A microscopical examination performed by an experienced concrete petrographer can provide information into whether a defect is a sign of serious problems, and how future defects can be avoided. Such examinations include observations of the overall condition of the concrete, composition and condition of the aggregate particles, occurrence and extent of cement paste-aggregate reactions, characteristics of cement paste, strength of the paste-aggregate bond, and parameters of the air-void system.
A petrographic examination can tell you if the concrete was adequately proportioned, adequately mixed, suitably compacted, and adequately finished and cured. Air-void parameters can be quantitatively determined. Microscopical observations can determine if the cement is properly hydrated, estimate the water-cement ratio, detect the presence of absence of fly ash or slag, and detect the presence or absence of reactions between aggregates and cement paste.
When submitting samples to a testing lab for petrographic examination, use samples that represent the problem. An ideal sample is a full-thickness core with at least a 2-inch diameter. If possible, also provide some samples from areas that do not show the problem.