What is the difference between 25 MPa and 32 MPa concrete?

25 MPa (approximately 3,600 PSI) and 32 MPa (approximately 4,600 PSI) are both standard ready-mix concrete strengths used in New Brunswick, but they serve different applications — and for most exterior concrete in NB, 32 MPa is the correct choice.

The number represents compressive strength: the load the concrete can bear per unit area before it fails, tested at 28 days. 32 MPa can handle 28% more compressive load than 25 MPa. But in NB residential concrete, the strength difference is less important than the durability difference that comes along with it.

Higher MPa concrete is not just stronger — it is denser and less permeable. To achieve higher compressive strength, the mix uses a lower water-to-cement ratio (less water relative to cement). The result is a denser, less porous paste with smaller, more disconnected pores. Fewer and smaller pores mean less water absorption, which means less freeze-thaw damage, less salt penetration, and better long-term durability in NB conditions.

CSA A23.1, the Canadian standard for concrete materials, classifies NB driveways, patios, and sidewalks as Exposure Class C-1 — concrete exposed to freeze-thaw cycles and de-icing chemicals. The minimum specification for C-1 exposure is 32 MPa with a 0.45 maximum water-to-cement ratio and 5–8% air content. A 25 MPa mix does not meet this exposure class specification.

When is 25 MPa appropriate?

• Interior basement floor slabs not exposed to weather


• Interior garage floor slabs with no salt exposure (less common in NB given salt-laden vehicles)


• Non-structural fill applications


• Some interior walls and columns in residential construction

When should you specify 32 MPa?

• Any exterior slab — driveways, patios, sidewalks, steps, porches, exposed aprons


• Foundation walls and footings


• Retaining walls


• Any concrete in coastal NB communities (Saint John, Shediac, Bathurst coastline)

In terms of cost, 32 MPa ready-mix in NB runs roughly $20–$30 more per cubic yard than 25 MPa. On a driveway using 8 cubic yards, that is a $160–$240 premium on a $6,000–$9,000 project. It is not a meaningful cost savings to downgrade — and the durability trade-off in NB's climate is severe. Stick with 32 MPa for all exterior concrete work.