• Journal of Conservation Science
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• v.9 no.1
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• pp.21-32
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• 2000

Rock composition of the Hwangsang-dong Granite Standing Sculptured Buddha (Treasure No. 1122) in the Kumi City is biotite-hornblende granodiorite which consists of about 30 pieces of individual rock blocks of same compositions. However, the cap rocks is pebble-bearing coarse sandstone. Rock blocks of the Standing Buddha and surrounding out crops occur well developed several joint systems of $N25^{\circ}$ to $45^{\circ}W$ strike and nearly vertical (70 to $85^{\circ}SE$) dipping. Rock blocks of the Standing Buddha showed vertical, horizontal and oblique joints, and those blocks are well supported by individual blocks. However, the junction part of the blocks are under dangerous situation due 10 seriously mechanical and chemical weathering. Host rock of the Standing Buddha belongs to the HW grade, therefore mostly rock-forming minerals of the granodiorite Standing Buddha altered with clay and iron hydroxide minerals by mineralogical and chemical weathering. Near surface of the Standing Buddha show spore and mycelium of green algaes, and a joint plane alive with weeds. We suggest that if structural stability for the Standing Buddha remove essentially a unstable rock blocks from the main body, and the main body necessitate supporting by rock bolting method because of repeated unstability and minimizing stress to the rock blocks. For the opened joint planes, fractured surface and alive weeds will attempt to fill in a petro-epoxy, petro-filler and biochemical treatments for the algaes, and ground water curtain and wall seems to be necessary for water flow and diminishing humidity of the Standing Buddha.

• Journal of the Korea Institute of Building Construction
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• v.17 no.2
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• pp.141-147
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• 2017

The purpose of this study is to develop an inorganic filling adhesive using MKP and borax based on Dead-burn magnesia and fly ash. First, basic experiments was conducted to derive the proper addition rate of MKP. And this experiment was carried out according to addition ratio of borax. The test items are measured for pot life, flexural strength, compressive strength, adhesive strength, tensile strength, ratio of temperature change, ratio of hardening shrinkage, radon gas and formaldehyde emission. As a result, the proper addition rate of phosphate was 35%. The pot time is about 10minutes, 15minutes and 25minutes according to addition rate of borax. The flexural strength and compressive strength were obtained at 12hours for minimum flexural strength of 8.0MPa and minimum compressive strength of 31.0MPa. The tensile strength was the least 4.1MPa, and the ratio of hardening shrinkage was maximum 2.4% and ratio of heat change was maximum - 0.3%, which satisfied all of the quality standards of 'KS F 4923' (epoxy resin for repairing concrete structures). Both Radon gas and formaldehyde emission was not detected.

• Composites Research
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• v.31 no.3
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• pp.88-93
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• 2018

In this study, damaged composite laminates were repaired by a stepped patch repair method using halloysite nanotube(HNT) and milled carbon(MC) reinforced composite materials with different amount of the particles. And the mechanical and structural effects of the particles on the interface between the damaged and repair surfaces were analyzed. At this time, after exposing them to a harsh environment of high temperature and humidity for a long time, the recovery rate of the material properties relative to the material forming the damaged plate was compared. As a result, at $70^{\circ}C$ high temperature distilled water, the hygroscopicity of the HNT/GFRP composites was significantly different from that of the MC/GFRP composites. Especially, 0.5, 1 wt. % HNT was added, the moisture absorption rate was the lowest and this was the factor that contributed to the mechanical strength increase. On the other hand, MC showed a high hygroscopic resistance only with a small amount, and the strength was different according to the action direction of the load, and the addition amount was also different.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.894-900
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• 1998

An interphase between carbon fiber and epoxy matrix was introduced to increase impact strength of carbon fiber reinforced composites (CFRC) without sacrificing the interlaminar shear strength. Flexible polymers, I. e., MVEMA (poly(methyl vinyl ether-co-maleic anhydride)) and EMA(poly(ethylene-co-maleic anhydride)), which have reactive functional groups were considered as interphase materials. Weight hain of MVEMA and EMA onto the surface of carbon fibers was evaluated by changing the parameters of electrodeposition process. Electrodeposition mechanism of polymers which have anhydride functional group was identified by IR spectroscopy, that is, the generation of $RCOO^-$ functional group by the attack of hydroxide anion in the basic solution was observed. The weight gain was increased by increasing concentration of polymers, current density, and electrodeposition time. However the excess generation of oxygen gas decreased the weight gain by removing the deposited polymers. Washing in the running water easily removed the deposited polymers which are on the fiber surface without bonding, as a results, only 0.5 wt% of deposited polymers are remained.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.990-995
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with ethylene diamine(EDA) and hexamethylene diamine(HMDA) in a stoichiometrically equivalent ratio. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure or chain length of curing agents. In contrast, the results show that the DGEBA/EDA system having the two carbons had higher values in the thermal stability, maximum conversion of epoxide, density, glass transition temperature, tensile modulus, flexural strength, and flexural modulus than the DGEBA/HMDA system having the six carbons, whereas the DGEBA/EDA cure system had relatively low values in the shrinkage(%), thermal expansion coefficient, tensile strength, and had similar values in the maximum exothermic temperature, and conversion of epoxide compared to the DGEBA/HMDA cure system. This findings indicate that packing ability in the HMDA structure affects the thermal and mechanical properties.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.125-132
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• 2006

Recently, surface finishing and protection materials were developed to restore performance of the deteriorated concrete and inhibiting corrosion of the reinforcing-bar. For this purpose, surface protection agent as well as coatings are used. Coatings have the advantage of low Permeability of $CO_2,\;SO_2$ and water. However, for coatings such as epoxy, urethane and acryl, long-term adhesive strength is reduced and the formed membrane of those is blistered by various causes. Also when organic coatings are applied to the wet surface of concrete, those have a problem with adhesion. On the other hand, surface protection agent penetrates into pore structure in concrete through capillary and cm make a dense micro structure in concrete as a result of filling effect. Furthermore, the chemical reaction between silicate from surface protection agent and cement hydrates can also make a additional hydration product which is ideally compatible with concrete body. The aim of this study is to examine the effect of penetrative surface protection agent(SPA) by evaluating several concrete durability characteristics. The results show that the concrete penetrated surface protection agent exhibited higher durability characteristics for instance, carbonation velocity coefficient, resistance to chemical attack and chloride ion penetration than the plain concrete. These results due to formation of a discontinuous macro-pore system which inhibits deterioration factors of concrete by changed the pore structure(porosity and pore size distributions) of the concrete penetrated surface protection agent.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.763-771
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• 2007

Over the last few decades, many researches have been conducted in order to find solution to the problem of corrosion in steel reinforced concrete. As a result, methods such as the use of stainless steel bars, epoxy coatings, and concrete additives, etc., have been tried. While effective in some situations, such remedies may still be unable to completely eliminate the problems of steel corrosion. Fiber reinforced polymer (FRP) elements are appealing as reinforcement due to some material properties such as high tensile strength, low density, and noncorrosive. However, due to the generally lower modulus of elasticity of FRP in comparison with the steel and the linear behavior of FRP, certain aspects of the structural behavior of RC members reinforced with FRP may be substantially different from similar elements reinforced with steel reinforcement. This paper presents the flexural behavior of one-way concrete slabs reinforced with FRP bars. They were simply supported and tested in the laboratory under static loading conditions to investigate their crack pattern and width, deflections, strains and mode of failure. The experimental results shows that behavior of the FRP reinforced slabs was bilinearly elastic until failure. Also, the results show that the FRP overreinforced concrete beams in this study can be safe for design in terms of deformability.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.85-91
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• 2011

Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of view. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the electric protection method, that is, either using an impressed current or a sacrificial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coating of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corrosion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally accepted that the corrosion resistance of bare steel tends to increase with a shift of the corrosion potential in the noble direction, the corrosion resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistances were considered to be apparently improved by the types of resin and additives.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.573-577
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• 2004

We have synthesized a Eu$^{2＋}$-activated Sr$_3$MgSi$_2$ $O_{8}$ blue phosphor and investigated an attempt to develop blue LEDs by combining it with a InGaN blue LED chip (Len=405 nm). The InGaN-based Sr$_3$MgSi$_2$ $O_{8}$：Eu LED Lamp shows two bands at 405 nm and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical transition of the Sr$_3$MgSi$_2$ $O_{8}$：Eu phosphor. The 460 m emission band is ascribed to a radiative recombination of Eu$^{2＋}$ impurity ions in the Sr$_3$MgSi$_2$ $O_{8}$ host matrix. As a consequence of a preparation of W blue LED Lamp using the Sr$_3$MgSi$_2$ $O_{8}$：Eu blue phosphor, the highest luminescence efficiency was obtained at the ration of epoxy/blue phosphor(1/0,202). At this time, the CIE chromaticity was x=0.1417 and y=0.0683.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.2
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• pp.210-230
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• 1995

To compare the wear resistance of four kinds of commercial acrylic resin teeth [SR-Orthosit PosterioresR(Ivoclar Co., Liechtenstein), Endura PosteriorR(Shofu Inc. Japan), trubyte IPN teethR(Dentsply International Inc., York,), Trubyte BiotoneR(dentsply Inermational Inc. Brazil) by means of the toothbrush abrasion method, the artificial resin teeth were embedded in epoxy resin with the occlusal surfaces aligned in one plane for a total of 40 blocks. There after, each lock was mounted in the arm of the toothbrush abrasion machine(K 236, Japan). Wear measurements were made on the three preconditioned states. Those were as follows : no treatment specimens, thermocycled specimens, and thermocycled specimens which were immeresed applied load of 400g during the buring the brushing cycle. At the end of the 30,000-stroke cycle, each specimen was removed, and weighed. The microhardness of four kinds of commercial resin teeth were determined by means of microhardness tester. Microhardness tests were performed on te no treatment specimens, thermocycled specimens, and thermocycled specimens with immersion in the denture cleansing solution. Finally, the comparison of thermal properties were perfomed using differential scanning calorimeter(DSC-1500). The following results were obtained : 1. In the case of no treatment teeth, the wear amount of endura Posterior(EN) was the greatest among the others(p<0.01), and the wear amount of three kinds of artificial resin teeth was increased in the order of Trubyte IPN teeth(IN), Trubyte Biotone(BN), SR-Orthosit Posteriores(SN) but there was no statistic significance(p>0.01). 2. The wear amount of Trubyte IPN teeth(IT) and Trubyte Biotone(BT), was increased due to thermocycling effect, but that of Endura Posteriores(ET) was decreased conversely(p<0.01). 3. Except for the SR-Orthosit Posteriores(STC), the wear amount of three kinds of artificial resing teeth(that is, ETC, ITC, BTC) was increased due to denture cleansing solution$(Cledent^R)$, but there was no statistic significance(p>0.01). But the wear amount of the SR-Orthosit Posteriores(STC) was the greatest among the others(p<0.01). 4. The wear amount of toothbrush was the greatest in case of contact with occlusal surface of SROrthosit Posteriores resin teeth(p<0.01). 5. the microhardness values(KHN) of the SR-Orthosit Posteriores was the highest among the experimental artificial resin teeth(p<0.01). 6. There was no relationship between microhardness valuse(KHN) and wear amount of four kinds of experimental artificial resin teeth(p<0.01). 7. The differential canning calorimetric property of four kinds of artificial resin teeth did not show endothermal or exothermal peak in the range of $100^{\circ}C$