Why does concrete work?

Concrete is manufactured by mixing the raw materials (see thus producing fresh concrete which is ready for processing.

During the first hours concrete hardens and during the course of the following weeks creates a solid structure of aggregate particles and cement paste or cement stone (cement paste is the compound of cement and water). The strengthening structure is created by hydration of the cement, for which only water (approx. 40 weight percent of the cement) but no air is required. During this process, the cement particles are transformed into long-chain crystals, thus generating a solid structure.

The consistency (workability) of concrete is decisively influenced by the water content, the water requirement of grading curve and the superfine particles. The pumpability is affected by the grading curve design and the ultrafines content.

The compressive strength depends on the density of the hardened cement paste. The density is determined by the water-cement ratio. The water that is not required for hydration results in pore formation, and consequently in a reduction of strength.

In Germany, the compressive strength of concrete is determined by means of cubes. Using compression presses, the breaking load is determined and converted for the pressure surface for the compressive strength.