Evaluation of the alkali–silica reactivity potential of sands

The alkali–silica reactivity potential of 20 different Quaternary natural aggregates (sands and gravels) from the Czech Republic has been evaluated by petrographic and dilatometric methods. Petrographic techniques, both qualitative (optical and scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) microscopy of thin sections) and quantitative (petrographic image analysis of thin sections), have been applied for the disused specimens. The dilation of the mortar-bar test specimens (according to ASTM C1260) ranged nine samples to the non-reactive, nine samples to reactive and two samples to potentially reactive categories. These categories, based on the dilation values, do not however satisfactorily correlate to the volumes of individual groups of aggregates identified petrographically in mortar-bars. More detailed petrographic examination showed the subdivision according to the presence/absence of deformation sings inhibitors and/or grain size. These results show that the optical microscopy of mortar-bar specimens provides detailed identification of alkali reactive samples according to their spatial relationship with ASR products. The same approach also allows direct identification of gels and alkali–silica reactive fragments.