Amorphisation mechanism of a flint aggregate during the alkali–silica reaction: X-ray diffraction and X-ray absorption XANES contributions

Flint samples at different stages of the Alkali–Silica Reaction were prepared and analyzed by X-ray diffraction (XRD) and silicon K-edge X-ray absorption near edge structure techniques (XANES). The results are compared to those of measurements performed on alpha quartz c-SiO2 and rough flint aggregate. The molar fraction of Q3 sites is determined as a function of the time of reaction. Up to 14 h of attack, the effect of the reaction seems of little importance. From 30 to 168 h, we showed an acceleration of the effect of the reaction on the crystal structure of the aggregate resulting in an amorphisation of the crystal. During this period, the amorphous fraction increases linearly with the number of Q3 sites. The results of the XANES confirm the amorphisation of the aggregate during the reaction and show the presence of silicon in a tetrahedral environment of oxygen whatever the time of attack.