Calculating the compressive strength of concrete requires a formula: CS = F ÷ A. The variables in the compressive strength of concrete formula are as follows: CS is compressive strength, F is the force at the point of failure, and A is the cross-sectional surface area.
Now let’s define a few terms. Then we’ll look at a basic experiment that helps illustrate how we might test the compressive strength of concrete.
The compressive strength of the concrete you are using for your structure depends on different factors, including cement strength, water-cement ratio, the quality of the concrete material, and how well you oversaw quality control when the concrete was produced.
What is compressive strength?
Compressive strength is the capability of a specific material or structure to carry a load on the surface without it cracking. Concrete has high compressive strength. (And relatively low tensile strength, which we’ve written about here.)
To test the concrete for specific compressive strength, you can use a cube.
The concrete will need to be mixed by hand, mixing the cement with fine aggregate on a watertight non-absorbent platform. Mix it until it is fully blended. Then add the coarse aggregate and mix it with the cement and fine aggregate and add water and mix until the concrete is the desired consistency.
You will also need to get your cubes ready by curing them, which involves storing them in moist air for 24 hours.
After this, submerge them in clear, fresh water until you are ready to use them for the test. This test is usually completed to evaluate the overall strength of the concrete at seven days, 14 days, and 28 days.
This process is often used to test concrete compressive strength for general construction. The strength for this industry varies from 15 MPa (2,200 psi) to 30 MPa (4,400 psi) and will go even higher for commercial and industrial structures.
The strength of the concrete will increase with age, so essentially, the concrete will get stronger, week after week. At 28 days, it should be at a 99% strength rate.
Ensuring that you have the right concrete mix helps in the development process to make sure that the concrete result is strong, durable, and built to stand the test of time. So, when you are working with cement, take special care during the water-to-cement ratio step, making sure the water is measured and monitored carefully. If the ratio is even slightly inaccurate, the concrete can weaken over time, or completely fail.
Our team at Columbia Precast Products can help answer your questions when it comes to concrete strength. We understand how important your structure’s concrete is and can help provide products with superior longevity. Contact us today to learn more.