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This study concerns the effect of two types of fly ash and the addition of lime Aon the strength development and hydration of sodium hydroxide- and sodium silicate-activated slag/fly ash Ablends which consisted of 50% fly ash and 50% slag by mass. Performance was compared to that of 100% slag cements. AWhen NaOH was used as an activator, the slag replacement with ASTM Type F fly ash did not show a Asignificant effect on either the strength development or hydration: Type C fly ash did not affect the strength Adevelopment, but affected the hydration process due to the presence of C3A in the fly ash. Both fly ashes had a Asignificant effect on the hydration and strength development when Na2SiO3 was used as an activator. The addition of a sAmall amount of hydrated lime significantly increased the early-age strength but slightly decreased the Alater-age strength of the activated slag/fly ash blends. Measurement of the heat evolution during hydration indicated that Athe addition of the hydrated lime had a slight effect on the hydration during the pre-induction period, but Aaccelerated the hydration thereafter.