Chemical Sequence and Kinetics of Alkali‐Silica Reaction Part I. Experiments

The deterioration induced by alkali‐silica reaction (ASR) is initiated by complicated heterogeneous chemical reactions. This study describes the experimental results obtained from the model reactant experiments focused on the kinetics of physical and chemical changes in the reactive aggregate‐simulated pore solution system undergoing ASR. Specifically, the study investigated the products formed by exposing reactive silica mineral (α‐cristobalite) to two alkali solutions in the presence of solid calcium hydroxide [Ca(OH)₂]. The experimental results showed that, as long as the Ca(OH)₂ remains in the system, the dissolution of the silica mineral proceeds at a constant rate and the only reaction product formed is the tobermorite‐type C–S–H. However, once the supply of Ca(OH)₂ in the system is exhausted, the level of dissolved silica ions starts to increase. At the same time, the previously formed C–S–H changes in composition by incorporating silicon and alkali ions from the solution. Continuous increase in the concentration of silica leads to formation of the ASR gel as a result of interaction between silica and alkali ions.