Sample Size Requirements


ASTM C 856 "Standard Practice for Petrographic Examination of Hardened Concrete"

Concrete Cores should be 3 to 4 inches in diameter.  For Horizontal concretes (i.e. slab-on-grade, slab-on-deck, etc.) drill through to the subase; for Vertical structures (i.e. wall, etc.) drill through the thickness when/where possible. 


If you are investigating a problem or signs of distress, the sample should contain said distress (i.e. take sample from over a crack, delaminated area, scaled area, etc.)

Report will include everything about:

(a) the concrete and its components i.e. coarse and fine aggregates, paste, and air-void system, along with if there is any issue with concrete per se;

(b) if there is any evidence of improper placement, consolidation, finishing, and curing techniques;

(c) effect of any potentially deleterious deicing chemicals or ‘salts’ on concrete - only if both concrete and construction practices are found acceptable; and

(d) deleterious or unsound component in the concrete.

  • For Scaling, Spalling, and related Issues - Usually, it is either or a combination of lousy concrete and improper construction practices that cause scaling and other surface distress.  Salt aggravates the problem, unless, a magnesium-based salt is used, in which case salt causes chemical erosion of paste and hence scaling (even in a good concrete).  Salt can also cause scaling if it is used at an early stage, i.e. immediately after the placement in a cold weather construction and/or prior to the attainment of concrete “maturity" (i.e. at least a 4000 psi compressive strength and a period of air drying).

  • For delamination and related issues, it will investigate whether air entrainment and/or finishing practices have contributed to the delamination.

  • For popout, mortar lift-off, staining, discoloration and related issues, it will investigate the material(s) responsible for distress, and their location and abundance in the core. Additional SEM-EDS services may be required for such investigation for additional cost.

Please note, our largest saw can accommodate a maximum of 9 inches.  Therefore, any sample exceeding 9 inches in length will be sectioned for sample preparation.  If sectioning of a sample is necessary the locations of all cuts will be noted in the report.

Example of Ideal Concrete Sample

See the Submitting Samples page for a list of information we request with new projects


ASTM C 457 "Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete"

CMC follows Procedure B (Modified Point-Count Method) of ASTM C 457, which requires a 12 square inch area for examination.   Diameter and length of cores can vary, provided the required surface area will be available.

Examples for Air-void Analysis

Don't See What You're Looking For?

Send us an email describing your project, add a few pictures if you can, and we would be happy to suggest suitable testing and sampling procedures.  Or just give us a Call.