• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.189-196
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• 2018

Degraded shear performance of reinforced concrete members with recycled coarse aggregate (RCA) compared to flexural strength is a problem. To address this, steel fibers can be used as concrete reinforcement material. In this study, the strength and deformation characteristics of SFRC beams using RCA were to be determined by shear tests. Major experimental variables include the volume fraction of steel fiber (0, 0.5%, 1%), the replacement rate of RCA (0%, 100%), and the shear span ratio (a/d = 1, 2). As a result of the experiment, the shear strength of the specimen increased as the rate of mixing steel fiber increased. For specimens with RCA and 1% steel fiber, the maximum shear strengths increased by 1.77 - 6.25% compared to specimens with normal coarse aggregate (NCA). On the other hand, at 0-0.5% steel fiber, the shear strengths of RCA specimens were reduced by 24.2% to 49.2% compared to NCA specimens. This indicates that reinforcement with 1% volume fraction of steel fiber greatly contributes to preventing shear strength reduction due to the use of RCA.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.1
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• pp.20-25
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• 2010

Fractionation effects of the slot-type and the hole-type screens of mutifractors were studied using a pilot multifractor. We used a slot screen of 0.15 mm, and two hole screens of 1.0 and 2.0 mm, respectively, in the study. We found hole-type screens were more effective for fractionation of fiber furnishes according to their fiber lengths. Slot-type screen was more effective to remove the shives from the accepted fiber furnishes. There existed a high regression coefficient between the fiber length differences and the freeness differences of the accepted and the rejected fiber furnishes.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.1
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• pp.13-19
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• 2010

Four waste paper mills in Korea, where multifractors, devices for fiber fractionation, were installed, were selected to investigate how effectively and how differently the multifractors were used. They all used slot-type screens. Effective fiber fractionations by fiber length were expected by the multifractors, but in reality, they were used for selecting fiber furnishes that were flexible and hydrated. Flakes, which meant large fiber bundles, were rejected effectively by the multifractors. There existed a high regression coefficient between the fiber length differences and the freeness differences of the accepted and the rejected fiber furnishes.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.40 no.2
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• pp.1-7
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• 2008

The trend of using more hardwood and recycled fibers, and closing more tightly of the paper mill white water system has resulted in build-up of fines as well as organic and inorganic contaminants in the white water. This changes in papermaking wet end requires developing chemical additive system that provides good fiber retention and drainage in closed white water system. In this study the effect of charge densities and chemical characteristics of microparticle systems consisted of cationic guar gums and anionic colloidal silica sols on drainage and retention have been examined. Results showed that higher charge density of cationic guar gum and anionic colloidal silica sol gave better retention and drainage. Particularly highly structured silica gave greater retention efficiency.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.3
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• pp.24-33
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• 2015

Linerboards containing wood flours were developed to increase solid contents in wet pressing process. Presence of wood flours in recycled fibers allowed passage of pressurized water at high wet pressing pressure, and increased solid contents while keeping the bulk of the board. The amount of wood flour addition should be controlled based on the intensity of the wet pressing pressure and the properties of the wood flours. Addition of cationic starch to the wood flour containing OCC furnish showed synergic increase of solid content and strength properties. Shapes of the wood flours such as spherical and rod type added to OCC furnish affected largely their solid content, drainage, and board physical properties.

• Resources Recycling
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• v.6 no.2
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• pp.12-21
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• 1997

Plastics waste constitutes approximately 23% by volume of the municipal solid waste(MSW) generated in the U.S. each year, and have slow rate of degradation in the environment. Therefore, there is a great deal of public pressure to recycle plastics, and more than 100 million people participate in the curbside recycling programs. Despite the high level of public interest, only 3.5% of the plastic are recycled, which is substantially lower than the recycle rates of other materials such as paper fibers, glass, and iron. Although a large part of the reason is due to the low price of virgin polymers, which in turn is due to the low price of oil, it is possible to make the plastics recycling as a profitable business by developing advanced technologies. In this communication, various methods of separating pplastics from metals and from each other are discussed.

• Journal of Adhesion and Interface
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• v.20 no.3
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• pp.87-95
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• 2019

In the present study, the effect of alkali treatment of rice straw on the flexural properties and impact strength of rice straw/recycled polyethylene composite was investigated. Alkali treatments were performed by means of two different methods at various sodium hydroxide (NaOH) concentrations. One is static soaking method and the other is dynamic shaking method. The composites were made by compression molding technique using rice straw/recycled polyethylene pellets produced by twin-screw extrusion process. The result strongly depends on the alkali treatment method and concentration. The shaking method done with a low concentration of 1 wt% NaOH exhibits the highest flexural and impact properties whereas the soaking method done with a high concentration of 10 wt% NaOH exhibits the highest properties, being supported qualitatively by the fiber-matrix interfacial bonding of the composites. The properties between the two highest property cases above-described are comparable each other. The study suggests that such a low concentration of 1 wt% NaOH may be used for alkali treatment of natural fibers to improve the flexural and impact properties of resulting composites, rather than using high concentrations of NaOH, 10 wt% or higher. Considering of environmental concerns of alkali treatment, the shaking method is preferable to use.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.438-444
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• 2019

In this study, the effect of polypropylene fiber on the freeze-thaw damage of mortar was evaluated experimentally. The effects of the reinforcing of polypropylene fiber on the compressive and bending performance of mortar after 300 cycles of freeze-thaw test were evaluated by comparing the normal mortar and the mortar with polyvinyl alcohol fiber. In addition, the mass loss, relative dynamic elastic modulus, and cumulated pore volume of mortar were measured by each cycle of freeze-thaw test. As a result, it was confirmed that the fiber reinforced mortar, regardless of the fiber type, was effective not only in maintaining the performance of the compressive strength and the bending strength but also suppressing the mass loss after the freeze-thaw test of 300 cycles. Meanwhile, it was confirmed that not only polyvinyl alcohol fibers but also polypropylene fibers can effectively act to suppress the damage of the mortar by freeze-thaw. However, in order to improve the freeze-thaw resistance of mortar mixed with polypropylene fiber, it is necessary to increase the bonding performance with the cement matrix which can be expected from polyvinyl alcohol fiber.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.571-580
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• 2020

In this study, an experimental study on storage media for thermal energy storage system was conducted. For thermal energy storage medium, concrete has excellent thermal and mechanical properties and also has various advantages due to its low cost. In addition, the ultra-high strength concrete reinforced by steel fibers exhibits excellent durability against exposure to high temperatures due to its high toughness and high strength characteristics. Moreover, the high thermal conductivity of steel fibers has an advantageous effect on heat storage and heat dissipation. Therefore, to investigate the temperature distribution characteristics of ultra-high-strength concrete, concrete blocks were fabricated and a heating test was performed by applying high-temperature thermal cycles. The heat transfer pipe was buried in the center of the concrete block for heat transfer by heat fluid flow. In order to explore the temperature distribution characteristics according to different shapes of the heat transfer pipe, a round pipe and a longitudinal fin pipe were used. The temperature distribution at the differnent thermal cycles were analyzed, and the thermal energy and the cumulated thermal energy over time were calculated and analyzed for comparison based on test results.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.433-439
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• 2023

In this study, the bonding performance of repair materials was evaluated on concrete repair surface to develop concrete repair materials based on UHPC (Ultra High Performance Concrete) which has high mechanical and durability performance. The ten test variables were applied considering the roughness and wet condition of the concrete surface subject to repair, the addition of polymer, and the use PP and PVA fibers in repair materials. The addition of the polymer caused a significant decrease in strength, which was thought to be due to the effect of the additional super plasticizer used to adjust workability. Also, flow was reduced by up to 13.8 % with the use of plastic-based fibers. As a result of evaluating the bond strength of the repair material considering the condition of the surface subject to repair, it was thought that in the case of using UHPC-based repair material, high bonding performance could be secured without any additional surface treatment as long as the surface of the base material was sound. In addition, UHPC-based repair materials showed high bonding performance even when the attachment surface was wet. In the future, research will be conducted on shot-crete application and gradient pouring for the development of UHPC-based repair materials, and continuous improvement in the repair material mixing property will be carried out to ensure economic efficiency and performance as a concrete structural repair material.