Sample Size Requirements
PETROGRAPHIC EXAMINATIONS OF CONCRETE
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.
AIR-VOID ANALYSIS OF CONCRETE
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.
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