1. Alkali-reaction mechanism

1.1 Different types of reaction

Taken as a whole, these reactions are a response by the minerals making up the aggregates (which were in a pH environment of around 7 prior to extraction) to an imbalance with the concrete environment, which often has a pH of over 13. These are solid-liquid chemical reactions in which the solid phase is constituted by the aggregates and the liquid phase by the highly alkaline interstitial solution of the concrete. These reactions are characterized by the fact that the reactive part of the aggregates is usually small and irregularly distributed, and that the aggressive solution contained in the material's microporosity is heterogeneously distributed. We can therefore assume that the deterioration observed on structures is the average result of the localized...