• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.131-136
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• 2013

The purpose of this study is to establish the flexural strengthening method of the concrete members. To accomplish this objective, a total of seven concrete beams were tested. From this study, it is found that the initial flexural stiffness and strength of the beams reinforced with NSM CFRP strips were significantly improved compared to the beam without CFRP strip. Failure of the beam reinforced with NSM strips is initiated by failure of NSM strips, eventually sudden explosive compressive failure in the loaded region. This strengthening method combined with NSM CFRP strips and high performance mortar for concrete cover recovery is evaluated by a good strengthening method for the strength, durability and good appearance of concrete structures.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.25-35
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• 2006

This paper investigates the mechanical characteristics of reinforced lightweight soil (RLS) using waste fishing net. RLS used in this experiment consists of dredged soil taken from construction site of Busan New Port, cement, air foam and waste fishing net. Several series of laboratory tests were performed to compare behavior characteristics between RLS and unreinforced lightweight soil, in which the reinforced effect by waste fishing net on RLS was evaluated. The experimental results of RLS indicated that the stress-strain relationship and the unconfined compressive strength are strongly influenced by the content of waste fishing net. Compressive strength of RLS Increased with the increase in curing time and generally increased by adding waste fishing net, but the amount of increase in compressive strength was not proportional to the content of waste fishing net. In this test, the maximum increase in compressive strength was obtained at 0.25% content of waste fishing net. On the other hand, water content of RLS rapidly decreased up to 7 days of curing time and converged to constant value.

• Journal of the Korean Geosynthetics Society
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• v.3 no.1
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• pp.43-52
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• 2004

Laboratory model tests were conducted to assess the behavior characteristics of geogrid reinforced earth walls using fiber-mixed soil backfill with different surcharge loads and reinforcement spacing. The models were built in the box having dimensions, 100cm tall, 140cm long, and 100cm wide. The reinforcements used were geonet(tensile strength, 0.79t/m) and geogrid(tensile strength, 2.26t/m). Decomposed granite soil(ML) with or without polypropylene fiber was used backfill material. Strain gauges and LVDTs were installed on the retaining walls to measure the strain of the reinforcements and the displacements of the wall facings.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.171-178
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• 2019

Fiber-reinforced polymer (FRP) composites have proved to be reliable as strengthening materials. Most of existing studies used single types of FRP composites. Therefore, in this experimental study, carbon FRP sheet, aramid FRP sheet, and hybrid FRP plate including glass fibers were fabricated, and the effect of pre-stressed FRP composites on flexural strengthening of reinforced concrete (RC) beams was investigated. In total, eight RC beam specimens were fabricated, including one control beam (specimen N) without FRP composites and seven FRP-strengthened beams. The main parameters were type of FRP composite, the number of anchors used for pre-stressing, and thickness of FRP plates. As a result, the beam strengthened with pre-stressed FRP plate showed superior performance to the non-strengthened one in terms of initial strength, strength and stiffness at yielding, and ultimate strength. As the number of anchors and thickness of FRP plate (i.e., amount of FRP plates) increased, the strengthening effect increased as well. When hybrid FRP plates were pre-stressed, the strengthening effect was higher in comparison with pre-stressed single type FRP plate.

• Elastomers and Composites
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• v.34 no.3
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• pp.253-261
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• 1999

The cure properties of rubber compounds containing different adhesive compositions were examined. As the amounts of tannin were increased in the adhesive composition, the scorch time was increased and cure rate was decreased due to the size and shape of tannin molecules. Also, the effect of adhesive composition on the adhesion between rubber and fiber was examined by TCAT(Tire Cord Adhesion Test), The reinforcing cords used in this study were mon ofilaments of nylon 610 and nylon 66. According to the results, the optimum adhesion strength between rubber and fiber could be obtained with adhesives whose molar ratios of formaldehyde/resorcinol were above 5/1 in the recipes. Although the level of dip pick-up(DPU) on the reinforcing cord affects the adhesion strength, the DPU of nylon 610 monofilament did not affect the adhesion strength because the level of DPU was constant regardless of the adhesive compositions. In this case, the adhesion strength with the adhesive composition could be explained with the behavior of tannin in the adhesive.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.87-94
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• 2002

In the preceding study, a series of results was presented according to factors like as attaching method of main bar, shear span to depth ratio, reinforcing method for different types of region among various factors, which could determine the properties of composite beams. Based on these results, this study was planned to investigate the structural behaviors of according to attaching method of main bar for composite beams(end-reinforced concrete(RC), center-steel concrete (SC)) varying ratio of tensile bar to steel mainly. Consequently, there were little difference according to attaching method of main bar. And as the ratio of tensile bar to steel increase, the efficiency of strength was high, but ductile capacity of beams could deteriorate. Therefore, to maximize the structural properties of composite beams, it was considered that the ratio of tensile bar to steel should be limited.

• Journal of the Korean Wood Science and Technology
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• v.22 no.2
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• pp.46-53
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• 1994

This study was conducted to investigate a feasibility of manufacturing wood fiber thermoplastic composites and to evaluate their mechanical properties. Wood fiber as a potential reinforcing filler was compounded with two thermoplastics (polypropylene and high density polyethylene) in high intensity thermokinetic plastic mixer aided with a wetting agent. It was found that wood fiber thermoplastic composites could be manufactured by injection molding process. The tensile and flexural strength of injection molded specimens were improved greatly with increasing wood fiber concentration. Tensile and flexural modulus increased proportionately with wood fiber concentration. Wood fiber provided reinforcement with thermoplastics in terms of strength and modulus. However, the percent elongation at break and energy to break were reduced with increasing wood fiber loadings. Impact strength also showed similar trend.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.337-345
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• 2009

The purpose of this study is to investigate the shear strengthening effectiveness of the beams strengthened with near surface mounted (NSM) and external bonded (EB) CFRP strips. A total of nine concrete beams were made and tested. From this study, it was found that the shear stiffness and strength of the beams strengthened with NSM and EB strips were significantly improved compared to the control beam. Failure of the beam strengthened with NSM and EB strips was initiated by shear cracks, propagated diagonally to the adjacent epoxy grooves without crossing the epoxy and finally sudden diagonal crack connecting the point of application of load and flexural crack was occurred. For the beam strengthened combined with NSM and EB CFRP strips, the tensile strains in the NSM CFRP strips were observed in the range of 0.35% to 0.45% and strains with EB strips were measured about 0.3%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.99-107
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• 2015

This study was aimed to investigate the difference in strength of Carbon Nanotube (CNT) reinforced cement mortars with different types of surfactants and doses. In the experimental program, CTAB, SDBS and TX10 which were common surfactants adopted to improve CNTs dispersion in fabricating CNT composites in many industrial fields were included and superplasticizer which was revealed to be effective to disperse CNTs especially in CNT reinforced cementitious composites were added as well. Superplasticizer presented less strength reduction in cement mortar and more strength gain by adding CNTs among four types of surfactants. Higher dosage of superplasticizer caused lower strength of cement mortar. Adding CNTs of 0.4 wt.% or less to cement didn't show strength enhancement by adding CNTs but 0.8 wt.% of CNTs resulted in strengthening effect after all. Finally, a combination of 0.1 wt.% of CNTs, superplasticizer and sonication treatment could lead to strength improvement by adding CNTs in cement mortar.

• Composites Research
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• v.24 no.5
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• pp.34-38
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• 2011

Carbon nanotubes (CNTs) have been widely investigated as reinforcements of CNT/polymer nanocomposites to enhance mechanical and electrical properties of polymer matrices since their discovery in the early 90's. Furthermore, the number of studies about incorporating CNTs into carbon fiber reinforced plastics (CFRP) to reinforce their polymer matrices is increasing recently. In this study, single-walled carbon nanotubes (SWNT) were dispersed in epoxy with 0.2 wt.% and 0.5 wt.%. Then, the SWNT/epoxy mixtures were processed to carbon fiber composites by a vacuum assisted resin transfer molding (VARTM) and a wet lay up method. The processed composite samples were tested for the interlaminar shear strength (ILSS). The relationship between the interlaminar shear strengths and processing, and the reinforcement mechanism of carbon nanotubes were investigated. CNT/epoxy nanocomposite specimens showed the increased tensile properties. However, the ILSS of carbon fiber composites was not enhanced by reinforcing the matrix with CNTs because of processing issues caused by increased viscosity of the matrix due to addition of CNTs particularly for a VARTM method.