# Design concrete strength after 28 days: the value of `k`_{t}

_{t}

## Eurocode 2 part 1-1: Design of concrete structures 3.1.2 (4)

If the concrete strength is determined at an age `t` > 28 days, the values `α _{cc}` and

`α`defined in § 3.1.6 (1)P and § 3.1.6 (2)P should be reduced by a factor

_{ct}`k`.

_{t}## Recommendation

The recommended value of `k _{t}` for the calculation of the concrete strength after 28 days is 0,85.