Curing time of concrete prior to freezing

Conclusions

• 1. The ice content in concrete increases with lower temperatures below freezing. For the same temperature below zero, the ice content is greater the lower the strength of concrete at freezing. The presence of unfrozen water is the reason for a gain in strength at below-freezing temperatures.

• 2. The ice content in water-saturated concrete of 50% R₂₈ strength is nearly twice that in nonsaturated corcrete, frozen at the same temperature. Therefore it is not permissible to saturate concrete when its strength has reached the full grade strength.

• 3. The critical compressive strength, i.e., the strength at which it is permissible to remove protective covering and expose concrete to freezing, depends on the grade of concrete and amounts to 30–50% of the grade strength, or 50–120 kg/cm².

• 4. When the requirements of strength, water-tightness and frost resistance are especially high, the concrete should have acquired the full grade strength before exposure to multiple cycles of freezing and thawing (whether at light frost or very low temperatures, during construction or during the life of the completed structure).

• 5. To avoid cracks in concrete in massive hydraulic structures using highly active cements, it is necessary to use preheated (by electric current) aggregates with subsequent thermal protection and, if necessary, peripheral heating of the structure.