• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.673-676
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• 2006

Steel FibreReinforced Shotcrete(SFRS) is one of the main tunnel support along with the rock bolt during the excavation and after the completion of the tunnel. In the standard qualification of the SFRS defined by Korea Highway Corporation, 28 day core specimen has to meet the compressive strength of 19.6 MPa and over 90 % fibre contents. Furthermore, for the 28 days brick shaped specimen made by shooting, flexural strength should be over 4.4 MPa and flexural toughness ratio which can be calculated from flexural toughness factor has to meet more than 68% of flexural strength. In shotcrete, accelerating agent is added for the rapid strength development. Silicate and aluminate type agents are known to develop shotcrete strength rapidly, however, has such problem to degrade the middle and long term strength. Hence, using poly carboxylic super plasticizer, it was aimed to enhance the quality of the shotcrete with the lower water-cement ratio and the same level of workability. The present paper shows the part of the field test result and its analysis.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.7 no.2
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• pp.209-222
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• 1997

Authors surveyed the ground water near the waste disposed from a fiberglass production factory to confirm the presence of glassfiber in the water and to determine the effect of sampling conditions and storage on the recovery of fibrous materials in the ground water. Sample was collected at every 4 hours for 48 hours consecutively. After finishing the 48 hours sample, water sampling was done from each tap after repeated turning on and off the water for 30 seconds at each time. Sample was collected in the two 1.5 liter polyethylene bottle after vigorously shaking the bottle with the same water several times with the flowing tap water. At each paired sample, one bottle was stored stand still at room temperature, and the other sample was filtered immediately after sampling. Water was filtered on the Mixed Cellulose Ester filter with negative pressure. Each sample was divided into upper and lower layer. The other bottle was stored at room temperature standstill for 7 days and filtered in the same fashion as the other pair of sample did. Each MCE filter was divided into 4 pieces and one piece was treated with acetone to make it transparent. Each prepared sample was observed by two researchers under the light and polarizing microscopy, scanning electron microscopy and energy dispersive X-ra microanalysis. Fibers were classified by the morphology and polarizing pattern under the polarizing microscope, and count was done. 1. There was a significant fluctuation in number of the fibers, but there was no specific demonstrable pattern. 2. Non-polarizing fibers frequently disappeared after 7 days's storage. But cluster of fibers were found at the wall of the same container by scratching technique. 3. Polarizing fibers were usually found in between the filter and the manicure pasted area. Possible explanations for this phenomenon will be that either these fibers are very light or have electronic polarity. Hence, these fibers are not able to be attached on the surface of slide glass. 4. Under the scanning electron microscopic examination, the fibers which are not refractive under the light microscopy were identified as glassfiber. Other fibers which is refractive under the polarizing microscopy were identified as magnesium silicate fibers. It is strongly suggested that development of standardized method of sample collection and measurement of fibrous material in the water is needed.

• Steel and Composite Structures
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• v.29 no.2
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• pp.201-218
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• 2018

In this study, the effects of magnesium sulfate on the mechanical performance and the durability of confined and unconfined geopolymer concrete (GPC) specimens were investigated. The carbon and basalt fiber reinforced polymer (FRP) fabrics with 1-layer and 3-layers were used to evaluate the performances of the specimens under static and cyclic loading in the ambient and magnesium sulfate environments. In addition, the use of FRP materials as a rehabilitation technique was also studied. For the geopolymerization process of GPC specimens, the alkaline activator has selected a mixture of sodium silicate solution ($Na_2SiO_3$) and sodium hydroxide solution (NaOH) with a ratio ($Na_2SiO_3/NaOH$) of 2.5. In addition to GPC specimens, an ordinary concrete (NC) specimens were also produced as a reference specimens and some of the GPC and NC specimens were immersed in 5% magnesium sulfate solutions. The mechanical performance and the durability of the specimens were evaluated by visual appearance, weight change, static and cyclic loading, and failure modes of the specimens under magnesium sulfate and ambient environments. In addition, the microscopic changes of the specimens due to sulfate attack were also assessed by scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that geopolymer specimens produced with nano-silica and fly ash showed superior performance than the NC specimens in the sulfate environment. In addition, confined specimens with FRP fabrics significantly improved the compressive strength, ductility and durability resistance of the specimens and the improvement was found higher with the increased number of FRP layers. Specimens wrapped with carbon FRP fabrics showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabrics. Both FRP materials can be used as a rehabilitation material in the sulfate environment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.1
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• pp.45-55
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• 2002

From the early 1980's, the New Austrian Tunnelling Method (NATM) has been developed as one of the standard tunnelling methods in Korea. Approximately 10 years ago, wet-mix shotcrete with sodium silicate (waterglass) accelerator was introduced and widely used to tunnel lining and underground support. However, this accelerator had some disadvantages due to the decrease of long-term strength compared to plain concrete (without accelerator) and low quality of the hardened shotcrete. In order to compensate for these disadvantages, recently developed alkali-free accelerator has been successfully demonstrated in numerous projects and applications as a new material to make tunnels more durable and safer. An experimental investigation was carried out in order to verify the strength behavior of wet-mix Steel Fiber Reinforced Shotcrete (SFRS) with alkali-free accelerator. Compressive strength, flexural strength, and flexural toughness were measured by testing specimens extracted from the shotcrete panels. From the results, wet-mix SFRS with alkali-free accelerator exhibited excellent strength improvement compared to the conventional shotcrete accelerator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.5
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• pp.277-282
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• 2015

During hot and humid weather, air-conditioners consume a large amount of electricity due to the large amount of latent heat. Simultaneous usage of a dehumidifier may reduce latent heat and reduce electricity consumption. In this study, dehumidification performance was measured for a small-sized dehumidification rotor made of inorganic fiber impregnated with metallic silicate within a constant temperature and humidity chamber. Regeneration to dehumidification depends on ratio, rotor speed, room temperature, regeneration temperature, room relative humidity and frontal velocity to the rotor. Results demonstrate an optimum area ratio (1/2), rotor speed (1.0 rpm), and regeneration temperature ($100^{\circ}C$) to achieve a dehumidification rate of 0.0581 kg/s. As the area ratio increases, the optimum rotation speed and the optimum regeneration temperature also increase. Above the optimum rotor speed, incomplete regeneration reduces dehumidification. Above the optimum regeneration temperature, increased temperature variation between regeneration and dehumidification reduces dehumidification. Dehumidification rate also increases with an increase of relative humidity, dehumidification temperature and flow velocity into the rotor.

• Composites Research
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• v.30 no.2
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• pp.84-93
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• 2017

This study investigates thermal and mechanical characterization of environmental barrier coating on the $SiC_f-SiC$ composites. The spherical environmental barrier coating (EBC) powders are prepared using a spray drying process for flowing easily during coating process. The powders consisting of mullite and 12 wt% of Ytterbium silicate are air plasma sprayed on the Si bondcoat on the LSI SiC fiber reinforced SiC composite substrate for protecting the composites from oxidation and water vapor reaction. We vary the process parameter of spray distance during air plasma spray of powders, 100, 120 and 140 mm. After that, we performed the thermal durability tests by thermal annealing test at $1100^{\circ}C$ for 100hr and thermal shock test from $1200^{\circ}C$ for 3000 cycles. As a result, the interface delamination of EBC never occur during thermal durability tests while stable cracks are prominent on the coating layer. The crack density and crack length depend on the spray distance during coating. The post indentation test indicates thermal tests influence on the indentation load-displacement mechanical behavior.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.427-434
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• 2005

An experimental investigation was carried out in order to verify the compressive strength, flexural strength, equivalent bending strength, rebound rate of shotcrete according to silicate accelerator, aluminate accelerator, cement mineral accelerator respectively and to especially evaluate the performance of shotcrete using cement mineral accelerator for high quality. The test result of compressive strength was showed that all accelerators were satisfied the required test value for each age, for the requirement of having the $75\%$ or higher compressive strength ratio to plain concretes at 28 days, cement mineral accelerator with $87\%$ compressive strength ratio was only satisfied. In flexural strength test, cement mineral accelerator was satisfied the flexural strength requirement in steel fiber reinforced shotcrete for each age. Aluminate type was conformed to the requirement for 28 days, but not at 1 day, silicate type was failed to satisfy standard requirement. Rebound rate was measured between $11{\~}19\%$ and cement mineral accelerator was showed comparatively lower rebound rate. Based on the test results, cement mineral accelerator exhibited excellent strength improvement and lower rebound rate compared to the conventional accelerator, its result is showed the possibility of making high performance shotcrete.

• Journal of Sericultural and Entomological Science
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• v.18 no.1
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• pp.27-39
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• 1976

In this study several kinds of spun silk yarn-synthetic filament compounded yarn was manufactured, and several fabrics woven from above mentioned silk compound yarn for evaluation of serviceability as clothing materials. The following results were obtained: 1. Degumming agents are in the order of sodium silicate, sodium hydroxide, sodium carbornate, soap and water. 2. When the concentration of sodium hydroxide is exceeded 3%, degradation of floss silk property is resulted because of excessive dissolving out of silk protein. 3. Degumming effect is much improved by concentration of degumming agent and less by its treating time. 4. Simultaneous application of more the 2 kinds of degumming agent is desirable for improvement of floss silk. 5. Application of natural organic acid brings very good results in keeping original scooping and color of the silk. 6. Load and elongation it increased by compound with synthetic filament yarn. 7. Even the evenness of compound yarn is largely dependent on the quality of floss silk and extent of degumming, the C.V.% of silk compound yarn in the experiment was 8-12%. 8. Single bath dyeing technique was impossible for their cloth, and dyeing was performed in 2 bath system separately for silk and synthetic fiber. 9. Shrinkage ratio due to the dyeing of fabric was 23% in case of polyester and spun silk fabric. 10. The final woven cloth can be applicable to (a) Blouse in care of thin cloth (compound silk fabric) (b) Korean costume for women in case of thick cloth. (compound hand spun silk fabric)

• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.177-182
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• 2006

In this work, we have prepared organophilic MMT having thermal stability by ion exchange reaction of various aromatic ammonium salts with MMT containing sodium ion. The organic modifiers having alkyl side chains and amine functional group were successfully synthesized by effectively introducing the surfaces of MMT via ion exchange reaction to form organophilic MMTs with a view to improve the reactivity and thermal stability. The WAXD patterns of organophilic MMT showed the more increased gallery spacing by $3.3{\AA}$ than that of the pristine MMT and also the onset of initial decomposition of organophilic MMT was $275^{\circ}C$ as determined by a thermogravimetric analysis. The polyimide (PI) nanocomposite films based on poly(amic acid) and organophilic MMT were prepared by a solution blending followed by cyclodehydration reaction. We have investigated the dispersity of organophilic MMTs in PI matrix by using WAXD and the effect of the organophilic MMT content on the mechanical properties of PI nanocomposite films was studied.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.9-15
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• 2010

Recently, the high-compressive strength concrete where the use is extending was weak in fire because of spalling that was occurring with rise of internal vapor pressure by high temperature. For preventing spalling of high-strength concrete in fire, Organic fibers have been using in concrete generally. By melting of organic fibers in concrete in fire, the internal moistures of concrete moves quickly to the outside, and so, preventing of spalling of high-strength concrete. But this method will be able to prevent the spalling of high-strength concrete, but makes the decrease of the concrete strength after fire. This study make a comparison between properties of preventing of spalling and remaining compressive strength of concrete using intumescence Alkali-Silicates fire-resistant material and that of concrete with organic fibers. Using organic fibers for preventing of spalling of concrete are P.P and Nylon fibers, and anti-fire intumescence material for protection of concrete surface is alkali-silicate materials. Fire resistance test executed as long as 3 hr under the flame temperature $1,200^{\circ}C$ over. In the case of concrete with P.P fibers, don't occurred the spalling, but the remaining compressive strength will not be able to measure, the concrete using intumescence Alkali-Silicates system fire-resistant material is not only preventing of the spalling but also the remaining compressive strength maintained until the maximum 96%.