Criteria to Accept Concrete Mixture Design

What is Concrete Mixture Design?

Acceptance criteria for concrete design mix

Concrete mixture design can be defined as a process that aims to obtain the type and proportion of ingredients that constitute the concrete batch. The mixture design should satisfy the strength and durability requirements.

A sound concrete mixture design serve as a basis for reliable concrete that is capable of resisting the imposed service load and environmental conditions in which this concrete serves.

Criteria to Accept Concrete Mixture Design

The Acceptance Criteria for a certain concrete mixture depends on the code you are working with but most of them will have the same principles for accepting the concrete mix.

Compressive strength acceptance criteria

For example, all specs will have acceptance criteria for concrete design mix regarding compressive strength.

Let us look at exemplary cases of acceptance criteria for concrete design mix:

The concrete shall be considered successful in terms of compressive strength if every tested sample gave a strength higher than the characteristic compressive strength. This is logical, of course, if all specimens passed the test, then concrete must be successful and comply with the strength requirements.

So, what happens if the strength of a sample from the tested group fails to achieve the characteristic compressive strength?

In this case, Code sets certain conditions that needs to be achieved in order for samples to pass the acceptance criteria.

For example, the criteria can be as follows:

The average strength determined from any group of four (or three depending on the code) consecutive test results should be the larger of: characteristic strength of the concrete + 0.83 * Standard deviation, or characteristic strength of concrete + 3 MPa.
Some codes specify additional requirements related to each individual specimen. For instance, the condition will be written as “The individual test result should be more than equal to characteristic strength of concrete minus 3 MPa”

If concrete did not specify the previous conditions, the concrete will be considered as “fail”

Flexural strength acceptance criteria

You may also find in the code you are working with, acceptance criteria for concrete design mix regarding flexural strength.

For example, the criteria can be as follows:

The mean strength determined from any group of four consecutive test results > the specified characteristic strength + 0.3 MPa.
The individual strength result > the specified characteristic strength + 0.3 MPa

It is frequently seen that construction engineers disregard the acceptance requirements for the concrete’s flexural strength under the justification that the flexural strength of the concrete is of no/little consequence because the tensile strength of the concrete is ignored in the strength design. However, the serviceability standards, such as the deflection of the structure, are determined by the flexural strength of the concrete. So, you may want to have a look at this too.

Criteria to Accept Concrete Mixture Design