Characteristic strength
Characteristic strength is the 28-day compressive strength a concrete grade is set to, the '32' in N32; a statistical value the supplier guarantees, not the average.
Ask Chalkline about this →Characteristic strength is the 28-day compressive strength a concrete grade is specified to, in megapascals (MPa). It is the “32” in N32: a 32 MPa characteristic strength at 28 days. The key point is that it is a statistical value, not the average of the test results. Under AS 1379 it is the strength below which not more than 5% of test results are permitted to fall, so the supplier batches to a higher mean target strength to make sure the characteristic value is reliably met across the natural variability of concrete.
This is why you cannot read a single cylinder break as the answer. One result below the grade number is not automatically a failure, and one result well above it does not mean the mix is over-strength. Acceptance under AS 1379 is judged statistically across a set of results against the characteristic strength, and that is the supplier’s responsibility for the concrete as delivered. What the builder controls, placing, compacting, and curing, can still drop the in-place strength below the characteristic value even when the delivered concrete was compliant.
Specify the grade by its characteristic strength (the engineer’s call: N20, N25, N32, N40), confirm the delivery docket states the grade ordered, and cure the slab properly so the in-place concrete actually reaches it. The characteristic strength feeds the structural design under AS 3600. See concrete grade and special-class concrete for strengths or performance beyond the standard grades.
Also known as: f’c, characteristic compressive strength, 28-day strength, grade strength.
Category: Materials / Concrete.
Related
See also
References
- AS 1379-2007 Specification and supply of concrete, Standards Australia (verified 2026-05-25)
- AS 3600:2018 Concrete structures, Standards Australia (verified 2026-05-25)
Last updated: 2026-05-30. Verified: 2026-05-25. Quarterly review for currency.