Read aloud as f prime c, it is the compressive strength the structure is designed around, such as 4,000 psi at 28 days. Strength tests pass when the average of any three consecutive tests meets f'c and no single test falls more than 500 psi below it, or more than 10 percent below when f'c exceeds 5,000 psi. The plant designs to a higher required average strength so the mix clears those rules with margin.
f'c is 5,000 at 56 days on this job because of the slag, so nobody panic over the 28-day breaks.
Also heard as
- f prime c
- specified strength
- design strength
Related terms
Compressive strength
The crushing load concrete can carry per unit area, the main property specified and tested for concrete.
Cylinder
A cast concrete test specimen, usually 4 by 8 in or 6 by 12 in, crushed to measure compressive strength.
Break
A cylinder strength test result, or the crushing of cylinders in the lab.
Mix design
The recipe for a concrete mix: the weights of cement, SCMs, water, aggregates and admixtures per cubic yard.
Core
A cylinder of hardened concrete drilled out of a structure to test its strength or inspect its condition.