Concrete can only be processed for a certain period of time before it sets. Depending on the type and composition of the concrete, its durability - and its resilience - is sometimes different. Everything you should know about it can be found in this article.
Workability of concrete
How long concrete remains "fresh", i.e. liquid, depends on several factors:
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- the respective concrete composition
- the set consistency of the concrete
- the type of concrete
- possibly added agents for a longer workability (for ready-mixed concrete)
The consistency of the concrete must be determined before construction begins. This is prescribed by DIN. It must not be changed during construction, not even by adding water to the finished concrete. This is strictly forbidden because a change in the so-called water-cement value (the ratio of water to cement in concrete) can have a massive negative impact on the strength of the concrete. This can seriously impair the load-bearing capacity of the components.
Concrete does not harden through evaporation of water, as is the case with plaster of paris, but through a chemical reaction of the cement paste contained in the concrete. This reaction takes place regardless of the water content in the concrete.
It is precisely for this reason that adding water is prohibited, as this only changes the water content in the concrete, but does not affect the chemical reaction when the cement paste sets. When checking the setting progress, it is only the progress of the chemical reaction of the cement paste that is assessed.
In technical language, liquid concrete is called fresh concrete, when the setting reaction of the cement paste has started, the concrete is usually called green concrete or young concrete. The concrete is only called hardened concrete after it has completely set.
The setting reaction continues afterwards, but the concrete is firm after just a few days. However, the reaction inside is finally complete - often only after several months, depending on the type of concrete.
Durability of fresh concrete as opposed to precast concrete
If you describe fresh concrete as self-mixed concrete, in contrast to ready-mixed concrete (15.69 € at Amazon *) and ready-mixed concrete, which are each prefabricated by the manufacturer, there are certainly concerns about the durability of concrete from own production.
The basic properties and the high durability of concrete stem from exact mixing ratios and an exactly adjusted water-cement ratio. When mixing concrete, however, only approximate mixing ratios are achieved - in contrast to ready-made concrete mixes, the strength of the concrete and thus the durability cannot be precisely tested and is therefore often not quite as high.
As a rule, this does not play a role in practice, especially for DIY or smaller projects. In the case of highly stressed components that absolutely have to achieve a certain load-bearing capacity, this is fundamentally important in order not to endanger the durability of the component. Here, "approximate mixtures" are neither permitted nor advisable.