• Computers and Concrete
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• v.5 no.1
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• pp.21-36
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• 2008

Steel fiber reinforced concrete is increasingly used day by day in various structural applications. An extensive experimentation was carried out with w/cm ratio ranging from 0.25 to 0.40, and fiber content ranging from zero to1.5 percent by volume with an aspect ratio of 80 and silica fume replacement at 5%, 10% and 15%. The influence of steel fiber content in terms of fiber reinforcing index on the compressive strength of high-performance fiber reinforced concrete (HPFRC) with strength ranging from 45 85 MPa is presented. Based on the test results, equations are proposed using statistical methods to predict 28-day strength of HPFRC effecting the fiber addition in terms of fiber reinforcing index. A strength model proposed by modifying the mix design procedure, can utilize the optimum water content and efficiency factor of pozzolan. To examine the validity of the proposed strength model, the experimental results were compared with the values predicted by the model and the absolute variation obtained was within 5 percent.

• Computers and Concrete
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• v.11 no.2
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• pp.149-167
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• 2013

The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52-80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• Computers and Concrete
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• v.22 no.5
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.101-109
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• 2008

Many researchers have reported that adding steel fiber to concrete improved its tensile and flexural strength significantly, but relatively few studies have been made on the compressive behavior of steel fiber-reinforced concrete. It is still less in case of high strength steel fiber-reinforced cementitious composites(SFRC). The main objective of this research is to examine the effect of adding steel fiber on the compressive strength of high strength SFRC using fiber reinforcing index(RI, $V_f(I_f/d_f)$). It was found from the study that compressive strength was noticeably increased in proportion to RI. In conclusion, the relationship between Reinforcing Index(RI) and compressive strength in case of high strength steel fiber-reinforced cementitious composites was suggested.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.209-220
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• 1999

This paper is aimed to evaluate the effectiveness of flexural toughness of slab panel structures($60{\times}60{\times}10$) reinforced by steel fiber instead of wire mesh. Steel fiber used in this study is double hooked Dramix type fiber. And the fiber length is 60mm, diameter is 0.8mm, Various assessment methods of toughness index are used to estimate the proper effectiveness. In this experimental study, we find that Johnston, JCI-SF4 and EFNARC method are more effective to assess the flexural toughness of slab panels than the others. And the steel fiber is very effective alternative material to reinforce slab panel structures instead of wire mesh. Fiber volume fraction of 0.5~0.75% is more useful than the others in enhancing the post-peak energy absorption and toughness index by Johnston's $I_{5.5}$ assessment method. And the slab panels reinforcing with steel fiber are more resistant to crack propagation than wire mesh reinforcing slabs.

• Computers and Concrete
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• v.9 no.2
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• Computers and Concrete
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• v.3 no.6
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• pp.389-400
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• 2006

This paper presents the investigations towards developing a better understanding on the contribution of steel fibers on the tensile strength of high-performance fiber reinforced concrete (HPFRC). An extensive experimentation was carried out with w/cm ratios ranging from 0.25 to 0.40 and fiber content ranging from zero to 1.5 percent with an aspect ratio of 80. For 32 concrete mixes, flexural and splitting tensile strengths were determined at 28 days. The influence of fiber content in terms of fiber reinforcing index on the flexural and splitting tensile strengths of HPFRC is presented. Based on the test results, mathematical models were developed using statistical methods to predict 28-day flexural and splitting tensile strengths of HPFRC for a wide range of w/cm ratios. The expressions, being developed with strength ratios and not with absolute values of strengths and are applicable to wide range of w/cm ratio and different sizes/shapes of specimens. Relationship between flexural and splitting tensile strengths has been developed using regression analysis and absolute variation of strength values obtained was within 3.85 percent. To examine the validity of the proposed model, the experimental results of previous researchers were compared with the values predicted by the model.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.1
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• pp.114-123
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• 2013

This study was performed to verify the structural reinforcing effect of recycled polyethylene terephthalate (PET) fiber. In order to verify the structural reinforcing capacity of RPET fiber, recycled PET fiber added RC slab specimens were prepared to examine the flexural capacity while those of plain concrete and those of added with PP fiber, and the behavior of the specimens were also evaluated. The result shows that the compressive strength reduces as the fiber volume fraction increases, and the rate of reduction varies from 2% to 7%. The result of the flexural capacity shows that the ultimate capacity of plain specimens is the highest compare to those fiber reinforced specimens, but it has shown that specimens reinforced by 5% PET fiber has the highest energy absorption and the ductility index. In the application of PET fiber in slab specimens has shown that ductility capacity have increased where the ultimate capacity decreasing. That is the different tendency of beam specimens, which the ultimate capacity and the ductility of those have both shown the improvement compare to plain concrete specimens, which means the reinforcing effect of PET fiber in slab is less strong than in beam. Therefore, the application of PET fiber in slab structures as reinforcement needs the proper mix proportion of concrete and volume fraction of PET fiber with deep consideration of the structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4
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• pp.95-106
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• 1992

This paper presents a comparative evaluation of five different types of steel fibers used as reinforcing material in concrete beams. Two types of plain and RC beams were prepared to compare the relative flexural behavior. The fibers used were dog bone (paddled), both ends hooked. コ-type straight. crimped and wavy type with aspect ratio of 43 to 75. Fiber volume fraction of 1 to 2% were used while shear span to depth ratio (aid) and steel ratio p were fixed. Fiber reinforcement effect index Ef and effective toughness index Te were adopted to evaluate fiber reinforcing effects. The effect of fiber reinforcement on flexural strength is higher in plain beams than in RC beams. Hooked and dog bone type fibers were found to be more effective than the other type ones in enhancing the flexural strength and post-peak energy absorption capacity of concrete beams.