The weather conditions when pouring the concrete slab have a great influence on its final quality. Specific measures should be taken to sink the slab in the best conditions, when it is cold or when it is very hot. And above all, whatever the weather, especially do not add water to your concrete on pain of reducing its resistance.
Concrete slab and bad weather
Influence of cold on concrete
It is quite possible to use concrete in winter by taking certain precautions during the pouring and hardening of the slab. Low temperatures brake and sometimes even prevent the concrete from hardening. The cold affects the resistance of the concrete before taking (fresh concrete) and after taking it (young concrete).
As a general rule, the placement of concrete is:
- not recommended when the temperature is less than -5° C
- possible between -5° C and 5° C using means of protection
The fall in winter temperatures a delay in the setting of concrete and an increase in the time required for curing. When the fresh concrete freezes, it completely stops the setting and hardening. On young concrete, the gel causes a swelling and a drop in strength of the concrete. It should be remembered that the earlier the concrete freeze is in the process, the more resistant the concrete is.
To pour concrete in winter, you must:
- to choose a concrete composition adapted to low temperatures: the water dosage is reduced and a water reducer can be added as well as setting and hardening accelerators
- manage to bring warmth to fresh concreteConcrete can be heated during manufacture (to be seen with the concrete plant) and then maintained at temperature by a heating system (ambient or formwork). He chooses the nearest concrete plant possible to reduce the transport time and therefore the cooling of the concrete
- use thermal protections as an insulating cover to cover the surface of the concrete slab (to be maintained for 72 hours)
Pouring concrete in hot weather
An outside temperature that is too high is as damaging to the concrete as the opposite. Concrete loses maneuverability when temperatures increase, its setting time is accelerated and the risk of cracking increases due to too rapid evaporation of water.
You can always put the concrete in place when it is hot. Just take a few precautions as soon as the outside temperature is (durably) higher than 25° C and much more, when the outside temperature is higher than 40° C.
To pour concrete when it's very hot, you have to:
- selectedr a concrete composition adapted to warm weather: it is possible to associate a retarding agent with a water reducer
- bring some freshness in concrete: the water used for the concrete can be cooled, the components (sand and chippings) moistened and the transport time between the power plant and the site reduced as much as possible by avoiding parking the truck in direct sunlight. Once poured concrete, we can cool the formwork
- use of sun protection and the wind to limit the evaporation of water (up to several days if necessary)
Learn more about "Dosages and compositin of concrete"