The silica dissolution degree involves the formation
of the bexternal C–S–H and/or C–K–S–H
gelsQ generally observed but the aim of this study is
to establish the consequences inside the flint
aggregate. The observations by optical microscopy
or SEM show alteration faces with the appearance
of pseudomorphosis zones in the depths of grains.
When the degradation increases, these zones grow
larger after the grains are corroded. The development
of pseudomorphosis zones corresponds to the
increase of Q3 sites [9] which is responsible for
amorphization of the flint aggregate. It is the mineralogical transformation of the flint aggregate
from crystalline to amorphous phases. This result
has led to the hypothesis of the structural swelling
of the flint aggregate to explain the expansion origin
[8,11]. The observation of different alteration stages
of grains for the same degradation time reveals the
heterogeneous behaviour of the flint aggregate
towards the alkali–silica reaction.