Activation of the fly ash pozzolanic reaction by hydrothermal conditions

The effect of hydrothermal treatment on the pozzolanic reaction of two kinds of Spanish fly ashes from coal combustion (ASTM class F) is discussed. Characterization of the compounds formed as a result of hydrothermal treatment and the changes provoked in the starting fly ashes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared (IR) spectroscopy. α-C2SH, CSH gel, different solid solutions of katoites (the cubic crystallographic variety of hydrogarnets series (C3ASH4)) and a mixed oxide (CaFe2O4) were formed depending on the kind of fly ash. The hydrated compounds are precursors of a new kind of low-energy cement called fly ash belite cement (FABC); besides, they have potential properties to intercalate toxic ions and therefore can be used as immobilization systems of these ions.The authors are thankful for the financial support of the CICYT (project no. MAT 95-0054) and the Power Station of Soto de Ribera and Velilla de Rio Carrion for the fly ash supplied.Peer reviewe