IN SITU TIME-RESOLVED X-RAY DIFFRACTION OF TOBERMORITE FORMATION PROCESS UNDER HYDROTHERMAL CONDITION: INFLUENCE OF REACTIVE Al COMPOUND

Hydrothermal formation reaction of tobermorite in the autoclaved aerated concrete (AAC) process has been investigated by in-situ X-ray diffraction. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used. XRD measurements were conducted in a temperature range of 100–190 °C throughout 12 h of reaction time with a time interval of 4.25 min under a saturated steam pressure. To clarify the tobermorite formation mechanism in the AAC process, the effect of Al addition on the tobermorite formation reaction was studied. As intermediate phases, non-crystalline calcium silicate hydrate (C-S-H), hydroxylellestadite (HE), and katoite (KA) were clearly observed. Consequently, it was confirmed that there were two reaction pathways via C-S-H and KA in the tobermorite formation reaction of Al containing system. In addition, detailed information on the structural changes during the hydrothermal reaction was obtained. INTRODUCTION Autoclaved aerated concrete (AAC) is widely used as a building material because of its superior heat-insulation efficiency and fire resistance (Grutzeck, 2005). A typical process for the AAC production includes hydrothermal treatment of a mixture of quartz sand, lime, cement, gypsum, and some other additives at high temperatures (typically, 180–200 °C) under a saturated steam pressure, which results in the formation of crystalline calcium silicate hydrates, namely, tobermorite (Ca5Si6O16(OH)2-4H2O). Since both the quantity and quality of tobermorite formed in the AAC significantly affect the mechanical properties of AAC (Mitsuda et al., 1992), understanding the mechanism of tobermorite formation during the hydrothermal treatment (i.e. autoclave process) is very important in AAC production. 59 Copyright ©JCPDS-International Centre for Diffraction Data 2011 ISSN 1097-0002 60