Extreme weather conditions are the enemy of every construction site, because weather conditions influence, among other things, the maturing process of the concrete. Summer temperatures accelerate curing, so that formwork can be removed much earlier or traffic clearances issued more quickly. Exactly the opposite occurs in winter. When outside temperatures are low, heating equipment has to be used. However, this creates enormous challenges – especially if the determination of the compressive strength of the concrete takes place via test cylinders, as is so often the case. Because if the curing conditions are not one hundred percent identical, the results are inevitably falsified. Intelligent concrete sensors can be a good solution here to prevent time delays and achieve consistent quality.
The strength development of concrete decreases massively at low outside temperatures. For comparison: At +5 degrees Celsius, the process takes about twice as long as at +20 degrees Celsius. At temperatures of -10 degrees Celsius, there is no strength development at all.
The concrete only becomes freeze-resistant after its protection period has expired, during which it must be kept at a temperature of at least +10 degrees Celsius for three days. Until then, there is a risk of frost damage, the remedial measures for which will be very complex and expensive.
Therefore, it is very important to have preventive protective measures ready in winter. These include:
- The use of special concrete compositions containing cements with a higher heat of hydration. The use of superplasticizers or additives such as fly ash should be avoided. In addition, the water/cement ratio should be reduced.
- A correspondingly high placing temperature of the fresh concrete. Recommended guide values: at air temperatures from +3 degrees Celsius, the concrete should have a temperature of at least +5 degrees Celsius, at even lower outside temperatures even at least +10 degrees Celsius
- Short transport times and avoidance of long waiting times on the construction site
- The right choice of formwork: wooden formwork dissipates heat more slowly than steel formwork
- Covering the concrete with thermal mats or heating tarpaulins, which prevent the hydration heat from escaping, or the use of hot air or heating coils
- Protection from drafts and rain or condensation water, since wind accelerates the evaporation of water in the fresh concrete and moisture increases the water-cement ratio