Abstract:
Alkali–aggregate reactions have been known for decades although the acceptance of their occurrence has been delayed
in some countries until the 1990s. Potential reactivity has been identified in most of the rock types used as aggregates
around the world. The most common reactive rocks are sedimentary (e.g. opaline sandstone) and metamorphic (e.g.
gneiss). However, igneous rocks such as granites have also proved to be reactive in some areas and innocuous in many
other regions. It has been concluded that the designation is not enough to label a rock as reactive and that microstructure
is very often the determinant factor of reactivity. In the present study a summary ismade on the state-of-the-art on alkali–
aggregate reactions. Emphasis is given on the identification of potentially reactive aggregates based on petrographic
methods. Examples from a large number of samples analysed in the scope of a research project are presented.
