The simple and practical answer is that normal concrete cures to its specified strength (ranging from 100 to 500 kg/m3) within 28 days. It should be strong enough to walk on in 48 hours, and at 7 days it should have 70% strength.

There is "fast concrete," which is generally specified to cure in 1, 3, 7, or 14 days. For projects that require a quick and orderly completion, contractors often opt for a fast-paced concrete so that the entire project can move forward without delay. Rapid concrete can be much more expensive because it has a much higher cement content, which increases the cost of production.

The longer and more scientific answer is that concrete never fully cures. This is because the cement particles react with the water in the mix (hydration), and as long as the cement comes into contact with moisture, even the smallest air bubbles continue to form bonds. This is minimal after reaching "full strength", but it is continuous.

Important factors affecting setting time:

• Humidity: excess will reduce resistance; shortage will lead to flaking.
• Temperature: affects the evaporation process.
• Mixture design: selection of the water-cement ratio, granulometry of the aggregate, its geological origin and selection of additives.