• 한국구조물진단유지관리공학회 논문집
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• 제13권6호통권58호
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• pp.126-134
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• 2009

일반적으로 철근콘크리트 건축물은 외부의 기후에 노출되어 있어 겨울에서 이른 봄까지 동결과 융해의 반복적인 작용에 영향을 받는다. 이러한 동결융해 작용은 콘크리트의 균열을 발생시키거나 콘크리트 표면의 박리를 일으켜 내구성 저하의 원인이 된다. 본 연구에서는 철근콘크리트 보의 동결융해 노출에 따른 휨 거동특성의 평가를 위해 주근비와 동결융해 사이클을 변수로 하였다. $-18{\sim}4^{\circ}C$의 온도범위에서 150 및 300 사이클의 동결융해에 노출시킨 실험체를 비롯하여 14개의 축소모형 실험체를 제작, 단조 및 반복하중 하에서 실험을 실시하였다. 실험결과를 통해 동결융해에 노출되어있는 철근콘크리트 보의 휨 거동특성을 평가하는데 기초적인 자료를 제시하고자 하였다.

• Geomechanics and Engineering
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• 제38권6호
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• pp.593-601
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• 2024

In this paper, the quantitative evaluation method is presented for the durability performance of mountain tunnel concrete linings experiencing freezing and thawing during winter season. To analyze the freeze-thaw characteristics of lining, the freezing time of the concrete lining was measured by the outside temperature. The heat flow analysis was conducted based on the freezing time measured through the indoor experiment, and based on this, the energy required to freeze the concrete lining by the temperature of the outside air could be analyzed. In addition, the temperature change during the winter season was measured through an instrument installed on the actual tunnel concrete lining, and based on the results of indoor and field experiments, criteria for freeze-thaw environment evaluation and progress evaluation were prepared. Also, an equation using the freezing index was proposed through regression analysis.

• 한국조리학회지
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• 제14권2호
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• pp.286-292
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• 2008

The purpose of this study was to examine the effects of freezing and thawing methods on the quality of pork meat. The freezing methods for pork meat were the cryogenic freezing with liquid nitrogen gas, fast freezing at $-70^{\circ}C$ and normal freezing at $-20^{\circ}C$. The thawing methods were tested on low temperature thawing at refrigerative temperature($4^{\circ}C$), room temperature($20^{\circ}C$), high temperature($60^{\circ}C$) and using microwave. The quality of pork meat frozen by cryogenic methods was better than those of fast and normal freezing methods. The cooking hardness of pork meat frozen by cryogenic method showed the highest value as 1,898 g. In case of fast freezing, the hardness of pork meat was 1,472 g and that of normal frozen pork meat was 1,541 g. The high cooking hardness value of cryogenic frozen pork meat showed that the cryogenic freezing method made less freeze damage like textural softness. The drip-loss of pork meat thawed at refrigerative temperature($4^{\circ}C$), room temperature($20^{\circ}C$), high temperature($60^{\circ}C$) were shown lower than that of microwave thawing. The cooking hardness of pork meat that was thawed by microwave showed the lowest value among the thawing methods. The cryogenic freezing was the most useful freezing method for preserving quality, decreasing the freeze damage of pork meat. And thawing at refrigerative temperature was the most effective method to prevent quality loss and weight loss by drip-loss.

• 동아시아식생활학회지
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• 제25권5호
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• pp.893-901
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• 2015

This study investigated the effects of thawing conditions on physiological activities and quality of peeled garlic. Peeled frozen garlic was analyzed after thawing at low temperature ($4^{\circ}C$), room temperature ($20^{\circ}C$), tap water ($20^{\circ}C$), radio frequency of 27.12 MHz, and 2.45 GHz in a microwave. As a result, the time required to thaw garlic to $0^{\circ}C$ by various thawing methods was shortest at2.45 GHz in a microwave, followed by $20^{\circ}C$ tap water, radio frequency of 27.12 MHz, $20^{\circ}C$, and $4^{\circ}C$. Microwave thawing was faster than other methods, but it resulted in significant non-uniformity of heating. The hardness of peeled garlic significantly decreased upon freeze-thawing, whereas it showed improved hardness upon radio-frequency thawing. Total color difference in garlic increased upon freeze-thawing, and it was not improved by various thawing methods. Antioxidant activities were determined for DPPH radical scavenging ability, SOD-like activity, and reducing power. Total phenolic compounds and flavonoids in garlic extract were measured as $3.222{\pm}0.214{\mu}g$ GAE/g and $0.149{\pm}0.03{\mu}g$ QE/g, respectively. The content of total phenolic compounds was significantly reduced by 2.45 GHz microwave thawing ($1.90{\pm}0.02{\mu}g$ GAE/g); however, flavonoid contents were slightly reduced under freezing and thawing conditions. The DPPH radical scavenging ability of garlic extracts was not affected by thawing methods; however, SOD-like activity and reducing power were slightly reduced by freeze-thawing. These results indicate that physiological activities were not improved by radio-frequency thawing; however, thawing time and maintain hardness were reduced compared with conventional thawing methods.

• 한국지반환경공학회 논문집
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• 제12권7호
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• pp.13-21
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• 2011

동절기와 해빙기의 기온차가 큰 지역에서는 일정 깊이까지 동결, 융해 작용이 반복적으로 발생하여 흙의 역학적 특성이 변화를 보이게 된다. 특히 세립분이 많은 흙인 경우 팽창과 수축을 통한 입자의 재배열 등으로 인하여 노반의 연약화가 많이 발생된다. 이러한 노반의 연약화는 지지력이 낮은 지반에서 반복하중이 재하 되었을 때 급격하게 나타날 수 있다. 본 연구에서는 국내의 철도 노반재료로 사용되는 대표 토질 3가지를 대상으로 세립분의 함유량, 간극비의 영향 등을 고려하여 동결융해 반복횟수에 따른 직접전단 시험을 실시하여 그 감소량을 정량적으로 평가하였으며, 이를 통하여 세립분의 함유량과 함수비 조건, 동결융해 횟수 등을 고려할 수 있는 전단강도 저감 모델 식을 제안하였다.

• 한국지형학회지
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• 제25권1호
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• pp.47-65
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• 2018

Frost shattering has traditionally been considered as one of the most effective process in rock weathering. Each slab specimens of five or six rhyolite, basalt and tuff was prepared and put in freeze-thaw cycles and repeated 300 times in the temperature of $-25^{\circ}C$ to $+30^{\circ}C$ and their weathering patterns and products were analyzed by surface observation, particle size, XRD and thin section. As the result, some changes were observed in weathering patterns and weathering products. Rock shattering was more active in waterlogging rather than atmospheric conditions, but there are many differences depending on the type of rock. Rhyolite is hardly weathered by 300 times freeze-thaw cycles and generates the least amount of weathering products. Weathering of Basalt is limited to the surface layer where water can be absorbed, and produces a few amount of platy-shape debris. Tuff are separated by blocky structure which the particles are aggregated along their edges rather than enlarged existing cracks/joins or generated new joints.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.795-798
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• 1999

Deterioration induced by the freezing and thawing in concrete often leads to the reduction in concrete durability by the cracking or surface spalling. In this paper, the deterioration prediction model for concrete structures subjected to the irregular freeze-thaw was proposed from the results of accelerated laboratory test using the constant temperature condition and acceleration factor from the in-situ weather data.

• 터널과지하공간
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• 제6권2호
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• pp.144-156
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• 1996

The deformation behaviors under uniaxial compressive cyclic loading were investigated for fresh rocks and freeze-thaw cycled samples. The Pocheon granite which is one of the most popular building stone in Korea was selected for tests. 0.5 Hz and 50% of dynamic strength were used as test conditions for frequency and fatigue span, respectively. For freezethaw procedure, sample were frozen for 3 hours under the temperature of -2$0^{\circ}C$ and then followed 3 hours thawing under the temperature of +2$0^{\circ}C$. Twenty seven samples were used as untreated and seventy three for freeze-thaw samples. No failure occurred up to 15000 cycles at the stress level of 60% of dynamic strength, indicating that the lowest strees level for fatigue failure may be around 60% of dynamic strength. Permanent strain and damping capacity curves show that there were three stages when rock behaves like under creep. Young's moduli were increased and Possion's ratios were decreased with the increase of the number of cycles. Possion's ratios varied more rapidly than Young's moduli did with the increase of the number of cycles. This may represent that most microcracks developed by fatigue stress are parallel to the axis of loading. The deformation behavior of freeze-thaw cycled samples were almost the same as that of untreated samples. However, the result of freeze-thaw cycled samples showed lower regression constant, indicating that the physical durability of rock is much lowered because of cyclic temperature variation.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.457-460
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• 2008

CFRP plates has been established as an effective method for rehabilitation and strengthening of concrete structures. The CFRP reinforcements are bonded to beams and slabs using structural adhesives. Adhesive strength can be affected by environmental exposure. During freezing-and-thawing cycling, temperature-induced stresses in the adhesive layer, due to differential thermal expansion between the CFRP and the substrate concrete, may lead to bond damage and contribute to or cause premature CFRP composite separation. This paper presents the results of experimental program undertaken to investigate the effects of freeze-thaw cycling (from -18 to $4^{\circ}C$) on the behavior and failure characteristics of RC beams strengthened in shear with CFRP plate using acoustic emission (AE) technique.

• Journal of Pharmaceutical Investigation
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• 제37권1호
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• pp.51-55
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• 2007

Solid lipid nanoparticles (SLNs) have been regarded to behave similar to the vegetable oil emulsions because emulsions of lipid melts are formed before lipid droplets being solidified to turn into SLNs. Compared to lipid emulsion, however, it has been more difficult to obtain stable SLNs and needs more extensive considerations on stabilizer and manufacturing process. In the present study, we tried to prepare phosphatidylcholine-based trymyristin (TM) SLNs using high pressure homogenization method and optimize the manufacturing variables such as homogenization pressure, number of homogenization cycles, cooling temperature, co-stabilizer and freeze-drying with cryoprotectants. Nano-sized TM particles could be Prepared using egg Phosphatidylcholine and pegylated phospholipids ($PEG_{2000}$PE) as stabilizers. Based on the optimization study, the dispersion was manufactured by homogenization under the pressure of 100 MPa for more than 5 cycles, and solidifying the intermediately formed lipid melt droplets by dipping in liquid nitrogen followed by thawing at room temperature. In addition, TM SLNs could be freeze-dried and then redispersed easily without significant particle size changes after freeze drying with 10% and 12.5% sucrose or trehalose. The TM SLNs established in this study can be used as delivery system for drugs and cosmetics.