• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.101-104
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• 2008

The cost of repairing the deterioration of concrete structures due to corrosion of the reinforcement steel has been the prominent figure in the maintenacne of the reinforced-concrete infrastructures. As an alternative material to steel reinforcement, the use of Fiber Reinforced Polymer (FRP) bar in concrete is being actively studied for the high resistance of chemical environment and high strength to weight ratio properties of FRP. However, there remain various aspects of FRP properties that still need to be studied before the standard design criteria can be established. One of the imminent issues is the bond between FRP and concrete. In this study, the bond-behavior of FRP bars in concrete is investigated via the pullout test with three varying parameters: surface condition of FRP bars, concrete compression strength, and cyclic loading patterns. As a result of experiment, the bond strength of GFRP increased with the concrete compression strength increasing and decreased with applying cyclic load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.1-8
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• 2017

An experimental study is needed a reinforcing method for seismic load to apply for RC structures because a lot of earthquakes have frequently happened in the world and those also collapsed infrastructures or damaged human lives. The reinforcing effect of PolyUrea (PU) appeared to be excellent under blast and impact about RC structures. In this study, Stiff Type PolyUrea (STPU) had developed by manipulating the ratio of the components of prepolymer and hardener of PU. And the durability performance evaluation of STPU for deterioration and chemical resistance has been performed. Acid environmental exposure test and ultraviolet (UV) exposure test have been performed as the durability performance evaluation for STPU. Concrete carbonation exposure test and freezing and thawing test for concrete coated with STPU have been performed. The experimental result showed that STPU has high resisting capacity and durability in all tests. Therefore, STPU would be used as seismic reinforcement materials.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.45-54
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• 2012

Various geosynthetics are widely applied to civil structures and waste landfill site for reinforcement and water resistance. The use of geosynthetics inevitably involves the coupled behaviors of different materials which include large displacement and strain-softening behaviors, etc. In this study, the effect of chemical element in the leachate on the interface shear strength under the cyclic loading condition was analyzed. The Multi-purpose Interface Apparatus (M-PIA) has been modified and cyclic direct shear tests have been performed. The submerging period of each specimen is 200 days. Additionally, the Field-Emission Scanning Electronic Microscopy (FIB) analysis has been also performed to induce the reason of the variation of disturbance function and verify the hypothesis on the decay-proof ability of geosynthetics. Consequently, the charateristics of chemical degradation of geosynthetic-soil interface are verified and the variation of the disturbance function is mainly caused by the different type of soil mineral decay, based on the FIB results.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.452-457
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• 2015

The physical properties, such as the heat resistance and thermal durability of the temperature difference fatigue resistance should be excellent when preparing an epoxy type resin for a neon transformer housing. In this study, 50 wt% of $SiO_2$ and silica were selected as a reinforcement and diluent filler for epoxy type resins, respectively. Thermal conductivity and thermal stability were measured as the mixing ratio varied upon the particle sizes. The optimal amount of the mixed silica was 50 wt%. Thermal stability was improved with increasing the amount of larger silica particles. The optimal mixing ratio of differently sized silica particles was 28/3 : 14/18 : 8/10 mesh = 1 : 1 : 1. From these results, it is thought that neon transformer is producible which has excellent thermal durability.

• Elastomers and Composites
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• v.36 no.4
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• pp.237-245
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• 2001

A study was made on the chemical treatment of silica and silane coupling agents, bistriethox ysilylpropyltetrasulfide(Si 69) and ${\gamma}$-mercaptopropyltrimethoxy silane (MPS) for reinforcement of silica formulation. The effects of chemical treatment method and the most popular two coupling agents were examined. The results clearly indicate that the wet method, coupling agent is combined chemically with the silica prior to mixing, has more dispersion, wetting ability, dynamic properties and stability than the dry method, coupling agent is premixed directly with the silica. The mixing was done using a bench-type kneader having two mixing cam and a two-roll mill, under approximately similar conditions. The physical properties of SBR vulcanizates give rise to marked improvements by addition of Si 69 and MPS in comparison with without silane coupling agents. The optimum amount of Si 69 and MPS was 2 w/w% by experiments in the dry method but was 4 w/w% by EA and TGA analysis in the wet method.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1186-1191
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• 1999

By using a liquid-mix precursor, we prepared the hollow glass spheres(HGS) as an additive of polymer compound which are used in the field of modifier, promoter, filler, and reinforcement. Liquid-mix precursor is a mixture of 40% sodium silicate aqueous solution, boric acid as a insolubilizing agent, and urea as a blowing agent. To obtain the precursor particles which are fed into a gas flame furnae, the above liquid-mix precursor was dried in oven and crushed with ball mill. We assumed the size of precursor particles ($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$), temperature of furnace($800{\sim}1200^{\circ}C$), and amount of urea(0~30 g) as the parameters affecting on the properties of HGS. As a result mean particle size of HGS increases with increasing the temperature of furnace and the amount of urea and with decreasing the size of precursor particles. Also, we found that incresing the amount of urea is related to a decrease of the crush strength of HGS.

• Elastomers and Composites
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• v.47 no.3
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• pp.238-245
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• 2012

Graphene oxide was synthesized from natural graphite, and its surface was modified using diisocyanatodicyclohexylmethane( $H_{12}MDI$). Isocyanate-graphene sheet(i-RGO) was obtained by reduction of surface modified GO. To select nanofiller having good dispersion with polyurethane, GO, i-RGO, natural graphite and thermal reduced graphite were analyzed, and then i-RGO was selected as a suitable nanofiller. PU/i-RGO nanocomposite was synthesized with various i-RGO contents to estimate effect of reinforcement on nanocomposite. Thermal stability, hardness, contact angle were increased with i-RGO contents due to i-RGO characteristic and crosslink bridge effect. But, tensile strength and elongation were decreased at i-RGO contents more than the 4 wt%. This phenomenon was interpreted by the excess formation of crosslink bridge.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.217-221
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• 2009

The use of the carbon nanotube (CNT) is superior to the general powder state materials in their thermal and chemical properties. Because its ratio of diameter to length (aspect ratio) is very large, it is known to be a type of ideal nano-reinforcement material. Based on this advantage, the existing carbon black of the semiconductive shield materials used in power cables can acquire excellent properties by the use of a small amount of CNTs. Therefore, we fabricated specimens using a solution mixing method. We investigated the thermal properties of the CNT, such as its storage modulus, loss modulus, and its tan delta using a dynamic mechanical analysis 2980. We found that a high thermal resistance level is demonstrated by using a small amount of CNTs. We also investigated the chemical properties of the CNT, such as the oxidation reaction by using Fourier transform infrared spectroscopy (FT-IR) made by Travel IR. In the case of the FT-IR tests, we searched for some degree of oxidation by detecting the carboxyl group (C=O). The results confirm a tendency for a high cross-linking density in a new network in which the CNTs situated between the carbon black constituent molecules show a bond using similar constructive properties.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.5-12
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• 2015

The construction of waste landfill sites has been increased due to recent expansion of various waste. Geotextiles are widely used for the purpose of reinforcement and protection of waste inside the landfill. Geotextile affects the shear behavior of waste landfill which forms the contact surface with soil. In this study, the effect of acidic and alkaline components in leachate has been analyzed through the laboratory experiment on the shear stress reduction of the contact surface of ground-geotextile under the cyclic load. For this purpose, a dynamic contact surface shear tester has been manufactured, and cyclic simple shear tests have been performed using geotextile and soil specimen which were immersed in chemical solutions for 60 and 840 days, respectively. Based on the Disturbed State Concept, the characteristics of shear stress on the contact surface of ground-geotextile due to chemical factors have been identified by the disturbance function.

• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.602-608
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• 2006

Carbon fiber (CF) reinforced papers using polyacrylonitrile (PAN) based CF and wood pulp were prepared by varying the lengths and the concentrations of CF, and the basis weight of paper to investigate adhesive state between CF and pulp, and physical properties and electrical conductivity of the paper. The reinforcement was caused by physical entanglement and adhesion at the interface of the different fibers rather than by chemical bonds. The tear strength and the thickness of the paper increased as increasing the concentration of CF, while the tensile and the burst strength of the paper decreased. The improved dispersion of CF in the paper was obtained from mixing shorter CF, but the maximum electrical conductivity of the paper was gained from mixing 10 mm chopped CF. The electrical conductivity of the paper increased sharply from 2 wt％ to 8 wt％ of CF showing S-curve, and increased linearly as increasing the basis weight of the paper. Therefore, in order to improve the electrical conductivity and the physical property of the paper, the increase of basis weight of the paper is also important as the increase of CF content in the paper.