• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.705-712
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• 2009

HPFRCCs (high-performance fiber reinforced cementitious composites), which is relatively more ductile and has the characteristic of high toughness with high fiber volume fractions, can be used in structures subjected to extreme loads and exposed to durability problems. In the case of PVA (polyvinyl alcohol) fiber, it is noted by former studies that around 2% fiber volume fractions contributes to the most effective performance at HPFRCCs. In this study, flexural tests were carried out to evaluate the flexural behavior of HPFRCCs and to optimize mix proportions. Two sets of hybrid fiber reinforced high performance specimens with total fiber volume fraction of 2 % were tested: the first set prepared by addition of short and long PVA fibers at different combination of fiber volume fractions, and the second set by addition of steel. In addition, in order to assess the performances of the HPFRCCs against to high strain rates, drop weight tests were conducted. Lastly, the sprayed FRP was applied on the bottom surface of specimens to compare their impact responses with non-reinforcing specimens. The experimental results showed that the specimen prepared with 1.6% short fibers (REC 15) and 0.4% long fiber (RF4000) outperformed the other specimens under flexure, and impact loading.

• Computers and Concrete
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• v.5 no.6
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• pp.509-524
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• 2008

Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.1 s.256
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• pp.89-96
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• 2007

A volume integral equation method (VIEM) is applied for the effective analysis of plane elastostatic problems in unbounded solids containing single isotropic inclusion of two different shapes considering composite fiber volume fraction. Single cylindrical inclusion and single square cylindrical inclusion are considered in the composites with six different fiber volume fractions (0.25, 0.30, 0.35, 0.40, 0.45, 0.50). Using the rule of mixtures, the effective material properties are calculated according to the corresponding composite fiber volume fraction. The analysis of plane elastostatic problems in the unbounded effective material containing single fiber that covers an area corresponding to the composite fiber volume fraction in the bounded matrix material are carried out. Thus, single fiber, matrix material with a finite region, and the unbounded effective material are used in the VIEM models for the plane elastostatic analysis. A detailed analysis of stress field at the interface between the matrix and the inclusion is carried out for single cylindrical or square cylindrical inclusion. Next, the stress field is compared to that at the interface between the matrix and the single inclusion in unbounded isotropic matrix with single isotropic cylindrical or square cylindrical inclusion. This new method can also be applied to general two-dimensional elastodynamic and elastostatic problems with arbitrary shapes and number of inclusions. Through the analysis of plane elastostatic problems, it will be established that this new method is very accurate and effective for solving plane elastic problems in unbounded solids containing inclusions considering composite fiber volume fraction.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.15-23
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• 2018

The purpose of this study is to evaluate the anchorage capacity of longitudinal bars for reinforced concrete exterior beam - column joints with steel fiber volume fractions. For this purpose, the steel fiber volume fraction was set to 0, 1, 2%, and the performance was compared with that of each other specimens. According to the test results, the maximum strength of EX-HK-NJR-0 decreased by 13% compared with the control specimen and EX-HK-NJR-1 decreased by 3% compared to the control specimen. However, when 2% of steel fiber was mixed, the maximum strength increased about 56% compared to the control specimen. The energy dissipation capacity of EX-HK-NJR-0 (when no transverse steel bars are placed) decreased by 61% compared to the control specimen. In addition, the energy dissipation capacity of the specimens with a steel fiber content of 1% decreased by 5% and 2% increased by 94% compared to control specimen. EX-HK-NJR-1,2 and the control specimen EX-HK-JR-0 experienced yielding of the reinforcing bars at the column interface before maximum strength development. However, when the EX-HK-NJR-0, the reinforcing bars at the column interface experienced yielding after maximum strength development. Therefore, reinforcement of steel fiber is considered to reduce the required development length for yielding of steel bars.

• Computers and Concrete
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• v.9 no.5
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• pp.389-402
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• 2012

In this study, the modulus of elasticity of low, normal and high strength steel fiber reinforced concrete has been predicted by developing a fuzzy logic model. The fuzzy models were formed as simple rules using only linguistic variables. A fuzzy logic algorithm was devised for estimating the elastic modulus of SFRC from compressive strength. Fibers used in all of the mixes were made of steel, and they were in different volume fractions and aspect ratios. Fiber volume fractions of the concrete mixtures have changed between 0.25%-6%. The results of the proposed approach in this study were compared with the results of equations in standards and codes for elastic modulus of SFRC. Error estimation was also carried out for each approach. In the study, the lowest error deviation was obtained in proposed fuzzy logic approach. The fuzzy logic approach was rather useful to quickly and easily predict the elastic modulus of SFRC.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.103-110
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• 2009

Since the mechanical properties of cement-based materials are time-dependent due to the prolonged cement hydration process, those of fiber reinforced concrete(FRC) may also be time-dependent. Toughness is one of important properties of FRC. Therefore, it should be investigated toughness development of FRCs with curing ages to fully understand the time-dependent characteristics of FRCs. To this end, the effect of curing ages on flexural toughness development of steel fiber reinforced concrete is studied. Three point bending test with notched beam specimen was adapted for this study. Hooked-end steel fiber(DRAMIX 40/30) was used as a fiber ingredient to investigate w/c ratio and fiber volume fraction effect on toughness development during curing. Three different water-cement ratios(0.44, 0.5 and 0.6) and fiber volume fractions(0%, 0.5% and 1%) were used as influence factors. Each mixture specimens were tested at five different ages, 0.5, 1, 3, 7 and 28 days. The study shows that flexure toughness development with age is quite different than other concrete material properties such as compressive strength. The study also shows that the toughness development trend correlates more closely to water/cement ratio than to fiber volume fraction.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.109-115
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• 2015

High performance fiber reinforced cementitious composite (HPFRCC) can provide high fracture energy absorption as well as high strength with high fiber volume fraction. The increased fracture energy helps resisting high frequency loadings, such as earthquake, impact or blast. This study investigates the flexural performance of slurry infiltrated fiber concrete (SIFCON), one of the important HPFRCC, with respect to varying fiber volume fraction. The maximum fiber volume fraction was 8.0 % and reduced to 6.0% by 0.5% and the maximum volume fraction is obtained by packing fibers with simple tapping by hands. The used fiber was a steel fiber with the length 30 mm and the diameter of 0.5 mm. The flexural strengths were 48.7 MPa at 8.0 % and 22.8 MPa at 6.0 %. The measured flexural strength is much higher compared to other cememtitious composite materials but decreased proportional to the fractions. This result implies that for SIFCON considered herein the reduced amount of steel fibers may affect its flexural performance in a negatively way. The flexural toughness, an index to represent the fracture energy absorption, also decreased with the reduced fiber amount.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.3 s.246
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• pp.260-268
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• 2006

The micromechanical approach was used to investigate the interfacial strain distributions of a unidirectional composite under transverse loading in which fibers were usually found to be randomly packed. Representative volume elements (RVE) for the analysis were composed of both regular fiber arrays such as a square array and a hexagonal array, and a random fiber array. The finite element analysis was performed to analyze the normal, tangential and shear strains at the interface. Due to the periodic characteristics of the strain distributions at the interface, the Fourier series approximation with proper coefficients was utilized to evaluate the strain distributions at the interface for the regular and random fiber arrays with respect to fiber volume fractions. From the analysis, it was found that the random arrangement of fibers had a significant influence on the strain distribution at the interface, and the strain distribution in the regular fiber arrays was one of special cases of that in the random fiber array.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.3
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• pp.197-203
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• 2013

In this study, the creep behaviors of amorphous steel fiber-reinforced concrete were investigated. Two different types of tests were carried out to evaluate the effect of amorphous steel fibers on the creep of concrete: compressive creep test and tensile creep test. Fiber volume fractions used in the test were 0.2% and 0.4% for tensile specimens, and 0.2% and 0.3% for compressive specimens. Based on the test results, the addition of fiber volume fraction of 0.2% into concrete could significantly reduce both compressive and tensile creep.

• KIEAE Journal
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• v.15 no.4
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• pp.45-52
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• 2015

Purpose: Foam concrete is the concrete that contains large amount of air voids inside. In general, the density of foam concrete depends on parameters like water/binder ratio, foam volume, aggregate and pozzolan content, etc. Method: In this study, the effect of foam volume and fly ash content on dry density is investigated intensively in order to find the relationship between each parameter and their abilities to counteract with each other. According to the above information, though there are quite a number of studies on the effect micro fiber on foam concrete at low volume fractions, there is still lack of information especially on the high fiber content side. The objective of the second study is to investigate further on the use of micro fiber at higher volume fraction and fill in the lacking information. Beside from this study, the investigation of the effect of micro-fiber (polypropylene) to enhance the properties of foam concrete is also carried out. Result: Of the two variables that are investigated in this study, the foam volume and the fly ash content, show significant effect on the properties of foam concrete. The foam volume tends to decrease the density and strength of foam concrete. In the second part of our study, a large fibre volume fraction is proved to be able to evidently increase the flexural strength of foam concrete up to about 40% due to the effect of fibre bridging over the crack and a significant number of fibres that intercepts the crack surfaces. However, the compressive strength is found to decrease severely due to the occurrence of large pores as the result of fibre being added into concrete mixture.