Three concretes from structures damaged by alkali aggregate reaction were studied. They were prepared with different aggregates: sandstone, granite (in both of them grains of quartz showed signs of deformation) and the third one mainly constituted by vulcanites. Thin cuts from concretes were analyzed with the petrographic microscope. Zeolites were identified as the main reaction product. They present the same optical characteristics in the three cases. Zeolites correspond to the group of clinoptilolite-heulandite (by XRD). They were also observad at SEM and analyzed by EDAX.