Introduction
The aim of this petrographic study is to have a better knowledge of the alteration faces and improve understanding of the mechanism by a description of the attack mode of alkali–silica reaction (ASR). The new chemical method development allows a quantitative measurement of the specific degree of ASR[9]. This method uses a chemical concrete subsystem: model reactor, involving the main ASR
reagents: flint aggregate, portlandite and KOH. The model reactor allows us to obtain higher reaction
degrees and thus to reveal the degradation mechanism. The measured reaction degrees are the degree
of silica dissolved and the Q3 site content, but these values are global. After different treatments, petrography on the altered flint aggregate from the model reactor allows a more accurate description of
the degradation on a grain level.