ABSTRACT
Reaction products observed in concrete structures altered by alkali-aggre gate reactions appear as gels and crystals. They have been characterised by : 1. their localisation around aggregates in cracks and pores of the cement
paste, in veins or cleavage planes inside aggregates and as concrete surface exudation
2. their microstructure as massive or textured gel and rose or lamella crystals 3. their elemental composition containing alkalis, silicium, calcium and minor
elements such as aluminium and iron 4. their coexistence with secondary products like ettringite and carbonates.
