REACTION MECHANISM OF THE HYDROTHERMALLY TREATED CAO-SIO2-AL2O3 AND CAO-SIO2-AL2O3-CASO4 SYSTEMS

摘要

Mixtures of CaO, amorphous SiO2 and kaolinite in the presence or absence of SO42- ions (added as CaSO4 .2H2O) were treated in suspension under hydrothermal conditions at temperatures of 80-200 degrees C. Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO2 mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO42- ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A* system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and a-C2SH by increasing the autoclaving temperature. In the C-S-A-CS system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-aluminate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, alpha-C2SH and anhydrite II are formed. In both systems the excess Al2O3 appeared as a hydrogarnet phase, C(3)ASH(4). [References: 22]