Effect of quartz content on the nature of Al-substituted 11 A tobermorite in Ahydrothermally treated CaO-AI2O3-SiO2-H2O systems

Lime-meta kaolin quartz mixtures containing varying amounts of quartz were Aprepared and hydrothermally cured at 180 C. The nature of hydration products with reaction time was studied using Aa combination of solid-state 27 Al MAS NMR, XRD, DTA-TGA, SEM and wet chemical techniques. Hydrogarnet always Apreceded Al-substituted II A tobermorite irrespective of the amount of quartz used and supplied most, if not Aall, of the Al to form Alsubstituted II A tobermorite. The availability of silicate anions from quartz Awas an important factor inproviding a sink for the Al species to be in tetrahedral coordination, it also offered a Ameans for controlling the extent of Al substitution into the 11 A tobermorite crystal lattice with reaction time and Athe extent of breakdown of the hydrogarnet. The growth of hydrogarnet was inhibited with increasing amounts of Aquartz, while the formation of Al-substituted II A tobermorite was accelerated. With increasing amounts of Aquartz, the crystallite size in the cdirection of Al-substituted II A tobermorite decreased and a change in its Amorphology was evident from platelets to aggregated petal-like, fine crystals.