For concreting at a high temperature, special protective measures must be in place from the start of concrete production to the end of curing. It is dependent on the outside temperature, air humidity, wind conditions, fresh concrete temperature, heat development, dissipation and the dimensions of the element.
Working with non-retarded concrete can become a problem at air temperatures higher than 25°C.
- Hydration is the chemical reaction of the cement and water. It begins immediately at contact, continues through stiffening to setting (initial setting) and finally to hardening of the cement paste.
- All chemical reactions are accelerated at elevated temperatures.
- Early stiffening makes placing concrete no longer possible. The use of retarded superplasticizers or superplasticizers combined with a set retarder are the usual countermeasures.
Retardation terms and dosing tables
Purpose of retardation: To extend the working time at a specific temperature.
Working time: The time after mixing during which the concrete can be correctly vibrated.
Free retardation: The initial setting is certain to start only after a specific time.
Targeted retardation: The initial setting starts at a specific time.
Decisive temperature for structural elements
|Structural element and retardation||Decisive temperature|
|Voluminous concrete cross sections||Fresh concrete temperature|
|Small concrete cross sections||Air temperature at placement point|
The higher temperature (fresh concrete or air temperature) is the decisive one for voluminous concrete cross sections with long retardation, and for small concrete cross sections with short retardation.