• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.15-18
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• 2007

The purpose of this study is to suggest a reference for an extensive evaluation about effectiveness of four types of fibers to control plastic shrinkage crack of concrete. So in this study for the practical use in construction field, the plastic shrinkage cracks shown from four types of concrete reinforced by mixing four types of fibers are quantitatively evaluated in points of the workability and compressive strength. Test showed that the mixing of Cl, N, P fibers except for C2 fibers decreased fluidity of fresh concrete. Compressive strengths of four types specimens were similar. Plastic shrinkage cracks were reduced by mixing each fiber, especially C2 fibers was very effective to prevent the plastic shrinkage crack. Therefore the reinforced concrete mixed with C2 fibers exhibited superior mechanical performance than the others.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.41 no.2
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• pp.47-54
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• 2009

Anatomical characteristics of kenaf were investigated in transverse, radial and tangential direction by optical and scanning electron micrograph. Kenaf was made up of bast fibers, wood fibers, vessels and parenchyma cells. Bast fibers were long slender cells with different types of pits. The shape of wood fibers were in various ways and pointed at the ends. The pits were observed on the surface of bast fibers. Kenafs were diffuse and radial porous. and composed of solitary pores and two or three radial pore multiples. Various types of vessels were observed. The pits showed alternate pitting and larger diameter than other cells. Parenchyma cells were rectangular or square with different shapes of pith parenchyma cells compared to conventional types of parenchyma cells in wood. The number of pith on the surfaces were small.

• Journal of the Korean Wood Science and Technology
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• v.35 no.2
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• pp.9-15
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• 2007

A comparative study of the structure and organization of the primary and secondary walls in different types of tropical plant waste fibers was carried out using transmission electron microscopy (TEM). The thickness of each layer was also measured using Image Analyzer. TEM micrographs haveconfirmed that cell wall structure of all six types of tropical plant waste fibers (empty fruit bunch, oil palm frond, oil palm trunk, coir, banana stem and pineapple leaf) has the same ultrastructure with wood fibre. The fibers consisted of middle lamella, primary and thick secondary wall with different thickness for different types of fibers. The secondary wall was differentiated into a $S_1$ layer, a unique multi-lamellae $S_2$ layer, and $S_3$ layer.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.1
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• pp.11-16
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• 2006

There are many counting rules for analyzing man-made mineral fibers. The representatives are the NIOSH Method 7400 A and B counting rules. The two rules have different rules of length-to-width ratio(aspect ratio) and diameter. The A rule counts only fibers $>5{\mu}m$ in length, and only fibers with aspect ratio >3:1. The B rule counts only ends of fibers $>5{\mu}m$ in length and $<3{\mu}m$ in diameter, and only fibers with aspect ratio ${\geq}5:1$. The A counting rule had been used before the B counting rule was introduced. The purpose of this study is to compare the A and B counting rules for airborne fibers from various man-made mineral fibers(glass wool fibers, rock wool fibers, refractory ceramic fibers, and continuous filament glass fibers) industries. There were significantly differences between the paired counts of A and B rules in all types of fibers(p<0.05). A rule counts/B rule counts(A/B ratios) were 1.52 for glass fibers, 1.53 for rock wool fibers, 1.19 for RCF, and 1.82 for continuous filament glass fibers. The counting results by A and B counting rules were highly correlated in glass wool fibers, rock wool fibers and refractory ceramic fibers(RCF) samples (r=0.96 for all types of fibers) except continuous filament glass fibers(r=0.82). Regression equations to correct for the differences between counting rules were presented in this paper.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.2
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• pp.134-139
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• 2012

Objectives: This study was conducted to study the analytical variability of A & B counting rules in counting using a phase contrast microscope airborne fibers collected on filters in man-made mineral or vitreous fibers (MMMFs) industries. Methods: Fibers in filters were counted using A & B rules of NIOSH Method 7400. Intra-counter and inter-counter variations by fiber type and density were obtained. The types of MMMFs analyzed were glass wool fiber, rock wool fiber, slag wool fiber, and refractory ceramic fibers. The densities of fibers classified were <20 $fibers/mm^2,$ 20 - <50 $fibers/mm^2$, 50 - <100 $fibers/mm^2,$ and ${\geq}100$ $fibers/mm^2,$ respectively. Results: Intra-counter relative standard deviations by rule A were 0.084, 0.102, 0.071 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.139, 0.120 and 0.142, respectively. Inter-counter relative standard deviations by rule A were 0.281, 0.296, 0.180 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.396, 0.337 and 0.238, respectively. Conclusions: Intra-counter variation was not different significantly among fiber types (p>0.05), but B rule variation for ceramic fibers approximately 2 times greater than corresponding A rule estimates, and intra-counter and inter-counter variations were higher in the low fiber density.

• 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.

• Computers and Concrete
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• v.26 no.5
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• pp.451-465
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• 2020

This paper presents experimental and numerical investigations on mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC) with four types of steel fibers; micro steel (MS), crimped (C), round crimped (RC) and hooked-end (H), in two fiber contents of 1% and 2% (by volume) and two lengths of 13 and 30 mm. Compression, direct tension, and four-point bending tests were carried out on four types of specimens (prism, cube, dog-bone and cylinder), to study tensile and flexural strength, fracture energy and modulus of elasticity. Results were compared with UHPC specimens without fibers, as well as with available equations for the modulus of elasticity. Specimens with MS fibers had the best performance for all mechanical properties. Among macro fibers, RC had better overall performance than H and C fibers. Increased fibers improved all mechanical properties of UHPFRC, except for modulus of elasticity, which saw a negligible effect (mostly less than 10%). Moreover, nonlinear finite element simulations successfully captured flexural response of UHPFRC prisms. Finally, nonlinear regression models provided reasonably well predictions of flexural load-deflection behavior of tested specimens (coefficient of correlation, R² over 0.90).

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.39 no.3
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• pp.1-11
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• 2007

To evaluate the quality of waste paper used for the manufacture of linerboard, the types of papers and foreign materials in compressed waste paper currently used were investigated. The recycled fibers were obtained from printing paper, newspaper, wrapping paper, white coated paperboard and corrugated container. Their fibers were observed by using a microscope, and the mechanical properties of the recycled papers manufactured from the recycled fibers were investigated. The compressed wastepaper was composed of 54% paperboard, 20% printing paper, and 20% newsprint. The content of foreign materials was about 4%, showing higher contents compared to 1% of foreign substances provided by Korea paper manufacturers' association. The types of foreign materials were various, which include vinyls, plastics, metals, woods, styrofoams, and cloths. Sound fibers were generally observed in the recycled fibers of printing papers and wrapping paper. The recycled fibers of white coated board, corrugated container and newsprint showed to be generally damaged. The whiteness of each recycled fiber were highly affected by pulp bleaching and ink-particle mixing conditions. The values of breaking length and burst index were lower than those for corrugating medium and liner board specified in KS. Although the anatomical characteristics of recycled fibers varied, their strengths appeared to be similar. This result may be explained by the use of non-deinked fiber.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.213-220
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• 2005

Penetration and health effect of fibers was related with their diameters and length. The purpose of this study is to characterize and compare the diameter and length of airborne man-made mineral fibers(MMMF) or synthetic vitreous fibers in the related industries. The average fiber length of the continuous filament glass, rock wool, refractory ceramic, and glass wool fibers production industries approximately 27, 28, 35, $50-105{\mu}m$. Airborne glass fibers were longest in all the type of MMMFs. The average diameters of airborne fibers generated from refractory ceramic, rock wool, glass wool, continuous filament glass fibers production industries were approximately 1.0, 1.6, 1.5-4 and $10{\mu}m$, respectively. The percentages of respirable fibers(<$3{\mu}m$) were 94% for RCFs, 73% for rock wool fibers, 61.0% for glass fibers, and 1.6% for filament glass fibers. The length of glass fibers were the longest in all types of fibers, and length of the others were similar. The refractory ceramic fibers were smallest in diameters and highest in fraction of respirable fibers.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.321-327
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• 1996

The result of an experimental study on the mechanical properties of different types of polypropylene fiber reinforced concrete are presented in this paper. This study has been performed to obtain the properties of PFRC such as slump, Vee-Bee time, compressive strength, tensile strength, flexural strength, toughness and resistance to impact. The test variables are fiber content, fiber types, fiber length and W/C ratio. Polypropylene fibers were effective in reinforcing the matrix. A remarkable increase in toughness was observed by the addition of polypropylene fibers.