Core sample
A cylinder of hardened concrete drilled directly out of the finished structure and tested, used to evaluate the concrete actually in place rather than a molded specimen.
What does core sample mean?
Coring is the tiebreaker when cylinder results are disputed, when curing was questionable, or when a structure's condition must be assessed years later. Core strengths are typically lower than cylinder strengths from the same concrete because of drilling damage, in-place curing, and geometry effects, and evaluation accounts for this. Cores also reveal thickness, consolidation quality, and reinforcement position.
In practice
Coring a slab is destructive and expensive, so it is a last resort after the paperwork and the field cure conditions have been reviewed.