How long does concrete take to cure?

Concrete reaches approximately 70% of its 28-day strength after 7 days under standard conditions (20°C, CEM I cement). Full 28-day strength takes 4 weeks. At lower temperatures, curing is slower — at 5°C, it may take 14+ days to reach 70% strength. GGBS cements are slower still. Curing continues for months but the rate diminishes significantly after 28 days.

What is the maturity method?

The maturity method estimates concrete strength based on the cumulative temperature-time history. Maturity = sum of (temperature x time). Higher temperatures accelerate curing. This allows early-age strength to be estimated without destructive testing. It's particularly useful for deciding when to strike formwork or load a slab.

When can I strike formwork?

Formwork can be struck when the concrete has gained sufficient strength to support its own weight plus any imposed loads. For vertical surfaces (walls, columns), this is typically 12-18 hours at 20°C. For soffits (beam/slab undersides), wait until the concrete reaches 70% of its design strength — typically 7+ days. Always follow the structural engineer's guidance.

What happens if concrete cures too cold?

Below 5°C, curing slows dramatically. Below 0°C, water in the concrete can freeze, causing permanent damage to the microstructure and significantly reducing final strength. Protect fresh concrete from frost with insulating blankets, heated enclosures or by using accelerating admixtures. Do not pour concrete if temperatures will fall below 2°C within 24 hours.

Does GGBS concrete cure slower?

Yes, CEM III (GGBS) cements gain strength more slowly than CEM I (OPC), especially in the first 7 days. At 7 days, GGBS concrete may only reach 50-60% of its 28-day strength versus 70% for OPC. However, GGBS concrete continues gaining strength beyond 28 days and often exceeds OPC strength at 56+ days. It also has better sulphate resistance.

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Concrete Curing Calculator — Strength Gain & Formwork Striking

Estimate concrete strength gain by temperature and mix type, with formwork striking time guidance.

Concrete Grade28-day strength: 30 N/mm²

Cement Type

Ambient Temperature

Average air temperature during curing

Target Strength

70% typical for formwork striking

How We Calculate This

This calculator estimates concrete strength gain based on temperature, cement type and target strength percentage, and suggests formwork striking times.

Strength estimation

Target Strength = Grade Strength x Target%
Estimated Days = (Target% / 70%) x 7 / (Temp Factor x Cement Factor)
Temperature factor: 1.0 at 20°C+, 0.8 at 10-19°C, 0.6 at 5-9°C, 0.4 below 5°C.

Formwork striking

Minimum 3 days at standard conditions. Longer at lower temperatures or with slower cement types. Soffits should not be struck until the concrete reaches at least 70% of design strength.