• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.317-326
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• 2022

This research performed single fiber pull-out test to evaluate the effect between fineness modulus of cement composites and the fiber bond performance (bond strength and pull-out energy). A synthetic fiber (polypropylene) and a steel fiber (hooked ends type) were inserted in the middle of dog bone shape specimens which were designed with fine aggregates of F. M. 1.96, 2.69, 3.43. The experiment results showed bond strength and pullout energy of synthetic fiber are improved as fineness modulus of cement composites increases. It is considered that the frictional resistance between synthetic fiber and cement composite increases as fineness modulus of cement composite increases and consume more energy while pull out the fiber from cement composite. However bond performance of steel fiber which resist pull out by mechanical behavior is less effected on fineness modulus of cement composite. It is considered that the mechanical fixedness of hooked ends exerts a greater effect on the pullout resistance than the frictional resistance between the cement composite and the steel fiber so F. M. of fine aggregate has a relatively small effect on the pullout resistance with the steel fiber.

• Computers and Concrete
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• v.24 no.1
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• pp.63-71
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• 2019

Thermal energy from high temperatures can cause concrete damage, including mechanical and chemical degradation. In view of this, the residual mechanical properties of high-strength fiber reinforced concrete with a design strength of 75 MPa exposed to $400-800^{\circ}C$ were investigated in this study. The test results show that the average residual compressive strength of high-strength fiber reinforced concrete after being exposed to $400-800^{\circ}C$ was 88%, 69%, and 23% of roomtemperature strength, respectively. In addition, the benefit of steel fibers on the residual compressive strength of concrete was limited, but polypropylene fibers can help to maintain the residual compressive strength and flexural strength of concrete after exposure to $400-600^{\circ}C$. Further, the load-deflection curve of specimen containing steel fibers exposed to $400-800^{\circ}C$ had a better fracture toughness.

• Computers and Concrete
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• v.14 no.3
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• pp.299-313
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• 2014

Effects of polypropylene (PP) fibers, steel fibers (SF) and hybrid on the properties of highstrength fiber reinforced self-consolidating concrete (HSFR-SCC) under different volume contents are investigated in this study. Comprehensive laboratory tests were conducted in order to evaluate both fresh and hardened properties of HSFR-SCC. Test results indicated that the fiber types and fiber contents greatly influenced concrete workability but it is possible to achieve self consolidating properties while adding the fiber types in concrete mixtures. Compressive strength, dynamic modulus of elasticity, and rigidity of concrete were affected by the addition as well as volume fraction of PP fibers. However, the properties of concrete were improved by the incorporation of SF. Splitting tensile and flexural strengths of concrete became increasingly less influenced by the inclusion of PP fibers and increasingly more influenced by the addition of SF. Besides, the inclusion of PP fibers resulted in the better efficiency in the improvement of toughness than SF. Furthermore, the inclusion of fibers did not have significant effect on the durability of the concrete. Results of electrical resistivity, chloride ion penetration and ultrasonic pulse velocity tests confirmed that HSFR-SCC had enough endurance against deterioration, lower chloride ion penetrability and minimum reinforcement corrosion rate.

• Journal of the Korea Institute of Building Construction
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• v.10 no.6
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• pp.67-75
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• 2010

In this paper, by using steel fiber, polypropylene fiber and these two hybrid fibers, the fire resistance performance and explosive properties of High Strength Concrete (HSC) with specified compressive strength of 40MPa are discussed. The paper also examines the bending resistance of the beam and the shearing resistance properties of non-reinforced HSC beam. This research helps to clarify the fire resistance of fiber HSC and its anti-explosion methods. The test results show that crack generation, explosion and carbonization can be effectively restrained when HSC is mixed with hybrid fibers under high temperature; furthermore, the maximum internal force and ductility are increased and the initial cracking can be restrained in the mechanical test.

• Journal of the Society of Disaster Information
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• v.7 no.4
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• pp.286-293
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• 2011

Accordingly architectural structure is getting high-rise and bigger, a use of high strength and high performance concrete has been increased. High performance concrete has cons of explosion in a fire. This explosion in the fire can cause the loss of the sheath on a concrete surface, therefore it effects that increasing a rate of heat transmission between the steel bar and inner concrete. Preventing this explosion of high performance concrete in the fire, many kinds of researches are now in progressing. Typically, researches with using polypropylene-fiber and steel-fiber can prove controling the explosion, but the reduction of mobility was posed as a problem of workability. Consequently, to solve the problem as mentioned above, concrete cans secure fire resisting capacity through the using of coating liquid, including Ester-lubricant and non-ionic characteristic surfactant. This research has been drawn a ideal condition in compressive strength areas of concrete by an experiment. When applying 13mm of polyamide fiber, proper fiber mixing volume by compressive strength areas of concrete more than 2.5kg in 160MPa. These amount of a compound can control the explosion.

• Fire Science and Engineering
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• v.25 no.5
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• pp.85-92
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• 2011

Along the fire resisting capacity of high strength concrete has been brought up as a social issue, and the Ministry of Land also had notified the control standard about it, the researches for improving the fire resisting capacity have been considerably activated these days. In this study, we performed a research for developing a high strength concrete, contains the fiber cocktail, which is a hybrid of polypropylene fiber as organic matter, and steel fiber. As we analyzed the temperature of the steel part during the fire test with 100 MPa high strength concrete, there was a tendency that the lower temperature comes out with the larger cross section, and the $600{\times}600mm$, $800{\times}800mm$ cross sectioned can secure the fire resistance capability, so the $600{\times}600mm$ is deducted as the optimal size if we consider the double economic feasibility. As well, among them the best qualified $600{\times}600mm$ shapes, the fiber cocktail hybrid of $1.5kg/m^3$ PP fiber and $40kg/m^3$ of steel, comes out the best ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.407-408
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• 2010

This study investigated fire resistance performance for ultra-high-strength concrete columns reinforced with various fibers such as polypropylene, nylon, and steel fibers. 24 small size column specimens were tested with standard heating curve of KS F 2257-1 for 3 hours. The main parameters were the aggregate types, the length of polypropylene fibers, and the content ratios of each fiber.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.65-66
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• 2015

In this study, it evaluate mecahnical performance and impact resistance performance of fiber reinforced concrete, fiber reinforced mortar and preplace grout mortar. steel fiber, nylon fiber and polypropylene fiber are reinforced 1vol.% 2vol.% 10vol.% by each fiber type. It evaluate impact resistance performance to use projectile 10mm of 400m/s velocity. As a result, mechnical performance and impact resistance performance of fiber reinforced preplace grout mortar are improved a lot by 10% fiber reinforced ratio.

• Structural Engineering and Mechanics
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• v.66 no.4
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• pp.477-485
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• 2018

This study aims to investigate the influence of individual and hybrid fiber on the local bond-slip behavior of medium and high strength concrete after exposure to different high temperatures. Tests were conducted on local pullout specimens (150 mm cubes) with a reinforcing bar embedded in the center section. The embedment lengths in the pullout specimens were three times the bar diameter. The parameters investigated include concrete type (control group: ordinary concrete; experimental group: fiber concrete), concrete strength, fiber type and targeted temperature. The test results showed that the ultimate bond stress in the local bond stress versus slip curve of the high strength fiber reinforced concrete was higher than that of the medium strength fiber reinforced concrete. In addition, the use of hybrid combinations of steel fiber and polypropylene fiber can enhance the residual bond strength ratio of high strength concrete.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.473-480
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• 2009

The 180 minutes fire test based on the standard curve of ISO-834 were conducted on three RC column specimens with different constant axial loading ratios to evaluate the fire performance of fiber cocktail (polypropylene+steel fiber) reinforced high strength concrete column. The columns were tested under three loading levels as 40%, 50%, and 61% of the design load. No explosive spalling has been observed and the original color of specimen surface has been changed to light pinkish grey. The maximum axial displacements of three specimens were 1.5~2.2 mm. There was no reduction in load bearing capacity of each specimen exposed to fire and no effect were observed on the fire performance within 61% of the design load. The tendencies of the results with loading, such as the temperature distribution of in concrete and the changes in temperature rise due to the water vaporization in concrete, are very similar to those without loading. The final temperatures of steel rebar after 180 minutes of fire test resulted in 491.4${^{\circ}C}$ for corner rebar, 329.0${^{\circ}C}$ for center rebar, and 409.8${^{\circ}C}$ for total mean of steel rebar. The difference of mean temperature between corner and center rebar was 153.7${^{\circ}C}$ㅍ. The tendency of temperature rise in concrete and steel rebar changed after 30~50 minutes from the starting time of the fire test because the heat energy influx into corner rebar is larger than that into center rebar. The cause of decrease in temperature rise was due to the water vaporization in concrete, the lower temperature gradient of the concrete with steel and polypropylene fiber cocktails, the moisture movement toward steel rebars and the moisture clogging.