Supplementary cementitious materials (SCMs) enhance early hydration of cement through the
provision of nucleation sites for the precipitation of hydration products. This effect contrasts
with the dilution effect of the mineral addition to the cementitious system. In fact, the net
effect on heat release during the first hours of hydration is the reduction of peak intensity.
Then, only when the specific heat is evaluated in terms of cement weight the actual effect of
the admixture on hydration may be assessed. In this sense, a clear difference may be expected
in accordance with the replacement ratio and fineness of the SCM. Increased specific surface
favors nucleation and it therefore enhances hydration. In this paper, cement pastes admixed
with slag, limestone and fly ash in three different fineness levels and three replacing ratios
were investigated through isothermal calorimetry. The filler effect of each SCM was in
relation with the fineness and replacing ratio, with higher impact on the aluminate reaction
than on the silicate reaction of cement
