• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.331-341
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• 2015

The main purpose of this study is reducing the cost and effort for characterization of tensile strength of fiber reinforced concrete, in order to use in structural design. For this purpose, in this study, test for fiber reinforced concrete was carried out. Because fiber reinforced concrete is consisted of diverse material, it is hard to define the correlation between mix proportions and strength. Therefore, compressive strength test and tensile strength test were carried out for the range of smaller than 100 MPa of compressive strength and 0.25~1% of steel fiber volume fraction. as a results of test, two types of tensile strength were highly affected by compressive strength of concrete. However, increase rate of tensile strength was decreased with increase of compressive strength. Increase rate of tensile strength was decreased with increase of fiber volume fraction. Database was constructed using previous research data. Because estimation equations for tensile strength of fiber reinforced concrete should be multiple variable function, linear regression is hard to apply. Therefore, in this study, we decided to use the ANN(Artificial Neural Network). ANN was constructed using multiple layer perceptron architecture. Sigmoid function was used as transfer function and back propagation training method was used. As a results of prediction using artificial neural network, predicted values of test data and previous research which was randomly selected were well agreed with each other. And the main effective parameters are water-cement ratio and fiber volume fraction.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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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.

• Advances in concrete construction
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• v.5 no.1
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• pp.75-86
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• 2017

An experimental work was carried out to study the effect of hybrid fiber on the tension stiffening and cracking characteristics of geopolymer concrete (GPC). A total of 24 concentrically reinforced concrete specimens were cast and tested under uniaxial tension. The grade of concrete considered was M40. The variables mainly consist of the volume fraction of crimped steel fibers (0.5 and 1.0%) and basalt fibers (0.1, 0.2 and 0.3%). The load deformation response was recorded using LVDT's. At all the stages of loading after the first cracking, crack width and crack spacing were measured. The addition of fibers in hybrid form significantly improved the tension stiffening effect. In this study, the combination of 0.5% steel fiber and 0.2% basalt fiber gave a better comparison than the other combinations.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.115-118
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• 1999

Tensile behavior of polypropylene fiber reinforced concrete due to restrained shrinkage has been investigated experimentally by ring and beam tests. Parameters include types of concrete, water-cement ratio, volume fraction of fiber and steel ratio. Results show that little influence of the addition of polypropylene(Vf=0.1%) has been observed as expected and results from other researches.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.215-227
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• 2015

In this study, twenty four steel-fiber reinforced concrete (SFRC) beams using recycled coarse aggregates (RCA) were manufactured to examine the shear behavior of SFRC and to determine the beams' ultimate shear strengths. The RCA replacement ratio was fixed at 30%. The variables studied in this investigation are: (1) shear span-to-depth ratios (a/d) of 2, 3 and 4; (2) longitudinal reinforcement ratio (${\rho}$) of 0.008 and 0.0127; and (3) steel fiber volume fractions ($V_f$) of 0, 0.5, 0.75 and 1%. Test results were analyzed and then compared with the findings and proposals of various other researchers. Based on the test results, the more steel fiber volume fraction is increased, the large crack resistance and shear strength are exhibited. Most of the experimental data is higher than the theoretical value. Therefore, steel-fiber reinforced concrete beams using recycled coarse aggregates are suggested to be applied for building structures.

• Computers and Concrete
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• v.21 no.1
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• pp.1-9
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• 2018

Electrical resistivity is a property associated with both the physical and chemical characteristics of concrete. It allows the evaluation of the greater or lesser difficulty with which aggressive substances penetrate the concrete's core before the dissolution of the passive film process and the consequent reinforcement's corrosion begin. This work addresses the steel fiber addition to concrete with two types and various contents from 0% to 1.3%, correlating it with its electrical resistivity. To that effect, 9 different mixes of steel fiber reinforced concrete (SFRC) were produced. The electrical resistivity was evaluated on the on six years aged SFRC by direct measurement at different frequency from 0.1 kHz to 100 kHz. The results indicate that steel fiber content is strongly conditioned by the type and quantity of the additions used. It was also found that long type of fibers has more effect on decreasing the electrical resistivity of concrete than short fibers. Therefore, they increase the corrosion risk of concrete depending on fiber volume fraction and moisture percentage.

• Advances in concrete construction
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• v.15 no.6
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• pp.405-417
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• 2023

While ultra-high performance concrete (UHPC) is commonly reinforced with micro straight steel fibers in existing applications, studies have indicated that the use of deformed steel macro-fibers leads to enhanced ductility and post-peak responses for UHPC structural elements, which is of particular importance for earthquake-resistant structures. However, there are potential concerns regarding the use of UHPC reinforced with macro-fibers due to the issues of workability and fiber distribution. The objective of this study was to address these issues by extensively investigating the restricted and non-restricted deformability, filling ability, horizontal and vertical velocities, and passing ability of UHPC containing macro hooked-end steel fibers. A new approach is suggested to examine the homogeneity of fiber distribution in UHPC. The influences of ultra-fine fillers and steel macro-fibers on the workability of fresh UHPC and the mechanics of hardened UHPC were examined. It was found that although increasing the ratio of quartz powder to cement led to an improvement in the workability and tensile strain hardening behavior of UHPC, it reduced the fiber distribution homogeneity. The addition of 1% volume fraction of macro-fibers in UHPC improved workability, but reduced its compressive strength, which is contrary to the effect of micro-fiber inclusion in UHPC.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.229-236
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• 2015

This paper describes the effect of aggregate size on compressive behavior of high-strength steel fiber reinforced concrete. The Specified compression strength is 60 MPa and the range of fiber volume fraction is 0~2%. The main variable is the aggregate size, which was used for the aggregate size of 8 and 20 mm. So, ten concrete mixtures were prepared and tested to evaluate the fresh and hardened properties of SFRC at curing ages (7, 14, 28, 56 and 91 days), respectively. Items estimated in this study are the fresh properties (air contents, slump), hardened properties (compressive strength, modulus of elasticity, post-peak response and compressive toughness). As a result, the aggregate size has little effect on the compressive strength and modulus of elasticity. On the other hand, the ductile behavior was shown after post peak and the compressive toughness was increasing as decreasing the aggregate size. These effects are clearly represented in the fiber volume fraction 2%, which are the point appeared fiber ball. It is considered that the decreasing the aggregate size has effect on the fiber dispersibility.

• Earthquakes and Structures
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• v.17 no.6
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• pp.567-575
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• 2019

In order to investigate the dynamic impact resistance of steel fiber reinforced full light-weight concretes, we implemented drop weight impact test on a total of 6 reinforced beams with 0, 1 and 2%, steel fiber volume fraction. The purpose of this test was to determine the failure modes of beams under different impact energies. Then, we compared and analyzed the time-history curves of impact force, midspan displacement and reinforcement strain. The obtained results indicated that the deformations of samples and their steel fibers were proportional to impact energy, impact force, and impact time. Within reasonable ranges of parameter values, the effects of impact size and impact time were similar for all volumetric contents of steel fibers, but they significantly affected the crack propagation mechanism and damage characteristics of samples. Increase of the volumetric contents of steel fibers not only effectively reduced the midspan displacement and reinforcement strain of concrete samples, but also inhibited crack initiation and propagation such that cracks were concentrated in the midspan areas of beams and the frequency of cracks at supports was reduced. As a result, the tensile strength and impact resistance of full light-weight concrete beams were significantly improved.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.4
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• pp.171-180
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• 2015

The variation in microstructure and texture during continuous annealing was examined in a series of 1.6% Mn-0.1% Cr-0.3% Mo-0.005% B steels with carbon contents in the range of 0.010 to 0.030%. It was found that microstructure of hot band consisted of ferrite and pearlite as a consequence of high coiling temperature, and eutectoid carbon content was between 0.011% and 0.016%. Martensite ranged in volume fraction from 1.5% to 4.0% when annealed at $820{\circ}C$ according to the typical continuous annealing cycle. The critical martensite content for the continuous yielding was about 4% from stress-strain curves. The continuous yielding was obtained in the 0.030% carbon steel and 0.010% to 0.020% carbon steels revealed some yield point elongation ranging from 0.8% to 2.2% in as-annealed conditions. Higher tensile strength in the higher carbon steel is due to both increase in the martensite volume fraction and ferrite grain refinement. Decreasing the carbon content to 0.01% strengthened the intensities of ${\gamma}$-fiber textures, resulting in the increase in the $r_m$ value, which was caused by the lower volume fraction of martensite. The higher carbon steels showed the lower $r_m$ value of about 1.0.