What is "Fck+4" in Concrete Test?

In the field of concrete and construction, "Fck+4" is a term used to refer to the target compressive strength of concrete. The "Fck" part of the term refers to the characteristic compressive strength of concrete, while the "+4" refers to an additional strength requirement.

 

When a concrete mix design is specified as "Fck+4," it means that the target compressive strength of the concrete is 4 MPa higher than the characteristic compressive strength (Fck) of the mix design. For example, if a mix design has an Fck of 30 MPa and is specified as Fck+4, then the target compressive strength of the concrete would be 34 MPa.

 

Specifying a higher target compressive strength than the characteristic compressive strength can be done for several reasons, such as to ensure greater durability or to account for potential variations in the concrete strength due to factors such as curing conditions, workmanship, or testing variability.