• 한국건축시공학회지
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• 제8권5호
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• pp.35-42
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• 2008

In this study, a sample was fabricated according to the recycled aggregate replacement level(0%, 30%, 60%), and the steel fiber mixing status in order to use recycled aggregate as a concrete alternative coarse aggregate, and then the materials and structural characteristics of recycled aggregate and steel fiber which impacted the reinforced concrete were analyzed. A conclusion was derived as follows. After considering the results of various material experiments and mock-up test, when a flexural strength and a ductility factor is increased and the replacement level is increased through mixing the steel fiber with the recycled aggregate concrete, the ductility and flexural strength reduction seems to be inhibited by adding the steel fiber. Also, it is indicated that the recycled aggregate has almost-similar compressive strength, tensile strength flexural strength and ductility capacity to the concrete which using the general gone even though the steel fiber is used and the replacement level is increased to 30%. Accordingly, the reinforced concrete frame using the steel fiber mixture and recycled aggregate seems to apply to the actual structure.

• 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.

• 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.

• Steel and Composite Structures
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• 제27권2호
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• pp.193-200
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• 2018

This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

• Computers and Concrete
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• 제32권2호
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• pp.173-184
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• 2023

In this study, mechanical, flexural post-cracking, and torsional behaviors of recycled steel fiber-reinforced concrete (RSFRC) incorporating steel fibers obtained from recycling of waste tires were investigated. Initially, three concrete mixes with different fiber contents (0, 40, and 80 kg/m³) were designed and tested in fresh and hardened states. Subsequently, the flexural post-cracking behaviors of RSFRCs were assessed by conducting three-point bending tests on notched beams. It was observed that recycled steel fibers improve the post-cracking flexural behavior in terms of energy absorption, ductility, and residual flexural strength. What's more, torsional behaviors of four RSFRC concrete beams with varying reinforcement configurations were investigated. The results indicated that RSFRCs exhibited an improved post-elastic torsional behaviors, both in terms of the torsional capacity and ductility of the beams. Additionally, numerical analyses were performed to capture the behaviors of RSFRCs in flexure and torsion. At first, inverse analyses were carried out on the results of the three-point bending tests to determine the tensile functions of RSFRC specimens. Additionally, the applicability of the obtained RSFRC tensile functions was verified by comparing the results of the conducted experiments to their numerical counterparts. Finally, it is noteworthy that, despite the scatter (i.e., non-uniqueness) in the aspect ratio of recycled steel fiber (as opposed to industrial steel fiber), their inclusion contributed to the improvement of post-cracking flexural and torsional capacities.

• 한국구조물진단유지관리공학회 논문집
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• 제4권4호
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• pp.161-169
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• 2000

Recycled aggregates were generated when concrete structures were dismembered. However, in concrete structures, because of durability, strength and toughness, recycled aggregates don't use generally. This study was done to use recycled aggregate in concrete structures. Problems of durability, strength, and toughness were caused troubles, when recycled aggregates were used, were solved as steel fibers and additives were added. Of course, steel fiber length, steel fiber contents, additive substitution, and recycled aggregate substitution were variables of this study. After flexural specimens($15{\times}15{\times}70cm$) with notch(45mm) were fabricated, basic strength tests were done and toughness was estimated using fracture mechanics parameters. The results suggest that JIC is a promising fracture criterion for all of these, while KIC(or GIC) almost certainly are not.

• 콘크리트학회논문집
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• 제28권3호
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• pp.357-363
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• 2016

순환골재는 천연골재의 고갈문제를 해결하고 고부가가치를 창출할 수 있는 등 건설, 환경산업 부분에서 상당한 효용성을 갖고 있다. 그러나 순환골재의 활용을 위한 사회적 기반이 정립되고 다양한 연구가 진행되었음에도 불구하고, 천연골재에 비해 품질이 떨어지는 문제 때문에 이를 사용한 콘크리트 구조물은 매우 적은 실정이다. 본 연구에서는 순환골재에 의한 콘크리트 성능저하를 보완하기 위한 방안으로서 강섬유를 혼입한 콘크리트의 역학적 특성 및 변형 특성을 검토하였다. 그 결과, 순환골재를 혼입한 콘크리트는 천연골재만을 사용한 콘크리트(plain)에 비해 낮은 압축강도 및 탄성계수를 나타내었으나, 강섬유의 혼입에 의해 plain과 동등 수준의 성능을 확보할 수 있었다. 또한, 건조수축 및 크리프계수에 있어서도 강섬유의 내부구속효과, 수분 이동 구속효과 및 강도의 증진 등에 기인하여 혼입률 0.5 Vol.%의 범위에서 plain과 유사한 거동을 나타낼 수 있었다. 따라서 순환골재 콘크리트를 적극적으로 활용하기 위한 방안으로서 강섬유의 혼입은 매우 효과적일 것으로 판단된다.

• 콘크리트학회논문집
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• 제12권5호
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• pp.93-99
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• 2000

The physical properties of freshly mixed steel fiber reinforced recycled concrete(SFRRC) were_investigated. Physical state and quality of fresh concrete were monitored batch by batch. the properties of freshly mixed SFRRC were determined in terms of slump, air content, superplasticizer, and bleeding ratio. Concrete mixtures were produced for three kinds of aggregate proportions. So, the experimental variables are various aggregate proportions, steel fiber contents(0, 0.5, 1.0, 1.5%) and steel length(30, 50, 60mm). From experimental results, optimum s/a by various experimental variables, variations of the slump by the air contents, and optimum superplasticizer to decrease unit water were presented.

• Advances in concrete construction
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• 제10권6호
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• pp.559-571
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• 2020

This study aimed to inspect the axial compression mechanical performance of basalt-fiber-reinforced recycled - concrete (BFRRC)-filled square steel tubular stub column. The replacement ratio of recycled coarse aggregate (RCA) and the basalt fiber (BF) dosage were used as variation parameters, and the axial compression performance tests of 15 BFRRC-filled square steel tubular stub column specimens were conducted. The failure mode and the load-displacement/strain curve of the specimen were measured. The working process of the BFRRC-filled square steel tubular stub column was divided into three stages, namely, elastic-elastoplasticity, sudden drawdown, and plasticity. The influence of the design parameters on the peak bearing capacity, energy dissipation performance, and other axial compression performance indexes was discussed. A mathematical model of segmental stiffness degradation was proposed on the basis of the degradation law of combined secant-stiffness under axial compression. The full-process curve equation of axial compressive stress-strain was proposed by introducing the influencing factors, including the RCA replacement ratio and the BF dosage, and the calculated curve agreed well with the test-measured curve.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2010년도 춘계 학술논문 발표대회 1부
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• pp.57-61
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• 2010

In this study, many concrete specimens were tested to investigate the variations of strength characteristics of high-strength concrete due to amount of recycled coarse aggregates, and to investigate the effect of steel-fiber reinforcement on concrete using recycled coarse aggregates. Test results showed that all of the variations of compressive, tensile and flexural strength appeared in linear reduction according to icrease the amount of recycled coarse aggregates, and steel-fiber reinforcement of 0.75% volumn of concrete recovered completely spliting tensile strength and flexual strength and recovered greatly compressive strength of concrete using recycled coarse aggregates of 100% displacement. And test results showed that the shear strength falled rapidly at 30% of replacement ratio so far as 34% of strength reduction ratio, but after that it falled a little within 3% up to the replacement ratio 100%, and steel-fiber reinforcement of 0.75% of concrete volumn recovered completely the deteriorated shear strength, moreover improved the shear strength above 50% rather than that of concrete using natural coarse aggregates.