There are three primary objectives for cold weather concreting: 1) Protect the newly placed concrete from damage due to early-age freezing; 2) Maintain curing conditions to ensure adequate strength gain; and 3) Protect concrete from thermal shock and related cracking at the end of the protection period.
If freshly placed concrete freezes, immediate and permanent damage may occur. Damage occurs because water (i.e., batch or mixing water) expands 9% in volume when it freezes. The formation of ice crystals and lenses, resulting paste expansion, and microcracking can reduce the compressive strength and increase the porosity of the hardened concrete (Figure 1).
Strength reductions up to 50% can occur if freezing takes place in the first few hours after placement or before the concrete attains a compressive strength of approximately 500 psi. Subsequent curing will not heal the damage and restore the concrete’s hardened properties.
Freshly placed concrete must be protected from early-age freezing until the amount of mixing water or the degree of saturation has been sufficiently reduced by the process of hydration, which describes the chemical reaction between the portland cement or cementitious materials and water.READ MORE