🏗️ Concrete Strength Development
Written and maintained by the PhDino author · Last reviewed 21 September 2026 · Checked against 2 independent reference calculations · how PhDino checks its numbers
Related standards: ACI 318
Estimating how much of its 28-day design strength concrete has gained at an earlier age.
Concrete doesn't reach its full design strength the moment it's poured — it gains strength over days and weeks as the cement hydrates. Construction schedules (like when it's safe to strip formwork or open a slab to traffic) often depend on knowing the strength at some age earlier than the standard 28-day test.
A maturity-type expression relating early-age strength to the 28-day strength is commonly used for a quick estimate, though real concrete mix designs (cement type, water-cement ratio, admixtures, curing temperature) all shift the actual curve.
Key formula
f'c(t) = f'c(28) × t / (4 + 0.85t)
Variables
- f'c(28)
- 28-day design compressive strength
- t
- age of the concrete in days
Notes & limitations
- This is a generic approximation for typical Type I cement under normal curing — it is not a substitute for actual cylinder break tests when strength verification matters (e.g. before removing shoring).
- Curing temperature has a large effect on early strength gain that this simple formula does not account for.
Related topics
Beam DeflectionHow much a beam sags under a uniform load, and the bending moment that causes it.Column BucklingHow much axial load a steel column can carry before it buckles: Euler's elastic formula, with the AISC reduction for stocky columns.Footing DesignSizing a square spread footing so the pressure it puts on the soil stays within what the soil can safely carry.Bolted Steel ConnectionsChecking whether a group of bolts can transfer a shear load, considering both bolt shear and plate bearing.Further reading
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Structures: Or Why Things Don't Fall Down by J. E. Gordon — A classic, non-mathematical explanation of how beams, arches, and materials actually carry load. (Bookshop.org UK, UK delivery only)
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