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Effect of Mixing and Placing in Hot Weather on Hardened Concrete Properties
Suyun Ham,Taekeun Oh 한국콘크리트학회 2013 International Journal of Concrete Structures and M Vol.7 No.2
Portland cement concrete exposed to high temperatures during mixing, transporting, casting, finishing, and curing can develop undesirable characteristics. Applicable requirements for such the hot weather concrete differ from country to country and government agencies. The current study is an attempt at evaluating the hardened properties of the concrete exposed to hot weather in fresh state. First of all, this study reviews the current state of understanding and practice for hot weather concrete placement in US and then roadway sites with suspected hot weather concrete problems were investigated. Core samples were obtained from the field locations and were analyzed by standard resonance frequency analysis and the boil test. Based on the results, there does not appear to be systematic evidence of frequent cracking problems related to high temperature placement. Thus, the suspicious deteriorations which are referable to hot weather concreting would be due to other factors.
Viscoelastic Properties of Fresh Cement Paste to Study the Flow Behavior
Choi, Myoungsung,Park, Kyoungsoo,Oh, Taekeun Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3
During concrete pumping, the migration and redistribution of particles occur in a pipe and the lubrication layer that forms between the bulk concrete and the pipe wall is the governing factor determining the flow behavior. In order to identify flow behavior of pumping, in this study, the viscoelastic properties related to the microstructural behavior of a flocculated suspension were examined by using dynamic oscillatory measurements. Cement paste is assumed to be a constituent material of the lubrication layer and ten cases of mixing design are employed by changing the proportions of mineral admixtures. The relationship between the yield stress obtained from the steady shear test and the dynamic modulus resulted from the oscillatory shear measurement was derived and the implications of the correlation are discussed. Moreover, based on the investigation of the viscoelastic properties with oscillatory measurements, the initial behavior of pumped concrete was analyzed systematically.
Viscoelastic Properties of Fresh Cement Paste to Study the Flow Behavior
Myoungsung Choi,Kyoungsoo Park,Taekeun Oh 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.3
During concrete pumping, the migration and redistribution of particles occur in a pipe and the lubrication layer that forms between the bulk concrete and the pipe wall is the governing factor determining the flow behavior. In order to identify flow behavior of pumping, in this study, the viscoelastic properties related to the microstructural behavior of a flocculated suspension were examined by using dynamic oscillatory measurements. Cement paste is assumed to be a constituent material of the lubrication layer and ten cases of mixing design are employed by changing the proportions of mineral admixtures. The relationship between the yield stress obtained from the steady shear test and the dynamic modulus resulted from the oscillatory shear measurement was derived and the implications of the correlation are discussed. Moreover, based on the investigation of the viscoelastic properties with oscillatory measurements, the initial behavior of pumped concrete was analyzed systematically.
Lee, Young Hak,Oh, Taekeun Hindawi Limited 2016 Advances In Materials Science And Engineering Vol.2016 No.1
<P>The traditional P-wave ultrasonic measurement has been used for the condition assessment of general reinforced concrete structures for a long time, but the effects of prestressing applied to concrete structures such as long-span buildings and bridges on ultrasonic pulse velocity have not been studied clearly. Therefore, this study analyzed the statistical distribution of P-wave ultrasonic pulse velocities in reinforced and prestressed concrete slabs of 3000 × 3000 mm with a thickness of 250 mm. In addition, we measured S- and R-waves to identify experimental consistency by statistical analysis using the Kolmogorov-Smirnov goodness-of-fit test. The experimental results show that the P-, S-, and R-wave velocities increased slightly (2-3%) when prestressing was applied. As expected, the S- and R-wave measurements show better statistical reliability and potential for in situ evaluation than the P-wave because they are less sensitive to confinement and boundary conditions. The experimental results in this study can be used when assessing the condition of prestressed concrete structures through the velocities of elastic waves.</P>
Evaluating the Dynamic Elastic Modulus of Concrete Using Shear-Wave Velocity Measurements
Lee, Byung Jae,Kee, Seong-Hoon,Oh, Taekeun,Kim, Yun-Yong Hindawi Publishing Corporation 2017 Advances In Materials Science And Engineering Vol.2017 No.1
<P>The objectives of this study are to investigate the relationship between static and dynamic elastic moduli determined using shear-wave velocity measurements and to demonstrate the practical potential of the shear-wave velocity method for in situ dynamic modulus evaluation. Three hundred 150 by 300 mm concrete cylinders were prepared from three different mixtures with target compressive strengths of 30, 35, and 40 MPa. Static and dynamic tests were performed at 4, 7, 14, and 28 days to evaluate the compressive strength and the static and dynamic moduli of the cylinders. The results obtained from the shear-wave velocity measurements were compared with dynamic moduli obtained from standard test methods (P-wave velocity measurements according to ASTM C597/C597M-16 and fundamental longitudinal and transverse resonance tests according to ASTM C215-14). The shear-wave velocity measured from cylinders showed excellent repeatability with a coefficient of variation (COV) less than 1%, which is as good as that of the standard test methods. The relationship between the dynamic elastic modulus based on shear-wave velocity and the chord elastic modulus according to ASTM C469/C469M was established. Furthermore, the best-fit line for the shear-wave velocity was also demonstrated to be effective for estimating compressive strength using an empirical relationship between compressive strength and static elastic modulus.</P>
( Myoung Jin Ji ),( Hyun Jeong Jeon ),( Taekeun Oh ),( Sung Soo Koong ),( Hyung Jin Choi ) 대한내과학회 2014 대한내과학회 추계학술대회 Vol.2014 No.1
Background: Adiponectin, an adipokine secreted by differentiated adipocytes, plays pivotal roles in the regulation of insulin action and metabolisms of glucose and lipids. It has anti-atherogenic properties and reduced serum adiponectin levels are associated with cardiovascular disease(CVD). This study investigated the association between adiponectin 45 T/G polymorphism and diabetic cardiovascular complications in Korean type 2 diabetes. Methods: Total of 758 Korean type 2 diabetic subjects from the Endocrinology clinic of Chungbuk National University Hospital were investigated. Cardiovascular complications were assessed according to the available medical records. All subjects were genotyped for the Adiponectin 45T/G polymorphism using the polymerase chain reaction- restriction fragment length polymorphism (PCR-RfiP) technique. Results: The prevalence of CVD was signifi cantly higher in the subjects with GG+TG genotype compared to those with TT genotype (17.5% vs. 9.8%, p=0.002). The prevalence of any other macrovascular complications, such as stroke, peripheral artery disease were not different according to the Adiponectin 45T/G genotype. Conclusions: Our fi ndings suggest that Adiponectin 45T/G polymorphism is associated with diabetic cardiovascular complication in type 2 diabetes. Adiponectin genotype could be used as a susceptibility marker to predict the risk of diabetic cardiovascular complication.
NATM 터널 굴진 시 안전관리를 위한 재해영향요인 및 중요도에 관한 연구
이영수,윤영근,오태근,Lee, YoungSoo,Yoon, Younggeun,Oh, Taekeun 국제문화기술진흥원 2022 The Journal of the Convergence on Culture Technolo Vol.8 No.6
In the NATM tunnel construction method for urban subway and underpass construction, various causes of disaster exist. In this study, in order to analyze the importance of disaster influencing factors during NATM tunnel excavation, the possible risk factors were analyzed through prior research such as drilling, charging and blasting, It was divided into the work items of wrinkle treatment, pumice cleanup, and support materials. Next, the final 21 detailed measurement indicators were selected through the FGI survey of related experts, and AHP (Analytic Hierarchy Process) analysis were conducted. As a result, it was found that the workers involved in the tunnel construction were the most influential disaster influencing factor.