STRUCTURAL DEGRADATION OF TOBERMORITE DURING VIBRATORY MILLING

Mechanochemistry of hydrothermally prepared Al-free and Al-substituted 1.1 nm tobermorite was studied using Si-29 NMR, XRD, and TGA-DTA, Tob ermorite has a double-chain structure and Al/Si substitution occurs pr eferentially at bridging tetrahedra, By using the vibration mill, both tobermorites were observed to decompose as a function of milling time to form amorphous C-S-H-like phases, The decomposition rate was highe r for the Al-substituted tobermorite. The decomposition process occurs mainly at the bridge portion of the silicate double chain. In the Al- substituted tobermorite, the breakage seems to occur preferentially at the points where Al has replaced Si, On heating the amorphous C-S-H-l ike phase, wollastonite is formed. However, no decrease was observed a t the wollastonite formation temperature.