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200㎫급 초고강도 콘크리트의 자기수축 특성에 관한 실험적 연구
하정수(Ha Jung-Soo),백민수(Paik Min-Su),손유신(Sohn Yu-Shin),이승훈(Lee Seung-Hoon),이영도(Lee Young-Do),정상진(Jung Sang-Jin) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.8
Low W/B ultra-high strength concrete has low porosity and discontinuous capillary tube in the cement milk. Within a few days after placement, autogenous shrinkage occur because of the quick drying from the self-desiccation. So, the possibility of cracking is higher than the normal strength concrete. In this study, the autogenous shrinkage deformation characteristics of ultra-high strength concrete that are different from the normal strength concrete were examined. A new shrinkage formula is suggested form the experiment data. The conclusion is as follows. 1) The 91days strength of the concrete combination that are W/B 12.5%, normal portland cement 55%, china silica fume 20%, GGBFS-2 20%, anhydrite 5% was the best result, 193.7㎫. So, it is the appropriate combination for the 200㎫ grade ultra-high strength concrete. 2) The autogenous shrinkage deformation of W/B 20% ultra-high strength concrete can be predicted using the suggested shrinkage formula.
하정수,한유정,Ha, Jung-Soo,Han, Yoo-Jeong 한국재료학회 2019 한국재료학회지 Vol.29 No.2
A powder mixture of 70 wt% $Al_2O_3$ and 30 wt% hydroxyapatite (HA) is sintered at $1300^{\circ}C$ or $1350^{\circ}C$ for 2 h at normal pressure. An $MgF_2$-added composition to make HA into fluorapatite (FA) is also prepared for comparison. The samples without $MgF_2$ show ${\alpha}$ & ${\beta}$-tricalcium phosphates (TCPs) and $Al_2O_3$ phases with no HA at either of the sintering temperatures. In the case of $1,350^{\circ}C$, a $CaAl_4O_7$ phase is also found. Densification values are 69 and 78 %, and strengths are 156 and 104 MPa for 1,300 and $1,350^{\circ}C$, respectively. Because the decomposition of HA produces a $H_2O$ vapor, fewer large pores of $5-6{\mu}m$ form at $1,300^{\circ}C$. The $MgF_2$-added samples show FA and $Al_2O_3$ phases with no TCP. Densification values are 79 and 87 %, and strengths are 104 and 143 MPa for 1,300 and $1,350^{\circ}C$, respectively. No large pores are observed, and the grain size of FA ($1-2{\mu}m$) is bigger than that of TCP ($0.7{\mu}m{\geq}$) in the samples without $MgF_2$. The resulting $TCP/Al_2O_3$ and $FA/Al_2O_3$ composites fabricated in situ exhibit strengths 6-10 times higher than monolithic TCP and HA.
하정수(Jung-Soo Ha),이건명(Gun-Myung Lee) 한국기계가공학회 2017 한국기계가공학회지 Vol.16 No.6
This study analyzed air suspension seat frame structure and vibration for 50 180 kg mass driver to obtain optimum seat design parameter values for the equivalent spring constant and damping coefficient. Various air suspension seat frames were designed following WTS-003 and KS B 6839 standards, and then evaluated using finite elements analysis. Resonance and vibration tests were performed according to the 78/764/EEC standard.
방정수(Jung Soo Bang),김영(Young Kim),박성춘(Sung Choon Park),하영수(Young Soo Ha) 대한두개저학회 2015 대한두개저학회지 Vol.10 No.1
Pleomorphic Xanthoastrocytoma is rare astrocyic neoplasm(WHO Grade II - III) of brain, accounting for less than 1% of all astrocytomas. PXAs are typically affects adolescent and young adults ; almost two-thirds of patients are under the age of 18 at initial occurrence. PXAs is generally located superficial cortically location, so the most common symptom is longstanding epilepsy. Despite its striking cellular appearance, PXAs has a favorable prognosis totally excised We report case of PXA, a 49-year-old male patient without long standing epilepsy. And we have reviewed imagings & histopathologic findings of PXAs
순환잔골재의 수분공급에 의한 고강도 콘크리트의 자기수축 저감
하정수 ( Ha Jung-soo ),김한식 ( Kim Han-sic ),조현준 ( Cho Hyun-jun ),이영도 ( Lee Young-do ) 한국건축시공학회 2017 한국건축시공학회 학술발표대회 논문집 Vol.17 No.2
This study aims to achieve an enhancement in the quality of high strength concrete through a reduction in autogenous shrinkage by supplying the moisture needed for hydration through recycled aggregates that retain high amounts of moisture. The result showed that, moisture supply increased with the higher replacement rate, autogenous shrinkage dropped by up to 60 percent. Also, compressive strength was increased by up to 10 percent.
간척지 기상조건에서의 온실 내부 공기유동 및 환기효율 분석
하정수 ( Jung-soo Ha ),이인복 ( In-bok Lee ) 한국농공학회 2013 한국농공학회 학술대회초록집 Vol.2013 No.-
Development of a large scale of farming region on reclaimed land has been increasing with the purpose of stable production of flower and crop by the demand of large consumption. So it needs a comprehensive technical development for greenhouse design which is suitable for specific climate of reclaimed land and able to cope with the climate change. At the present in Korea, the standard design of greenhouse is not appropriate to apply because it was suggested many years ago and is not proper for today's climate. Among the standard, a heat balance equation for ventilation requirements coming from Japan at 1960s has been used but there is some ambiguous part on the application to Korea's greenhouse design. Therefore, it is necessary to upgrade a technique of greenhouse built on reclaimed land. In this study, a proper ventilation design of greenhouse was studied through the analysis of internal airflow and ventilation efficiency according to the various environmental conditions. A program of CFD(Computational Fluid Dynamics) was used to make a greenhouse airflow simulation model and did a comparison analysis for validation of two results which are CFD simulation, PIV(Particle Image Velocimetry) and wind-tunnel test. Single even span type of greenhouse was used to validate the results. To induce the proper design of CFD model with high accuracy, mesh size, turbulence model and laminar zone to maintain a wind profile were considered based on the results of validation test. It was validated with velocity distribution on specific lines in the middle of greenhouse. From the computed results, the R<sup>2</sup> values were 0.99, 0.99 in case of the side opening case each external velocities(1m/s, 1.5m/s) and its RMSE values were 0.08, 0.24. At side-roof opening case, R<sup>2</sup> values 0.98, 0.98, RMSE values 0.29, 0.50 were calculated. It has been studied to make a proper simulation model from validation results and evaluate the airflow, natural ventilation and ventilation requirements at various greenhouse types and environmental conditions.