Does NB building code require air-entrained concrete for exterior work?

Yes — the National Building Code as adopted in New Brunswick, combined with CSA A23.1 (the concrete materials and construction standard), effectively requires air-entrained concrete for all exterior concrete exposed to freezing and thawing in a moist or wet environment. For New Brunswick, that means every exterior concrete surface — driveways, patios, sidewalks, steps, porches, exposed foundation walls — requires an air-entrained mix.

The code language specifies concrete exposure categories, and NB exterior flatwork falls into the most demanding category: Class C-1 or C-2 exposure, meaning concrete exposed to freezing and thawing in a moist condition and to de-icing chemicals. For this exposure class, CSA A23.1 requires 5-8% total air content for concrete with 20 mm (3/4 inch) aggregate, along with a maximum water-to-cement ratio of 0.45 and a minimum 32 MPa compressive strength. These requirements work together — the air entrainment provides freeze-thaw resistance, the low water-cement ratio improves density and reduces permeability, and the higher strength provides durability.

The practical reason this requirement exists is straightforward and worth understanding as a homeowner. NB experiences 150+ freeze-thaw cycles per year — among the highest in Canada. Without air entrainment, water enters the microscopic pores in concrete, freezes, expands by 9%, and fractures the concrete matrix from the inside out. The surface scaling and spalling you see on old NB driveways is almost always the result of non-air-entrained concrete (or inadequately air-entrained concrete) failing under this relentless cycle.

Air entrainment works by introducing billions of microscopic air bubbles (4-7% of the concrete volume) using a chemical admixture added at the ready-mix plant. These tiny bubbles act as pressure relief valves — when water freezes and expands in adjacent pores, it has somewhere to go without fracturing the cement paste. The result is concrete that can withstand decades of NB freeze-thaw cycles rather than failing within 3-7 years.

When ordering ready-mix concrete for any exterior NB project, always specify: air-entrained mix, 6% air content (±1%), 25-32 MPa, with a maximum 0.45 water-to-cement ratio. Reputable NB ready-mix suppliers deliver this as a standard exterior mix — it should cost only $10-$20 per cubic yard more than standard non-air-entrained concrete. Never let a contractor talk you out of air entrainment on exterior work to save a few dollars. The cost difference on a 400 sq ft driveway is less than $100, but the difference in service life is 20-30 years.

For interior concrete (basement floors, interior garage slabs in heated spaces), air entrainment is less critical. But for any concrete that will experience New Brunswick winters, there is no debate — air entrainment is mandatory.