation between the steel fiber percentage in the mix, strike angle and curing time which could be considered for improving structural behavior of the fiber-reinforced concrete.

• 한국구조물진단유지관리공학회 논문집
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• 제25권6호
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• pp.209-217
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• 2021

이 논문은 고강도 후크형 강섬유 보강량과 형상비에 따른 콘크리트의 압축 및 휨 성능에 미치는 영향에 대하여 다룬다. 이를 위하여 총 10개 콘크리트 배합이 계획되었다. 설계기준강도 30 MPa인 콘크리트에 형상비(l/d)가 64, 67, 80인 강섬유를 0.25%, 0.50%, 0.75% 혼입하여 강섬유 보강콘크리트가 제조되었다. 형상비 64, 67, 80인 강섬유의 인장강도는 각각 2,000, 2,400, 2,100 MPa이다. 시험 결과로부터 고강도 후크형 강섬유의 혼입량은 콘크리트의 압축 및 휨 성능에 영향을 미치는 것으로 나타났다. 강섬유 혼입량이 증가함에 따라 푸아송비 및 압축인성은 향상되었으나 콘크리트의 압축강도 및 탄성계수에 큰 변화를 보이지 않았다. 강섬유 보강 콘크리트의 균열발생후 휨거동의 특성을 나타내는 잔여 휨강도 및 노치에서 시작된 균열면에서 에너지 소산능력은 강섬유의 혼입률 및 형상비에 따라 크게 좌우되었다. 특히 MC2010에서 정의된 사용 및 극한 상태한계에서의 잔여 휨강도는 강섬유 혼입량과 형상비가 증가함에 따라 증가되었다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권3호
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• pp.84-91
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• 2022

본 연구에서는 반복하중을 받는 대각선 철근콘크리트 커플링 보의 강섬유 형상비와 혼입률에 따른 이력거동을 분석하기 위한 실험적 연구를 수행하였다. 강섬유의 형상비와 혼입률을 주요변수로 설정하였으며, 국내 건축구조기준에서 제시한 연결보의 횡방향 보강량이 약 53% 완화된 4개의 실험체를 제작하였다. 실험에서는 ACI 374.2R-13에 따른 변위제어법으로 반복하중 실험을 수행하였으며, 실험 결과 강섬유가 혼입된 모든 실험체가 현행 구조기준에서 제시하는 공칭전단강도를 상회함을 확인하였다. 강섬유의 형상비가 증가할수록 대각선 철근의 좌굴을 방지하고 강섬유의 브리징 효과로 콘크리트의 균열면 증가를 방지하였다. 강섬유가 혼입된 실험체의 전단강도, 강성감소 및 에너지 소산능력은 강섬유가 혼입되지 않은 Vf0 실험체보다 우수하였다. 따라서 강섬유 철근콘크리트가 횡철근의 디테일을 완화할 수 있다고 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 가을 학술발표회 논문집
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• pp.76-81
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• 1992

Short, randomly disturbed steel fibers in concrete increase tensile strength and ductility of concrete under direct tension. These improvements are results form crack arrest mechanisms of steel fibers in concrete. These mechanisms are theoretically considered in this study and verification on the adequancy of different spacing for predicting tensile strength of SFRC are assessed. Results indicate that better correlation exists between experimental result and the spacing concept which take into account the effect of boundaries as well as vibration on reorientation of steel fibers inside concrete. Also considered is the modeling of stress-crack opening relationships in post-peak region of SFRC under tension which bass its deviation on micromechanics of fiber pull-out. Satisfactoring results are observed between tests results and the prediction of the model.

• 한국구조물진단유지관리공학회 논문집
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• 제2권3호
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• pp.188-193
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• 1998

An experimental study was performed on the pull-out behavior of 90-deg standard hooks from exterior beam-column connections. The effects of lateral confinement and fiber reinforcement of joint area were investigated. It was concluded ; (1) Substitution of the transverse column (confining) reinforcement with steel fibers at the joint region effectively reduces the extent of cracking in exterior joints caused by pull-out of hooked bars; and (2) The strength and ductility of hooked bars under pull-out forces are positively influenced by substituting the conventional confining reinforcement of exterior joints with steel fibers. Application of steel fibers to exterior joints seems to be an effective technique for improving the anchorage conditions of hooked bars, and also for reducing the congestion of reinforcement in exterior beam-column connections.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.373-378
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• 2003

The cement-based composites have relatively low tensile strength and toughness. The fiber addition is one of the most important ways of increasing the toughness of concrete. The steel fibers have been used conventionally in the shotcrete of tunnel lining. Recently, the structural synthetic fibers were developed and used frequently in some actual tunnel shotcreting in foreign countries. Now types of synthetic fibers have been developed in this study. The purpose of this study is to explore the strength and toughness characteristic of the concrete reinforced with synthetic fibers developed in this study. The result were compared with those of steel fiber reinforced concrete. It is seen that the performance of synthetic fiber reinforced concrete is good as much as that of steel fiber reinforced concrete, while the synthetic fibers have advantages in corrsion resistance and economy.