Abstract
To clarify the formation mechanism of tobermorite（5CaO・6SiO2・5H2O）, one of the crystalline calcium silicate hydrates, we have investigated the formation of tobermorite during hydrothermal processing by in situ X-ray diffraction analysis using high-energy X-rays from a synchrotron radiation source and 29Si and 27Al solid state NMR. Specifically, the effects of γ-Al2O3 and gypsum addition on tobermorite formation were studied. Acceleration of tobermorite formation by γ-Al2O3 and gypsum addition was clearly observed. Al3＋ ion suppressed quartz dissolution, and SO42－ ion increased the concentration of Ca2＋ ion in the liquid phase. Consequently, higher Ca/Si ratio in the liquid phase kept an average chain length of Si-tetrahedron in the C-S-H structure a low level, and obstructed formation of the cross link of the chains. And the structural changes of the C-S-H by addition of Al3＋ and SO42－ ions were clearly observed. The tobermorite formation mechanisms in these systems were also examined.
