• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.313-320
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• 2013

In this study, performance of fiber-reinforced polymer-modified mortar was studied for the development of eco-friendly materials for high performance repair and reinforcement. The general cement mortar and eco-friendly UM resin was mixed with a certain percentage for increased durability. To increase the strength of the polymer-modified mortar, PVA fiber, steel fiber and hybrid fiber were added at a constant rate. Hybrid fiber is contains the same percentage of PVA fiber and steel fiber. In order to determine the strength properties of fiber-reinforced polymer-modified mortar, the compressive strength test, the splitting tensile strength test and the flexural strength test were performed. And, in order to determine the durability properties of fiber-reinforced polymer-modified mortar, water absorption test and chemical resistance test were performed. From the experimental results, polymer-modified mortar using UM resin was improved durability. And the tensile strength and flexural strength increased, which were the vulnerability of fiber reinforced polymer-modified mortar. From this study, fiber-reinforced polymer-modified mortar using eco-friendly UM resin can be used to repair and reinforcement for the external exposure of concrete structures to improve the durability.

• Journal of the Korea Institute of Building Construction
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• v.17 no.5
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• pp.465-471
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• 2017

In this study, oxidized graphene nanoplatelet(GO) was prepared by oxidizing graphene nanoplatelet(GNP) with nitric acid in order to solve the problem of dispersion of GNP, one of nano materials. The surface chemical composition of the prepared GO was analyzed by fourier transform infrared spectroscopy(FT-IR) before incorporation into the epoxy paint, and the dispersibility in the solvent was confirmed. Meanwhile, GNP/Epoxy and GO/Epoxy paint were prepared by mixing GNP, GO with 0.1, 0.3, 0.5 and 1.0wt.% in epoxy paint and the mechanical properties were evaluated. As a result, GNP/Epoxy and GO/Epoxy paints showed better mechanical properties than Neat Epoxy which did not incorporate GNP, GO. Especially, when 0.3wt.% of GO was incorporated into epoxy resin, it showed higher tensile strength than Neat Epoxy. It was confirmed that acid treatment of GNP was effective in improving the mechanical properties of epoxy paint.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.208-216
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• 2023

In this study, using the Delphi method, 20 responses to 4 questions (need for launch safety control, top-priority considerations for ensuring public safety during launch, necessary improvements for securing maritime safety, and maritime safety threat factors) regarding launch vehicles and public safety were obtained from experts, and their importance was evaluated to analyze the factors that threaten the reinforcement of maritime safety around launch sites and flight paths when launching. According to the results of an analytic hierarchy process (AHP) analysis, the consistency ratio of the four questions was 4.8%, which is lower than CR ≤ 0.1(10%), and the consistency percentage of the lower measurement indicators was 3.9~5.7%. The derived importance and priority of maritime safety threat factors during launching were in the following order: Substantial human and physical damage in case of launch accidents(0.36), Prepare legal bases (e.g., penalty details) regarding maritime control(0.32), Secure the safety of personnel, equipment, and facilities in danger zone(0.31), Unauthorized entry of vessels in maritime control zones and non-compliance to restrictions(0.30). This article can serve as a reference for strengthening maritime safety in areas around launch sites and flight paths.

• 보존과학연구
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• s.25
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• pp.171-195
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• 2004

This research presents an evaluation of the weathering and deterioration state of the Wanggung-ri five-storied stone pagoda in the Iksan (National Treasure No. 289) and suggests conservational schemes. A deterioration map of the pagoda was drawn from the aspects of petrological, physical, chemical, biological, structural and artificial weathering.The rock properties consisting of the pagoda were medium-grained biotite granite that had leucocratic phenocryst developed in parts. The body of each story suffered severely from the secondary contamination that turned the colors into light grey, pitch dark, yellowish brown, and reddish brown as well as granular decomposition, exfoliation and peel-off. The roof stones were heavy exfoliated or peeled off in most of the cases. In addition to the fine cracks, there were layered cracks on the corners. The roof stones of the3rd and 4th story in the north and west side had some stones fall-off, while those of the 2ndstory in the north side had steel reinforcement filled for a fixing purpose. Those of the 5th story showed big gaps that must have originated from cracks and were easily subject to granular decomposition and rainfall. The inside clay filler was missing in the lower part of the roof stones of the 4th and 5th story and the supporting stones, which were thus covered by light grey or pitch dark sediments. The contact area of the materials was about 70 % in the parts where there was a space due to the filler missing and washigher than 90 % in the lower parts of the pagoda. About 90 % or more of the roof stones surface of each story were covered by aerial plants that formed a thick biological mat. Thus it seemed necessary to come up with the conservational measures to remove the plans living on the surface of the stone materials, with the plans to prevent rain from falling inside, and with the water repellent and hardening treatments to postpone the surface weathering of the rock properties. All those measures and plans must be based on the results of long-term monitoring and thorough detail investigations.

• Journal of the Korean Geosynthetics Society
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• v.3 no.2
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• pp.39-45
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• 2004

Geocomposite mechanically bonded with woven type geotextile and nonwoven geotextile was used to examine to the long-term creep deformation behaviors by the SIM(Stepped Isothermal Method). The temperature steps were $26^{\circ}C$, $40^{\circ}C$, $54^{\circ}C$, $68^{\circ}C$, $82^{\circ}C$ and loading levels were 40%, 50%, 60% of designed strength for stepped isothermal method. Results of creep tests are showing that their strain were lower than 10% during 10,000 hours(GRI GS 10). Also, the effect of weft injection density to the creep deformation behaviors were examined. The weft densities of 0%, 50%, 100% of the original weft density showed the creep strain within 10% and the creep strain was increased with the decrease of weft injection density.

• International Journal of Concrete Structures and Materials
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• v.9 no.2
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• pp.241-254
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• 2015

A lot of reinforced concrete (RC) structures in Syria went out of service after a few years of construction. This was mainly due to reinforcement corrosion or chemical attack on concrete. The use of blended cements is growing rapidly in the construction industry due to economical, ecological and technical benefits. Syria is relatively rich in scoria. In the study, mortar/concrete specimens were produced with seven types of cement: one plain Portland cement (control) and six blended cements with replacement levels ranging from 10 to 35 %. Rapid chloride penetration test was carried in accordance with ASTM C 1202 after two curing times of 28 and 90 days. The effect on the resistance of concrete against damage caused by corrosion of the embedded steel has been investigated using an accelerated corrosion test by impressing a constant anodic potential. The variation of current with time and time to failure of RC specimens were determined at 28 and 90 days curing. In addition, effects of aggressive acidic environments on mortars were investigated through 100 days of exposure to 5 % $H_2SO_4$, 10 % HCl, 5 % $HNO_3$ and 10 % $CH_3COOH$ solutions. Evaluation of sulfate resistance of mortars was also performed by immersing in 5 % $Na_2SO_4$ solution for 52 weeks. Test results reveal that the resistance to chloride penetration of concrete improves substantially with the increase of replacement level, and the concretes containing scoria based-blended cements, especially CEM II/B-P, exhibited corrosion initiation periods several times longer than the control mix. Further, an increase in scoria addition improves the acid resistance of mortar, especially in the early days of exposure, whereas after a long period of continuous exposure all specimens show the same behavior against the acid attack. According to results of sulfate resistance, CEM II/B-P can be used instead of SRPC in sulfate-bearing environments.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.46-49
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• 2008

Recycling glass fiber, 'F-fiber,' was obtained by the separation of the roving layer from waste FRP and the concrete products or structures were considered for its application. Experiment was carried out for the bending strength of aggregate (2.45 of cement) by weight and F-fiber (density of 1.45, volume ratio to all of the aggregate and the cement). Whereas the specimen containing 1% F-fiber showed the bending strength 23% higher than that without F-fiber after curing far 28 days, the one with 0.5% F-fiber did not give any change. It could be found, therefore, that the minimum mixing amount should be larger than 0.5% fur the strength reinforcement. One of the reinforcing concrete product, bench flume, containing 1% F-fiber showed 21% increment of bending strength In contrast to that without F-fiber.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.445-448
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• 2008

The unsaturated polyester(UP) and epoxy resin have a superior material properties and a chemical resistance using sewerage pipes rehabilitation. However, UP and epoxy have not a low temperatures harding, the requirement $8{\sim}11$ hours long times harding and heating system used by reinforcement liner. This study is to evaluate the effects of low temperature harding properties methyl methacrylate(MMA) monomer using expanded polystyrene(EPS) and UP in addition of initiator and promoters. From the test result, viscosity tends to increase with increasing EPS and UP contents. However, harding time change of the MMA resins which it follows in addition of the initiator and promoter.

• Advanced Composite Materials
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• v.18 no.2
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• pp.187-195
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• 2009

Much attention has been paid to the processing of inorganic whisker, especially calcium carbonate whisker, which can be used as reinforcement materials of polymer composite due to its low price. Unfortunately, the present synthesis technique of calcium carbonate whisker starts from calcinations of limestone, which involves high energy consumption and furthermore is a highly environment polluting reaction. In this report, needle-like aragonite was synthesized with a reversible solution reaction from limestone without calcination. Optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to characterize the morphology and crystal structure of intermediates as well as that of the product, aragonite. GCC (grinding calcium carbonate) powder was dissolved in an aqueous solution of magnesium sulfate with reflux and air flush. EDTA titration was used to evaluate reaction rate of the dissolution. A kinetics equation of the dissolution reaction was constructed, which displayed second-order kinetics with respect to the concentration of magnesium sulfate. A rate constant of $0.0015\;l^{-3}{\cdot}mol^{-1}{\cdot}h^{-1}$ was obtained. The dissolution reaction gave fiber-like magnesium hydroxide sulfate and gypsum crystal. Then needle-like aragonite with a length of $9.13\;{\pm}\;1.02\;{\mu}m$ and an aspect ratio of $5.64\;{\pm}\;1.37$ was synthesized from the dissolution product with $CO_2$ bubbling at $70^{\circ}C$.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.39-46
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• 2008

The end plates of fuel cell assemblies are used to fasten the inner stacks, reduce the contact pressure, and provide a seal between Membrane-Electrode Assemblies (MEAs). They therefore require sufficient mechanical strength to withstand the tightening pressure, light weight to obtain high energy densities, and stable chemical/electrochemical properties, as well as provide electrical insulation. The design criteria for end plates can be divided into three parts: the material, connecting method, and shape. In the past, end plates were made from metals such as aluminum, titanium, and stainless steel alloys, but due to corrosion problems, thermal losses, and their excessive weight, alternative materials such as plastics have been considered. Composite materials consisting of combinations of two or more materials have also been proposed for end plates to enhance their mechanical strength. Tie-rods have been traditionally used to connect end plates, but since the number of connecting parts has increased, resulting in assembly difficulties, new types of connectors have been contemplated. Ideas such as adding reinforcement or flat plates, or using bands or boxes to replace tie-rods have been proposed. Typical end plates are rectangular or cylindrical solid plates. To minimize the weight and provide a uniform pressure distribution, new concepts such as ribbed-, bomb-, or bow-shaped plates have been considered. Even though end plates were not an issue in fuel cell system designs in the past, they now provide a great challenge for designers. Changes in the materials, connecting methods, and shapes of an end plate allow us to achieve lighter, stronger end plates, resulting in more efficient fuel cell systems.