섬유보강 MPC 모르타르의 초기 경화 및 수축 특성에 관한 실험적 연구

이현기(Lee, Hyeongi),이인희(Lee, Inhee),이종미(Lee, Jongmi),오홍섭(Oh, Hongseob) 한국방재학회 2017 한국방재학회논문집 Vol.17 No.3

일반적으로 콘크리트 구조물은 다양한 환경에 노출되어 복합적인 성능저하 인자로 인한 손상이 가속화됨에 따라 보수공법 및 재료의 수요가 급증하고 있다. 이에 따라 다양한 계열의 보수재료가 개발 및 연구되고 있으며, 본 연구에서는 마그네시아 인산염 복합체(Magnesia Phosphate Composite, MPC) 모르타르를 보수재료로 적용하고자 한다. MPC모르타르는 마그네시아와 인산칼륨이 주요 결합재의 역할을 하여 급속한 반응성을 통한 조기 강도 증진에 효과적이고, 반응 생성물의 결합성이 견고하여 물리적 성능 및 내구성이 우수하다. 하지만 이와 같은 급속한 반응 속도는 팽창 및 반응열에 따른 미세 균열의 발생 가능성이 내제되어있어 지연제 및 섬유를 활용하여 경화속도 및 균열을 제어하고자 한다. 그 결과, MPC 모르타르의 경우 붕산을 지연제로 혼입한 경우 조기 강도 및 가사 시간 확보 측면에서 우수한 효과를 나타내었으며, 셀룰로오스 섬유로 보강된 경우반응에 따른 팽창 및 건조수축을 제어하는 데에 효과적인 것으로 판단된다. Recently, there is an increase in the demand for repair methods and materials for concrete structures that are damage due to combined deterioration from being exposed to various environments. Thus, this study proposed MPC (Magnesia Phosphate Composite) mortar as a rapid repair material. The magnesia and potassium phosphate in MPC react as a main binder and are effective in increasing early strength through quick reactivity, and because MPC has a substantial chemistry bonding structure, MPC also has excellent physical performance and durability. But because this rapid reactivity inherently has issues related to microcracking caused by expansion and reaction heat, retarder and fibers are proposed to be used to control the hardening rate and cracking. The results confirmed that when mixing in boric acid as a retarder, the MPC mixture showed excellent performance in early strength and secure in work time, and also that when reinforcing the mixture with cellulose fiber, MPC was effective in controlling expansion and shrinkage.

동결융해 환경에서의 제설염 종류와 표면강화제 처리에 따른 콘크리트의 표면박리 저항성 및 평가방법에 관한 연구

이현기(Lee, Hyeongi),이인희(Lee, Inhee),이종미(Lee, Jongmi),오홍섭(Oh, Hongseob) 한국방재학회 2017 한국방재학회논문집 Vol.17 No.4

본 연구의 목적은 제설염의 종류 및 구체강화제의 처리 유무에 따른 콘크리트 표면 박리저항성을 평가하고, 3D 스캐닝에 의해 표면상태를 평가하는 기법을 제안하고자 하였다. 본 연구에서는 국내에서 많이 사용되고 있는 다양한 습염식 제설염을 국외의 스케일링 시험법에 따라 콘크리트 표면에 표면강화제를 변수로 하여 박리실험을 실시하였다. 실험결과 무기질계 구체강화제를 사용한 경우 스케일링 저항성이 크게 향상되는 것으로 나타났으며, 규산나트륨계열의 강화제의 경우에는 박리가 상대적으로 많이 진행되었다. 또한 본 연구에서는 콘크리트 표면 박리를 평가하기 위하여 3D 스캐닝을 사용하여 박리량을 평가하는 법을 제안하고자 하였다. The objectives of this research study were to evaluate and discuss the scaling resistance of concrete surface due to freeze-thaw effect according to both the type of saline solution that was applied in compliance with overseas standards, and the treatment of the concrete surface hardener. Further, the accuracy of the evaluation method was assessed utilizing 3-D imaging technologies to determine the scaling resistance of concrete surface. This research study comparatively analyzed the scaling resistance of concrete surfacefor deicing agents that are currently used in domestic pre-wetting spray systems. Comparisons were made according to the saline solution that is used in compliance with overseas scaling resistance evaluation standards, the type of concrete surface hardener used, and whether the concrete had undergone a surface treatment. The results based on the concrete surface hardener treatment manifested superior results when mineral silane-based treatment agents were used. In order to provide a more quantitatively reliable evaluation, a concrete surface scaling resistance evaluation method utilizing 3-D scanning technologies was proposed in this research study.

Butanol Production using Clostridium pasteurianum Strains by Glycerol and Glucose mixed Substrate Fermentation

HyeonGi MOON,Joungmin LEE,Yu-Sin JANG,Sang Yup LEE 한국생물공학회 2015 한국생물공학회 학술대회 Vol.2015 No.4

Finite Element Study on the Micro-cavity Effect in OLED Devices

Hyeongi Lee,Youngwook Hwang,Taeyoung Won 대한전자공학회 2014 Journal of semiconductor technology and science Vol.14 No.1

In this paper, we discuss on the optimal design scheme of the bilayer OLED (Organic Light Emitting Diodes) with micro-cavity structure. We carried out the optical simulation on the OLED device and calculated optimal scale of devices with taking the micro-cavity effect into account. Our emission model is based upon an ensemble of radiating dipole antennas. Consequently, we applied Maxwell’s equation to this sequence, followed by the analysis on the electrical behaviors of OLED device using Poisson’s equation. It contains carrier injection and transportation mechanism. In this process, we found out the thickness of each layer can affect the recombination rate at the emission layer. Therefore, we optimized the thickness of each layer to improve the efficiency of the device.

Impact of Energy Level Shift of Hole Injection Layer on the Recombination Rate in OLEDs

Lee, Hyeongi,Won, Taeyoung American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.3

<P>This paper reports the numerical study on the impact of energy level variation of the hole injection layer (HIL) in the organic light emitting diodes (OLEDs). We used a thin CuPc layer for the hole injection and S-TAD (2,2',7,7'-tetrakis-(N, N-diphenylamino)-9,9-spirobifluoren) for the hole transfer layer, S-DPVBi (4,4'-bis (2,2'-diphenylvinyl) -1,1'-spirobiphenyl) for the emission layer, and Alq3 (Tris (8-hyroxyquinolinato) aluminium) for the electron transfer layer. Device B has tri-layer structure except HIL. We used three models which are four layer structures for our simulation. HIL of Device A has 5.3 eV of highest occupied molecular orbital (HOMO) level and 3.8 eV of lowest unoccupied molecular orbital (LUMO) level. Also, we varied the LUMO level and HOMO level of the thin CuPc layer, which are named as Device C and Device D, respectively. Our numerical study represented that Device D has the most amount of recombination rate due to Device D has the most carrier density in the emission layer. Device A has 4.381x10(25) cm(-3)s(-1) of recombination, Device B has 6.439x10(25) cm(-3)s(-1) of recombination and Device D has 7.499x10(25) cm(-3)s(-1) of recombination. Consequently, nevertheless the insertion of HIL does not always improve recombination rate and we observed the recombination rate can improve about 16% according to HOMO level of HIL.</P>

Production of Mixed-Alcohol Fuel Using Engineered Clostridium Strains

HyeonGi MOON,Joungmin LEE,Yu-Sin JANG,Sang Yup LEE 한국생물공학회 2015 한국생물공학회 학술대회 Vol.2015 No.4

Light conversion efficiency of top-emitting organic light-emitting diode structure.

Lee, Hyeongi,Won, Taeyoung American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.11

<P>Top-emitting organic light-emitting diodes (OLEDs) with a microcavity structure are presented in this paper. We performed a finite element (FE) analysis of a trilayer OLED that was inserted between the reflective layer and the semi-reflective layer of a device. We carried out an optical analysis of this OLED device and calculated the optimal width between the reflective layer and the semi-reflective layer to consider the microcavity effect. Our simulation revealed that the thickness of each layer can affect the recombination rate at the emission layer. We used five OLED devices. Device A is a reference device with a 42.5 nm hole transport layer (HTL), a 15 nm emission layer (EML) and a 45 nm electron transport layer (ETL). We varied the thickness of the HTL of Device A to 20 nm and 65 nm, and designated these devices as Device B and Device C, respectively. We also varied the thickness of the ETL of Device A to 20 nm and 65 nm, and designated these devices as Device D and Device E, respectively. As the thickness of the HTL and the ETL are decreased, a higher recombination rate is achieved. However, the highest recombination rate does not necessarily correspond to the highest external quantum efficiency (EQE) owing to the resonance effect. Our simulation revealed that the overall thickness of the device seems to be a more significant factor owing to the path of light.</P>

Finite Element Study on the Micro-cavity Effect in OLED Devices

Lee, Hyeongi,Hwang, Youngwook,Won, Taeyoung The Institute of Electronics and Information Engin 2014 Journal of semiconductor technology and science Vol.14 No.1

In this paper, we discuss on the optimal design scheme of the bilayer OLED (Organic Light Emitting Diodes) with micro-cavity structure. We carried out the optical simulation on the OLED device and calculated optimal scale of devices with taking the micro-cavity effect into account. Our emission model is based upon an ensemble of radiating dipole antennas. Consequently, we applied Maxwell's equation to this sequence, followed by the analysis on the electrical behaviors of OLED device using Poisson's equation. It contains carrier injection and transportation mechanism. In this process, we found out the thickness of each layer can affect the recombination rate at the emission layer. Therefore, we optimized the thickness of each layer to improve the efficiency of the device.

Performance evaluation of concrete incorporating glass powder and glass sludge wastes as supplementary cementing material

Lee, Hyeongi,Hanif, Asad,Usman, Muhammad,Sim, Jongsung,Oh, Hongseob Elsevier 2018 JOURNAL OF CLEANER PRODUCTION Vol.170 No.-

<P><B>Abstract</B></P> <P>The purport of this study is to efficiently recycle waste glass, one of silica-based industrial by-products, and use it as a cement substitute for sustainable construction. Waste glass powder (WGP) and waste glass sludge (WGS) were manufactured from the waste glass and their feasibility, for use in concrete as partial replacement of cement, was evaluated. 20% of cement (by weight) was replaced with WGP and WGS and the resulting concretes were tested for mechanical properties and durability. Porosity and phase identification studies were also carried out. After 90-day age, the WGS incorporated concrete exhibited the highest compressive strength. Also, it was found that WGS incorporation in concrete led to reduced porosity due to their greater pozzolanic activity owing to the inherent amorphous nature of WGS. Investigations on frost resistance and chloride ions penetrability further showed that these glass wastes are better in improving these properties. After 50 cycles of freezing – thawing, the concretes incorporated with WGP and WGS showed lower mass loss as compared to normal concrete, by 24% and 36% respectively. Also, WGS incorporation resulted in 24% reduction in chloride ion diffusion coefficient. Summarily, the results indicate that WGS is superior in enhancing mechanical, microstructural, and durability – related properties of concrete and as such its use in concrete shall help sustainable development due to efficient waste utilization, reduced associated carbon dioxide emissions, and lower production costs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Glass powder and glass sludge wastes are used as cement replacement in concrete. </LI> <LI> Fresh and hardened state properties are evaluated. </LI> <LI> Durability – related properties of developed concretes are investigated. </LI> <LI> WGS proved to be the most efficient in reducing porosity and improving durability. </LI> </UL> </P>

IEC 61850 표준분석을 통한 스마트그리드 상호운용성 확보방안

이현기(Lee hyeongi),정명현(Chung myunghyun) 한국정보과학회 2014 정보과학회지 Vol.32 No.9