This observation of external surfaces shows alteration
of the flint aggregate increasing with the reaction degree. At the beginning of the reaction, after 14 h degradation, observation shows a small proportion
of altered grains (Fig. 6). Enlargement of a grain
which begins to be degraded presents an irregular
aspect (Fig. 7). After 48 h degradation, the alteration
increases and appears as a more and more perturbed
evolution of faces (Fig. 8). Enlargement of an altered
grain shows that the surface is more irregular as if
corroded with the opening of the microporosity (Fig.
9). Fig. 8 also shows the coexistence between
unaltered and altered grains. A heterogeneity of
aggregate behaviour towards the reaction is noted
because all the grains do not react at the same rate
during the degradation. At the end of the reaction,
almost all the grains are altered, often with a high degradation level. Fig. 10 shows a very altered grain. Fig. 11 reveals a completely crumbled surface