What is the difference between air-entrained and regular concrete?

Air-entrained concrete has billions of microscopic air bubbles intentionally introduced into the mix; regular (non-air-entrained) concrete does not. Those tiny bubbles — typically 4–7% of the mix volume — are the single most important feature protecting concrete from New Brunswick's relentless freeze-thaw cycles.

Here is the problem that air entrainment solves: concrete is not perfectly solid. It has microscopic pores and capillaries that absorb water. When that water freezes, it expands by about 9%. In a non-air-entrained concrete, there is nowhere for that expanding ice to go, so it fractures the concrete matrix from the inside. Do this 150+ times per year — which is typical for New Brunswick — and within 3–7 years you have spalling, scaling, and surface deterioration. The concrete surface flakes away in layers, exposing the aggregate, and the damage accelerates from there.

Air entrainment works by creating a network of tiny, closely-spaced air voids distributed throughout the concrete. When water in the pores begins to freeze and expand, it has somewhere to go — into the adjacent air void — without building up the hydraulic pressure that fractures the concrete. The result is concrete that survives freeze-thaw cycling without surface damage.

The technical difference is straightforward: air-entrained concrete uses a chemical admixture (an air-entraining agent) added at the ready-mix plant during batching. The mixer introduces the bubbles, and the plant controls the air content to hit the 4–7% target. You cannot reliably add air entrainment on-site — it must be specified when you order from the ready-mix plant.

In terms of strength, air entrainment reduces compressive strength slightly — roughly 200–300 PSI for every 1% of air added. A 3,500 PSI (25 MPa) mix with 6% air will be somewhat less strong than the same mix without air. For most exterior flatwork applications in NB, this tradeoff is completely acceptable. The durability benefit enormously outweighs the minor strength reduction.

Regular concrete — without air entrainment — has its place: interior slabs, basement floors, slabs under cover that will never be exposed to freeze-thaw cycles or de-icing salt. For interior applications, non-air-entrained concrete is fine and costs a few dollars less per cubic yard.

For anything outdoors in New Brunswick — driveways, patios, sidewalks, steps, porches, exposed aggregate surfaces — always specify air-entrained concrete. It is the difference between a 5-year lifespan and a 30-year lifespan.