• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.161-164
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• 2008

In recent years, carbon fiber-reinforced polymer (CFRP) has been widely used for repairing and/or strengthening structural elements in concrete. Not enough test data, however, are available to predict the long-term performance of the repaired and improved structures exposed to weathering. The objective of this research is to study the effect of freeze-thaw cycling on the behavior of reinforced concrete (RC) beams strengthened in shear with carbon fiber sheet. Six small-scale RC beams (100mm${\times]$100mm${\times]$400mm) were strengthened with CFRP in shear, subjected to up to 400 cycles freeze-thawing from -17${\sim}4^{\circ}C$, and tested to failure in four-point bending. Test result, there was no significant damage to carbon fiber sheet strengthened concrete beams had been suffered 30 cycles of freeze-thawing, and more over 60 cycles of freezing-thawing brought about a reduction in resistance of only 25% of the initial level.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.627-636
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• 2011

Recently, to prevent explosive spalling of high-strength concrete (HSC) members, the usage of nylon fiber instead of polypropylene fiber has increased. Past experimental studies have been conducted to examine the spalling and mechanical properties of HSC with nylon fibers when exposed to elevated temperature. However, the previous studies on HSC with nylon fibers subjected to high temperatures were performed only on the properties such as spalling, compressive strength, and elastic modulus rather than investigations on to the behaviors such as thermal strain, total strain, steady state creep, and transient creep. Therefore, in this study thermal strain, total strain, steady state creep, and transient creep of HSC mixed with nylon fibers with water to binder ratio of 0.30 to 0.15 were tested. The experimental results showed that nylon fibers did not affect the performance of HSC with nylon fibers at high temperatures. However, HSC with nylon fibers generated a larger transient creep strain than that of HSC without fibers and normal strength concrete.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.726-736
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• 2003

Concrete columns confined with high-strength fiber composites can enhance its strength as well as maximum strain. In recent years, several equations have been developed to predict the behavior of the concrete columns confined with fiber composites. While the developed equations can predict the compressive strength of the confined columns with reasonable agreement, these equations are not successful in predicting the observed maximum strain of the columns. In this paper, a total of 61 test results is analysed to propose an equation to predict both compressive strength and maximum strain of concrete cylinders. The proposed equation takes into account the effects of confining pressure and cylinder size. Furthermore, in order to verify the proposed stress-strain curve for concrete cylinders, six cylindrical specimens were tested. Comparisons between the observed and calculated stress-strain curves of the tested cylinders showed reasonable agreement.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.101-112
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• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of geo-structures damaged from differential settlement. The purpose of this research is to improve the compressive strength and degree of grout using reinforcing fibers and blast furnace slag powder. In this regard, this study has conducted uniaxial compression tests for the specimens with high ratios (higher than 50%) of blast furnace slag powder. The carbon fiber content was increased by 0, 0.5, and 1.0% to coMpare its compressive strength with that of aramid fiber. The uniaxial compressive strength increased with the increase of fiber content and the bridging activity by fiber in cement tended to increase uniaxial compressive strength. Based on the results, it was confirmed that the aramid fiber has a gel time of 14 seconds and the uniaxial compressive strength is more than 3 Mpa coMpared to carbon fiber.

• Journal of the Society of Disaster Information
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• v.8 no.3
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• pp.223-233
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• 2012

Steel fiber is high stiffness and large weight. So, Pumping hose to rupture of the safety management is difficult. Steel fiber caused by corrosion of the deterioration of durability and high-rebound losses are needed for the improvements. Thus, the revised regulations in 2009 by a steel fiber to reinforce other materials is possible. Variety of fiber reinforcement material for concrete review of applicability is needed. Steel fiber strength than the other fibers is large and by the geometry of the fibers are attached to improve performance. However, compared to steel fiber organic fibers and low modulus of elasticity and tensile strength of fiber and agglomeration occurs in the concrete to be used as reinforcement material is difficult. In this regard, the present study as a single object in the micro-fiber bouquet sharp entanglement through make muck attach surface area, distributed fibers from surfactant of the surface enhanced polyamide fibers, steel fiber and PP fiber reinforced concrete by comparing the scene to provide a basis for the use.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.667-675
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• 2004

This paper presents the failure mode and strengthening design of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer(CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, the presence of anchor, and strengthening in compression. In this study, there are different failure types with increasing the CFRP grid strengthening reinforcement. On the low strengthening level, CFRP grid in repair mortar cover ruptures. On the moderate strengthening level, there is a debonding shear failure in the interface of carbon FRP grid because of the excessive shear deformation. On the high strengthening level, diagonal shear failure occurs. With the increasing of FRP grid reinforcement, the strengthening effect increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure which result in sudden loss in the resisting load capacity. CFRP rupture failure is desirable, because CFRP ruptured concrete slab keeps the same load capacity and ductility haying before strengthening even after failure. Finally, design guideline and procedure are given for strengthening of concrete slab with CFRP grid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.61-69
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• 2019

In this study, the flexural strength and curvature ductility factor of single and hybrid fiber reinforced ultra high strength concrete flexural members with conventional steel rebar were evaluated by experimental program with 3-UHSC beams. Test specimens were loaded by 4-pointed flexural loading. According to the test results, hybrid fiber reinforced UHPC test specimens had higher moment resisting capacity and ductility. For the safe design of hybrid fiber reinforced UHPC, test specimens were analyzed according to the sectional analysis method with material models suggested by K-UHPC design recommendation. Current K-UHPC design recommendation predict the moment resisting capacity of member conventionally and over-estimated the ductility.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.1-12
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• 1993

Four series of fiber reinforced concrete beams without shear reinforcement were tested to determine their cracking shear strengths and ultimate shear capacities. Results of tests on 36 reinforced concrete beams (including 21 containing steel fibers) are reported. Four parameters were varied in the study, namely, the concrete compressive strength, volume fraction of fibers, shear span-to-depth ratio, and the tensile steel reinforcement. The effects of fiber incorporation on failure modes, deflections, cracking shear strength, and ultimate shear strength have been examined. Resistance to shear stresses have been found to be improved by the inclusion of fibers. Based on these investigations, a method of computing the shear strength of steel fiber reinforced concrete beam is suggested. The comparisons between computed values and experimentally observed values are shown to verify the proposed theoretical treatment.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.189-197
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• 2003

In this paper, deformation characteristics of fiber-mixed-soils were studied at small strain range(0.0001%～1%) using resonant column test and triaxial test, and reinforcement effect was evaluated by the measure of maximum shear moduli. The effects of the major parameters such as fiber content, aspect ratio and fiber type on reinforcement were comparatively assessed. The specimens were remolded from Jumunjin Sand randomly mixed with discrete polypropylene staple fibers. Maximum shear moduli of fiber-mixed-soils increased by up to 30% and modulus reduction was also restrained in nonlinear range. Shear moduli increased as the aspect ratio increases. The reinforcement was more effective with fibrillated fiber than with monofilament fiber. The most effective reinforcement was achieved with the specimen of 0.3 % fiber content.

• Journal of the Korea Institute of Building Construction
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• v.17 no.4
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• pp.321-329
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• 2017

Concrete is a semi-brittle material, so its compressive strength is high but its tensile strength is low. The use of fiber-reinforced concrete to improve the disadvantages of such concrete can be an effective way to toughen effective toughness, and the performance is improved by using steel fiber reinforced concrete for structures that are vulnerable to bending forces. However, alternative materials are required due to corrosion of steel fiber and lowering of workability. The purpose of this study is to evaluate the availability of replacing steel fiber reinforced concrete by evaluating physical properties, mechanical properties and drying shrinkage properties of concrete using macro forta fiber with excellent diffusibility. Experimental results show that the macro forta fiber has better fluidity and mechanical performance than the steel fiber reinforced concrete. It was also confirmed that the crack resistance of concrete using Macro Forta fiber is effective in improving structural cracking and drying shrinkage resistance compared to steel fiber reinforced concrete.