This study concerns the effect of two types of fly ash and the addition of
lime on the strength development and hydration of sodium hydroxide- and sod
ium silicate-activated slag/fly ash blends which consisted of 50% fly ash a
nd 50% slag by mass. Performance was compared to that of 100% slag cements.
When NaOH was used as an activator, the slag replacement with ASTM Type F
fly ash did not show a significant effect on either the strength developmen
t or hydration, Type C fly ash did not affect the strength development, but
affected the hydration process due to the presence of C(3)A in the fly ash
. Both fly ashes had a significant effect on the hydration and strength dev
elopment when Na2SiO3 was used as an activator: The addition of a small amo
unt of hydrated lime significantly. increased the early-age strength but sl
ightly decreased the later-age strength of the activated slag/fly ash blend
s. Measurement of the hear evolution during hydration indicated that the ad
dition of the hydrated lime had a slight effect on rite hydration during th
e pre-induction period, but accelerated the hydration thereafter.