Best solution for cold weather concreting at temperatures down to -20°C
In cases when the ambient temperature falls below 5°C, the usual concrete placing methods no longer apply. The low temperature hinders the normal cement hydration process, thus preventing the concrete from hardening. In addition, when the water freezes, it increases its volume causing the concrete structure to crack.
Due to these reasons, in cases when the temperature is lower than 5°C, it is necessary to apply special methods of cold weather concreting which include:
• Heating one or more of the concrete materials (water, aggregate or cement);
• Fixing thermal insulation material to the surface of the formwork;
• Using admixtures for cold weather concreting.
As part of its product range, ADING offers several established admixtures for placing concrete at temperature down to -20°C:
HIDROZIM-T - Admixture for cold weather concreting. It regulates cement hydration at low temperatures and prevents the water in the concrete mixture from freezing by eliminating the risk of concrete degradation.
HIDROZIM FLUID– Complex admixture for cold weather concreting with additional plasticising properties. Just like HIDROZIM-T, it is used for cold weather concreting and it provides additional improvement of the strength properties and easier placement of the concrete.
Admixtures are dosed in the fresh concrete mix and the dosage depends on the ambient temperature, the temperature of the fresh concrete and the dimension of the section in which the concrete is to be placed. At ambient temperature between +5°C and -10°C, we recommend that you use the admixture HIDROZIM-T or HIDROZIM FLUID in quantity of 0.5 to 1.0% of the amount of cement in the concrete. For a standard MB30 pumped concrete, it would be a dosage of 2.0 to 3.5 kg/m3. When concrete is prepared in a small concrete mixer, the process of placing concrete is much slower and therefore it is necessary to put more admixture (3.0 – 4.0 kg/m3). It means that a 50 kg bag of cement requires admixture in the amount of 0.3 to 0.5 kg (0.25 to 0.4 litres).
Note:The specific weight of Hidrozim-T and Hidrozim Fluid amounts to approximately 1.30 kg/dm3 (1 litre of Hidrozim-T or Hidrozim Fluid weighs approximately 1.30 kg). Accordingly, if the admixture is measured in litres, it should be noted that 1 kg of the admixture amounts to 0.75 litres.
If HIDROZIM FLUID is used when preparing the concrete, the amount of water added to the fresh concrete mix should be reduced for approximately 10% (until obtaining the desired consistency for placing the concrete).
When placing concrete at temperature between -10°C and -20°C, it is necessary to add larger amount of the admixture HIDROZIM-T or HIDROZIM FLUID ranging between 1.0 and 2.0% of the amount of cement in the concrete.
Additional recommendations: The temperature of the fresh concrete mix at the moment of placing may not be lower than +5°C (for sections narrower than 10 cm it should be above +10°C) and its placing should be done as fast as possible (in order to reduce temperature loss during the preparation, transport and placement of the concrete). The surface of the fresh concrete must be thermally insulated (by using wooden or plastic formworks, and the fresh concrete should be covered, while the formworks should be panelled with nylon sheets, mineral wool, expanded polystyrene, geo-textile, etc.).
Depending on the required concrete class and strength, when placing concrete in cold weather it is very important to comply with the prescribed aggregate to cement ratio, as well as with the prescribed water to cement ratio (W/C ratio).