# What Is Meant By “Compressive Strength of Concrete”?

Before concrete is used in a construction project, different tests are run to test the strength and properties of the concrete. This is to ensure that the concrete product meets the necessary requirements for the job specification. After all, the properties of the concrete will determine the longevity, cost and other essential aspects of the project.

One of the most important properties that must be checked for is the compressive strength of concrete- that is the ability of the concrete to withstand large loads which tend to compress it (i.e decrease its size). The compressive strength of concrete is important in indicating how the concrete performs and therefore whether or not it will meet the requirements of the job.

## How To Calculate The Compressive Strength Of Concrete?

Compressive strength is calculated using some pretty complex data and formulas, but in simple terms, it involves the concrete being ‘squashed’ (under carefully controlled conditions of course). Here’s how it works:

In order to calculate compressive strength of concrete, the material is tested by exerting a downward force on top of a cylindrical/ cubic object whilst an equal and opposite force is applied upwards (‘squashing’ the object).

The object is ‘squashed’ until it fails and this is why a cylindrical or cubic object is used rather than an actual concrete product. The cylindrical/ cubic object also provides the necessary flat, parallel surface from which the necessary data measurements can be made. These data points are the cross-sectional area of the object and a measure of the force applied to the object at the moment it fails.

Once these data points have been taken, the compressive strength of concrete can be calculated using this formula:

CS = F ÷ A, where CS is the compressive strength, F is the force or load at the point of failure and A is the initial cross-sectional surface area.

Compressive strength is measured in psi (pounds per square inch). The higher the psi the stronger, and consequently more expensive the concrete is. The minimum psi required depends on the project, however, in general, the bare psi level for any concrete project begins at around 2,500 psi. That said, in Bahrain and the Middle East, we tend to use N/sq.mm (Newton per millimetre square) instead of psi, with 2500 psi being equivalent to 17.23 N/sq.mm. 20 N/sq.mm is typically the lowest grade of concrete used in construction projects and is generally used for non-structural purposes.

In general, the material is tested after 7 days and then again after 28 days, and you can read more about the ins and outs of the process here.

## Other Ways To Measure Strength

Whilst calculating the compressive strength of concrete is the most common form of strength measurement, other properties do need to be considered. These include testing for the tensile strength and flexural strength of concrete. Whilst tensile strength refers to the concrete’s resistance to cracking or breaking under tension, flexural strength is a measure of the concrete’s ability to withstand bending. Both these measurements are equally as crucial as compressive strength when it comes to ensuring the right concrete products are selected for a project.

At Al Manaratain, we ensure that all our concrete products are monitored and controlled to meet international requirements. For more information on our commitment to quality control, please read the information available on our website or get in touch.