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Kim, Hongseop,Kim, Gyuyong,Lee, Sangkyu,Son, Minjae,Choe, Gyeongcheol,Nam, Jeongsoo Elsevier 2019 Composites. Part B, Engineering Vol.160 No.-
<P><B>Abstract</B></P> <P>The compressive and tensile behavior of fiber-reinforced cementitious composites is significantly affected by the bonding and pull-out properties between matrix and reinforced fiber, as well as the fracture properties of the fibers. In addition, an increase in strain rate according to loading conditions influences the fracture behavior between the fiber and matrix. Steel fiber-reinforced cementitious composites with high flexural and tensile strength, toughness, and crack resistance are widely used in tunnels and plant structures. However, the high specific gravity and stiffness of steel fibers can cause rupture of concrete pump tubes, increase the rebound volume of shotcrete, and decrease durability by corrosion of fiber. Therefore, it is necessary to study the development and application of organic fiber which has similar mechanical properties to steel fiber and does not cause corrosion. In this study, polyamide fibers having the same aspect ratio as the hooked steel fibers, which are widely used as reinforcing fibers for concrete, have been developed. And strain rate effect on the compressive and tensile behaviors of bundle-type polyamide fiber-reinforced cementitious composite and hooked steel fiber-reinforced cementitious composite were evaluated. The results showed that the effect of strain rate over different fiber types influenced the tensile behavior more significantly than the compressive behavior. In polyamide fiber-reinforced cementitious composite (PAFRCC), a fracture behavior of fiber was observed regardless of a strain rate, and the tensile behavior of PAFRCC was influenced more by tensile strength of polyamide fiber itself than a bonding stress between fiber and matrix. In hooked steel fiber-reinforced cementitious composite (HSFRCC), a bonding stress between hooked steel fiber and matrix (frictional force at the interface between fiber and matrix, mechanical bond of the hooked part) influenced the tensile behavior significantly. Fracture properties that straightened pulled out the fiber from the matrix were observed at static tensile loading condition. However, non-straightened hooked steel fiber was observed along with the fracture of matrix due to an increase in mechanical bonding force of the hooked part and the bonding stress between the fiber and the matrix.</P>
Hydration Heat and Autogenous Shrinkage of High-Strength Mass Concrete
Kim, Gyuyong,Lee, Euibae,Koo, Kyungmo Architectural Institute of Japan 2009 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEE Vol.8 No.2
<P>In this study, to evaluate autogenous shrinkage of high-strength mass concrete with specimen size and hydration delay effects, the thermal deformation was calculated using thermal expansion coefficient (TEC) corrected by the maturity method, and was subtracted from measured total deformation. And the properties and relations of hydration heat and autogenous shrinkage at early ages were numerically analyzed. In test and analysis results, hydration temperature is affected by specimen conditions such as size and admixture, and change of hydration temperature could affect autogenous shrinkage; the higher hydration temperature and the greater autogenous shrinkage. There is a close relationship between hydration temperature and autogenous shrinkage at early ages, especially between HHV (hydration heating velocity) and ASV (autogenous shrinking velocity); the higher HHV, the higher ASV and the greater ultimate autogenous shrinkage. The points where hydration temperature and autogenous shrinkage start to increase rapidly are due to the consumption of gypsum in the cement hydration process, and are strongly related to the setting time.</P>
Kim, Gyuyong,Lee, Euibae,Kim, Youngsun,Khil, Baesu Architectural Institute of Japan 2010 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEE Vol.9 No.2
<P>In this study, to reduce the HHV of the high-strength mass concrete at early ages, PCM that could absorb the occurred hydration heat was applied, and the changes of autogenous shrinkage and the relationship between the hydration temperature and autogenous shrinkage were investigated. The addition of the PCM leads to a decrease of the fluidity and an increase of the air content in concrete. The acceleration of the cement hydration process by the PCM leads to an early setting and a higher development of the compressive strength and elastic modulus of concrete at very early ages. The function of PCM could be worked below the original melting point due to the eutectic effect. While the hydration temperature and HHV of high-strength mass concrete can be decreased with the use of the PCM. A close relationship could be found between the hydration temperature and autogenous shrinkage; the higher the HHV, the higher the ASV and the greater the ultimate autogenous shrinkage.</P>
Kim, Gyuyong,Kim, Youngsun,Lee, Taegyu Architectural Institute of Japan 2010 JOURNAL OF ASIAN ARCHITECTURE AND BUILDING ENGINEE Vol.9 No.2
<P>The deformation of building frameworks can lead to critical disasters such as building collapse. Loads, thermal expansion and creep are generally known factors, which cause deformation. High temperature due to fire can also be one of the major factors since concrete deterioration can affect the performance of building structures and eventually can weaken the frameworks. It is, however, difficult to estimate the influence of fire on concrete structures and evaluate the performance of fire resistance design. Many researchers have carried out experiments using small-scale specimens to tackle this issue and it was shown that specimens can reflect the real behavior of structures reasonably well. Nonetheless, it is challenging to achieve uniform temperature rise throughout the specimens while heating the structure as concrete has low thermal conductivity. Many different heating methods were used in recent studies to overcome this problem; however, one cannot compare the results directly to other results due to the variation of the experiment conditions. In this study, therefore, a new heating and loading method was suggested which combines the existing heating systems. Several experiments were carried out to show that a new method can maintain uniform temperature while heating so that the experiment can produce more accurate data.</P>
김규동 ( Gyu Dong Kim ),이승훈 ( Sung Hoon Lee ),김규용 ( Gyuyong Kim ),손유신 ( Yu Shin Sohn ),김한준 ( Han Joon Kim ) 한국건축시공학회 2003 한국건축시공학회 학술발표대회 논문집 Vol.3 No.1
This paper reports the application of high strength concrete designed as 800㎏/㎠ on the columns and belt wall of Tower Palace Ⅲ. The concrete should meet or exceed the requirements of slump of 23cm, σ18H of 100㎏/㎠, σ91th of 800㎏/㎠. The concrete mixings with 4 different domestic Silica fumes were investigated. Laboratory tests, the pilot productions of batcher plant and the full-scale mock up tests were performed. As results of site application, all test results are satisfied with the requirements of columns and belt wall.