Petrographic examination is useful for identifying aggregates that are susceptible to alkali-aggregate reactions, lack freeze-thaw durability, are soft or incompetent, have deleterious coatings or excessive fines, and more. DRP has extensive experience with aggregate QA/QC for use in concrete or other cement-based materials following procedures described in ASTM C295, Guide for Petrographic Examination of Aggregates for Concrete. We have done petrographic examination on aggregates from all over North America, Central and South America, Asia, and scattered Pacific Islands.
You have to love them. Granitic aggregate fresh from the Colorado Front Range.
Cross-polarized reflected light photomicrograph of thin section of a beautiful basalt.
Cross-polarized transmitted light photomicrograph of thin section of chalcedonic chert, which is often highly susceptible to alkali-silica reaction.
Cross-polarized photomicrograph of microcracks (green & yellow arrows) in concrete affected by alkali-carbonate reaction. Red arrows highlight deposits of brucite in voids.
Photograph of a popout and staining from pyrrhotite in the coarse aggregate. The concrete showed evidence of sulfuric acid attack near the reactive particle.
Photograph of an absorptive limestone particle that caused cracking (arrows) and popouts in an airfield pavement.