• Computers and Concrete
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• v.20 no.4
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• pp.491-502
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• 2017

In this research, the application of ultrasonic pulse velocity (UPV) test as a nondestructive method for estimating some of the mechanical and dynamic properties of reactive powder concrete (RPC) containing steel and polyvinyl alcohol (PVA) fibers, as well as their combination was explored. In doing so, ten different mix designs were prepared in 19 experimental groups of specimens containing three different volume contents of steel fibers (i.e., 1, 2, and 3 %) and PVA fibers (i.e., 0.25, 0.5, and 0.75 %), as well as hybrid fibers (i.e., 0.25-0.75, 0.5-0.5, and 0.75-0.25 %). The specimens in these groups were prepared under the two curing regimes of normal and heat treatment. Moreover, the UPV test results were employed to estimate the compressive strength, dynamic modulus, shear modulus, and Poisson's ratio of the RPC concrete and to investigate the quality level of the used concrete. At the end, the effect of the specimen shape and in fact the measuring distance length on the UPV results was explored. The results of this research suggest that the steel fiber-containing RPC specimens demonstrate the highest level of ultrasonic pulse velocity as well as the highest values of the mechanical and dynamic properties. Moreover, heat treatment has a positive effect on the density, UPV, dynamic modulus, Poisson's ratio, and compressive strength of the RPC specimens, whereas it leads to a negligible increase or decrease in the shear modulus and static modulus of elasticity. Furthermore, the specimen shape affects the UPV of fiber-lacking specimens while negligibly affecting that of fiber-reinforced specimens.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.509-510
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• 2009

In strengthening reinforced concrete beams using fiber reinforced polymer sheets, brittle structural failures occur due to the linear stress-strain relationship of the fibers. Hybrid fiber reinforced polymer sheets using two different types of fibers were investigated in this study

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.276-279
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• 2004

Concrete is one of the principal materials for the structure and it is widely used all over the world. but it shows extremely brittle failure under bending and tensile load. Recently to improve such a poor property. High Performance Fiber Reinforced Cementitious Composites (HPFRCC) have been developed. and it are defined by an ultimate strength higher than their first cracking strength and the formation of multiple cracking during the inelastic deformation process. This study is to develop the hybrid HPFRCC with high ductility and strain capacity in bending and tensile load. and the three-point bending test on hybrid HPRFCC reinforced with micro and macro fibers is carried out in this paper. As the results of the bending tests. hybrid HPFRCCs reinforced with PVA40+SF and PVA100+PVA660 showed the high ultimate bending stress, multiple cracks and displacement hardening under bending load.

• Composites Research
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• v.23 no.3
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• pp.50-57
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• 2010

It is important to detect fibers in the sectional image of fiber reinforced cementitious composites (FRCC), since the fiber distribution is a crucial factor to predict or evaluate the mechanical performance of FRCC. In this paper, we investigated the fluorescence characteristics of Polyvinyl Alcohol (PVA) fibers, Polyethylene Terephthalate (PET) fibers, Polyethylene (PE) fibers, and Polypropylene (PP) fibers used in Engineered Cementitious Composites (ECC), which is a special kind of FRCC that incorporates synthetic fibers and exhibits extremely ductile behavior in uniaxial tension, to detect each fiber according to its type. Furthermore, optimum excitation and emission wavelengths were proposed on the basis of maximum difference of Relative Fluorescence Intensity (RFI) between two types of fibers used in the hybrid ECC. Optimum threshold values to discriminate two types of fibers using statistical tools were also proposed. Finally, images of four types of fibers obtained using a fluorescence microscope are compared.

• Advances in concrete construction
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• v.10 no.3
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• pp.195-209
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• 2020

This study investigates the behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with hybrid macro-micro steel and macro steel-polypropylene (PP) fibers. Compression, direct and indirect tension tests were carried out on cubic and cylindrical, dogbone and prismatic specimens, respectively. Three types of macro steel fibers, i.e., round crimped (RC), crimped (C), and hooked (H) were combined with micro steel (MS) and PP fibers in overall ratios of 2% by volume. Additionally, numerical analyses were performed to validate the test results. Parameters studied included, fracture energy, tensile strength, compressive strength, flexural strength, and residual strength. Tests showed that replacing PP fibers with MS significantly improves all parameters particularly flexural strength (17.38 MPa compared to 37.71 MPa). Additionally, the adopted numerical approach successfully captured the flexural load-deflection response of experimental beams. Lastly, the proposed regression model for the flexural load-deflection curve compared very well with experimental results, as evidenced by its coefficient of correlation (R²) of over 0.90.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.78-85
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• 2023

This study evaluates the performance of reinforced concrete columns using hybrid fiber sheets for structural behavior. The purpose of this method is to improve the load-bearing capacity of the reinforced structure by impregnating a hybrid fiber sheet, which is woven by arranging aramid and glass fibers uniaxially and attached to an aged concrete structure requiring reinforcement with epoxy. In particular, not only the weight reduction of the material obtained by using a fiber lighter than the steel material, but also the low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element. The low-strength, high-toughness fiber element among the fibers used delays the brittle fracture of the high-strength, low-toughness fiber element, resulting in weight reduction compared to steel. The study conducted structural tests on four specimens, with the hybrid reinforcement method and failure mode as main variables. Specimen size and loading conditions were chosen to be comparable with previous studies. The structural performance of the specimen was evaluated using energy dissipation capacity and ductility. Analysis shows that excellent results can be obtained with the hybrid fiber sheet reinforcement.

• Computers and Concrete
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• v.25 no.6
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• pp.509-516
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• 2020

Adding fibers improves concrete performance in respect of strength and plasticity. There are numerous fibers for use in concrete that have different mechanical properties, and their combination in concrete changes its behavior. So, to investigate the behavior of the fiber reinforced concrete, an in vitro study was conducted on concrete with different fiber compositions including different ratios of steel, polypropylene and glass fibers with the volume of 1%. Two forms of fibers including single-stranded and aggregated fibers have been used for testing, and the specimens were tested for compressive strength and dividable tensile strength (splitting tensile) to determine the optimal ratio of the composition of fibers in the concrete reinforced by hybrid fibers. The results show that the concrete with a composition of steel fibers has a better performance than other compounds. In addition, by adding glass and propylene fibers to the composition of steel fibers, the strength of the samples is reduced. Also, if using the combination of fibers is required, the use of a combination of glass fibers with steel fibers will provide a better compressive strength and tensile strength than the combination of steel fibers with propylene.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.1
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• pp.41-51
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• 2004

FRP re-bar in concrete structures could be used as a substitute of steel re-bars for that cases in which aggressive environment produce high steel corrosion, or lightweight is an important design factor, or transportation cost increase significantly with the weight of the materials. But FRP fibers have only linearly elastic stress-strain behavior; whereas, steel re-bar has linear elastic behavior up to the yield point followed by large plastic deformation and strain hardening. Thus, the current FRP re-bars are not suitable concrete reinforcement where a large amount of plastic deformation prior to collapse is required. The main objectives of this study in to evaluate the tensile behavior and the fracture mode of hybrid FRP re-bar. Fracture mode of hybrid FRP re-bar is unique. The only feature common to the failure of the hybrid FRP re-bars and the composite is the random fiber fracture and multilevel fracture of sleeve fibers, and the resin laceration behavior in both the sleeve and the core areas. Also, the result of the tensile and interlaminar shear stress test results of hybrid FRP re-bar can provide its excellent tensile strength-strain and interlaminar stress-strain behavior.

• Journal of the Korean Society of Clothing and Textiles
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• v.38 no.3
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• pp.372-385
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• 2014

Lignin is an abundant natural polymer in the biosphere and second only to cellulose; however, it is under-utilized and considered a waste. In this study, lignin was fabricated into nanofibers via electrospinning. The critical parameters that affected the electrospinnability and morphology of the resulting fibers were examined with the aim to utilize lignin as a resource for a new textile material. Poly(vinyl alcohol) (PVA) was added as a carrier polymer to facilitate the fiber formation of lignin, and the electrospun fibers were deposited on polyester (PET) nonwoven substrate. Eleven lignin/PVA hybrid solutions with a different lignin to PVA mass ratio were prepared and then electrospun to find an optimum concentration. Lignin nano-fibers were electrospun under a variety of conditions such as various feed rates, needle gauges, electric voltage, and tip-to-collector distances in order to find an optimum spinning condition. We found that the optimum concentration for electrospinning was a 5wt% PVA precursor solution upon the addition of lignin with the mass ratio of PVA:lignin=1:5.6. The viscosity of the lignin/PVA hybrid solution was determined as an important parameter that affected the electrospinning process; in addition, the interrelation between the viscosity of hybrid solution and the electrospinnability was examined. The solution viscosity increased with lignin loading, but exhibited a shear thinning behavior beyond a certain concentration that resulted in needle clogging. A steep increase in viscosity was also noted when the electrospun system started to form fibers. Consequently, the viscosity range to produce bead-free lignin nanofibers was revealed. The energy dispersive X-ray analysis confirmed that lignin remained after being transformed into nanofibers. The results indicate the possibility of developing a new fiber material that utilizes biomass with resulting fibers that can be applied to various applications such as filtration to wound dressing.

• Fibers and Polymers
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• v.5 no.2
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• pp.105-109
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• 2004

The synthesis of titanium dioxide nanofibers with 200-300nm diameter was presented. The new inorganic-organic hybrid nanofibers were prepared by sol-gel processing and electrospinning technique using a viscous solution of titanium isopropoxide (TiP)/poly(vinyl acetate) (PVAc). Pure titanium dioxide nanofibers were obtained by high temperature calcination of the inorganic-organic composite fibers. SEM, FT-IR, and WAXD techniques were employed to characterize these nanofibers. The titanium dioxide nanostructured fibers have rougher surface and smaller diameter compare with PVAc/TiP composite nanofibers. The anatase to rutile phase transformation occurred when the calcination temperature was increased from $600^{\circ}C$ to $1000^{\circ}C$.