• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.41-50
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• 2014

This study evaluated the bonding property of fiber and flexural behavior of fiber reinforced concrete. Amorphous steel fiber, hooked steel fiber and polyamide fiber was used for evaluation of bonding property and flexural behavior. As a result, the hooked steel fiber was pulled out from matrix when peak stress. However amorphous steel fiber occurred shear failure because bonding strength between fiber and matrix was higher than tensile strength of fiber. Polyamide fibers occurred significantly displacement to peak stress because of elongation of fiber. After that peak stress, fiber was cut off. Amorphous steel fiber reinforced concrete had a greater maximum flexural load compared with hooked steel fiber reinforced concrete because bonding performance between fiber and matrix was high and mixed population of fiber was many. However flexural stress was rapidly reduced in load-deflection curve because of shear failure of fiber. Flexural stress of hooked steel fiber reinforced concrete was slowly reduced because fiber was pulled out from the matrix. In the case of polyamide fiber reinforced concrete, flexural stress was rapidly lowered because of elongation of fiber. However flexural stress was increased again because of bonding property between polyamide fiber and matrix. The pull-out properties of the fiber and matrix has effect on the deformation capacity and flexural strength of fiber reinforced concrete.

• Elastomers and Composites
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• v.46 no.3
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• pp.218-222
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• 2011

The effect of cycled temperature change on the mechanical properties of wood flour(50 wt.% and 70 wt.%) polypropylene WPC(Wood Plastic Composites) was investigated in this study. Flexural modulus and flexural strength of the WPC showed a decrease due to the degradation of interfacial adhesion between polymer matrix and wood flour by the freeze-thaw test regardless of the cycled number. At the higher loading level of wood flour, the reduction of the flexural modulus was remarkable. After the cycled heat-freeze test, it was found that the flexural modulus and flexural strength of the WPC were lower at the high temperature ($60^{\circ}C$) and higher at the low temperature ($-20^{\circ}C$). At the low temperature ($-20^{\circ}C$) which is below glass transition temperature of polypropylene ($-10^{\circ}C$), WPC is in a glassy state which brings about the high stiffness and strength. At the high temperature ($60^{\circ}C$), the flexural modulus and flexural strength of the WPC with 50 wt.% wood flour were lower because of the increase of polymer ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.149-156
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• 2021

FRP has been proposed to replace the steel as a reinforcement in the concrete structures for addressing the corrosion issue. However, FRP-Rebar does not behave in the same manner as steel because the properties of FRP are different. For example, FRP-Rebar has a high tensile strength, low stiffness, and linear elastic behavior which results in a difference bonding mechanism to transfer the load between the reinforcement and the surrounding concrete. Therefore, bonding behavior between FRP-Rebar and concrete has to be investigated using the bonding test. So, Pull-out test has been used to estimate bond behavior because it is simple. However, the results of pull-out test have a difference with flexural-boding behavior of FRP-Rebar concrete member. So, it is needed to evaluate the real fleuxral-bonding behavior. In this study, the evaluation method to flexural-bonding behavior of FRP-Rebar concrete member was reviewed and compared. It was found that the most accurate evaluation method for the fleuxral-bonding behavior of FRP-Rebar concrete member was splice beam test, however, the size and length of specimen have to increase than other test method and the design and analysis of splice beam is complex. Meanwhile, characteristics of concrete could be reflected by using arched beam test, unlike hinged beam test which is based on the ignored change of moment arm length in equilibrium equation. However, the possibility of shear failure exists before the flexural-bonding failure occur.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.249-256
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• 2008

The durability of marine concrete structure is severely degraded by corrosion due to penetration and diffusion of chloride. So, many researches have been performed to improve the durability in marine concrete structure. In this study, the concrete members mixed with the mineral admixtures(SF and BFS), the epoxy-coated steel, and corrosion inhibitors are prepared, and four-point bending test of specimens are performed to investigate the flexural behaviors and the applicability for marine concrete structure. From the test results, the mineral admixtures and inhibitors are useful for safety against the initial cracking and the bending resistance in specimens. When the durable material is used in specimen, the tensile stress of reinforcing rod was less variable in same bending span length, and the durable member showed a stable behavior. And it is evaluated that the crack spacing is not larger in specimen used the durable material.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.30-39
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• 2017

This paper concerns flexural strength of reinforced concrete beams containing recycled coarse aggregate (RCA) with compressive strength ranging from 31 to 38 MPa. The experimental parameters were replacement ratio of RCA and rebar ratio. Replacement ratio of RCA was 0, 30, 50 and 100%, and rebar ratio was 0.50, 0.79 and 1.14%. The RCA concrete beams were tested by using four-point bending test, and experimental results were discussed regarding crack and failure patterns, load-deflection relationship. Crack pattern of concrete beams with RCA was similar to that of concrete beams with natural coarse aggregate (NCA) but overall crack spacing of concrete beams with RCA was smaller than that of concrete beams with NCA. The crack width of RCA and NCA concrete beams was similar to each other. In addition, the test results of flexural strength were compared to the design code predictions. The design code predictions for flexural strength underestimated the experimental results. Therefore, the design code predictions for flexural strength of RCA concrete beams would offer conservative design.

• 한국도로학회:학술대회논문집
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• 2009.11a
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• pp.531-534
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• 2009

• 한국도로학회:학술대회논문집
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• 2006.03a
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• pp.33-36
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• 2006

• 한국도로학회:학술대회논문집
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• 2005.11a
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• pp.203-206
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• 2005

• Tunnel and Underground Space
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• v.29 no.6
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• pp.532-541
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• 2019

Even though shotcrete is a main support for securing the stability of tunnel, the performance of shotcrete is not properly checked due to various difficulties arisen from the characteristics of materials themselves which constitute shotcrete, such as steel fibers and accelerators, and the on-site quality control. In this study, the actual conditions of shotcrete applied to expressway tunnel construction sites were tried to find out, and then some improvement was tried to derive. For this purpose, the characteristics of steel fibers and accelerators supplied to the expressway construction sites were investigated. Also, shotcrete specimens were prepared at the tunnel sites and performance tests were carried out. For steel fiber, domestic production states were investigated, and carbon content and tensile strength were measured using the steel fibers collected in the construction sites. For three types of accelerators such as aluminate, cement mineral and alkali-free, basic properties and total amount of alkali contents were analyzed. Shotcrete specimens were prepared using on-site shotcrete machine with regard to mix designs and types of accelerators. Using these specimens, uniaxial compression tests and flexural tests were performed. As the results, compressive strength, flexural strength, flexural toughness, and etc. were compared with types of acclerators and mix designs.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.185-196
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• 2006

Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.