• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.253-254
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• 2012

In this study, it carried out measurement experiment Ca(OH)₂ and chemically bound water to verify Ca(OH)₂ and chemically bound water prediction model out of hydration model of cement incorporating blast furnace slag. It compared and analyzed prediction results using prediction model with measurement results of Ca(OH)₂ quantity using thermogravimetric differential temperature analysis and chemically bound water quantity using electronic furnace. It agrees well experiments results with prediction results.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 가을학술발표대회논문집
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• pp.191-192
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• 2023

This study, evaluated the effect of changes in the chemical composition of cement on the hydration reaction for carbon neutrality. For this purpose, changes in the chemical bound water and heat of hydration between current cement and past cement were compared. As a result, it was found that both the chemically bound water and heat of hydration of currently used cement decreased.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.565-566
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• 2009

Supplementary cementing materials (SCM), such as silica fume, slag, and low-calcium fly ash, have been widely used as mineral admixtures in high strength and high performance concrete. Due to the chemical and physical effect of SCM on hydration, compared with Portland cement, hydration process of cement incorporating SCM is much more complex. This paper presents a numerical hydration model which is based on multi-component concept and can simulate hydration of cement incorporating SCM. The proposed model starts with mixture proportion of concrete and considers both chemical and physical effect of SCM on hydration. Using this proposed model, this paper predicts the following properties of hydrating cement-SCM blends as a function of hydration time: reaction ratio of SCM, calcium hydroxide content, heat evolution, porosity, chemically bound water and the development of the compressive strength of concrete. The prediction results agree well with experiment results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.465-466
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• 2010

In this paper, an integrated system is proposed which can evaluate both the early-age properties and durability performance of concrete structures. This integrated system starts with a hydration model which considers both Portland cement hydration and chemical reactions of supplementary cementing materials (SCM). Based on the degree of hydration of cement and mineral admixtures, the amount of reaction products, the early age heat evolution, chemically bound water, porosity, the early age short-term mechanical behaviors, shrinkage and early-age creep are evaluated as a function of curing age and curing conditions. Furthermore, the durability aspect, such as carbonation of blended concrete and chloride attack, are evaluated considering both the material properties and surrounding environments. The prediction results are verified through experimental results.

• Journal of Forest and Environmental Science
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• 제35권3호
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• pp.141-149
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• 2019

Nanocellulose, which can exist as either cellulose nanocrystals or cellulose nanofibrils, has been used as a biomaterial for drug delivery owing to its non-immunogenicity, biocompatibility, high specific area, good mechanical properties, and variability for chemical modification. Various water-soluble drugs can be bound to and released from nanocelluloses through electrostatic interactions. The high specific surface area of nanocellulose allows for high specific drug loading. Additionally, a broad spectrum of drugs can bind to nanocellulose after facile chemical modifications of its surface. Controlled release can be achieved for various pharmaceuticals when the nanocellulose surface is chemically modified or physically formulated in an adequate manner. This review summarizes the potential applications of nanocelluloses in drug delivery according to published studies on drug delivery systems.

• Advances in materials Research
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• 제4권1호
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• pp.13-22
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• 2015

Concrete suffers strength loss when subjected to elevated temperatures during an accidental event such as fire. The loss in strength of concrete is mainly attributed to decomposition of C-S-H gel and release of chemically bound water, which begins when the temperature exceeds $500^{\circ}C$. But it is unclear about how much strength loss occurs in different stages of heating, retention and cooling regimes. This work is carried out to separate the total strength loss into losses during different stages of heating, retention and cooling. Tests were carried out on both Ordinary Portland Cement (OPC) based concrete and Ground Granulated Blast Furnace Slag (GGBFS) blended concrete for $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$ with a retention period of 1 hour for each of these temperature levels. Furnace cooling was adopted throughout the experiment. This study reports strength loss contribution during heating, retention and cooling regimes for both OPC based and GGBFS based concretes.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.35-35
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• 2010

Understanding the mechanistic details of heterogeneous catalytic reactions will provide a way to tune the selectivity between various competing reaction channels. In this regard, catalytic decomposition of alcohols over the rutile $TiO_2$(110) surface as a model oxide catalyst has been studied to understand the reaction mechanism employing the temperature-programmed desorption (TPD) technique. The $TiO_2$(110) model catalyst is found to be active toward alcohol dehydration. We find that the active sites are bridge-bonded oxygen vacancies where RO-H heterolytically dissociates and binds to the vacancy to produce alkoxy (RO-) and hydroxyl (HO-). Two protons adsorbed onto the bridge-bonded oxygen atoms (-OH) readily react with each other to form a water molecule at ~500 K and desorb from the surface. The alkoxy (RO-) undergoes decomposition at higher temperatures into the corresponding alkene. Here, the overall desorption kinetics is limited by a first-order decomposition of intermediate alkoxy (RO-) species bound to the vacancy. We show that detailed analysis on the yield and the desorption temperatures as a function of the alkyl substituents provides valuable insights into the reaction mechanism. After the catalytic role of the oxygen vacancies has been established, we employed x-ray photoelectron spectroscopy to further study the surface electronic structure related to the catalytically active defective sites. The defect-related state in valence band has been related to the chemically reduced $Ti^{3+}$ defects near the surface region and are found to be closely related to the catalytic activity of the $TiO_2$(110) surface.

• 콘크리트학회논문집
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• 제16권5호
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• pp.597-604
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• 2004

본 연구는 실리카퓸을 사용한 고강도 콘크리트의 고온하의 압축강도의 저하 및 공극률 변화를 통하여 강도 감소와 공극구조와의 연관성을 검토하였다. 또한, 실리카퓸 혼입의 유무와 각 가열온도에서의 시멘트 수화물의 탈수에 의한 공극특성의 변화에 관한 기초 데이터를 제공하고자 하였다. 연구결과, 실리카퓸의 혼입에 따른 필러효과 및 물-결합재비의 차로 인해 공극률 및 공극분포는 다르게 나타났다. 가열온도가 상승함에 따라 공극률도 점진적으로 증가하는 경향을 보였다. 또한, $600^{\circ}C$ 이상의 고온에서의 경향성은 더욱 현저하였다. 가열온도의 상승에 따라 $0.1{\~}0.5{\mu}m$공극의 증가는 현저하였으며 이는 모세관 공극의 수분의 증발 및 C-S-H계 수화물 및 수산화칼슘이 분해되어 결합수가 탈수한 결과이다. 고열에 의한 신축도 콘크리트 내부의 미세균열을 발생시켜 공극률 증가를 유발한다. 이러한 공극률 증가는 가열온도에 따라 일정한 경향성을 띠므로 화해를 입은 콘크리트의 수열온도 및 국부적인 성능저하를 예측할 수 있을 것으로 기대된다.

• 콘크리트학회논문집
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• 제14권1호
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• pp.118-125
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• 2002

콘크리트는 수화과정을 통하여 재료가 성숙되고, 경화된다. 수화의 진행은 엄밀한 의미에서 재령에 의하지 않고 수화도에 의해 제어되므로, 경화가 진행되는 콘크리트의 모든 재료특성과 미세구조 형성과정은 수화도에 의해 정식화되는 것이 바람직하다. 기존 연구는 주로 양생온도가 수화발열속도에 미치는 영향을 고려한 반응함수 개념을 주로 사용하였고, 또한 내부 수분상태의 영향을 습도함수의 형태로 고려한 연구결과는 실제 수화기구를 반영하지 못하고 단지 각 연구자의 실험조건과 배합조건에만 부합하는 결과를 보인다. 따라서 본 연구는 기존 제안식의 단점을 보완하기 위하여 수화기구와 미세구조 형성 과정에 기초하여 반응속도함수를 모델링하였다. 수화반응속도는 온도 및 수분상태에 따라 변화하므로, 본 연구에서는 수화발열 속도에 영향을 미치는 인자로, 시멘트 종류, 물-시멘트비 등의 배합특성과 양생온도 빛 세공조직의 내부수분상태를 고려하였다. 똔 연구에서 제시한 콘크리트의 수화도 예측모델은 기존의 온도영향만을 주로 고려하는 반응속도함수를 콘크리트내부의 수분분포 상태를 고려하여 모델을 개선하였으며, 이는 실제 측정한 수화도에 매우 근접하여 그 유용성을 검증하였다. 또한 수화도의 정의와 제시한 모델을 이용하여 콘크리트 요소내의 온도, 습도 덴 수화도를 수치적으로 결정하여 단열온도상승곡선을 정확히 모사 할 수 있었다. 제안된 모델은 수화가 진행되는 콘크리트의 여러 역학적 특성 및 미세구조 형성과정을 적절히 표현하고, 수화과정이 온도 및 습도상태를 결정하는 초기재령 콘크리트의 단면 내 온 습도상태를 추정하여 궁극적으로 초기재령 콘크리트의 균열 위험성을 평가하는데 유용하게 이용될 수 있을 것으로 사료된다.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2017년도 춘계공동학술대회
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• pp.107-107
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• 2017

3D bioprinting is a technology to produce complex tissue constructs through printing living cells with hydrogel in a layer-by-layer process. To produce more stable 3D cell-laden structures, various materials have been developed such as alginate, fibrin and gelatin. However, most of these hydrogels are chemically bound using crosslinkers which can cause some problems in cytotoxicity and cell viability. On the other hand, thermosensitive hydrogels are physically cross-linked by non-covalent interaction without crosslinker, facilitating stable cytotoxicity and cell viability. The examples of currently reported thermosensitive hydrogels are poly(ethylene glycol)/poly(propylene glycol)/poly(ethylene glycol) (PEG-PPG-PEG) and poly(ethylene glycol)/poly(lactic acid-co-glycolic acid) (PEG/PLGA). Chitosan, which have been widely used in tissue engineering due to its biocompatibility and osteoconductivity, can be used as thermosensitive hydrogels. However, despite the many advantages, chitosan hydrogel has not yet been used as a bioink. The purpose of this study was to develop a bioink by chitosan hydrogel for 3D bioprinting and to evaluate the suitability and potential ability of the developed chitosan hydrogel as a bioink. To prepare the chitosan hydrogel solution, ${\beta}-glycerolphosphate$ solution was added to the chitosan solution at the final pH ranged from 6.9 to 7.1. Gelation time decreased exponentially with increasing temperature. Scanning electron microscopy (SEM) image showed that chitosan hydrogel had irregular porous structure. From the water soluble tetrazolium salt (WST) and live and dead assay data, it was proven that there was no significant cytotoxicity and that cells were well dispersed. The chitosan hydrogel was well printed under temperature-controlled condition, and cells were well laden inside gel. The cytotoxicity of laden cells was evaluated by live and dead assay. In conclusion, chitosan bioink can be a candidate for 3D bioprinting.