Role of Tobermorite Seeding Crystals on the Rate of Hardening of Autoclaved Calcium Silicate Materials

摘要

Influence, of tobermorite crystals on the rate of hydrothermal reaction of CaO-SiO{sub}2 (quartz) mixtures was investigated. Mixtures of calcium oxide and silica (as the production recipe in sand lime bricks) in the presence and absence of tobermorite crystals were moulded and hydrothermally tested at 10 atmosphere (183℃). Hydration kinetics and physico-chemical properties of the prepared samples were investigated for specimens hydrothermally heated for different autoclaving periods namely: 2,4,6,12 and 24 hours. Mechanical properties were correlated to the rates of development of binding phases (hydration products). The results indicate that addition of tobermorite crystals accelerate the reaction between quartz and lime and enhance the rate of transformation of semicrystalline calcium silicate hydrates to crystalline tobermorite. This leads to an improvement in mechanical properties at short processing time. However, at longer periods there was a decline in mechanical properties due to an increase of the contents of crystalline materials, which were associated with an increase in porosity.