The minimum temperature for pouring concrete is approximately 5 ° C. That is, this indicator is considered critical - up to this figure you can carry out any work with concrete in normal mode. However, it must be remembered that the optimum temperature for pouring concrete is 17-25 ° C, since such conditions allow you to get the maximum strength of the solution. If the pouring temperature of the concrete is close to 5 ° C, the mortar is likely to be less solid and durable and will not reach the performance declared for the brand. Even when carrying out work at critical temperatures, it should be remembered that the solidification time can increase significantly.
However, sometimes it becomes necessary to carry out construction work in the winter at low temperatures. There may be several reasons:
- limited construction time in summer due to adverse climatic conditions;
- the need for concrete pouring on loose soils;
- seasonal reduction in prices for materials, including cement;
- reduction in the cost of work by specialized firms due to the low demand for their services.
There are two main technologies that can be used for concreting in the cold season.
The first is that concrete is poured at negative temperatures on heated reinforcement, which can be played by ordinary electrodes. A standard 12-volt cable is connected to the valve, through which current flows. This is quite enough for the metal rods to glow and heat up the solution, preventing it from freezing. The disadvantages of this method are obvious - in addition to the use of special materials, you will have to spend a fair amount on electricity.
In addition, pouring concrete at low temperatures can be carried out using warm formwork. The essence of this technology is to warm the solution with special heat-insulating materials, such as polystyrene or mineral wool. But here there are drawbacks - it is necessary to cover the concrete from all sides, which leads to a large consumption of auxiliary materials and an increase in the time of work.
Concrete pouring at low temperatures: general recommendations
- All materials (sand, gravel) that will be used to obtain the solution should not contain ice and snow. It’s best to warm them up.
- All work must be carried out for the shortest possible time so that the solution does not have time to freeze.
- At low temperatures, concrete pouring must be done at a time. Pouring parts is not recommended, as cracks may appear between the layers, which will make the concrete less durable.
- Various additives, such as potash, sodium nitrite, lignosulfonate, calcium chloride , sodium formate and others, will help increase the adhesion and hardening of concrete. However, it should be noted that each such additive has side effects. For example, calcium chloride can cause corrosion of the reinforcement.
Thus, we can conclude that concrete pouring at negative temperatures should be carried out only if it is not possible to postpone this stage of construction work until more favorable conditions occur.