How do freeze-thaw cycles affect concrete in New Brunswick?

Freeze-thaw cycles are the single most destructive force acting on exterior concrete in New Brunswick — and NB's 150+ freeze-thaw cycles per year make it one of the most challenging concrete environments in Canada. Understanding this process explains why concrete specification, material selection, and sealing are not optional extras in this province.

The mechanism of freeze-thaw damage is physical at the microscopic level. Hardened concrete is not a solid mass — it contains a network of microscopic capillary pores that form during the curing process as excess water evaporates. When exterior concrete is exposed to rain, snow melt, or condensation, water enters these pores. When temperatures drop below 0°C, that water freezes. Ice occupies 9% more volume than liquid water. In a small capillary pore, that 9% expansion generates internal pressures up to 290 MPa — far exceeding the tensile strength of concrete, which is typically 2-5 MPa. The result is microscopic fractures in the cement paste matrix.

One cycle of this causes almost imperceptible damage. But 150 cycles per year, year after year, produces cumulative damage that becomes very visible: surface scaling (the surface layer peels away in thin sheets), spalling (larger chunks break off), and deep cracking. A concrete driveway without air entrainment in NB will typically begin showing surface scaling within 3-5 years and will look worn and pitted within 7-10 years. The same driveway with properly air-entrained concrete and a quality sealer can last 30-40 years.

De-icing salt compounds the problem dramatically. When sodium chloride dissolves in water, it lowers the freezing point to as low as -20°C. This means the concrete surface experiences more freeze-thaw cycles than the ambient temperature alone would cause — water that would stay liquid at -5°C instead freezes and thaws repeatedly as temperatures fluctuate in the -5°C to -15°C range. Salt also creates an osmotic pressure difference on either side of the concrete surface that draws water deeper into the slab, introducing more water to freeze in more pores. NB roads are heavily salted from November through April, and salt-laden slush reaches every driveway and walkway in Moncton, Fredericton, Saint John, and every NB community.

The solution is threefold: first, specify air-entrained concrete (5-8% air content) for all exterior flatwork — the microscopic air bubbles provide pressure relief cavities so freezing water has somewhere to expand without fracturing the paste. Second, use a low water-to-cement ratio (0.45 or less) to reduce the volume of capillary pores. Third, apply a quality penetrating sealer (silane/siloxane) every 2-3 years to block water entry at the surface.

For coastal communities like Saint John, Shediac, and Bathurst, salt air adds another layer of degradation by introducing chloride ions that penetrate even properly specified concrete over time. Minimum 32 MPa mixes and more frequent sealing (every 2 years) are recommended for coastal NB.