Special-class concrete
Special-class (S grade) concrete is specified beyond the AS 1379 normal-class N grades, for exposure, high-early or low-shrinkage mixes, and needs a written spec.
Ask Chalkline about this →Special-class concrete (S grade) is concrete the engineer specifies to performance requirements beyond the normal-class range of AS 1379. Where normal class is the standard off-the-shelf N grades (N20 to N50), special class covers anything outside that envelope: exposure-classified concrete, high early strength, low-shrinkage mixes, a nominated water-cement ratio, a specified admixture or fibre dose, or strengths above N50.
It is not just a richer N grade; it is a separate category under AS 1379, and that has consequences. Special-class concrete costs more, needs a written specification (you cannot order it by a grade number alone), and carries extra sampling and test-record obligations, because the supplier has to demonstrate the specified performance rather than a standard grade. It is also not interchangeable with an N grade on the docket: if the engineer nominated S, an N32 truck does not satisfy the spec even where the strength number looks similar.
You see special-class on aggressive-exposure elements (marine, sulfate soils), suspended slabs needing low shrinkage or high early strength to strip formwork sooner, and architectural concrete. Read the engineer’s specification and the delivery docket together: confirm the docket states the special-class requirements that were ordered, and keep the test records, because special-class acceptance rests on them. See concrete grades.
Also known as: S grade concrete, special-grade concrete, performance-specified concrete.
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.