• 한국건축시공학회지
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• 제12권5호
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• pp.503-509
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• 2012

In this study, the potential use of indigenous natural loess(Hwangtoh) as a new construction material, via alkali activation in conjunction with microwave heating, was investigated. Hwangtoh pastes with three different mix proportions of varying alkali liquid concentrations at a constant liquid-to-Hwangtoh ratio of 0.55 were prepared. Through the investigation it was found that it is possible to prepare Hwangtoh paste with $19.02N/mm^2$ at the age of 4 hours with the alkali solution of 8M NaOH and 1:4.5 mass ratio of liquefied $Na_2SiO_3$ at the curing temperature of $60^{\circ}C$ by microwave heating. The strength development at early age of the alkali activated Hwangtoh paste specimens may be attributed to both a higher rate of reaction and moisture evaporation due to microwave heating.

• 한국세라믹학회지
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• 제53권6호
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• pp.707-711
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• 2016

A small diameter of SiC fiber mat can produce much higher heat under microwave irradiation than the other types of SiC materials. Fabrication of high strength SiC fiber consists of iodine vapor curing on polycarbosilane precursor and heat treatment process. The curing stage of polycarbosilane fiber was maintained at $150-200^{\circ}C$ in a vacuum condition under the iodine vapor to fabricate a high thermal radiation SiC fiber. The structure and morphology of the fibers were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG) and scanning electron microscopy (SEM). In this study, the thermal properties of SiC fiber mats under microwave have been analyzed with an IR thermal camera and its image analyzer. The prepared SiC fiber mats radiated high temperature with extremely high heating rate up to $1100^{\circ}C$ in 30 seconds. The fabricated SiC fiber mats were not oxidized after the heat radiation process under the microwave irradiation.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.160-161
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• 2022

This study is to investigate the temperature history over time of the cement mortar to confirm the bubble sheet insulation effect using the heat generat sheet. As a result of the experiment, it was confirmed that the heating effect was 6℃ higher on average than other types of sheets when the heating sheet is attached on the bottom of the double layered bubble sheet. For future research, it is planned to verify the heating performance by using the heating sheet under the same environmental conditions as the heating performance will be verified.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1994년도 추계 학술발표 강연 및 논문 개요집
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• pp.125-126
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• 1994

The chemorheological changes and kinetics during curing reaction of an silica filled epoxy system (DGEBA with curing agent Polyxoypropylenediamine) were investigated. This study concentrates on the influence of silica on the reaction kinetics and rheological behavior of the eopxy system. The concentration of the filler was varied 0~200phr. Curing behavior of the silica filled epoxy system was measured at various heating rates with DSC. Conversion was also measured by integrating the obtained DSC curve and Kinetic parameters measured by using the nonlinear regression method. DSC experiments showed that the presence of silica was found to accelerate the progress of the curing reaction and of reduce the heat of reaction compared with that of unfilled epoxy systems . Rheological experiments were conducted on a Physica by using a disposable parallel plate fixture. Material properites were measured such as the elastic modulus(G′), the loss modulus(G"), the loss tangent(tan $\delta$), and the viscosity was at the initial stahe, and the more the silica filler was added, and the lower the gel temperature was in the epoxy system. In this study it is concluded that the curing of the silica filled epoxy system was found to be accelerated, as silica was added to the epoxy compound.

• Computers and Concrete
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• 제33권3호
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• pp.309-324
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• 2024

Internal curing, a widely used method for mitigating early-age shrinkage in concrete, also offers notable advantages for concrete durability. This paper explores the potential of internal curing by partial replacement of sand with fine lightweight aggregate for enhancing the behavior of high-performance concrete at elevated temperatures. Such a technique may prove economical and safe for the construction of skyscrapers, where explosive spalling of high-performance concrete in fire is a potential hazard. To reach this aim, the physico-mechanical features of internally cured high-strength concrete specimens, including mass loss, compressive strength, strain at peak stress, modulus of elasticity, stress-strain curve, toughness, and flexural strength, were investigated under different temperature exposures; and to predict some of these mechanical properties, a number of equations were proposed. Based on the experimental results, an advanced stress-strain model was proposed for internally cured high-performance concrete at different temperature levels, the results of which agreed well with the test data. It was observed that the replacement of 10% of sand with pre-wetted fine lightweight expanded clay aggregate (LECA) not only did not reduce the compressive strength at ambient temperature, but also prevented explosive spalling and could retain 20% of its ambient compressive strength after heating up to 800℃. It was then concluded that internal curing is an excellent method to enhance the performance of high-strength concrete at elevated temperatures.

• 콘크리트학회논문집
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• 제15권4호
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• pp.541-548
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• 2003

본 연구는 내한촉진제를 사용한 콘크리트의 현장 적용성을 알아보기 위한 기초적인 실험으로서, 실물부재시험을 통해 각종 양생방법에 따른 온도이력 및 강도특성을 검토하고 한중콘크리트에서 실구조물과 동일한 강도이력을 가질 수 있도록 강도관리용 공시체의 적정 양생방법을 평가하기 위한 것이다. 실물부재시험에서 양생방법에 따른 온도이력은 일반콘크리트(단열양생), 일반콘크리트(급열양생), 내한촉진제 콘크리트 및 일반콘크리트(양생막 양생) 순으로 크게 저하하는 경향을 보이고 있었다. 강도특성은 양생조건이 열악한 양생막 내 외부에서의 일반콘크리트 공시체의 경우에는 초기동해에 따른 강도발현 저하를 보인 반면에 내한촉진제 콘크리트의 경우에는 재령이 경과할수록 계속적인 강도발현을 보이고 있어 내한촉진제의 사용에 따른 동결온도 저하효과 및 저온환경하에서의 경화촉진효과를 나타내고 있었다. 한중콘크리트의 강도관리용 공시체의 적정 양생방법을 검토한 결과, 부재 내부에 매립하여 양생한 경우 및 간이단열양생을 실시한 경우에 있어서의 구조체 콘크리트와의 온도이력은 다소 차이를 나타내고 있지만, 코어강도와는 비교적 근사하게 나타나고 있어 구조체 강도평가를 위한 이들 양생방법의 유효성을 확인할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제21권6호
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• pp.557-561
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• 2000

Various enaryloxynitriles-terminated reactive polymer precursors containing rigid aromatic units were prepared from various diamines and 1-(p-formylphenyl)-1-phenyl-2,2-dicyanoethene (1). Arylate end-capped model compounds linked with azomethine bond were also prepared by reacting p-formylphenyl benzoate with diamines to compare the curing ability. The oligomers were highly soluble in polar aprotic solvents such as N,N-dimethylformamide, dimethylsulfoxide and N-methyl-2 -pyrrolidinone. They generally showed an exothermic curing process between $280-350^{\circ}C$, attributable to the thermal crosslinking of the dicyanovinyl group in DSC analysis, and no weight loss at curing temperature. Upon heating the polymer precursors, heat-resistant and insoluble network polymers were obtained. Thermogravimetric analyses of the precursors containing rigid aromatic units showed thermal stability with a 77-92% residual weight at $500^{\circ}C$ under nitrogen.

• Restorative Dentistry and Endodontics
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• 제14권1호
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• pp.41-56
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• 1989

The purpose of this study was to examine the effect of temperature dependence of the behavior on the physical properties of posterior composite resins. Three light cure posterior composite resins (Heliomolar, Litefil-P, and P-50) and one chemical cure posterior composite resin (Bisfil-II) were used as experimental materials. Composite resin was placed in a cylindrical brass mold (2.5 mm high and 6.5 mm inside diameter) that was rested on a glass plate. Another flat glass was placed on top of the mold, and the plate was tightly clamped together. After the mold had been filled with the light cure composite material, the top surface was cured for 30 seconds with a light source. Chemical cure resin specimens were made in the same manner as above. Three hundreds and twenty composite resin specimens were constructed from the four composite materials. One hundred and sixty specimens of them were placed in a heater at $50^{\circ}C$, $75^{\circ}C$, $100^{\circ}C$, $125^{\circ}C$, $150^{\circ}C$, $175^{\circ}C$ and $200^{\circ}C$ for 5 minutes or 10 minutes respectively before compressive strengths were measured. Another one hundred and sixty specimens were tested for the diametral tensile strengths in the same way as above. They were randomly divided into eight groups according to the mode of heating methods as follows and stored in distilled water at $37^{\circ}C$ for 24 hours. Group $37^{\circ}C$ - specimens were stored at $37^{\circ}C$ in distilled water for 24 hours. Group $50^{\circ}C$ - specimens were heated at $50^{\circ}C$ after curing. Group $75^{\circ}C$ - specimens were heated at $75^{\circ}C$ after curing. Group $100^{\circ}C$ - specimens were heated at $100^{\circ}C$ after curing. Group $125^{\circ}C$ - specimens were heated at $125^{\circ}C$ after curing. Group $150^{\circ}C$ - specimens were heated at $150^{\circ}C$ after curing. Group $175^{\circ}C$ - specimens were heated at $175^{\circ}C$ after curing. Group $200^{\circ}C$ - specimens were heated at $200^{\circ}C$ after curing. Twenty specimens of each of four composite resins were respectively made by insertion of materials into same mold for examining the dimensional changes between before and after heating. The final eighty specimens were stored in distilled water at $37^{\circ}C$ for 24 hours before testing the dimensional changes. Compressive and diametral tensile strengths were measured crosshead speed 1mm/minute and 500Kg in full scale with a mechanical testing machine (DLC 500 Type, Shimadzu Co., Japan). Dimensional changes were determined by measuring the diametral changes of eighty specimens with micrometer (Mitutoyo Co., Japan). Results were as follows: 1. Diametral tensile strengths of specimens in all groups were increased with time heated compared with control group except for that in group $50^{\circ}C$ and the maximum diametral tensile strength was appeared in the specimen of Litefil-P heated for 10 minutes at $100^{\circ}C$. In heliomolar and P-50, it could be seen in the specimen heated for 10 minutes at $150^{\circ}C$, but in Bisfil-II, it could be found in the specimen heated for 5 minutes at $150^{\circ}C$. 2. Compressive strengths of specimens in all groups was tended to be also increased with time heated but that in group $50^{\circ}C$ and the maximum compressive strengths were showed in the same specimens conditioned as the diametral tensile strengths of four composite materials tested. 3. In Heliomolar, Litefil-P, and Bisfil-II, it was decreased in diameters of resin specimens between before heating and increased in diameters of resin specimens after storing in distilled water, but it was not in P-50. 4. There is little difference in diametral tensile strengths, compressive strengths, and dimensional changes followed by heating the resin specimens for 5 minutes and 10 minutes, but there is no statistical significances.

• Journal of the Korean Wood Science and Technology
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• 제42권3호
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• pp.339-345
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• 2014

집성재의 생산성 향상을 위한 고주파 가열 경화기술에 대해 연구하였다. 고주파가 유전체에 가해지면 내부에서 에너지 손실에 의한 발열이 발생한다. 집성재를 구성하는 라미나와 접착제는 유전체이므로 집성재에 고주파를 주사하면 내부에서 발열이 발생한다. 집성재 제조에 이용되는 대부분의 상온 경화형 접착제는 고온에서 빠른 경화가 이루어지므로 고주파 가열 기술을 이용하면 집성재 내부 접착층의 온도를 상승시킴으로써 빠른 경화를 유도할 수 있다. 본 연구에서는 낙엽송재와 phenol-resorcinol-formaldehyde (PRF) 접착제의 유전 특성을 평가하고, 집성재 내부의 접착층의 빠른 경화를 유도하는 고주파 가열 경화 기작을 이론적으로 분석하였다. 연구 결과, 온도상승인자인 PRF 접착제의 상대손실계수가 낙엽송재의 상대손실계수에 비해 높았으나, 온도상승저해인자인 밀도와 비열도 높았다. 그러나 상대손실계수의 비율이 온도상승저해인자의 비율보다 높기 때문에 고주파 가열에 의한 발열량은 접착제에서 더 높을 것으로 예상된다. 이러한 실험 결과를 이용한 이론적 접근을 바탕으로, 접착층이 목표온도까지 상승하기 위한 ISM 영역의 고주파 주파수 별 전기장의 상대 세기를 추정하였다.

• 한국축산식품학회지
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• 제43권4호
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• pp.580-593
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• 2023

The purpose of this study was to analyze whether seawater has positive effects on appearance characteristics, such as CIE a^*, and to determine the gas composition concentration that is suitable for maintaining it. Pork hind meat was cured with four types of curing agent for 5 d at 4℃. The different curing agents comprised the control salt, control nitrite pickling salt (CN), treatment brine, and treatment bittern (BT). The cured hams were cooked at 65℃ for 4 h and packaged at O₂:N₂ gas ratios of 7:3, 8:2, and 9:1 for 3 wk. The physicochemical properties were assessed immediately after heating the sample, and the color properties were measured after a 3 wk storage period. Based on the correlation results of the physicochemical properties, BT had a higher curing and cooking yield than the other treatments, owing to its high salinity. Results of color properties for BT (7:3) and CN (8:2) showed similar color CIE L^*, CIE a^* chroma, and hue angle values. Therefore, BT can be said to be a sous-vide curing agent suitable for preserving the color of ham, and a high nitrogen concentration of 30% helps to maintain the appearance of seawater sous-vide ham.