Concreting is only possible at high temperature if special protective measures are provided. There 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. For example the concrete should be protected from drying out during transport.
The fresh concrete not be hotter than +300C during placing and installation without protective measures.
Working with non-retarded concrete can become a problem at air temperature higher than 250C:
- Hydration is the chemical reaction of the cement and water. It begin 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 temperature.
As a result of early stiffening placing the concrete is no longer possible. The normal countermeasures are the use of retarded superplasticizers or superplasticizers combined with a set retarder.