The material used in this study is a flint-type reactive aggregate coming from the north of France. The
aggregate described by Bulteel [8] has the following characteristics. The flint aggregate comes from siliceous
concretion of biochemical origin, precipitates from the start of diagenesis in chalky deposit still
uncemented. After alteration and dissolution of chalk, these flint nodules have been accumulated on the valley
bottom or on a coastal bar. This material is currently used as aggregate, especially for concrete. This
aggregate was crushed to 0.16–0.63 mm. X-ray fluorescence examination gives a composition close
to 99% SiO2 (Table 1) and X-ray diffraction detected only quartz lines in this aggregate. Elements other than
Si have not been studied. The flint crystal lattice has been characterised by crossed polarisation 29Si solid
state NMR spectroscopy [9]. This crystal lattice constitutes SiO2 Q4 tetrahedra and Q3 SiO5/2H
bsilanolQ tetrahedra. The Q3 mole fraction measured by thermogravimetry is close to 0.07.
The mineralogy of the flint aggregate is determined by optical microscopy. The preparation of the thin
sections is carried out on a (6.3–8 mm) size distribution of the aggregate obtained after crushing. These thin sections are observed by optical microscopy in trans-