• Advances in concrete construction
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• 제16권3호
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• pp.127-139
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• 2023

In this study, the steel fiber and the polypropylene fiber were used to enhance the mechanical properties of fully recycled coarse aggregate concrete. Natural crushed stone was replaced with recycled coarse aggregate at 100% by volume. The steel fiber and polypropylene fiber were used as additive material by incorporating into the mixture. In this test two parameters were considered: (a) steel fiber volume ratio (i.e., 0%, 1%, 1.5%, 2%), (b) polypropylene fiber volume ratio (i.e., 0%, 0.1%, 0.15%, 0.2%). The results showed that compared with no fiber, the integrity of cubes or cylinders mixed with fibers after failure was better. When the volume ratio of steel fiber was 1~2%, the width of mid-span crack after flexural failure was 5~8 mm. In addition, when the volume ratio of polypropylene fiber was 0.15%, with the increase of steel fiber content, the static elastic modulus and toughness of axial compression first increased and then decreased, and the flexural strength increased, with a range of 6.5%~20.3%. Besides, when the volume ratio of steel fiber was 1.5%, with the increase of polypropylene fiber content, the static elastic modulus decreased, with a range of 7.0%~10.5%. The ratio of axial compression toughness first increased and then decreased, with a range of 2.2%~8.7%. The flexural strength decreased, with a range of 2.7%~12.6%. On the other hand, the calculation formula of static elastic modulus and cube compressive strength of fully recycled coarse aggregate with steel-polypropylene fiber was fitted, and the optimal fiber content within the scope of the test were put forward.

• Computers and Concrete
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• 제4권1호
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• pp.19-32
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• 2007

This paper is concentrated on the behaviors of five different types of fiber reinforced concrete (FRC) in uniaxial tension and flexural impact. The complete stress-strain responses in tension were acquired through a systematic experimental program. It was found that the tensile peak strains of concrete with micro polyethylene (PEF) fiber are about 18-31% higher than that of matrix concrete, those for composite with macro polypropylene fiber is 40-83% higher than that of steel fiber reinforced concrete (SFRC). The fracture energy of composites with micro-fiber is 23-67% higher than that of matrix concrete; this for macro polypropylene fiber and steel fiber FRCs are about 150-210% and 270-320% larger than that of plain concrete respectively. Micro-fiber is more effective than macro-fiber for initial crack impact resistance; however, the failure impact resistance of macro-fiber is significantly larger than that of microfiber, especially macro-polypropylene-fiber.

• Advances in concrete construction
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• 제16권1호
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• pp.1-20
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• 2023

This study presents the experimental results performed to evaluate the effects of Polyvinyl-alcohol (PVA) and Polypropylene (PP) fibers on the fresh and residual mechanical properties of the hybrid fiber reinforced SCC before and after the exposure of 250℃, 500℃ and 750℃ temperatures. The compressive and splitting tensile strength, modulus of rupture (MOR), ultrasonic pulse velocity (UPV) as well as toughness and weight loss were investigated at different temperatures. PVA and PP fibers were added into SCC mixtures having only macro steel fiber and also having binary hybridization of both macro and micro steel fiber. The results showed that the use of micro steel fiber replaced by macro steel fiber improved the fresh and hardened properties compared to the use of only macro steel fiber. Moreover, it was emphasized that PVA or PP enhanced the residual flexural performance of SCC, generally, while it negatively influenced the workability, weight loss, UPV and the residual strengths with regards to the use of single steel fiber and binary steel fiber hybridization. Compared to the effect of synthetic fibers, PP had slightly more positive effect in the view of workability while PVA enhanced the residual mechanical properties more.

• Advances in concrete construction
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• 제10권4호
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• pp.319-332
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• 2020

The impacts of reinforcing concrete matrix with steel fibers, polypropylene fibers and recycled plastic fibers using different volume fractions of 0.15%, 0.5%, 1.5% and 2.5% on the compressive and tensile characteristics are experimentally investigated in the current research. Also, flexural behavior of plain concrete (PC) beams, shear performance of reinforced concrete (RC) beams and compressive characteristics of both PC and RC columns reinforced with recycled plastic fibers were studied. The experimental results showed that the steel fibers improved the splitting tensile strength of concrete higher than both the polypropylene fibers and recycled plastic fibers. The end-hooked steel fibers had a positive effect on the compressive strength of concrete while, the polypropylene fibers, the recycled plastic fibers and the rounded steel fibers had a negative impact. Compressive strength of end-hooked steel fiber specimen with volume fraction of 2.5% exhibited the highest value among all tested samples of 32.48 MPa, 21.83% higher than the control specimen. The ultimate load, stiffness, ductility and failure patterns of PC and RC beams in addition to PC and RC columns strengthened with recycled plastic fibers enhanced remarkably compared to non-strengthened elements. The maximum ultimate load and stiffness of RC column reinforced with recycled plastic fibers with 1.5% volume fraction improved by 21 and 15%, respectively compared to non-reinforced RC column.

• Computers and Concrete
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• 제22권2호
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• pp.209-220
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• 2018

In order to evaluate the effect of hybrid fibers on the flexural performance of tunnel segment at room temperature, twelve reinforced self-consolidating concrete (SCC) symmetric inclination beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their hybridizations were studied under combined loading of flexure and axial compression. The results indicate that the addition of mono steel fiber and hybrid fibers can enhance the ultimate bearing capacity and cracking behavior of tested beams. These improvements can be further enhanced along with increasing the content of steel fiber and macro PP fiber, but reduced with the increase of the reinforcement ratio of beams. The hybrid effect of steel fiber and macro PP fiber was the most obvious. However, the addition of micro PP fibers led to a degradation to the flexural performance of reinforced beams at room temperature. Meanwhile, the hybrid use of steel fiber and micro polypropylene fiber didn't present an obvious improvement to SCC beams. Compared to micro polypropylene fiber, the macro polypropylene fiber plays a more prominent role on affecting the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC symmetric inclination beams at room temperature by taking appropriate effect of hybrid fibers into consideration was proposed. The prediction results using the proposed model are compared with the experimental data in this study and other literature. The results indicate that the proposed model can estimate the ultimate bearing capacity of SCC symmetric inclination beams containing hybrid fibers subjected to combined action of flexure and axial compression at room temperature.

• 대한토목학회논문집
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• 제34권6호
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• pp.1677-1685
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• 2014

섬유를 콘크리트의 보강재로 소량 혼입한 섬유 보강 콘크리트는 콘크리트의 인장저항 능력과 연성능력을 향상시킬 수 있다. 최근에는 강섬유의 적용성이 확대됨에 따라 강섬유 길이의 연장을 통해 보강의 효과를 증대시키고 있다. 섬유의 길이 연장은 동일한 시공성과 품질성을 위해 섬유 혼입률을 동시에 감소시킬 필요가 있다. 따라서, 본 연구에서는 35mm, 60mm 길이의 강섬유와 화학적인 안정성과 내구성, 경제성 등이 우수한 보강 재료로 평가되어지고 있는 폴리프로필렌 섬유에 대해 섬유혼입률 1.0% 이하에서의 휨 성능을 평가하였다. 강섬유 혼입률이 0.25% 이상, 폴리프로필렌 섬유는 혼입률 0.5% 이상에서 균열강도 도달 후 취성 파괴되는 무보강보의 파괴거동을 개선하는 효과가 나타났다. 다만, 폴리프로필렌 섬유가 혼입된 보강 콘크리트는 균열 이후 deflection-softening 거동을 보였다. 그러나, 0.5%이상의 폴리프로필렌이 혼입된 보강보는 균열 이후 최대강도가 균열강도의 약 60~80%정도 강도회복을 보였으며, 강섬유에 비해 균열 이후 응력감소현상을 지연시키는 경향이 뛰어난 것으로 판단된다. 결론적으로 폴리프로필렌 보강콘크리트는 0.75% 혼입률 이상에서는 충분히 만족할 만한 구조적 휨 성능 향상을 보일 수 있을 것으로 판단된다. 특히, 폴리프로필렌 1.0% 보강 콘크리트의 에너지 흡수 성능은 0.5%, 0.75%가 혼입된 강섬유 보강 콘크리트의 에너지 흡수성능과 거의 비슷한 것으로 평가되었다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2020년도 봄 학술논문 발표대회
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• pp.132-133
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• 2020

The aim of this study is to evaluate the combination effect of amorphous steel fiber and polypropylene fiber on spalling of the 150MPa level ultra high strength concrete. Considering spalling has a great relationship with water vapor pressure, this paper is focusing on water vapor pressure. The test specimens were heated accordance with ISO-834 Standard Curve using electric heating furnace, the depth of 10mm water vapor pressure formation was tend to get faster and spalling damage become severe when the mixing proportion of amorphous steel fiber increase. When using ultra high strength concrete reinforced with amorphous steel fiber, further research about proper mixing proportion of polypropylene fiber.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.315-325
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• 2017

The purpose of the paper is to determine the influence of two widely used steel fibers and polypropylene fibers on the sulphate crystallization resistance, freeze-thaw resistance and surface wettability of ultra-high performance concrete (UHPC). Tests were carried out on cubes and cylinders of plain UHPC and fiber reinforced UHPC with varying contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Extensive data from the salt resistance test, frost resistance test, dynamic modulus of elasticity test before and after freezing-thawing, as well as the contact angle test were recorded and analyzed. Fiber hybridization relatively increased the resistance to salt crystallization and freeze-thaw resistance of UHPC in comparison with a single type of fiber in UHPC at the same fiber volume fraction. The experimental results indicate that hybrid fibers can significantly improve the adhesion properties and reduce the wettability of the UHPC surface.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.623-636
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• 2012

The aim of the current work is to describe the flexural behaviour of simply supported concrete beams with tension reinforcement spliced at mid-span. The parameters included in the study were the type of the concrete, the splice length and the configuration of the hooked splice. Fifteen beams were cast using an ordinary concrete mix and two fiber reinforced concrete mixes incorporating steel and polypropylene fibers. Each concrete mix was used to cast five beams with continuous, spliced and hooked spliced tension steel bars. A test beam was reinforced on the tension side with two 12 mm bars and the splice length was 20 and 40 times the bar diameter. The hooked bars were spliced along 20 times the bar diameter and provided with 45-degree and 90-degree hooks. The test results in terms of cracking and ultimate loads, cracking patterns, ductility, and failure modes are reported. The results demonstrated the consequences due to short splices and the improvement in the structural behaviour due to the use of hooks and the confinement provided by the steel and polypropylene fibers.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.29-37
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• 2016

The paper presents a research project on the tensile properties of RPC mixed with both steel and polypropylene fibers after exposure to $20-900^{\circ}C$. The direct and the indirect tensile strength (in bending) were measured through tensile experiment on dog-bone specimens and bending experiment on $40{\times}40{\times}160mm$ prisms. RPC microstructure was analyzed using scanning electron microscope. The results indicate that, steel fibers can significantly improve the tensile performance of hybrid fiber-reinforced RPC, whereas polypropylene fibers have no obvious effect on the tensile performance. With increasing temperature, the flexural and axial tensile strength of hybrid fiber-reinforced RPC substantially decrease linearly, which attributes to the deteriorating microstructure. Based on the experimental results, equations are established to express the decay of the flexural and tensile strength with increasing temperature.