• 한국건설순환자원학회논문집
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• 제11권2호
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• pp.145-152
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• 2023

본 연구에서는 알칼리 이온의 침출을 완화하기 위해 전기화학적 처리로 100일 동안 수중 환경에 침지된 시멘트 페이스트의 표면을 현미경으로 관찰하였다. 계면 영역에서의 미수화물 입자와 공극률을 정량적으로 평가하기 위하여 주사 전자 현미경을 통해 후방 산란 전자(BSE) 이미지를 얻었다. 그 결과, 전기화학적 처리에 의해 표면부의 공극률이 크게 감소한 반면, 전하 상태에서 제한된 수화반응에 의해 미수화 입자는 다소 증가한 것으로 나타났다. 전기화학적 처리에서, C-S-H 겔에 존재하는 Ca²⁺ 이온은 공극수 내의 OH^- 이온과 Ca(OH)₂ 형태로 침전되어 C-S-H 겔을 낮추면서 동시에 Ca(OH)₂를 증대시킬 수 있다. 실질적으로 알칼리 침출에 대한 위험성은 전기화학적인 처리 하에서 제한된 이온화 매트릭스에 의해 감소될 수 있다.

• 한국세라믹학회지
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• 제37권5호
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• pp.410-417
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• 2000

In this study the effects of specifics surface area of cement, addition amount of gypsum and substitution ratio of gypsum anhydrite ont he physical properties of cement mortars were investigated by measruements of setting time, flow, compressive strength and hydration heat evolution rate. The results showed that fluidity of mortars was increased by 40 wt.% of maximum flow change with the decreasing specific surface area of cement from 3,500$\textrm{cm}^2$/g to 3,300${\pm}$50$\textrm{cm}^2$/g and affected by the relationship between the cement and balancing between the chemical activityof cement and solubility of calcium sulfate are desirable to prevent the fluidity of concrete from decreasing by high temperature in summer season.

• Computers and Concrete
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• 제21권4호
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• pp.419-429
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• 2018

Climate changes, such as increasing of $CO_2$ concentration and global warming, will impact on the carbonation service life of concrete structures. Moreover, slag blended concrete has a lower carbonation resistance than control concrete. This study presents a probabilistic numerical procedure for evaluating the impact of climate change on carbonation service life of slag blended concrete. This numerical procedure considers both corrosion initiation period and corrosion propagation period. First, in corrosion initiation period, by using an integrated hydration-carbonation model, the amount of carbonatable substances, porosity, and carbonation depth are calculated. The probability of corrosion initiation is determined through Monte Carlo method. Second, in corrosion propagation period, a probabilistic model is proposed to calculate the critical corrosion degree at surface cracking, the probability of surface cracking, and service life. Third, based on the service life in corrosion initiation period and corrosion propagation period, the whole service life is calculated. The analysis shows that for concrete structures with 50 years service life, after considering climate changes, the service life reduces about 7%.

• 한국응용과학기술학회지
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• 제28권3호
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• pp.313-320
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• 2011

Encapsulation of L-ascorbic acid(AA) into BGsome was attempted to improve its stability. BGsome is a bio-compatible vesicular system prepared by dispersion of hydrated liquid crystalline phase formed through hydration of 1,3-butylene glycol(BG)-dissolved lecithin with an aqueous solution containing hydrophilic component. The characteristics of AA encapsulated BGsome, such as droplet size, surface charge, and solution appearance, was investigated. The concentration of AA solution had considerable effect on droplet size and surface charge of BGsome. Several tens nanometer droplet made by sonication treatment did not showed any change of size with storage time. Stability of AA was improved by encapsulation into BGsome, which was verified through DPPH test and HPLC assay.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3140-3141
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• 2008

The output power efficiency of the fuel cell system depends on the demanded current, stack temperature, air excess ratio, hydrogen excess ratio and inlet air humidity. Thus, it is necessary to determine the optimal operation condition for maximum power efficiency. In this paper, we developed a dynamic model of fuel cell system which contains mass flow model, diffusivity gas layer model, membrane hydration and electrochemistry model. In order to determine the maximum output power and minimum use of hydrogen in a certain power condition, response surface methodology (RSM) optimization based on the proposed PEMFC stack model is presented. The results provide an effective method to optimize the operation condition under varied situations.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.711-714
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• 2004

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. In order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the coefficient of air convection, which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, boiling and layer effects. Finally, the prediction model for equivalent coefficient of air convection was theoretically proposed. The coefficient of air convection in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with types of form. For determining the initial coefficient of air convection, boiling effects must be considered. The coefficient of air convection is affected by boundary layer with respect to the distance from the surface.

• 대한화장품학회지
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• 제43권4호
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• pp.297-307
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• 2017

피부 특성은 다양한 내부 또는 외부 요인의 영향을 받는다. 이 연구는 아시아 여성들의 피부 특성을 조사 및 비교하기 위해 수행되었다. 우리는 7개국(말레이시아, 인도네시아, 베트남, 태국, 인도, 중국 및 한국)에서 1,500명의 아시아인의 피부 물리적 변수 및 지역 간 차이를 평가하였다. 경피 수분 손실, pH, 피부 수분, 피지함량, 피부 민감도, 탄력, 눈가 주름 및 피부 밝기의 값을 측정하였다. 인도 여성들은 다른 국가들의 여성들보다 피부 수분량, 피지량 및 민감도 점수가 낮게 나타났고, 더 어두운 피부색을 갖는 것으로 조사되었다. 또한, 모든 부위의 피부 표면 pH는 7개국 중 가장 높게 나타났다. 베트남인은 가장 낮은 수치의 피부 표면 pH 값을 보였다. 한국인과 중국인은 일반적으로 탄력성이 높고 적은 눈가 주름을 가진 것으로 나타났다. 피부 수분과 경피 수분손실량은 민감도와 양의 상관 관계가 있었으며, 주름과 민감도 간에는 음의 상관 관계가 있었다. 본 연구 결과는 해당 지역이나 지역과 관련된 명확한 추세는 없었다. 피부 물리적 매개 변수는 지역적 차이에 대한 이해와 함께 다양한 요인(피부 관리 습관, 라이프스타일 및 개인 민감도)에 대한 연구도 함께 진행되어야 할 것이다.

• 한국지반신소재학회논문집
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• 제20권4호
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• pp.1-7
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• 2021

본 연구에서는 건설공사시 시멘트 사용에 따른 탄소배출 저감과 천연모래 고갈에 따른 대응방안으로 산화그래핀 및 다공성 장석을 적용하였다. 산화그래핀은 부착특성을 증가시키기 위해 (3-aminopropyl)trimethoxysilane으로 기능화 시켰으며, 이를 적용하여 표준배합 모르타르 대비 시멘트 함량을 5% 감소시킨 배합조건으로 공시체를 제작하여 압축강도를 평가하였다. 다공성 장석과 기능화된 산화그래핀이 적용된 시편과 표준배합시편의 압축강도는 각각 26MPa, 28MPa로 큰 편차를 보이지 않았으며, 지반구조물에서 요구하는 시멘트 모르타르의 압축강도를 만족하는 것으로 평가되었다. 시멘트 함량감소에도 적정강도를 유지할 수 있는 원인으로는 다공성 장석에 대표적 포졸란 성분인 SiO₂와 Al₂O₃가 다량으로 함유되어 수화과정에서 Ca(OH)₂와의 반응을 증가시켰고, 나노크기의 그래핀 표면이 수화생성물이 활발히 반응할 수 있는 반응면으로 작용하였으며, Carboxyl 작용그룹의 강력한 공유결합 특성이 수화물의 결합강도를 증가시켰기 때문에 시멘트 함량을 감소시켰음에도 적정한 압축강도가 유지되었던 것으로 판단된다.

• Computers and Concrete
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• 제23권5호
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• pp.351-359
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• 2019

In this study, the calcium hydroxide, an inherent product of cement hydration, was treated using biomimetic carbonation method of incorporating stearic acid to generate the hydrophobic calcium carbonate on concrete surface. Carbonation reaction was carried out at various $CO_2$ pressure and temperatures and utilizing the Scanning Electron Microscope (SEM), chloride-ion penetration test apparatus, and compression test machine to investigate the hydrophobicity, durability, and mechanical properties of the synthesized products. Experimental results indicate that the calcium stearate may change the surface property of concrete from hydrophilicity to hydrophobicity. Increasing reaction temperature can change the particles from irregular shapes to needle-rod structures with increased shear stress and thus favorable to hydrophobicity and microhardness. The contact angle against water for the concrete surface was found to increase with increasing $CO_2$ pressure and temperature, and reached to an optimum value at around $90^{\circ}C$. The maximum static water contact angle of 128.7 degree was obtained at the $CO_2$ pressure of 2 atm and temperature of $90^{\circ}C$. It was also found that biomimetic carbonation increased the permeability, acid resistance and chloride-ion permeability of the concrete material. These unique results demonstrate that the needle-rod structures of $CaCO_3$ synthetized on concrete surface could enhance hydrophobicity, durability, and mechanical properties of concrete.

• 대한건축학회논문집:구조계
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• 제34권2호
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• pp.49-56
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• 2018

The use of highly absorptive materials in cement-based materials is increasing for internal curing purpose. However, calculation of correct absorption capacity of such materials is not easy, which leads to change in the effective water-to-cement ratio of cement paste by either absorbing or releasing water. In this study, effective absorption capacity of a highly absorptive material was found using isothermal calorimetry. Moreover, the effect of specific surface area was investigated. It was found that the method was capable of finding effective water absorption capacity of activated carbon fiber. For the activated carbon fiber used in this research, the effect of specific surface area was negligible because the high BET surface area was due to micropores less than 1nm, which does not affect the rate of hydration curve. Thus, the effective absorption capacity of such materials can be found successfully using this method.