[EN] The fly ashes are incorporated to the portland cement and concrete as active additions, due to their capacity for reacting with the lime, principally originated during the hydration of the portland cement, and forming hydraulic compounds. In this paper a study of the evolution of the fly ash - calcium hydroxide reaction by the time, is presented. Ten fly ashes from Spanish power stations are selected. They are different in the original coal, chemical composition, … No previous treatment (sieving, grinding, …) had been made on the fly ashes. The study of the behaviour of every fly ash with the lime are carried out by a chemical test at several ages. With the use of the instrumental technique, X-ray diffraction and infrared absorption spectroscopy, it has been verified the disappearance of existent mineralogical components in the original samples as well as the formation of compounds coming from the fly ash - lime reaction (hydrated calcium aluminates, …). The effect of the CaO content of the fly ash is observed.

Peer reviewed