The strength of concrete increases with age, and hydration of cement continues for months. For normal portland cement, the increase of strength with time, relative to 28-day strength may be assumed as follows:
- After 7 days – 0,67.
- After 14 days – 0,86.
- After 28 days – 1,00.
- After 3 months – 1,17.
- After 6 months – 1,23.
- After 1 year – 1,27.
- After 2 years – 1,31.
- After 5 years – 1,35.