The kinetics of portlandite production (Fig. 4) was different for
the two pastes: while the portlandite content of the reference
paste increased continuously over time, it stopped increasing when
andesite was present and reached a plateau after 7 days. The difference
(D) between the two curves characterized the consumption of
portlandite by andesite silica, counteracting its production due to
the hydration of C2S and C3S. This could be interpreted as a sign
of a pozzolanic activity.