• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.465-471
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• 2009

To prevent the explosive spalling of the high strength concrete and control the rise of temperature in the steel rebar during fire, a fiber cocktail method has been proposed simultaneously with the use of polypropylene and steel fiber. After applying the fiber cocktail (polypropylene and steel fibers) into the mixture of high strength concrete with a compressive strength of between 40 and 100 MPa and evaluating the thermal properties at elevated temperatures, the fire test was carried out on structural members in order to evaluate the fire resistance performance. Two column specimens were exposed to the fire without loading for 180 minutes based on the standard curve of ISO-834. No explosive spalling has been observed and the original color of specimen surface was changed to light pinkish grey. The inner temperature of concrete dropped rapidly starting from 60mm deep. After 60 minutes of exposure to the fire, the temperature gradient of fiber cocktail reinforced high strength concrete was measured as 2.2oC/mm, which is approximately 5 times less than that of normal concrete. The final temperatures of steel rebar after 180 minutes of fire test resulted in 488.0oC for corner rebar, 350.9oC for center rebar, and 419.5oC for total mean of steel rebar. The difference of mean temperature between corner and center rebar was 137.1oC The tendency of temperature rise in concrete and steel rebar changed between 100oC and 150oC 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.93-102
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• 2016

The purpose of this paper is to investigate the flexural behavior of high-strength steel fiber-reinforced concrete beams with compressive strength of 130 MPa. The paper presents experimental research results of steel fiber-reinforced concrete beams with steel fiber content of 1.0% by volume and steel reinforcement ratio of less than 0.02. Both of normal-strength rebar and high-strength rebar were used in the test beams. Modeling as well as compressive and tensile strength test of high-strength steel fiber-reinforced concrete was performed to predict the bending strength of concrete beams. Tension modeling was performed by using inverse analysis in which load-crack mouth opening displacement relationship was considered. The experimental results show that high-strength steel fiber-reinforced concrete beams and the addition of high-strength rebar is in favor of cracking resistance and ductile behavior of beams. For beams reinforced with normal-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.81 to 1.42, whereas for beams reinforced with high-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.92 to 1.07. The comparison of bending strength from numerical analysis with the test results showed a reasonable agreement.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.63-66
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• 2000

This paper describes the need for a ductile Fiber Reinforced Plastic(FRP) reinforcement for concrete structures. Using the material hybrid and geometric hybrid, it is demonstrated that the pseudo-ductility characteristic can be generated in FRP rebar. Ductile hybrid FRP bars were successfully fabricated at 4mm and l0mm nominal diameters using an hand lay up method. Tensile specimens from these bars were tested and compared with behavior of FRP rebar and steel bar

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.57-62
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• 2000

This paper describes the need for a ductile Fiber Reinforced Plastic(FRP) reinforcement for concrete structures. Using the material hybrid and geometric hybrid. it is demonstrated that the pseudo-ductility characteristic can be generated in FRP rebar. Ductile hybrid FRP bars were successfully fabricated at 4mm and 10mm nominal diameters using an hand lay up method. Tensile specimens from these bars were tested and compared with behavior of FRP rebar and steel bar

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.1
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• pp.9-16
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• 2009

For reinforced concrete members, bond strength is one of the important factors between the two materials: the concrete and the reinforcing element. The bond strength of Aramid Fiber Reinforced Polymer (AFRP) rebar was tested using the pull-out method. Presented were comparison results of the bond strength between AFRP rebar and deformed steel bars from the test. Embedded lengths and diameters of the rebar were taken into account as parameters. The bond stress-slip responses and failure modes of AFRP rebar were evaluated. It was found that the bond stress-slip responses of AFRP rebar were similar to those of deformed steel bars. As the diameter of rebar increased, the pull-out load increased. In addition, it was shown that the bond strength of an AFRP rebar was approximately 54% compared with that of a deformed steel bar.

• 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.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.57-58
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• 2022

Reinforced concrete (RC) structures play a significant role in the construction industries. An embeddable solid-state reference electrode (ESSRE) was used to evaluate the corrosion status of steel rebar in the concrete of various cover thicknesses that exposed to the maritime environment (3.5 % NaCl) in this study. From the open circuit potential measurement (OCP), the passive state, the corrosion uncertainty, and the 90% probability of corrosion state of the steel rebars in the concrete were monitored by ESSRE. From the electrochemical impedance spectroscopy (EIS) method, severe corrosion was observed at the exposure period of 1510, 1847, 2350, and 3020 h for C10, C15, C20, and C30 concrete, respectively. The results confirm that the ESSRE can be useful to identify the corrosion occurrence and severe corrosion of steel rebar embedded in different cover depth concrete structures.

• Advances in concrete construction
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• v.8 no.4
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• pp.247-255
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• 2019

Several reinforced concrete structures that get deteriorated by rebar corrosion are retrofitted using Carbon Fiber Reinforced Polymer (CFRP). When rebar comes in direct contact with CFRP, rebar may corrode, as iron is more active than carbon. Progression of corrosion of rebar in strengthened RC structures has been carried out when rebar comes in direct contact with CFRP. The experimentation is carried out in two phases. In phase I, corrosion of bare steel bar is monitored by making its contact with CFRP. In phase II, concrete specimens with surface bonded CFRP were casted and subjected to the realistic exposure conditions keeping direct contact between rebar and CFRP. Progression of corrosion has been monitored by various parameters: Half-cell potential, Tafel extrapolation and Linear Polarisation Resistance. On termination of exposure, to find residual bond stress between rebar and concrete, pull-out test was performed. Rebar in contact with CFRP has shown substantially higher corrosion. The level of corrosion will be more with more area of contact.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.53-58
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• 2003

Concrete structures move wholly with concrete and rebar, so they endure external force, but recently the embedded rebar in concrete has been corroded by environmental, physical and chemical factors, the embedded rebar corrosion influences concrete structure to deteriorate structure capacity. To revaluate effect to deterioration of concrete structure according to corrosion of rebar, the researcher mostly examined into corrosion rebar and complex relation of concrete. In that there are flexural strength deterioration of corrosion concrete structure and the bond strength of concrete. But It has not sufficiently studied about physical characteristic of corrosion rebar itself. In this study I will compare specification of rebar through corrosion experiment with corrosion ratio of rebar according to diameter and revaluate. And will investigate the effect to strength characteristic of rebar according to corrosion ratio.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.53-58
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• 2003

Concrete structures move wholly with concrete and rebar, so they endure external force, but recently the embedded rebar in concrete has been corroded by environmental, physical and chemical factors. the embedded rebar corrosion influences concrete structure to deteriorate structure capacity. To revaluate effect to deterioration of concrete structure according to corrosion of rebar, the researcher mostly examined into corrosion rebar and complex relation of concrete. In that there are flexural strength deterioration of corrosion concrete structure and the bond strength of concrete. But It has not sufficiently studied about physical characteristic of corrosion rebar itself. In this study I will compare specification of rebar through corrosion experiment with corrosion ratio of rebar according to diameter and revaluate. And I will investigate the effect to strength characteristic of rebar according to corrosion ratio.