What is concrete maturity?
Maturity is a quantity derived from the temperature of the concrete and the curing time, indicating how far the concrete has hardened. In practice the figure used is nearly always weighted maturity, which tells you whether the compressive strength required for striking formwork, stressing or loading has been reached.
The underlying rule is simple: time + temperature = compressive strength. Or, as a rule of thumb: equal weighted maturity means equal strength, however that maturity was accumulated.
Why it is used
Cement hydrates faster at higher temperature. Concrete curing at 25 °C in summer reaches a given strength in far fewer hours than the same mix at 5 °C in winter. Anyone working to a fixed “wait three days” rule strikes too early in winter and unnecessarily late in summer.
By monitoring concrete temperature continuously — with thermocouples or wireless sensors cast into the element — and computing maturity, you know at any moment how much strength is there.
The calculation
The basic form of weighted maturity is:
Rg = Σ (t × T)ⁿ × Cⁿ where t is the time step (for example each hour), T is the concrete temperature in degrees Celsius and C is the C-value of the cement used. The C-value expresses how strongly a cement responds to temperature; rapid Portland cements behave differently from blast-furnace cements.
Written out per hour:
Rg,n = 10 × { C^(0.1 × Tn − 1.245) − C^(−2.245) } / ln C The relationship between maturity and compressive strength is mix-specific: you need a calibration curve for the particular mix, established from test cubes.
Practical tips
- Place the sensor at the coldest point of the element, usually at a corner or in a thin section, not in the heart of a thick slab
- Ask the ready-mix supplier for the C-value and the calibration curve; never borrow values from another project
- Cold-weather concreting: cover up and insulate the formwork — that builds maturity rather than waiting for it
- Never strike on instinct in frost; striking too early costs strength and durability permanently
Related terms
- Compressive strength
- Formwork
- Reinforcement
- Shrinkage crack
- Mortar
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