Concrete is made of cement, sand, gravel and crushed stone. Engineers determine how much of each part they need to acquire the required properties. They create concrete mixes according to the material available and the strength it needs to uphold.
Engineers establish a mix or mixes and then create a number of samples, in the form of blocks, with the particular mix. A Lab analyst then measures, weighs the block and puts it in a pressure frame. The frame is a cabinet with reinforced glass. Inside, two steel plates, one on top, one at the bottom.
The analyst puts the cement block between the plates and presses a few buttons on the console to start the test. The plates press against the block with an incrementally higher force. A data logger registers the whole process and plots a graph showing the force exerted over time.
After a few minutes, the block snaps. It has reached the breaking point.
The analyst repeats the process every few days with more blocks of the same mix. He collects all the data for the engineers who can be certain that the concrete mix achieved the properties required for the project.