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Choi M.S.,Korea Institute of Construction Technology | Choi M.S.,Korea Advanced Institute of Science and Technology | Kim Y.S.,Korea Testing and Measurement Group | Kim J.H.,Ulsan National Institute of Science and Technology | And 2 more authors.
Construction and Building Materials | Year: 2014

During concrete pumping, a lubrication layer is formed at the interface between the concrete and the pipe. The pumpability highly depends on the characteristics of this layer. In this study, a method to enhance the pumpability by externally imposing an electromagnetic field on the pipe was suggested and experimentally verified. The electromagnetic field activates the free movement of the water molecules so that the layer is expected to become more slippery. Pumping tests with a 1000 m long pipeline were conducted with and without applying an electromagnetic field. When the electromagnetic field was imposed, the same discharge rate could be obtained with a 30% reduction in the pump pressure, and a 15% increase in the velocity under the same pump pressure was observed. The tests revealed that the imposition of an electromagnetic field was very effective in improving the pumpability. © 2014 Elsevier Ltd. All rights reserved. Source


Shin S.W.,Pukyong National University | Lee J.,Daewoo E&C Co. | Kim J.-S.,Hanwha Research Institute of Technology | Shin J.,Korea Maritime and Ocean University
Smart Structures and Systems | Year: 2016

The stress dependence of ultrasonic wave velocity is known as the acoustoelastic effect. This effect is useful for stress monitoring if the acoustoelastic coefficient of a subject medium is known. The acoustoelastic coefficients of metallic materials such as steel have been studied widely. However, the acoustoelastic coefficient of concrete has not been well understood yet. Basic constituents of concrete are water, cement, and aggregates. The mix proportion of those constituents greatly affects many mechanical and physical properties of concrete and so does the acoustoelastic coefficient of concrete. In this study, influence of the water-cement ratio (w/c ratio) and the fine-coarse aggregates ratio (fa/ta ratio) on the acoustoelastic coefficient of concrete was investigated. The w/c and the fa/ta ratios are important parameters in mix design and affect wave behaviors in concrete. Load-controlled uni-axial compression tests were performed on concrete specimens. Ultrasonic wave measurements were also performed during the compression tests. The stretching coda wave interferometry method was used to obtain the relative velocity change of ultrasonic waves with respect to the stress level of the specimens. From the experimental results, it was found that the w/c ratio greatly affects the acoustoelastic coefficient while the fa/ta ratio does not. The acoustoelastic coefficient increased from 0.003073 MPa-1to 0.005553 MPa-1when the w/c ratio was increased from 0.4 to 0.5. On the other hand, the acoustoelastic coefficient changed in small from 0.003606 MPa-1to 0.003801 MPa-1when the fa/ta ratio was increased from 0.3 to 0.5. Finally, it was also found that the relative velocity change has a linear relationship with the stress level of concrete. © Copyright 2016 Techno-Press, Ltd. Source


Amin M.N.,National University of Sciences and Technology | Kim J.-S.,Hanwha Research Institute of Technology | Dat T.T.,SsangYong Construction | Kim J.-K.,Korea Advanced Institute of Science and Technology
IES Journal Part A: Civil and Structural Engineering | Year: 2010

In this study, we investigate and improve the testing methods for more accurate measurement of the early-age autogenous shrinkage (AS) in concrete. During the first 24 h after casting, the temperature of concrete rises due to hydration heat and causes the simultaneous development of thermal deformation (TD) and AS. Because there is no general agreement on evolution of coefficient of thermal expansion (CTE) in the literature, the most commonly adopted approach of subtracting the TD based on an assumed constant value of CTE results in incorrect values of early-age AS. To avoid such errors, we propose improvements in measuring rig and control of hydration-induced temperature, which serves as an aid in achieving isothermal conditions in concrete specimens right after casting. The validity of the proposed improvements is investigated by performing a series of tests under semi-adiabatic (including TD) and artificially controlled isothermal conditions (excluding TD). Results indicate that the AS calculated from semi-adiabatic tests is significantly underestimated at early ages, which is probably due to considering inaccurate values of CTE at early ages. Therefore, we recommend the incorporation of proposed improvements into existing test methods or that an appropriate method of determining the evolution of CTE be considered. © 2010 The Institution of Engineers, Singapore. Source


Kim J.K.,POSCO | Kim J.-S.,Hanwha Research Institute of Technology | Kwon S.H.,Myongji University
KSCE Journal of Civil Engineering | Year: 2014

A new prestressing strand was recently developed. The objective of this study is to investigate and provide the mechanical properties of the new strand, as these properties are essential in the design and construction of prestressed concrete structures. The experimental program includes a tensile test, a fatigue test, a relaxation test, and a stress corrosion test. In the tensile test, an optimal gripping method was initially determined and the measured ultimate strength was found to be higher the nominal strength of the new strand. The new strand does not exhibit any degradation in its mechanical performance after fatigue loading. Compared to the existing strand with the strength of 1,860 MPa, the new strand also showed equal or enhanced performance in the stress relaxation and the stress corrosion tests. © 2014 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg. Source

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