High-calcium fly ash as the fourth constituent in concrete: problems, solutions and perspectives

Abstract

Even though Hellenic high-calcium fly ashes of different origin are widely used by the cement industry for the production of several CEM II types of cements according to EN 197-1, their systematic use in concrete still presents some difficulties. This inhibits the establishment of specifications for their addition. Main problems concerning the quality are focused on variations in chemical and mineralogical composition, necessity for supplementary grinding, high proportion of free-CaO and periodically high proportion of SO3 content. These problems as well as the solutions, for every day use by the concrete industry, applied during the construction of a dam, are discussed, in this paper. To overcome these problems, untreated fly ash was cheaply upgraded by grinding at a specially designed ball mill, with simultaneously hydration, for the reduction of free-CaO. Details also (i) for fly ash variations in relation to their origin, (ii) the grinding plant and (iii) the industrial production of fly ash, are given. Finally, in a separate chapter of this paper, aiming to explain the treatment of fly ashes followed during their industrial production, data of the mechanical strength of mixtures of cements incorporating fly ashes with different treatment, concerning their free-CaO and their fineness, are given. (A) Reprinted with permission from Elsevier.