• Title/Summary/Keyword: Curing method

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Pull-off Strength of Jagged Pin-reinforced Composite Hat Joints (요철핀으로 보강된 복합재 모자형 체결부 구조의 강도 연구)

  • Kwak, Byeong-Su;Kim, Dong-Gwan;Kweon, Jin-Hwe
    • Composites Research
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    • v.31 no.6
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    • pp.323-331
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    • 2018
  • The effect of stainless steel jagged-pin reinforcement on the pull-off strength of the composite hat-joint was studied by the test. The pins were physically and chemically surface-treated and inserted in the thickness direction over the interface where the skin and stiffener meet. The specimens including the jagged-pins were made by co-curing process. Diameters of the jagged-pins were 0.3, 0.5 and 0.7 mm. The pin areal densities were set to 0.5 and 2.0% based on the interface area where the skin and stiffener meet. The specimens using 0.3 mm diameter normal (un-jagged) pins with 2.0% areal density were additionally fabricated and tested to investigate the pin shape effect on the pull-off strength. The pull-off strengths of specimens reinforced with 0.5% areal density by 0.3, 0.5, and 0.7 mm diameter pins were 45, 19 and 9% higher than those of un-reinforced specimens, respectively. In case with 2.0% pin areal density, the strengths were 127, 45, and 11% higher than those of un-reinforced specimens, respectively. The test results show that the higher pin areal density results in the higher strength when the pin diameter is the same. When the pin areal density is the same, the smaller pin diameter leads to higher strength. When the joints using jagged-pins and normal pins in 2.0% areal density with 0.3 mm diameter, the joints of jagged-pins showed the 64% higher strength. From the results of this study, it was confirmed that jagged-pin reinforcement can be an effective method for improving the pull-off strength of composite hat-joint.

Morphology control of glassy carbon coating layer to additive ethylene glycol and phenolic resin (페놀수지 및 에틸렌 글리콜을 첨가한 유리질 카본 코팅층의 물성 제어)

  • Joo, Sang Hyun;Joo, Young Jun;Lee, Hyuk Jun;Sim, Young Jin;Park, Dong Jin;Cho, Kwang Youn
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.32 no.3
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    • pp.89-95
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    • 2022
  • In this study, glassy carbon coating was performed on the graphite using a phenolic resin and a curing agent was mixed with ethylene glycol as an additive to form the uniform surface. The phenolic resin was dried and cured under the environments of hot air, then converted into a glassy carbon layer by pyrolysis at 500~1,500℃. FTIR, XRD, SEM analysis, and density/porosity/contact angle measurement were performed for characterization of glassy carbon. The pyrolysis temperature for high-quality glassy carbon was optimized to be about 1,000℃. As the content of the additive increased, the effect of reducing surface defects on the coated surface, reduction of porosity, increase of contact angle, and increase of density were investigated in this study. The method of forming a glassy carbon coating layer through an additive is expected to be applicable to graphite coating and other fields.

Vibration Damping Ratio Performance Evaluation According to the Polymer Mixing Rate of SBR-based Polymer Modified Mortar through Ultrasonic Pulse Analysis (초음파 펄스 분석을 통한 SBR계 폴리머 혼입 모르타르의 폴리머 혼입률에 따른 진 동감쇠비 성능 평가)

  • Jeong, Min-Goo;Jang, Jong-Min;Lee, Han-Seung
    • Journal of the Korea Institute of Building Construction
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    • v.22 no.6
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    • pp.543-551
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    • 2022
  • The mechanical performance and vibration damping ratio performance of a specimen according to the polymer mixing rate were evaluated for polymer modified mortar. As a polymer, Styrene Butadiene Rubber(SBR) liquid polymer with a solid content of about 49~51% was used, and the polymer content was increased by liquid 5%. The specimen was 40*40*160(mm), and after curing, compressive strength, flexural strength, and vibration damping ratio were measured using the ultrasonic pulse method. As a result, it was found that the compressive strength decreased as the polymer was mixed, but the flexural strength was increased. The vibration damping ratio increased by 11% at 5% polymer, 28% at 10% polymer, 33% at 15% polymer, and 72 at 20% polymer. I was found that the incorporation of the polymer was very effective to reduce the vibration of the mortar. In addition, through SEM and SEM-EDS analysis, it is determined that the cause of vibration reduction due to polymer mixing is that the polymer film formed in the transition zone of aggregate and internal voids buffered the vibration of the mortar inside. Taken together, in the scope of this study, the appropriate polymer mixing ratio for reducing the vibration of mortar is judged to be about 7.5%.

Study on Microstructure and Electrical Properties of Cement Mortar Containing Conductive Fibers (전도성 섬유가 함유된 시멘트 모르타르의 미세구조 및 전기적 특성 연구)

  • Park, Jong-Gun;Seo, Dong-Ju;Lim, Doo-Yeol;Lee, Yu-Jae;Heo, Gwang-Hee
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.3
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    • pp.72-83
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    • 2022
  • This paper studied the effect on the microstructure, electrical properties, and compressive strength of cement mortar containing carbon fiber (CF) and steel fiber (SF), which are conductive materials. The resistivity of conductive fiber-reinforced cement mortar (FRCM) was measured using the 4-probe method, and the compressive strength was measured based on the compression test. Their performance was compared and reviewed with plain mortar (PM). Furthermore, the surface shape and composition of the fracture surface of the conductive FRCM were analyzed using a scanning electron microscope (SEM) and an energy disperse X-ray spectrometer (EDS). The results showed that the resistivity gradually increased as the curing time increased in all specimens, whereas the resistivity decreased significantly as the fiber volume fraction increased. Adding steel fibers up to 1.25% did not affect the resistivity of cement mortar considerably. On the contrast, the resistivity of carbon fiber was somewhat decreased even at low contents (ie, 0.1 to 0.3%), and thereafter, it was significantly decreased. The percolation threshold of the conductive CFRCM containing CF used in this experiment was 0.4%, and it is judged to be the optimum carbon fiber dosage to maximize the conductive effect while maintaining the compressive strength performance as much as possible. For the surface shape and composition analysis of conductive FRCM, the fracture surface was observed through SEM-EDS. These results are considered to be very useful in establishing the microstructure mechanism of reinforcing fibers in cement mortars.

Recycling Organic Sludge into Modification Block by Hydrothermal Carbonization (HTC) (열수가압탄화공법을 적용한 유기성 슬러지의 응용 블록 제조에 관한 연구)

  • Hyewon Park;Minah Oh;Seungjin Oh;Woori Cho;Jinman Chang;Jai-young Lee
    • Clean Technology
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    • v.29 no.2
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    • pp.102-108
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    • 2023
  • This study applied a hydrothermal carbonization (HTC) method to carbonize sewage sludge in order to satisfy the criteria of the Waste Management Act for recycled products and to explore the possibility of recycling sludge into modification blocks. Cement was mixed with carbonized sludge generated at the optimal temperature and reaction time during HTC. After that, the compressive strengths of the modification blocks were measured by conducting both a performance and leaching test. The results of the leaching test showed that heavy metals were not detected, and the specific gravity and absorption rates were less than 1.7 and 10%, respectively, indicating that all species satisfied the criteria. The results of the compressive strength test showed that a mixing ratio of 5% and 7% with cement cured for 28 days satisfied the criteria of A, B, and C type blocks but a mixing ratio of 3% with cement did not satisfy the criteria of A type blocks after 28 days. However, after additional curing for 42 days, the mixing ratio of 3% also satisfied the A type block criteria. Therefore, the optimal mixing ratio of carbonized sludge and cement was considered to be between 3% and 5% and confirmed that the modified blocks could be utilized as aggregates.

Electrochemical Studies on the Corrosion Performance of Steel Embeded in Activated Fly Ash Blended Concrete (활성화된 플라이애쉬 혼입콘크리트의 철근부식거동에 관한 전기화학적 연구)

  • Song, Ha-Won;Lee, Chang-Hong;Lee, Kewn Chu;Velu, Saraswathy
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.6
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    • pp.97-108
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    • 2008
  • The use of fly ash to replace a portion of cement has resulted significant savings in the cost of cement production. Fly ash blended cement concretes require a longer curing time and their early strength is low when compared to ordinary Portland cement(OPC) concrete. By adopting various activation techniques such as physical, thermal and chemical method, hydration of fly ash blended cement concrete was accelerated and thereby improved the corrosion-resistance of concrete. Concrete specimens prepared with 10-40% of activated fly ash replacement were evaluated for their open circuit potential measurements, weight loss measurements, impedance measurements, linear polarization measurements, water absorption test, rapid chloride ion penetration test and scanning electron microscopy (SEM) test and the results were compared with those for OPC concrete without fly ash. All the studies confirmed that up to a critical level of 20-30% replacement; activated fly ash cement improved the corrosion-resistance properties of concrete. It was also confirmed that the chemical activation of fly ash better results than the other methods of activation investigated in this study.

A Study on Chloride Binding Capacity of Various Blended Concretes at Early Age (초기재령에서 각종 혼합콘크리트의 염소이온 고정화능력에 관한 연구)

  • Song, Ha-Won;Lee, Chang-Hong;Lee, Kewn-Chu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.5
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    • pp.133-142
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    • 2008
  • This paper studies the early-aged chloride binding capacity of various blended concretes including OPC(ordinary Portland cement), PFA(pulversied fly ash), GGBFS(ground granulated blast furnace slag) and SF(silica fume) cement paste. Cement pastes with 0.4 of a free water/binder ratio were cast with chloride admixed in mixing water, which ranged from 0.1 to 3.0% by weight of cement and different replacement ratios for the PFA, GGBFS and SF were used. The content of chloride in each paste was measured using water extraction method after 7 days curing. It was found that the chloride binding capacity strongly depends on binder type, replacement ratio and total chloride content. An increase in total chloride results in a decrease in the chloride binding, because of the restriction of the binding capacity of cement matrix. For the pastes containing maximum level of PFA(30%) and GGBFS(60%) replacement in this study, the chloride binding capacity was lower than those of OPC paste, and an increase in SF resulted in decreased chloride binding, which are ascribed to a latent hydration of pozzolanic materials and a fall in the pH of the pore solution, respectively. The chloride binding capacity at 7 days shows that the order of the resistance to chloride-induced corrosion is 30%PFA > 10%SF > 60%GGBFS > OPC, when chlorides are internally intruded in concrete. In addition, it is found that the binding behaviour of all binders are well described by both the Langmuir and Freundlich isotherms.

Design and Full Size Flexural Test of Spliced I-type Prestressed Concrete Bridge Girders Having Holes in the Web (분절형 복부 중공 프리스트레스트 콘크리트 교량 거더의 설계 및 실물크기 휨 실험 분석)

  • Han, Man Yop;Choi, Sokhwan;Jeon, Yong-Sik
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.3A
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    • pp.235-249
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    • 2011
  • A new form of I-type PSC bridge girder, which has hole in the web, is proposed in this paper. Three different concepts were combined and implemented in the design. First of all, a girder was precast at a manufacturing plant as divided pieces and assembled at the construction site using post-tensioning method, and the construction period at the site will be reduced dramatically. In this way, the quality of concrete can be assured at the manufacturing factory and concrete curing can be well controlled, and the spliced girder segments can be moved to the construction site without a transportation problem. Secondly, a numerous number of holes was made in the web of the girder. This reduces the self-weight of the girder. But more important thing related to the holes is that about half of the total anchorages can be moved from the girder ends into individual holes. The magnitude of negative moment developed at girder ends will be reduced. Also, since the longitudinal compressive stresses are reduced at ends, thick end diaphragm is not necessary. Thirdly, Prestressing force was introduced into the member through multiple stages. This concept of multi-stage prestressing method overcomes the prestressing force limit restrained by the allowable stresses at each loading stage, and maximizes the magnitude of applicable prestressing force. It makes the girder longer and shallower. Two 50 meter long full scale girders were fabricated and tested. One of them was non-spliced, or monolithic girder, made as one piece from the beginning, and the other one was assembled using post-tensioning method from five pieces of segments. It was found from the result that monolithic and spliced girder show similar load-deflection relationships and crack patterns. Girders satisfied specific girder design specification in flexural strength, deflection, and live load deflection control limit. Both spliced and monolithic holed web post-tensioned girders can be used to achieve span lengths of more than 50m with the girder height of 2 m.

Confucian Cultivation of Mind and Meditation - The Care Model of Cultivation Applied by Toe-gye' 『The Method on Preservation of Human mind (活人心方)』 (유가 공부론과 명상 - 퇴계 활인심방(活人心方)을 응용한 수양치료 모형 -)

  • Lee, Yun-do
    • The Journal of Korean Philosophical History
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    • no.28
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    • pp.363-386
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    • 2010
  • The purpose of this study is to examine the relationship between theory of Confucian moral cultivation and meditation. Recently our community is more interested in 'a disease of mind'. A view of world, life, values which derived from the distorted perception of 'a disease of mind' can not be treated by psychiatric methods. In this sense, 'a disease of mind' is different from psychiatric illness. In this reason, alternative therapies applying philosophy, literature, arts, and humanities are attracting attention. Meditation is also one of them. In general, Meditation has been developed in Buddhism, but its method is closely related with Confucianism. Buddhist meditation has a pessimistic view of the reality in human life, but that of Confucian philosophy has laid stress on the reality and ego in human life. At this point, the Confucian meditation could provide a clue of solution for us in treatment of a disease of human mind. So Confucian moral cultivation and meditation have a great significance for the treatment of this disease as a methodology. In general, mental healing or psychotherapy has been proceeded by way of dialogue. 'Talking Cure' was conceived to let clients themselves recognize their current situation and find out the problem: "what happened and what's wrong" in their minds. But it does not have a high possibility of successful cure for subjects who are in the state of frustration, confusion, and lost of value. And also it is very difficult to apply to special institutions such as correctional institutions and military soldier who are targeted by current application of Humanities therapy. On this sense, it seems to be valuable to apply Confucian cultivation of mind and meditation which have emphasized the importance of mind-control for this. This study tries to examine theoretically how to relate the Confucian cultivation of mind with meditation, and to suggest a model of Humanities therapy that could be applied by Toe-gye's 『The Method on Preservation of Human mind(活人心方)』. Although Confucian cultivation of mind could present a meaningful theory for curing the disease of mind, it is very difficult to put the theory into practice. It is because Confucian cultivation of mind in itself is a kind of instruction that you need to do in all of your life, and essentially it is difficult to expect a temporary effect by performance or practice. So a cure model of Confucian cultivation of mind will be suggested on this assumption and limitations. This model is attempted on the main purpose of Humanities therapy in accordance with the development of a Korean model.

The Empirical Exploration of the Conception on Nursing (간호개념에 대한 기초조사)

  • 백혜자
    • Journal of Korean Academy of Nursing
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    • v.11 no.1
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    • pp.65-87
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    • 1981
  • The study is aimed at exploring concept held by clinical nurses of nursing. The data were collected from 225 nurses conviniently selected from the population of nurses working in Kang Won province. Findings include. 1) Nurse's Qualification. The respondents view that specialized knowledge is more important qualification of the nurse. Than warm personality. Specifically, 92.9% of the respondents indicated specialized knowledge as the most important qualification while only 43.1% indicated warm personality. 2) On Nursing Profession. The respondents view that nursing profession as health service oriented rather than independent profession specifically. This suggests that nursing profession is not consistentic present health care delivery system nor support nurses working independently. 3) On Clients of Nursing Care The respondents include patients, family and the community residents in the category of nursing care. Specifically, 92.0% of the respondents view that patient is the client, while only 67.1% of nursing student and 74.7% of herself. This indicates the lack of the nurse's recognition toward their clients. 4) On the Priority of Nursing care. Most of the respondents view the clients physical psychological respects as important component of nursing care but not the spiritual ones. Specially, 96.0% of the respondents indicated the physical respects, 93% psychological ones, while 64.1% indicated the spiritual ones. This means the lack of comprehensive conception on nursing aimension. 5) On Nursing Care. 91.6% of the respondents indicated that nursing care is the activity decreasing pain or helping to recover illness, while only 66.2% indicated earring out the physicians medical orders. 6) On Purpose of Nursing Care. 89.8% of the respondents indicated preventing illness and than 76.6% of them decreasing 1;ai of clients. On the other hand, maintaining health has the lowest selection at the degree of 13.8%. This means the lack of nurses' recognition for maintaining health as the most important point. 7) On Knowledge Needed in Nursing Care. Most of the respondents view that the knowledge faced with the spot of nursing care is needed. Specially, 81.3% of the respondents indicated simple curing method and 75.1%, 73.3%, 71.6% each indicated child nursing, maternal nursing and controlling for the communicable disease. On the other hand, knowledge w hick has been neglected in the specialized courses of nursing education, that is, thinking line among com-w unity members, overcoming style against between stress and personal relation in each home, and administration, management have a low selection at the depree of 48.9%,41.875 and 41.3%. 8) On Nursing Idea. The highest degree of selection is that they know themselves rightly, (The mean score measuring distribution was 4.205/5) In the lowest degree,3.016/5 is that devotion is the essential element of nursing, 2.860/5 the religious problems that human beings can not settle, such as a fatal ones, 2,810/5 the nursing profession is worth trying in one's life. This means that the peculiarly essential ideas on the professional sense of value. 9) On Nursing Services. The mean score measuring distribution for the nursing services showed that the inserting of machine air way is 2.132/5, the technique and knowledge for surviving heart-lung resuscitating is 2.892/s, and the preventing air pollution 3.021/5. Specially, 41.1% of the respondents indicated the lack of the replied ratio. 10) On Nurses' Qualifications. The respondents were selected five items as the most important qualifications. Specially, 17.4% of the respondents indicated specialized knowledge, 15.3% the nurses' health, 10.6% satisfaction for nursing profession, 9.8% the experience need, 9.2% comprehension and cooperation, while warm personality as nursing qualifications have a tendency of being lighted. 11) On the Priority of Nursing Care The respondents were selected three items as the most important component. Most of the respondents view the client's physical, spiritual: economic points as important components of nursing care. They showed each 36.8%, 27.6%, 13.8% while educational ones showed 1.8%. 12) On Purpose of Nursing Care. The respondents were selected four items as the most important purpose. Specially,29.3% of the respondents indicated curing illness for clients, 21.3% preventing illness for client 17.4% decreasing pain, 15.3% surviving. 13) On the Analysis of Important Nursing Care Ranging from 5 point to 25 point, the nurses' qualification are concentrated at the degree of 95.1%. Ranging from 3 point to 25, the priorities of nursing care are concentrated at the degree of 96.4%. Ranging from 4 point to 16, the purpose of nursing care is concentrated at the degree of 84.0%. 14) The Analysis, of General Characteristics and Facts of Nursing Concept. The correlation between the educational high level and nursing care showed significance. (P < 0.0262). The correction between the educational low level and purpose of nursing care showed significance. (P < 0.002) The correlation between nurses' working yeras and the degree of importance for the purpose of nursing care showed significance (P < 0.0155) Specially, the most affirmative answers were showed from two years to four ones. 15) On Nunes' qualification and its Degree of Importance The correlation between nurses' qualification and its degree of importance showed significance. (r = 0.2172, p< 0.001) 0.005) B. General characteristics of the subjects The mean age of the subject was 39 ; with 38.6% with in the age range of 20-29 ; 52.6% were male; 57.9% were Schizophrenia; 35.1% were graduated from high school or high school dropouts; 56.l% were not have any religion; 52.6% were unmarried; 47.4% were first admission; 91.2% were involuntary admission patients. C. Measurement of anxiety variables. 1. Measurement tools of affective anxiety in this study demonstrated high reliability (.854). 2. Measurement tools of somatic anxiety in this study demonstrated high reliability (.920). D. Relationship between the anxiety variables and the general characteristics. 1. Relationship between affective anxiety and general characteristics. 1) The level of female patients were higher than that of the male patient (t = 5.41, p < 0.05). 2) Frequencies of admission were related to affective anxiety, so in the first admission the anxiety level was the highest. (F = 5.50, p < 0.005). 2, Relationship between somatic anxiety and general characteristics. 1) The age range of 30-39 was found to have the highest level of the somatic anxiety. (F = 3.95, p < 0.005). 2) Frequencies of admission were related to the somatic anxiety, so .in first admission the anxiety level was the highest. (F = 9.12, p < 0.005) 0. Analysis of significant anxiety symptoms for nursing intervention. 1. Seven items such as dizziness, mental integration, sweating, restlessness, anxiousness, urinary frequency and insomnia, init. accounted for 96% of the variation within the first 24 hours after admission. 2. Seven items such as fear, paresthesias, restlessness, sweating insomnia, init., tremors and body aches and pains accounted for 84% of the variation on the 10th day after admission.

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