• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.3
• /
• pp.28-39
• /
• 2014

This paper reviews past literatures relevant to fire-resistance properties of high strength concrete and investigates spalling mechanism of high strength concrete in fire. First, literatures were reviewed on spalling occurrence and fire-resistance methods. Second, a chemical change of concrete components in an elevated temperature was presented. Finally, the mechanism of the spalling occurrence and spalling resistance were examined in terms of hybrid fiber content. The focus of the experimental study as part of this research is to investigate the effects of fire on the variation of thermal properties of high strength concrete, which tends to be used in super tall buildings. This experimental study was devised to investigate the fire-resistance performance of high strength concrete containing hybrid fibers. A total of 48 test specimens were exposed to high temperature ranging from $100^{\circ}C$ to $700^{\circ}C$, including room temperature (${\sim}20^{\circ}C$). Test results provide valuable information regarding fire-resistance properties of strength concrete with 100 MPa or greater.

• Composites Research
• /
• v.26 no.2
• /
• pp.129-134
• /
• 2013

The strength of adhesive joints employed in composite structures under cryogenic environments, such as LNG tanks, is affected by thermal residual stress generated from the large temperature difference between the bonding process and the operating temperature. Aramid fibers are noted for their low coefficient of thermal expansion (CTE) and have been used to control the CTE of thermosetting resins. However, aramid composites exhibit poor adhesion between the fibers and the resin because the aramid fibers are chemically inert and contain insufficient functional groups. In this work, electrospun meta-aramid nanofiber-reinforced epoxy adhesive was fabricated to improve the interfacial bonding between the adhesive and the fibers under cryogenic temperatures. The CTE of the nanofiber-reinforced adhesives were measured, and the effect on the adhesion strength was investigated at single-lap joints under cryogenic temperatures. The fracture toughness of the adhesive joints was measured using a Double Cantilever Beam (DCB) test.

• Journal of Adhesion and Interface
• /
• v.19 no.1
• /
• pp.13-18
• /
• 2018

At ruthenium (Ru) catalyst was exposed from the atmosphere, the degree of catalyst activation decreased. The change of catalyst activity with the number of days of exposure to air for the Ru catalyst was confirmed using the surface tension method quantitatively. Mechanical properties and surfactant change after polymerization by DCPD using Ru catalyst for each air exposure day was evaluated. The Ru catalyst mixed with a dilution agent was exposed in the air and color was monitored for each day. Surface tension was measured using Wilhelmy and PTFE and associated with different catalyst activities. Heat was measured in real time during polymerizing DCPD with Ru catalyst. After polymerization, tensile strength was measured for p-DCPD and the change of material property was measured. Interfacial properties were also evaluated via microdroplet pull-out tests between glass fiber and p-DCPD. The surface tension was stable until the 4 days (33 dyne/cm) whereas the surface energy increased at the 10 days (34 dyne/cm), which could be correlated with oxidation of the catalyst. Tensile property and interfacial shear strength (IFSS) was also stable until the 4 days (tensile strength: 38 MPa and IFSS: 26 MPa) whereas the mechanical property decrease at 10 days (tensile strength: 15 MPa and IFSS: 3 MPa) dramatically.

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

• 보존과학연구
• /
• s.32
• /
• pp.25-35
• /
• 2011

Wood vinegar and Asarum sieboldii Miquel were selected as candidate materials showed antimicrobial activity and insect repellent activity. These natural pesticides have its own color and these could cause color difference on fabric materials. In the present study, we investigated the color difference of undyed and dyed fabrics to evaluate negative effect of wood vinegar and A. sieboldii Miquel. Undyed and dyed fabrics were exposed to natural pesticides of various concentrations for six months in relative humidity 70% and temperature $28^{\circ}C$. After exposure of pesticides, color difference (${\Delta}E*$) were investigated at two weeks intervals for six months. As a results, dyed cotton, silk and undyed silk fabrics exposed wood vinegar were not nearly changed in their colors, but color of only undyed cotton fabric was clearly changed by wood vinegar. Especially color difference by wood vinegar on undyed cotton fabric was most distinct as the concentration increased. On the other hand, all of fabrics exposed A. sieboldii Miquel were not nearly changed in their colors for six months. Therefore, this study first suggests that wood vinegar and A. sieboldii Miquel as natural insecticides could be used to conserve for textile cultural properties from insects and microorganism, but wood vinegar couldn't use the high concentration on undyed cotton fabric.

• Journal of the Korean Society for Railway
• /
• v.11 no.4
• /
• pp.357-363
• /
• 2008

This study investigates the durability of carbon/epoxy composites for use on train car bodies under a salt water spray environment. Salt water solution with 5% NaCl, similar to natural salt water, was used for the salt water environmental tests. The specimens were obtained from a composite panel consisting of an epoxy matrix reinforced with T700 carbon fabric. The specimens were exposed to the salt water environment for up to 12 months. Mechanical tests were performed to obtain tensile properties, flexural properties, and shear properties. Dynamic mechanical analysis was used to measure such thermal properties as storage modulus, loss modulus, and tan $\delta$. Also FT/IR tests were conducted to investigate changes in chemical structure with exposure. The results revealed that fiber-dominated mechanical properties were not affected much by exposure time, but matrix-dominated mechanical properties decreased with increasing exposure time. Storage modulus was not very sensitive to exposure time, but glass transition temperature was affected, slightly decreasing with increasing exposure time. Although the peak intensity of FT/IR curves was affected slightly by exposure time, the peak shape and peak location of FT/IR curves were not noticeably changed. Carbon/epoxy composites used for this study were relatively stable to the salt water environment.

• Journal of Radiation Protection and Research
• /
• v.33 no.4
• /
• pp.161-166
• /
• 2008

In order to determine the effect of extremely low frequency electromagnetic fields (ELF-EMF) on the frequency of micronuclei (MN), aneuploidy and chromosomal rearrangement induced by bleomycin (BLM) in human fibroblast cells, a 60 Hz ELF-EMF of 0.8 mT field strength was applied either alone or with ELM throughout the culture period and a micronucleus-centromere assay was performed. Our results indicate that the frequencies of MN, aneuploidy and chromosomal rearrangement induced by ELM increased in a dose-dependent manner. The exposure of cells to 0.8 mT ELF-EMF followed by ELM exposure for 3 hours led to significant increases in the frequencies of MN and aneuploidy compared to BLM treatment for 3 hours alone (p<0.05), but no significant difference was observed between field exposed and sham exposed control cells. The obtained results suggest that low density ELF-EMF could act as an enhancer of the initiation process of BLM rather than as an initiator of mutagenic effects in human fibroblast.

• Microbiology and Biotechnology Letters
• /
• v.35 no.4
• /
• pp.316-324
• /
• 2007

We studied the effects of genistein obtained from glycolysis of genistin, a kind of phytoestrogen present in soybeans, on cell proliferation and type I pN collagen synthesis in normal human dermal fibroblasts(NHDF). Cell proliferation was increased significantly with genistein treatment at 54-year aged NHDF. Genistein increased cell proliferation more strongly in cells form old doner than young doner. The senescence-associated ${\beta}$-galatosidase activity was decreased in NHDF from 77-year old doner with genistein treatment. Type I pN collagen synthesis was increased with genistein treatement in UVA treated and non-treated NHDF. The increasement of collagen synthesis was more effective in aged cells than young cells. Type I pN collagen synthesis was also increased with genistein treatment in collagen matrix culture with NHDF from sun-exposed and non-exposed skin from 54-year old doner. Genistein treatment inhibited MMP-1 synthesis in old NHDF but not in young NHDF. In conclusion, genistein may be a useful agent for preventing intrinsic aging as well as photoaging.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.29 no.2 s.43
• /
• pp.1-35
• /
• 2003

새 천년으로 들어선 2000년도부터 우리나라의 65세 이상 노령인구는 $7.1{\%}$를 차지하게 되어 본격적인 노령화사회 (UN에서 65세 이상인구가 총 인구의 $7{\%}$ 이상일 경우 노령화 사회로 정의)로 진입하였다. 평균수명의 계속적인 증가에 따라 노인 인구는 급격히 늘어날 전망이며, 따라서 노인성 질환의 발생도 늘어나게 되어 가정 또는 사회가 떠 맡아야할 경제적, 정신적 부담은 더욱 증가하게 된다. 건강하고 행복한 인생의 황혼기를 보내는 것은 인간의 권리이며 누구나 바라는 소망이다. 피부의 노화현상은 심장질환, 암 등에 못지 않게 중요하며, 노인의 경제적, 사회적 활동을 심각하게 위축시키고 있다. 피부노화를 예방하고 노인성 피부질환을 치료할 수 있는 방법을 개발함으로써 노인의 경제, 사회활동을 활동적으로 유지시킬 수 있다. 피부노화는 크게 두 종류로 나눌 수 있다. 그 한가지는 내인성노화(intrinsic aging)로서 세월이 흘러감에 따라 피할 수 없는 노화 현상을 말한다. 두번째는 광노화 (photoaging)로서 오랫동안 햇빛에 노출된 얼굴, 손등, 목뒤 등의 피부에서 관찰되는 노화현상을 말하는 것으로 내인성노화 현상과 자외선에 의한 영향이 합쳐진 결과로 발생한다. 광노화 현상은 자외선의 노출을 피하면 예방할 수 있는 피부노화 현상이다. 내인성 노화는 햇빛에 노출되지 않은 피부에서 주로 관찰된다. 임상적 특징은 비교적 경미하며, 잔주름, 피부건조증, 탄력감소 등을 들 수 있다. 그러나 광노화의 임상적 특징은 내인성 노화에 비하여 심하고, 일찍부터 관찰된다. 내인성 노화에 비하여 굵고 깊은 주름이 발생하며, 잔주름도 많이 발생한다. 햇빛에 노출된 피부에 불규칙한 색소침착이 발생하며 일광흑자 (solar lentigo) 등의 색소질환이 증가한다. 피부가 매우 거칠고, 건조해지며, 탄력성이 감소하여 심한경우 피부가 처지게 된다. 피부노화의 대표적인 증상은 주름살이며, 아직까지 그 발생기전에 대하여는 여러 가지 학설이 있으나 정확히 알려져 있지 않다. 피부에 존재하는 교원질, 탄력섬유등 기질단백질의 손상이 피부 주름살의 주 원인으로 알려져 있다. 또한 얼굴에 존재하는 근육의 분포와 움직임, 유전적 소인, 자외선, 흡연, 폐경, 산화적 손상, 열 등 여러 원인이 복합적으로 작용할 것으로 생각된다. 피부주름살의 원인을 밝히고, 원인인자가 피부주름살을 초래하는 분자생물학적 기전을 이해함으로써 주름살을 예방하고 치료할 수 있는 새로운 방법을 개발할 수 있다.

• Composites Research
• /
• v.30 no.2
• /
• pp.77-83
• /
• 2017

Liquid silicon infiltration, which is one of the methods of producing fiber reinforced ceramic composites, has several advantages such as low fabrication cost and good shape formability. In order to confirm LSI process feasibility of SiC fiber, $SiC_f/SiC$ composites were fabricated using three types of SiC fibers (Tyranno SA, LoxM, Tyranno S) which have different crystallinity and oxygen content. Composites that were fabricated with LSI process were well densified by less than 2% of porosity, but showed an obvious difference in 3-point bending strength according to crystallinity and oxygen content. When composites in LSI process was exposed to a high temperature, crystallization and micro structural changes were occurred in amorphous SiOC phase in SiC fiber. Fiber shrinkage also observed during LSI process that caused from reaction in fiber and between fiber and matrix. These were confirmed with changes of process temperature by SEM, XRD and TEM analysis.