Concreting is only permissible in freezing temperatures if special protective measures are taken. They must be in place from the start of concrete production to the end of curing. They depend on the outside temperature, air humidity, wind conditions, fresh concrete temperature, heat development and dissipation and the dimensions of the concrete pour. The fresh concrete must not be colder than +5 °C during placement and installation without additional protective measures. The mixing water and aggregates should be preheated if necessary.
Low temperatures retard the cement setting. At temperatures below -10°C the chemical processes of the cement stop (but continue after warming). Dangerous situations arise if concrete freezes during setting, i.e. without having a certain minimum strength. Structural loosening occurs, with a corresponding loss of strength and quality. The minimum strength at which concrete can survive one freezing process without damage is >5 N/mm2 (Sika recommendation >10 N/mm2) and the main objective is to reach this freeze resistance strength as quickly as possible.
1. Minimum temperature
According to EN 206-1, the fresh concrete temperature on delivery must not be below +5 °C for setting to be possible. (This varies for thin, fine structured elements) The concrete should be protected from heat loss during handling and after placing.
2. Reduction of w/c-ratio
The lowest possible water content leads to a rapid increase in initial strength. In addition, there is also less moisture available which could freeze. Superplasticizers allow a low w/c-ratio while retaining good workability.
3. Hardening acceleration
The use of SikaRapid® gives maximum hardening acceleration when there are high initial strength requirements. (Time to reach 10 N/mm 2 at 0°C in days)
|Concrete||Control mix||With 1% SikaRapid®|
|CEM I 300 kg/m³|
w/c = 0.40
|4 Days||1 Day|
|CEM I 300 kg/m³|
w/c = 0.50
|8 Days||2 Days|
4. Use of CEM I 52.5
The more finely ground, top grade cements are known to produce a more rapid increase in initial strength. Superplasticizers guarantee the best workability with a low w/c-ratio.
Protective measures on site
- No concreting against or on frozen existing concrete
- The steel reinforcement temperature must be more than 0°C
- Install the concrete quickly and immediately protect it from heat loss and evaporation
- For slabs: Heat the formwork from below if necessary
- Check air/ambient and concrete temperatures and the strength development regularly
- Extend the formwork dismantling and striking times!