Abstract
This paper investigates hydrothermal synthesis of calcium silicate hydrates by using of cenosphere to find how to use cenosphere beneficially. Cenosphere is lightweight hollow sphere particle which is included in fly ash. The cenosphere in this study is collected from disposal water pool of coal ash in Japan where cenosphere float at the top. Then the cenosphere was dried and sifted through 425（μm）sieve. The density of cenosphere was about 0.76（g/cm3）and median particle size was 127（μm）. Chemical composition of cenosphere was as same as that of ordinary fly ash in Japan. Cenosphere was composed by glass（67.1％）and mullite（26.2％）mainly. The amount of α-quartz in cenosphere（2.4％）was much smaller than fly ash. About hydrothermal reaction in Ordinary Portland Cement - silica powder system containing cenosphere, the density of hardened samples could be controlled by the amount of cenosphere and water. The density of samples with cenosphere 40mass％ - 60mass％ was from 0.60（g/cm3）to 0.84（g/cm3）, and at that time the range of compressive strength of samples was from 6.5（N/mm2）to 15.6（N/mm2）. The surface of cenosphere was reacted and generation of dense reaction layer was observed, however the surface was remained firm. Thickener prevented levitation of cenosphere effectively and enabled synthesis of nearly homogeneous hardened samples with no material segregation.
