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Suh, Heongwon,Jee, Hyeonseok,Kim, Jihoon,Kitagaki, Ryoma,Ohki, Shinobu,Woo, Seungmin,Jeong, Keunhong,Bae, Sungchul Elsevier 2020 Construction and Building Materials Vol.235 No.-
<P><B>Abstract</B></P> <P>This study investigates the effects of rehydration conditions (different hydration durations at 20 °C/60% relative humidity (RH) and in water) on the mechanical and atomic structural recovery of cement paste heated to temperatures of 200, 500, 800, and 1000 °C. Variations in the mass, bulk density, compressive strength, and surface morphology of the paste due to heating and rehydration were characterized. In addition, variations in the hydration products and the mean chain length (MCL) of calcium silicate hydrates (C-S-H) in the pastes due to heating and rehydration were analyzed using X-ray diffraction and <SUP>29</SUP>Si solid-state nuclear magnetic resonance spectroscopy (<SUP>29</SUP>Si NMR), respectively. The compressive strength of the cement paste heated up to 500 °C recovered much more when the paste was placed in water while hot and water-rehydrated for 24 h than when it was rehydrated at 20 °C/60% RH. This mechanical recovery could be induced by accelerated hydration, which results in the formation and enhanced silicate polymerization of C-S-H. <SUP>29</SUP>Si NMR analysis further indicated that the mechanical recovery of cement paste was correlated linearly with the increase in the MCL of C-S-H. In contrast, no mechanical recovery was observed in the cement pastes heated at 800 °C and 1000 °C after rehydration due to the decomposition of C-S-H.</P> <P><B>Highlights:</B></P> <P> <UL> <LI> Effects of rehydration on the mechanical recovery of heated OPC pastes were studied. </LI> <LI> Rehydrating in water while hot recovered the OPC paste after heating up to 500 °C. </LI> <LI> The mechanical recovery of OPC pastes was linearly correlated with MCL of C-S-H. </LI> </UL> </P>
Heesup Choi,Hyeonggil Choi,Myungkwan Lim,Masumi Inoue,Ryoma Kitagaki,Takafumi Noguchi 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.1
In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.
A Novel Wilms Tumor 1 (WT1) Target Gene Negatively Regulates the WNT Signaling Pathway
Kim, M.S.,Yoon, S.K.,Bollig, F.,Kitagaki, J.,Hur, W.,Whye, N.J.,Wu, Y.-P.,Rivera, M.N.,Park, J.Y.,Kim, H.-S. The American Society for Biochemistry and Molecula 2010 The Journal of biological chemistry Vol.285 No.19