What PSI concrete should be used for a foundation in New Brunswick?

For residential foundations in New Brunswick, specify a minimum 25 MPa (3,500 PSI) concrete mix, and 30 MPa (4,350 PSI) is strongly recommended for full basement walls, footings, and any concrete exposed to NB's ground conditions. In metric-standard Canada, concrete strength is specified in megapascals (MPa) rather than PSI — your ready-mix supplier and contractor will work in MPa.

Why 25 MPa is the minimum, not the target: The NB Building Code (National Building Code of Canada) sets 20-25 MPa as the minimum for foundation concrete depending on exposure class, but minimum code compliance and best practice are not the same thing. NB's saturated clay soils, high water tables in areas like Moncton, Dieppe, and Riverview, and the aggressive freeze-thaw environment at and below grade all argue for a stronger, denser concrete mix.

The exposure class system matters here. CSA A23.1 (the Canadian concrete standard) classifies concrete exposure by conditions. Below-grade concrete in NB soil that is regularly saturated falls into Exposure Class C-2 (concrete exposed to moderate sulphates or chlorides in soil or water), which requires a minimum 30 MPa mix with a low water-to-cement ratio of 0.50 or less. If your site has high sulphate content in the soil — possible in some NB regions — Exposure Class S-2 may apply, requiring Type HS cement and 35 MPa.

Water-to-cement ratio is as important as strength. A lower water-to-cement ratio (0.45-0.50) produces denser, less permeable concrete that resists water infiltration and chemical attack far better than a higher-ratio mix with the same strength rating. Specify this with your ready-mix order, and never allow water to be added at the jobsite to improve workability.

Air entrainment for below-grade concrete: While air entrainment is most critical for exterior flatwork exposed to freeze-thaw cycles, it is also appropriate for below-grade concrete in NB where the frost line extends 4-5 feet down and the concrete near grade will experience freeze-thaw cycling. Most NB foundation contractors specify an air-entrained mix throughout the wall pour.

For footings specifically — which are fully below grade and protected from freeze-thaw at depth — 25 MPa is typically sufficient if the water-to-cement ratio is controlled and the concrete is placed on undisturbed soil. But if you are going to be there with a ready-mix truck anyway, using 30 MPa throughout the foundation is a small cost difference for meaningful long-term benefit.

Typical ready-mix pricing in NB for 25-30 MPa air-entrained foundation concrete runs $190-$250 per cubic yard delivered. New Brunswick Concrete can match you with experienced foundation contractors who specify the right mix for local conditions.