Alkali-aggregate reaction-identifying reactive silicates in complex aggregates by ESEM observation of dissolution features

In general, quartz is the most reactive mineral in both aggregates. Feldspar, biotite and chlorite exhibit dissolution phenomena, and liberate alkalis and calcium. Various morphological types of gels are formed as precipitates on the polished surface: thin calcium silicate hydrate structures exhibiting card house morphology; small agglomerates (2-20 μm) with a smooth surface; and large agglomerates (20-500 μm) characteristic of common ASR reaction products. These gels mainly consist of Si and Ca with variable amounts of Na, Mg, Fe and Al.