ABSTRACT
Reactive silicates which are present in some aggregates can react with the alkaline sodium or potassium oxides produced by the hydration of ordinary Portland cement. This is usually termed alkali-silicate reaction (ASR), but may be known as the alkali-aggregate reaction. It creates a gel around the aggregate, producing an increase in its volume. The effect is uncommon in the UK. The susceptible UK aggregates are of the siliceous type, for example opal.
