Hydration of high alumina cement-silica fume composite with addition of Portland cement or sodium polyphosphate under hydrothermal treatment

摘要

Various hydrothermal curing regimes were used to investigate the hydration and physical characteristics of two kinds of inorganic binder composites: high alumina cement-silica fume-Portland cement and high alumina cement-silica fume-sodium polyphosphate. Simultaneous thermal analysis (DTA and TG) was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Two kinds of products are formed. The first ones consist of C_3AH_6, AH_3, calcium carbonate (C-C) as a product of carbonation, and C_3AH_(1.5) resulted from the partial decomposition of C_3AH_6 under higher hydrothermal pressure. The second ones are the products formed by acid-base reaction between monocalcium aluminate and sodium polyphosphate to form NaCaPO_4·xH_2O and Al_2O_3·xH_2O that could convert to chemically bonded ceramic binders like hydroxyapatite (Ca_5(PO_4)_3OH) and gibbsite (Al(OH)_3). These two hydroceramic products formed under these conditions act also as binder and could be useful as cement binders for the protection of petroleum, gas, or geothermal wells. Mercury intrusion porosimeter was used for the estimation of the pore structure parameters of the composites. It turned up that longer curing time coupled with higher hydrothermal pressure has improved the pore structure of the first composite, while that of the second has remained unchanged.